APPARATUS AND METHODS FOR CHARACTERIZING A RESERVOIR

BACKGROUND

Historically, boreholes (also known as wellbores, or simply wells) have been drilled to seek out subsurface formations (also known as downhole reservoirs) containing highly desirable fluids, such as oil, gas or water. A borehole is drilled with a drilling rig that may be located on land or over bodies of water, and the borehole itself extends downhole into the subsurface formations. The borehole may remain ‘open’ after drilling (i.e., not lined with casing), or it may be provided with a casing (otherwise known as a liner) to form a ‘cased’ borehole. A cased borehole is created by inserting a plurality of interconnected tubular steel casing sections (i.e., joints) into an open borehole and pumping cement downhole through the center of the casing. The cement flows out the bottom of the casing and returns towards the surface through a portion of the borehole between the casing and the borehole wall, known as the ‘annulus.’ The cement is thus employed on the outside of the casing to hold the casing in place and to provide a degree of structural integrity and a seal between the formation and the casing.

Various techniques for performing formation evaluation (i.e., interrogating and analyzing the surrounding formation regions for the presence of oil and gas) in open, uncased boreholes have been described, for example, in U.S. Pat. Nos. 4,860,581 and 4,936,139. FIGS. 1A and 1B illustrate a known formation testing apparatus according to the teachings of these patents. The apparatus A of FIGS. 1A and 1B is of modular construction, although a unitary tool is also useful. The apparatus A is a downhole tool that can be lowered into the well bore (not shown) by a wire line (not shown) for the purpose of conducting formation evaluation tests. The wire line connections to tool A as well as power supply and communications-related electronics are not illustrated for the purpose of clarity. The power and communication lines that extend throughout the length of the tool are generally shown at 8. These power supply and communication components are known to those skilled in the art and have been in commercial use in the past. This type of control equipment would normally be installed at the uppermost end of the tool adjacent the wire line connection to the tool with electrical lines running through the tool to the various components.

As shown in the embodiment of FIG. 1A, the apparatus A has a hydraulic power module C, a packer module P, and a probe module E. Probe module E is shown with one probe assembly 10 which may be used for permeability tests or fluid sampling. When using the tool to determine anisotropic permeability and the vertical reservoir structure according to known techniques, a multiprobe module F can be added to probe module E, as shown in FIG. 1A. Multiprobe module F has sink probe assembly 14, and horizontal probe assembly 12. Alternately, a dual packer module P is commonly combined with the probe module E for vertical permeability tests.

The hydraulic power module C includes pump 16, reservoir 18, and motor 20 to control the operation of the pump 16. Low oil switch 22 provides a warning to the tool operator that the oil level is low, and, as such, is used in regulating the operation of the pump 16.

The hydraulic fluid line 24 is connected to the discharge of the pump 16 and runs through hydraulic power module C and into adjacent modules for use as a hydraulic power source. In the embodiment shown in FIG. 1A, the hydraulic fluid line 24 extends through the hydraulic power module C into the probe modules E and/or F depending upon which configuration is used. The hydraulic loop is closed by virtue of the hydraulic fluid return line 26, which in FIG. 1A extends from the probe module E back to the hydraulic power module C where it terminates at the reservoir 18.

The pump-out module M, seen in FIG. 1B, can be used to dispose of unwanted samples by virtue of pumping fluid from the flow line 54 into the borehole, or may be used to pump fluids from the borehole into the flow line 54 to inflate the straddle packers 28 and 30. Furthermore, pump-out module M may be used to draw formation fluid from the wellbore via the probe module E or F, or packer module P, and then pump the formation fluid into the sample chamber module S against a buffer fluid therein. This process will be described further below.

The bi-directional piston pump 92, energized by hydraulic fluid from the pump 91, can be aligned to draw from the flow line 54 and dispose of the unwanted sample though flow line 95, or it may be aligned to pump fluid from the borehole (via flow line 95) to flow line 54. The pump-out module can also be configured where flow line 95 connects to the flow line 54 such that fluid may be drawn from the downstream portion of flow line 54 and pumped upstream or vice versa. The pump-out module M has the necessary control devices to regulate the piston pump 92 and align the fluid line 54 with fluid line 95 to accomplish the pump-out procedure. It should be noted here that piston pump 92 can be used to pump samples into the sample chamber module(s) S, including overpressuring such samples as desired, as well as to pump samples out of sample chamber module(s) S using the pump-out module M. The pump-out module M may also be used to accomplish constant pressure or constant rate injection if necessary. With sufficient power, the pump-out module M may be used to inject fluid at high enough rates so as to enable creation of microfractures for stress measurement of the formation.

Alternatively, the straddle packers 28 and 30 shown in FIG. 1A can be inflated and deflated with borehole fluid using the piston pump 92. As can be readily seen, selective actuation of the pump-out module M to activate the piston pump 92, combined with selective operation of the control valve 96 and inflation and deflation of the valves I, can result in selective inflation or deflation of the packers 28 and 30. Packers 28 and 30 are mounted to outer periphery 32 of the apparatus A, and may be constructed of a resilient material compatible with wellbore fluids and temperatures. The packers 28 and 30 have a cavity therein. When the piston pump 92 is operational and the inflation valves I are properly set, fluid from the flow line 54 passes through the inflation/deflation valves I, and through the flow line 38 to the packers 28 and 30.

As also shown in FIG. 1A, the probe module E has a probe assembly 10 that is selectively movable with respect to the apparatus A. Movement of the probe assembly 10 is initiated by operation of a probe actuator 40, which aligns the hydraulic flow lines 24 and 26 with the flow lines 42 and 44. The probe 46 is mounted to a frame 48, which is movable with respect to apparatus A, and the probe 46 is movable with respect to the frame 48. These relative movements are initiated by a controller 40 by directing fluid from the flow lines 24 and 26 selectively into the flow lines 42, 44, with the result being that the frame 48 is initially outwardly displaced into contact with the borehole wall (not shown). The extension of the frame 48 brings the probe 46 adjacent the borehole wall and compresses an elastomeric ring (called a packer) against the borehole wall, thus creating a seal between the borehole and the probe 46. Since one objective is to obtain an accurate reading of pressure in the formation, which pressure is reflected at the probe 46, it is desirable to further insert the probe 46 through the built up mudcake and into contact with the formation. Thus, alignment of the hydraulic flow line 24 with the flow line 44 results in relative displacement of the probe 46 into the formation by relative motion of the probe 46 with respect to the frame 48. The operation of the probes 12 and 14 is similar to that of probe 10, and will not be described separately.

Having inflated the packers 28 and 30 and/or set the probe 10 and/or the probes 12 and 14, the fluid withdrawal testing of the formation can begin. The sample flow line 54 extends from the probe 46 in the probe module E down to the outer periphery 32 at a point between the packers 28 and 30 through the adjacent modules and into the sample modules S. The vertical probe 10 and the sink probe 14 thus allow entry of formation fluids into the sample flow line 54 via one or more of a resistivity measurement cell 56, a pressure measurement device 58, and a pretest mechanism 59, according to the desired configuration. Also, the flow line 64 allows entry of formation fluids into the sample flow line 54. When using the module E, or multiple modules E and F, the isolation valve 62 is mounted downstream of the resistivity sensor 56. In the closed position, the isolation valve 62 limits the internal flow line volume, improving the accuracy of dynamic measurements made by the pressure gauge 58. After initial pressure tests are made, the isolation valve 62 can be opened to allow flow into the other modules via the flow line 54.

When taking initial samples, there is a high prospect that the formation fluid initially obtained is contaminated with mud cake and filtrate. It is desirable to purge such contaminants from the sample flow stream prior to collecting sample(s). Accordingly, the pump-out module M is used to initially purge from the apparatus A specimens of formation fluid taken through the inlet 64 of the straddle packers 28, 30, or vertical probe 10, or sink probe 14 into the flow line 54.

The fluid analysis module D includes an optical fluid analyzer 99, which is particularly suited for the purpose of indicating where the fluid in flow line 54 is acceptable for collecting a high quality sample. The optical fluid analyzer 99 is equipped to discriminate between various oils, gas, and water. U.S. Pat. Nos. 4,994,671; 5,166,747; 5,939,717; and 5,956,132, as well as other known patents, all assigned to Schlumberger, describe the analyzer 99 in detail, and such description will not be repeated herein.

While flushing out the contaminants from apparatus A, formation fluid can continue to flow through the sample flow line 54 which extends through adjacent modules such as the fluid analysis module D, pump-out module M, flow control module N, and any number of sample chamber modules S that may be attached as shown in FIG. 1B. Those skilled in the art will appreciate that by having a sample flow line 54 running the length of the various modules, multiple sample chamber modules S can be stacked without necessarily increasing the overall diameter of the tool. Alternatively, as explained below, a single sample module S may be equipped with a plurality of small diameter sample chambers, for example by locating such chambers side by side and equidistant from the axis of the sample module. The tool can therefore take more samples before having to be pulled to the surface and can be used in smaller bores.

Referring again to FIGS. 1A and 1B, flow control module N includes a flow sensor 66, a flow controller 68, piston 71, reservoirs 72, 73 and 74, and a selectively adjustable restriction device such as a valve 70. A predetermined sample size can be obtained at a specific flow rate by use of the equipment described above.

The sample chamber module S can then be employed to collect a sample of the fluid delivered via flow line 54. If a multi-sample module is used, the sample rate can be regulated by flow control module N, which is beneficial but not necessary for fluid sampling. With reference to upper sample chamber module S in FIG. 1B, a valve 80 is opened and one of the valves 62 or 62A, 62B is opened (whichever is the control valve for the sampling module) and the formation fluid is directed through the sampling module, into the flow line 54, and into the sample collecting cavity 84C in chamber 84 of sample chamber module S, after which valve 80 is closed to isolate the sample, and the control valve of the sampling module is closed to isolate the flow line 54. The chamber 84 has a sample collecting cavity 84C and a pressurization/buffer cavity 84p. The tool can then be moved to a different location and the process repeated. Additional samples taken can be stored in any number of additional sample chamber modules S which may be attached by suitable alignment of valves. For example, there are two sample chambers S illustrated in FIG. 1B. After having filled the upper chamber by operation of shut-off valve 80, the next sample can be stored in the lowermost sample chamber module S by opening shut-off valve 88 connected to sample collection cavity 90C of chamber 90. The chamber 90 has a sample collecting cavity 90C and a pressurization/buffer cavity 90p. It should be noted that each sample chamber module has its own control assembly, shown in FIG. 1B as 100 and 94. Any number of sample chamber modules S, or no sample chamber modules, can be used in particular configurations of the tool depending upon the nature of the test to be conducted. Also, sample module S may be a multi-sample module that houses a plurality of sample chambers, as mentioned above.

It should also be noted that buffer fluid in the form of full-pressure wellbore fluid may be applied to the backsides of the pistons in chambers 84 and 90 to further control the pressure of the formation fluid being delivered to the sample modules S. For this purpose, the valves 81 and 83 are opened, and the piston pump 92 of the pump-out module M must pump the fluid in the flow line 54 to a pressure exceeding wellbore pressure. It has been discovered that this action has the effect of dampening or reducing the pressure pulse or “shock” experienced during drawdown. This low shock sampling method has been used to particular advantage in obtaining fluid samples from unconsolidated formations, plus it allows overpressuring of the sample fluid via piston pump 92.

It is known that various configurations of the apparatus A can be employed depending upon the objective to be accomplished. For basic sampling, the hydraulic power module C can be used in combination with the electric power module L, probe module E and multiple sample chamber modules S. For reservoir pressure determination, the hydraulic power module C can be used with the electric power module L and the probe module E. For uncontaminated sampling at reservoir conditions, the hydraulic power module C can be used with the electric power module L, probe module E in conjunction with fluid analysis module D, pump-out module M and multiple sample chamber modules S. A simulated Drill Stem Test (DST) test can be run by combining the electric power module L with the packer module P and the sample chamber modules S. Other configurations are also possible and the makeup of such configurations also depends upon the objectives to be accomplished with the tool. The tool can be of unitary construction a well as modular, however, the modular construction allows greater flexibility and lower cost to users not requiring all attributes.

The individual modules of the apparatus A are constructed so that they quickly connect to each other. Flush connections between the modules may be used in lieu of male/female connections to avoid points where contaminants, common in a wellsite environment, may be trapped

Flow control during sample collection allows different flow rates to be used. In low permeability situations, flow control is very helpful to prevent drawing formation fluid sample pressure below its bubble point or asphaltene precipitation point.

Thus, once the tool engages the wellbore wall, fluid communication is established between the formation and the downhole tool. Various testing and sampling operations may then be performed. Typically, a pretest is performed by drawing fluid into the flow line by selectively activating a pretest piston. The pretest piston is retracted so the fluid flows into a portion of the flow line of the downhole tool. The cycling of the piston through a drawdown and buildup phase provides a pressure trace that is analyzed to evaluate the downhole formation pressure, to determine if the packer has sealed properly, and to determine if the fluid flow is adequate to obtain a diagnostic sample.

It follows from the above discussion that the measurement of pressure and the collection of fluid samples from formations penetrated by open boreholes is well known in the relevant art. Once casing has been installed in the borehole, however, the ability to perform such tests is limited. There are hundreds of cased wells which are considered for abandonment each year in North America, which add to the thousands of wells that are already idle. These abandoned wells have been determined to no longer produce oil and gas in necessary quantities to be economically profitable. However, the majority of these wells were drilled in the late 1960's and 1970's and logged using techniques that are primitive by today's standards. Thus, recent research has uncovered evidence that many of these abandoned wells contain large amounts of recoverable natural gas and oil (perhaps as much as 100 to 200 trillion cubic feet) that have been missed by conventional production techniques. Because the majority of the field development costs such as drilling, casing and cementing have already been incurred for these wells, the exploitation of these wells to produce oil and natural gas resources could prove to be an inexpensive venture that would increase production of hydrocarbons and gas. It is, therefore, desirable to perform additional tests on such cased boreholes.

In order to perform various tests on a cased borehole to determine whether the well is a good candidate for production, it is often necessary to perforate the casing to investigate the formation surrounding the borehole. One such commercially-used perforation technique employs a tool which can be lowered on a wireline to a cased section of a borehole, the tool including a shaped explosive charge for perforating the casing, and testing and sampling devices for measuring hydraulic parameters of the environment behind the casing and/or for taking samples of fluids from said environment.

Various techniques have been developed to create perforations in cased boreholes, such as the techniques and perforating tools that are described, for example, in U.S. Pat. Nos. 5,195,588; 5,692,565; 5,746,279; 5,779,085; 5,687,806; and 6,119,782.

The '588 patent by Dave describes a downhole formation testing tool which can reseal a hole or perforation in a cased borehole wall. The '565 patent by MacDougall et al. describes a downhole tool with a single bit on a flexible shaft for drilling, sampling through, and subsequently sealing multiple holes of a cased borehole. The '279 patent by Havlinek et al. describes an apparatus and method for overcoming bit-life limitations by carrying multiple bits, each of which are employed to drill only one hole. The '806 patent by Salwasser et al. describes a technique for increasing the weight-on-bit delivered by the bit on the flexible shaft by using a hydraulic piston.

Another perforating technique is described in U.S. Pat. No. 6,167,968 assigned to Penetrators Canada. The '968 patent discloses a rather complex perforating system involving the use of a milling bit for drilling steel casing and a rock bit on a flexible shaft for drilling formation and cement.

Despite such advances in formation evaluation and perforating systems, a need exists for a downhole tool that is capable of perforating the sidewall of a wellbore and performing the desired formation evaluation processes. Such a system is also preferably provided with a probe/packer system capable of supporting the perforating tool and/or pumping capabilities for drawing fluid into the downhole tool. It is further desirable that this combined perforating and formation evaluation system be provided with a bit system capable of even long term use, and be adaptable to perform in a variety of wellbore conditions, such as cased or open hole wellbores. It is further desirable that such as system provide a probe/packer assembly that is less prone to the problems of differential sticking of the tool body to the borehole wall, and reduces the risk of damaging the probe assembly during conveyance. It is further desirable that such a system have the ability to perforate a selective distance into the formation, sufficient to reach beyond the zone immediately around the borehole which may have had its permeability altered, reduced or damaged due to the effects of drilling the borehole, including pumping and invasion of drilling fluids.

SUMMARY

One embodiment of the present disclosure provides an apparatus for characterizing a subsurface formation includes a tool body adapted for conveyance within a borehole penetrating the subsurface formation, a probe assembly carried by the tool body for sealing off a region of the borehole wall, and an actuator for moving the probe assembly between a retracted position and a deployed position. The retracted position is typically used during conveyance of the tool body to the desired position within the borehole and the deployed position is used for sealing off a region of the borehole wall. The apparatus further includes a perforator for penetrating a portion of the sealed-off region of the borehole wall by projecting the perforator through an opening or port in the probe assembly, wherein the perforator penetrates at least one structure such as a consolidated formation, a casing and/or cement. The apparatus further includes a power source disposed in the tool body and operatively connected to the perforator for operating the perforator. The apparatus further includes a flow line extending through a portion of the tool body and fluidly communicating with the perforator, the actuator, the probe assembly, or a combination thereof; and a pump carried within the tool body operatively coupled to the flow line.

Another embodiment of the present disclosure provides a method for characterizing a subsurface formation. The method includes the steps of conveying a tool body within a borehole penetrating the subsurface formation to a desired position and sealing off a region of the borehole wall. Specifically, the method includes the steps of a) conveying a tool body within a borehole wherein the tool body carries a probe assembly, an actuator for moving the probe assembly between a retracted position used during conveyance of the tool body and a deployed position used for sealing off a region of the borehole wall, a perforator, a power source disposed in the tool body and operatively connected to the perforator for operating the perforator, and a pump operatively coupled to the flow line, b) sealing off a region of the borehole wall using the probe assembly, and c) projecting the perforator through an opening or port in the probe assembly for penetrating a portion of the sealed-off region of the borehole wall using the power source, wherein the perforator penetrates at least one of a consolidated formation, casing and cement.

In another embodiment, the method further comprises pumping fluid in the flow line using the pump.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the above recited features and advantages of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to the embodiments thereof that are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments and are therefore not to be considered limiting of its scope.

FIGS. 1A-1B are schematic illustrations of a prior art formation tester for use in open hole environments.

FIG. 2 is a schematic illustration of a prior art formation tester for use in cased hole environments.

FIG. 3 is schematic illustration of an improved formation tester for use in open hole or cased hole environments in accordance with the present disclosure.

FIGS. 4A-4B are detailed sequential illustrations, partially in section, of one embodiment of a deployable probe assembly in accordance with one aspect of the present disclosure.

FIGS. 5A-5B are detailed sequential illustrations, partially in section, of a second embodiment of the deployable probe assembly.

FIGS. 6A-6B are detailed sequential illustrations, partially in section, of a third embodiment of the deployable probe assembly.

FIG. 7 is a detailed illustration, partially in section, of a fourth embodiment of the deployable probe assembly.

FIG. 8 is a schematic illustration of an improved formation tester employing dual inflatable packers in accordance with another aspect of the present disclosure.

FIGS. 9A, 9B, and 9C are detailed sequential illustrations, partially in section, of one embodiment of a dual bit configuration for perforating the walls of a cased hole in accordance with another aspect of the present disclosure.

FIGS. 10A, 10B, and 10C are detailed sequential illustrations, partially in section, of a second embodiment of the dual bit configuration for perforating the walls of a cased hole.

FIGS. 11A, 11B, and 11C are detailed sequential illustrations, partially in section, of a third embodiment of the dual bit configuration for perforating the walls of a cased hole.

FIGS. 12A, 12B, and 12C are detailed sequential illustrations, partially in section, of a fourth embodiment of the dual bit configuration for perforating the walls of a cased hole.

FIG. 13 is a schematic illustration of a tool string in which an improved formation tester in accordance with the present disclosure may be implemented for use in open hole or cased hole environments.

FIG. 14 is a pressure graph that may be acquired while performing a stress or fracture test performed at a perforation of the walls of an open hole or a cased hole.

FIGS. 15A and 15B are respectively a front perspective illustration and a top side cross section illustration of a stress or fracture test that may be performed with the formation tester of FIG. 13.

FIG. 16 is a graph illustrating a method for determining the maximum and minimum horizontal stresses in the formation and their orientations.

DETAILED DESCRIPTION

FIG. 2 depicts a perforating tool 212 for formation evaluation. The tool 212 is suspended on a cable 213, inside steel casing 211. This steel casing sheathes or lines the borehole 210 and is supported with cement 210b. The borehole 210 is typically filled with a completion fluid or water. The cable length substantially determines the depths to which the tool 212 can be lowered into the borehole. Depth gauges can determine displacement of the cable over a support mechanism (e.g., sheave wheel) and determines the particular depth of the logging tool 212. The cable length is controlled by a suitable known means at the surface such as a drum and which mechanism (not shown). Depth may also be determined by electrical, nuclear or other sensors which correlate depth to previous measurements made in the well or to the well casing. Also, electronic circuitry (not shown) at the surface represents control communications and processing circuitry for the logging tool 212. The circuitry may be of known type and does not need to have novel features.

The tool 212 of FIG. 2 is shown having a generally cylindrical body 217 equipped with a longitudinal cavity 228 which encloses an inner housing 214 and electronics. Anchor pistons 215 force the tool-packer 217b against the casing 211 forming a pressure-tight seal between the tool and the casing and serving to keep the tool stationary.

The inner housing 214 contains the perforating means, testing and sampling means and the plugging means. This inner housing is moved along the tool axis (vertically) through the cavity 228 by the housing translation piston 216 secured to a portion of the body 217 but also disposed within the cavity 228. This movement of the inner housing 214 positions, in the respective lower-most and upper-most positions, the components of the perforating and plugging means in lateral alignment with the lateral body opening 212a within the packer 217b. Opening 212a communicates with the cavity 228 via an opening 228a into the cavity.

A flexible shaft 218 is located inside the inner housing and conveyed through a tubular guide channel 214b which extends through the housing 214 from the drive motor 220 to a lateral opening 214a in the housing. A drill bit 219 is rotated via the flexible shaft 218 by the drive motor 220. This motor is held in the inner housing by a motor bracket 221, which is itself attached to a translation motor 222. The translation motor moves drive motor 220 by turning a threaded shaft 223 inside a mating nut in the motor bracket 221. The flex shaft translation motor thus provides a downward force on the drive motor 220 and the flex shaft 218 during drilling, thus controlling the penetration. This drilling system allows holes to be drilled which are substantially deeper than the tool diameter, but alternative technology (not shown) may be employed if necessary to produce perforations of a depth somewhat less than the diameter of the tool.

For the purpose of taking measurements and samples, a flow line 224 is also contained in the inner housing 214. The flow line is connected at one end to the cavity 228—which is open to formation pressure during perforating—and is otherwise connected via an isolation valve (not shown) to the main tool flow line (not shown) running through the length of the tool which allows the tool to be connected to sample chambers.

A plug magazine (or alternatively a revolver) 226 is also contained in the inner housing 214. After formation pressure has been measured and samples taken, the housing translation piston 216 shifts the inner housing 214 to move the plug magazine 226 into position aligning a plug setting piston 225 with openings 228a, 212a and the drilled hole. The plug setting piston 225 then forces one plug from the magazine into the casing, thus resealing the drilled hole. The integrity of the plug seal may be tested by monitoring pressure through the flow line while a “drawdown” piston is actuated. The resulting pressure should drop and then remain constant at the reduced value. A plug leak will be indicated by a return of the pressure to formation pressure after actuating the drawdown piston. It should be noted that this same testing method is also used to verify the integrity of the tool-packer seal before drilling commences. The sequence of events is completed by releasing the tool anchors. The tool is then ready to repeat the sequence.

FIG. 3 depicts a downhole formation evaluation tool 300 positioned in an open hole wellbore. The tool includes a body 301 adapted for conveyance within a borehole 306 penetrating the subsurface formation 305. The tool body 301 is well adapted for conveyance within a borehole via a wireline W, in the manner of conventional formation testers, but is also adaptable for conveyance within a drillstring (i.e., conveyed while drilling). The apparatus is anchored and/or supported against the side of the borehole wall 312 opposite a probe assembly 307 by actuating anchor pistons 311.

The probe assembly (also referred to as simply “probe”) 307 is carried by the tool body 301 for sealing off a region 314 of the borehole wall 312. A piston actuator 316 is employed for moving the probe assembly 307 between a retracted position (not shown in FIG. 3) for conveyance of the tool body and a deployed position (shown in FIG. 3) for sealing off the region 314 of the borehole wall 312. The actuator of this embodiment preferably includes a plurality of pistons connected to the probe assembly 307 for moving the probe between retracted and deployed positions, and a controllable energy source (preferably a hydraulic system) for powering the pistons. The probe assembly 307 preferably includes a compressible packer 324 mounted to a piston-deployed plate 326 to create the seal between the borehole wall 312 and the formation of interest 305.

A perforator, including a flexible drilling shaft 309 equipped with drill bit 308 and driven by a motor assembly 302, is employed for penetrating a portion of the sealed-off region 314 of the borehole wall 312 bounded by the packer 324. The flexible shaft 309 conveys rotational and translational power to the drill bit 308 from the drive motor 302. The action of the perforator results in lateral bore or perforation 310 extending partially through the formation 305.

The tool 301 further includes a flow line 318 extending through a portion of the tool and fluidly communicating with the formation 305, via perforation 310, by way of the perforator pathway 320 and the pathway 322 defined by the actuator and the packer (both pathways considered to be extended components of the flow line 318) for admitting formation fluid into the tool body 301. A pretest piston 315 is also connected to flow line 320 to perform pretests.

A pump 303 is also carried within the tool body for drawing formation fluid into the tool body via the flow line 318 and the pathway 320. A sample chamber 321 is further carried within the tool body 301 for receiving formation fluid from the pump 303. Additionally, instruments may be carried within the tool body 301 for measuring pressure, and for analyzing formation fluid drawn into the tool body (e.g., like optical fluid analyzer 99 from FIG. 1) via the flow line 318 and the pump 303. The pump 303 may be of similar construction to the pump 92 of FIG. 1A. Further, the tool 300 may be of modular construction, and the pump 303 may be implemented in a pump-out module similar to the pump-out module M of FIGS. 1A. In particular, the pump 303 may be implemented with a bi-directional piston pump, energized by hydraulic fluid from a hydraulic pump (not shown). The pump 303 is aligned to draw a formation fluid sample from the pathway 320 and dispose of an unwanted portion of the formation fluid sample in the wellbore via a dump flow line (not shown), or it may be reversed to pump fluid from the borehole (via the dump flow line) into the pathway 320. In the later case, the tool 300 may be used to inject wellbore fluid in the formation though the perforation 310 extending partially through the formation 305. With adequate power, the pump 303 may be used to inject wellbore fluid at sufficiently high rates to enable creation of fractures for stress measurement of the formation, as further detailed thereafter.

It should be noted here that the pump 303 can be used to pump samples into the sample chamber 321 as mentioned above, including overpressuring such samples as desired. In addition, the pump 303 may be used to pump samples out of sample chamber 321. In that case, the sample chamber 321 may be adapted for conveying an injection fluid in the borehole 306. The injection fluid may be disposed in the sample chamber 321 at the surface, before lowering the tool 300 in the wellbore 306. Alternatively, the injection fluid may be collected downhole, for example by collecting a formation fluid at a different depth (e.g. gas from the top a reservoir, water from the bottom of a reservoir, etc.) The pump 303 may be provided with control devices useful to accomplish constant pressure or constant rate injection if desirable.

Once the perforation(s) or hole(s) 310 have been created, the flow line 318 can freely communicate formation fluid to these components for downhole evaluation and/or storage. The pump 303 is not essential, but is quite useful for controlling the flow of formation fluid through the flow line 318. Formation evaluation and sampling may occur at multiple hole-penetration depths by drilling further into the formation 305. Preferably, such a hole extends through the damaged zone surrounding the borehole 306 and into the connate fluid zone of the formation 305.

Turning now to FIGS. 4A-4B, an alternate formation evaluation tool 400 is depicted. FIG. 4A shows the probe assembly 407 in the retracted position for conveyance of the tool 400. FIG. 4B shows the probe assembly 407 moving towards the extended position for sealing off a region of the borehole wall 412. The tool 400 employs a perforator that includes at least one flexible drilling shaft 409 equipped with a drill bit 408 at an end thereof for penetrating a portion of the sealed-off region 414 of the borehole wall 412 (and casing and cement if present). It is preferred that the drill bit 408 of this embodiment be made from diamond for open-hole use, but will preferably employ other materials (e.g., tungsten carbide) for cased-hole use (described in detail below), which improves the ability to penetrate the formation 405 to a desired lateral depth. A drilling motor assembly 402 is provided for applying torque and translatory force to the drilling shaft 409. The perforator of this embodiment further includes a semi-rigid tubular guide 420 for directing the translatory path of the flexible drilling shaft 409, so as to effect a substantially normal penetration path by the drill bit through the borehole wall 412.

As illustrated by the sequence of FIGS. 4A-4B, the tubular guide 420 is semi-flexible, permitting it to flex and move with the deployment of the probe assembly 407. The hydraulically-induced force of the pistons 416 deploy and compresses the packer element 424 against the wall 412 of the borehole 405. The tubular guide 420 is connected at one end to the drilling motor assembly 402, and is connected at another end to the probe assembly 407. The tubular guide 420 serves two purposes. First, it provides sufficient rigidity to impose a reactive force on the flexible shaft 409 that permits the shaft to move under the force provided by the drive motor 402. Second, the tubular guide 420 connects a flow line (not shown in FIGS. 4A-4B) in the apparatus 400 to probe plate 426, and thus acts as an extension of the tool's flow line.

FIGS. 5A-5B depict another alternate formation evaluation tool 500 conveyed within a borehole penetrating a formation 505. FIG. 5A shows the probe assembly 507 in the retracted position. FIG. 5B shows the probe assembly 507 moving towards the extended position for engagement with the wellbore wall. The tool includes a tubular guide 520 defined by a channel extending through a portion of the tool body 501. In this alternative embodiment, the tubular guide includes a laterally-protuberant portion 530 of the tool body 501 through which a portion of the guide-defining channel extends. In this manner, bit 508 at the end of the flexible drilling shaft 509 is guided through the central opening in the probe assembly 507 towards the borehole wall 512. A bellows 535 is used to fluidly connect the tubular guide 520 (which serves as part of a flow line within the tool) in the tool body 500 to the probe assembly 507 as the probe assembly is deployed by the action of hydraulic pistons 516 on probe plate 526, compressing packer element 524 against the wall 512 of the formation 505 to seal off the region 514.

A further alternative formation evaluation tool 600 being conveyed in a borehole penetrating a formation 605 is illustrated in FIGS. 6A-6B. FIG. 6A shows a probe assembly 607 in the retracted position, while FIG. 6B shows the probe assembly 607 moving to the extended position for engagement with the wellbore wall 612. Pistons 616 are provided to extend and retract the probe assembly 607. A tube guide 620 includes a substantially rigid tubular portion 632 of the probe assembly 607 that is concentric with a portion of the channel 621 that substantially defines the tubular guide 620. The tubular portion 632 may be used to fluidly connect the tool body 601 (more particularly, tubular guide 620) to the probe assembly 607. Thus, when pistons 616 deploy the probe plate 626 towards the borehole wall 612 so as to compress the packer element 624 and seal of a region 614 (see FIG. 6B) the perforation (not shown) formed by flexible shaft 609 and drill bit 608 conducts fluid from the formation 605 to the tool 600. The tubular portion 632 is preferably flexible so as to bend as the probe assembly 607 is deployed, such that the tubular portion 632 maintains physical engagement with the lateral protuberant portion 630 of the tool body 601, thereby maintaining the fluid connection with the tool body 601. The addition of a spherical joint (not shown) between the sliding tubular portion 632 and the probe plate 626 may reduce the preference of the sliding tubular portion 632 to be bendable.

FIG. 7 depicts another alternate formation evaluation tool 700 including a tool body 701 conveyed in a borehole penetrating a formation 705. This alternative is similar to that of FIGS. 6A-6B, in that a tubular guide 720 includes a substantially rigid tubular portion 732 of a probe assembly 707 that is concentric with a portion of the channel 721 that substantially defines the tubular guide 720. The primary differences here are that the probe plate 726 is relatively narrow, and the rigid tubular portion 732 of the probe assembly 707 also serves as an actuator piston (see annular protuberance 734 within hydraulically-pressurized annulus 736). FIG. 7 also shows an anchoring system 711 for positioning and supporting the tool 700 within the borehole. One further difference is the use of a separate flow line 780 that is connected at one end thereof to a cavity 770 within which the probe portion 732 is reciprocated. The flow line 780 is otherwise connected via an isolation valve (not shown) to the main tool flow line (not shown) running through the length of the tool which allows the tool to be connected to sample chambers. Thus, in this embodiment, the tubular guide 720 does not serve as a means for sampling formation fluid (although the tubular guide may experience formation pressure).

FIG. 8 depicts another alternate formation evaluation tool 800 disposed in a borehole 812 penetrating a formation 805. In this embodiment, the probe assembly 807 includes a pair of inflatable packers 824 each carried about axially-separated portions of the tool body 801. The packers 824 are well adapted for sealingly engaging axially-separated annular regions of the borehole wall 812. In this embodiment, the actuator for the assembly 800 includes a hydraulic system (not shown) for selectively inflating and deflating the packers 824.

FIG. 8 further illustrates an alternative perforator having utility in the present disclosure. Thus, explosive charge 809 is useful for creating a perforation 810 in the formation 805. Other suitable perforating means include a hydraulic punch and a coring bit, either of which are useful for creating perforations through the borehole wall. Thus, the embodiment shown is effective for admitting formation fluid into flow line 818 for collection in a sample chamber 811 with the aid of a pump 803.

FIGS. 9-12 depict alternative versions of a dual drill bit assembly usable in connection with perforating tools, such as the perforating tools of FIGS. 2 and 3. As shown in FIG. 9A, the dual bit assembly may be used to penetrate the wall 912 of a borehole 906 penetrating a subsurface formation 905. The borehole 906 may be equipped with a casing string 936 secured by concrete 938 filling the annulus between the casing and the borehole wall. An anchor system 911 is carried by the tool 900 for supporting the tool within the cased borehole 906, or more particularly within the casing string 936.

An embodiment of the dual drill bit perforating assembly 970 is shown in FIGS. 9A-9C as including a tool body 900 adapted for conveyance within a borehole, such as the cased borehole 906 having a borehole wall 912. FIG. 9A depicts the dual bit system in the retracted position for conveyance within a borehole. FIG. 9B depicts the system in a first drilling configuration. FIG. 9C depicts the system in a second drilling configuration. This apparatus uses a dual bit system to drill successive, collinear holes through the sidewall 912 of the borehole and the formation (essentially rock) together with casing and cement if present. A first drilling shaft 909a has a first drill bit 908a connected to an end thereof. The first bit is preferably suited for perforating a portion of the steel casing 936 lining the borehole wall 912. A second drilling shaft 909b, which is flexible, has a second drill bit 908b connected to an end thereof. The second drill bit is preferably suited for extending through a perforation formed in the casing 936 and perforating the concrete layer 938 and a portion of the formation 905. A drilling motor assembly (not shown) is employed for applying torque and translatory force to the first and second drilling shafts 909a, 909b.

A mechanism, in the form of a coupling assembly 950, provides the means by which both drilling shafts 909a, 909b can be driven from a single motor drive. The coupling assembly includes a set of engaging spur gears 940, 942, an intermediate shaft 944, and a right-angle gear box 946. The coupling assembly is useful for selectively coupling the drilling motor assembly to the first and second drilling shafts. The second drilling shaft 909b is selectively operatively connected to the gear train whereby torque applied to the second drilling shaft 909b by the drilling motor assembly is preferably not transferred through the coupling gear train 950 to the first drilling shaft 909a unless the second drilling shaft 909b is retracted sufficiently to dispose the second drill bit 908b into engagement with the spur gear 942.

Thus, for example, for drilling through the steel casing, the second (flexible) drilling shaft 909b may be retracted within the tubular guide 920 until the second drill bit 908b engages spur gear 942, as shown in FIG. 9B. This engagement induces rotation of intermediate rotary shaft 944. This rotary shaft in turn drives the first drilling shaft 909a, through the right angle gear mechanism 946. The first drilling shaft 909a is mechanically coupled to the first drill bit 908a, which is preferably a carbide bit suitable for drilling steel. A hydraulic piston (not shown) may be employed with a thrust bearing to increase the weight on bit to a level necessary to drill the steel casing 936.

Once the casing has been perforated, the concrete layer 938 and the formation 905 are drilled by reversing the direction of the translation motor to retract the first drilling shaft 909a and/or by retracting the hydraulic piston (if provided). This retraction step creates enough room for the second (flexible) drilling shaft 909b to be inserted through the hole in the casing 936, as shown in FIG. 9C. The flexible shaft then continues the drilling operation through the cement layer 938 and steel casing 936, under the torque and translatory driving force provided by the drive motor system.

FIGS. 10A-10C show another embodiment of the dual bit perforating system 1070. FIG. 10A depicts the dual bit system in the retracted position for conveyance within a borehole. FIG. 10B depicts the system in a first drilling configuration. FIG. 10C depicts the system in a second drilling configuration. In these figures, the second drilling shaft 1009b has a defined drilling path defined by tubular guide 1020b, and the coupling assembly includes a bit coupling 1008c connected to an end of the first drilling shaft 1009a opposite the first drill bit 1008a. A means is provided for selectively moving the first drilling shaft 1009a between a holding position in tubular guide 1020a (see FIGS. 10A and 10C) and a drilling position in tubular guide 1020b (see FIG. 10B). The drilling position is located in the drilling path (i.e., tubular guide 1020b) of the second drilling shaft 1009b, thereby enabling the second drill bit 1008b (which is specially designed for engagement) to engage the bit coupling 1008c and drive the first drilling shaft 1009a.

The moving means may move the first drilling shaft by a pivoting motion as shown in the dual bit perforating system 1070 of FIGS. 10A-10C or by a translatory motion as shown in the dual bit perforating system 1170 of FIGS. 11A-11C. A hydraulic piston-assist mechanism, as mentioned above, can be used here as well to provide the appropriate weight-on-bit for the casing drilling operation, and can be further used as the moving means. Thus, the hydraulic mechanism can be used to retract (by pivoting or translation) the first drilling shaft assembly 1109a back into the tool body 1103, and out of the way 1120b of the second drilling shaft 1109b and back to the holding position 1120a. Then, the second drilling shaft 1109b and second drill bit 1108b are free to translate and rotate through pathway 1120b so as to drill through the formation rock.

FIGS. 12A-12C depict another dual bit perforating system 1270 including tool body 1203. In these figures, the first and second drilling shafts 1209a, 1209b each have respective defined drilling paths 1220a, 1220b. Here, the coupling assembly includes a bit coupling 1208c connected to an end of the first drilling shaft 1209a opposite the first drill bit 1208b, and a means including a whipstock 1250 for selectively moving the second drilling shaft 1209b from its drilling path 1220b to the drilling path 1220a of the first drilling shaft 1209a. This has the effect of positioning the second drill bit 1208b for engagement with the bit coupling 1208c, whereby the second drilling shaft 1209b drives the first drilling shaft 1209a. In other words, the specially designed rock bit on the end of the flexible shaft 1209b interfaces with the bit coupling 1208c on the end of the casing bit shaft 1209a. Thus, a rotary motion of the casing bit 1208a is applied by rotation of the second (flexible) drilling shaft 1209b.

The casing drilling shaft 1209a is preferably mechanically connected to a hydraulic assist mechanism (not shown). The hydraulic assist mechanism provides the required weight-on-bit for the casing drilling operation, and retracts the casing bit assembly back into the tool body 1200 when required. When drilling the steel casing, the tool 1200 is translated downwardly (see FIG. 12B) to ensure the second drilling shaft enters the first drilling path, via the whipstock 1250, at the proper elevation. When drilling the formation rock, the tool 1200 is translated upwardly (see FIG. 12C) to ensure the second drilling shaft enters the second drilling path 1220b at the proper elevation, at which time the second drilling shaft 1209b and second drill bit 1208b are free to begin drilling rock via drilling path 1220b.

The above dual bit embodiments may require an additional mechanical operation to position the steel bit 1208a in the lower position (FIG. 12B) for drilling steel and for moving the first drilling shaft 1209a upwardly and out of the way (FIG. 12C) for drilling the formation. This mechanical operation could be accomplished by the addition of selected hydraulic components—e.g., additional solenoids and hydraulic lines to the existing systems—that are within the level of ordinary skill in the relevant art.

FIG. 13 depicts a schematic of a tool string 1300 in which an improved formation tester in accordance with the present disclosure may be implemented for use in open hole or cased hole environments. As shown, the tool string 1300 may be lowered in a borehole 1322, having a casing 1320 which is supported by the formation via a cement sheath 1321. However, the tool string 1300 may alternatively be deployed in an uncased or open borehole. The tool string 1300 may be suspended in the borehole 1322 via a wireline cable (not shown) and a logging head (not shown). Alternative conveyance means includes lowering the tool string 1300 via a drill string, or any other conveyance means known in the art.

To provide vertical support to the tool and to fix a top portion 1302 of the tool string 1300 to the wellbore wall so that a bottom portion 1305 of the tool string 1300 can be rotated with respect to the formation, the tool string 1300 comprises a wireline anchor 1310. The wireline anchor 1310 can selectively be extended into frictional engagement with the casing 1320 (or a wall of the wellbore 1322 in the cases the tool string 1300 is deployed in an open borehole). To orient or align the bottom portion 1305 of the tool string 1300 with a desired orientation, the tool string 1300 comprises a powered orienting sub 1311 comprising an electrical motor affixed to the top portion 1302 of the tool string and in particular to the wireline anchor 1310, the electrical motor being operatively coupled to a shaft affixed to the bottom portion 1305 of the tool string. To provide rotary movement between the top portion and bottom portion of the tool string 1300, the tool string 1300 comprises a swivel 1312, through which the motor shaft is disposed. The swivel is configured to permit the bottom part 1302 of the tool string to be turned at any angle relative to the wireline anchor 1310. To facilitate setting the probe and sealingly engaging a region of the borehole wall adjacent to one side of the tool body while supporting the tool body against a region of the casing (or the borehole wall) opposite the one side of the tool body, the tool string 1300 includes a flex joint 1313 configured to permit non coaxial alignment between the top portion 1302 and the bottom portion 1305 of the tool string.

To measure the deviation of the bottom portion 1305 of the tool string, and/or the azimuth of the bottom portion 1305 relative to a fixed reference (e.g. the Earth magnetic field), the tool string 1300 includes an inclinometry device 1314. The inclinometry device 1314 may be implemented with device similar to a GPIT tool, provided by Schlumberger Technology Corporation. The bottom portion 1305 of the tool string 1300 also includes a formation tester 1315, which may be similar to the formation evaluation tool 300 described in FIG. 3, or any other formation tester described therein.

While the tool string 1300 has been described as including an anchor 1310, a powered orientating sub 1311, a swivel 1312, and a flex joint 1313, alternate implementations may be used wherein one or more of these components is omitted or duplicated in the downhole tool string. For example, such components may be omitted if the formation evaluation tool 1315 is conveyed via a drill string (not shown).

In operation, the formation tester 1315 is used to create a perforation 1323, wherein the perforation penetrates at least one structure such as a consolidated formation, casing or cement. This enables the formation surrounding the perforation to be tested. For example, a pump or a pretest piston (not shown) can be used to pump samples out of a sample chamber (not shown) disposed in the formation tester 1315. Additionally, instruments may be carried within the formation tester 1315 for measuring pressure, temperature, or flow rate of formation fluid drawn into the tool body or injection fluid injected into the formation. As shown in FIG. 13, the formation tester 1315 may be used to inject wellbore fluid from the borehole into the formation though the perforation 1323. With adequate power, the wellbore fluid may be injected at a sufficient rates for initiating and propagating a fracture 1325. Where the formation tester 1315 is lowered within an open hole, the perforation 1323 should extent sufficiently deep into the formation so that the created fracture 1325 does not communicate with an unsealed portion of the wellbore 1322. Alternatively, the formation tester 1315 may be implemented using the formation tester 800 described in FIG. 8.

FIG. 14 is a pressure graph that may be acquired while performing a stress or fracture test at a perforation of the wall(s) of an open hole or a cased hole. Specifically, FIG. 14 shows a typical pressure curve 1400 that may be observed when testing a formation.

One or more selected fluids may first be controllably injected through the perforation 1323 until a desired pressure level 1410 higher than the formation pressure is obtained. Once this pressure level is achieved, the fluid injection may be stopped and the pressure drop monitored during a leak-off test. The results of the leak-off test may be analyzed to determine mobility of the injected fluid into the formation and/or permeability of the formation. In the case the formation tester 1315 is lowered into the wellbore, the leak-off test results may provide an indication of the integrity of the bond between the casing 1320 and the cement 1321, and between the cement 1321 and the formation. Indeed, if high injection flow rates do not result in a significant increase of the pressure level 1410 above the formation pressure, the cement may not be adequately bonded. The results of the leak-off test (e.g. the injected fluid mobility) may further be used for estimating a pumping rate for initiating and/or propagating a fracture into the formation.

After the leak-off test is terminated, the injection may be restarted and continued until a breakdown pressure 1411 is achieved and the fracture 1425 is initiated at the perforation 1423. At this point, the fracture 1425 typically propagates rapidly and the pressure drops to the fracture propagation pressure 1412, a pressure level characteristic of the formation being tested. It should be appreciated that the breakdown pressure 1411 is usually significantly higher than the pressure required for propagating the fracture 1412. For example the breakdown pressure is in some cases increased by the drilling process in the vicinity of the borehole, as such drilling process sometimes promotes the clogging or cementing of the porosity by mud solids. Drilling a small hole or perforation 1423 past the zone affected by the drilling process may facilitate initiating the fracture at a reduced breakdown pressure.

Thus, the formation tester of the present disclosure may be used to advantage for initiating fracture where other formation testers would fail to increase the pressure in the sealed interval sufficiently to initiate the fracture, due to pump operating limitations such as maximum differential pressure, maximum flow rate, and the like.

To control the propagation of the fracture 1325, the injection may advantageously be performed with a pre-test piston, allowing a better control of the fluid injected volume and/or the injection flow rate. For example, the injection flow rate may be interrupted at any time after the fracture has been initiated, and the initial shut in pressure (ISIP) 1413 may be determined. As known in the art, the ISIP value is higher than the fracture closure pressure 1414, which in turn is indicative of the formation stress normal to the fracture propagation plane. A second injection cycle may be initiated to further propagate the fracture. In that case, the injection flow rate may be increased above the propagation pressure (see pressure data point 1420) a number of times as desired to extend the fracture 1325. For example, the ISIP measurement may be repeated and its evolution with the injected volume may be quantified. An additional advantage of the formation tester 1315 as shown implemented in the tool string 1300 on FIG. 13 is that the fracture 1325 propagates, at least initially, in a plane that is aligned with the perforation 1323. Thus, when measuring the ISIP at the early stage of the propagation, it is possible to determine a level of formation stress normal to fracture planes selectively oriented by the orientation of the perforation 1323, as further detailed in FIGS. 15A and 15B.

FIGS. 15A and 15B, respectively, show a front perspective illustration and a top side cross section illustration of a stress or fracture test that may be performed with the formation tester of FIG. 13. In particular, the tool string 1300 shown in FIG. 13 may be used to perform a plurality of stress or fracture tests at a predetermined depth in the wellbore 1500. The depth may be determined from open hole logs to identify a formation of interest and/or cased hole logs to identify a zone having a likely integer bond between cement and casing and cement and formation thereby permitting a stress test to be performed.

Referring to FIGS. 15A and 15B, six perforations 1520 are drilled sequentially in the formation 1505 in essentially the same plane. Where the tool string 1300 is used in a cased hole, the perforation preferably penetrates a casing 1507 and a cement sheath 1503. After each hole is drilled, a fracture is initiated in that hole and propagated (only one fracture 1530 is depicted for clarity in FIG. 15 A). The pumping used to inject fracturing fluid is stopped and a closure stress 1414 is determined by methods well known in the industry. After the closure stress has been determined, the hole may be plugged if desired and the formatin tester 1315 rotated. The fracturing test is then repeated for a new perforation 1520. Preferably, the perforations 1520 are positioned sufficiently apart so that any mutual interference is negligible and does not result in substantial error in the estimated closure stress for each fracture. The perforation orientation θ of each perforation is measured using the inclinometry device 1314 with respect to a fixed reference (depicted as the x and y coordinate system in FIG. 15A). The closure stress 1414 measured at a particular depth (or a cluster of depths) as a function of the perforation orientation may be used to determine the values minimum and the maximum horizontal stresses in the formation 1505, respectively depicted as 1510 and 1511 in FIG. 15B. Further, the minimum and maximum horizontal stress direction may also be determined, as further detailed in FIG. 16.

FIG. 16 is a graph illustrating a method for determining the maximum and minimum horizontal stress values (respectively 1610 and 1611) in the formation and their orientations. In particular, FIG. 16 shows multiple data points 1620 that are obtained from measured closure stresses as shown in FIG. 14 (see e.g. closure stresses levels 1412 and 1420 measured at one perforation). The data points 1620 comprise an abscissa equal to two times the perforation orientation θ, and an ordinate equal to the measured closure stress at that perforation orientation. In FIG. 16, the data points 1620 are wrapped over a 360° angle interval. A curve 1600 is obtained by fitting a sinusoid to the data points 1600, and represents a closure stress as a function of two times the perforation orientation θ. The maximum and minimum horizontal stress values (respectively 1610 and 1611) are obtained from the maximum and minimum values of the curve 1600, respectively. The stress orientation relative to the reference is obtained from the abscissa coordinate of the maximum and minimum values divided by two.

While specific embodiment involving fracture and/or stress test have been disclosed, injection as understood herein is not limited to fracture and/or stress determination.

In view of all of the above, and the figures, those skilled in the art will recognize that the present disclosure introduces an apparatus comprising: a downhole tool configured for conveyance within a borehole penetrating a subterranean formation, wherein the downhole tool comprises: a probe assembly configured to seal a region of a wall of the borehole; a perforator configured to penetrate a portion of the sealed region of the borehole wall by projecting through the probe assembly; a fluid chamber comprising a fluid; and a pump configured to inject the fluid from the fluid chamber into the formation through the perforator. The pump may be configured to inject the fluid from the fluid chamber into the formation through the perforator after the perforator has penetrated the portion of the sealed region of the borehole wall and before the perforator has been removed from the penetrated portion of the sealed region of the borehole wall. The perforator may be configured to penetrate at least one of a consolidated formation, a casing, and cement. The downhole tool may further comprise a tool body housing at least a portion of the probe assembly, the perforator, the fluid chamber, and the pump, and the tool body may be configured for conveyance within the borehole via at least one of a wireline and a drillstring. The downhole tool may further comprise an anchor system configured to support the tool body against a region of the borehole wall opposite the sealed region the borehole wall. The downhole tool may further comprise an actuator configured to move the probe assembly between a retracted position and a deployed position, wherein the probe assembly is configured to seal the region of the borehole wall when in the deployed position. The probe assembly may comprise a substantially rigid plate and a compressible packer element coupled to the plate, and the actuator may comprise: a plurality of pistons connected to the plate and configured to move the probe assembly between the retracted and deployed positions; and a controllable energy source configured to power the pistons. The perforator may comprise: a shaft; a drill bit; and means for applying torque and translatory force to the shaft to project the drill bit through the probe assembly into the sealed region of the borehole wall. The downhole tool may further comprise an inclinometry device configured to measure a perforation orientation. The downhole tool may further comprise: means for measuring a closure stress; and means for determining at least one of a minimum horizontal stress value, a maximum horizontal stress value, and a horizontal stress orientation relative to a reference, based on the measured closure stress. The downhole tool may further comprise means for determining formation permeability based on at least one of the injected fluid and a result of the fluid injection. The downhole tool may further comprise means for determining mobility of the fluid injected into the formation.

The present disclosure also introduces a method comprising: conveying a downhole tool within a borehole penetrating a subterranean formation, wherein the downhole tool comprises a probe assembly, a perforator, and a fluid chamber; sealing a region of a wall of the borehole wall using the probe assembly; projecting the perforator through the probe assembly to penetrate a portion of the sealed region of the borehole wall; and injecting fluid from the fluid chamber into the formation through the perforator. Injecting the fluid from the fluid chamber into the formation through the perforator may be performed after the perforator has penetrated the portion of the sealed region of the borehole wall and before the perforator has been removed from the penetrated portion of the sealed region of the borehole wall. The method may further comprise: removing the perforator from the penetrated portion of the sealed region of the borehole wall after injecting the fluid from the fluid chamber into the formation through the perforator; and repeating the sealing, projecting, injecting, and removing steps at each of plurality of orientations of the downhole tool. The method may further comprise: measuring a closure stress at each of the plurality of orientations of the downhole tool; and determining at least one of a minimum horizontal stress value, a maximum horizontal stress value, and a horizontal stress orientation relative to a reference, based on the resulting plurality of closure stress measurements. The method may further comprise determining a permeability of a portion of the formation based on at least one of the injected fluid and a result of the fluid injection. The method may further comprise determining mobility of the fluid injected into the formation. The method may further comprise performing a leak-off test on the subterranean formation. Conveying the downhole tool within the borehole may comprise conveying the downhole tool via at least one of a wireline and a drill string.

It will be understood from the foregoing description that various modifications and changes may be made in the various and alternative embodiments of the present disclosure without departing from its true spirit.

The Abstract at the end of this disclosure is provided to comply with 37 C.F.R. §1.72(b) to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

APPARATUS AND METHODS FOR CHARACTERIZING A RESERVOIR

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CPC

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