Abstract:
Composite tubular casing with hardened material between thin pipe-in-pipe increasing the bending capability of the casing wall delivers high collapse resistance. Solid Expandable technology allows substantial wellbore slimming at the expense of collapse resistance. By combining both technologies, cost effective high collapse resistance wellbore construction can be achieved.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation in part of application Ser. No. 10/416,773 filed Oct. 8, 2001 now U.S. Pat. No. 7,490,676 and a continuation in part of application Ser. No. 11/953,335 filed Dec. 10, 2007 now U.S. Pat. No. 8,069,900. The entire disclosures of the prior applications are incorporated herein by this reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to well casing requiring mechanical performances enhancement mostly in collapse resistance in-situ or after installation. 
     BACKGROUND ART 
     New methods for installation of tubular structures in well have recently been introduced like solid expandable systems but have reduced mechanical performances, mostly in collapse resistance. 
     The U.S. Pat. No. 7,159,666 and U.S. Pat. No. 8,069,900 of the applicant, offer slimming capability without collapse resistance reduction, but at the expense of a radical change of practice which create a substantial barrier entry. 
     DISCLOSURE OF INVENTION 
     The purpose of the invention is to enhance the mechanical performances of Solid Expandable Technology by having the external thin casing installed with solid expansion technology cooperating with an internal thin gas tight integral string for a strong collapse resistance wellbore construction. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The purposes, objects and characteristics of the invention will be more apparent after reading the description which follows referring to the drawings in which: 
         FIGS. 1 to 3  are sequence views of a well cased with Monobore solid expandable technology enhanced, after TD has been reached, in collapse resistance by composite tubular configuration according to a first embodiment of the invention. 
         FIGS. 4 to 6  illustrate a simplified alternative adapted to non Monobore solid expandable. 
     
    
    
     DETAILED DESCRIPTION 
     To make the understanding of the following description easier, we will use the term longitudinal when it is parallel to the direction of the tubular structure, and the term radial to indicate that it is somewhat in the plan perpendicular to the direction of the tubular structure. For casing applications, acknowledging that the string went down in the well vertically, we will use top, bottom, downward, upward, upper or lower. 
     It is common knowledge that collapse resistance is increased when the ratio of T (Wall Thickness) over D (Diameter) increases. 
     On another hand, radially enlarged solid steel pipe which characterize the Solid Expandable technology has a tendency to decrease the casing wall thickness and further decrease the collapse resistance due to the Bauschinger effect. 
     But by filling with hardenable material the annulus space between two thin wall concentric casings, the combined T/D (T=Wall Thickness over Diameter) increases substantially and so the collapse resistance. 
     Referring to  FIG. 1 , a well  91  has been drilled. To illustrate the possible variation we assume that the well has been drilled through impervious ground zone  90  (consolidated rock) and permeable ground zone  89 . The well has been cased by known solid MonoBore expandable casing with a first length of casing  92  having a bottom bell  93  receiving a second expandable casing  94  featuring a packing seal  95  at the bottom to achieve sealing arrangement with impervious ground zone  90 . A third length of casing  96  (not expanded yet) is shown being run on running tool  97  connected to running string  98 . All these length of casing are made from the assembly of straight length of round pipe with known T/C coupling  100 . Presently when T/C coupling are expanded in the plastic range, they loose their gas-tight capability. 
     Referring to  FIG. 2 , the third length of casing  96   a  has been expanded and the top sealed to sealed ground zone  90 . It will be recognized by the man skilled in the art that the presence of impervious ground zone  90  is not mandatory to achieve the composite tubular according to the invention and if impervious ground zone  90  are not considered to simplify length of casing connections, a bell type connection arrangement between first length  92  et second length  94  can be installed between second length  94  and third length  96   a.    
     Then assuming that third length is the last casing, the well having reached the producing zone, a final length of casing  101  is lowered to cover the three previous lengths  92 ,  94  and  96   a . This final length of casing  101  could have advantageously the same manufactured size than the three others. Centralizing of the casings can be achieved with the coupling  104  protuberance featuring possibly some flow-by slits or conventional casing centralisers. 
     Hardenable material  103  like cement is circulated between the fourth length of casing  101  preferably from the bottom up via the cement shoe  102  and the 3 previous lengths  92 ,  94  and  96   a  to built a high performance sandwich wall. Since the T/C couplings  104  of the fourth length of casing  101  have not been expanded, they retain their gas-tight capability offering a gas-tight production casing. This composite/sandwich configuration illustrated in  FIG. 3  is very advantageous because it requires only thin wall casing to be installed which are more easily set as MonoBore/MonoDiameter expandable casing reducing the percentage of strain required for their installation. 
     Again, cementing of the outer casing  92 ,  94  and  96   a  to the drilled hole is not necessary to achieved the High Performance capability composite tubular structure according to the invention, only the space between the inner casing  101  and the three outer casing  92 ,  94  and  96   a  must be filled with a hardenable material. In case of outer casing interruption due to the presence of impervious ground layer  90 , the sandwich structure is then achieved by using the consolidated sealed terrain as outer layer but its strength have been verified and the pollution of the cement is minimum which is not the case when the cement goes in contact with permeable ground. 
     Referring to  FIG. 4 , a simplified alternative without using MonoBore configuration is illustrated. The need of installing bell  93  is removed and the configuration is well suitable in case of well reentry. 
     Second and third casing  92   a  and  94   a  are set as liner of their preceding casing, the solid expandable technology being mostly used to reduce the bore radius losses due to casing coupling  100  clearance. 
     The internal string  101  is not expanded and therefore retains its gas tight capability and can be part of a mixed diameter string with enlarged casing size  105  due to the staggered outer casing diameter. 
     To compensate for hardening material setting shrinkage and it is also considered advantageous to maintain pressure and continue supplying hardenable material while setting or curing. A substantial pressure of a minimum of 60% of the well capability is advantageous. 
     While the improvements by creating composite tubular structure downhole has been shown in some of its forms, it should be apparent to those skilled in the art that it is not so limited, but it is susceptible to various changes without departing from the scope of the invention.