An Improved Cementing Method for Solid Expandable Tubulars

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 90923, "Improved Method of Cementing Solid Expandable Tubulars," by Charles Fanguy, SPE, Dan T. Mueller, and Dale R. Doherty, SPE, BJ Services Co., prepared for the 2004 SPE Annual Technical Conference and Exhibition, Houston, 26-29 September. Failure of cement slurry to remain fluid and stable after placement can prevent successful expansion of solid expandable tubulars (SETs). The 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. The full-length paper describes the premixed-slurry properties and quality-assurance/quality-control (QA/QC) procedures that are required for successful expansion of SETs. The paper also provides test methods and procedures used for fluidity-time testing as well as case histories of successful SET cementation. Introduction There are several challenges when cementing SETs. The primary challenge is to obtain “fluidity” time at static wellbore conditions. Fluidity time is defined as the time the cement slurry exhibits a static gel strength of less than 100 lbf per 100 ft2. True fluidity time is required to ensure that gellation does not occur during the expansion phase that follows cement-slurry placement in the annulus. Gelation can result in “voids” or bypassed mud above the pre-expansion top of cement. Severe gelation also can cause formation breakdown and lack of zonal isolation. In addition to gelation, density segregation and settling can occur during extended static periods at bottomhole conditions. This also can lead to bypassed drilling fluids and potential formation breakdown. These challenges, along with low displacement rates and lack of available centralization, complicate the primary cementing process. Because of these challenges, many expandable liners have been squeezed after expansion as opposed to being cemented before expansion. The technologies and methods described in the full-length paper have led to an increase in the success rate associated with cementing SETs. As this technology becomes more accepted and mainstream, increased focus will be placed on cementing techniques and technologies that can enable complete zonal isolation in the entire annulus. Premixed Cement System A storable, premixed cement system is used for cementing expandable liners. These pre-mixed slurries are blended at a bulk plant before arrival at the wellsite. After the slurry is mixed, liquid samples of slurry are sent to a laboratory so that physical properties can be verified. Properties that are tested include free fluid, fluid-loss control, thickening time, fluidity time, gel-strength development, and compressive-strength development. These properties can be modified with liquid additives if necessary. Premixed slurries also exhibit several characteristics that are beneficial for use with expandable liners. These slurries contain specialized additives that ensure slurry stability under extended storage conditions, so fluidity time at wellbore conditions is easily achieved. These slurries also have improved rheological properties and improved tolerance to mud contamination, as exhibited by contamination tests conducted with both destructive and non-destructive compressive-strength testing. The improved rheologies and resistance to contamination have helped to obtain zonal isolation even with low displacement rates and no centralization.