Research and application of cement slurry system in Sulige leakage wells

In the Sulige gas field in China, the single-stage primary full-hole cementing technique is applied, which effectively improve the load bearing capability of the casing string. However, leakage of cement slurry was observed in some low-pressure leakage wells during operations. To ensure that cement slurry effectively plug the formations under different pressure conditions to avoid loss, this paper analyzes the characteristic of circulation loss in the Sulige gas field, and proposes the low-density high-strength leak-preventive cement slurry system with innovative hollow ball micro-powder as the light-weight-additives. Evaluation test in lab shows that the system is characterized by low density, high compressive strength and low gas permeability. Under certain conditions, the strength of cement reaches 18 MPa in 120 hours and exceeds 20 MPa in 360 hours. The system has been tested in 5 wells, revealing successful cementing operation, no loss during one-trip return of slurry to the wellhead, and a cement quality of over 95% at the first interface and over 85% at the second interface in the leakage layer. The results meet the technical requirements of single-stage primary full-hole cementing in low-pressure leakage formations in the Sulige gas field.