Multi-scale fracture modelling and its application in shale gas geology and engineering integration

Geology and engineering integration is essential to improve shale gas productivity and efficiency because of the complex geological settings in shale reservoirs.Moreover, the multi-scale natural fracture network is a key component in the integrated geoscience model.To predict the impact of natural fractures on the drilling and fracturing of marine shale gas horizontal wells in southern China, the spatial distribution and stress status of natural fractures were analyzed from the perspective of multiple disciplines including geophysics, geology, petrophysics, and geomechanics.First, seismic pre-stack gathers were conditioned, such as denoising, flattening, and frequency raising gathers, and the partial gathers with a high signal-to-noise ratio in the target layer were selected to stack the ant tracking input.Strict quality control of the ant tracking results was conducted through the manual interpretation of the fracture system, drilling complex events, and horizontal well image log interpretation.The large-, meso-, and small-scale natural fracture predictions of the Longmaxi/Wufeng formation obtained by ant tracking were analyzed, and the discrete fracture model was established by incorporating imaging log interpretation and the multi-scale fracture intensity predicted by ant tracking.According to the different rock stiffness levels with different scales of fractures, the equivalent principle was used to analyze and test the influence of fractures of different scales on mechanical parameters, and geomechanical modeling was used to predict the in-situ stress state of natural fractures.The results indicate that the impact of natural fractures on drilling is not only related to their scale but also to the slip tolerance of the fracture surface, that is, the stability of the fracture.The higher the slip tolerance, the worse the stability of the fracture and the more likely it is to generate mud loss when a horizontal well is drilled.The case study proved that the geomechanical model incorporated the influence of natural fractures and was suitable for hydraulic fracture simulation, allowing the investigation of the interaction between hydraulic fractures and natural fractures during the fracturing process, and optimization of the fracturing design of horizontal wells.