Formation of Complex Fracture Networks in the Wolfcamp Shale: Calibrating Model Predictions with Core Measurements from the Hydraulic Fracturing Test Site

Abstract

Natural fractures are a crucial factor in determining fracture and well spacing in horizontal wells. Their attributes affect the created fracture network and thereby the well producivity and EUR. However, information about the properties of natural fractures is seldom available. In this study, we used a detailed core description from the Hydraulic Fracture Test Site (HFTS), funded by the DOE and an industry consortium, to obtain in-situ natural fracture distribution data. The data was used as input into a hydraulic fracturing simulator to model fracture growth in the presence of natural fractures. The results obtained were then compared with field observations of cores taken from a slant infill well drilled into the hydraulically fractured rock. The core taken from the slant well located adjacent to the hydraulically fractured well is used to characterize the natural fractures (density and orientation). A two-dimensional discrete fracture network (DFN) is generated based on the core description. Nine coring operations are simulated on the created DFN to generate synthetic core descriptions. Attributes (length and density) of natural fractures are calibrated to match the results obtained from simulated coring operations with real core data. Multi-stage hydraulic fracturing simulations are performed using the calibrated DFN, and the results are presented in this paper. The core analysis identified three different types of fractures: hydraulic fractures, intact natural fractures, and natural fractures activated by hydraulic fractures. The density and orientations obtained from the core description provide valuable insights on the complex fracture growth behavior. The number of created fractures (propped and unpropped) far exceeds the number of perforations. This indicates the formation of complex fracture networks likely caused by the interaction of the hydraulic fracture with natural fractures and bed boundaries during propagation. A heel-side bias of fluid and proppant distribution within a stage was also observed. The effect of inter-stage stress shadowing on fracture growth could also be inferred.