Integrated Evaluation Approach and Implications of High Permeability Streaks in Giant Carbonate OilField

Abstract

Abstract This paper covers a super giant carbonate oilfield in the Middle East that has enjoyed pressure support and voidage maintenance, primarily with peripheral water injection and pattern development in some reservoir units over the last decades. However, premature and non-uniform water front advancement has been a great challenge, resulting in early and uncontrolled water breakthrough with some wells becoming inactive due to increasing watercut. This challenge is mostly attributed to reservoir heterogeneity and particularly to the presence of un-mapped high permeability streaks (greater than 1Darcy) in the carbonate reservoir, usually resulting in by-passed oil and high value of Remaning Oil Saturation with poorer sweep efficiency. As a result, aiming to reach the desired ultimate recovery factor has become a challenge. A multidisciplinary approach involving the integration of various datasets, including geology (core facies and core description), geophysics (seismic stratigraphy), petrophysics (open hole logs, cased hole saturation time-lapse logs, and cased hole production logs), reservoir and production engineering (actual wells performance), and drilling data (mud losses, pilot hole) etc, were used to identify the high permeability streaks aerially and vertically within the reservoir. These high permeability streaks were then tested in the 3D dynamic model with various sensitivities to assess the impact on the reservoir performance in order to improve the match with the actual performance. The preliminary results were further validated by acquiring more data and gaining deeper understanding from Pulse Neutron logs, Injection and Production Logging, Flow tests, Pressure Transient Analysis etc. In order to reactivate inactive wells, increase production performance, and improve the sweep efficiency, targeted water shut-off was carried out to isolate the watered out intervals. Injection and Production logging gave more insights to understanding injection conformance and reservoir performance with adequate measures taken to ensure optimal reservoir management. In addition, areas with by-passed oil were targeted with revised well completion, infill drilling and artificial lift strategies. This paper describes the approach used, challenges encountered, results obtained, and the way forward.