Figure 1. Fitting of adsorption model and experimental data
Figure 2. FHH curve determines the bound state of adsorbed water
Under the background of the growing demand for oil and gas resources in the world economy, the development and utilization of unconventional shale gas resources has attracted much attention. Shale gas reservoirs have unique characteristics of storage and low permeability, and horizontal well completion and hydraulic fracturing technologies are developed. The key technologies of shale gas reservoirs. However, in the hydraulic fracturing process, only a small part of the fracturing fluid is recovered during the cleaning stage. Most of the fracturing fluid is trapped in the shale formation. The water lock problem seriously affects the shale gas. Effective development of reservoirs. The study of the gas-water flow mechanism in shale gas reservoirs has important theoretical implications for the efficient development of shale gas reservoirs.
In recent years, researchers from the Institute of Mechanics at the Chinese Academy of Sciences, the China Petroleum Exploration and Development Institute, and the Lawrence Berkeley National Laboratory have collaborated with researchers to make series of progresses in the gas-water flow mechanism of shale gas reservoirs.
The researchers designed a shale water adsorption and desorption and absorption device, studied the characteristics of water adsorption, desorption and infiltration of shale, revealed the mechanism of adsorption, desorption and adsorption of shale water, and established a numerical model for adsorption and diffusion of shale water. The results show that water adsorption in shale is closely related to organic carbon content and mineral composition. The GAB isothermal model can describe and predict its adsorption process, while the FHH curve can be used to distinguish the boundary state of the adsorbed water; there is a serious lag in water adsorption and desorption of shale. Phenomenon, water with a capillary capacity of up to 1 MPa can be driven out of the shale. The water lock problem severely restricts the effective development of shale gas reservoirs. Shale gas production is mainly related to fracturing areas that are not in contact with fracturing fluids. Related.
Based on the Knudsen number, the researchers divided flow patterns at different scales of shale gas and analyzed the characteristics and influencing factors of gas flow under each flow mode; based on the dust gas model and the generalized Langmuir model. (Extended Langmuir Model), using the TOUGH2 simulation program to study the diffusion and adsorption process of shale gas, and analyze the influence of pressure, temperature and permeability changes on the diffusion and adsorption of shale gas. The results show that the ratio of pressure change to each flow state The influence is very large and the influence of temperature on it is almost the same. The adsorption affects the total mass flux of shale gas. The dust model is more suitable for describing the diffusion process of low-permeability reservoir media when the permeability is lower than 1.0×10.-15m2At that time, the change of permeability has little effect on the diffusion and adsorption rate of shale gas. The above results are of important theoretical significance for the diffusion and adsorption flow, productivity evaluation and fracturing design of shale gas reservoirs.
The related research results were published in Water Resources Research, Energies, Transport in Porous Media, Journal of Natural Gas Science and Engineering, etc. The study was conducted by the U.S. Department of Energy, the National Twelfth Five-Year Plan and the Thirteenth Five-Year Plan for National Major Oil and Gas Technology. Special projects, funded by China Scholarship Council, China Petroleum Exploration and Development Research Institute, and Young Scientists Fund of Fluid-solid Coupling Key Laboratory of Chinese Academy of Sciences.
