Investigation of Microscopic Pore Structure and Permeability Prediction in Sand-Conglomerate Reservoirs

The microscopic pore structure of sand-conglomerate rocks plays a decisive role in its exploration and development of such reservoirs. Due to complex gravels-cements configurations and resultant high heterogeneity in sand-conglomerate rocks, the conventional fractal dimensions are inadequate to fully characterize the pore space. Based on the Pia Intermingled Fractal Units (IFU) model, this paper presents a new variable-ratio factor IFU model, which takes tortuosity and boundary layer thickness into consideration, to characterize the Triassic Karamay Formation conglomerate reservoirs in the Mahu region of the Junggar Basin, Northwest China. The modified model has a more powerful and flexible ability to simulate pore structures of porous media, and the simulation results are closer to the real conditions of pore space in low-porosity and low-permeability reservoirs than the conventional Pia IFU model. The geometric construction of the model is simplified to allow for an easing of computation. Porosity and spectral distribution of pore diameter, constructed using the modified model, are generally consistent with actual core data. Also, the model-computed permeability correlates well with experimental results, with a relative error of less than 15%. The modified IFU model performs well in quantitatively characterizing the heterogeneity of sand-conglomerate pore structures, and provides a methodology for the study of other similar types of heterogeneous reservoirs.