Preventing Lost Circulation Using Lightweight Slurries with Reticular Systems: Depleted Reservoirs in Southern Mexico

Abstract

Abstract In southern Mexico, 65% of the oil and 74% of the gas production comes from Mesozoic formations—naturally fractured carbonates—with a high potential for loss of circulation. Lost circulation during drilling and cementing often leads to formation damage and can severely impact well costs. This paper describes the implementation of lightweight (9.17 lbm/gal) slurries and a reticular product technology to avoid losses while cementing and to improve zonal isolation and postcement job evaluation. Applying this combination of technologies improved the success ratio of primary isolation of the wells. Lightweight cementing slurries with reticular systems were used in two wells in Mexico: Copano 32 on the development side and Malva 201 for exploratory cementing. The wells were drilled underbalanced and, in both cases, lost circulation was a problem during drilling. Circulation of the cementing slurry was regained while cementing and returns reached the designed cement top, avoiding the anticipated remedial cementing job. The pressure behavior during cementing clearly showed the plugging effect of the slurries in the formation; periodic low-pressure intervals were encountered before the final constant increase in pressure, which indicated that the designed cement job had been achieved. In these wells, implementation of lightweight slurries and reticular-product technology prevented cement invasion into the production zone. Savings in rig downtime and improved zonal isolation led to a significant reduction in costs during the construction of the wells. The cementing solution represented at least a 300% cost savings related to the cementing process and confirmed that lightweight cement slurries with reticular products are a viable solution for the depleted reservoirs in southern Mexico and for similar wells around the world where lost circulation problems of this kind exist.