Methods And Apparatus For Testing Earth Formations

Abstract

In the representative embodiments of the new and improved methods and apparatus for testing earth formations disclosed herein, fluid-admitting means are placed into sealing engagement with a potentially-producible earth formation and selectively-operable valve means on the fluid-admitting means are opened to place a filtering medium situated between the fluid-admitting means and a flow line in communication with the isolated formation. Then, before testing is commenced, well bore fluids are introduced into the flow line and discharged through the filtering medium in a reverse direction and into the earth formation for cleaning the filtering medium of potentially-plugging materials before connate fluids are introduced into the fluid-admitting means.

Description

Heretofore, the typical wireline formation testers (such as the tool disclosed in U.S. Pat. No. 3,011,554) which have been most successful in commercial service have been limited to attempting only a single test of one selected formation interval. Those skilled in the art will appreciate that once one of these typical tools is positioned in a well bore and a sampling or testing operation is initiated, the tool cannot be again operated without first removing it from the well bore and reconditioning various tool components for another run. Thus, even should it be quickly realized that a particular sampling or testing operation already underway will probably be unsuccessful, the operator has no choice except to discontinue the operation and then return the tool to the surface. This obviously results in a needless loss of time and expense which would usually be avoided if another attempt could be made without having to remove the tool from the well bore.

One of the most significant problems which have heretofore prevented the production of a commercially successful repetitively-operable formation-testing tool has been in providing a suitable arrangement for reliably establishing fluid or pressure communication with imcompetent or unconsolidated earth formations. Although the several new and improved testing tools respectively shown in U.S. Pat. No. 3,352,361, U.S. Pat. No. 3,530,933, U.S. Pat. No. 3,565,169 and U.S. Pat. No. 3,653,436 are especially arranged for testing unconsolidated formations, for one reason or another these tools are not adapted for performing more than one testing operation during a single run in a given well bore. For example, as described in these patents, each of these new and improved testing tools employs a tubular sampling member which is cooperatively associated with a filtering medium for preventing the unwanted entrance of unconsolidated formation materials into the testing tool. Experience has shown, however, that although these new and improved filtering arrangements are highly successful for a single operation, subsequent tests cannot be reliably performed since particles of mudcake and exceptionally-fine formation materials will often coat or plug the filtering medium. Thus, following each test, the testing tool must be returned to the surface and the filtering medium thoroughly cleaned to achieve an acceptable level of operating reliability.

Accordingly, it is an object of the present invention to provide new and improved formation-testing methods and apparatus for reliably obtaining multiple measurements of one or more fluid or formation characteristics as well as selectively collecting one or more samples of connate fluids, if desired, from incompetent or unconsolidated earth formations.

This and other objects of the present invention are attained in the practice of the new and improved methods described herein by placing normally-closed fluid-admitting means having filtering means cooperatively arranged therewith into sealing engagement with an earth formation, opening communication between the filtering means and the earth formation, and discharging well bore fluids in a reverse direction through the filtering medium and into the formation for cleansing the filtering medium of unwanted possibly-plugging matter such as mudcake and loose formation materials. To further achieve the objects of the present invention, formation-testing apparatus is provided with fluid-admitting means adapted to be sealingly engaged with a potentially-producible earth formation. To limit the entrance of loose formation materials into the fluid-admitting means, filtering means are disposed in the fluid-admitting means. Normally-closed valve means are cooperatively arranged in the fluid-admitting means for selective movement to an open position for opening communication between an isolated earth formation and the filtering means. Means are further provided for discharging well bore fluids in 13 reverse direction through the filtering means upon opening of the valve means for flushing possibly-plugging materials away from the filtering means.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by way of the following description of exemplary apparatus employing the principles of the invention as illustrated in the accompanying drawings, in which:

FIG. 1 depicts the surface and downhole portions of a preferred embodiment of new and improved formation-testing apparatus for practicing the invention and incorporating its principles;

FIGS. 2A and 2B together show a somewhat-schematic representation of the formation-testing tool illustrated in FIG. 1 as the tool will appear in its initial operating position; and

FIGS. 3-5 A and B respectively depict the successive positions of various components of the new and improved tool shown in FIGS. 2A and 2B during the course of a typical testing and sampling operation.

Turning now to FIG. 1, a preferred embodiment of a new and improved sampling and measuring tool 10 incorporating the principles of the present invention is shown as it will appear during the course of a typical measuring and sampling operation in a well bore such as a borehole 11 penetrating one or more earth formations as at 12 and 13. As illustrated, the tool 10 is suspended in the borehole 11 from the lower end of a typical multiconductor cable 14 that is spooled in the usual fashion on a suitable winch (not shown) at the surface and coupled to the surface portion of a tool-control system 15 as well as typical recording and indicating apparatus 16 and a power supply 17. In its preferred embodiment, the tool 10 includes an elongated body 18 which encloses the downhole portion of the tool control system 15 and carries selectively-extendible tool-anchoring means 19 and new and improved fluid-admitting means 20 arranged on opposite sides of the body as well as one or more tandemly-coupled fluid-collecting chambers 21 and 22.

As is explained in greater detail in a copending application, Ser. No. 313,235 by Harold J. Urbanosky filed Dec. 8, 1972, the new and improved formation-testing tool 10 of the present invention and the control system 15 are cooperatively arranged so that, upon command from the surface, the tool can be selectively placed in any one or more of five selected operating positions. As will be subsequently described briefly, the control system 15 will function to either successively place the tool 10 in one or more of these positions or else cycle the tool between selected ones of these operating positions. These five operating positions are simply achieved by selectively moving suitable control switches, as schematically represented at 23 and 24, included in the surface portion of the system 15 to various switching positions, as at 25-30, so as to selectively apply power to different conductors 31-37 in the cable 14.

Turning now to FIGS. 2A and 2B, the preferred embodiment of the entire downhole portion of the control system 15 as well as the tool-anchoring means 19, the fluid-admitting means 20 and the fluid-collecting chambers 21 and 22 are schematically illustrated with their several elements or components depicted as they will respectively be arranged when the new and improved tool 10 is fully retracted and the switches 23 and 24 are in their first or "off" operating positions 25. In the preferred embodiment of the selectively-extendible tool-anchoring means 19 schematically illustrated in FIG. 2A, an upright wall-engaging anchor member 38 along the rear of the tool body 18 is coupled in a typical fashion to a longitudinally-spaced pair of laterally-movable piston actuators 39 and 40 of a typical design mounted tranversely on the tool body 18. As will be subsequently explained, the lateral extension and retraction of the wall-engaging member 38 in relation to the rear of the tool body 18 is controlled by the control system 15 which is operatively arranged to selectively admit and discharge a pressured hydraulic fluid to and from the piston actuators 39 and 40.

borehole fluid-admitting means 20 employed with the preferred embodiment of the new and improved tool 10 are cooperatively arranged for sealing-off or isolating selected portions of the wall of the horehole 11; and, once a selected portion of the borehole wall is packed-off or isolated from the well bore fluids, establishing pressure or fluid communication with the adjacent earth formations. As depicted in FIG. 2A, the fluid-admitting means 20 preferably include an annular elastomeric sealing pad 41 mounted on the forward face of an upright support member or plate 42 that is coupled to a longitudinally-spaced pair of laterally-movable piston actuators 43 and 44 respectively arranged transversely on the tool body 18 for moving the sealing pad in relation to the forward side of the tool body. Accordingly, as the control system 15 selectively supplies a pressured hydraulic fluid to the piston actuators 43 and 44, the sealing pad 41 will be moved laterally between a retracted position adjacent to the forward side of the tool body 18 and an advanced or forwardly-extended position.

By arranging the annular sealing member 41 on the opposite side of the tool body 18 from the wall-engaging member 38, the lateral extension of these two members will, of course, be effective for urging the sealing pad into sealing engagement with the adjacent wall of the borehole 11 and anchoring the tool 10 each time the piston actuators 39, 40, 43 and 44 are extended. It will, however, be appreciated that the wall-engaging member 38 as well as its piston actuators 39 and 40 would not be needed if the effective stroke of the piston actuators 43 and 44 would be sufficient for assuring that the sealing member 41 can be extended into firm sealing engagement with one wall of the borehole 11 with the rear of the tool body 18 securely anchored against the opposite wall of the borehole. Conversely, the piston actuators 43 and 44 could be similarly omitted where the extension of the wall-engaging member 38 alone would be effective for moving the other side of the tool body 18 forwardly toward one wall of the borehole 11 to place the sealing pad 41 into firm sealing engagement therewith. However, in the preferred embodiment of the formation-testing tool 10, both the tool-anchoring means 19 and the fluid-admitting means 20 are made selectively extendible to enable the tool to be operated in boreholes of substantial diameter. This preferred design of the tool 10, of course, results in the overall stroke of the piston actuators 39 and 40 and the piston actuators 43 and 44 being kept to a minimum so as to reduce the overall diameter of the tool body 18.

To conduct connate fluids into the new and improved tool 10, the fluid-admitting means 20 further include an enlarged tubular member 45 having an open forward portion coaxially disposed within the sealing pad 41 and a closed rear portion which is slidably mounted within a larger tubular member 46 secured to the rear face of the plate 42 and extended rearwardly therefrom. By arranging the nose of the tublar fluid-admitting member 45 to normally protrude a short distance ahead of the forward face of the sealing pad 41, extension of the fluid-admitting means 20 will engage the forward end of the fluid-admitting member with the adjacent surface of the wall of the borehole 11 as the annular sealing pad is also forced thereagainst for isolating that portion of the borehole wall as well as the nose of the fluid-admitting member from the well bore fluids. To selectively move the tubular fluid-admitting member 45 in relation to the enlarged outer member 46, the smaller tubular member is slidably disposed within the outer tubular member and fluidly sealed in relation thereto as by sealing members 47 and 48 on inwardly-enlarged end portions 49 and 50 of the outer member and a sealing member 51 on an enlarged-diameter intermediate portion 2 of the inner member.

Accordingly, it will be appreciated that by virtue of the sealing members 47, 48 and 51, enclosed piston chambers 53 and 54 are defined within the outer tubular member 46 and on opposite sides of the outwardly-enlarged portion 52 of the inner tubular member 45 which, of course, functions as a piston member. Thus, by increasing the hydraulic pressure in the rearward chamber 53, the fluid-admitting member 45 will be moved forwardly in relation to the outer tubular member 46 as well as to the sealing pad 41. Conversely, upon the application of an increased hydraulic pressure to the forward piston chamber 54, the fluid-admitting member 45 will be retracted in relation to the outer member 46 and the sealing pad 41.

Pressure or fluid communication with the fluid-admitting menas 20 is controlled by means such as a generally-cylindrical valve member 55 which is coaxially disposed within the fluid-admitting member 45 and cooperatively arranged for axial movement therein between a retracted or open position and the illustrated advanced or closed position where the enlarged forward end 56 of the valve member is substantially, if not altogether, sealingly engaged with the forwardmost interior portion of the fluid-admitting member. To support the valve member 55, the rearward portion of the valve member is axially hollowed, as at 57, and coaxially disposed over a tubular member 58 projecting forwardly from the transverse wall 59 closing the rear end of the fluid-admitting member 45. The axial bore 57 is reduced and extended forwardly along the valve member 55 to a termination with one or more transverse fluid passages 60 in the forward portion of the valve member just behind its enlarged head 56.

To provide piston means for selectively moving the valve member 55 in relation to the fluid-admitting member 45, the rearward portion of the valve member is enlarged, as at 61, and outer and inner sealing members 62 and 63 are coaxially disposed thereon and respectively sealingly engaged with the interior of the fluid-admitting member and the exterior of the forwardly-extending tubular member 58. A sealing member 64 mounted around the intermediate portion of the valve member 55 and sealingly engaged with the interior wall of the adjacent portion of the fluid-admitting member 45 fluidly seals the valve member in relation to the fluid-admitting member. Accordingly, it will be appreciated that by increasing the hydraulic pressure in the enlarged piston chamber 65 defined to the rear of the enlarged valve portion 61 which serves as a piston member, the valve member 55 will be moved forwardly in relation to the fluid-admitting member 45. Conversely, upon application of an increased hydraulic pressure to the forward piston chamber 66 defined between the sealing members 62 and 64, the valve member 55 will be moved rearwardly along the forwardly-projecting tubular member 58 so as to retract the valve member in relation to the fluid-admitting member 45.

Those skilled in the art will, of course, appreciate that many earth formations, as at 12, are relatively unconsolidated and are, therefore, readily eroded by the withdrawal of connate fluids. Thus, to prevent any significant erosion of such unconsolidated formation materials, the fluid-admitting member 45 is arranged to define an internal annular space 67 and a flow passage 68 in the forward portion of the fluid-admitting member, and a tubular screen 69 of suitable fineness is coaxially mounted around the annular space. In this manner, when the valve member 55 is retracted, formation fluids will be compelled to pass through the exposed forward portion of the screen 69 ahead of the enlarged head 56, into the annular space 67, and then through the fluid passage 60 into the fluid passage 57 and the tubular member 58. Thus, as the valve member 55 is retracted, should loose or unconsolidated formation materials be eroded from a formation as connate fluids are withdrawn therefrom, the materials will be stopped by the exposed portion of the screen 69 ahead of the enlarged head 56 of the valve member thereby quickly forming a permeable barrier to prevent the continued erosion of loose formation materials once the valve member halts.

A sample or flow line 70 is cooperatively arranged in the formation-testing tool 10 and has one end coupled, as by a flexible conduit 71, to the fluid-admitting means 20 and its other end terminated in a pair of branch conduits 72 and 73 respectively coupled to the fluid-collecting chambers 21 and 22. To control the communication between the fluid-admitting means 20 and the fluid-collecting chambers 21 and 22, normally-closed flow-control valves 74-76 of a similar or identical design are arranged respectively in the flow line 70 and in the branch conduits 72 and 73 leading to the sample chambers. For reasons which will subsequently be described in greater detail in explaining the methods and apparatus of the present invention, a normally-open control valve 77 which is similar to the normally-closed control valves 74-76 is cooperatively arranged in a branch conduit 78 for selectively controlling communication between the well bore fluids exterior of the tool 10 and the upper portion of the flow line 70 extending between the flow-line control valve 74 and the fluid-admitting means 20.

As illustrated, the control valve 77 employed in the present invention is comprised of a valve body 79 cooperatively carrying a typical piston actuator 80 which is normally biased to an elevated position by a spring 81 of a predetermined strength. A valve member 82 coupled to the piston actuator 80 is cooperatively arranged for blocking fluid communication between the inlet and outlet fluid ports of the control valve whenever the valve member is moved to its lower position. The control valves 74-76 are similar to the control valve 77 except that a spring of selected strength is respectively arranged in each for normally biasing each of these valve members to a closed position.

As shown in FIGS. 2A-2B, a branch conduit 83 is coupled to the flow line 70 at a convenient location between the sample chamber control valves 75 and 76 and the flow-line control valve 74, with this branch conduit being terminated at an expansion chamber 84 of a predetermined volume. A reduced-diameter displacement piston 85 is operatively mounted in the chamber 84 and arranged to be moved between selected upper and lower positions therein by a typical piston actuator shown generally at 86. Accordingly, it will be appreciated that upon movement of the displacement piston 85 from its lower position as illustrated in FIG. 2A to an elevated or upper position, the combined volume of whatever fluids that are then contained in the branch conduit 83 as well as in that portion of the flow line 70 between the flow-line control valve 74 and the sample chamber control valves 75 and 76 will be correspondingly increased.

As best seen in FIG. 2A, the preferred embodiment of the control system 15 further includes a pump 87 that is coupled to a driving motor 88 and cooperatively arranged for pumping a suitable hydraulic fluid such as oil or the like from a reservoir 89 into a discharge or outlet line 90. Since the tool 10 is to be operated in well bores, as at 11, which typically contain dirty and usually corrosive fluids, the reservoir 89 is preferably arranged to totally immerse the pump 87 and the motor 88 in the clean hydraulic fluid. Inasmuch as the formation-testing tool 10 must operate at extreme depths, the reservoir 89 is provided with an inlet 91 for well bore fluids and an isolating piston 92 is movably arranged in the reservoir for maintaining the hydraulic fluid contained therein at a pressure about equal to the hydrostatic pressure at whatever depth the tool is then situated. A spring 93 is arranged to act on the piston 92 for maintaining the pressure of the hydraulic fluid in the reservoir 89 at an increased level slightly above the well bore hydrostatic pressure so as to at least minimize the influx of well bore fluids into the reservoir. In addition to isolating the hydraulic fluid in the reservoir 89, the piston 92 will also be free to move as required to accommodate volumetric changes in the hydraulic fluid which may occur under different well bore conditions. One or more inlets, as at 94 and 95, are provided for returning hydraulic fluid from the control system 15 to the reservoir 89 during the operation of the tool 10.

The fluid outlet line 90 is divided into two major branch lines which are respectively designated as the "set" line 96 and the "retract" line 97. To control the admission of hydraulic fluid to the "set" and "retract" lines 96 and 97, a pair of normally-closed solenoid-actuated valves 98 and 99 are cooperatively arranged to selectively admit hydraulic fluid to the two lines as the control switch 23 at the surface is selectively positioned; and a typical check valve 100 is arranged in the "set" line 96 downstream of the control valve 98 for preventing the reverse flow of the hydraulic fluid whenever the pressure in the "set" line is greater than that then existing in the fluid outlet line 90. Typical pressure switches 101-103 are cooperatively arranged in the "set" and "retract" lines 96 and 97 for selectively discontinuing operation of the pump 87 whenever the pressure of the hydraulic fluid in either of these lines reaches a desired operating pressure and then restarting the pump whenever the pressure drops below this value so as to maintain the line pressure within a selected operating range.

Since it is preferred that the pump 87 be a positive-displacement type to achieve a rapid predictable rise in the operating pressures in the "set" and "retract" lines 96 and 97 in a minimum length of time, the control system 15 also provides for temporarily opening the outlet line 90 until the motor 88 has reached its rated operating speed. Accordingly, the control system 15 is cooperatively arranged so that each time the pump 87 is to be started, the control valve 99 (if it is not already open) as well as a third normally-closed solenoid-actuated valve 104 will be temporarily opened to bypass hydraulic fluid directly from the output line 90 to the reservoir 89 by way of the return line 94. Once the motor 88 has reached operating speed, the bypass valve 104 will, of course, be reclosed and either the "set" line control valve 98 or the "retract" line control valve 99 will be selectively opened as required for that particular operational phase of the tool 10. It should be noted that during those times that the "retract" line control valve 99 and the fluid-bypass valve 104 are opened to allow the motor 88 to reach its operating speed, the check valve 100 will function to prevent the reverse flow of hydraulic fluid from the "set" line 96 when the "set" line control valve 98 is open.

Accordingly, it will be appreciated that the control system 15 cooperates for selectively supplying pressured hydraulic fluid to the "set" and "retract" lines 96 and 97. Since the pressure switches 101 and 102 respectively function only to limit the pressures in the "set" and "retract" lines to a selected maximum pressure range commensurate with the rating of the pump 87, the new and improved control system 15 is further arranged to cooperatively regulate the pressure of the hydraulic fluid which is being supplied at various times to selected portions of the system. Although this regulation can be accomplished in different manners, it is preferred to employ a number of pressure-actuated control valves such as shown schematically at 105-108 in FIGS. 2A and 2B. As shown in FIG. 2A, the control valve 105, for example, includes a valve body 109 having a valve seat 110 coaxially arranged therein between inlet and outlet fluid ports. The upper portion of the valve body 109 is enlarged to provide a piston cylinder 111 carrying an actuating piston 112 in coincidental alignment with the valve seat 110. A spring 113 of a predetermined strength is arranged for normally urging the actuating piston 112 toward the valve seat 110 and a control port 114 is provided for admitting hydraulic fluid into the cylinder 111 at a sufficient pressure to overcome the force of this spring whenever the piston is to be selectively moved away from the valve seat. Since the control system 15 operates at pressures no less than the hydrostatic pressure of the well bore fluids, a relief port 115 is provided in the valve body 109 for communicating the space in the cylinder 111 above the actuating piston 112 with the reservoir 89. A valve member 116 complementally shaped for seating engagement with the valve seat 110 is cooperatively coupled to the actuating piston 112 as by an upright stem 117 which is slidably disposed in an axial bore 118 in the piston. A spring 119 of selected strength is disposed in the axial bore 118 for normally urging the valve member said enclosed into seating engagement with the valve seat 110.

Accordingly, in its operating position depicted in FIG. 2A, the control valve 105 (as well as the valve 106) will simply function as a normally-closed check valve. This is to say, in this operating position, hydraulic fluid can flow only in a reverse direction whenever the pressure at the valve outlet is sufficiently greater than the inlet pressure to elevate the valve member 116 from the valve seat 110 against the predetermined closing force pressure-actuated by the spring 119. On the other hand, when sufficient fluid pressure is applied to the control port 114 for elevating the actuating piston, opposed shoulders, as at 120, on 23 the stem 117 and the piston 112 will engage for elevating the valve member 116 from the valve seat 110.

As shown in FIGS. 2A and 2B, it will be appreciated that the control valve 107 (as well as the valve 108) is similar to the control valve 105 except that in the first-mentioned control valve, the valve member 121 is preferably rigidly coupled to its associated actuating piston 122. Thus, the control valve 107 (as well as the valve 108) has no alternate checking action allowing reverse flow and is simply a normally-closed pressure-actuated valve for selectively controlling fluid communication between its inlet and outlet ports. Hereagain, the hydraulic pressure at which the control valve 107 (as well as the valve 108) is to selectively open is governed by the predetermined strength of the spring 123 normally biasing the valve member 121 to its closed position.

The "set" line downstream of the check valve 100 is comprised of a low-pressure section 124 having one branch 125 coupled to the fluid inlet of the control valve 107 and another branch 126 which is coupled to the fluid inlet of the control valve 105 to selectively supply hydraulic fluid to a high-pressure section 127 of the "set" line which is itself terminated at the fluid inlet of the control valve 108. To regulate the supply of hydraulic fluid from the low-pressure section 124 to the high-pressure section 127 of the "set" line 96, a pressure-communicating line 128 is coupled between the low-pressure section and the control port of the control valve 105. Accordingly, so long as the pressure of the hydraulic fluid in the low-pressure section of the "set" line 96 remains below the predetermined actuating pressure required to open the control valve 105, the high-pressure section 127 will be isolated from the low-pressure section 124. Conversely, once the hydraulic pressure in the low-pressure line 124 reaches the predetermined actuating pressure of the valve 105, the control valve will open to admit the hydraulic fluid into the high-pressure line 127.

The control valves 107 and 108 are respectively arranged to selectively communicate the low-pressure and high-pressure sections 124 and 127 of the "set" line 96 with the fluid reservoir 89. To accomplish this, the control ports of the two control valves 107 and 108 are each connected to the "retract" line 97 by suitable pressure-communicating lines 129 and 130. Thus, whenever the pressure in the "retract" line 97 reaches their respective predetermined actuating levels, the control valves 107 and 108 will be respectively opened to selectively communicate the two sections 124 and 127 of the "set" line 96 with the reservoir 89 by way of the return line 94 coupled to the respective outlets of the two control valves.

As previously mentioned, in FIGS. 2A-2B the tool 10 and the sub-surface portion of the control system 15 are depicted as their several components will appear when the tool is retracted. At this point, the wall-engaging member 38 and the sealing pad 41 are respectively retracted against the tool body 18 to facilitate passage of the tool 10 into the borehole 11. To prepare the tool 10 for lowering into the borehole 11, the switches 23 and 24 are moved to their second or "initialization" positions 26. At this point, the hydraulic pump 87 is started to raise the pressure in the "retract" line 97 to a selected maximum to be certain that the pad 41 and the wall-engaging member 38 are fully retracted. As previously mentioned, the control valves 99 and 104 will be momentarily opened when the pump 87 is started until the pump motor 88 has reached its operating speed. At this time also, the control valve 77 is open and that portion of the flow line 70 between the closed flow-line control valve 74 and the fluid-admitting means 20 will be filled with well bore fluids at the hydrostatic pressure at the depths at which the tool 10 is then situated.

When the tool 10 is at a selected operating depth, the switches 23 and 24 are advanced to their third positions 27. Then, once the pump 87 has reached its rated operating speed, the hydraulic pressure in the output line 90 will rapidly rise to its selected maximum operating pressure as determined by the maximum or "off" setting of the pressure switch 101. As the pressure progressively rises, the control systems 15 will successively function at selected intermediate pressure levels for sequentially operating the several control valves 105-108 as described fully in the aforementioned copending application, Ser. No. 313,235.

Turning now to FIG. 3, selected portions of the control system 15 and various components of the tool 10 are schematically represented to illustrate the operation of the tool at about the time that the pressure in the hydraulic output line 90 reaches its lowermost intermediate pressure level. To facilitate an understanding of the operation of the tool 10 and the control system 15 at this point in its operating cycle, only those components which are then operating are shown in FIG. 3.

At this time, since the control switch 23 (FIG. 1) is in its third position 27, the solenoid valves 98 and 104 will be open; and, since the hydraulic pressure in the "set" line 96 has not yet reached the upper pressure limit as determined by the pressure switch 101, the pump motor 88 will be operating. Since the control valve 105 (not shown in FIG. 3) is closed, the high-pressure section 127 of the "set" line 96 will still be isolated from the low-pressure section 124. Simultaneously, the hydraulic fluid contained in the forward pressure chambers of the piston actuators 39, 40, 43 and 44 will be displaced (as shown by the arrows as at 131) to the "retract" line 97 and returned to the reservoir 89 by way of the open solenoid valve 104. These actions will, of course, cause the wall-engaging member 38 as well as the sealing pad 41 to be respectively extended in opposite lateral directions until each has moved into firm engagement with the opposite sides of the borehole 11.

It will be noticed in FIG. 3 that hydraulic fluid will be admitted by way of branch hydraulic lines 132 and 33 to the enclosed annular chamber 53 to the rear of the enlarged-diameter portion 52 of the fluid-admitting member 45. At the same time, hydraulic fluid from the piston chamber 54 ahead of the enlarged-diameter postion 52 will be discharged by way of branch hydraulic lines 134 and 135 to the "retract" line 97 for progressively moving the fluid-admitting member 45 forwardly in relation to the sealing member 41 until the nose of the fluid-admitting member 45 engages the wall of the borehole 11 and then halts. The sealing pad 41 is then urged forwardly in relation to the now-halted tubular member 45 until the pad sealingly engages the borehole wall for packing-off or isolating the isolated wall portion from the well bore fluids.

It should also be noted that although the pressured hydraulic fluid is also admitted at this time into the forward piston chamber 66 between the sealing members 62 and 64 on the valve member 55, the valve member is temporarily prevented from moving rearwardly in relation to the inner and outer tubular members 45 and 46 inasmuch as the control valve 106 (not shown in FIG. 3) is still closed thereby temporarily trapping the hydraulic fluid in the rearward piston chamber 65 to the rear of the valve member. The significance of this delay in the retraction of the valve member 55 will be subsequently explained.

As also illustrated in FIG. 3, the hydraulic fluid in the low-pressure section 124 of the "set" line 96 will also be directed by way of a branch hydraulic line 136 to the piston actuator 86. This will, of course, result in the displacement piston 85 being elevated as the hydraulic fluid from the piston actuator is returned to the "retract" line 97 by way of a branch hydraulic conduit 137. As will be appreciated, elevation of the displacement piston 85 in the expansion chamber 84 will be effective for significantly decreasing the pressure initially existing in the isolated portions of the branch line 83 and the flow line 70 between the still-closed flow-line control valve 74 and the still-closed chamber control valve 75 and 76 (not seen in FIG. 3). The purpose of this pressure reduction will be subsequently explained.

Once the wall-engaging member 38, the sealing pad 41 and the fluid-admitting member 45 have respectively reached their extended positions as illustrated in FIG. 3, it will be appreciated that the hydraulic pressure delivered by the pump 87 will again rise. Then, once the pressure in the output line 90 has reached its second intermediate level of operating pressure, the control valve 106 will open in response to this pressure level to now discharge the hydraulic fluid previously trapped in the piston chamber 65 to the rear of the valve member 55 back to the reservoir 89.

As illustrated, in FIG. 4, once the control valve 106 opens, the hydraulic fluid wil be displaced from the rearward piston chamber 65 by way of branch hydraulic lines 138, 139 and 135 to the "retract" line 197 as pressured hydraulic fluid from the "set" line 96 surges into the piston chamber 66 ahead of the enlarged-diameter portion 61 of the valve member 55. This will, of course, cooperate to rapidly drive the valve member 55 rearwardly in relation to the now-halted fluid-admitting member 45 for establishing fluid or pressure communication between the isolated portion of the earth formation 12 and the flow passages 57 and 60 in the valve member by way of the filter screen 69.

Although this is not fully illustrated in FIG. 4, it will be recalled from FIGS. 2A and 2B that the control valves 74-76 are initially closed to isolate the lower portion of the flow line 70 between these valves as well as the branch line 83 leading to the pressure-reduction chamber 84. However, in keeping with the principles of the present invention, the flow-line pressure-equalizing control valve 77 will still be open at the time the control valve 106 opens to retract the valve member 55 as depicted in FIG. 4. Thus, as the valve member 55 progressively uncovers the filtering screen 69, well bore fluids at a pressure greater than that of any connate fluids which may be present in the isolated earth formation 12 will be introduced into the upper portion of the flow line 70 and, by way of the flexible conduit member 71, into the rearward end of the tubular member 58. As these high-pressure well bore fluids pass into the annular space 67 around the filtering screen 69, they will be forcibly discharged (as shown by the arrows 140) from the forward end of the fluid-admitting member 45 for washing away any plugging materials such as mudcake or the like which may have become deposited on the internal surface of the filtering screen when the valve member 55 fitst uncovers the screen. Thus, to attain the objects of the present invention, the control system 15 is operative for providing a momentary outward surge or reverse flow of well bore fluids for cleansing the filtering screen 69 of unwanted debris or the like before a sampling or testing operation is commenced.

It will be appreciated that once the several components of the formation-testing tool 10 and the control system 15 have reached their respective positions as depicted in FIG. 4, the hydraulic pressure in the output line 90 will again quickly increase to its next intermediate pressure level. Once the pump 87 has increased the hydraulic pressure in the output line 90 to this next predetermined intermediate pressure level, the control valve 105 will selectively open as depicted in FIG. 5A. As seen there, opening of the control valve 105 will be effective for now supplying hydraulic fluid to the high-pressure section 127 of the "set" line 96 and two branch conduits 141 and 142 connected thereto for successively closing the control valve 77 and then opening the control valve 74.

In this manner, as depicted by the several arrows at 143 and 144, hydraulic fluid at a pressure representative of the intermediate operating level will be supplied by way of a typical check valve 145 to the upper portion of the piston cylinder 146 of the normally-open control valve 77 as fluid is exhausted from the lower portion thereof by way of a conduit 147 coupled to the "retract" line 97. This will, of course, be effective for closing the valve member 82 so as to now block further communication between the flow line 70 and the well bore fluids exterior of the tool 10. Simultaneously, the hydraulic fluid will also be admitted into the lower portion of the piston cylinder 148 of the control valve 74. By arranging the biasing spring 81 for the normally-open control valve 77 to be somewhat weaker than the biasing spring 149 for the normally-closed control valve 74, the second valve will be momentarily retained in its closed position until the first valve has had time to close. Thus, once the valve 77 closes, as the hydraulic fluid enters the lower portion of the piston chamber 148 of the control valve 74, the value member 150 will be opened as hydraulic fluid is exhausted from the upper portion of the chamber through a typical check valve 151 and a branch return line 152 coupled to the "retract" line 97.

It will be appreciated therefore, that with the tool 10 in the position depicted in FIGS. 5A and 5B, the flow line 70 is now isolated from the wall bore fluids and is in communication with the isolated portion of the earth formation 12 by way of the flexible conduit 71. It will also be recalled from the preceding discussion of FIG. 3 that the branch flow line 83 as well as the portion of the main flow line 70 between the flow-line control valve 74 and the sample chamber control valves 75 and 76 were previously expanded by the upward movement of the displacement piston 85 in the reduced-volume chamber 84. Thus, upon opening of the flow-line control valve 74, the isolated portion of the earth formation 12 will be communicated with the reduced-pressure space represented by the previously-isolated portions of the flow line 70 and the branch conduit 83.

Of particular interest to the present invention, it should be noted that should the formation 12 be relatively unconsolidated, the rearward movement of the valve member 55 in cooperation with the forward movement of the fluid-admitting member 45 will allow only those loose formation materials displaced by the advancement of the fluid-admitting member into the formation to enter the fluid-admitting member. This is to say, the fluid-admitting member 45 can advance into the formation 12 only by displacing loose formation materials; and, since the space opened by the rearward displacement of the valve member 55 is the only place into which the loose formation materials can enter, further erosion of the formation materials will be halted once the fluid-admitting member has been filled with loose materials as shown in FIG. 5B. On the other hand, should a formation interval which is being tested be relatively well-compacted, the advancement of the fluid-admitting member 45 will be relatively slight with its nose making little or no penetration into the isolated earth formation. It will, of course, be appreciated that the nose of the fluid-admitting member 45 will be urged outwardly with sufficient force to at least penetrate the mudcake which typically lines the borehole walls adjacent to permeable earth formations. In this situation, however, the forward movement of the fluid-admitting member 45 will be unrelated to the rearward movement of the valve member 55 as it progressively uncovers the filtering screen 69. In either case, the sudden opening of the valve 74 will cause mudcake to be pulled to the rear of the screen 69 to leave it clear for the subsequent passage of connate fluids.

AS best seen in FIGS. 5A and 5B, therefore, should there be any producible connate fluids in the isolated earth formation 12, the formation pressure will be effective for displacing these connate fluids by way of the fluid-admitting means 20 into the flow line until such time that the lower portion of the flow line 70 and the branch conduit 83 are filled and pressure equilibrium is established in the entire flow line. By arranging a typical pressure-measuring transducer, as at 153 (or, if desired, one or more other suitable transducers) in the flow line 70, one or more measurements representative of the characteristics of the connate fluids and the formation 12 may be transmitted to the surface by a conductor 154 and, if desired, recorded on the recording apparatus 16 (FIG. 1). The pressure measurements provided by the transducer 153 will, of course, permit the operator at the surface to readily determine the formation pressure as well as to obtain one or more indications representative of the potential producing ability of the formation 12. The various techniques for analyzing formation pressures as well known in the art and are, therefore, of no significance to understanding the present invention.

It will be recognized, of course, that by virtue of the purging action which was previously provided by the outflowing well bore fluids in the practice of the present invention, there is a reasonable assurance that the filtering screen 69 will have been cleared of plugging materials such as mudcake of formation materials that may otherwise plug the fluid-admitting means 20. However, the sudden introduction of connate fluids into the flow line 70 will also be effective for clearing the screen 69 of residual plugging materials.

The measurements provided by the pressure transducer 153 at this time will indicate whether the sealing pad 41 has, in fact, established complete sealing engagement with the earth formation 12 inasmuch as the expected formation pressures will be recognizably lower than the hydrostatic pressure of the well bore fluids at the particular depth which the tool 10 is then situated. This ability to determine the effectiveness of the sealing engagement will, of course, allow the operator to retract the wall-engaging member 38 and the sealing pad 41 without having to unwittingly or needlessly continue the remainder of the complete operating sequence.

Assuming, however, that the pressure measurements provided by the pressure transducer 153 show that the sealing pad 41 is firmly seated, the operator may leave the formation-testing tool 10 in the position shown in FIGS. 5A and 5B as long as it is desired to observe as well as record the pressure measurements. As a result, the operator can determine such things as the time required for the formation pressure to reach equilibrium as well as the rate of increase and thereby obtain valuable information indicative of various characteristics of the earth formation 12 such as permeability and porosity. Moreover, with the new and improved tool 10, the operator can readily determine if collection of a fluid sample is warranted.

Once the several components of the tool 10 and the control system 15 have moved to their respective positions shown in FIGS. 5A and 5B, the hydraulic pressure will again rise until such time that the "set" line pressure switch 101 operates to halt the hydraulic pump 87. Inasmuch as the pressure switch 101 has a selected operating range, in the typical situation the pump 87 will be halted shortly after the control valve 77 closes and the control valve 74 opens. At this point in the operating cycle of the tool 10, once a sufficient number of pressure measurements have been obtained, a decision can be made whether it is advisable to obtain one or more samples of the producible connate fluids present in the earth formation 12. If such samples are not desired, the operator can simply operate the control switches 23 and 24 for retracting the wall-engaging member 38 as well as the sealing pad 41 without further ado.

On the other hand, should a fluid sample be desired, the control switches 23 and 24 (FIG. 1) are advanced to their next or so-called "sample" positions 28 to open, for example, a solenoid valve 155 (FIG. 2B) for coupling pressured hydraulic fluid from the high-pressure section 127 of the "set" line 96 to the piston actuator 156 of the sample chamber control valve 75. This will, of course, be effective for opening the control valve 75 to admit connate fluids through the flow line 70 and the branch conduit 72 into the sample chamber 21. If desired, a "chamber selection" switch 157 in the surface portion of the system 15 could also be moved from its "first sample" position 158 to its so-called "second sample" position 159 (FIG. 1) to energize a solenoid valve 160 (FIG. 2B) for opening the control valve 76 to also admit connate fluids into the other sample chamber 22. In either case, one or more samples of the connate fluids which are present in the isolated earth formation 12 can be selectively obtained by the new and improved tool 10.

Upon moving the control switches 23 and 24 to their so-called "sample-trapping" positions 29, the pump 87 will again be restarted. Once the pump 87 has reached operating speed, it will commence to operate much in the same manner as previously described and the hydraulic pressure in the output line 90 will begin rising with momentary halts at various intermediate pressure levels.

Accordingly, when the control switches 23 and 24 have been placed in their "sample trapping" positions 29, the solenoid valve 99 will open to now admit hydraulic fluid into the "retract" line 97. By means of the electrical conductor 103a (FIG. 1), however, the pressure switch 103 is enabled and the pressure switch 102 is disabled so that in this position of the control switches 23 and 24 the maximum operating pressure which the pump 87 can initially reach is limited to the pressure at the lower operating pressure level determined by the pressure switch 103. Thus, by arranging the control valve 108 to open in response to a hydraulic pressure corresponding to this predetermined pressure level, hydraulic fluid in the high-pressure section 127 of the "set" line 96 will be returned to the reservoir 89 by means of the return line 94. As the hydraulic fluid in the high-pressure section 127 returns to the reservoir 89, the pressure in this portion of the "set" line 96 will be rapidly decreased to close the control valve 105 once the pressure in the line is insufficient to hold the valve open. Once the control valve 105 closes, the pressure remaining in the low-pressure section 124 of the "set" line 96 will remain at a reduced pressure which is nevertheless effective for retaining the wall-engaging member 38 and the sealing pad 41 fully extended.

As the hydraulic fluid is discharged from the lower portion of the piston actuator 156 by way of the still-open solenoid valve 155 and fluid from the "retract" line 97 enters the upper postion of the actuator by way of a branch line 161, the chamber control valve 75 will close to trap the sample of connate fluids which is then present in the sample chamber 21. Similarly, should there also be a fluid sample in the other sample chamber 22, the control valve 76 can also be readily closed by operating the switch 157 to reopen the solenoid valve 160. Closure of the control valve 75 (as well as the valve 76) will, of course, be effective for trapping any fluid samples collected in one or the other or both of the sample chambers 21 and 22.

Once the control valve 75 (and, if necessary, the control valve 76) has been reclosed, the control switches 23 and 24 are moved to their next or so-called "retract" switching positions 30 for initiating the simultaneous retraction of the wall-engaging member 38 and the sealing pad 41. In this final position of the control switch 24, the pressure switch 103 is again rendered inoperative and the pressure switch 102 is enabled so as to now permit the hydraulic pump 87 to be operated at full rated capacity for attaining hydraulic pressures greater than the first intermediate operating level in the "retract" cycle. Once the pressure switch 103 has again been disabled, the pressure switch 102 will now function to operate the pump 87 so that the pressure will now quickly rise until it reaches the next operating level.

At this point, hydraulic fluid will be supplied through the "retract" line 97 and the branch hydraulic line 147 for reopening the pressure-equalizing control valve 77 to admit well bore fluids into the flow line 70. Opening of the pressure-equalizing valve 77 will admit well bore fluids into the isolated space defined by the sealing pad 41 so as to equalize the pressure differential existing across the pad. Hydraulic fluid displaced from the upper portion of the piston chamber 146 of the control valve 77 will be discharged through a typical relief valve 161 which is arranged to open only in response to pressures equal or greater than that of this present operating level. The hydraulic fluid displaced from the piston chamber 146 through the relief valve 161 will be returned to the reservoir 89 by way of the branch hydraulic line 141, the high-pressure section 127 of the "set" line 96, the still-open control valve 108, and the return line 94.

When the hydraulic pressure in the output line 90 has either reached the next operating level or, if desired, a still-higher level, pressured hydraulic fluid in the "retract" line 97 will reopen the control valve 107 to communicate the low-pressure section 124 of the "set" line 96 with the reservoir 89. When this occurs, hydraulic fluid in the "retract" line will be admitted to the "retract" side of the several piston actuators 39, 40, 43 and 44. Similarly, the pressured hydraulic fluid will also be admitted into the annular space 54 in front of the enlarged-diameter piston portion 52 for retracting the fluid-admitting member 45 as well as into the annular space 66 for returning the valve member 55 to its forward position. The hydraulic fluid exhausted from the several piston actuators 39, 40, 43 and 44 as well as the piston chambers 54 and 66 will be returned directly to the reservoir 89 by way of the high-pressure section 124 of the "set" line 96 and the control valve 107. This action will, of course, retract the wall-engaging member 38 as well as the sealing pad 41 against the tool body 18 to permit the tool 10 to be either repositioned in the well bore 11 or returned to the surface if no further testing is desired.

It should be noted that although there is an operating pressure applied to the upper portion of the piston cylinder 148 for the flow-line control valve 74 at the time that the control valve 77 is reopened, a normally-closed relief valve 162 which is paralleled with the check valve 151 is held in a closed position until the increasing hydraulic pressure developed by the pump 87 exceeds the operating level used to retract the wall-engaging member 38 and the sealing pad 41. At this point in the operating sequence of the new and improved tool 10, the flow-line control valve 74 will be reclosed.

The pump 87 will, of course, continue to operate until such time that the hydraulic pressure in the output line 90 reaches the upper limit determined by the setting of the pressure switch 102. At some convenient time thereafter, the control switches 23 and 24 are again returned to their initial or "off" positions 25 for halting further operation of the pump motor 88 as well as reopening the solenoid valve 104 to again communicate the "retract" line 97 with the fluid reservoir 89. This completes the operating cycle of the new and improved tool 10.

Referring again to FIG. 4, it will be appreciated that the new and improved methods of the present invention will assure that communication will be established between the flow line 70 and the formation, as at 12, before any measurements or samples are taken. For example, should the interior surface of the filtering screen 69 become unduly coated with particles of the relatively-impermeable mudcake as the valve member 55 moves to its rearward position, opening of the valve member will be effective for developing a significant reverse flow of the higher-pressure well bore fluids through the screen 69 and into the lower-pressure formation 12. Similarly, should extremely-fine particles of sand or the like from the formation 12 be lodged against the interior surfaces of the filter medium 69, this reverse flow of well bore fluids will be effective for cleansing the filter before any tests are made.

Accordingly, in keeping with the objects of the present invention, since the control valve 77 is open to admit well bore fluids into the upper portion of the flow line 70, when the valve member 55 is opened the filtering screen 69 will be thoroughly cleansed by the outward surge of well bore fluids. Thus, when the formation 12 is subsequently communicated with the reduced or atmospheric pressure initially present n the previously-isolated lower portion of the flow line 70, producible connate fluids in the isolated portion of the formation will be drawn into the flow line. It will, of course, be recognized that if, on the other hand, there are no producible connate fluids in the formation 12, the pressure readings provided by the transducer 153 will simply indicate little or no pressure rise in the flow line 70. In either case, the operator at the surface will be reliably assured that a failure to obtain a significant pressure increase in the flow line measurements is in fact caused by a non-producible formation and is not unknowingly attributed to a tightly-plugged filter screen 69 instead. Moreover, the new and improved methods of the present invention are of equal advantage when a sample of connate fluids is to be taken as well. Thus, instead of obtaining little or no flow of fluid which would occur with at least a partially-blocked screen 69, the reverse flushing of the filter will assure the operator that the screen is clean so that formation fluids are free to flow into the tool 10. This can clearly reduce the time required to perform a typical testing operation.

While only a particular embodiment of the present invention and one mode of practicing the invention have been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects; and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

Claims

What is claimed is:

1. A method for testing earth formations traversed by a well bore and comprising the steps of:

engaging fluid-admitting means coupled by a filtering medium to a fluid passage against a wall surface of said well bore adjacent to an earth formation believed to contain producible connate fluids for isolating said wall surface from fluids in said well bore and placing said fluid-admitting means in position for receiving connate fluids from said earth formation;

discharging said well bore fluids from said fluid passage in a reverse direction through said filtering medium and into said fluid-admitting means and said earth formation for cleansing said filtering medium; and, thereafter,

communicating said fluid passage with an enclosed chamber initially at a reduced pressure for drawing producible connate fluids from said earth formation and in the opposite direction through said filtering medium and into said fluid passage to obtain a filtered sample of said connate fluids in said enclosed chamber.

2. The method of claim 1 further including the additional step of:

measuring the pressure in saidenclosed chamber and said fluid passage for obtaining at least one pressure measurement indicative of at least one characteristic of said earth formation.

3. The method of claim 1 further including the additional steps of:

monitoring at least one characteristic of said filtered sample drawn into said fluid passage for obtaining a series of measurements representative of the production characteristics of said earth formation; and, thereafter,

discontinuing further communication between said fluid passage and said enclosed chamber for trapping said filtered sample therein.

4. The method of claim 1 further including the additional steps of:

monitoring at least one characteristic of said filtered sample drawn into said fluid passage for obtaining a series of measurements representative of the production characteristics of said earth formation; and, thereafter,

expelling said filtered sample from said enclosed chamber.

5. A method for testing earth formations traversed by a well bore and comprising the steps of:

urging fluid-admitting means including a normally-closed fluid-sampling member coupled by a filtering medium to a fluid passage into sealing engagement with a wall surface of said well bore adjacent to an earth formation believed to contain producible connate fluids for isolating said wall surface from fluids in said well bore and placing said fluid-sampling member in position for subsequently communicating with said earth formation;

opening said fluid-sampling member and admitting said well bore fluids into said fluid passage for passing said well bore fluids through said filtering medium and said fluid-sampling member into said earth formation to cleanse said filtering medium sand said fluid-sampling member of potentially-plugging materials;

closing communication between said well bore fluids and said fluid passage; and, thereafter,

coupling an enclosed reduced-pressure chamber to said fluid passage for drawing producible connate fluids from said earth formation through said fluid-sampling member and said filtering medium and into said fluid passage to obtain a filtered sample of said connate fluids in said enclosed chamber.

6. The method of claim 5 further including the additional step of:

uncoupling said enclosed chamber from said fluid passage for collecting said filtered sample.

7. The method of claim 5 further including the additional steps of:

monitoring the pressure in said fluid passage for obtaining a series of pressure measurements representative of the production characteristics of said earth formation; and

uncoupling said enclosed chamber from said fluid passage for collecting said filtered sample in said enclosed chamber.

8. The method of claim 5 further including the additional steps of:

monitoring the pressure in said fluid passage for obtaining a series of pressure measurements representative of the production characteristics of said earth formation;

expelling said filtered sample from said enclosed chamber and uncoupling said enclosed chamber from said fluid passage;

reclosing said fluid-sampling member;

reducing the pressure in said enclosed chamber;

removing said fluid-admitting means from said wall surface and urging said fluid-admitting means into sealing engagement with another wall surface of said well bore adjacent to another earth formation believed to contain producible connate fluids for isolating said other wall surface from said well bore fluids and placing said fluid-sampling member in position for subsequently communicating with said other earth formation;

re-opening said fluid-sampling member and re-admitting said well bore fluids into said fluid passage for passing said well bore fluids through said filtering medium and said fluid-sampling member into said other earth formation to recleanse said filtering medium and said fluid-sampling member of potentially-plugging materials;

reclosing communication between said well bore fluids and said fluid passage;

recoupling said enclosed chamber to said fluid passage for drawing producible connate fluids from said other earth formation through said fluid-sampling member and said filtering medium and into said fluid passage to obtain a filtered sample of said connate fluids from said other earth formation in said enclosed chamber; and

remonitoring the pressure in said fluid passage for obtaining a second series of pressure measurements representative of the production characteristics of said other earth formation.

9. The method of claim 5 further including the additional steps of:

monitoring the pressure in said fluid passage for obtaining a series of pressure measurements representative of the production characteristics of said earth formation;

coupling a sample receiver at a reduced pressure to said fluid passage for collecting filtered connate fluids from said earth formation in said sample receiver;

closing said sample receiver for entrapping connate fluids collected therein;

expelling said filtered sample from said enclosed chamber and uncoupling said enclosed chamber from said fluid passage;

reclosing said fluid-sampling chamber;

removing said fluid-admitting means from said wall surface and urging said fluid-admitting means into sealing engagement with another wall surface of said well bore adjacent to another earth formation believed to contain producible connate fluids for isolating said other wall surface from said well bore fluids and placing said fluid-sampling member in position for subsequently communicating with said other earth formation;

re-opening said fluid-sampling member and re-admitting said well bore fluids into said fluid passage for passing said well bore fluids through said filtering medium and said fluid-sampling member into said other earth formation to recleanse said filtering medium and said fluid-sampling member of potentially-plugging materials;

reclosing communication between said well bore fluids and said fluid passage;

recoupling said enclosed chamber to said fluid passage for drawing producible connate fluids from said other earth formation through said fluid-sampling member and said filtering medium and into said fluid passage to obtain a filtered sample of said connate fluids from said other earth formation in said enclosed chamber; and

remonitoring the pressure in said fluid passage for obtaining a second series of pressure measurements representative of the production characteristics of said other earth formation.

10. The method of claim 9 further including the additional step of:

following the remonitoring step, coupling a second sample receiver at a reduced pressure to said fluid passage for collecting filtered connate fluids from said other earth formation in said second sample receiver; and

closing said second sample receiver for entrapping connate fluids collected therein.

11. The method of claim 5 further including the additional steps of:

monitoring the pressure in said fluid passage for obtaining a series of pressure measurements representative of the production characteristics of said earth formation;

expelling said filtered sample from said enclosed chamber and uncoupling said enclosed chamber from said fluid passage;

reclosing said fluid-sampling member;

reducing the pressure in said enclosed chamber;

removing said fluid-admitting means from said wall surface and urging said fluid-admitting means into sealing engagement with another wall surface of said well bore adjacent to another earth formation believed to contain producible connate fluids for isolating said other wall surface from said well bore fluids and placing said fluid-sampling member in position for subsequently communicating with said other earth formation;

re-opening said fluid-sampling member and re-admitting said well bore fluids into said fluid passage for passing said well bore fluids through said filtering medium and said fluid-sampling member into said other earth formation to recleanse said filtering medium and said fluid-sampling member of potentially-plugging materials;

reclosing communication between said well bore fluids and said fluid passage;

recoupling said enclosed chamber to said fluid passage for drawing producible connate fluids from said other earth formation through said fluid-sampling member and said filtering medium and into said fluid passage to obtain a filtered sample of said connate fluids from said other earth formation in said enclosed chamber;

remonitoring the pressure in said fluid passage for obtaining a second series of pressure measurements representative of the production characteristics of said other earth formation;

coupling a sample receiver at a reduced pressure to said fluid passage for collecting filtered connate fluids from said other earth formation in said sample receiver; and

closing said sample receiver for entrapping connate fluids collected therein.

12. A method for testing earth formations traversed by a well bore and comprising the steps of:

urging fluid-admitting means including a fluid passage coupled by a filtering medium to a fluid-sampling member having a normally-closed forward end and a rearward portion to the rear of said filtering medium into sealing engagement with a wall surface of said well bore adjacent to an earth formation believed to contain producible connate fluids for isolating said wall surface from fluids in said well bore and placing said closed end of said fluid-sampling member into position for subsequently receiving connate fluids from said earth formation;

opening said normally-closed forward end of said fluid-sampling member and admitting said well bore fluids into said fluid passage for passing said well bore fluids through said filtering medium and said fluid-sampling member into said earth formation to cleanse said filtering medium and said fluid-sampling member of potentially-plugging materials;

closing communication between said well bore fluids and said fluid passage;

expanding the volume of an enclosed test chamber coupled to said fluid passage downstream of said filtering medium for reducing the pressure in said fluid passage and said test chamber to about atmospheric pressure;

after said test chamber is expanded, coupling said test chamber to said fluid passage at a speed sufficient to quickly induct a filtered sample of producible connate fluids from said earth formation into said expanded test chamber for momentarily reducing the pressure of said connate fluid sample to about atmospheric pressure and displacing loose plugging materials from said wall surface into said rearward portion of said fluid-sampling member to the rear of said filtering medium; and

monitoring the pressure in said expanded test chamber for obtaining a series of pressure measurements indicative of the production capabilities of said earth formation.

13. The method of claim 12 further including the additional step of:

recording said pressure measurements for obtaining a record representative of the pressure characteristics of said earth formation as connate fluids are produced therefrom.

14. The method of claim 12 further including the additional step of:

after the pressure-monitoring step, coupling an enclosed sample chamber to said fluid passage downstream of said filtering medium for collecting another filtered sample of connate fluids from said earth formation.

15. The method of claim 12 further including the additional steps of:

after the pressure-monitoring step, reducing the volume of said test chamber for expelling said sample of connate fluids into said well bore;

uncoupling said test chamber from said fluid passage;

reclosing said normally-closed forward end of said fluid-sampling member;

re-opening said normally-closed forward end of said fluid-sampling member and re-admitting said well bore fluids into said fluid passage for again passing said well bore fluids through said filtering medium and said fluid-sampling member into said earth formation to recleanse said filtering medium and said fluid-sampling member for potentially-plugging materials;

reclosing communication between said well bore fluids and said fluid passage;

re-expanding the volume of said test chamber for again reducing the pressure in said fluid passage and said test chamber to about atmospheric pressure;

after said test chamber is re-expanded, re-coupling said re-expanded test chamber to said fluid passage at a speed sufficient to quickly induct a second filtered sample of producible connate fluids into said re-expanded test chamber for momentarily reducing the pressure of said second sample to about atmospheric pressure and displacing additional loose plugging materials from said wall surface into said rearward portion of said fluid-sampling member to the rear of said filtering medium; and

re-monitoring the pressure in said re-expanded test chamber for obtaining a second series of pressure measurements indicative of the production capabilities of said earth formation.

16. The method of claim 15 further including the additional step of:

after obtaining said pressure measurements, coupling an enclosed sample chamber to said fluid passage downstream of said filtering medium for collecting another filtered sample of connate fluids from said earth formation.

17. The method of claim 15 further including the additional steps of:

after obtaining said pressure measurements, reducing the volume of said test chamber again for expelling said second sample into said well bore;

reclosing said normally-closed forward end of said fluid-sampling member; and

disengaging said fluid-admitting means from said wall surface.

18. The method of claim 12 further including the additional steps of:

after the pressure-monitoring step, coupling an enclosed sample chamber to said fluid passage downstream of said filtering medium for collecting another filtered sample of connate fluids from said earth formation;

reducing the volume of said test chamber for expelling said sample of connate fluids into said well bore;

uncoupling said test chamber from said fluid passage;

reclosing said normally-closed forward end of said fluid-sampling member;

re-expanding the volume of said test chamber for again reducing the pressure in said fluid passage and said test chamber to about atmospheric pressure;

disengaging said fluid-admitting means from said wall surface and urging said fluid-admitting means into sealing engagement with another wall surface of said well bore adjacent to another earth formation believed to contain producible connate fluids for isolating said other wall surface from said well bore fluids;

re-opening said normally-closed forward end of said fluid-sampling member and re-admitting said well bore fluids into said fluid passage for aga1n passing said well bore fluids through said filtering medium and said fluid-sampling member into said other earth formation to recleanse said filtering medium and said fluid-sampling member of potentially-plugging materials;

reclosing communication between said well bore fluids and said fluid passage;

re-coupling said re-expanded test chamber to said fluid passage at a speed sufficient to quickly induct a second filtered sample of producible connate fluids into said re-expanded test chamber for momentarily reducing the pressure of said second sample to about atmospheric pressure and displacing loose plugging materials from said other wall surface into said rearward portion of said fluid-sampling member to the rear of said filtering medium; and

re-monitoring the pressure in said re-expanded test chamber for obtaining a second series of pressure measurements indicative of the production capabilities of said other earth formation.

19. The method of claim 18 further including the additional steps of:

after obtaining said second series of pressure measurements, coupling an enclosed sample chamber to said fluid passage downstream for collecting another sample of connate fluids from said other earth formation.

20. The method of claim 18 further including the additional steps of:

after obtaining said second series of pressure measurements, reducing the volume of said test chamber again for expelling said second sample into said well bore;

uncoupling said test chamber from said fluid passage;

re-closing said normally-closed end of said fluid-sampling member; and

disengaging said fluid-admitting means from said other wall surface.

21. Formation-testing apparatus adapted for suspension in a well bore traversing earth formations and comprising:

a body having a fluid passage adapted to receive connate fluids;

fluid-admitting means on said body including a fluid-sampling member having a forward end adapted to be selectively engaged with a well bore wall for isolating a portion thereof from well bore fluids, first valve means normally closing said forward end of said fluid-sampling member, and filtering means coupling said fluid passage to said fluid-sampling member to the rear of said first valve means;

means on said body and selectively operable for positioning said fluid-admitting means against a well bore wall to place said fluid-sampling member in communication with earth formations beyond said well bore wall; and

control means including second valve means selectively coupling said fluid passage to the exterior of said body for discharging well bore fluids through said fluid passage and in a reverse direction through said filtering means and into an earth formation to cleanse said filtering means of potentially-plugging material upon opening of said first valve means.

22. The formation-testing apparatus of claim 21 further including:

pressure-measuring means adapted for providing an indication of the pressure conditions in said fluid passage.

23. The formation-testing apparatus of claim 21 further including:

sample-collecting means on said body including a sample chamber, and means selectively operable for coupling said sample chamber to said fluid passage to receive connate fluids entering said fluid-admitting means.

24. The formation-testing apparatus of claim 23 further including:

pressure-measuring means adapted for providing an indication of the pressure conditions in said fluid passage.

25. The formation-testing apparatus of claim 21 further including:

pressure-reducing means on said body including an enclosed test chamber, and means selectively operable for varying the volume of said test chamber including piston means movable back and forth between a first position reducing the volume of said test chamber and a second position sufficiently expanding the volume of said test chamber to reduce the pressure in said test chamber to about atmospheric pressure;

pressure-measuring means adapted for providing indications representative of the pressure conditions in said test chamber; and

control means selectively operable after movement of said piston means to said second position and including third valve means for coupling said test chamber to said fluid passage at a speed sufficient to induct a sample of producible connate fluids from an earth formation in communication with said fluid-admitting means into said fluid passage and said expanded test chamber for momentarily reducing the pressure of a connate fluid sample to about atmospheric pressure.

26. The formation-testing apparatus of claim 25 further including:

a sample chamber on said body, and fourth valve means selectively operable for coupling said sample chamber to said fluid passage to receive connate fluids entering said fluid-sampling member.