Reservoir engineering geological characteristics and stimulation in Xujiahe Formation, Xinchang gas field, Western Sichuan Depression, Sichuan Basin

Reservoir stimulation is a key technology to develop the tight gas reservoir in the Western Sichuan Basin. The second member of the Xujiahe Formation (hereinafter referred to as Tx2), a typical deep tight formation, is characterized by tightness, strike-slip fault stress state with minor principal stress close to vertical stress, and well-developed fractures within, and the effect of reservoir simulation is quite limited at the early stages. The engineering geological evaluation and analysis of the previous hydraulic fracturing operation in the Xujiahe Formation are carried out, and three types of double sweet spots (namely, the sweet spot both geologically and geomechanically) are determined based on lithofacies, petrology, physical properties and natural fractures. Among others, the fault-fracture type could be developed by nitrogen drilling, small-scale fracturing and acidizing; the bedding-parallel fracture type could be developed by the near-wellbore deep plugging removing and integrated stimulation technique; and the pore type needs to be fractured by volume fracturing under ultra-high pressure. In practice, Well X8-2 encountering fault-fracture type sweet spot achieves a steady open flow rate of 53×104 m3/d through nitrogen drilling, and Well XS101 encountering pore type sweet spots achieves a steady production rate of 15×104 m3/d through large-scale volume fracturing. The success of Wells X8-2 and SX101 shows that these technologies are effective in stimulation of the tight gas reservoirs, thus being applicable for the effective development of natural gas resources in the Xujiahe Formation, Western Sichuan Depression. © 2021, OIL & GAS GEOLOGY Editorial Board. All right reserved.