Surge chamber assembly and method for perforating in dynamic underbalanced conditions

A surge chamber assembly (70) for use in a wellbore includes a housing (80) having one or more openings (112), a surge chamber (100) and a combustion chamber (98). The openings (112) provide fluid communication between the exterior (82) of the housing (80) and the surge chamber (100). A sleeve (114) is slidably positioned within the housing (80) and has a first position wherein fluid communication through the openings (112) is prevented and a second position wherein fluid communication through the openings (112) is allowed. A combustible element (124) is positioned in the combustion chamber (98) such that combusting the combustible element (124) generates pressure in the combustion chamber (98) that actuates the sleeve (114) from the first position to the second position.

TECHNICAL FIELD OF THE INVENTION

This invention relates, in general, to perforating a cased wellbore that traverses a subterranean hydrocarbon bearing formation and, in particular, to a surge chamber assembly that is installed within the tool string and is operated to create a dynamic underbalanced pressure condition in the wellbore during such perforating.

BACKGROUND OF THE INVENTION

Without limiting the scope of the present invention, its background will be described with reference to perforating a subterranean formation using shaped charge perforating guns, as an example.

After drilling the various sections of a subterranean wellbore that traverses a formation, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within the wellbore. This casing string increases the integrity of the wellbore and provides a path for producing fluids from the producing intervals to the surface. Conventionally, the casing string is cemented within the wellbore. To produce fluids into the casing string, hydraulic openings or perforations must be made through the casing string, the cement and a short distance into the formation.

Typically, these perforations are created by detonating a series of shaped charges that are disposed within the casing string and are positioned adjacent to the formation. Specifically, one or more charge carriers or perforating guns are loaded with shaped charges that are connected with a detonator via a detonating cord. The charge carriers are then connected within a tool string that is lowered into the cased wellbore at the end of a tubing string, wireline, slick line, coil tubing or other conveyance. Once the charge carriers are properly positioned in the wellbore such that the shaped charges are adjacent to the formation to be perforated, the shaped charges may be fired. If more than one downhole zone is to be perforated, a select fire perforating gun assembly may be used such that once the first zone is perforated, subsequent zones may be perforated by repositioning and firing the previously unfired shaped charges without tripping out of the well.

The perforating operation may be conducted in an overbalanced pressure condition, wherein the pressure in the wellbore is greater than the pressure in the formation or in an underbalanced pressure condition, wherein the pressure in the wellbore is less than the pressure in the formation. When perforating occurs in an underbalanced pressure condition, formation fluids flow into the wellbore immediately after the casing is perforated. This inflow is beneficial as perforating generates debris from the perforating guns, the casing and the cement that may otherwise remain in the perforation tunnels and impair the productivity of the formation. As clean perforations are essential to a good perforating job, perforating underbalanced condition is preferred. It has been found, however, that due to safety concerns, maintaining an overbalanced pressure condition during most well completion operations is preferred. For example, if the perforating guns were to malfunction and prematurely initiate creating communication paths to a formation, the overbalanced pressure condition will help to prevent any uncontrolled fluid flow to the surface.

A need has therefore arisen for an apparatus and method for perforating a cased wellbore that create effective perforation tunnels. A need has also arisen for such and apparatus and method that provide for safe installation and operation procedures. Further, a need has arisen for such an apparatus and method that provide for the reuse of certain of the perforating string components.

SUMMARY OF THE INVENTION

The present invention disclosed herein comprises an apparatus and method for perforating a cased wellbore that create effective perforation tunnels. The apparatus and method of the present invention also provide for safe installation and operation procedures as well as for the reuse of certain of the perforating string components. Broadly stated, the present invention is directed to a downhole tool for use within a wellbore that includes a housing having a combustion chamber positioned therein, a combustible element positioned in the combustion chambers and an actuable member. The actuable member is actuated from a first operating configuration to a second operating configuration responsive to combustion of the combustible element.

In one aspect, the present invention is directed to a method for actuating a downhole tool. The method includes the steps of disposing a combustible element within a combustion chamber of the downhole tool, positioning the downhole tool within a wellbore and combusting the combustible element to actuate the downhole tool from a first operating configuration to a second operating configuration.

More specifically, the present invention is directed to a surge chamber assembly for use within a tool string in a wellbore. The surge chamber assembly includes a housing having one or more openings, a surge chamber and a combustion chamber. The openings provide fluid communication between the exterior of the housing and the surge chamber. A sleeve is slidably positioned within the housing in either a first position wherein fluid communication through the openings is prevented or a second position wherein fluid communication through the openings is allowed. A combustible element is positioned in the combustion chamber such that combusting the combustible element generates pressure that actuates the sleeve from the first position to the second position allowing fluids to enter the surge chamber from the wellbore, thereby creating a dynamic underbalanced pressure condition in the wellbore.

In one embodiment, the combustible element further comprises a propellant, a solid fuel, a rocket fuel, potassium chlorate, potassium perchlorate, nitrocellulose plasticized fuels or the like. The surge chamber assembly may further include a flange positioned within the housing between the surge chamber and the combustion chamber. In this embodiment, the flange may include one or more passageways the provide fluid communication between the combustion chamber and the sleeve. A shear pin may extend between the sleeve and the flange in order to selectively prevent the sleeve from being actuated from the first position to the second position until a predetermined force is applied to the sleeve by the pressure in the combustion chamber. A biasing member may be operably associated with the sleeve to prevent axial movement of the sleeve once the sleeve has been actuated to the second position. A detonating cord may be disposed within the housing and operably positioned relative to the combustible element such that a detonation of the detonating cord ignites the combustible element.

In another aspect, the present invention is directed to a surge chamber assembly for use in a wellbore that includes a housing having first and second sets of openings, a surge chamber and a pair of combustion chambers oppositely disposed relative to the surge chamber. The openings provide fluid communication between the exterior of the housing and the surge chamber. First and second sleeves are slidably positioned within the housing relative to the first and second sets of openings, respectively. Each sleeve has a first position wherein fluid communication through the relative openings is prevented and a second position wherein fluid communication through the relative openings is allowed. A combustible element is positioned in each of the combustion chambers such that combusting each of the combustible elements actuates one of the sleeves from its first position to its second position.

In a further aspect, the present invention is directed to a tool string for use in a wellbore. The tool string includes first and second surge chamber assemblies and at least one perforating gun positioned between the first and second surge chamber assemblies. Each of the first and second surge chamber assemblies includes a housing having one or more openings, a surge chamber and a combustion chamber. The openings provide fluid communication between the exterior of the housing and the surge chamber. A sleeve is slidably positioned within the housing and has a first position wherein fluid communication through the openings is prevented and a second position wherein fluid communication through the openings is allowed. A combustible element is positioned in the combustion chamber such that combusting the combustible element actuates the sleeve from the first position to the second position.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially toFIG. 1, a plurality of surge chamber assemblies of the present invention operating from an offshore oil and gas platform are schematically illustrated and generally designated10. A semi-submersible platform12is centered over a submerged oil and gas formation14located below sea floor16. A subsea conduit18extends from deck20of platform12to wellhead installation22including subsea blow-out preventers24. Platform12has a hoisting apparatus26and a derrick28for raising and lowering pipe strings such as work sting30.

A wellbore32extends through the various earth strata including formation14. A casing34is cemented within wellbore32by cement36. Work string30includes various tools such as a plurality of perforating guns and a plurality of surge chamber assemblies. When it is desired to perforate formation14, work string30is lowered through casing34until the perforating guns are properly positioned relative to formation14. Thereafter, the shaped charges within the string of perforating guns are sequentially fired, either in an uphole to downhole or a downhole to uphole direction. Upon detonation, the liners of the shaped charges form jets that create a spaced series of perforations extending outwardly through casing34, cement36and into formation14, thereby allow formation communication between formation14and wellbore32.

In the illustrated embodiment, wellbore32has an initial, generally vertical portion38and a lower, generally deviated portion40which is illustrated as being horizontal. It should be noted, however, by those skilled in the art that the shaped charge perforating guns and the surge chamber assemblies of the present invention are equally well-suited for use in other well configurations including, but not limited to, inclined wells, wells with restrictions, non-deviated wells and the like.

Work string30includes a retrievable packer42which may be sealingly engaged with casing34in vertical portion38of wellbore32. At the lower end of work string30is a gun string, generally designated44. In the illustrated embodiment, gun string44has at its upper or near end a ported nipple46below which is a time domain firer48. Time domain firer48is disposed at the upper end of a tandem gun set50including first and second guns52and54. In the illustrated embodiment, a plurality of such gun sets50, each including a first gun52and a second gun54are utilized. Each gun set50may have at least one orienting fin (not pictured) extending therefrom to insure that the gun set is disposed off-center with regard to casing34as described in U.S. Pat. No. 5,603,379 issued to Halliburton Company on Feb. 18, 1997, which is hereby incorporated by reference. While tandem gun sets50have been described, it should be understood by those skilled in the art that any arrangement of guns may be utilized in conjunction with the surge chamber assemblies of the present invention.

Specifically, between each gun set50is a surge chamber assembly56which serves as a connector for connecting adjacent gun sets50together. Further, surge chamber assemblies56may serve in the function of a spacer which separates adjacent gun sets50. As will be discussed in detail below, surge chamber assemblies56each include a housing having openings that allows for fluid communication from the wellbore32to a surge chamber positioned within the housing. A sleeve is slidably positioned within the housing to selectively permit and prevent fluid communication through the openings. A combustion chamber is positioned in fluid communication with the sleeve. A combustible element is positioned in the combustion chamber such that, upon ignition, the combustible element produces a combustion event that creates pressure within the combustion chamber that actuates the sleeve to enable fluid communication from the wellbore32into the surge chamber.

The surge chambers of the surge chamber assemblies56are preferably at atmospheric pressure during installation into wellbore32and prior to actuation of the sleeves. Accordingly, upon actuation of the sleeves, a fluid surge from wellbore32into the surge chambers is generated which creates a dynamic underbalanced condition within wellbore32. This dynamic underbalanced condition improves the quality of the perforations generated by gun sets50as formation fluids will enter wellbore32and the surge chambers immediately after the perforations are created. This surge of fluid cleans the perforation tunnels of any debris created during the perforation process and helps to prevent the perforation tunnels from having a low permeability. Importantly, the present invention allows for the sequential firing of the perforating guns50and the operating of surge chamber assemblies56using timers or other control circuits such that segments of the production interval or intervals may be perforated and allowed to flow then after a time delay, other segments of the production interval or intervals may be perforated and allowed to flow.

FIG. 2depicts a surge chamber assembly70according to the present invention that is generally designated70. Surge chamber assembly70includes an upper tandem72that may be connected to a perforating gun as part of a gun string. Positioned within upper tandem72is a support member74that receives a booster positioned at the upper end of a detonating cord76. Detonating cord76is positioned within a detonation passageway78that traverses the length of surge chamber assembly70. As depicted, a housing80having an exterior82is threadably and sealingly coupled to upper tandem72.

Housing80includes upper housing section84, connector86, intermediate housing section88, connector90and lower housing section92, each of which are threadably and sealingly coupled to the adjacent housing section. Lower housing section92is threadably and sealingly coupled to lower tandem94. A support member96is positioned within lower tandem94that receives the booster positioned at the lower end of detonating cord76. Lower tandem94may be connected to a perforating gun at its lower end. As such, a detonation of the detonating cord in a perforating gun above surge chamber assembly70will be propagated through surge chamber assembly70to a perforating gun below surge chamber assembly70via detonating cord76.

It should be apparent to those skilled in the art that the use of directional terms such as top, bottom, above, below, upper, lower, upward, downward, etc. are used in relation to the illustrative embodiments as they are depicted in the figures, the upward direction being toward the top of the corresponding figure and the downward direction being toward the bottom of the corresponding figure. As such, it is to be understood that the downhole components described herein may be operated in vertical, horizontal, inverted or inclined orientations without deviating from the principles of the present invention.

In a downhole operational embodiment, exterior82includes the wellbore, perforations and portions of the formation that are proximate housing80. The interior of housing80includes a combustion chamber98, a surge chamber100and a combustion chamber102. A flange104is positioned between combustion chamber98and surge chamber100. Flange104includes a plurality of passageways106, only two of which are depicted. A flange108is positioned between combustion chamber102and surge chamber100. Flange108includes a plurality of passageways110, only two of which are depicted. Detonating cord76passes through an opening in the center flanges104,108.

Upper housing section84includes a plurality of openings112, only two of which are visible inFIG. 2. Openings112allow for fluid communication between exterior82and surge chamber100. A sliding sleeve114is fitted within upper housing section84to selectively allow and prevent fluid communication through openings112. In the illustrated closed position of surge chamber assembly70, shear pins116secure sliding sleeve114to flange104. It should be appreciated by those skilled in the art that although only two shear pins116are illustrated and described, any number of shear pins may be utilized in accordance with the force desired to shift sliding sleeve114. In the closed position, a pair of seals118,120prevent fluid communications through openings112. In addition, a biasing member such as snap ring122is positioned exteriorly of sleeve114. Passageways106through flange104provide for fluid communication between combustion chamber98and sliding sleeve114.

A combustible element which is illustrated as a propellant124is positioned within combustion chamber98and secured in place with a propellant sleeve126. Preferably, propellant124is a substance or mixture that has the capacity for extremely rapid but controlled combustion that produces a combustion event including the production of a large volume of gas at high temperature and pressure. Propellant124is preferably a solid but may be a liquid or combination thereof. In an exemplary embodiment, propellant124comprises a solid propellant such as nitrocellulose plasticized with nitroglycerin or various phthalates and inorganic salts suspended in a plastic or synthetic rubber and containing a finely divided metal. Moreover, in this exemplary embodiment, propellant124may comprise inorganic oxidizers such as ammonium and potassium nitrates and perchlorates. Most preferably, potassium perchlorate is employed. It should be appreciated, however, that substances other than propellants may be utilized. For example, explosives such as black powder or powder charges may be utilized.

Lower housing section92includes a plurality of openings128, only two of which are visible inFIG. 2. Openings128allow for fluid communication between exterior82and surge chamber100. A sliding sleeve130is fitted within lower housing section92to selectively allow and prevent fluid communication through openings128. In the illustrated closed position of surge chamber assembly70, shear pins132secure sliding sleeve130to flange108. In the closed position, a pair of seals134,136prevent fluid communications through openings128. In addition, a biasing member such as a snap ring138is positioned exteriorly of sleeve130. Passageways110through flange108provide for fluid communication between combustion chamber102and sliding sleeve130. A combustible element which is illustrated as a propellant140is positioned within combustion chamber102and secured in place with a propellant sleeve142.

The operation of the surge chamber assembly70of the present invention will now be described with reference toFIGS. 3 and 4which depict an upper portion of surge chamber assembly70. When it is desirable to operate surge chamber assembly70, an explosion in the form of a detonation is propagated through surge chamber assembly70via detonating cord76. As one skilled in the art will appreciate, the explosion of detonation cord76is an extremely rapid, self-propagating decomposition of detonating cord76that creates a high-pressure-temperature wave that moves rapidly through surge chamber assembly70. The explosion of detonating cord76ignites propellant124and causes a combustion once propellant124reaches its autoignition point, i.e., the minimum temperature required to initiate or cause self-sustained combustion.

When the explosion of detonation cord76is within combustive proximity of propellant124, propellant124ignites. The combustion of propellant124produces a large volume of gas which pressurizes combustion chamber98. As one skilled in the art will also appreciate, the combustion of propellant124is an exothermic oxidation reaction that yields large volumes of gaseous end products of oxides at high pressure and temperature. In particular, the volume of oxides created by the combustion of propellant124within combustion chamber98provides the force required to actuate sliding sleeve114. More specifically, the pressure within combustion chamber98acts on sliding sleeve114until the force generated is sufficient to break shear pins116. Once shear pins116are broken, sliding sleeve114is actuated to an open position such that openings112are not obstructed and fluid communication from exterior82to surge chamber100is allowed, as best seen inFIG. 4. The lower portion of upper housing section84includes a radially expanded region144that defines a shoulder146. As sliding sleeve114slides into contact with the upper end of connector86, snap ring122expands to prevent further axial movement of sleeve114.

Likewise, as best seen inFIG. 2, when the explosion of detonation cord76is within combustive proximity of propellant140, propellant140ignites. The combustion of propellant140produces a large volume of gas which pressurizes combustion chamber102. The pressure within combustion chamber102acts on sliding sleeve130until the force generated is sufficient to break shear pins132. Once shear pins132are broken, sliding sleeve130is actuated to an open position such that openings128are not obstructed and fluid communication from exterior82to surge chamber100is allowed. In the illustrated embodiment, the lower portion of upper housing section92includes a radially expanded region148that defines a shoulder150. As sliding sleeve130slides into contact with the lower end of connector90, snap ring138expands to prevent further axial movement of sleeve130.

Prior to detonation of detonating cord76, the wellbore in which the gun string and one or more surge chamber assemblies70is positioned may preferably be in an overbalanced condition. During operation, a series of perforating guns and surge chamber assemblies70operate substantially simultaneously. This operation allows fluids from within the wellbore to enter the surge chambers which dynamically creates an underbalanced pressure condition. This permits the perforation discharge debris to be cleaned out of the perforation tunnels due to the fluid surge from the formation into the surge chambers. The cleansing inflow continues until a stasis is reached between the pressure in the formation and the pressure within the casing. Hence, surge chamber assembly70of the present invention ensures clean perforation tunnels by providing a dynamic underbalanced condition. Addition series of perforating guns and surge chamber assemblies70may thereafter be operated which will again dynamically create an underbalanced pressure condition for the newly shot perforations.

Referring now toFIG. 5, therein is illustrated an alternate embodiment of an upper portion of a surge chamber assembly of the present invention in a closed position that is generally designated170. Surge chamber assembly170includes an upper tandem172that may be connected to a perforating gun as part of a gun string. Positioned within upper tandem172is a support member174that receives a booster positioned at the upper end of a detonating cord176. Detonating cord176is positioned within a detonation passageway178that traverses the length of surge chamber assembly170in the manner described above with reference to surge chamber assembly70ofFIG. 2. As depicted, a housing180having an exterior182is threadably and sealingly coupled to upper tandem172.

Housing180includes upper housing section184as well as additional housing sections (not pictured) such as those described above with reference to surge chamber assembly70ofFIG. 2. In a downhole operational embodiment, exterior182includes the wellbore, perforations and portions of the formation that are proximate housing180. In the illustrated upper portion of surge chamber assembly170, the interior of housing180includes a combustion chamber198and surge chamber200. A flange204is positioned between combustion chamber198and surge chamber200. Flange204includes a plurality of passageways206, only two of which are depicted. Detonating cord176passes through an opening through the center flange204.

Upper housing section184includes a plurality of openings212, only two of which are visible inFIG. 5. Openings212allow for fluid communication between exterior182and surge chamber200. A sliding sleeve214is fitted within upper housing section184to selectively allow and prevent fluid communication through openings212. In the illustrated closed position of surge chamber assembly170, shear pins216secure sliding sleeve214to flange204. In the closed position, a pair of seals218,220prevent fluid communications through openings212. Unlike surge chamber assembly70ofFIG. 2, however, sleeve214does not carry a snap ring exteriorly thereof and upper housing section184does not include a radially expanded portion.

A combustible element which is illustrated as a propellant224is positioned within combustion chamber198and secured in place with a propellant sleeve226. The operation of surge chamber assembly170is substantially identical to the operation of surge chamber assembly70ofFIG. 2except that sleeve214will not be secured to upper housing section184after actuation.

Referring now toFIG. 6, therein is illustrated an further alternate embodiment of an upper portion of a surge chamber assembly of the present invention in a closed position that is generally designated270. Surge chamber assembly270includes an upper tandem272that may be connected to a perforating gun as part of a gun string. Positioned within upper tandem272is a support member274that receives a booster positioned at the upper end of a detonating cord276. Detonating cord276is positioned within a detonation passageway278that traverses the length of surge chamber assembly270in the manner described above with reference to surge chamber assembly70ofFIG. 2. As depicted, a housing280having an exterior282is threadably and sealingly coupled to upper tandem272.

Housing280includes upper housing section284as well as additional housing sections (not pictured) such as those described above with reference to surge chamber assembly70ofFIG. 2. In a downhole operational embodiment, exterior282includes the wellbore, perforations and portions of the formation that are proximate housing280. In the illustrated upper portion of surge chamber assembly270, the interior of housing280includes a combustion chamber298and surge chamber300. A flange304is positioned between combustion chamber298and surge chamber300. Flange304includes a plurality of passageways306, only two of which are depicted. Detonating cord276passes through an opening through the center flange304.

Upper housing section284includes a plurality of openings312, only two of which are visible inFIG. 6. Openings312allow for fluid communication between exterior282and surge chamber300. A sliding sleeve314is fitted within upper housing section284to selectively allow and prevent fluid communication through openings312. In the illustrated closed position of surge chamber assembly270, shear pins316secure sliding sleeve314to flange304. In the closed position, a pair of seals318,320prevent fluid communications through openings312. Unlike surge chamber assembly70ofFIG. 2, however, sleeve314does not carry a snap ring exteriorly thereof and upper housing section284does not include a radially expanded portion. Instead, sleeve314includes a sleeve extension322that slides within a radially reduced portion324of upper housing section284. Radially reduced portion324includes a seal326.

A combustible element which is illustrated as a propellant328is positioned within combustion chamber298and secured in place with a propellant sleeve330. The operation of surge chamber assembly270is substantially identical to the operation of surge chamber assembly70ofFIG. 2except that sleeve314will not be secured to upper housing section284after actuation.