Method for completing wells
United States Patent Bell et al.  
 METHOD FOR COMPLETING WELLS Inventors: Larry N. Bell; Charles R. Knowles,  
 both of Anchorage, Alaska; Frank J. Schuh, Dallas, Tex.  
 [73] Assignee: Atlantic Richfield Company, Los  
 Angeles, Calif.  
 [22] Filed: Apr. 29, 1974 [2|] Appl. No.: 465,181  
 [52] US. Cl. 166/285; loo/DIG. 1 [5|] Int. Cl E2lb 33/14 [58] Field of Search 166/285, DIG. l, 292, 29]  
 [56] References Cited UNITED STATES PATENTS 3,0l3.608 l2/l96l Church 166/285 X 3,l93.0l() 7/1965 Bielstein l66/285 3,373.8ll 3/1968 Burtch 166/292 X 3.4l6,602 ill/1968 Boughton lob/292 3.502.l48 3/1970 Slagle et al.. l66/292 3.56l,53l 2/l97l Miller lob/285 3.84l.404 Ill/I974 Harmon lob/DIG. l X  
 Primary Examiner-Stephen J. Novosad Attorney, Agent, or FirmRoderick W. MacDonald [57] ABSTRACT A method for completing a well whose wellbore passes through a permafrost zone wherein in at least part of the permafrost zone, concentric outer and inner casing strings are placed in the wellbore, the outer casing string having conductor means for establishing communication between the exterior of the outer casing and the annulus between the inside of the outer casing and the outside of the inner casing so that after placing cement in the various annuli around the various casing strings, the cement in the annulus between the outer and inner casing strings can be washed out utilizing the conductor means, and thereafter the wash fluid can be purged from said annulus by way of said conductor means using a gas. The purged annulus is then refilled with cement which has a carefully controlled water content so that this cement and its adjacent casing will not be subjected to stress due to freezing of substantial amounts of water. This invention also applies to a well casing shoe which has a cylindrical body adapted to fit on a section of casing, the body carrying a conductor means having an aperture therein for communicating between the interior and exterior of the body. The aperture can have a rupture means therein for preventing fluid such as drilling mud or cement from entering the conductor means before the washing step is to be carried out. This invention also applies to a well casing string composed of a plurality of easing sections, the casing string carrying a conductor means according to this invention for establishing communication between the interior and exterior of the string. For example, the casing string can carry a casing shoe which in turn carries a conductor means.  
 4 Claims, 3 Drawing Figures PATENTEU W 8 I975 sumznrg FIG. 3  
 FlG.2  
 FIG.3  
 METHOD FOR COMPLETING WELLS BACKGROUND OF THE INVENTION Heretofore, in completing a well, such as an oil and- /or gas well, whether in or out of permafrost areas, various sizes and lengths of easing strings are set in the wellbore. The casing strings extend to various depths and are set concentrically about one another in the wellbore. Thus, in a given well, there can be at least two casing strings, each casing string composed of a plurality of individual sections of easing pipe. The casing strings are concentrical with but spaced from one another to provide annular spaces therebetween. The inner or smaller diameter casing string extends to a greater depth in the wellbore than the next larger diameter or outer casing string. Normally, the annuli between adjacent casing strings and between a casing string and the wall of the wellbore are filled with cement. The cement conventionally contains substantial amounts of water. In permafrost wells, care should be taken that substantial amounts of liquid water from the drilling fluid and cement do not remain in the permafrost zone because the water can freeze into solid ice and cause undesirable pressure to build up in the well.  
 SUMMARY OF THE INVENTION It has been found that it is quite important that elevated pressures due to liquid water freezing be avoided in an annulus between two concentric strings of easing because damage to one or both casing strings is more likely to occur in this annulus than in the annulus between a casing string and the wall of the wellbore.  
  Thus, according to this invention, special precaution is taken to insure that the cement disposed in an annulus between two casing strings has a very carefully controlled water content, i.e., a very low water content, and that there is essentially no residual drilling fluid present so that there is not sufficient water in the annulus to cause any damage to the casing strings should that water freeze into solid ice.  
  The method according to this invention relates to the steps of completing a well in the permafrost zone using at least one set of inner and outer concentric strings of easing, the inner string extending to a depth lower than the outer string, wherein the annulus caused by the overlapping of the inner and outer strings of easing, after cementing all of the casing but before the cement hardens, is subjected to a washing step to wash the cement out of this annulus. The wash fluid is thereafter forcibly displaced from the annulus by a gas so that the annulus between the two casing strings is thoroughly purged. Thereafter the purged annulus is filled with a cement composition which is very carefully controlled as to its low water content.  
  This invention also employs apparatus which uses a conductor means for establishing communication between the interior and exterior of the outer casing string so that the above-described washing and gas purging steps can be accomplished in the annulus where the inner and outer casing strings overlap. The conducting means can be carried on the casing string or on a casing shoe on the casing string. The conductor means preferably contains a rupture means which is intact when the outer and inner easing strings are set in the wellbore so that when the first cementing step is carried out cement cannot enter the conductor means.  
 Thereafter, when it is desired to carry out the washing and gas purging steps, the rupture means is broken such as by pressuring up the washing fluid to establish communication between the interior and exterior of the outer casing string by way of the conductor means.  
  Accordingly, it is an object of this invention to provide a new and improved method for completing wells in permafrost.  
  Other aspects, objects and advantages of this invention will be apparent to those skilled in the art from this disclosure and the appended claims.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a cross section ofthe elevation of a well completed in accordance with this invention.  
  FIG. 2 shows the cross section of the elevation of a well casing shoe in accordance with this invention.  
  FIG. 3 shows a transverse cross section of the casing shoe of FIG. 2.  
 DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 there is shown permafrost l which extends from the earths surface 2 down to level 3 below which is unfrozen ground 4. Wellbore 5 is composed of two sections, the upper section 6 being ofa larger cross sectional diameter than the lower portion 7. Outer and inner casing strings 8 and 9, respectively, are placed concentric with one another within wellbore 5 so that string 8 extends to the bottom 10 of wellbore portion 6 while inner string 9 extends below the lower end of string 8 down into lower portion 7 and even below the end of the permafrost at level 3. Thus, there is provided a first annulus which extends between the outer surface of outer string 8 and the wellbore wall of portion 6 as designated by arrow I2. A second annulus is provided between the interior of easing 8 and the exterior of casing 9 as represented by arrow 13 and extends longitudinally the length of overlap between casings 8 and 9 in the permafrost as shown by bracket 14. A third annulus extends between the outside of string 9 and the wellbore wall of portion 7 as shown by arrow 15 and also extends longitudinally from the bottom of second annulus 14 to the bottom I7 of easing string 9 as shown by bracket 16.  
  Casing string 8 carries at the bottom thereof conducting means 20 which has an aperture 21 therein. Conduit means 22 is connected to aperture 2I and extends to the earths surface. A blowout preventer means for closing the annulus between casings 8 and 9 is provided at 23, and pipe means 24 and 25 are provided below and above, respectively, blowout preventer 23. Pipes 24 provide access to second annulus 13 even after blowout preventers 23 are closed. Annuli l2, l3, and 15 are shown in FIG. 1 to be filled with cement from the bottom of the wellbore to the earth&#39;s surface.  
  In practicing the method of this invention, after emplacing the concentric casing strings 8 and 9 with the outer casing string carrying a conductor means with a conduit means connected thereto as shown in FIG. I, and after placing cement in all three annuli as shown in FIG. I, but before the cement hardens, the cement in annulus I3 which is the cement between the two casing strings must be carefully treated to prevent leaving substantial amounts of liquid water in that annulus I3.  
  Conductor means 20 preferably has a rupture means or some other type of breakable plug in aperture 21 during the initial emplacement of cement in annuli l2.  
  l3. and 15. The rupture means is shown in more detail in FIG. 2 hereinafter. The rupture means in aperture 21 prevents cement from passing into conduit means 22. When the initial cementing step is completed and before the cement has hardened. it is then desirable to break the rupture means thereby establishing communication between the interior. i.e.. annulus I3. and the exterior. i.e.. annulus 12, of easing string 8. Thus. communication is. in effect. established from pipes 24 andfor 25 to annulus 13 through casing string 8 by way of conductor means 20, and to the earths surface by way of conduit means 22.  
  A washing fluid such as liquid water or a hydrocarbon or other liquid readily available at the drill site can then be employed to wash the still fluid cement out of annulus I3 using conduit means 22 and thereby removing substantially all material (cement, drilling fluid. etc.) from annulus I3 and leaving behind primarily only wash fluid. The wash fluid can be introduced by way of conduit means 22 and removed by way of pipes 24 and/or 25, or introduced by pipes 24 and/or 25 and removed by way of conduit means 22, or a combination thereof in any sequence of steps or repetition of steps desired so long as the primary object of the displacement of substantially all of the material from annulus 13 by wash fluid is achieved.  
  Thereafter. the remaining wash fluid. which extends for the length 14 of annulus l3 and fills conduit means 22. is forced or otherwise purged from annulus l3 and conduit means 22 by pressurization with a gas such as air or any other suitable gas for forcing substantially all the washing fluid from the annulus and the conduit means. This leaves an essentially empty annulus I3 which can then be filled with a cement composition V which has a very carefully controlled water content. This second cement composition can be a much more expensive cement composition than that used in the initial cementing step since all it has to fill is annulus l3, annuli l2 and I5 already being filled with a less expensive cement composition. By following this method it is made relatively certain that no water or drilling fluid contaminated cement is left between casing strings 8 and 9 in permafrost zone 1.  
  FIG. 2 shows a well casing shoe which can be used in the embodiment of FIG. I. FIG. I shows conducting means to be carried by and at the bottom end of easing string 8. FIG. 2 shows a casing shoe having a right cylindrical body 30 which has at its upper or first end 31 a threaded portion for ease of attachment to the lower end ofa casing string such as casing string 8 and which also has at a lower point thereof such as the bottom or second end 32 of body 30 conductor means with aperture 2]. The conductor means 20 does not have to be at the very bottom of easing 8 or body 30. The conductor means can be at an intermediate point along casing 8 or body 30. but is preferably in the lower half of casing 8 whether it is carried by the casing or a casing shoe. Upper end 33 of aperture 2] is threaded to receive a threaded end of conduit means 22 as shown in FIG. I. Aperture 2I contains therein an unbroken rupture means 34, composed of graphite. or aluminum or any other suitable material. so that fluid cannot pass through aperture 2] until rupture means 34 is broken. The first and second ends of body are open so that fluid can pass from the interior of the casing string out through the bottom of the casing string and vice versa.  
  FIG. 3 shows body 30 of FIG. 2 to carry two conducting means 20 on opposite sides thereof. According to this invention one or more than two conducting means can also be employed on the casing shoe or on the easing itself as desired. The shoe of FIG. 2 does not have to be placed at the bottom end of easing string 8 but could be applied to an intermediate point thereof if desired, but it is preferable that the conductor means be at or near the bottom of easing string 8 so that the majority of annulus 13 is subjected to the washing and gas purging stepsv Of course. a conventional wellhead can be employed at the earths surface for easing strings 8 and/or 9 but is not shown for sake of simplicity. Also, wellbore portion 7 can extend below the level shown in FIG. 1 but normally. after all cementing steps are completed, the wellbore will then be drilled deeper by passing a drill bit and drill string through the interior of casing 9 and drilling through the cement below end 17 of easing 9 and on into the unfrozen earth 4.  
 EXAMPLE In a situation where permafrost zone 1 extends to about 2.000 feet below earths surface 2, 20 inch diameter casing string 8 is set about eighty feet below the earth&#39;s surface. i.e.. at the bottom of wellbore portion 6 while l3% inch diameter casing string 9 extends to about 2.700 feet below the earths surface 2. Two-inch tubing is employed for conduit means 22 and aperture 2I contains an aluminum rupture disk which has a burst pressure of about 200 psig. Annuli l2. l3, and 15 are cemented in a conventional manner which conventional cement normally used in permafrost regionsv Before the cement in annulus 13 sets. water is pumped down conduit means 22 at sufficient pressure to burst the rupture means in the aperture 21 so that water rises from the bottom of annulus 13 toward the earths surface pushing ahead of it and/or mixing and carrying with it the cement and any residual drilling fluid in that cement and any other material present in annulus 13. This washed out material is recovered at the earths surface by way of pipes 24 and/or 25. Thereafter. blowout pre venter 23 is closed and water is pumped by way of pipes 24 into the top of annulus I3 down to the bot tom of that annulus. through aperture 21. and up conduit means 22 to the earths surface. After this reverse washing step. rig air is used to force the water wash fluid remaining in annulus I3 and conduit means 22 to the earth&#39;s surface by injecting the air by way of pipes 24 into the top of annulus l3 and forcing the water out of annulus 13 into conduit means 22 and out of conduit means 22 to the earth&#39;s surface. Normally. about eighty cubic feet per minute of air at about I50 psig can be employed to accomplish the purging step. Thereafter. annulus I3 is recemented using cement with essentially no free water. i.e.. using no more water than is required to hydrate the cement.  
  Reasonable variations and modifications are possible within the scope of this disclosure without departing from the spirit and scope of this invention.  
  The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:  
  I. A method for completing a well whose wellbore passes through a permafrost zone comprising. in at least a portion of said permafrost zone. placing in said wellbore a first casing means which carries near the lower end thereof a conductor means for passing fluid between the inside and outside of said first casing means, said conductor means initially having a rupture means for preventing the passage of fluid therethrough, said first casing means being spaced from the wellbore wall to provide a first annulus. conduit means extending in said first annulus from said conductor means to the surface of the earth, placing a second casing means inside said first casing means but spaced therefrom to provide a second annulus between said first and second casing means. said second casing means extending below the lower end of said first casing means to provide a third annulus around that portion of said second casing means which extends below said lower end of said first casing means, placing cement in said first. second and third annuli, before said cement hardens. breaking said rupture means. circulating a washing fluid through said second annulus-conductor meansconduit means assembly to wash substantially all material out of said second annulus, forcing with a gas substantially all washing fluid from said second annulusconductor means-conduit means assembly. and placing in said second annulus cement with a controlled water content.  
  2. A method according to claim 1 wherein said washing fluid is liquid water and said gas is air.  
  3. A method according to claim 1 wherein after placing cement in said first, second, and third annuli, wash fluid is passed down said conduit means to break said rupture means. and cement and any other material in said second annulus is washed out of that annulus to the earths surface by passing wash fluid (a) down said conduit means and up said second annulus, (b) down said second annulus and up said conduit means. or (c) a combination of (a) and (b), and thereafter said wash fluid is forced out of said second annulus by forcing a gas down said second annulus and up said conduit means.  
  4. A method according to claim 3 wherein said wash fluid is liquid water and said gas is air.