US3536148A - Formation-sampling apparatus - Google Patents

Description

United States Patent [72] Inventor George W. Brock Houston, Texas [21] Appl. No. 813,575 [22] Filed April 4, 1969 [45] Patented Oct. 27, 1970 [7 3] Assignee Schlumberger Technology Corporation New York, New York a corporation of Texas [54] FORMATION-SAMPLING APPARATUS 18 Claims, 3 Drawing Figs.

52 US. Cl. 175/26, 175/78 [51] lnt.Cl E2lb 49/06 [50] Field ofSearch 175/77, 78, 24, 26, 27

[56] References Cited UNITED STATES PATENTS 1,935,105 11/1933 Woollen 175/26 3,039,543 6/1962 Loocke 175/26 3,173,500 3/1965 Stuart et al. 175/77 3,430,716 3/1969 Urbanosky 175/78' Primary.Examiner- David H. Brown Attorneys- Donald H. Fidler, William J. Beard, Ernest R.

Archambeau, David L. Moseley, Edward M. Roney and William R. Sherman Patented, 0d. 27,1970 I George W Brock INVENTOR /4 BY 5 K FORMATION-SAMPLING APPARATUS Heretofore, formation samples have usually been obtained from previously-drilled boreholes by explosively propelling into the adjacent wall of a borehole one or more so-called core-taking bullets having appropriately arranged forward cutting edges. As these tubular bullets penetrate the borehole wall, a generally-cylindrical core of the exposed formation materials is usually driven into each bullet so that, when the bullets are subsequently retrieved, these cores can be recovered at the surface for examination. Although such coretaking bullets have been highly successful, the samples obtained thereby are only from spaced intervals along the borehole. It is apparent, of course, that the most ideal arrangement is to obtain continuous samples of considerable length from the formation intervals of interest in a given borehole.

To obtain such continuous samples, new and improved formation-sampling tools, such as that shown in U.S. Pat. No. 3,430,716, have been recently introduced to the industry. In these tools, a pair of rotatable outwardly-converging cutting wheels are cooperatively arranged to be extended outwardly and cut their way into the exposed face of an adjacent formation. Then, as they are slowly raised, the rotating cutting wheels cut away an elongated wedge-shaped formation sample from the borehole wall. This elongated sample is caught by the tool and recovered upon return of the tool to the surface. As described in detail in U.S. Pat. No. 3,427,580, these new and improved formation-sampling tools have included unique electronic circuitry adapted,,among other things, for monitoring the operation of an electrical motor that rotatably drives the formation-cutting wheels. By means of this new and improved monitoring circuitry, whenever the driving motor tends to slow or become overloaded, further advancement of the cutting wheels is momentarily halted to prevent the motor from slowing below an efficient rotative speed. Thus, where the cutting resistance of a formation being sampled would otherwise tend to at least significantly reduce the rotative speed of the cutting wheels, this unique speed-monitoring circuitry has been highly effective for enabling these new and improved tools to secure samples from even such formations. Although this new and improved monitoring circuitry has been usually reliable, there is, however, always the everpresent desire to simplify and improve even a superior tool.

Accordingly, it is an object of the present invention to provide new and improved formation-sampling apparatus having formation-cutting means that are adapted to be driven at effective cutting speeds and selectively advanced at controlled rates so as to prevent reduction of the cutting speeds below an effective operating range.

This and other objects of the present invention are attained by formation-sampling apparatus including formation-cutting means operatively driven at a selected cutting speed by a fluidpowered driver which has an operating characteristic that varies in relation to the cutting resistance encountered by the cutting means. F luid-powered means are provided for advancing the cutting means between selected positions for obtaining a formation sample, with these advancing means being coupled to control means responsive to variations in the aforementioned operating characteristic to selectively regulate the speed of advancement in accordance with the aforesaid cutting resistance.

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 an exemplary formation-sampling tool arranged in accordance with the present invention and in position in a borehole to obtain a formation sample; I

FIG. 2 shows the formation-cutting means and the upper portion of the sample receiver of the tool shown in FIG. 1; and

FIG. 3 is schematic representation of a preferred arrange-v ment of new and improved control means for selectively regulating the operation of the formation-cutting means of the exemplary tool.

Turning now to FlG. 1, a formation-sampling tool 10, arranged in accordance with the present invention and conveniently assembled as a number of tandemly-connected housings 11-14, is shown suspended from a cable 15 in a borehole 16. As illustrated, the tool 10 has been positioned in the borehole 16 for formation-cutting means, such as a pair of converging similar cutting wheels 17, that are selectively operated by new and improved control means 18 for collecting an elongated sample 19 from the exposed face of an earth formation 20 for deposit within a sample receiver 21 in the lowermost housing 14.

The upper housing 11 of the tool 10 preferably encloses suitable circuitry (such as that described in U.S. Pat. No. 3,427,580) for locating the tool at a desired position in the borehole 16 as well as for selectively controlling the tool from the surface by way of various electrical conductors in the suspension cable 15. The next-lower housing 12 encloses a tool-anchoring system 22 (such as that described in U.S. Pat. No. 3,430,698) which preferably includes a pair of hydraulically-actuated pistons 23 for selectively extending a wall-engaging anchor 24 on the rear of the tool 10 laterally against one side of the borehole l6 and shifting the forward face of the sampling tool in the opposite direction. To selectively actuate the wall-engaging member 24 from the surface, the toolanchoring system 22 includes a hydraulic pump 25 in the housing 12 which is arranged to selectively pump-hydraulic fluid into piston chambers behind and ahead of the pistons 23. By maintaining an increased hydraulic pressure behind the pistons 23, the anchor 24 will, of course, urge the forward face of the tool 10 against the opposite wall of the borehole 16 with sufficient force to anchor the tool in a selected position.

The next-lower housing 13 of the tool 10 encloses the cutting wheels 17 that are preferably mounted for rotation in converging vertical planes about outwardly-diverging axes lying generally in the same horizontal plane. As more fully described in U.S. Pat. No. 3,430,714, the cutting wheels 17 are uniquely arranged relative to one another so that, when extended, their peripheral edges will project through a longitudinal opening 26 in the forward wall of the housing 13 and all but come together at about the point of intersection of the three aforementioned planes. Thus, by selectively moving the rotating wheels 17 upwardly between spaced positions, the generally wedge-shaped or triangular prismatic sample 19 will be cut from the adjacent formation 20.

The lowermost housing 14 of the tool 10 encloses the sample receiver 21 which is preferably adapted for reliably segregating formation samples as they are successively collected. If desired, the sample receiver 21 may be arranged as shown in U.S. Pat. No. 3,430,7l6. Alternatively, the sample receiver 21 may also be arranged as shown in U.S. Pat. application, Ser. No. 765,383 filed October 7, l968, so that a plurality of upright dividers therein (not shown here) are sequentially positioned to respectively isolate successively-collected formation samples as the tool 10 is operated. in either event, the tool 10 can be efficiently employed on a single trip in the borehole 16 to recover several formation samples that will be individually deposited in the sample receiver 21 in predetermined positions.

As best seen in FIG. 2, the cutting wheels 17 are dependently carried by a longitudinally-movable enclosure 27 adapted to be driven in alternate directions by fluid-powered means which preferably include a pair of upright tubular members 28 (only one shown) mounted along its rear wall and slidably disposed about substantially longer, paralleled upright rods 29 (only one shown)'positioned adjacent to the rear wall of the tool housing 13 and secured thereto only at their upper and lower ends. The opposite ends ofthese tubular members 28 are slidably sealed around the elongated rods 29 and a piston member 30 (only one shown) is fixed at an intermediate position on each of the elongated rods to define separate upper and lower fluid- tight pressure chambers 31 and 32 within the internal bore of its associated tubular member.

Accordingly, as will subsequently described in more detail, upon operation of the control means 18 to develop a 7 speed of travel along the elongated rods 29 in relation to the stationary tool housing 13. Similarly, when the control means 18 function to impose a higher pressure in the lower pressure chambers 32 than thatin the upper pressure chambers 31, the

' enclosure 27 will travel at a corresponding downward speed along the rods 29. Thus, as will be later discussed, the control means 18 are selectively operated from the surface to accomplish the desired travel of the enclosure back and forth along the-elongated rods 29 between designated upper and lower positions in relation to the anchored tool 10.

By arranging a typical bellows or piston (neither shown) at a convenient point in a wall of the enclosure 27, the hydraulic fluid in the enclosure and pressure chambers 31 and 32 will be maintained at a pressure at least equal to the hydrostatic pres-.

sure of fluids or so -called mud" in the borehole 16. In this manner, by pressure balancing the interior of the enclosure 27 in relation to the borehole hydrostatic pressure, the fluid pressures that are developed in the chambers 31 and 32 need only to be sufficient to overcome friction, the weight of the enclosure, and whatever cutting resistance that may be encountered by the cutting wheels 17. I

To powerthe cutting wheels l7,'the control means 18 in- A elude a fluid-powered driver or fluid-driven motor 33, with this motor being fitted into the enclosure 27 and operatively connected by suitable power-transmission means 34 to a rightangle .gear drive 35 having outwardly-diverging shafts (as at v 36) at an angle to one another for rotatively driving the cutting wheels. By locating the fluid-powered motor 33 in the enclosure 27, it will, of course. be pressure balanced. Similarly, as shown in U.S. Pat. No. 3,430,7l4, by enclosing the power-transmission means 34 in an oil-filled tube (not seen in FIG. 2) sealingly coupled between the enclosure 27 and outwardly. outwardly-biased pins 38 (only one seen in FIG. 2) mounted near the lower ends of each of the pivoted begin cutting their way into the'formation 20. Then, as the rotating cutting wheels 17 move furtherupwardly from their 7 position at 8" to their position at C", they will be cutting into the formation along a straight vertical path of a length determined by the vertical height of the shorter grooves 41. After reaching their position at C", the cutting wheels'17 will be retracted as they move still further upwardly and cut their way toward their upper position at D. Thus, once the c0nverging cutting wheels 17 have reached the upper position at D", a prismatic sample, as at 19, with tapered ends will have been cut out of the formation 20 for deposit in the core receiver 21 therebelow.

To divert the guide pins 38 into the lower inclined grooves 43 as the enclosure 27 moves upwardly, an abutment 45 is provided across the lower portion of each of the longer grooves 42, with the lower faces of these abutments being extended along the line of the downwardly-facing wall of the lower inclined grooves 43 to facilitate the redirection of guide pins. Similarly, when the enclosure 27 is to beretumed from its uppermost position (as shown .at in FIG. 2), it is preferred that the guide pins 38 reenter the upper grooves 44 so that the cutting wheels 17 will return to their initial lower position at A by passing back through their respective kerfs which they previously cut into the formation 20. In this manner, the return travel of the rotating cutting wheels 17 will be effective to dislodge the formation sample should it still be in the complementary cavity cut in the formation 20. Thus, an abutment 46 (similar to those at is located across each of the longer longitudinal grooves 42, with the upper faces of these abutments being a continuation of the lower side walls of the upper inclined grooves 44. The height of each abutment 45 and 46 is made less than the total depth of its associated inclined groove so that the shorter enclosure guides (not arms 37 are slidably disposed in a system of inwardly-facing grooves39 (only one system seen in H0. 2) in'the interior side walls of the intermediate housing 13 on opposite sides of the longitudinal opening 26 therein. These groove systems 39 are preferably arranged so that upward longitudinal travel of the enclosure 27 from its full-line position to its dashed-line position shown at 40 in FIG. 2 will be effective (through the coaction -of the guide pins 38 in their respective groove systems) to direct the cutting wheels 17 and gear drive 35 along the path A-B-C-D schematically depicted in FIG. 2. Then, upon downward travel of the enclosure 27 back to its full-line position shown in F IG. 2, the guide pins 38 will return the cutting wheels 17 and gear drive 35 in the opposite direction to their initial positions.

As seen in FlG. 2, the groove systems 39 each have two parallel longitudinal grooves 41 and 42 of unequal length and laterally spaced apart from one another. The shorter forwardmost grooves 41 are connected at their opposite ends to the longer grooves 42.by oppositely-directed rear'wardly- inclined grooves 43 and 44 which respectively intersect the longer grooves at longitudinally-spaced intermediate points. To

further stabilize the enclosure 27 as it moves between its longitudinally-spacedupper and lower positions, outwardly-projecting guides (not shown) are respectively arranged on the A'B, they will be moving'upwardly and outwardly asthey shown) can pass freely'up and down the longitudinal groove 42 without striking the abutments. Thus, as the spring-biased guide pins 38 reach. the abrupt faces of either of the abutments 45 or 46, the cutting wheels 17 will be directed outwardly as desired. 3

Turning now to FlG.- 3, the new and improved control means 18 have been schematically depicted to facilitate the explanation of their unique operation. 'As previously mentioned, the cutting wheels 17 are operatively driven by the fluid-powered motor 33. Accordingly, to selectively drive the cutting wheels 17, fluid-pumping means 47, such as an electric motor 48 coupled to a hydraulic pump 49, adapted for deliversistance, the torque required to maintain the cutting wheels at a selected speed willbe correspondinglyilow. Conversely, as

the cutting wheels 17. are encountering a greater cutting resistance, the corresponding increase in torque required to maintain their cutting speed will result in a proportionallygreater fluid pressure in the fluid conduit 50.

As previously mentioned, traversal of. the enclosure 27 between its longitudinally-spaced positions is accomplished by selectively varying the fluid pressures within the upper and lower pressure chambers 31 and 32 in the upright tubular members 28 on the rear of the enclosure. Thus, it 'will be appreciated that the direction of travel of the enclosure 27 is determined by whetherit is the upperor the lower pressure chambers 31 and 32 that are at a higher pressure, with the speed of this travel being governed by the magnitude of the pressure differential between the upper and lower chambers.

Accordingly, to selectively regulate the longitudinal travel of the cutting wheels 17, the output of the fluid pump 49 is coupled by a fluid conduit 51 to the lowerpressure chambers 32 for varying the fluid pressure therein over a range corresponding in proportion to the range of torque requirements of the cutting wheels; and meansare provided for maintaining the upper pressure chambers 31 at a selected pressure that remains higher than that in the lower chambers so long as the cutting wheels are efficiently working. In other words, if, for example, the cutting wheels 17 are encountering little or no cutting resistance, their minimal torque requirements will result in a corresponding and reduced fluid pressure in the lower chambers 32. Thus, by imposing a higher pressure in the upper chambers 31, the enclosure 27 and cutting wheels 17 will be moved upwardly at a speed that is directly related to the minimal cutting resistance that the cutting wheels are encountering at that moment. On the other hand, should the cutting wheels 17 move into a formation interval that is somewhat more difficult to cut, the resulting increase in torque requirements will, in turn, require a higher output pressure from the fluid pump 49 to maintain the rotative speed of the cutting wheels. This resulting increase of fluid pressure in the lower chambers will, of course, proportionally decrease the pressure differential between the pressure chambers 31 and 32 and correspondingly reduce the longitudinal speed of the enclosure 27 and cutting wheels 17.

It will be appreciated, therefore, that by maintaining the upper pressure chambers 31 at a selected fluid pressure that corresponds to the predictable output pressure of the fluid pump 49 when it is operating at or near its maximum rating, further upward travel of the enclosure 27 will cease whenever the torque requirements of the cutting wheels 17 approaches the capability of the fluid-pumping means 47 to maintain the cutting wheels at an effective rotative speed. Thus, if this selected pressure imposed in the upper chambers 31 is about equal to the discharge pressure of the pump 49 at the upper limit of its pressure range, upward travel of the enclosure 27 will halt whenever the torque requirements of the cutting wheels 17 are at their upper limit. On the other hand, by setting this selected pressure imposed in the upper chambers 31 to be slightly less than the above-mentioned upper limit of the pump 49, the advancement of the cutting wheels 17 will be halted before the cutting wheels begin to lose speed. Then, should the discharge pressure of the fluid pump 49 continue to increase, the enclosure 27 will be reversed to free the cutting wheels 17. Withdrawal of the cutting wheels 17 will, of course, quickly reduce their torque requirements so that they will again be advanced when the discharge pressure of the pump 49 drops below the selected pressure in the upper chambers 31.

By using this above-mentioned criteria for selecting the pressure to be maintained in the upper pressure chambers 31, the longitudinal advancement speed of the cutting wheels 17 will be regulated in direct relation to the relative cutting resistance of the earth formation being sampled. This will, of course, means that as the cutting wheels 17 are cutting relatively-soft formations, they will be advanced at a faster speed than when the formation being sampled is more difficult to cut. Moreover, the control means 18 of the present invention assure that further advancement of the cutting wheels 17 will cease altogether whenever the formation being sampled would otherwise cause the wheels to stall or even significantly slow.

Accordingly, as the cutting wheels 17 encounter particularly-hard formation intervals, the advancement or upward travel of the cutting wheels will proportionally decrease as the cutting resistance increases. Once the enclosure 27 halts, even if the pressures in the upper end and lower pressure chambers 31 and 32 are equal, the weight of the enclosure may cause it to drop back at least a short distance. However, even the enclosure 27 does not drop, the cutting wheels 17 will ultimately cut away a sufficient clearance space to reduce the torque requirements and correspondingly lower the output pressure of the pump 49. Once this pressure is again reduced, the unbalanced pressures in the upper and lower chambers 31 and 32 will, of course, again move the enclosure 27 upwardly. Thus, there may well be situations where the enclosure 27 will alternately advance and retrogress in relatively-short increments to progressively cut away a formation sample.

As seen in FIG. 3, in the preferred manner of arranging the control means 18, the pressure in the upper pressure chambers 31 is maintained at a selected pressure by means such as a fluid pump 52 that is appropriately adapted to have a relatively-constant discharge pressure at least over the range of flow rates necessary to keep the upper chamber filled as it is expanding. Although the pump 52 could, just as well be driven by the motor 48, it is preferred to employ a separate driver such as an electric motor 53. The output of the pump 52 is, of course, connected by a conduit 54 to the upper chambers 31, with an appropriate conduit 55 supplying fluid to the pump.

it should be noted that inasmuch as the enclosure 27 is filled with a suitable hydraulic fluid, the enclosure will serve as a supply reservoir for both pumps 49 and 52 as well as for receiving the discharge flow from the fluid motor 33.

Some provisions must, of course, be provided for returning the enclosure 27 downwardly once it reaches its uppermost position 40 (FIG. 2). Accordingly, in the preferred manner of accomplishing this, a normally-closed bypass valve 56 is coupled between the outlet and inlet conduits 54 and 55 of the fluid pump 52. Thus, once the enclosure 27 has reached its upper limit of travel, the valve 56 may be selectively opened, as by a typical solenoid actuator 57, to allow the hydraulic fluid in the upper chambers 31 to return to the reservoir space within the enclosure. Once this higher pressure in the upper chambers 31 is relieved, it will, of course, be appreciated that the enclosure 27 will return downwardly to its initial lower position. Similarly, since the fluid pump 52 will be operating even when the enclosure 27 is halted, a relief valve 58 is conv nected to the conduit 54 and adapted to open at about a pressure corresponding to the discharge pressure of the pump 49 when the cutting wheels 17 are about to stall.

It should be understood that the fundamental function of the control means 18 is to selectively impose upwardly-acting forces on the enclosure 27 that are sufficient to lift the weight of the enclosure as well as to advance the cutting wheels 17 at a regulated rate of travel through an earth formation. Thus, where the elongated rods 29 are of equal diameter above and below the fixed piston members 30 as illustrated in FIG. 2, when the pressures in the upper and lower chambers 31 and 32 are equal, the resulting upwardly-directed and downwardly-directed pressure forces are, of course, also equal. It will be appreciated, therefore, that by making the lower portions of the upright rods 29 below the piston members 30 larger than the upper portions of the rods, a correspondingly-lesser pressure in the upper chambers 31 will still be effective to provide an equivalent upwardly-directed force.

Accordingly, it will be appreciated that the present invention has provided new and improved formation-sampling apparatus having selectively-regulated formation-cutting means for obtaining samples from earth formations traversed by a borehole. Although changes and modifications may be made in the disclose embodiment without departing from the broad principles of the invention as set forth in the claims, by selectively regulating the rate of advancement of the formationcutting means, the formation-cutting means will be operated in a more-efficient manner. Moreover, since the advancement speed of the formation-cutting means is regulated in response to the cutting resistance being encountered, there is little or no risk that the cutting means will be damaged or broken during the course of a sampling operation.

I claim:

1. Apparatus adapted for use in a well bore and comprising: a support adapted for suspension in a well bore; a body movably mounted on said support and adapted for travel relative thereto between spaced positions; cutting means operatively arranged on said body for movement in relation thereto for cutting away materials encountered thereby as said body travels between said spaced positions to carry said cutting means along a selected path; first fluid-powered means adapted for operatively driving said cutting means to cut away such materials, said first fluid-powered means having an operating characteristic that variesin relation to the cutting resistance encountered by said cutting means; second fluidpowered means adapted for operatively driving said body between said spaced positions; and control means responsive to said operating characteristic of saidfirst fluid powered means operatively coupled to second fluid-powered'means."

and adapted for regulating travel of said body in accordance travellongitudinally in relation to said support for carrying.

said formation-cutting means along a substantially linear path adjacent to said support.

4. The apparatus of claim 3 wherein said cutting means include a pair of rotatable cutting wheels respectively arranged in converging planes having an intersection to one side of said support; and said first fluid-powered means are adapted for rotatively driving said cutting wheels'at a selected rotative speed.

5. Apparatus adapted for cutting into thewall of a well bore' 7 and comprising; a support adapted for suspension in a well bore; a body movably mounted on said support and adapted for travel therealong between longitudinally-spaced positions; at least one cutting wheel operatively arranged on said'body forrotation in relation theretoand'adapted for cutting into an adjacent wall of a well bore as said body travels between said longitudinally-spaced positions to carry said rotating cutting wheel along a corresponding longitudinal path; means including a fluid-driven motorcoupled to said cutting'wheel and adaptedforoperatively driving said cutting wheel to cut into such walls, and fluid-pumping means'coupled to said fluiddriven motor and adapted for predictably supplyinga motive 'fluid thereto, in accordancewith variations in the torque requirements of said cutting wheel upon cutting into such walls; fluid-powered means adapted for operatively driving said body between said longitudinallyspaced positions; and control means responsive to selected variations in the supply of motive fluid to said fluid-driven motor operatively coupled to said fluid-powered meansand-adapted for regulating longitudinal travel of said body in accordance with such variations in the torque requirements of said cuttingwheel. I

6. The apparatusof claim 5 wherein said control means further include means operable, upon arrival of said body at I one of said longitudinally-spaced positions from another of i said longitudinally-spaced positions, for returning said body t said other longitudinally-spaced position. 1

7; The apparatus of claim 5 wherein said control means further include first means responsive to said selected variations in the supply of motive fluid to said fluid-driven motor for moving said body from one of said longitudinally-spaced positions toward another of said.longitudinally-spaced positions at a rate of travel directly related to the torque requirements of said cutting wheel below a selected torque, and second means operable for halting travel of said body toward said other position whenever the torque requirements of said cutting wheel are greater than said selected torque.

. 8. The apparatus of claim 7 wherein said control means further include means operable, upon arrival of said body at said other position, for returning said body to said one position.

9. Apparatus adapted for obtaining samples of earth formav tions traversed by a borehole and comprising: a support I adapted for. suspension in a borehole; a bodyfmovably mounted on said support and adapted for travel thereon between longitudinally-spaced positions; formation-cutting means including a pair of rotatable cutting wheels respectively arranged in converging planes having an intersection to one side of said support and operatively arranged on said body for cutting away elongated samples of formation materials as said cuttingwheels are carried along a borehole adjacent to such formations by travel of said body in one direction between said longitudinally-spaced positions; fluid-powered means adapted for rotatively driving said cutting wheels over a selected range of rotative torques to cut away such formation materials and including a fluid-driven motor operatively coupled to said cutting wheels, and fluid-pumping means coupled to said fluid-driven motor andadapted for supplying a motive fluid thereto at varying pressures proportionally related to the torque requirements of said cutting wheels; first means imposing a selected force on said bodyformoving said body at a selected speed of travel in said one direction between said longitudinally-spaced positions; and second means responsive to the torque requirements of said cutting wheels adapted for regulating the speed of travel of said body in said one direction in accordance with such torque requirements and including piston means operatively arranged between said body and said support and adapted for driving said body in the opposite direction upon application of fluid pressure to said piston means, and conduit means directing the fluid pressure of a motive fluid supplied to said fluid-driven motor to said piston means for developing corresponding forces on said body in relation to variations in such fluid pressures to oppose said selected force. I

10. The fluid-sampling apparatus of claim 9 wherein said control means further include means operable upon arrival of said body at its final position for returning said body to its original position.

11. Apparatus adapted forobtaining samples of earth formations traversed by a borehole and comprising: support adapted for suspension in a borehole; a body movably mounted on said support and adapted for travel thereon between first and second longitudinally-spaced positions; formationcutting means including a pair. of rotatable cutting wheels respectively arranged in converging planes having an intersection to one side of said support and operatively arranged on said body to carry said cutting jwheels along a borehole adjacent to such formations for cutting away elongated samples of formation materials as said body travels from said first position to said second position; fluid-powered means adapted for rotatively driving said cutting wheels to cut away, such formation materials and including a fluid-drivenmotor operatively coupled to said cutting wheels for driving said wheelsover aselected range of rotative torques, and fluid-pumping means coupled to saidfluid-driven motor and adapted for supplying a motive fluid thereto over a range of fluid pressures proportionally related to said range of rotative and including first and second pressure chambers respectively adapted for driving said body away from said first position upon application of a higher fluid pressure in said first chamber than that in said second chamber and for driving said body away from said second position upon application of a higher fluid pressure in said second chamber than that in said first chamber; means operative for imposing a selected fluid pressure in said first chamber for moving said body at a selected speed of travel from said first position to said second position; and conduit means directingthe varying fluid pressures of a motive fluid supplied to said fluid-driven motor to said second chamber for reducing said selected speed of travel of said body in proportion to increases of such varying fluid pressures.

12. The fluid-sampling apparatus of claim 11 wherein said piston means include: an elongated rod secured between longitudinally-spaced locations on said support and leaving a free I span therebetween, a tubular member secured in an upright position to said body coaxiallydisposed over said free span of said rod and fluidly sealed in relation thereto at spaced locations to define an enclosed annular space therebetween, and a piston member secured at an intermediate location on said free span of said rod and slidably engaged within said tubular member to define said first chamber on one side of said piston member and said second chamber on the opposite side of said piston member.

13. The fluid-sampling apparatus of claim 11 wherein said means for imposing a selected fluid pressure in said first chamber include second fluid-pumping means adapted for developing a selected fluid pressure, and second conduit means directing such a selected fluid pressure to said first chamber.

14. The fluid-sampling apparatus of claim 13 further including valve means coupled to said first chamber and selectively operable for relieving such a selected fluid pressure from said first chamber to return said body from second position to said first position.

15. Apparatus adapted for use in a well bore and comprising: a support adapted to be positioned in a well bore; an elongated rod mounted uprightly along said support and secured thereto at the upper and lower ends of said rod; a body including a tubular member coaxially mounted on said rod and adapted for vertical travel therealong in alternate directions; piston means including first and second sealing means on said tubular member slidably sealing the upper and lower ends thereof to said rod, and a piston member secured to an intermediate portion of said rod and slidably received within said tubular member to define therein upper and lower pressure chambers above and below said piston member; at least one cutting wheel arranged for rotation in a vertical plane operatively coupled to said body for cutting into an adjacent well bore wall and making vertical cuts therealong as said body travels in relation to said support; a fluid-driven motor operatively coupled to said cutting wheel for rotatively driving said cutting whee] over a selected range of rotative torques; fluidpumping means coupled to said fluid-driven motor and adapted for supplying a motive fluid thereto over a range of fluid pressures proportionally related to said range of rotative torques required by said cutting wheel; and control means adapted for regulating the speed of travel of said body in accordance with the torque requirements of said cutting wheel and including means adapted for imposing a selected fluid pressure within one of said pressure chambers to move said body in one of said alternate directions, and means responsive to variations in fluid pressure of a motive fluid supplied to said fluid-driven motor for imposing varying fluid pressures in the other of said pressure chambers for varying the speed of travel of said body in said one direction in accordance with variations in the torque requirements of said cutting wheel.

16. The apparatus of claim 15 wherein said varying fluid pressures to be imposed in said other pressure chamber are lower than said selected fluid pressure imposed in said one pressure chamber so that increases in said varying fluid pressures will reduce said speed of travel and decreases in said varying fluid pressures will increase said speed of travel.

17. The apparatus of claim 15 wherein said varying fluid pressures to be imposed in said other pressure chamber are lower than said selected fluid pressure with an upper limit thereof being about equal to said selected fluid pressure imposed in said one pressure chamber so that decreases in said varying fluid pressures will increase said speed of travel and increases in said varying fluid pressures will progressively decrease said speed of travel until said body is halted when said upper limit of said varying fluid pressures is reached.

18. The apparatus of claim 15 wherein said varying fluid pressures to be imposed in said other pressure chamber are lower than said selected fluid pressure with an upper limit thereof being somewhat higher than said selected fluid pressure imposed in said one pressure chamber so that decreases in said varying fluid pressures will increase said speed of travel and increases in said varying fluid pressures will progressively decrease said speed of travel until said body is halted when said varying fluid pressures equal said selected fluid pressure and said body is moved in the other of said alternate directions when said upper limit of said varying fluid pressures is reached.

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