Flasked pressure housing

A system for containing electronics positioned in a downhole tubular. The system includes a pressure housing, a rigid end piece, a compliant end piece, an inner tubular member, one or more annular standoffs, and a chassis. The pressure housing is supported within the downhole tubular. The rigid end piece and the compliant end piece are fixedly coupled within opposing ends of the pressure housing. The inner tubular member is disposed within the pressure housing and has opposing ends. One of the opposing ends is coupled to the rigid end piece, and the other of the opposing ends is free to move relative to the compliant end piece. The chassis is disposed within the inner tubular member and houses the electronics. Each standoff is disposed between the inner tubular member and the pressure housing and includes at least one radially extending portion compressed therebetween.

Not Applicable.

BACKGROUND

To form an oil or gas well, a bottom hole assembly (BHA), including components such as a motor, steering assembly, one or more drill collars, and a drill bit, are coupled to a length of drill pipe to form a drill string. Tools including electronic instrumentation are typically positioned on the BHA to obtain measurements of the downhole environment while drilling. Once assembled, the drill string is then inserted downhole, where drilling and data collection by the tools commence.

The downhole tools and their associated electronic instrumentation must be able to operate near the surface as well as many thousands of feet below. Since temperature within a wellbore tends to increase with increasing depth, the tools may be subjected to severe thermal loads, depending on the depth of the wellbore. Moreover, during drilling, the tools experience vibrational loads due to operation of the drill bit and pressure loads from drilling mud passing through and around the drill string. In some circumstances, the tools are exposed to wellbore temperatures and pressures exceeding 200° C. (473° K) and 20,000 psi (approximately 138,000 kPa).

The maximum operating temperature limit of electronic instrumentation in the downhole tools can be significantly less than the surrounding wellbore temperature, depending on wellbore depth, and may be no more than 125° C. (398° K). As a consequence, prolonged exposure of the downhole tools to the severe thermal environment of the wellbore may cause the temperatures of the electronic instrumentation to exceed their maximum operating limit, thereby resulting in reduced service life and perhaps failure of the tools.

Servicing or replacement of the downhole tools necessitates the drill string be pulled from the wellbore. Once the tools are repaired or replaced, the drill string is then run into the wellbore again, and drilling may resume. Given the costs associated with interrupting drilling and pulling the drill string from the wellbore, apparatus which prolong the service life of electronic instrumentation included within the downhole tools are particularly desirable.

SUMMARY

A system for containing electronics positioned in a downhole tubular is disclosed. In some embodiments, the system includes a pressure housing, a rigid end piece, a compliant end piece, an inner tubular member, one or more annular standoffs, and a chassis. The pressure housing is supported within the downhole tubular. The rigid end piece and the compliant end piece are fixedly coupled within opposing ends of the pressure housing. The inner tubular member is disposed within the pressure housing and has opposing ends. One of the opposing ends is coupled to the rigid end piece, and the other of the opposing ends is free to move relative to the compliant end piece. The chassis is disposed within the inner tubular member and houses the electronics. Each standoff is disposed between the inner tubular member and the pressure housing and includes at least one radially extending portion compressed therebetween.

In other embodiments, the system includes a pressure housing supported within the downhole tubular, a rigid end piece, a compliant end piece, a thin-walled tubular member, and a chassis. The rigid end piece and the compliant end piece are sealingly engaged within opposing ends of the pressure housing. The tubular member is disposed within the pressure housing and has opposing ends. One of the opposing ends is sealingly engaged with the rigid end piece, and the other of the opposing ends is sealingly engaged with the compliant end piece. The chassis is disposed within the tubular member and houses the electronics.

Further, some system embodiments include a drill string suspended into a wellbore, a drill collar positioned within the drill string, the drill collar including a bore through which a drilling fluid flows, a mounting plate disposed within the bore of the drill collar; and a flasked pressure housing coupled to the mounting plate and suspended within the bore of the drill collar. The flasked pressure housing includes an outer housing, a rigid end piece, a compliant end piece, a thin-walled inner tubular member, one or more annular standoffs, and a chassis. The rigid end piece and the compliant end piece are fixedly coupled within opposing ends of the outer housing. The inner tubular member is disposed within the outer housing and has opposing ends. One of the opposing ends is coupled to and in sealing engagement with the rigid end piece. The other of the opposing ends is sealingly engaged with the compliant end but free to move relative to the compliant end piece. The chassis is disposed within the inner tubular member and houses electronics. Each standoff includes at least one radially extending portion compressed between the inner tubular member and the outer housing.

Thus, embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices and systems. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments, and by referring to the accompanying drawings.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

Referring toFIG. 1, a drilling system100including a flasked pressure housing, or flask,105in accordance with the principles disclosed herein is depicted. Drilling system100further includes a drill string110suspended from a rig115into a wellbore120. Drill string110includes a plurality of drill pipe sections125, to which a BHA130is coupled. BHA130includes a drill bit135and a drill collar140within which flask105is disposed. Drill collar140is a thick-walled tubular that provides weight on drill bit135for drilling. BHA130may include other components, such as but not limited to a drill sub, a motor, a steering assembly, a stabilizer, and additional drill collars. During drilling, drilling fluid, or “drilling mud,” is circulated down through drill string110to lubricate and cool drill bit135, as well as to provide a vehicle for removal of drill cuttings from wellbore120. After exiting drill bit135, the drilling fluid returns to the surface through an annulus145between drill string110and wellbore120.

In this embodiment, rig115is land-based. In other embodiments, flask105may be positioned within a drill string suspended from a rig on a floating platform. Moreover, flask105may be positioned within other tubulars positioned in drill string110, rather than drill collar140. Furthermore, flask105need not be disposed in a drill string, as illustrated by this embodiment, but may be positioned within a downhole tubular suspended by wireline, coiled tubing, or other similar device.

Referring next toFIG. 2, an enlarged view of drill collar140with flask105mounted therein is shown. Drill collar140is structurally coupled between two adjacent components150,155of drill string110positioned uphole and downhole, respectively, of drill collar140. In some embodiments, including that illustrated byFIG. 2, component150is a section of drill pipe125, and component155is a stabilizer for controlling the trajectory of drill bit135as drilling progresses. Drill collar140includes a flowbore160extending therethrough. Flowbore160is fluidicly coupled with components150,155to enable the flow of drilling mud from the surface through drill string110to drill bit135.

Flask105is disposed within flowbore160and structurally coupled to drill collar140via a mounting plate165, such that mounting plate165suspends flask105within flowbore160. Drilling mud passing through drill collar140flows through openings (not shown in the illustrated cross-section) in mounting plate165and around flask105, substantially uninhibited by either mounting plate165or flask105. Further, flask105is electrically coupled to electrical wiring (not shown) extending through drill pipe section150to enable transmission of power from a source positioned on drill string110and/or the surface to flask105, and transmission of measurements collected by electronics disposed within flask105to the surface and/or a data storage device positioned on drill string110.

During drilling operations, drilling mud is injected from the surface through drill string110, including drill collar140, to cool drill bit135. As the drilling fluid flows through flowbore160of drill collar140around flask105toward drill bit135, the drilling mud exerts a pressure load on flask105. The pressure load so exerted is dependent upon the depth of wellbore120, and can be in excess of 20,000 psi (approximately 138,000 kPa). In addition to the pressure load, flask105experiences vibrational loads, which during drilling operations, propagate from drill bit135along BHA130through drill collar140and mounting plate165to flask105. Flask105also experiences thermal loads due to the high temperature of the surrounding wellbore environment. As will be described, flask105is configured to withstand the pressure and vibrational loads and to insulate the electronics disposed therein from the potentially excessive thermal load.

Turning toFIG. 3, a cross-section of flask105is shown. Flask105includes a tubular outer pressure housing200sealed at one end with a rigid end piece205and at the other end with a compliant end piece210. End pieces205,210are coupled to outer pressure housing200such that when outer pressure housing200elongates due to exposure to a thermal load220from the surrounding wellbore120and subsequently contracts due to the removal or reduction of thermal load220, end pieces205,210displace with outer pressure housing200. In some embodiments, end pieces205,210are welded to, or threaded into, outer pressure housing200. The thickness of outer pressure housing200is selected to withstand a pressure load225from drilling mud passing through drill collar140and a vibrational load230imparted to outer pressure housing200by virtue of its structural coupling to drill collar140via mounting plate165. In at least some embodiments, outer pressure housing200is made of a material having a yield strength of at least 120,000 psi (approximately 827,500 kPa), such as but not limited to nickel718or austenitic stainless, and has a thickness of ¼ of an inch (approximately 6.35 mm).

Flask105further includes an inner tubular235disposed within outer pressure housing200and extending longitudinally, or axially, between end pieces205,210. Inner tubular235is coupled at one end to either rigid end piece205or compliant end piece210, and therefore outer pressure housing200, such as by welding or other equivalent means. The other end of inner tubular235is not coupled to the opposing end piece205,210, and therefore outer pressure housing200, but is free to move relative to outer pressure housing200. Allowing one end of inner tubular235to remain uncoupled from outer pressure housing200eliminates the transfer of tensile and compressive loads from outer pressure housing200to inner tubular235as outer pressure housing200elongates and contracts in response to changes in thermal load220. In this embodiment, end240of inner tubular235is coupled to rigid end piece205, while end245of inner tubular235remains uncoupled to compliant end piece210and hence is free to move relative to outer pressure housing200.

Inner tubular235further includes an inner bore250within which one or more chassis255are inserted. InFIG. 3, only one chassis255is shown for the sake of simplicity, although in practice, there may be more. Electronics260, such as but not limited to instruments and sensors for measuring downhole conditions, are mounted within each chassis255. Ends240,245of inner tubular235are sealed with respect to end pieces205,210, respectively, to isolate bore250containing chassis255and electronics260mounted therein from a chamber215formed by the sealed annulus between outer pressure housing200and inner tubular235.

As previously described, flask105is subjected to thermal load220from the surrounding wellbore environment. To minimize convective heat transfer from outer pressure housing200to inner tubular235, a vacuum is pulled on chamber215via one or more sealable ports285formed in rigid end piece205. Minimizing this source of heat to inner tubular235reduces the amount of heat which is subsequently transferred via conduction from inner tubular235through chassis255to electronics260and thus assists electronics260in remaining within its operational temperature limits.

Flask105further includes one or more collet standoffs265disposed between inner tubular235and outer pressure housing200and extending longitudinally between end pieces205,210. InFIG. 2, three collet standoffs265are shown within flask105, while inFIG. 3, only one is shown for simplicity. Turning toFIG. 4, collet standoff265includes a plurality of support members270extending longitudinally between two end coupling members275and a plurality of standoffs280, each standoff280extending radially outward from a support member270. Standoffs280may be formed as components distinct from support members270and subsequently coupled thereto or formed integrally with a support member270. Each end coupling member275is annular and has an inner diameter290configured to allow inner tubular235to extend therethrough, such that ends240,245of inner tubular235are proximate end pieces205,210, respectively, as described above and shown inFIG. 3. Referring toFIG. 3, collet standoff265is configured such that when inner tubular235is inserted therethrough and collet standoff265with inner tubular235therein is subsequently inserted within outer pressure housing200, as shown, radially extending standoffs280are compressed between outer pressure housing200and support members270of collet standoff265, and end coupling members275essentially support and centralize inner tubular235within collet standoff265. As a result, inner tubular235and outer pressure housing200effectively move together as a single unit in response to vibration load230.

By virtue of the design of flask105, there are a number of paths300,305,310, illustrated inFIG. 5, along which heat may be conducted from outer pressure housing200, which is subject to thermal load225from the surrounding wellbore environment, to electronics260disposed within inner tubular235. In accordance with the principles disclosed herein, flask105is configured to minimize conductive heat transfer along each such path300,305,310. By virtue of contact between adjacent components, heat may be conducted from outer pressure housing200to electronics260along paths300,305, which extend from outer pressure housing200through end pieces205,210, respectively, inner tubular235, and chassis255to electronics260. To minimize conductive heat transfer along these paths300,305, inner tubular235is configured to be thin-walled, meaning the wall thickness of inner tubular235is no thicker than necessary to withstand mechanical loads imparted to inner tubular235and to support chassis255with electronics260disposed therein. In some embodiments, the thickness of inner tubular235is approximately 0.05 inches (approximately 1.27 mm).

Heat may also be conducted along path310from outer pressure housing200through each standoff280and support member270coupled thereto of collet standoff265, inner tubular235, and chassis255to electronics260. To minimize the amount of heat conducted along these paths320, the number of standoffs280is selected to be no greater than necessary to withstand mechanical loads imparted to collet standoff265while still supporting inner tubular235disposed therein. Moreover, each standoff280is configured to have a minimal cross-section in engagement with outer pressure housing200.

In some embodiments, collet standoff265is configured to support two lbf(approximately 8.9 N) over every foot (approximately 0.3 in) of its length. To accommodate this strength requirement while at the same minimizing heat conduction along paths320, collet standoff265is made of titanium due to its strength and relatively moderate thermal conductivity. Moreover, the axial spacing between adjacent standoffs280is approximately six inches (approximately 152 mm).

Heat may also be transferred from outer pressure housing200to inner tubular235by radiative heat exchange between the inner surface325of outer pressure housing200and the outer surface330of inner tubular235. To reduce or minimize this source of heat to inner tubular235, surface330of inner tubular235may be coated with a material335to promote reflection of heat radiated from outer pressure housing200. Alternatively, or additionally, surface325may be coated with a material340to reduce the amount of heat radiated from outer pressure housing200.

To assemble flask105, electronics260are disposed within one or more chassis255, which, in turn, are then inserted within inner tubular235. Inner tubular235is next inserted within outer pressure housing200, and end240of inner tubular235is coupled to rigid end piece205. One or more collet standoffs265are then inserted between inner tubular235and outer pressure housing200at desired locations along the length of inner tubular235. Timer tubular235is then sealed at both ends240,245with respect to end pieces205,210, respectively, to isolate bore250. Ends205,210are coupled to and sealingly engaged with pressure housing200such that ends205,210also sealingly engage pressure housing200and chamber215is isolated from the atmosphere surrounding flask105. To complete assembly of flask105, a vacuum is pulled on chamber215between inner tubular235and outer pressure housing200.

Once assembled, flask105is then mounted within drill collar140via mounting plate165. Finally, electronics260within inner tubular235are electrically coupled to electrical wiring extending from drill pipe section150, so that power may be supplied to electronics260and any measurements taken by electronics260may be transmitted to the surface and/or a storage location on drill string110. When drill string110is fully assembled, drill string110is suspended from rig115and used to create wellbore120.

During drilling operations, drilling fluid is delivered through drill string110, including flowbore160of drill collar140, to drill bit135. Upon exiting drill bit135, the drilling fluid returns to the surface via annulus145between drill string110and wellbore120. As drilling operations progress, electronics260may be actuated to collect measurements and transmit collected data to the surface and/or a storage device positioned on drill string110. As electronics260perform their intended functions, flask105protects electronics260from pressure load225exerted by the drilling mud on outer pressure housing200, vibration loads230propagated from drill bit135to outer pressure housing200by way of mounting plate165, and thermal loads220from the surrounding wellbore environment. Thus, flask105assists electronics260to remain intact and below their operational temperature limits so that electronics260are able to collect measurements and perform other of their intended functions while positioned downhole and exposed to the surrounding wellbore environment.

While the preferred embodiment of this invention has been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied, so long as the methods and apparatus retain the advantages discussed herein. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.