Research on Discrete Numerical Simulation of Fracture-Cave Unit in Carbonate Reservoir

Fracture-cave units in the carbonate reservoir are seriously discrete and random in the distribution, so existing numerical simulation is not fit for the reservoir. A regular discrete fracture-cave distribution mode was established according to geophysical recognition and prediction results of caves and fractures in the carbonate reservoir as well as statistical characteristics of physical parameters;then, a discrete numerical simulation method was developed for the fracture-cave unit based on fracture connection flow coefficient and elastic accumulation coefficient of caves. It took account of fracture anisotropism, non-Darcy effect of fracture fluids and gravity differentiation effect of cave oil-water. Feasibility and reliability of this simulation method were verified based on production history data of TK472C single-well fracture-cave unit and TK630 multi-well fracture-cave unit. The results showed that, the discrete numerical simulation method of fracture-cave reservoir was feasible and reliable and could be used for numerical simulation of the carbonate reservoir. Finally, effects of injection-production parameters on water-flooding development were analyzed based on geological model of TK472C single-well fracture-cave unit and TK630 multi-well fracture-cave unit subject to history matching. The results showed that, bottom water driving should be selected in the fracture-cave reservoir with strong bottom water;a certain amount of water could be injected into the fracture-cave unit with weak bottom water to increase formation energy and control bottom water coning to some extent;for TK630 multi-well fracture-cave unit, water injection and fluid production rate of 3% could be taken when the recovery percentage was up to 8%-10%, in order to reach the better water-flooding development.