Improved Method of Cementing Solid Expandable Tubulars

Abstract

Abstract The successful isolation of solid expandable tubulars (SET) with cement presents a considerable engineering challenge. The primary task in slurry design is to maintain "true fluidity" at static downhole conditions. The slurry must remain both fluid and stable after placement until the expansion process is completed. Failure of the slurry to remain fluid and stable after placement can prevent the successful expansion of the SET. This property, of being both stable and fluid, is difficult to achieve with conventional cement technology because conventional slurries tend to settle under downhole conditions after an extended period of quiescence. This instability leads to density segregation and potential formation breakdown in the lower sections of the well. A second obstacle that must be overcome to successfully cement a SET is inter-particle attraction (gellation) that can occur once the cement slurry is placed. Minimizing inter-particle attraction/gellation reduces the likelihood of forming voids or channels (micro-annuli) in the finished cement sheath, which can jeopardize effective zonal isolation, the essential performance requirement of any well cementing operation. The test method currently used to evaluate the properties of conventional cement slurries during the anticipated expansion time is the API RP-10B modified hesitation squeeze simulation. Unfortunately, this test method does not simulate accurately the conditions under which the cement will be placed. For example, the test procedure does not allow adequate time for gellation tendencies to occur. Gel strengths are broken every time the consistometer motor is turned on, producing gel strength values that have no more than ten minutes to develop. This test method also does not provide a means to account for any potential delays that may occur during the expansion of the SET. To enhance accuracy and reliability in SET cementing operations, a test method which incorporates testing storable premixed cement slurries for fluidity time at static conditions as opposed to using the API modified hesitation squeeze procedure has been successfully employed in field applications. This paper will describe the premixed slurry properties and QA/QC procedures that are required for successful expansion of the SET. This paper will also provide test methods and procedures used for fluidity time testing as well as case histories of successful SET cementation.