Constraints of three-dimensional geological modeling on reservoir connectivity: A case study of the Huizhou depression, Pearl River Mouth basin, South China Sea

The Z21 gas field is the only one gas field in the Huizhou depression. The distributions of sandstone and mudstone in the adjacent west zone control the extent of the Z21 gas field, making the confirmation of the reservoir connectivity between the west zone and main zone (RCWM) crucial. In this study, a practical workflow was proposed to confirm the RCWM. First, the sandstone and mudstone distributions were modeled by a sequential indicator simulation, using the vertical proportion curves as constraints. The porosity and permeability distributions were then predicted using a sequential Gaussian simulation based on sandstone and mudstone models. The sandstone, mudstone, and physical property models were treated as components of a geological embryonic model (GEM) prior to the RCWM confirmation. Different hypotheses on the RCWM of the GEMs were drawn, bringing variations to the GEMs and the GEMs turned to be different new models. These new models were then applied to numerical simulations, not only to perform quality checks, but also to attain the simulated formation pressure coefficients (Pfcs) and couple the study with the current formation pressure coefficients (Pfcc) derived from the modular formation dynamics tester (MDT). A hypothesis is negated if the Pfcs is not equal or approximately equal to the Pfcc. A coupled result was iteratively generated until the RCWM was confirmed. This coupling study on reservoir connectivity makes use of general geological reservoir models and highlights the ingenious designs based on different hypotheses of the RCWM to generate reliable results. Coupling study shows that distributions of formation pressure in the west zone of Z21 field are largely affected by a low-permeability belt and RCWM is proved weak due to the existence of the low-permeability belt.