Key technology of Large Scale Acid Fracturing in Fault-Karst Carbonate Reservoir of S Well with Ultra-Deep Well Depth and Ultra-High Temperature

Abstract

The target formation of S well is a typical carbonate reservoir, which has ultra-deep depth and ultra-high temperature, with a buried depth of 8 270.0 m, a temperature of 182 ℃, extremely complex engineering and geological conditions and wellbore conditions, leading to great challenges in acid fracturing treatment. It is necessary to carry out targeted optimization research of acid fracturing treatment. Based on the detailed analysis of the three challenges of acid fracturing in this well, the compound acid fracturing treatment of Backfilling well section to centralize treatment + Acid damage to reduce fracture pressure + Combining shallow placement of pipe string and low injection rate of weighted fracturing fluid to increase injection rate+ Pad fluid to open the reservoir and extend the fracture + Alternative injection to create high conductivity fracture + Autogenous acid to dredge the far fault-karst is proposed. A set of acid fracturing fluid system with resistance to ultra-high temperature is optimized through experiments, and different acid fracturing fluid scales are recommended by numerical simulation, and finally the large-scale acid fracturing scheme is optimized. Acid fracturing fluid system with resistance to ultra-high temperature includes polymer fracturing fluid resisting 180 ℃, pressure weighted guar gum fracturing fluid and cross-linked acid resisting 160 ℃, and autogenous acid. The optimal fracturing fluid scale is 1 000~1 200 m3 and the acid fluid scale is 800~1 000 m3. After the large-scale acid fracturing of S well, the test production of natural gas is 10.45×104 m3/d, which makes a breakthrough in the exploration of Shunbei NO.4 fault zone and provides valuable experience for the large-scale acid fracturing of similar reservoirs.