Apparatus For Testing Earth Formations

Abstract

In the representative embodiment of the new and improved apparatus for testing earth formations disclosed herein, fluid-admitting means are selectively extended into sealing engagement with a potentially-producible earth formation and a selectively-operable valve on the fluid-admitting means is opened to place a filtering medium arranged on the fluid-admitting means into communication with the isolated formation without inducing the erosion of loose formation materials as the testing is conducted. Then, when the testing is completed, the fluid-admitting means are retracted and the valve is reclosed in readiness for subsequent testing operations.

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 sample 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 incompetent 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.

Accordingly, it is an object of the present invention to provide new and improvded formation-testing 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 earth formations of any nature.

This and other objects of the present invention are attained by providing formation-testing apparatus having selectively-extendible fluid-admitting means adapted for movement into sealing engagement with a potentially-producible earth formation to isolate a portion thereof from the well bore fluids. To limit loose formation materials which may be present in the isolated formation from plugging the fluid-admitting means, filtering means are disposed in the fluid-admitting means. Selectively-operable valve means are cooperatively arranged in the fluid-admitting means for selective movement between an open position to open communication between an isolated earth formation and the filtering means and a normal closed position blocking 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 new and improved formation-testing apparatus including a preferred embodiment of fluid-admitting means incorporating the principles of the present invention;

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 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 sand sampling operation to illustrate the operation of the fluid-admitting means of the present invention.

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 arranged on opposite sides of the body from new and improved fluid-admitting means 20 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 filed Dec. 8, 1972. by Harold J. Urbanosky filed simultaneously herewith, the new and improved formation-testing tool 10 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 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 transversely 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.

The fluid-admitting means 20 of the present invention are cooperatively arranged for sealing-off or isolating selected portions of the wall of the borehole 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, in the preferred embodiment, the fluid-admitting means 20 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 of the present invention 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 tubular 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 just before 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. The significance of this sequence of engagement will be subsequently explained. 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 52 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 means 20 of the present invention 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 with slits or apertures 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, 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 new and improved fluid-admitting means 20.

As illustrated, the control valve 77 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 hydraostatic 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 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 116 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. That 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 imposed 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 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 96 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 system 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 filed Dec. 8, 1972.

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 133 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 portion 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 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. In this manner, mudcake immediately ahead of the fluid-admitting member 45 will be displaced radially away from the nose of the fluid-admitting member so as to minimize the quantity of unwanted mudcake which will subsequently be admitted into the fluid-admitting means 20. Those skilled in the art will appreciate the significance of this unique arrangement.

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 valves 75 and 76 (not shown 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 will be displaced from the rearward piston chamber 65 by way of branch hydraulic lines 138, 139 and 135 to the "retract" line 97 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. This unique flexibility of operation provided by the fluid-admitting means 20 of the present invention is, of course, highly significant.

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, 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 first uncovers the screen. Thus, 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 valve 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 FIG. 5, the flow line 70 is now isolated from the well 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 further 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 within the forward end of the fluid-admitting member 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 by 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.

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. This freedom of action is, of course, possible by virtue of the flexibility of operation of the new and improved fluid-admitting means 20.

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 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 the solenoid valve 160 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 again 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 admit hydraulic fluid into the "retract" line 97. By means of the electrical conductor 103a, 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 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 sufficient 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 portion of the actuator by way of the 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 14. 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. 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 contron 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.

Accordingly, it will be appreciated that the fluid-admitting means 20 of the present invention enable the new and improved tool 10 to be selectively operated as required for meeting any situation which may be reasonably expected to occur during a formation-testing operation. For example, with the formation-sampling apparatus disclosed in U.S. Pat. No. 3,653,436, once operation of the tool shown there is initiated, further sampling operations cannot be conducted with removing the tool and reconditioning various components thereof. This is, of course in clear contrast to the versatility permitted by the selectively-operable fluid-admitting means 20 of the present invention and the new and improved tool 10.

While only a particular embodiment of the present invention has 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. Formation-testing apparatus adapted for suspension in a borehole traversing earth formations and comprising:

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

fluid-admitting means on said body and including a fluid-sampling member having a tubular forward portion adapted to be engaged with a borehole wall for isolating a surface thereof from well bore fluids;

means selectively operable for positioning said fluid-sampling member against a borehole wall to establish communication with earth formations therebeyond;

first means adapted for limiting the entrance of plugging materials into said first fluid passage including a second fluid passage in said fluid-sampling member and coupled to said first fluid passage, and filtering means cooperatively arranged on a wall of said fluid-sampling member between said second fluid passage and with tubular forward portion for retaining plugging materials within said fluid-sampling member as filtered connate fluids pass through said filtering means and enter said second fluid passage;

second means adapted for controlling the entrance of plugging materials and connate fluids into said fluid-sampling member and including a valve member coaxially arranged in said fluid-sampling member for movement between an advanced position within said tubular forward portion blocking communication into said fluid-sampling member and a retracted position to the rear of said tubular forward portion for uncovering said filtering means and defining a space for receiving plugging materials entering said tubular forward portion; and

valve-control means cooperatively arranged for selectively moving said valve member back and forth between its said advanced and retracted positions.

2. The formation-testing apparatus of claim 1 wherein said second fluid passage includes an annular chamber formed around an intermediate interior wall portion of said fluid-sampling member between said advanced and retracted positions of said valve member; and said filtering means include a tubular screen coaxially mounted in said fluid-sampling member around said annular chamber.

3. The formation-testing apparatus of claim 1 further including:

sealing means cooperatively arranged on said fluid-admitting means around said tubular forward portion and adapted for packing-off a borehole wall around said tubular forward portion.

4. The formation-testing apparatus of claim 1 further including:

means cooperatively mounting said fluid-sampling member on said body for movement relative thereto between a laterally-extended position and a retracted position; and

control means cooperatively arranged for selectively moving said fluid-sampling member back and forth between its said extended and retracted positions.

5. The formation-testing apparatus of claim 1 further including:

sample-receiving means on said body and adapted for receiving filtered connate fluids entering fluid passages; and

control means cooperatively arranged for selectively coupling said sample-receiving means to said first fluid passage.

6. Formation-testing apparatus adapted for suspension in a borehole traversing earth formations and comprising:

a body having a chamber adapted to receive connate fluids;

fluid-admitting means on said body and including a tubular fluid-sampling member having a forward portion adapted to be engaged with a borehole wall for isolating a surface thereof from well bore fluids and receiving connate fluids from earth formations therebeyond;

means selectively operable for positioning said fluid-sampling member against a borehole wall and including first piston means cooperatively arranged on said body for movement between a first position to engage said fluid-sampling member with a borehole wall and a second position to disengage said fluid-sampling member from a borehole wall;

means coupling said fluid-sampling member to said chamber and including fluid-passage means between said chamber and an intermediate portion of said fluid-sampling member, and filtering means cooperatively arranged on said intermediate portion of said fluid-sampling member for limiting the entrance of loose materials into said fluid-passage means;

means for controlling the admission of connate fluids and loose materials into said fluid-sampling member and including a valve member coaxially arranged in said fluid-sampling member for movement between an advanced position in said forward portion for blocking communication into said fluid-sampling member and a retracted position to the rear of said intermediate portion for exposing said filtering means, and second piston means cooperatively coupled to said valve member and adapted for movement between a first position to place said valve member in its said advanced position and a second position to place said valve member in its said retracted position; and

control means cooperatively coupled to said first and second piston means for selectively moving said first and second piston means back and forth between their respective positions.

7. The formation-testing apparatus of claim 6 further including:

pressure-monitoring means for providing indications at the surface indicative of the pressure of connate fluids in said chamber.

8. The formation-testing apparatus of claim 6 further including:

valve means in said fluid-passage means and cooperatively coupled to said control means for selectively entrapping connate fluids in said chamber.

9. The formation-testing apparatus of claim 6 further including:

a wall-engaging member movably mounted on said body on the opposite side thereof from said forward portion of said fluid-sampling member and cooperatively coupled to said first piston means for movement thereby between an extended wall-engaging position and a retracted position against said opposite body side.

10. The formation-testing apparatus of claim 6 further including:

means cooperatively coupling said fluid-sampling member to said body for movement relative to one side thereof between a laterally-extended position and a retracted position; and

means cooperatively coupling said fluid-sampling member to said first piston means for movement thereby between its said laterally-extended position and its said retracted position upon movement of said first piston means between said first and second positions thereof.

11. The formation-testing apparatus of claim 10 further including:

a wall-engaging member movably mounted on said body on the opposite side thereof and cooperatively coupled to said first piston means for movement thereby between an extended wall-engaging position and a retracted position against said opposite body side upon movement of said first piston means between said first and second positions thereof.

12. Formation-testing apparatus adapted for suspension in a borehole traversing earth formations and comprising:

a body having a chamber adapted to receive connate fluids;

fluid-admitting means on said body and including a tubular fluid-sampling member cooperatively arranged for lateral movement in relation to said body between retracted and extended positions, fluid-passage means between said fluid-sampling member and said chamber, a tubular filter coaxially arranged on said fluid-sampling member covering said fluid-passage means for limiting the entrance of loose materials into said fluid-passage means, and first piston means coupled to said fluid-sampling member and cooperatively arranged for moving said fluid-sampling member back and forth between its said retracted and extended positions;

means for controlling the admission of connate fluids and loose materials into said fluid-sampling member and including a valve member coaxially disposed in said fluid-sampling member and cooperatively arranged for movement through said tubular filter between an advanced closed position where said valve member is substantially sealingly engaged with the forward portion of said fluid-sampling member ahead of said tubular filter and a retracted open position to the rear thereof where said tubular filter is in communication with said forward portion, and second piston means coupled to said valve member and cooperatively arranged for moving said valve member back and forth between its said open and closed positions; and

control means cooperatively arranged for selectively operating said first and second piston means to move said fluid-sampling member and said valve member between their respective said positions.

13. The formation-testing apparatus of claim 12 further including:

a wall-engaging member movably mounted on said body on the opposite side thereof from said fluid-admitting means and cooperatively arranged for movement between a retracted position against said opposite body side and an extended wall-engaging position for urging said fluid-admitting means against a borehole wall; and

third piston means cooperatively coupled to said wall-engaging member and said control means for selectively moving said wall-engaging member between its said retracted and extended positions.

14. The formation-testing apparatus of claim 12 wherein said fluid-admitting means further include:

packoff means cooperatively mounted on said body and around said forward portion of said fluid-sampling member for establishing sealing engagement with a borehole wall to isolate said forward portion of said fluid-sampling member from borehole fluids.

15. The formation-testing apparatus of claim 14 further including:

a wall-engaging member movably mounted on said body on the opposite side thereof from said fluid-admitting means and cooperatively arranged for movement between a retracted position against said opposite body side and an extended wall-engaging position for urging said fluid-admitting means against a borehole wall; and

third piston means cooperatively coupled to said wall-engaging member and said control means for selectively moving said wall-engaging member between its said retracted and extended positions.

16. The formation-testing apparatus of claim 14 further including:

means including a movable member cooperatively coupling said packoff means and said fluid-sampling member to said body for movement relative to one side thereof between a laterally-extended position and a retracted position; and

third piston means cooperatively coupled to said movable member and said control means for selectively moving said movable member between its said retracted and extended positions.

17. The formation-testing apparatus of claim 16 further including:

a wall-engaging member movably mounted on said body on the opposite side thereof from said fluid-admitting means and cooperatively arranged for movement between a retracted position against said opposite body side and an extended wall-engaging position for urging said fluid-admitting means against a borehole wall; and

fourth piston means cooperatively coupled to said wall-engaging member and said control means for selectively moving said wall-engaging member between its said retracted and extended positions.

18. The formation-testing apparatus of claim 17 wherein said control means are cooperatively arranged for operating said third and fourth piston means in unison.

19. The formation-testing apparatus of claim 16 wherein said forward portion of said fluid-sampling member projects outwardly beyond said packoff means in said retracted position of said fluid-sampling member for engaging a borehole wall in advance of said packoff means.

20. The formation-testing apparatus of claim 12 further including:

pressure-monitoring means for providing indications at the surface indicative of the pressure of connate fluids in said chamber.

21. The formation-testing apparatus of claim 12 further including:

valve means in said fluid-passage means and cooperatively coupled to said control means for selectively entrapping connate fluids in said chamber.