Pressure Transient Analysis of Horizontal Wells in a Naturally Fractured Reservoir

Abstract

ABSTRACT This paper presents case histories for a number of horizontal well pressure tests in the Bakken Formation of the Williston Basin. The Bakken formation is a very rich organic source rock with extensive natural fracturing present due to regional tectonics, localized structure, and internal expulsion forces. Numerous operators are currently attempting to exploit this vast resource with the utilization of horizontal wells. Pressure surveys have been carried out on a number of these horizontal wells. The pressure transient tests were generally designed to obtain information related to original reservoir pressures and the potential skin damage effects. However, complexities introduced by horizontal well dynamics have made it difficult to interpret these welltests using conventional techniques. A combination of analytical and numerical methods is used to provide a consistent interpretation of the well tests taking into account the possible dual porosity nature of the reservoir. In addition, the orientations of the wells provide some evidence to support arguments about permeability anisotropy in the reservoir. Anisotropic effects are of special interest in horizontal well applications as a critical consideration in the orientation of horizontal wellbores. To date, the orientation of horizontal wells has been relatively random and has been directly influenced by both geographic or land consideration, and structural interpretation. Numerical studies have been carried out on a state-of-the-art numerical simulator which provides specific capabilities for horizontal completions, local grid refinement, and dual porosity/permeability systems.