Characteristics of gas-water flow during gas injection in two-dimensional porous media with a high-permeability zone

A marginal gas injection method was previously proposed based on two-dimensional (2-D) homogeneous porous media, and the feasibility of isolating the oil shale pyrolysis zone from the surrounding hydrological environment had been demonstrated. The gas-water flow characteristics and dynamics during gas injection in 2-D porous media with a high-permeability zone (HPZ) were studied further based on the presence of a HPZ after fracturing oil shale reservoirs. A series of experiments were performed when the gas-injection point was located outside, at the boundary, or inside the HPZ (Case1-3). The HPZ enriched the injected gas, and in Cases 2 and 3, the gas inside the HPZ permeated to the low-permeability zone (LPZ) on both sides, forming two wing tributaries. However, in Case 1, water flowed into the HPZ in the opposite direction. In Cases 2 and 3, the direction of the local pressure gradient on both sides of the HPZ was completely opposite, indicating that the distribution of the pressure field was the direct cause of the gas-water flow characteristics. Therefore, the water-stopping effect of gas injection is primarily reflected in the HPZ. Additionally, the effect was best when the gas-injection point was set at the boundary or inside of the HPZ. These results were verified using reservoir-scale simulations and tests, in which the water yield decreased to ~ 100 kg/d. Subsequently, we recommended the sites of gas-injection wells for water stopping. All results are expected to provide strategies and theories for dealing with the adverse hydrological environment in large-scale oil shale in situ exploitation.

Automated summary

This study further investigates the influence of high-permeability zones on gas injection in 2-D porous media, demonstrating the feasibility of isolating the oil shale pyrolysis zone from the surrounding hydrological environment. The results indicate that the gas-water flow characteristics are directly affected by the distribution of local pressure fields, and the water-stopping effect of gas injection primarily occurs in the high-permeability zone, with the best results achieved when the gas-injection point is set at the boundary or inside the high-permeability zone.