Study and Application of a High-Performance Salt-Resistant Cement Slurry

High-pressure salt and gypsum beds prevail in the Missan Oilfield in Iraq. In well cementing, tight hole resulting from the creeping of salt layers, increasing salinity of cement slurries from hole washout and salt dissolution, narrow drilling window and reduced displacing efficiency pose challenges to the well cementing jobs. Cement slurries formulated with semi-saturated NaCl solution and 3%-5% KCl solution are widely used presently and have the shortages of low compressive strength of set cement and poor bonding between casing string and cement sheath and between cement sheath and bore hole wall. To solve these problems, a cement slurry was formulated with a slat solution containing 25% NaCl and 5% KCl, and other additives of choice, such as filter loss reducer, dispersant and retarder. As a high-performance salt-resistant cement slurry, it is free from the high rheology and high thixotropy previously encountered when cement slurries are brought into contact with salt. Laboratory study showed that this cement slurry is able to inhibit the dissolution of salt. A cement slurry of 2.39 g/cm³ can be made with only 30% hematite at a minimum, which not only saves money, but also greatly improves the compressive strength of the set cement. The 24-hour compressive strength of this cement slurry is 48 MPa, almost doubling the compressive strengths of the set cement of cement slurries presently in use. The 24-hour compressive strength of the cement slurry being contaminated is still greater than 14 MPa. These characteristics of the new cement slurry satisfy the needs of cementing the salt and gypsum beds in the Missan Oilfield, Iraq, making the cement slurry worth spreading in this oilfield.