Patent Publication Number: US-8973675-B2

Title: Flasked pressure housing

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more detailed description of the disclosed embodiments, reference will now be made to the accompanying drawings, wherein: 
         FIG. 1  is a cross-sectional view of a drilling system with a flasked pressure housing in accordance with the principles disclosed herein; 
         FIG. 2  is an enlarged, cross-sectional view of the flasked pressure housing mounted within a drill collar of the drilling system of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of the flasked pressure housing of  FIG. 2 ; 
         FIG. 4  is a perspective view of the collet standoff of the flasked pressure housing of  FIG. 3 ; and 
         FIG. 5  is a schematic representation of conductive heat transfer paths between the outer pressure housing and the electronics disposed within the inner tubular of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS 
     Referring to  FIG. 1 , a drilling system  100  including a flasked pressure housing, or flask,  105  in accordance with the principles disclosed herein is depicted. Drilling system  100  further includes a drill string  110  suspended from a rig  115  into a wellbore  120 . Drill string  110  includes a plurality of drill pipe sections  125 , to which a BHA  130  is coupled. BHA  130  includes a drill bit  135  and a drill collar  140  within which flask  105  is disposed. Drill collar  140  is a thick-walled tubular that provides weight on drill bit  135  for drilling. BHA  130  may 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 string  110  to lubricate and cool drill bit  135 , as well as to provide a vehicle for removal of drill cuttings from wellbore  120 . After exiting drill bit  135 , the drilling fluid returns to the surface through an annulus  145  between drill string  110  and wellbore  120 . 
     In this embodiment, rig  115  is land-based. In other embodiments, flask  105  may be positioned within a drill string suspended from a rig on a floating platform. Moreover, flask  105  may be positioned within other tubulars positioned in drill string  110 , rather than drill collar  140 . Furthermore, flask  105  need 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 to  FIG. 2 , an enlarged view of drill collar  140  with flask  105  mounted therein is shown. Drill collar  140  is structurally coupled between two adjacent components  150 ,  155  of drill string  110  positioned uphole and downhole, respectively, of drill collar  140 . In some embodiments, including that illustrated by  FIG. 2 , component  150  is a section of drill pipe  125 , and component  155  is a stabilizer for controlling the trajectory of drill bit  135  as drilling progresses. Drill collar  140  includes a flowbore  160  extending therethrough. Flowbore  160  is fluidicly coupled with components  150 ,  155  to enable the flow of drilling mud from the surface through drill string  110  to drill bit  135 . 
     Flask  105  is disposed within flowbore  160  and structurally coupled to drill collar  140  via a mounting plate  165 , such that mounting plate  165  suspends flask  105  within flowbore  160 . Drilling mud passing through drill collar  140  flows through openings (not shown in the illustrated cross-section) in mounting plate  165  and around flask  105 , substantially uninhibited by either mounting plate  165  or flask  105 . Further, flask  105  is electrically coupled to electrical wiring (not shown) extending through drill pipe section  150  to enable transmission of power from a source positioned on drill string  110  and/or the surface to flask  105 , and transmission of measurements collected by electronics disposed within flask  105  to the surface and/or a data storage device positioned on drill string  110 . 
     During drilling operations, drilling mud is injected from the surface through drill string  110 , including drill collar  140 , to cool drill bit  135 . As the drilling fluid flows through flowbore  160  of drill collar  140  around flask  105  toward drill bit  135 , the drilling mud exerts a pressure load on flask  105 . The pressure load so exerted is dependent upon the depth of wellbore  120 , and can be in excess of 20,000 psi (approximately 138,000 kPa). In addition to the pressure load, flask  105  experiences vibrational loads, which during drilling operations, propagate from drill bit  135  along BHA  130  through drill collar  140  and mounting plate  165  to flask  105 . Flask  105  also experiences thermal loads due to the high temperature of the surrounding wellbore environment. As will be described, flask  105  is configured to withstand the pressure and vibrational loads and to insulate the electronics disposed therein from the potentially excessive thermal load. 
     Turning to  FIG. 3 , a cross-section of flask  105  is shown. Flask  105  includes a tubular outer pressure housing  200  sealed at one end with a rigid end piece  205  and at the other end with a compliant end piece  210 . End pieces  205 ,  210  are coupled to outer pressure housing  200  such that when outer pressure housing  200  elongates due to exposure to a thermal load  220  from the surrounding wellbore  120  and subsequently contracts due to the removal or reduction of thermal load  220 , end pieces  205 ,  210  displace with outer pressure housing  200 . In some embodiments, end pieces  205 ,  210  are welded to, or threaded into, outer pressure housing  200 . The thickness of outer pressure housing  200  is selected to withstand a pressure load  225  from drilling mud passing through drill collar  140  and a vibrational load  230  imparted to outer pressure housing  200  by virtue of its structural coupling to drill collar  140  via mounting plate  165 . In at least some embodiments, outer pressure housing  200  is made of a material having a yield strength of at least 120,000 psi (approximately 827,500 kPa), such as but not limited to nickel  718  or austenitic stainless, and has a thickness of ¼ of an inch (approximately 6.35 mm). 
     Flask  105  further includes an inner tubular  235  disposed within outer pressure housing  200  and extending longitudinally, or axially, between end pieces  205 ,  210 . Inner tubular  235  is coupled at one end to either rigid end piece  205  or compliant end piece  210 , and therefore outer pressure housing  200 , such as by welding or other equivalent means. The other end of inner tubular  235  is not coupled to the opposing end piece  205 ,  210 , and therefore outer pressure housing  200 , but is free to move relative to outer pressure housing  200 . Allowing one end of inner tubular  235  to remain uncoupled from outer pressure housing  200  eliminates the transfer of tensile and compressive loads from outer pressure housing  200  to inner tubular  235  as outer pressure housing  200  elongates and contracts in response to changes in thermal load  220 . In this embodiment, end  240  of inner tubular  235  is coupled to rigid end piece  205 , while end  245  of inner tubular  235  remains uncoupled to compliant end piece  210  and hence is free to move relative to outer pressure housing  200 . 
     Inner tubular  235  further includes an inner bore  250  within which one or more chassis  255  are inserted. In  FIG. 3 , only one chassis  255  is shown for the sake of simplicity, although in practice, there may be more. Electronics  260 , such as but not limited to instruments and sensors for measuring downhole conditions, are mounted within each chassis  255 . Ends  240 ,  245  of inner tubular  235  are sealed with respect to end pieces  205 ,  210 , respectively, to isolate bore  250  containing chassis  255  and electronics  260  mounted therein from a chamber  215  formed by the sealed annulus between outer pressure housing  200  and inner tubular  235 . 
     As previously described, flask  105  is subjected to thermal load  220  from the surrounding wellbore environment. To minimize convective heat transfer from outer pressure housing  200  to inner tubular  235 , a vacuum is pulled on chamber  215  via one or more sealable ports  285  formed in rigid end piece  205 . Minimizing this source of heat to inner tubular  235  reduces the amount of heat which is subsequently transferred via conduction from inner tubular  235  through chassis  255  to electronics  260  and thus assists electronics  260  in remaining within its operational temperature limits. 
     Flask  105  further includes one or more collet standoffs  265  disposed between inner tubular  235  and outer pressure housing  200  and extending longitudinally between end pieces  205 ,  210 . In  FIG. 2 , three collet standoffs  265  are shown within flask  105 , while in  FIG. 3 , only one is shown for simplicity. Turning to  FIG. 4 , collet standoff  265  includes a plurality of support members  270  extending longitudinally between two end coupling members  275  and a plurality of standoffs  280 , each standoff  280  extending radially outward from a support member  270 . Standoffs  280  may be formed as components distinct from support members  270  and subsequently coupled thereto or formed integrally with a support member  270 . Each end coupling member  275  is annular and has an inner diameter  290  configured to allow inner tubular  235  to extend therethrough, such that ends  240 ,  245  of inner tubular  235  are proximate end pieces  205 ,  210 , respectively, as described above and shown in  FIG. 3 . Referring to  FIG. 3 , collet standoff  265  is configured such that when inner tubular  235  is inserted therethrough and collet standoff  265  with inner tubular  235  therein is subsequently inserted within outer pressure housing  200 , as shown, radially extending standoffs  280  are compressed between outer pressure housing  200  and support members  270  of collet standoff  265 , and end coupling members  275  essentially support and centralize inner tubular  235  within collet standoff  265 . As a result, inner tubular  235  and outer pressure housing  200  effectively move together as a single unit in response to vibration load  230 . 
     By virtue of the design of flask  105 , there are a number of paths  300 ,  305 ,  310 , illustrated in  FIG. 5 , along which heat may be conducted from outer pressure housing  200 , which is subject to thermal load  225  from the surrounding wellbore environment, to electronics  260  disposed within inner tubular  235 . In accordance with the principles disclosed herein, flask  105  is configured to minimize conductive heat transfer along each such path  300 ,  305 ,  310 . By virtue of contact between adjacent components, heat may be conducted from outer pressure housing  200  to electronics  260  along paths  300 ,  305 , which extend from outer pressure housing  200  through end pieces  205 ,  210 , respectively, inner tubular  235 , and chassis  255  to electronics  260 . To minimize conductive heat transfer along these paths  300 ,  305 , inner tubular  235  is configured to be thin-walled, meaning the wall thickness of inner tubular  235  is no thicker than necessary to withstand mechanical loads imparted to inner tubular  235  and to support chassis  255  with electronics  260  disposed therein. In some embodiments, the thickness of inner tubular  235  is approximately 0.05 inches (approximately 1.27 mm). 
     Heat may also be conducted along path  310  from outer pressure housing  200  through each standoff  280  and support member  270  coupled thereto of collet standoff  265 , inner tubular  235 , and chassis  255  to electronics  260 . To minimize the amount of heat conducted along these paths  320 , the number of standoffs  280  is selected to be no greater than necessary to withstand mechanical loads imparted to collet standoff  265  while still supporting inner tubular  235  disposed therein. Moreover, each standoff  280  is configured to have a minimal cross-section in engagement with outer pressure housing  200 . 
     In some embodiments, collet standoff  265  is configured to support two lb f  (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 paths  320 , collet standoff  265  is made of titanium due to its strength and relatively moderate thermal conductivity. Moreover, the axial spacing between adjacent standoffs  280  is approximately six inches (approximately 152 mm). 
     Heat may also be transferred from outer pressure housing  200  to inner tubular  235  by radiative heat exchange between the inner surface  325  of outer pressure housing  200  and the outer surface  330  of inner tubular  235 . To reduce or minimize this source of heat to inner tubular  235 , surface  330  of inner tubular  235  may be coated with a material  335  to promote reflection of heat radiated from outer pressure housing  200 . Alternatively, or additionally, surface  325  may be coated with a material  340  to reduce the amount of heat radiated from outer pressure housing  200 . 
     To assemble flask  105 , electronics  260  are disposed within one or more chassis  255 , which, in turn, are then inserted within inner tubular  235 . Inner tubular  235  is next inserted within outer pressure housing  200 , and end  240  of inner tubular  235  is coupled to rigid end piece  205 . One or more collet standoffs  265  are then inserted between inner tubular  235  and outer pressure housing  200  at desired locations along the length of inner tubular  235 . Timer tubular  235  is then sealed at both ends  240 ,  245  with respect to end pieces  205 ,  210 , respectively, to isolate bore  250 . Ends  205 ,  210  are coupled to and sealingly engaged with pressure housing  200  such that ends  205 ,  210  also sealingly engage pressure housing  200  and chamber  215  is isolated from the atmosphere surrounding flask  105 . To complete assembly of flask  105 , a vacuum is pulled on chamber  215  between inner tubular  235  and outer pressure housing  200 . 
     Once assembled, flask  105  is then mounted within drill collar  140  via mounting plate  165 . Finally, electronics  260  within inner tubular  235  are electrically coupled to electrical wiring extending from drill pipe section  150 , so that power may be supplied to electronics  260  and any measurements taken by electronics  260  may be transmitted to the surface and/or a storage location on drill string  110 . When drill string  110  is fully assembled, drill string  110  is suspended from rig  115  and used to create wellbore  120 . 
     During drilling operations, drilling fluid is delivered through drill string  110 , including flowbore  160  of drill collar  140 , to drill bit  135 . Upon exiting drill bit  135 , the drilling fluid returns to the surface via annulus  145  between drill string  110  and wellbore  120 . As drilling operations progress, electronics  260  may be actuated to collect measurements and transmit collected data to the surface and/or a storage device positioned on drill string  110 . As electronics  260  perform their intended functions, flask  105  protects electronics  260  from pressure load  225  exerted by the drilling mud on outer pressure housing  200 , vibration loads  230  propagated from drill bit  135  to outer pressure housing  200  by way of mounting plate  165 , and thermal loads  220  from the surrounding wellbore environment. Thus, flask  105  assists electronics  260  to remain intact and below their operational temperature limits so that electronics  260  are 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.