| Summary: | 碩士 === 國立成功大學 === 資源工程學系 === 103 === The purpose of this paper is to analyze pore pressure as function of time and, based on critical stress fracture theory, to calculate the critical pore pressure that causes faults to react. We also estimated the potential of fault slips in situ.
The Mohr–Coulomb failure criterion and Coulomb friction criteria are used as basic theory in this study. We used them in critical stress fracture theory to derive critical pore pressure equation, which is expressed by minimum horizontal stress, vertical stress, maximum horizontal stress, the coefficient of internal friction, and the fault plane’s normal vector. The solution was verified both in an infinite reservoir and in a no-flow boundary reservoir by comparing the results of the proposed analytical solution with the output of a standard numerical solution. We used pressure change with time at specific locations, wellbore locations, and fault locations in the reservoir, which showed that the pressure solution could be used to forecast pressure change with time at any location in the reservoir. Then, using the pressure solution to analyze pore pressure change with time, we calculated the critical pore pressure that causes faults to slip, and we estimated the potential of fault slip in an ideal model. Using this ideal model, we assumed the same reservoir parameters, fluid parameters, and stress state to investigate the effect of fault dips and the coefficient of internal friction on critical pore pressure.
We selected a depleted reservoir in the Tiezhanshan KCL layer as the target. Using a simulator to obtain a structural model by digitizing the layer’s top structure and fault location, developing a geological model by inputting geological parameters, fluid parameters, and stress states. The numerical model was developed by using a simulator and entering well configurations and operating conditions into the geological model. We studied whether carbon dioxide injection caused fault slips in faults that were originally present in the KCL layer. We also output pressure change with time at the locations that, based on the numerical analysis, had greater possibilities for fault slips. These locations included (1) the longest distance from the injector to the fault, (2) the highest corner of the fault, and (3) the shortest distance from the injector to the fault. The critical pressure perturbation 200 years after injection at these locations was calculated, and the potential of a fault slip at these locations was estimated using critical pressure perturbation.
|
|---|
