Optimum Well Completion Strategies in Tight Oil Reservoirs

Abstract

Hydraulic fracturing is currently the completion of choice in most tight reservoirs; however, the ultimate performance of fractured wells is severely affected by the interfering effects inside the fracture and inter fractures. Previous simulation studies investigated the effects of well spacing and fracture length on well productivity in low-permeability oil and gas reservoirs. It was shown that the most important parameters for determining the optimum fracture length are the formation permeability and the stimulated reservoir volume. Although a number of studies have examined the performance of horizontal fractured wells and fracture geometry effect, fracture spacing and intersecting angles in vertical and horizontal wells should be further investigated. This study presents the results of a tight oil reservoir in the Bakken shale. Reservoir parameters considered include local rock stresses, rock compressibility, absolute and relative permeability, and porosity. The well-completion parameters included fracture length, height, width, conductivity, number and spacing between fractures, fracture intersecting angle, and cased vs. open-hole completion. Fracture modeling considered rigorous description of the hydraulic fracture properties and finite difference reservoir modeling. Economically attractive reserves recovery were modeled through multiple fracture placements in a 10,000 ft horizontal well. Numerical simulation showed that oil recovery increased between 8 to 15% while net present value (NPV) increased 8 to 24%, as the number of fractures increased. Based on the critical assumptions in the study (permeability, natural fracture distribution and stress orientation), an optimum number of fractures was identified. Open hole completions provided better performance in most cases, and recovery was greater for a higher number of contributing perpendicular vs. longitudinal fractures. The results of the study may hopefully be used to improve the understanding of the role of fracture geometry, spacing and open/cased-hole completion strategy to enhance operators optimum completion design.