Apparatus For Detecting The Entry Of Formation Gas Into A Well Bore

Abstract

In the preferred embodiment of the invention disclosed herein, a new and improved well tool which is adapted to be coupled in a drill string adjacent to a drill bit includes inner and outer telescoping members which are cooperatively arranged to define an expansible sample chamber for entrapping a discrete sample of drilling mud from a borehole adjacent to the drill bit in a drill string upon telescoping movement of the inner and outer members. Valve means are cooperatively arranged between the telescoping members for selectively closing the sample chamber upon further movement of the telescoping members to expand the sample chamber. In this manner, by coupling force-measuring means to a drill string coupled to the tool the force required to fully expand the chamber is measured for providing a surface indication which is indicative of the percentage of gas entrained in the collected sample.

Parent Case Text

This application is a division of copending application Ser. No. 235,989, filed Mar. 20, 1972.

Description

Those skilled in the art will, of course, appreciate that while drilling an oil or gas well, a drilling fluid or so-called "mud" is customarily circulated through the drill string and drill bit and then returned to the surface by way of the annulus defined between the walls of the borehole and the exterior of the drill string. In addition to cooling the drill bit and transporting the formation cuttings removed thereby, the mud also functions to maintain pressure control of the various earth formations as they are penetrated by the drill bit. Thus, it is customary to selectively condition the drilling mud for maintaining its specific gravity or density at a sufficiently high level where the hydrostatic pressure of the column of mud in the borehole annulus will be sufficient to prevent or regulate the flow of high-pressure connate fluids which may be contained in the formations being penetrated by the drill bit.

It is, however, not at all uncommon for the drill bit to unexpectedly penetrate earth formations containing gases at pressures greatly exceeding the hydrostatic head of the column of drilling mud at that depth which will often result in a so-called "blowout". It will be appreciated that unless a blowout is checked, it may well destroy the well and endanger lives and property at the surface. Thus, to be abundantly safe, it might be considered prudent to always maintain the density of the drilling mud at excessively-high levels just to prevent such blowouts from occurring. Those skilled in the art will appreciate, however, that excessive mud densities or so-called "mud weights" significantly impair drilling rates as well as quite often unnecessarily or irreparably damage potentially-producible earth formations which are uncased. As a matter of expediency, therefore, it is preferred to condition the drilling mud for maintaining its density at a level which is just sufficient to at least regulate, if not prevent, the unexpected entry of high-pressure formation fluids into the borehole and instead rely upon one or more of several typical operating techniques for hopefully detecting the presence of such formation fluids in the borehole.

Many techniques have, of course, been proposed for detecting the presence of such high-pressure fluids in the borehole with varying degrees of accuracy. For example, detection techniques which may be used include observing changes in the rotative torque and the longitudinal drag on the drill string, monitoring differences between the flow rates of the inflowing and outflowing streams of the drilling mud, as well as measuring various properties of the returning mud stream and the cuttings being transported to the surface thereby. Those skilled in the art will appreciate, however, that none of the several techniques which are presently employed will reliably and immediately detect the entry of high-pressure gases into the borehole. For example, variations of torque or drag on the drill string are not always reliable indications since borehole conditions entirely unrelated to the presence of high-pressure gases in the borehole mud can be wholly responsible for causing significant variations in these parameters. On the other hand, although such techniques as monitoring of the mud flow rates or measuring the physical characteristics of the returning mud stream may reliably indicate the entrance of high-pressure formation gases into the borehole, the interval of time required for a discrete volume of mud containing such gases to reach the surface may well be in the order of several hours. This, of course, will usually be too late to permit preventative measures to be taken in time to avoid a disastrous blowout.

Accordingly, it is an object of the present invention to provide new and improved apparatus for reliably detecting the entrance of even minor amounts of formation gas into a borehole being drilled and then immediately providing a positive indication at the surface that such gases are present.

This and other objects of the present invention are attained by arranging a tool to include a pair of telescoped members which are adapted to be tandemly coupled in a drill string for selective movement between extended and contracted telescoped positions. Piston means are cooperatively arranged between the telescoping members for defining an expansible sample chamber having a minimum volume when the telescoping tool members are in one of their telescoped positions and a selected greater volume whenever the tool members are moved to an intermediate position. Valve means are cooperatively arranged between the telescoped members for entrapping drilling mud drawn into the sample chamber in response to the initial movement of the telescoping members toward their other telescoped position. In this manner, upon closure of the valve means and further movement of the telescoped members, the volume of the sample chamber will be sufficiently expanded to insure that the pressure of the entrapped mud sample will be reduced to at least the saturation pressure of a gas-containing mud sample at ambient borehole temperatures. In this manner, when the tool is coupled in a drill string, a measurement of the force applied to the drill string for accomplishing the expansion of the sampling chamber will enable determinations to be readily made at the surface as to whether or not the drilling mud sample is free of entrained formation gas.

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 schematically illustrates a portion of a typical rotary drilling rig and its associated equipment and a drill string along with a new and improved tool arranged in accordance with the present invention;

FIGS. 2A and 2B are successive, enlarged cross-sectional views of a preferred embodiment of the tool of the present invention shown in FIG. 1;

FIGS. 3 and 4 are cross-sectional views respectively taken along the lines 3--3 and 4--4 in FIG. 2A;

FIG. 5 is a detailed elevational view, partially in cross-section, of one portion of the tool depicted in FIGS. 2A and 2B;

FIGS. 6 and 7 successively depict various positions of the tool illustrated in FIGS. 2A and 2B during its operation; and

FIGS. 8A-8D graphically represent certain operational principles of the tool of the present invention.

Turning now to FIG. 1, a new and improved testing tool 10 arranged in accordance with the present invention is depicted as being tandemly coupled in a typical drill string 11 comprised of a plurality of joints of drill pipe 12, one or more drill collars 13, and a rotary drilling bit 14. As is customary, the drilling operation is accomplished by means of a typical drilling rig 15 which is suitably arranged for drilling a borehole 16 through various earth formations, as at 17, until a desired depth is reached. To accomplish this, the drilling rig 15 conventionally includes a drilling platform 18 carrying a derrick 19 which supports conventional cable-hoisting machinery (not shown) suitably arranged for supporting a hook 20 which is coupled thereto by means of a weight-measuring device 21 having an indicator or recorder 22 arranged therewith. As is customary, the hoisting hook 20 supports a so-called "swivel" 23 and a tubular "kelly" 24 which is coupled in the drill string 11 to the uppermost joint of the drill pipe 12 and is rotatively driven by a rotary table 25 operatively arranged on the rig floor. The borehole 16 is filled with a supply of drilling mud for maintaining pressure control of the various earth formations, as at 17; and the drilling mud is continuously circulated between the surface and the bottom of the borehole during the course of the drilling operation for cooling the drill bit 14 as well as for carrying away earth cuttings as they are removed by the drill bit. To circulate the drilling mud, the drilling rig 15 is provided with a conventional mud-circulating system including one or more high-pressure circulating pumps (not shown) that are coupled to the kelly 24 and the drill string 11 by means of a flexible hose 26 connected to the swivel 23. As is typical, the drilling mud is returned to the surface through the annulus in the borehole 16 around the drill string 11 and discharged via a discharge conduit 27 into a so-called "mud pit" (not shown) from which the mud-circulating pumps take suction.

Turning now to FIGS. 2A and 2B, an enlarged cross-sectional view is depicted of the well tool 10. As seen there, the new and improved testing tool 10 includes an elongated tubular mandrel 28 which is coaxially arranged in an elongated tubular body 29 and adapted for longitudinal movement in relation thereto between the contracted position illustrated in FIG. 2A and 2B, an intermediate position as shown in FIG. 6, and a fully-extended position as depicted in FIG. 7. The body 29 is reduced slightly, as at 31, and provided with one or more elongated longitudinal grooves cooperatively arranged to slidably receive a corresponding number of outwardly-projecting splines 32 on the mandrel 28 for co-rotatively securing the telescoping members to one another (FIG. 2A). In this manner, the telescoping members 28 and 29 are co-rotatively secured to one another for transmitting the rotation of the drill pipe 12 through the testing tool 10 to the drill collars 13 and the drill bit 14 therebelow. Opposed shoulders 33 and 34 at the lower ends of the splines 32 and the reduced body portion 31 define the upper limit of telescopic movement of the telescoping members 28 and 29 relative to one another. It will also be appreciated that the opposed shoulders 35 and 36 provided by the upper ends of the mandrel 28 and the body 29, respectively, will cooperate to define the lower travel limit or fully-contracted position of these two telescoping members.

To couple the tool 10 into the drill string 11, a socket is formed in the upper end of the mandrel 28 and appropriately threaded, as at 37, for threaded engagement with the lower end of the next adjacent joint of drill pipe 12. The lower end of the body 29 is either similarly arranged or provided with male threads, as at 38, adapted for threaded engagement within a complementary threaded socket on the upper end of the next-adjacent drill collar as at 13. In the preferred embodiment of the well tool 10, a fluid seal 39 is provided in a reduced portion 40 of the axial bore 30 of the body 29 for sealing engagement with the lowermost portion 41 of the mandrel 28; and one or more wipers 42 are arranged around the upper end of the body 29 to remove accumulations of mud and the like from the splines 32 and the exterior of the mandrel.

Of particular significance to the present invention, the new and improved testing tool 10 is further arranged to define an expansible fluid-sampling chamber 43 between the inner and outer members 28 and 29 which is selectively expanded and contracted upon longitudinal movements of the telescoping members in relation to one another. An elongated tubular piston 44 is telescopically arranged in the enlarged bore 30 between the mandrel 28 and the body 29 and adapted for sliding movement relative to the body between the lower position illustrated in FIGS. 2A and 2B and an elevated position to be subsequently described with reference to FIGS. 6 and 7. Sealing means, such as a suitable O-ring 45 cooperatively arranged around the lower end of the piston 44, are provided for fluidly sealing the piston in relation to the body 29.

The piston 44 is cooperatively arranged to provide an enlarged interior chamber 46 which is separated from the sample chamber 43 by an inwardly-directed annular shoulder 47 on the piston and having its upper face suitably shaped, as at 48, for defining an annular valve seat. A tubular valve member 49 coaxially disposed in the enlarged chamber 46 is fluidly sealed around an intermediate portion 50 of the mandrel 28 by a seal 51 and rotatively coupled to the piston 44 by complementary threads as at 52. In its usual or open position, the valve member 49 is elevated in the chamber 46 between the piston 44 and the mandrel 28 for selectively maintaining an annular sealing member 53 around the lower end of the valve member out of seating engagement with the valve seat 48. Lateral ports, as at 54 and 55, are respectively arranged in the body 29 and in the piston 44 to provide fluid communication between the borehole 16 and the enlarged chamber 46. Thus, as illustrated in FIGS. 2A and 2B, so long as the valve member 49 is not engaged with the valve seat 48, the sample chamber 43 is in communication with the borehole 16 by way of the enlarged chamber 46.

As will subsequently be described in further detail, the new and improved testing tool 10 is cooperatively arranged so that upward movement of the mandrel 28 in relation to the body 29 (or, conversely, downward travel of the body in relation to the mandrel) will initially be effective for expanding the sample chamber 43 to a predetermined volume to induct a corresponding volume of drilling mud. Thereafter, further relative movement between the mandrel 28 and the body 29 will function to seat the valve member 49 on the valve seat 48 for sealing off the sample chamber 43 before continued telescopic movement of the inner and outer members cooperates to then further expand the sample chamber for reducing the pressure of the entrapped mud sample.

Accordingly, to accomplish these several functions, selectively-operable means 56 are provided for alternately latching the piston member 44 to first the mandrel 28 and then to the body 29 in response to the relative movement of these inner and outer members over their full span of travel. In the preferred embodiment of the present invention, the latching means 56 are comprised of a plurality of outwardly-biased upright latching fingers 57 which are uniformly spaced around the upper end of the piston member 44 (FIG. 3) and respectively shaped as shown in FIG. 2A to provide one or more outwardly-facing teeth 58 and, preferably, a single inwardly-facing detent or locking projection 59. As best seen in FIG. 2A, a downwardly-opening annular recess 60 formed around an enlarged-diameter upper portion 61 of the mandrel 28 is cooperatively arranged for releasably receiving the tips of the fingers 57 to keep them retracted inwardly for retaining the inwardly-projecting detents 59 in an outwardly-facing circumferential groove 62 around the mandrel 28 until the piston 44 and the valve member 49 are carried upwardly to their positions shown in FIG. 6. It will be appreciated, of course, that so long as the fingers 57 are trapped in the annular recess 60, the detents 59 will remain in the annular mandrel groove 62 for latching the piston 44 to the mandrel 28 as it travels upwardly in relation to the body 29.

To selectively release the piston 44 from the mandrel 28 and latch the piston to the body 29 to permit further upward travel of the mandrel independently of the piston, the latching means 56 further include one or more inwardly-facing circumferential grooves 63 which are formed in the interior wall of the body bore 30 at a selected height above the mandrel groove 62 when the mandrel and the body are in their respective positions shown in FIGS. 2A and 2B. To accurately position the teeth 58 in relation to the circumferential body grooves 63 when the piston 44 is raised to the position shown in FIG. 6, an inwardly-projecting guide key 64 is arranged on the body 29 within the annular space 65 around the exterior of the piston 44 and adapted to contact an enlarged shoulder 66 on the lower end of the piston. Once the key 64 is contacted by the shoulder 66, the piston 44 will be halted against further upward movement in relation to the body 29 so that, as the mandrel 28 continues its upward travel, the enlarged mandrel portion 61 will be pulled away from the now-stationary piston to release the outwardly-biased fingers 57 from the confining recess 60. As shown in FIG. 7, this will, of course, free the fingers 57 for expansion to shift their respective latching teeth 58 into the adjacent circumferential grooves 63 formed in the interior wall of the body 29.

It will, of course, be appreciated that the above-described upward movements of the mandrel 28 in relation to the body 29 (or corresponding downward movements of the body in relation to the mandrel) will also carry the valve member 49 upwardly along with the piston member 44 by virtue of their interengaged threads 52. As previously mentioned, however, the valve member 49 must be moved downwardly in relation to the piston 44 to seat the sealing member 53 on the valve seat 48 and block further communication with the sample chamber 43.

Accordingly, to accomplish this selective movement of the valve member 49 in relation to the piston member 44, the new and improved measuring tool 10 is also cooperatively arranged to rotate the valve member downwardly along the threads 52 and into seating engagement with the valve seat 48 in response to upward travel of the mandrel 28 in relation to the body 29 and the piston. As best seen in FIGS. 4 and 5, this rotational movement of the valve member 49 is achieved by arranging an inwardly-projecting pin 67 on the valve member and slidably disposing the free end of the pin in a groove 68 having a semi-helical upper portion and a longitudinal lower portion which is formed in the adjacent outer surface of the mandrel 28. To secure the piston 44 against rotation, a pin 69 is mounted on the piston and projected through an elongated slot 70 extending partway around the valve member 49 so that the free end of this pin will also be slidably disposed within the longitudinal portion of the mandrel groove 68. Since the splines 32 co-rotatively secure the mandrel 28 to the body 29, the pin 69 will, therefore, be effective for securing the piston 44 against rotation as the valve member 49 is rotated along the threads 52.

It will, therefore, be appreciated that by coordinating the angular extent of the semi-helical portion of the groove 68 and the slot 70 as well as the longitudinal spacing between the upper and lower ends of the semi-helical groove portion with the pitch of the threads 52, the pin 67 will be effective as a cam to rotate the valve member 49 downwardly along the threads on the piston member 44 as the mandrel 28 is moved longitudinally upwardly in relation thereto. This downward travel of the valve member 49 will, of course, be effective for firmly seating the sealing member 53 on the valve seat 48. It will be recognized also that the further upward movement of the mandrel 28 will simply carry the longitudinal lower portion of the mandrel groove 68 upwardly in relation to the pins 67 and 69.

Accordingly, it will be recognized that with the tool 10 arranged as described, the initial lower position of the mandrel 28 in relation to the body 29 will locate the piston 44 at the bottom of the sample chamber 43 as shown in FIGS. 2A and 2B. The valve member 49 will be slightly elevated in relation to the valve seat 48 so that the sample chamber 43 will be in communication with the borehole 16 by way of the enlarged chamber 46 and the ports 54 and 55. Upon upward travel of the mandrel 28 in relation to the body 29, the piston 44 and the valve member 49 will be carried upwardly by the latching engagement of the detents 59 in the mandrel groove 62 until the piston shoulder 66 contacts the body key 64. At this point, as seen in FIG. 6, the latching teeth 58 will be adjacent to the circumferential grooves 63 so that with the piston member 44 now being halted by the key 64, the continued upward travel of the mandrel 28 will release the latching fingers 57 for outward movement into their respective latching groove 63. Simultaneously, the interaction of the semi-helical portion of the mandrel groove 68 with the pin 67 will cooperatively rotate the valve member 49 downwardly along the threads 52 to urge the sealing member 53 into seating engagement with the valve seat 48.

It will be appreciated, therefore, that the upward travel of the piston member 44 between its positions shown respectively in FIGS. 2A-2B and FIG. 6 will induct a sample of drilling mud into the expanding sample chamber 43, with the total volume of this sample being determined upon closure of the valve member 49 on the valve seat 48. Thus, once the valve member 49 is seated on the valve seat 48, communication is blocked between the sample chamber 43 and the borehole 16.

As previously mentioned, once the sample chamber 43 is closed, it is necessary to then further expand the sample chamber. Accordingly, to accomplish this, the lowermost portion 41 of the mandrel 28 is reduced in relation to the adjacent mandrel portion 50 and located in relation to the shoulder 71 defining the lower end of the sample chamber 43 so as to preferably emerge into the sample chamber just as the valve member 49 becomes tightly seated on the seat 48. Thus, with the valve member 49 now closing off the sample chamber 43, further upward movement of the mandrel 28 in relation to the body 29 (or, conversely, downward movement of the body relative to the mandrel) will progressively increase the volume of the enclosed sample chamber in direct proportion to the length of the reduced mandrel portion 41 which is between the seals 39 and 51. Stated another way, the volume of the sample chamber 43 will progressively expand as more of the larger-diameter mandrel portion 50 moves above the upper seal 51 and is replaced by the smaller-diameter mandrel portion 41. The maximum-available expansion volume of the sample chamber 43 will, of course, be represented by the difference in diameters between the two mandrel portions 41 and 50 and the longitudinal spacing between the seals 39 and 51.

To determine whether or not gas is present in the drilling mud, the telescoping members 28 and 29 of the new and improved tool 10 are initially fully contracted in relation to one another so that the piston 44 and the valve member 49 will be in their respective positions as depicted in FIGS. 2A and 2B. So long as the valve member 49 is elevated within the enlarged chamber 46 and is out of contact with the valve seat 48, the drilling mud in the borehole 16 immediately exterior of the fluid-sampling tool 10 will be free to enter the sample chamber 43 by way of the ports 54 and 55 to fill the lowermost portion of the enlarged bore 30 below the piston 44 and above the seal 39.

It will be appreciated that if the drill string 11 is elevated, the mandrel 28 will be free to travel upwardly relative to the longitudinally-stationary body 29 until the shoulder 34 engages the shoulder 33. Conversely, if the drill string 11 is maintained at the same vertical or longitudinal position in relation to the borehole 16 while the drill string is being rotated, as the drill bit 14 progressively cuts away the formation materials in contact therewith the weight of the drill collars 13 will carry the body 29 downwardly in relation to the longitudinally-stationary mandrel 28 until such time that the shoulder 33 contacts the shoulder 34. Thus, in either event, the net effect will be to progressively move the telescoped members 28 and 29 as well as the piston 44 and the valve member 49 from their respective positions illustrated in FIGS. 2A and 2B toward their respective positions illustrated in FIG. 6.

It will be appreciated, therefore, that upon expansion of the free space within the axial bore 30 as the piston 44 moves upwardly in relation to the body 29, the piston member will induct a discrete volume of the drilling mud into the sampling chamber 43. As previously described with reference to FIGS. 6 and 7, the valve member 49 will remain disengaged from the valve seat 48 until such time that the piston 44 is latched to the body 29 and the valve member is rotated downwardly along the threads 52. Once this occurs, as depicted in FIG. 6, it will be recognized that a discrete volume of the drilling mud will then be entrapped within the sample chamber 43 as defined at that time between the lower face of the piston 44 and the seal 39. Accordingly, any further upward movement of the mandrel 28 in relation to the body 29 must result in an expansion of the sample chamber 43 and, therefore, a corresponding reduction of the pressure of the entrapped sample of the drilling mud before the tool 10 can assume the position illustrated in FIG. 7.

To understand the principles of the operation of the new and improved tool 10, it must be recognized that the physical characteristics of the mud sample entrapped in the sample chamber 43 will determine the sequence of events upon further upward movement of the mandrel 28 beyond the position shown in FIG. 6. First of all, those skilled in the art will appreciate that if only a gas were entrapped in the sample chamber 43, further upward travel of the mandrel 28 from its intermediate position shown in FIG. 6 toward its fully-extended position depicted in FIG. 7 would simply cause the entrapped gas to expand accordingly. Thus, in this unlikely situation, there would be no significant forces restraining upward travel of the mandrel 28. The pressure of the entrapped gas sample would merely be reduced in keeping with the general gas laws.

As a result, an observer at the surface viewing the weight indicator 22 will note a steady increase in the measured reading as upward movement of the drill string 11 progressively picks up the weight of the drill pipe 12 and the mandrel 28. Once the shoulder 35 is disengaged from the shoulder 36, the weight indicator 22 will show the entire weight of the kelly 24, the drill pipe 12, and the mandrel 28. This reading will, of course, remain unchanged until the shoulder 34 engages the shoulder 33. From that point on, continued upward movement of the drill string 11 will again produce a continued increase in the reading shown on the indicator 22 until the drill bit 14 is picked up from the bottom of the borehole 16. The total reading shown on the weight indicator 22 will, of course, then be the full weight of the entire drill string 11.

As shown in FIG. 8A, the readings, W, of the weight indicator 22 in this particular situation when plotted against the upward travel, D, of the drill string 11 will be generally as graphically represented by the curve 72. These readings will, therefore, first follow an ascending sloping line, as at 73, until the shoulder 35 is first disengaged from the shoulder 36. The indicated weight, W, will then, as indicated at 74, remain constant over that portion of the tool stroke, d.sub.1, where the shoulder 35 is moving away from the shoulder 36 and until the valve member 49 is seated on the valve seat 48. As previously mentioned, when a gas is trapped in the sample chamber 43 by closure of the valve member 49, the remaining travel, d.sub.2, of the mandrel 28 will be without significant restraint so that the reading on the weight indicator 22 will remain substantially unchanged (as graphically represented at 75 in FIG. 8A) until the shoulder 34 engages the shoulder 33. Thereafter, as graphically represented at 76, further upward travel, D, of the drill pipe 12 will again produce an increasing reading, W, on the weight indicator 22 as the weight of the drill collars 13 is progressively added to that of the drill pipe already supported by the hook 20.

Accordingly, it will be recognized that if only a purely-gaseous sample is trapped in the sample chamber 43, the readings on the weight indicator 22 will generally be as represented by the curve 72 in FIG. 8A. The abrupt changes, as at 77 and 78 respectively, in the slope of the curve 72 will clearly define the points during the testing operation when the shoulder 35 is disengaging from the shoulder 36 and when the shoulder 34 is engaging the shoulder 33. Those skilled in the art will appreciate, therefore, that readings such as those just described will be readily apparent at the surface since the respective weights of the drill pipe 12 on the one hand and those of the drill collars 13 and the drill bit 14 on the other hand are always known with a fair degree of accuracy.

The situation just described will, of course, be significantly different where closure of the valve member 49 traps a sample in the sample chamber 43 that is entirely a liquid. If this is the case, continued upward travel of the drill pipe 12 will simply be incapable of producing further extension of the mandrel 28 in relation to the body 29 until or unless the forces tending to pull the piston 44 and the body apart are sufficient to reduce the pressure of the entrapped liquid sample to its saturation pressure at the existing ambient borehole temperature. This will, of course, induce flashing of the entrapped liquid sample. In this event, once flashing of the liquid sample commences, the mandrel 28 will then be free to move upwardly toward its extended position until the shoulder 34 engages the shoulder 33.

As shown in FIG. 8B, therefore, the readings, W, on the indicator 22 will generally vary as represented by the graph 79 where the entrapped sample is initially completely liquid but is ultimately reduced to its saturation pressure at the ambient borehole temperatures. Initial upward movement of the mandrel 28 toward its intermediate position (FIG. 6) will again cause a steady increase in the reading, W, on the weight indicator 22 until the shoulder 35 disengages from the shoulder 36 (the point 80 on the curve 79). Then, there will be no further increase in weight (as shown by the line segment 81) until the valve 49 is seated on its associated seat 48 (the point 82 on the curve 79). Further upward travel, D, of the drill pipe 12 will then produce a second steady increase of observed weight as shown at 83 on the curve 79.

Once the forces tending to further separate the mandrel 28 and the body 29 are sufficient to reduce the pressure of the entrapped liquid sample to its saturation pressure at the ambient temperature and flashing of the sample is commenced, as shown at 84 in FIG. 8B, there will be no significant increase in the reading on the weight indicator 22 until the shoulders 33 and 34 are engaged to begin imposing the combined weight of the drill collars 13 and the bit 14 onto the hook 20. This will then cause an increasing reading, W, on the indicator as shown at 85.

The third situation that may occur is where a wholly-liquid sample is trapped in the sample chamber 43 but the forces tending to separate the mandrel 28 and the body 29 are insufficient to induce flashing of the trapped liquid sample. It will be appreciated that this can occur where, for a given size of the piston 44, there is an insufficient number of drill collars 13 in the drill string 11 below the tool 10 to impose a sufficient downward force on the tool for allowing the mandrel 28 to be fully extended. Thus, the combined weight of the drill collars 13 and the drill bit 14 is a limiting factor for determining whether a completely-liquid sample will be flashed during the operation of the new and improved tool 10. As shown in FIG. 8C, therefore, this situation is graphically represented at 86. It will be recognized that the curve 86 is similar to the left-hand portion of the curve 79 in FIG. 8B so further explanation is believed unnecessary. It should be noted, of course, that the shoulder 34 will not engage the shoulder 33 so that further extension of the mandrel 28 will be halted just after the valve member 49 has closed.

The situation graphically illustrated in FIG. 8D is where a liquid mud sample has only a small percentage of entrained gas. This is, of course, what would usually be expected where a high-pressure gas is initially entering the borehole 16 and a blowout is possibly commencing. As shown in FIG. 8D by the curve 87, the initial operation of the tool 10 will be similar to the previously-described situations. Once, however, the valve 49 is seated, as at 88 on the curve 87, the continued upward travel of the drill pipe 12 will induce movement of the mandrel 28 toward its fully-extended position with substantially less force being required than where the entrapped sample is wholly liquid. This will be readily understood when it is realized that the presence of entrained gas in an entrapped liquid sample will make the saturation pressure of the mixture correspondingly higher than that of a purely liquid sample. Thus, less force is required to fully extend the telescoping members 28 and 29. This is graphically represented by the curved segment 89 of the curve 87.

Accordingly, it will be recognized by considering FIGS. 8A-8D, that the relationship of the force applied for elevating the drill pipe 12 to fully extend the telescoping members 28 and 29 will be wholly dependent upon the physical state of the sample which is entrapped in the sample chamber 43 upon closure of the valve member 49. Thus, as shown in FIG. 8A, if the entrapped sample is purely gas, there will be no significant increase in the force required to move the telescoping members 28 and 29 from their fully-contracted position to their fully-extended position. On the other hand FIGS. 8B and 8C demonstate that if the entrapped sample is solely a liquid, once the valve member 49 has been seated, there will be a significant and readily-recognizable increase in the force required to move the telescoping members 28 and 29 to their fully-extended position -- if such is ever reached. As graphically represented in FIG. 8D, the presence of even a small percentage of gas which may be entrapped in an otherwise wholly-liquid sample will produce only a slowly-ascending increase of the weight reading, W, on the indicator 22. Accordingly, it will be recognized that in any of the four above-described situations, observing the readings, W, of the weight indicator 22 in conjunction with the upward travel, D, of the exposed end of the drill pipe 12 will provide a readily-detectable surface indication of the state of the drilling mud which is then adjacent to the testing tool 10 of the present invention.

The preceding descriptions have assumed that the testing operations were conducted by elevating the drill pipe 12 in relation to the drilling platform 18. It will be appreciated, however, that identical reactions will be obtained where the drill pipe 12 is maintained at about the same longitudinal position as the drill string 11 is being rotated. If this is the situation, it will be recognized that as the drill bit 14 continues to cut away at the bottom of the borehole 16, the weight of the drill collars 13 and the drill bit will tend to carry the body 29 downwardly in relation to the longitudinally-stationary mandrel 28 and the piston member 44. Thus, the same results as previously described will be obtained.

In other words, downward movement of the drill bit 14 will progressively carry the body 29 downwardly in relation to the longitudinally-stationary piston member 44 so that the valve member 49 will ultimately be closed. Thereafter, the weight reading, W, which will be registered by the indicator 22 will again be determined by the nature or state of the entrapped fluid within the sample chamber 43. Stated another way, since the combined weight of the drill collars 13 and the drill bit 14 represent the maximum force which can be effective for moving the testing tool 10 to its fully-extended position, the above detailed descriptions are equally applicable regardless of whether it is the mandrel 28 which is being moved upwardly in relation to the longitudinally-stationary body 29 or it is the body which is being moved downwardly in relation to the longitudinally-stationary mandrel. In either case, easily-recognized surface indications will be provided to warn the observer of an impending blowout.

From the foregoing description of the new and improved testing tool 10, it will be appreciated from FIGS. 8A-8D that an observer at the surface can readily deduce from the changes in the weight readings, W, on the indicator 22 in association with upward movement of the drill string 11 whether or not gas is then present in the borehole 16 in the vicinity of the drill collars 13. Thus, a simple "go-no go" type of test can be reasily performed during the course of the drilling operation merely by elevating the drill string 11 a sufficient distance to fully extend the telescoping members 28 and 29 of the testing tool 10 and observing the resulting effects as visibly displayed on the weight indicator 22. A test of this nature can, of course, be rapidly conducted with no appreciable interruption of the drilling operation. Moreover, if necessary, several tests can be conducted for verification by simply lowering the drill string 11 to expel the first sample and reposition the various elements of the testing tool 10.

It should be noted that the new and improved testing tool 10 is also capable of performing the above-described test without raising the drill string 11. Thus, at any time during a drilling operation, if the drill string 11 is slacked off to be certain that the telescoping members 28 and 29 of the testing tool 10 are in their respective fully-telescoped positions, as the drilling operation commences the drill bit 14 will progressively deepen the borehole 16 to move the telescoping members toward their extended positions. An observer can, therefore, note the time interval required for the telescoped members 28 and 29 of the testing tool 10 to move to the point where the valve member 49 is first seated. This time interval can, of course, be readily determined at the surface since the pronounced cessation of the increasing weight indicatons which occurs once the full weight of the drill pipe 12 is suspended on the hook 20 will identify when the telescoping members 28 and 29 first start moving and the next change in the weight indicator will show when the valve member 49 is first seated.

Once it is known how long it takes for the valve member 49 of the testing tool 10 to be closed, it can be safely assumed that the same time interval will be required for the telescoping members 28 and 29 to move to their fully-extended positions since the valve closes at a known point in the stroke of the tool. A proportional relationship will, of course, always exist between the times required and d.sub.1 and d.sub.2 irrespective of the actual point in the stroke of the telescoping members 28 and 29 that the valve member 49 is seated. Accordingly, by observing the variations in the indicated weight, W, during this second time interval, an observer can reliably deduce whether gas is then present in the borehole 16 adjacent to the drill collars 13. Hereagain, if during drilling an indication is routinely obtained that gas is or may be present, it is quite easy to lower the drill string 11 to expel the mud sample then in the testing tool 10 and then either continue drilling or else elevate the drill string to make a second test for verifying the first test.

It has been found, however, that the new and improved testing tool 10 of the present invention can also be employed for quantitatively measuring with a fair amount of precision the amount of gas entering the borehole 16 during the course of the drilling operation. As previously described, the various dimensions of the testing tool 10 are, of course, known. Thus, by measuring the additional force, .DELTA.W, required to extend the mandrel 28 from just after the point that the fluid sample has been entrapped to the point where the mandrel is fully-extended, a unique relationship between this force and the tool displacement, d.sub.2, is determined by the percentages of gas -- if any -- which is then entrained in the entrapped sample. As previously described with reference to FIGS. 8B and 8C, if the entrapped sample is wholly liquid, the rapid changes in the indicated weight, W, on the indicator 22 through the stroke, d.sub.2, of the mandrel 28 will provide a positive indication at the surface that the entrapped sample is wholly free of any entrained gas. Conversely, the force required for moving the mandrel 28 to its fully-extended position will be directly related to the percentage of gas which is then entrained in the entrapped fluid sample. This unique relationship is expressed by the equation:

% gas (by volume) = d.sub.1 /d.sub.2 {[(P.sub.h .times. A)/(W.sub.2 - W.sub.1)]-1} .times. 100% Eq. 1

where,

d.sub.1 = longitudinal displacement of the telescoping members 28 and 29 required to induct a sample of mud into the sample chamber 43;

d.sub.2 = maximum longitudinal displacement of the telescoping members 28 and 29 between the point where the valve 49 is closed to the point where the telescoping members are fully extended;

P.sub.h = hydrostatic pressure of the drilling mud at the depth at which the sample is being taken;

A = cross-sectional area of the piston 44;

W.sub.1 = weight indication at the time a sample is being inducted into the sample chamber 43; and

W.sub.2 = weight indication when the telescoping members 28 and 29 are first fully extended.

It should also be understood that once the sample is trapped in the sample chamber 43, the force being indicated on the weight indicator 22 at any given point during the continued movement of the telescoping members 28 and 29 will be directly related to the amount of entrained gas in the sample. This relationship is best expressed by the following equation:

% gas (by volume) = (.DELTA.d/d.sub.2)[(W.sub.max - W)/W].times. 100% Eq. 2

where,

.DELTA.d = longitudinal displacement of the telescoping members 28 and 29 between the point where the valve 49 is closed to the point where the measurement is being made;

d.sub.2 = maximum longitudinal displacement of the telescoping members 28 and 29 between the point where the valve 49 is closed to the point where the telescoping members are fully extended;

W = weight indication at the time the measurement is being taken less the weight of the drill pipe 12 above the tool 10. This latter weight must be corrected to account for the buoyancy of the drill pipe in the particular drilling mud being used; and

W.sub.max = the product of depth, mud density, and the area of the piston 44.

Accordingly, it will be appreciated that the present invention has provided new and improved apparatus for detecting the entry of presence of gas in a borehole being excavated and signaling this event to the surface. In operating the tool of the present invention, a discrete sample of drilling mud from the borehole is periodically trapped within an expansible sampling chamber defined between a pair of telescoping members coupled to a drill string adjacent to the drill bit. By moving the drill string so as to expand the sampling chamber, the pressure of the entrapped sample is reduced to at least the saturation pressure of a gas-containing drilling mud at the borehole ambient temperature. Then, by measuring the force required to expand the sampling chamber, the presence or absence of formation gas in the drilling fluid can be determined; and, if desired, these force measurements may be used to derive quantitative measurements which are representative of the percentage of gas entrained in the discrete sample.

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. A well tool adapted for coupling into a drill string carrying a drill bit for excavating a borehole and cooperatively arranged for determining whether formation gas is in the drilling mud therein, said well tool comprising:

inner and outer tubular members telescopically arranged together for upward and downward movements relative to one another between longitudinally-spaced first, second and third positions;

fluid-sampling means including fist piston means movably disposed between said telescoped members and cooperatively arranged for defining an enclosed fluid chamber having a reduced volume with said first piston means in one position and an increased volume with said first piston means in another position;

first means reponsive to movement of said telescoped members from their said first position to their said second position for carrying said first piston means from said one position to said other position for inducting a predetermined volume of drilling mud into said fluid chamber whenever said first piston means reach said other position;

second means for controlling the admission of drilling mud into said fluid chamber and including valve means cooperatively arranged for terminating fluid communication with said fluid chamber when said first piston means reach said other position to entrap a sample of drilling mud in said fluid chamber; and

second piston means responsive only to movement of said telescoped members from their said second position toward their said third position for further increasing the volume of said fluid chamber to expand a sample of drilling mud entrapped therein.

2. The well tool of claim 1 wherein said first piston means include an annular piston member coaxially arranged between said telescoped members; and said first means include means releasably coupling said annular piston member to one of said telescoping members whenever said telescoping members are between their said first and second positions, and means responsive only to positioning of said telescoping members at their said second position for selectively uncoupling said annular piston member from said one telescoping member and recoupling said annular piston member to the other of said telescoping members whenever said telescoping members are between their said second and third positions.

3. The well tool of claim 1 wherein said valve means include an annular valve member coaxially arranged between said telescoped members; and said second means include means operatively coupling said annular valve member to said first piston means for movement relative thereto between an open position with said first piston means in said one position and a closed position in response to movement of said first piston means to said other position.

4. The well tool of claim 1 wherein said first piston means include an annular piston member coaxially arranged between said telescoped members and having an annular valve seat arranged thereon; said valve means include an annular valve member coaxially arranged between said telescoped members for movement between an open position out of engagement with said annular valve seat and a closed position in engagement with said annular valve seat for terminating fluid communication with said fluid chamber; said first means include means releasably coupling said annular piston member to one of said telescoping members whenever said telescoping members are between their said first and second positions, and means reponsive only to positioning of said telescoping members at their said second position for selectively uncoupling said annular piston member from said one telescoping member and recoupling said annular piston member to the other of said telescoping members whenever said telescoping members are between their said second and third positions; and said second means include means operatively coupling said annular valve member to said annular piston member for movement relative thereto between its said open and closed positions, and means operatively coupling said annular valve member to said one telescoping member for moving said annular valve member to its said closed position in response to movement of said telescoped members to their said second position.

5. A well tool adapted for coupling into a drill string carrying a drill bit for excavating a borehole and cooperatively arranged for determining whether formation gas is in the drilling mud therein, said well tool comprising:

a tubular outer member having an axial bore with adjoining enlarged and reduced portions;

a tubular inner member telescopically disposed for movement in said outer member and having an enlarged portion received in said enlarged bore portion and a reduced portion received in said reduced bore portion of said axial bore;

means defining an enclosed fluid chamber between said telescoped members and including first seal means on said outer member within said reduced bore portion and sealingly engaged with said reduced portion of said inner member, and an annular piston member coaxially arranged between said telescoped members within said enlarged bore portion and sealingly engaged therewith for defining an enclosed fluid chamber having a reduced volume whenever said piston member is in one position with respect to said first seal means and an increased volume whenever said piston member is in another position spaced further away from said first seal means;

means for controlling the admission of drilling mud into said fluid chamber including passage means between the exterior of said outer member and said fluid chamber, an annular valve seat on said piston member and within said passage means, an annular valve member coaxially arranged between said telescoped members and adapted for movement between a passage-opening position and a passage-closing position in engagement with said valve seat, and second seal means cooperatively arranged on one of said annular members and sealingly engaged with said enlarged portion of said inner member;

first means releasably coupling said piston member to said inner member for carrying said piston member from its said one position to its said other position as said telescoped members are moved from a retracted position to an extended position;

second means responsive to movement of said telescoped members to their said extended position for moving said valve member to its said passage-closing position as said piston member reaches its said other position; and

third means responsive to movement of said telescoped members to their said extended position for releasably coupling said piston member to said outer member to free said piston member from said inner member as said telescoped members are moved from their said extended position toward a further extended position to progressively bring said reduced portion of said inner member into said fluid chamber between said first and second seal means and correspondingly further expand the volume of said flui chamber.

6. The well tool of claim 5 wherein said second means include threaded means intercouplng said valve member and said piston member and adapted for carrying said valve member longitudinally in relation to said piston member between its said passage-opening and passage-closing positions upon rotation of one of said annular members relative to the other of said annular members, and cam means cooperatively arranged between said one rotatable annular member and one of said telescoped members and adapted for roatating said one rotatable annular member in response to movement of said telescoped members to their said extended position to move said valve member into engagement with said valve seat.

7. The well tool of claim 5 wherein said first means include first detent means cooperatively arranged between said inner member and said piston member for releasably coupling said piston member to said inner member, and stop means cooperatively arranged between said outer member and said piston member for halting said piston member in its said other position to enable further longitudinal movement of said inner member in relation to said piston member to release said first detent means from said inner member; and said third means include second detent means cooperatively arranged between said piston member and said outer member for coupling said piston member to said outer member to retain said piston member in its said other position.