Modeling of Hydraulic Fracture Height Containment in Laminated Sand and Shale Sequences

Abstract

Abstract The results of hydraulic fracture modeling in a hydrocarbon reservoir consisting of laminated sand and shale sequences are presented. Work previously published by other authors addresses hydraulic fracture growth characteristics in layered intervals, but little published information is available for growth in thin-bedded reservoirs. For the purposes of this paper, thin beds are considered to be on the order of less than 6 inches (15 cm) in thickness. In certain reservoirs, there may be thousands of these thin beds involved in influencing hydraulic fracture growth. The hydraulic fracture modeling is based on data from the North LaBarge Shallow Unit (NLBSU) located in the Green River basin of Wyoming. The NLBSU produces hydrocarbons from the Cretaceous-age Mesaverde interval. This reservoir is comprised of laminated sand and shale sequences. Hydraulic fracturing is necessary for economic production. Actual field data from two NLBSU wells is used in the analysis. The data includes stimulation treatment pressures and information, as well as a radioactively tagged fracture treatment. The hydraulic fracture modeling software GOHFER is used in the analysis. GOHFER is used based on its ability to approximate decoupled rock deformation with shear-slip, and its extensive use in the industry. The results of this study strongly indicate that the sand and shale laminations present in the Mesaverde reservoir act as a hydraulic fracture height containment mechanism. Two events are presented as the reasons for this observed containment. First, shear slippage is prevalent due to the numerous interfaces present in the subject depositional environment. These interfaces inhibit fracture growth through shear failure. Second, the contrast in rock mechanical property values between the sand and shale intervals reduce the fracturing energy available for fracture propagation. Further research in this area is strongly recommended due to the significant oil and gas reserves associated with this type of reservoirs. These additional research areas include laboratory investigations and field work with tiltmeter and microseismic analysis. Meanwhile, fracture modelers are strongly encouraged to evaluate the effects of laminations in their modeling efforts.