Study On Fluid - Solid Coupling Of Liquid - Phase Invasion Process Of Pore - Fractured Tight Sandstone

Tight sand gas is an important component of unconventional gas resources. However, low permeability is the main characteristic of tight gas reservoirs. Moreover, tight gas reservoirs can be easily subjected to a number of different damage mechanisms during drilling and completion operations. Fluid invasion is one of the main damage mechanisms, which may lead to prevent gas reservoirs from discovering in time and evaluating accurately, lower final gas recovery, increase exploration and development cost, and slow down the exploration and exploitation progress. Therefore, it is crucial to understand the law of fluid invasion, the effect of matrix and fracture deformation on fluid invasion, and quantify the invasion radius, which can provide a further understanding of fluid invasion. The article focuses on fractured tight gas reservoirs, by comprehensive utilization of theoretical research, laboratory experiment and numerical simulation method to reveal the mechanism of fluid invasion under hydro-mechanical coupling. The main works of thesis are as follows:(1) Take Sichuan HC area Xujiahe formation as resarch project, reservoir property analysis was carried out, which provided basic petrophysical parameters for further study.(2) Make clear the law of fluid invasion and the distribution characteristic of fluid in fractured tight gas reservoir by visualization experiments.(3) A dual porosity dual permeability model for characterizing fluid invasion in fractured tight sandstone was established. The related code was developed, and was verified by a classic case, which provided a basis for the futher study.(4) Research on matrix and fracture deformation mechanism was conducted by using experiment and simulation method. For studying the effect of seepage pressure and confine pressure on fracture aperture, a series of seepage tests on fractured cores were carried out. The results show that the increase of seepage pressure will disturb the normal stress balance of fracture face, which cause the increase of fracture aperture and the increase of fracture permeability. Make clear the effect of normal deformation and dilatation on hydro-mechanical coupling by numerical simulation. The relationship between volumetric change and matrix petrophysical parameter was analyzed based on linear elastic theory.(5) The research on fluid invasion under hydro-mechanical coupling was carried out. Based on double media theory, convection diffusion equation and previous study, a dual porosity dual permeability model for characterizing fluid invasion under hydro-mechanical coupling was established. The related code was developed, and was verified by available experimental data.(6) A transient numerical simulation was carried out for revealing the dynamic characteristic of fluid invasion under hydro-mechanical coupling. The results show that during the invasion process the pressure difference between matrix and fracture has peak value. The radius of fluid invasion was calculated, and the water saturation profile around the wellbore at different times was obtained.