Preventing Lost Circulation by Use of Lightweight Slurries with Reticular Systems: Depleted Reservoirs in Southern Mexico

Abstract

Summary 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 post-cement 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: a development well (Copano 32) and an exploration well (Malva 201). The wells were drilled underbalanced, and in both cases, lost circulation was a problem during drilling and cementing. Using this technology, circulation of the slurry was regained while cementing and returns reached the designed cement top, avoiding an anticipated remedial cementing job. The pressure behavior during cementing clearly showed the plugging effect of the fiber-laden slurry in the formation; periodic low-pressure intervals were encountered before the final constant increase in pressure, which indicated that the designed-cement job objectives had been achieved. In these wells, implementation of lightweight slurries and reticular-product technology prevented further 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. He also confirmed that lightweight cement slurries with reticular products are a viable solution for the depleted reservoirs, in southern Mexico and similar wells around the world, in which lost-circulation problems of this kind exist.