Experimental and theoretical investigation on the conductivity of complex fracture network in unconventional gas reservoirs

With the depletion of conventional oil and gas resources, unconventional oil and gas resources have become crucial as alternative hydrocarbon sources. Unconventional gas reservoirs typically have low porosity and permeability, requiring reservoir stimulation to create complex fracture network. Unlike single fracture, the fracture network exhibits complicated structures due to multiple fractures and their various distribution manners. To study the conductivity of complex fracture network, a new conductivity chamber is designed based on the discretized fracture network model. Experiments and orthogonal analysis are conducted to investigate the effect of critical influential factors such as fracture network structure, fracture height, proppant concentration, proppant diameter, and proppant type on the conductivity of complex fracture network. The experimental results demonstrate that compared to the single fracture, the conductivity of T-shape, F-shape, E-shape, ╪-shape, and Ɨ-shaped fracture networks increased by 49%, 131%, 150%, 188%, and 201%, respectively. Closure pressure and secondary fracture distribution significantly impact the conductivity of complex fracture network. Proppant diameter and proppant concentration also have substantial effects. Compared with existing experimental studies focusing on single fracture conductivity, this study presents experimental research on the conductivity of complex fracture network, thereby addressing a research gap in this field. Through synergistic integration of the Kozeny-Carman hydrodynamic theory with the hydraulic-electrical analogy principle, an innovative model of fracture network conductivity is formulated. The advantage of the proposed fracture network conductivity model lies in its systematic integration of theoretical analysis with experimental validation methodologies, effectively bridging the gap between computational predictions and laboratory observations. This study provides valuable insights for optimizing volume fracturing in tight reservoirs, facilitating their rapid and efficient development.