Abstract:
According to some embodiments, a borehole deployable apparatus is described that can be used to generate strong vibrations in a subterranean rock formation. In some embodiments, the apparatus accelerates a mass using mechanisms built into the tool and causes the mass to strike the borehole wall. The mechanisms can control the mass acceleration, and the frequency of strikes. In some embodiments, the apparatus is designed for use in the field of petroleum recovery where the vibrations are used to create or re-establish a flow rate for the fluids in the formation.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/570,650 filed Dec. 14, 2011, the contents of which are incorporated herein by reference in its entirety. 
    
    
     FIELD 
     This patent specification generally relates to the field of wave stimulation in subterranean rock formations. This patent specification relates more specifically to the generation of vibrations in the formation using tools positioned within a borehole. 
     BACKGROUND 
     Wave stimulation is a known technique for enhancing oil recovery from oil-bearing formations. For example, known techniques include generating shock waves by releasing a compressed liquid or by fluidic oscillation within the borehole. Strong vibrations are known to cause oil droplets to coalesce and form larger bulbs of oil that can move and be produced. These vibrations may also change the wettability of the rock. These effects can help increase fluid production from oil wells. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor intended to be used as an aid in limiting the scope of the claimed subject matter. 
     According to some embodiments, a system is described for generating vibrations in a subterranean rock formation. The system includes: a tool body adapted to be deployable in a 
     wellbore; a translatable mass member mounted to the tool body such that the mass member is able to translate along a first direction towards an interior surface of the wellbore when the tool body is deployed in the wellbore; a contacting surface oriented to contact the interior surface of a wellbore (e.g., either the borehole wall or a casing); and an actuator subsystem mounted within the tool body and fixed to the mass member and configured to translationally accelerate in said first direction towards the interior surface of the wellbore such that the contacting surface imparts energy into the interior surface of the wellbore when the tool body is deployed in the wellbore thereby generating vibrations within a subterranean rock formation surrounding the wellbore so as to stimulate production from the formation. 
     According to some embodiments, the subterranean rock formation is hydrocarbon bearing, and the flow of a hydrocarbon bearing fluid is improved by the generated vibrations in the formation, for example by facilitating coalescence of oil droplets into larger bulbs and/or altering wettability of surfaces within the rock formation. According to some embodiments the actuator subsystem uses one or more pistons to convert gas or hydraulic pressure into motion of the mass member. According to some other embodiments an electric motor can be used in the actuator subsystem. 
     According to some embodiments, the contacting surface is configured to strike the interior surface of the wellbore and the contacting surface forms part of the translatable mass member. According to some other embodiments, the contacting surface is on a contacting mass member that is separate from the translatable mass member; and the translatable mass member strikes the contacting mass member. 
     According to some embodiments, one or more anchoring members are moveably mounted on the tool body so as to facilitate stable positioning of the tool body within the wellbore when the mass member strikes the interior surface of the wellbore. The contacting surface of the mass member can have a curvature that is substantially the same to an expected curvature of the interior surface of a wellbore. According to some embodiments more than one translatable mass member can be used which can be actuated simultaneously or in sequence. According to some embodiments, the tool body can be configured for short-term application and can be deployed in the wellbore via a wireline cable, coiled tubing, or on a drilling bottom hole assembly during a drilling process. 
     According to some embodiments a method for generating vibrations in a subterranean rock formation is described. The method includes: deploying a tool body into a wellbore at a depth within the subterranean rock formation; and linearly accelerating a mass member from the tool body such that the mass member translates towards an interior surface of the wellbore so as to cause a contacting surface to impart energy into the interior surface of the wellbore, thereby generating vibrations within the subterranean rock formation 
     According to some embodiments where the tool body is configured for short-term deployment the tool body can be re-positioned at second depth within the wellbore and the accelerating of the mass member can be repeated so as to cause to strike the interior surface of the wellbore at a second location, prior to retrieving the tool body from the wellbore to an above-ground location. 
     According to some embodiments, the tool body is configured for long-term deployment in the wellbore. In some cases the tool body is configured to be deployed prior to insertion of production tubing within the wellbore, and in other cases the production tubing is removed from the wellbore prior to deploying of the tool body, and the production tubing is reinstalled following deployment of the tool body. According to some embodiments, the tool body is configured for long-term downhole deployment via a slim tool deployment technique. 
     According to some embodiments, an apparatus is described that can be used to generate strong vibrations in the formation. In some embodiments, the apparatus translationally accelerates a mass using mechanisms built into the tool and causes the mass to strike the borehole wall. The mechanisms can control the mass acceleration, and the frequency of strikes. In some embodiments, the apparatus is designed for use in the field of petroleum recovery where the vibrations are used to create or re-establish a flow pass for the fluids in the formation. 
     Further features and advantages of the subject disclosure will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject disclosure is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of embodiments of the subject disclosure, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein: 
         FIG. 1  is a diagram illustrating an apparatus that uses an accelerating mass to strike the borehole wall, thereby generating vibrations in the formation and achieving wave stimulation, according to some embodiments; 
         FIGS. 2-1 ,  2 - 2  and  2 - 3  show cross sections of an apparatus for generating vibrations for stimulation purposes, according to some embodiments; 
         FIG. 3-1  shows an apparatus for generating vibrations in which air pressure is converted in to mass motion, according to some embodiments; 
         FIG. 3-2  shows an apparatus for generating vibrations for stimulation purposes, according to some other embodiments; 
         FIG. 4  is a cross-section of an apparatus for generating vibrations for stimulation purposes, according to some embodiments; 
         FIG. 5  shows an apparatus for generating vibrations in which an electric motor is used to move a mass for striking a borehole wall, according to some embodiments; and 
         FIG. 6  shows a wellsite in which a borehole tool is being deployed for generating vibrations in a subterranean formation for stimulation purposes, according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the subject disclosure only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the subject disclosure. In this regard, no attempt is made to show structural details in more detail than is necessary for the fundamental understanding of the subject disclosure, the description taken with the drawings making apparent to those skilled in the art how the several forms of the subject disclosure may be embodied in practice. Furthermore, like reference numbers and designations in the various drawings indicate like elements. 
     As used herein, the terms acoustic wave or vibrations refer to the vibrations induced into the subject formation and may be of frequencies generally referred to as seismic, sonic, or ultrasonic.  FIG. 1  is a diagram illustrating an apparatus that uses an accelerating mass to strike the borehole wall, thereby generating acoustic waves in the formation and achieving wave stimulation, according to some embodiments. Tool  124  is shown deployed in a borehole  110  formed within formation  100 . A section of borehole wall  122  is shown where tool  124  is disposed at a particular depth. The tool  124  is equipped with a mass  126  that can be projected out of the tool body and strike the borehole wall  122 . The tool  124  is also equipped with one or more anchors  128  and  130  to position the tool  124 . According to some embodiments, the accelerated mass  126  is a piece of metal projected from the downhole tool  124 . The tool  124  has a cylindrical structure, and in some cases more than one mass may be projected from its surface to strike the borehole wall  122 . 
       FIGS. 2-1 ,  2 - 2  and  2 - 3  show cross sections of an apparatus for generating acoustic waves for stimulation purposes, according to some embodiments. Tool  124  is shown suspended in borehole  110  having borehole wall  100 . In the case of  FIG. 2-1 , when the mass  126  strikes the borehole wall  122 , the force associated with the mass  126  and its acceleration is partially transferred to the formation  100  creating an acoustic wave traveling in the formation  100 . The area of the strike zone depends on the surface area of the mass  126  and the curvature of the mass  126  relative to that of the borehole wall  122 . The shape of mass surface  126  may be chosen to have substantially the same curvature as the borehole wall  122  if maximum area of acoustic excitation is desired. 
     When the area is reduced the exerting force is concentrated in a small area and can generate higher-pressure waves in the formation  100 . In an extreme case, when the mass surface is reduced to a point, such as shown by mass  127  in the example of  FIG. 2-2 , the borehole wall  122  can be indented or permanently damaged. The damage can lead to perforation or microcracks in the rock structure for formation  100 . According to some embodiments, both of the cases (shown in  FIG. 2-1  and  FIG. 2-2 ) have useful applications in the field of oil well production.  FIG. 2-3  shows a case where the stimulation tool  124  is being deployed in a region of borehole  110  that is cased with a casing  210 . In such embodiments, the mass  126  can strike the casing  210  transmitting some of the vibrations to the formation  100  immediately behind the casing  210 . Some of the energy will also be transmitted through the casing  210  and excite areas of formation  100  above and below the strike point depth shown in  FIG. 2-3 . 
     According to some embodiments, the mechanism of projecting the mass towards the borehole wall can use air (or other gas), liquid (hydraulic), or an electric motor. In the case where air is used, it is provided from the earth surface according to some embodiments.  FIG. 3-1  shows an apparatus for generating acoustic waves in which air pressure is converted in to mass motion, according to some embodiments. In the embodiments of  FIG. 3-1 , a cylinder  312  having an inner cross sectional area=A 1  is equipped with a piston  310 , and is located inside the tool  124 . An O-ring  332  is positioned within a groove of piston  310  as shown to form a seal with the inner wall of cylinder  310 . The cylinder  310  is filled with air to a pressure P 1 . The piston  310  is compressed to increase the pressure inside the piston to a pressure P 2 &gt;=P 1 . Those skilled in the art will recognize that this structure is a so-called accumulator. Depending on the available air pressure there may or may not be a need for the accumulator. Once the desired pressure P 2  is reached a three way valve  320  is opened to deliver the pressurized air to a second cylinder  314  having a second piston  316  with cross sectional area A 2 &lt;A 1 . As in the case of piston  310 , piston  316  has an O-ring  334  for sealing. The rush of air into the second cylinder accelerates the second piston to a linear motion. The second piston is directly or indirectly connected to the mass  126 , which is then projected out of the tool body and strikes the borehole wall (not shown). If the second piston  316  is not directly connected to the mass  126 , the piston  316  can be arranged to strike the back of the mass  126 , which is of interest in some applications. 
     Note that valve  320  can be used to reciprocate the mass for the next cycle. As a result, in this embodiment, valve  320  is an important component that controls the frequencies achievable by the described apparatus. 
     According to some embodiments, the gas source is on the surface, and the gas is supplied via a gas supply tube  308 . When the source of compressed air (or other gas) is at the surface, the tool can be made simpler than the case where the source is downhole. The drawback, however, is that one has to have high pressure tube  308  running along the length of the well. According to some embodiments, an alternative approach provides an air tank and a pump within the tool. In this case, the gas supply tube  308  runs to another section of the tool string where the tank and pump are positioned (not shown). 
     According to some embodiments, other fluids, such as hydraulic fluid for example, can also be used for driving the piston and the mass, instead of air. In this case, a small reservoir of hydraulic fluid  330  is provided in the tool and there is no need for high pressure tubing to run along the length of the well, unless that is desired. 
       FIG. 3-2  shows an apparatus for generating vibrations for stimulation purposes, according to some other embodiments. In this case the mass  328  is applied to the borehole wall  122  using springs  340  and  342 , which are independent of the second piston  316 . The second piston  316  in this case is fixed to an intermediate mass  326 . The piston  316  accelerates mass  326  to strike mass  328 , thereby imparting energy into mass  328  to generate waves in formation  100 . The arrangement as shown in  FIG. 3-2  has been found to help to stabilize the tool  124  within the borehole. 
     It has been found that by linearly accelerating the moving mass (e.g., mass  126  or mass  326 ) such that it translates towards the borehole wall, such as shown and described herein can generate relatively large amplitude vibrations within the surrounding formation. The amplitudes are significantly greater than can be generated by other techniques such as by rotating or whirling a mass in a circular motion or by bending or distorting a mass such as by piezoelectric bending actuators. 
       FIG. 4  is a cross-section of an apparatus for generating vibrations for stimulation purposes, according to some embodiments. In the case shown in  FIG. 4 , symmetrically placed pistons are used to drive masses in different directions. The driving can be done simultaneously or in sequence. In the example of  FIG. 4 , four pistons are used, although other numbers of pistons can be used according to other embodiments. 
       FIG. 4  is a cross sectional view of the tool  404  at the level of cylinders  414 ,  424 ,  434  and  444 . Cylinder  414  houses piston  416  that applies force to mass  418 . An O-ring  412  sits within a groove of piston  416  to form a seal with the cylinder  414 . Similarly, cylinders  424 ,  434  and  444  house pistons  426 ,  436  and  446  respectively, which apply force to masses  428 ,  438  and  448  respectively. For clarity, the mechanism and the plumbing by which the pressurizing fluid is connected to the pistons are not shown, but it is similar or identical to that shown in  FIG. 3-1 , according to some embodiments. As the pressurizing fluid enters the four cylinders  414 ,  424 ,  434  and  444 , it pushes the pistons  416 ,  426 ,  436  and  446  outward which in turn causes masses  418 ,  428 ,  438  and  448  to accelerate and strike the borehole wall (in cases where the borehole is uncased at the location of the tool) or strike the casing  210  (in cases where the borehole is cased at the location of the tool). 
       FIG. 5  shows an apparatus for generating vibrations in which an electric motor is used to move a mass for striking a borehole wall, according to some embodiments. According to some embodiments, a gearbox is used between the motor and the mass to control the velocity of the mass and the amount of energy imparted to the formation. In the embodiment shown in  FIG. 5 , the tool  124  includes electric motor  542  that rotates the vertical shaft  544 , which is connected to the gear box  546 . The gear box  546  in this case transforms the rotational motion of shaft  544  to the translational motion of mass  518  which in turn strikes the borehole wall and generates acoustic vibrations in the formation. 
       FIG. 6  shows a wellsite in which a borehole tool is being deployed for generating vibrations in a subterranean formation for stimulation purposes, according to some embodiments. Shown is a stimulation tool  124  being deployed in a borehole  110  formed within subterranean rock formation  100 . In the case shown in  FIG. 6 , the tool  124  is being deployed in borehole  110  via a wireline  610  from wireline truck  620 . However, according to some embodiments, the mode of deploying the stimulation tool  124  depends on a number of factors including the life of the well and whether it is horizontal or vertical well. The stimulation tool  124  can be deployed using other technologies such as for example using coiled tubing, or during a drilling operation on a bottom hole assembly. According to some embodiments, as described hereinabove, an air compressor  612  can be used and connected to the tool  124  via gas tube  308 . 
     According to some embodiments, the tool  124  can be deployed for either short-term application or long-term application. In an example of short-term application, the tool  124  is deployed in the well  110  which has just been cased. According to some embodiments, the wellbore  110  in the region of interest of formation  100  can have open hole completion, where there is direct access to the formation and the mass can strike the formation directly. 
     According to some other embodiments, the wellbore  110  in the region of interest of formation  100  can be cased with perforations. In this case the mass (or masses) of tool  124  can strike the casing, which then transmits some of the vibrations to the formation immediately behind the casing. Some of the energy will be transmitted through the pipe and excite areas above and below the strike point. 
     In an example of a long-term application, according to some embodiments, the tool  124  may be deployed before the production pipes are installed. In this case the connections to the tool for power, control, and possibly compressed air can go through a pipe. According to other long-term application embodiments, the well  110  is already completed and is producing, then the production pipes are removed and tool  124  is deployed, followed by a re-installation of the production pipes. According to yet other long-term application embodiments, the well  110  is already completed and is producing, then depending on the inner diameter of the pipe, a slim version of the tool  124  can be deployed. 
     Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.