Study On Crack Propagation Mechanism Of Low Permeability Reservoir In Water Injection Development

Waterflooding, as the most economic and effective technology, has been widely applied to improve oil recovery in low permeability reservoir development at home and abroad. From a macroscopic view:When water injection pressure is too small, the formation energy is not supplement effectively, crude oil recovery yield will be greatly decreased, however, when water injection pressure is too large, water swept volume decline, and it will also reduce recovery of crude oil. The research results on the mechanism of viscoelastic fluid’s micro-displacement show that, for the pore-fracture dual media, capillary pressure can absorb water and drain oil easily when seepage velocity is slow, and driving force play a significant role in oil recovery when seepage velocity is high. Therefore, either from the viewpoint of the micro or from macro, determining injection-production parameters is very important for the influence law of reservoir crack propagation.Based on plenty of theoretical and experimental researches, this paper reveals the dynamic variation of the reservoir fracture mechanics in the development process, as well as the influence factors such as water injection parameters on the influence law of crack propagation by the way of theoretical analysis, numerical simulation and field data contrast check. Combining with geomechanics, rock-soil mechanics, fracture mechanics and seepage flow mechanics and so on, a seepage-damage-stress coupling mathematical model of the reservoir fracture was established, at last, using the Rock Failure Process Analysis System (RFPA) to simulate the dynamic extension process of the fracture reservoir under the condition of different injection-production parameters, and analyze comprehensively the dynamic change rule of the seepage and stress in the reservoir. Comparing reservoir fracture state under a variety of working conditions, the best state injection-production parameters of crack propagation was concluded. The research results can provide important theoretical guidance to transform reservoirs and optimize well pattern arrangement in low permeability development.The main research achievements are as follows:1. The dynamic variation mechanics of the fractureAccording to the practical geological characteristics of Toutai field, the fracture criterion was established to describe the crack shape changes in the extension process.2. Crack propagation mathematical model was established1) Based on rock-soil mechanics, fracture mechanics and seepage flow mechanics, the seepage-stress-damage coupling model of the low permeability reservior was established.2) The crack propagation process under different conditions has been simulated by the finite element method, this paper analyze the dynamic change rules of the seepage and stress, and crack propagation mechanism.3) Comparing simulation results with the field data, it is found out that the research results coincides with observational data in the Toutai field, the research results can provide important theoretical guidance to the waterflooding development in low permeability reservoir.