Modeling Naturally Fractured Tight Carbonate Reservoirs – A Case Study

Abstract

Kuwait Oil Company (KOC) is engaged in an early phase of development of a giant, tight, fractured carbonate play within the State of Kuwait, spread over a large area covering six fields. The producing reservoirs belong to the geological Formations of Toarcian to Tithonian age. Some reservoirs are characterized by very low porosity and permeability and productivity of these reservoirs is driven by the natural fracture system. This paper described the approach followed in developing a 3D fracture model for these reservoirs. Carefully planned data acquisition resulted in a rich suite of dataset consisting of image logs, conventional cores covering the target pay zones in a number of wells. Analysis of these data gave a clear understanding about fracture orientation, density, aperture, and other fracture parameters. Special 3D seismic processing was carried out to derive a volume curvature attribute, which was able to detect and identify the fracture corridors away from the wells. Structural geological analysis resulted in an understanding of the tectonic history of the area, which helped in genetically relating the identified fracture orientations with the structural evolution. A discrete fracture network was developed for these reservoirs combining the well and seismic attribute data. Parameters like aspect ratio, orientation and aperture of fractures was assigned to different fracture sets based on this analysis. The apertures were corrected for the present day stress effect based on the borehole breakout data. This fracture model was upscaled into the 3D geological model to get the fracture porosity and the permeability tensors. The fracture model was validated by history matching pressure build up and production data and was used for dynamic flow simulation studies for the field development planning.