SYSTEMS AND METHODS FOR INERTIAL CAVITATION INCEPTION AT HIGH STATIC PRESSURES

Description

BACKGROUND

Cavitation occurs when the pressure of a liquid falls below a liquid's vapor pressure (i.e., the “cavitation threshold”), leading to the formation of small vapor-filled cavities (bubbles) in the liquid. Cavitation can occur either unintentionally, for example, on the surface of ships'propeller blades, or be created deliberately, for example, by using a high-power acoustic (ultrasonic) source. Cavitation processes are widely used in medicine, chemical engineering, etc. Typically, cavitation is observed and/or used at relatively low static pressures (up to several atmospheres) because the cavitation threshold rapidly increases with the rise of the static pressure, making it progressively more difficult to induce cavitation at high static pressures (i.e., tens or hundreds of atmospheres). However, cavitation may be of interest in the oil and gas industry, particularly within boreholes drilled into hydrocarbon reservoirs where the static pressures may be high and hence cavitation is difficult to initiate and sustain. Consequently, there is a pressing need for a means for eliciting cavitation at high static pressures.

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 is it intended to be used as an aid in limiting the scope of the claimed subject matter.

In general, in one aspect, embodiments disclosed herein relate to an apparatus for inertial cavitation inception at high static pressures. The apparatus includes a cavitation chamber, an acoustic source, and a fluid channel in communication with the cavitation chamber and configured to dispense a fluid into the cavitation chamber.

In general, in one aspect, embodiments disclosed herein relate to methods for inertial cavitation inception at high static pressures. The methods include installing an apparatus in a borehole, wherein the apparatus include a cavitation chamber configured to enhance an amplitude of acoustic waves, an acoustic source configured to emit focused acoustic waves into the cavitation chamber, and a fluid channel configured to dispense a fluid into the cavitation chamber. The methods further include activating the acoustic source in the cavitation chamber; dispensing the fluid into the cavitation chamber; and dispensing an epoxy resin into a fracture in the borehole.

In general, in one aspect, embodiments disclosed herein relate to systems for inertial cavitation inception at high static pressures. The systems may include an apparatus, wherein the apparatus include a cavitation chamber configured to enhance amplitude of acoustic waves, an acoustic source configured to emit the acoustic waves into the cavitation chamber, a fluid channel configured to dispense a fluid into the cavitation chamber, a first container to hold cavitation nuclei and dispense the cavitation nuclei into the fluid, a second container configured to hold a gas and to dispense the gas into the fluid, a fluid container configured to hold the fluid, and a pump configured to pump the fluid from the fluid container through fluid channel. The systems further include a coiled tubing or a drill pipe, configured to contain the fluid channel, an epoxy resin configured to combine with a curing agent and form a cross-linked resin, and a bottomhole assembly, configured to contain the apparatus.

Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

Specific embodiments of the disclosed technology will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency.

FIG. 1 shows a drilling system in accordance with one or more embodiments.

FIG. 2 shows a system for cavitation in a borehole in accordance with one or more embodiments.

FIG. 3 shows a system for supplying a fluid, cavitation nuclei, and a lightweight fluid to a borehole in accordance with one or more embodiments.

FIG. 4 shows a flowchart of a method in accordance with one or more embodiments.

DETAILED DESCRIPTION

In the following detailed description of embodiments of the disclosure, numerous specific details are set forth in order to provide a more thorough understanding of the disclosure. However, it will be apparent to one of ordinary skill in the art that the disclosure may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

Throughout the application, ordinal numbers (e.g., first, second, third, etc.) may be used as an adjective for an element (i.e., any noun in the application). The use of ordinal numbers is not to imply or create any particular ordering of the elements nor to limit any element to being only a single element unless expressly disclosed, such as using the terms “before,” “after,” “single,” and other such terminology. Rather, the use of ordinal numbers is to distinguish between the elements. By way of an example, a first element is distinct from a second element, and the first element may encompass more than one element and succeed (or precede) the second element in an ordering of elements.

In the following description of FIGS. 1-4, any component described with regard to a figure, in various embodiments disclosed herein, may be equivalent to one or more like-named components described with regard to any other figure. For brevity, descriptions of these components will not be repeated with regard to each figure. Thus, each and every embodiment of the components of each figure is incorporated by reference and assumed to be optionally present within every other figure having one or more like-named components. Additionally, in accordance with various embodiments disclosed herein, any description of the components of a figure is to be interpreted as an optional embodiment which may be implemented in addition to, in conjunction with, or in place of the embodiments described with regard to a corresponding like-named component in any other figure.

It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a cavitation chamber” includes reference to one or more of such cavitation chambers.

Terms such as “approximately,” “substantially,” etc., mean that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those of skill in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

It is to be understood that one or more of the steps shown in the flowcharts may be omitted, repeated, and/or performed in a different order than the order shown. Accordingly, the scope disclosed herein should not be considered limited to the specific arrangement of steps shown in the flowcharts.

Although multiple dependent claims are not introduced, it would be apparent to one of ordinary skill that the subject matter of the dependent claims of one or more embodiments may be combined with other dependent claims.

The present disclosure is directed to systems and methods for cavitation inception at high pressures. The methods may overcome high-pressure difficulties inherent in borehole conditions. The methods may use an apparatus comprising multiple acoustic sources, multiple means of creating cavitation nuclei, and multiple means for placing the cavitation nuclei downhole. The methods may additionally heat the fluid, lower the fluid level, employ venturi devices, employ a lightweight fluid, and make use of a cavitation chamber especially designed with an acoustic resonance structure. The system may allow for employing the apparatus down a borehole by attaching it to a bottom hole assembly. The methods may succeed in creating cavitation in a borehole fluid by lowering the cavitation threshold and/or lowering the borehole fluid static pressure. The systems and methods further allow for the use of encapsulated nodules containing a curing agent. These nodules are pumped into a cavitation chamber along with an epoxy resin mixed with a fluid and cavitation nuclei. Cavitation causes the cavitation nuclei to rupture the nodules and thus mix the curing agent with the epoxy resin in the fluid and produce a cross-linked resin. The resulting cross-linked resin is pumped into the borehole where it may inhibit fluid flow into a fracture intersecting a borehole, thereby preventing loss of circulation within the borehole. Alternatively, the nodules may contain the epoxy resin and the curing agent may be mixed into the fluid and pumped into the cavitation chamber.

Before further presenting exemplary embodiments of the claimed invention, typical elements of a drilled oil well are presented for context since embodiments of the systems and methods may operate within a borehole. FIG. 1 presents these elements in accordance with one or more embodiments.

As shown in FIG. 1, a borehole path (103) may be drilled by a drill bit (105) attached by a drillstring (106) to a drill rig located on the surface (107) of the earth. Although the drilling system (100) shown in FIG. 1 is used to drill a borehole (117) on land, the drilling system (100) may also be a marine borehole drilling system. The example of the drilling system (100) shown in FIG. 1 is not meant to limit the present disclosure. The drill rig may include framework, such as a derrick (108), to hold drilling machinery. The top drive (110) sits at the top of the derrick (108) and provides torque, typically a clockwise torque, via the drive shaft (112) to the drillstring (106) in order to drill the borehole (117). The borehole (117) may traverse a plurality of overburden (114) layers and one or more cap-rock (116) layers to a hydrocarbon reservoir (104) within the subterranean region of interest (102). In accordance with one or more embodiments, the extended bandwidth seismic dataset may be used to plan a borehole (117) including a borehole path (103) and drill a borehole (117) guided by the borehole path (103). The borehole path (103) may be a curved borehole path or a straight borehole path. All or part of the borehole path (103) may be vertical, and some borehole paths (103) may be deviated or have horizontal sections.

Prior to the commencement of drilling, the borehole plan may be generated. The borehole plan may include a starting surface (107) location of the borehole (117), or a subsurface location within an existing borehole (117), from which the borehole (117) may be drilled. Further, the borehole plan may include a terminal location that may intersect with the target zone (118), e.g., a targeted hydrocarbon-bearing formation and a planned borehole path (103) from the starting location to the terminal location. In other words, the borehole path (103) may intersect a previously located hydrocarbon reservoir (104).

A borehole planning system (150) may be used to generate the borehole plan. The borehole planning system (150) may comprise one or more computer processors in communication with computer memory containing the geophysical and geomechanical models, the extended bandwidth seismic dataset, information relating to drilling hazards, and the constraints imposed by the limitations of the drillstring (106) and the drilling system (100). The borehole planning system (150) may further include dedicated software to determine the planned borehole path (103) and associated drilling parameters, such as the planned borehole diameter, the location of planned changes of the borehole diameter, the planned depths at which casing (124) will be inserted to support the borehole (117) and to prevent formation fluids entering the borehole (117), and the drilling mud weights (densities) and types that may be used during drilling the borehole (117).

A borehole (117) may be drilled using a drill rig that may be situated on a land drill site, an offshore platform, such as a jack-up rig, a semi-submersible, or a drill ship. The drill rig may be equipped with a hoisting system, such as a derrick (108), which can raise or lower the drillstring (106) and other tools required to drill the well. The drillstring (106) may include one or more drill pipes connected to form a conduit and a bottomhole assembly [BHA] (120) disposed at the distal end of the drillstring (106). The BHA (120) may include a drill bit (105) to cut into subsurface (122) rock. The BHA (120) may further include measurement tools, such as a measurement-while-drilling (MWD) tool and logging-while-drilling (LWD) tool. MWD tools may include sensors and hardware to measure downhole drilling parameters, such as the azimuth and inclination of the drill bit (105), the weight-on-bit (WOB), and the torque. The LWD measurements may include sensors, such as resistivity, gamma ray, and neutron density sensors, to characterize the rock formation surrounding the borehole (117). Both MWD and LWD measurements may be transmitted to the surface (107) using any suitable telemetry system, such as mud-pulse or wired-drill pipe, known in the art. A BHA (120) may also be used to lower a tool into a borehole (117) in order to perform operations such as those introduced below, i.e., to facilitate inertial cavitation inception at high static pressures.

The near surface is typically made up of loose or soft sediment or rock, so large diameter casing (124), e.g., “base pipe” or “conductor casing,” is often put in place while drilling to stabilize and isolate the borehole (117). At the top of the base pipe is the wellhead, which serves to provide pressure control through a series of spools, valves, or adapters. Once near-surface drilling has begun, water or drilling fluid may be used to force the base pipe into place using a pumping system until the wellhead is situated just above the surface (107) of the earth.

Drilling may continue without any casing (124) once deeper, or more compact rock is reached. While drilling, a drilling mud system (126) may pump drilling mud from a mud tank on the surface (107) through the drill pipe. Drilling mud serves various purposes, including pressure equalization, removal of rock cuttings, and drill bit (105) cooling and lubrication.

At planned depth intervals, drilling may be paused and the drillstring (106) withdrawn from the borehole (117). Drill pipe or coiled tubing may then be lowered into the borehole (117) with tools attached at the end. The tubing may allow fluid to be delivered into the borehole (117) at depth. The tools may take measurements or perform operations in the borehole environment. Alternatively, sections of casing (124) may be connected and inserted and cemented into the borehole (117). Casing string may be cemented in place by pumping cement and mud, separated by a “cementing plug,” from the surface (107) through the drill pipe. The cementing plug and drilling mud force the cement through the drill pipe and into the annular space between the casing (124) and the borehole wall. Once the cement cures, drilling may recommence. The drilling process is often performed in several stages. Therefore, the drilling and casing cycle may be repeated more than once, depending on the depth of the borehole (117) and the pressure on the borehole walls from surrounding rock.

A drilling system (100) may be disposed at and communicate with other systems in the well environment. The drilling system (100) may control at least a portion of a drilling operation by providing controls to various components of the drilling operation. In one or more embodiments, the system may receive data from one or more sensors arranged to measure controllable parameters of the drilling operation. As a non-limiting example, sensors may be arranged to measure WOB, drill RPM, flow rate of the mud pumps (GPM), and ROP of the drilling operation. Each sensor may be positioned or configured to measure a desired physical stimulus. Drilling may be considered complete when a target zone (118) is reached, or the presence of hydrocarbons is established.

During drilling or after the completion of a well, it may be necessary to alter the environment within the borehole (117) through chemical or physical means for a production-related purpose. For example, the systems and methods described herein may be used to perform such an alteration in the form of the release of a controlled cross-linked resin in case of lost circulation within a borehole (117). Such a loss of circulation may occur when a fracture intersects the borehole (117) and drilling mud drains from the borehole (117). Loss of circulation may be catastrophic during drilling, for example causing the collapse of the borehole (117), and/or loss of a drillstring (106). Thus, there is a need to restore circulation expeditiously during active drilling. The cross-linked resin will effectively allow for the plugging of the “hole” caused by the fracture, thus preserving borehole circulation.

The release of the cross-linked resin may require inducing cavitation nuclei within the fluid dispersed into the borehole (117). It is known that the cavitation threshold rapidly increases with static fluid pressure. Thus, the cavitation is normally infeasible in borehole conditions and standard methods fail. The present disclosure proposes systems and methods for overcoming this problem and generating cavitation at high pressures in the borehole environment. These methods represent ways to either lower the borehole static pressure or lower the cavitation threshold and may be used individually or in various combinations.

In accordance with some embodiments, the methods include a cavitation chamber within which cavitation (the creation of bubbles in a fluid) may occur. FIG. 2 presents a cross section of the cavitation chamber (201) along with other embodiments presented below that aid in facilitating cavitation. The cavitation chamber (201) may be configured to enhance amplitude of acoustic waves (207) emitted within. An acoustic source (206)—in this embodiment, an ultrasonic emitter—may be configured to emit the acoustic waves (207) into the cavitation chamber (201), and may be located near the cavitation chamber (201). The cavitation chamber (201) may be cylindrical in shape so as to better focus the waves (207) emitted by the acoustic source (206). However, this is not a limitation of the method. Any shape that enhances the effect on cavitation of the waves produced by the acoustic source may be used. Furthermore, an array of acoustic sources (204) may be used instead of a single source. Cavitation nuclei (210) may be added to fluid (203) pumped into the borehole (117); these nuclei are chemicals or gases that facilitate easier creation of cavities (bubbles) in the fluid (203). The acoustic source (206) (or array of acoustic sources (204)) may also be aligned axially to increase cavitation within the fluid (203) that is introduced to the borehole (117), passes through the cavitation chamber (201), and out the BHA into the annulus of the borehole (117). The frequency range of the acoustic waves (207) emitted by the ultrasonic emitter or array of acoustic sources (204) may be selected to induce the maximum amount of cavitation. Lower frequencies are sufficient for a lower cavitation threshold. In addition, lower frequencies resonate in a larger volume than higher frequencies. In the case of an array of acoustic sources (204), the array may be activated simultaneously or in a special pattern to affect a chosen zone. Using an array of acoustic sources (204) will have better localization within the cavitation chamber (201) at the tradeoff of a decreased volume. Alternatively, a less focused field may result in a larger cavitation volume. The acoustic source (206) or array of acoustic sources (204), located on the outer surface of the cavitation chamber (201), excite the cavitation chamber walls to create resonance, lowering the fluid pressure at antinodes.

The source signature of the acoustic waves (207) may be a continuous harmonic signal. A bi-frequency signal can also be used, which is known to reduce power consumption. Other types of source signals may be used as well. An ultrasonic emitter may be preferred, although other source frequency ranges are possible. The ultrasonic emitter may be supplied with the energy through a battery that may be activated using mud pulse telemetry when the cavitation initiation is required.

A fluid channel (202), configured to dispense the fluid (203) into the cavitation chamber (201), is connected to a fluid container ((351), shown in FIG. 3) for the fluid. The reservoir may be located within the borehole (117), or it may be located upon the surface (107). In the case where the reservoir is located upon the surface (107), a pump will dispense the fluid through the fluid channel (202), down the borehole (117), and into the cavitation chamber (201). The fluid channel (202) may be contained within the drill pipe used during drilling. Alternately, the fluid channel (202) may be contained in coiled tubing used during an intervention when the drill pipe has been removed from the borehole (117). An epoxy resin that will react with the curing agent contained in nodules may be added to the fluid (203) before dispensing the fluid (203) into the cavitation chamber (201) through a drill bit nozzle (255) or other outflow unit that delivers fluids back into the borehole.

Another method that may enhance the cavitation process includes using a venturi device (212). Venturi devices (212) make use of the Bernoulli effect, where an increase in fluid velocity leads to a local decrease in fluid pressure. The venturi device (212) may be configured to flow the fluid (203) into the cavitation chamber (201) and lower the fluid pressure of the fluid (203) flowing through the fluid channel (202). The venturi device (212) may be a throttle or a nozzle but is not limited to these particular shapes. Any shape that creates the Bernoulli effect may be used as a venturi device (212). The venturi device (212) relies on lowering the pressure of the fluid (203) to facilitate cavitation. As fluid (203) is pumped through a fluid channel (202) and out of the venturi device (212) (such as a nozzle) into the cavitation chamber (201), the venturi device (212) creates a low-pressure area within the cavitation chamber (201).

Cavitation nuclei (210) may be used to lower the pressure at which cavitation may occur. Cavitation nuclei (210) may be chemical additives within the fluid, or aphrons (bubbles) that act as catalysts for cavitation.

In FIG. 2, liquid additives containing cavitation nuclei (210) are shown in the cavitation chamber (201). Combining the cavitation nuclei (210) with the acoustic source (206) or array of acoustic sources (204) enhances the pressure antinode occurring in the axial region of the chamber, thus facilitating cavitation. The cavitation nuclei (210) may be contained in a first container ((361) in FIG. 3) located on the surface (107) or in the borehole (117). The cavitation nuclei (210) are deployed from the first container (361) into the cavitation chamber (201) through a first channel (363). The first container may also hold the nodules containing epoxy resin within them. In this embodiment, the nodules and cavitation nuclei (210) would be dispersed at the same time from the same first container (361) into the cavitation chamber (201). This, however, is not a limitation of the method. The cavitation nuclei (210) and the nodules may be held in separate containers.

Another method that may facilitate cavitation is adding a gas to the fluid. The addition of the gas to the fluid lowers the cavitation pressure of the fluid. A second container (371) may be configured to hold the gas and to dispense the gas into the fluid. The second container (371) may be located in the borehole (117) or it may be located at the surface (107). The gas is deployed from the second container (371) into the cavitation chamber (201) through a second channel (373).

Yet another method to facilitate cavitation by lowering the static fluid pressure is to use a second, lighter fluid, here referred to as a lightweight fluid. The lightweight fluid is a second fluid, lighter than the fluid (203) normally used in the borehole (117), and may be substituted for it. Additionally, the level of the fluid within the borehole (117) may be lowered, thus lowering the pressure at the depth where the cavitation chamber (201) is located. Furthermore, the fluid (203) used in the cavitation chamber (201) may be heated to lower the cavitation threshold. The fluid may be heated by a heating device (226). It may be heated before or after entering into the cavitation chamber (201). It may be heated within the borehole (117) or within a container on the surface before being pumped into the borehole (117).

The cavitation chamber (201), acoustic source (204), and any other tool that facilitates cavitation may be attached to the BHA (120) and lowered as a unit to the appropriate depth in the borehole (117). All the complimentary methods to facilitate cavitation are combined synergistically in the fluid (203) to create cavitation bubbles (205). In one or more embodiments, the BHA (120) is positioned upstream of the borehole wall of the lost circulation zone. “Upstream” in this sense is relative to the circulation pathway of borehole fluid. Being positioned upstream based upon the flow of the borehole fluid permits the cavitation chamber (201) and associated tools to initiate a treatment, such as generation of a sonic frequency, such that the cross-linked epoxy resin may form near the lost circulation zone. If the borehole fluid is circulating downhole through the drill pipe and uphole in a borehole annulus, the BHA (120) may be positioned downhole of the lost circulation zone. The borehole annulus is the void between the drillstring (106) and the borehole wall. The borehole fluid is shown in FIG. 2 flowing into the borehole (117) through the drill bit (105) and uphole via the borehole annulus. Alternatively, if the borehole fluid is circulating downhole through the wellbore annulus, the BHA (120) may be positioned uphole of the face of the lost circulation zone. In such an instance, the cross-linked epoxy resin would traverse down the borehole to the lost circulation zone through the borehole annulus.

FIG. 3 shows an embodiment of a system used to deliver cavitation nuclei (210) into the borehole (117). A fluid container (351) may be configured to hold the fluid (203) (that may contain a curing agent) that will be pumped into the borehole (117). In one or more embodiments, a first container (361) may be configured to hold cavitation nuclei (210) (and nodules that contain the epoxy resin within them) and then dispense the cavitation nuclei (210) (and nodules) into the fluid in the BHA (120). The first container (361) in this embodiment is located at the surface (107), but in an alternate embodiment it may also be located within the borehole (117). Furthermore, the BHA (120) may be configured with the first container (361) attached to it. A second container (371) may be configured to contain the gas on the surface, as well. However, a container with gas may also be deployed within the borehole (117). The first channel (363) allows the cavitation nuclei (210) to be dispensed from the first container (361) into the borehole (117) using a pump. Similarly, a second channel (373) allows the gas to be dispensed through the borehole (117) and into the cavitation chamber (201) using another pump. Finally, the fluid channel (202) allows the fluid (with the curing agent) to be dispensed through the borehole (117) and into the cavitation chamber (201) using yet another pump.

In FIG. 3, several cavitation nuclei (210) are shown within the cavitation chamber (201) in the BHA (120). There, once cavitation occurs, the nodules are burst, the epoxy resin mixes with the curing agent, and the resulting cross-linked resin is circulated into the borehole (117) along with the borehole fluid (203). Once in the borehole fluid, the mix may come into contact with a fracture (345) which has created a lost circulation zone. The cross-linked resin may coat and fill the fracture (345), thus causing the loss of borehole fluid into the formation and restoring circulation in the borehole (117).

FIG. 4 presents a workflow of an embodiment of the method for eliciting cavitation. In Step 410, an apparatus is installed in a borehole (117). In one or more embodiments, the apparatus includes a cavitation chamber (201) configured to enhance the amplitude of acoustic waves. The apparatus further includes an acoustic source (206) configured to emit focused acoustic waves into the cavitation chamber (201). The apparatus also includes a fluid channel (202) that is configured to dispense fluid into the cavitation chamber (201). The structure of the cavitation chamber (201) is configured to enhance the amplitude of acoustic waves (207). The acoustic source (206) is configured to emit the acoustic waves (207) into the cavitation chamber (201). The fluid channel (202) may run from a fluid container (351) at the surface to the cavitation chamber (201) and may be configured to dispense the fluid (203) into the cavitation chamber (201). The acoustic source (206) may be a single source or an array of acoustic sources (204). The acoustic source (206) may be capable of emitting acoustic waves (207) at a single frequency or multiple frequencies simultaneously. In particular, the acoustic signal emitted by the acoustic source may be a bi-frequency signal, which, in some cases, may aid in eliciting cavitation. The acoustic source may also be axially aligned in the borehole (117) to help elicit cavitation, and it may be powered by a battery. The acoustic source may be activated by a telemetric pulse from the surface (107).

In Step 420, the acoustic source is activated in the cavitation chamber (201). The effect of the acoustic source (206) on the cavitation chamber (201) is to locally lower the fluid pressure in the fluid (203). In Step 430, the fluid (203) may be dispensed into the cavitation chamber. The properties of fluid in the borehole (117) may be altered to allow for cavitation. This alteration of fluid properties may be performed by adding a gas to the fluid, pumping a lightweight fluid into the resonance structure, increasing the temperature within the borehole (117), decreasing the height of the fluid column in the borehole (117), or some combination of these methods. Cavitation nuclei (210) may be used to help elicit cavitation. Furthermore, a gas may be added to the fluid in the cavitation chamber (201) to lower static pressure. The cavitation nuclei (210) may be aphrons (i.e., foams). Furthermore, a specially-shaped venturi device (212) may be installed in the borehole (117) that increases pressure locally, thus helping to elicit cavitation. This venturi device (212) may be a nozzle. It may also be a throttle. Other shapes may also be used.

After dispensing the fluid (203) into the cavitation chamber and eliciting cavitation, in Step 440 the curing agent contained in nodules may mix with an epoxy resin in the fluid. This may form a cross-linked resin in the borehole (117). The cross-linked resin may enter fractures, restore lost circulation, and prevent the escape of borehole fluid into the surrounding formation.

In summary, in accordance with some embodiments, cavitation initiation in a borehole (117) is achieved as follows: an acoustic source (206) is introduced into a borehole (117) together with an energy source (for example, a battery or other source of electrical power). A fluid (203) that contains gas and/or cavitation nuclei (210) may be pumped into the borehole (117), or the gas and/or cavitation nuclei may be introduced, in situ, into the fluid (203) in the borehole (117). Pressure may be lowered by using a specially-shaped venturi device (212), by lowering the free surface level of the fluid (203), by using a lightweight fluid, or by a combination of these methods. (The free surface level of the fluid refers to the depth of the air-fluid interface within the borehole (117); lowering the depth of this interface lowers the amount of weight at depth due to the fluid column, and therefore lowers the static pressure of the fluid.) Once the composition is in place and the pressure is lowered, the acoustic source (206) is activated using mud pulse telemetry or by any other means of communication known in the art. The acoustic source creates the acoustic field, which acts on the fluid (203) that possibly contains the cavitation nuclei (210). For further facilitation of cavitation, a specially designed source pulse (e.g., bi-frequency pulse), may be used. The source may be activated in a particular zone in the borehole (117), where cavitation is required.

Embodiments disclosed herein provide the following improvements and advantages: the possibility to initiate the cavitation at downhole pressures, special design of the source, and special measures to lower downhole pressure. Thus, embodiments use the acoustic field (ultrasonic, sonic), which may be specially designed and act on the fluid with or without the nuclei (possibly specially created (introducing them into the fluid)), with a source signal (possibly on-purpose designed) to initiate the cavitation downhole. This allows for enabling the inertial cavitation at downhole (high) pressure. Possible utilization of these techniques is curing agent release for controlled epoxy resin crosslinking in case of lost circulation.

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.