MULTI-SCALE 3-D MODELING OF YANCHANG SHALE GEOLOGICAL STRUCUTRE CONSIDERING LAMINAS AND FRACTURE NETWORKS

Outcrops and core observations show that sandy and tuff aceous laminas and natural fractures are well developed in the continental shale gas reservoir. This study reports the distribution of laminas and natural fracture networks at different scales and established the 3-D geological structure models, with data obtained from outcrops, wells and cores of Yanchang shale from southern Ordos Basin. Firstly, based on two-dimensional fracture field investigations, a 3-D joint network model of the study area was built using the Monte Carlo simulation method. Then the laminations were identified from macroscopic scales to microscopic scales with multiple probe techniques. Statistical analysis of multi-scale layer thickness suggested that the average thickness of layers at multiple scales showed a fractal feature, with average layer thickness of 2.26 m, 2.09 dm, 1.70 cm, 1.48 mm and 11.7 μm, corresponding to meter scale, decimeter scale, centimeter scale, millimeter scale and 10-micro meter scale respectively, and that the layer thickness at studied scales all followed with an exponential probability distribution. The fitting curves indicated that most of laminas at each scale were relatively thin. In other words, the thicker the layer, the less the number of layers contained in shale. Finally, the lamination models were constructed and superposed over the joint network model to generate 3-D geological structure models at various scales. The models were validated by reproducing fracture and lamina parameters, which were fairly close to those measurements of realistic geological bodies in the study area. The findings of this work could shed light on the characterization and modeling of geological structure for the numerical simulation and physical model test of hydraulic fracturing in shale gas reservoir.