Hydraulic fracture treatments are used in low permeability shale reservoirs in order to provide conductive pathways from the reservoir to the wellbore. The success of these treatments is highly reliant on the created fracture conductivity. Optimizing fracture designs to improve well performance requires knowledge of how fracture conductivity is affected by rock and proppant characteristics.
This study investigates the relationship between rock characteristics and laboratory measurements of propped and unpropped fracture conductivity of outcrop sample from the Eagle Ford shale and the Fayetteville shale. Triaxial compression tests were performed on core specimens in order to determine the Young's Modulus and Poisson's Ratio of the outcrop samples. Profilometer surface scans were also performed to characterize the fracture topography.
The results from this study show that the main factors affecting fracture conductivity are closure stress and proppant characteristics (concentration, size, and strength). For unpropped fractures, the fracture topography is the main factor in determining fracture conductivity. The topography interaction of the two surfaces determines the fracture width. Higher Young's Modulus helps maintain fracture width by resisting deformation as closure stress increases compared with lower Young's Modulus. For propped fractures, the more influential factor in determining fracture conductivity is proppant characteristics (concentration, size, and strength). At a proppant monolayer placement, the major mechanism for conductivity loss is proppant embedment, leading to decreased fracture width. A higher Young's Modulus reduces the proppant embedment and better maintains fracture conductivity as closure stress increases. For a multilayer proppant pack concentration, the effect of rock characteristics is negligible compared to the effect of proppant pack characteristics.