Study On Mechanism And Optimization Of Gas Injection For Oil In Cave - Type Reservoir

Some fracture-cave units controlled by single well in fractured-vuggy carbonate reservoirs lack natural energy, which leads to rapid decline of production. Having applied the water huff and puff, Tahe Oilfield has improved their exploitation. However, the effect of water injection weakens in the production process. So it is necessary to seek new method for exploitation of fractured-vuggy reservoirs. Focusing on the research of gas huff and puff mechanism in fractured-vuggy reservoirs, this thesis has investigated the theoretical model of fluid flow mechanism and exploitation methods of fractured-vuggy reservoirs home and abroad. Taking Tahe Oilfield for example, this thesis referred to the technology of gravity drainage, analyzed the mechanism of gas huff and puff, and utilized the model of TK404well to research the feasibility of gas huff and puff and optimize its simulation.With the case study of the4th District of Tahe Oilfield, a typical fractured-vuggy carbonate reservoir in China, this thesis analyzed the geological features of fractured-vuggy reservoirs, evaluated the effect of water injection exploitation and concluded that after water injection, some fracture-cave units will face the problems of increased water cut and a great amount of remaining oil exists in structural high positions. Following the steps of gas huff and puff, this thesis conducted a theoretical analysis from the aspects of energy, gravity drainage and miscible displacement. Based on the experimental data of PVT, this thesis conducted a history match of the formation fluid features of Tahe Oilfield and evaluated the possibility of miscible flooding. Under the guidance of the mathematical model of equivalent medium, this thesis built an ideal vug model to conduct a numerical simulation research on gas huff and puff mechanism with Eclipse. As for the influence factors of gas huff and puff, gas type for injection, formation fluid viscosity, unit’s connectivity and well positions were discussed and analyzed. Finally, by utilizing the geological model and means of production of TK404well of Tahe Oilfield, a numerical simulation is carried out, a gas huff and puff project design is made on the basis of history match, and an optimized research is conducted with regard to the injection pattern, cycle injection volume, injection rate, soaking time, production rate and the number of injection cycle.From intensive research this thesis drew conclusions:during gas huff and puff, the density difference between displacing phase and displaced phase plays the key role, while energy supplementing and miscible displacement play minor roles. These research results may contribute to the development of gas huff and puff in fractured-vuggy reservoirs.