Hydraulic Fracturing Evaluation and Design Optimization in the W2 Platform Using a Coupled DFN and FEM Model
摘要
The Weiyuan shale gas field faces challenges in fracturing effectiveness due to thin reservoirs and significant horizontal stress variations. This study focuses on the A1 platform of W2 well area, a numerical model for hydraulic fracturing was established using an integrated geologic-engineering approach, coupling the Discrete Fracture Network (DFN) with the Finite Element Method (FEM) to comprehensively incorporate reservoir heterogeneity, natural fracture distribution and the in-situ stress. The fracturing effects of three types of well deployment patterns (sloping well, wide-well spacing, and narrow-well spacing) are systematically analyzed. The results indicated that: (1) the average main hydraulic fracture length reached 124.1 m; (2) large natural fracture zones are the primary cause of well interference, due to excessive fluid leak-off and activation of natural fractures; (3) the stress-shadow effect from synchronized fracturing inhibited fracture growth, leading to fracture steering or the formation of asymmetric fracture networks; (4) under the existing construction parameters, an unstimulated area of approximately 300 m was identified. Based on the above problems, the optimization strategy is proposed: the uniformity of fracture network coverage can be enhanced by reducing fluid volume per stage (by 600 ~ 800 m3) or adjusting cluster design in sections prone to interference. Additionally, well spacing is recommended to be optimized within a range of 220 ~ 500 m. The results of the study provide a theoretical basis for the efficient development of shale gas in complex geological conditions.