Enhancing Wellbore Integrity for Well Subject to Fracturing: Improving Cement Sheath Flexibility and Ensuring Long-Term Cost-Effective Well Integrity - A Case Study

Abstract

Abstract In Fracturing operations, the cement sheath is likely to be compromised due to mechanical stresses. This could lead to well integrity issues in the long-run. To maintain the well-bore integrity and sustainment of subject stresses throughout the life cycle of the well-bore, flexibility in the cement sheath placed behind the casing can be a differentiating factor, incrementing in the life cycle of the well-bore and reducing the risk of mechanical failure in case of well subjected to high-pressure stress cycles during the fracturing operation. Developing intraparticle flexibility in cement is challenging and involves altering the mechanical properties of set cement by adding flexible particles with an average particle size ranging from 100-400 microns and not greater than 500 microns. The flexible particles tend to improve the mechanical properties of set cement in terms of impact resistance, fracture toughness and to a lesser extent tensile strength. Depending upon the formation, additional properties in the cement slurries can be incorporated using Anti-gas migration, fluid loss control, Compressive strength enhancer, and expansion additive to prevent post-setting cement shrinkage and improve cement bonding between the cement-formation and cement-casing with time as the expansion takes place. This paper demonstrates the working principle and practical applications of engineered solutions for long-term well integrity challenges during post-job cyclic stresses in which flexible particles were incorporated to render the set cement properties. Designed cement exhibits more resistance to impact and improves its long-term integrity from severe static and dynamic stresses. The slurry system aims to yield low young modulus and high flexural strength. The technology is the appropriate solution in cases where the set cement is subjected to severe stresses during fracturing jobs. The technology was utilized in both 9-5/8″ sections and 7″ liner with flexible cement to achieve zonal isolation. Cement-designed properties were tested in the lab to confirm the desired young modulus (<6000 MPa) and poison's ratio properties. However, this paper will focus on job designing and execution of 7″ liner jobs using flexible cement. The mechanical properties were plugged in to stress check simulator with planned mechanical cyclic stresses to confirm cement sheath integrity post-fracturing job. The well was subjected to a multi-stage (10-successive stage) fracturing operation with a maximum pressure of up to 3,700 psi in each stage and a pumping rate of 24 bpm (per stage), with cumulative fluid pumped= (2,104 bbl). The well was observed post frac and completion and no well-bore integrity issues were reported post fracturing job. The well was subjected to a multi-stage fracturing operation with a maximum pressure of upto 3,700 psi and a pumping rate of 24 bpm, with cumulative fluid pumped2,104 bbl. The well was observed post-frac and completion and no wellbore integrity issues were reported post-fracturing job. This approach improves wellbore integrity during fracturing operations by modifying the mechanical with the addition of flexible particles. This enhances the set cement's mechanical properties; Laboratory testing and simulations validate its effectiveness. Field application shows successful zonal isolation and no integrity issues post-fracturing.