Innovative Combination of Dynamic Underbalanced Perforating with Emulsified Acid and Non-Damaging Viscoelastic Surfactant-Based Fluids Boost Productivity in Low-Permeability Naturally-Fractured Carbonates

Abstract

The fields in southeastern Mexico have produced from Cretaceous and Jurassic-age naturally-fractured carbonate reservoirs since the early 1970s. Many recent exploratory wells drilled and completed in these high-pressure, high-temperature formations have yielded unsatisfactory results due to a combination of causes, including severe drilling-induced formation damage to low-matrix permeability reservoirs. Conventional completion and stimulation treatments to remove and bypass the damage have yielded satisfactory results in some cases but not in others. To increase productivity from new discoveries, an integrated approach to the completion and stimulation of low-permeability naturally-fractured carbonate reservoirs is proposed.An innovative technique, combining dynamic under-balanced perforating with a highly-stable emulsified acid and a nondamaging viscoelastic surfactant-based acid, is presented in this paper. Three successful applications in southeastern Mexico are documented, including a low-productivity development well; a well originally perforated and stimulated using conventional technology; and an exploratory well, resulting in substantial production increases in all three cases. These applications served to prove that the combined effect of the proposed completion and stimulation technologies was the enabler to achieve superior production results. The highly-retarded emulsified acid pumped through clean perforating tunnels produces longer fracture penetrations, positively impacting the performance of low-permeability reservoirs and resulting in improved production responses. At the same time, the viscoelastic system reduces leakoff, which is necessary to extend fracture lengths further in the reservoir. The fluids combined in a high-rate pumping technique that consisted of alternating stages of emulsified acid, main acid, and diverter reduced the creation of wormholes near the wellbore, thus increasing the penetration of the treatment in the reservoir.