NEW STOCHASTIC ASSESSMENT OF FRACTURE INTERCONNECTIVITY AND IMPLICATION FOR HYDRAULIC FRACTURING OPTIMIZATION FOR UNCONVENTIONAL FRACTURED RESERVOIRS

Recent developments in hydraulic fracturing technology have facilitated high gas production rates from shale and have had a strong impact on the U.S. gas supply and markets. The interconnectivity of a fracture system may significantly alter the reservoir hydrologic properties in that interconnected fractures can provide preferred and complicated paths for fluid flow and transport, thus enhancing the reservoir heterogeneity. Accurate characterization of fracture network will increase understanding of the unconventional reservoir heterogeneity and provide important information for hydraulic fracturing optimization in unconventional fractured reservoirs.

We have developed a workflow for stochastic assessment of the interconnectivity of fracture network based on discrete fracture network (DFN) modeling and 3-D fracture permeability characterization. Fracture networks are realized and visualized using the stochastic distributions of fracture properties (size, orientation, spacing, aperture, etc.) as measured from field investigations, well logs, and/or core data. Fracture permeability is characterized with a 3-D full permeability tensor technique to account for the geometry of each individual fracture. Three typical scenarios of fracture systems have been analyzed for detailed fracture interconnectivity assessment. For a fracture system with moderately to highly concentrated fractures, the interconnectivity of fractures is generally low, which indicates that the hydraulic fracturing will be most effective only if the hydraulic fracture is perpendicular to the mean direction of the fracture system. A DFN model with randomized fracture orientations could yield high fracture interconnectivity with no preferred direction. Modeling of fracture interconnectivity indicates that there exists no preferred direction for hydraulic fracturing to be most effective.

The proposed method has been applied to the Devonian Chattanooga Shale in Alabama. Two fracture sets have been identified and modeled into a DFN model. Hydraulic pathway analysis indicates that hydraulic fracturing can be equally effective for hydrocarbon fluid/gas exploration as long as its orientation is not aligned with that of the regional system fractures.