Volume 41: Energy Transitions toward Carbon Neutrality: Part IV

Study on water invasion law and development strategy of fractured gas reservoir based on pore throat structure Zechuan Wang, Leng Tian, Jinbu Li, Junguo Dong, Feng Xiao, Lian Zhao, Qinghua Tian, Xiaolong Chai

Abstract

In this paper, a systematic technology is developed to study the influence of pore-throat structure and fracture development on the water invasion behavior of fractured gas reservoirs, quantitatively characterize the law of water invasion, and then formulate a reasonable working system. In the experiment, nuclear magnetic resonance ( NMR ) and high-pressure mercury injection ( HPMI ) were used to characterize the pore structure of the core samples, and the distribution of the invaded water phase in the pore throat was clarified. The effect of water phase distribution on gas phase permeability was obtained by displacement test. Based on the existing capillary bundle model, three types of gas-water microscopic occurrence and seepage modes are divided from the microscopic pore-throat structure. Furthermore, considering the high conductivity of fractures in the reservoir, a mathematical model was formulated and generalized to characterize the seepage characteristics of fractured gas reservoirs. In this way, the effects of pore-throat structure and fracture development degree on water invasion law are comprehensively examined and analyzed. Subsequently, the model was promoted and applied to the dynamic prediction and scheme formulation of a fractured gas reservoirs. The research shows that during the flow of edge-aquifer along the fracture, it will invade the matrix under the action of large capillary force and reserve in a large number of small pore throats, thus forming a large amount of closed residual gas. which greatly restricts the gas recovery rate and recovery rate of the reservoirs. The simulation shows that the production pressure difference in the study area should be controlled within 5 MPa, and the early strong drainage measures at the edge should be used to assist in increasing production. Reasonable water control measures can improve the recovery rate of gas reservoirs by more than 15 %.

Keywords fractured gas reservoir, pore throat structure, water invasion law, development strategy