Compositional simulation of fractured shale reservoir with distribution of nanopores using coupled multi-porosity and EDFM method

Shale reservoir contains highly heterogenous pore systems due to the wide-range distributions of nanopores in shale matrix and hydraulic/natural fractures. To explicitly include pore size distribution in simulation of shale reservoir, a multi-porosity model is applied to subdivide the matrix into multiple continua based on experimental pore size data. Each continuum has its own pore size, porosity and permeability, as well as other petrophysical properties. Besides, the embedded discrete fracture model (EDFM) is coupled with multi-porosity model to describe the complex fractures networks with any angles and intersections. To evaluate effects of pore size distribution on production, compositional simulation is conducted in a fractured shale reservoir using different number of continua in shale matrix. Simulation results show that the use of multiple continua results in lower oil and gas production. Different pressures, oil and gas saturations and compositions are observed in different continua. To further investigate the effects of distribution of nanopores, oil-gas capillary pressure is rigorously calculated in every continuum. The existence of large capillary pressure leads to different fluid properties in different size of nanopores. Moreover, capillary pressure reduces oil and gas recovery and alters compositions of residuals. The effects of capillary pressure are more significant in the low permeable continua due to smaller pore sizes.