Cement-Shrinkage Measurement in Oilwell Cementing—A Comparative Study of Laboratory Methods and Procedures

Abstract

Summary Cement-sheath shrinkage after placing the cement slurry in the annulus has been of concern in oilwell cementing because of the potential detrimental effects that shrinkage can have on long-term zonal isolation. This paper compares several methods for measuring cement shrinkage under a variety of conditions including those downhole. Using the various methods, cement shrinkage in environments where the cement slurry is either closed to or open to external water sources was measured, and the values were compared. The methods used for measurement under atmospheric conditions were based on American Petroleum Institute (API) test apparatus (balloon and ring mold) and flask methods currently used in laboratories. Measurements under pressure were performed using the balloon and ring-mold methods, in-house designed equipment, and commercial equipment. The values obtained by the different methods are discussed. Procedure modifications are proposed for measuring volume changes to cement slurries on the basis of placement time, shear history, and gel-strength development. The results presented in this work can be used to test shrinkage characteristics of cement slurries in the laboratory under downhole conditions and to select a cement system that is fit for purpose.