Zonal Isolation Best Practices Helped in Maintaining Well Integrity and Achieved EOR Objectives in Highly Fractured Carbonate Reservoirs Case Study From Steam Injection Wells in Issaran Field in Egypt
Authors: Mohamed Sherif , Ali Ahmed , Bhaisora Devesh , Hassan Wael , Nabil Emad , El Moqadem Hamdy 
Published: February 2017

Thermal injection is a key method for enhanced oil recovery (EOR). During thermal injection, special steam injection wells are drilled to heat the crude oil in the formation to reduce its viscosity and help improve oil recovery. Zonal isolation of steam injection wells can be challenging because the temperature of steam on surface can reach up to 500°F. Regardless, achieving all zonal isolation objectives on the first attempt is necessary because any remedial treatments in such wells could adversely impact well integrity.

This paper discusses best practices used for zonal isolation of steam injection wells in the Issaran field, Egypt. This field is located approximately 290 km southeast of Cairo and 3 km inland from the western shore of the Gulf of Suez. This field was discovered in 1981 and covers an area of 20,000 acres. This is among one of the few heavy oil fractured carbonate reservoirs in the world. During 2012 to 2015, more than 40 wells were drilled and successfully cemented in this area.

Because of the unique characteristics of the fractured reservoir, special lightweight high-compressive-strength cement slurry was designed to help ensure the equivalent circulating density (ECD) during cementing would be less than the formation fracture gradient. During laboratory testing, this slurry was exposed to downhole steam temperatures for more than 10 days to determine its long-term compressive strength and evaluate the potential for strength retrogression.

As a contingency to minimize losses during cementing, glass fibers were added to the cement slurry. The secondary purpose of these special fibers was to increase the tensile strength of the cement slurry. To help improve the mechanical properties of the slurry, special elastomers were also added. Finite element analysis (FEA) was performed to calculate the desired Young's modulus and Poisson's ratio of the cement slurry, and the concentration of the elastomers was adjusted accordingly.

Although the wells had minor deviations, casing centralization was optimized to help ensure homogenous distribution of the cement slurry in the annulus. Mud displacement and filter-cake removal are also key parameters for a successful cementing operation, so a tuned rheology spacer was designed to help achieve rheological hierarchy based on the rheological parameters of the mud and the cement. Surfactants were added to help erode the mud filter cake before the cementing operation. Also, three-dimensional (3D) modeling was performed to help optimize displacement efficiency and mud removal before the cementing operation.

Post-cementing operations in all wells showed that the designed cement slurry was suitable for such applications and resulted in achieving all of the objectives of zonal isolation. This paper provides details of the slurry design parameters and best practices and can be used as a reference for cementing such systems in the future.