Research and application of stimulation fluid technology for deep marine carbonate rocks

Abstract

In view of the characteristics of deep marine carbonate reservoirs in the Sichuan Basin, such as a deep burial depth (5000–8120 m), high temperatures (150°C-180 °C), a large inclination toward wells, and large acid-rock reaction rate, a high-temperature gelled acid and a preflush containing a self-generating acid that matched with the high-temperature gelled acid were developed. The results of laboratory evaluation showed that the viscosity of the high-temperature gelled acid at 180 °C was 30 mPa·s, with a corrosion rate lower than 70 g/m2·h.The drag reduction and acid-rock reaction rates reached 64%–71% and 1.569 × 10−4 mol/cm2·s respectively, demonstrating obvious retarding performance. In addition, the viscosity of the preflush containing a self-generating acid (after shearing at 160 °C for 1 h)remained at 200 mPa·s. Compared with a full injection of the high-temperature gelled acid, the acid-etched fracture conductivity after an alternate injection of the preflush containing self-generating and high-temperature gelled acids increased by more than 50%. Field application showed that the high-temperature gelled acid played a vital role in connecting fractures where as the preflush containing self-generating acid demonstrated an outstanding fracture-formation ability. After a three-stage alternate injection (a preflush containing self-generating and gelled acids), a remarkable stimulation effect was achieved for increase natural gas production.