Integrating Drilling-Fluid Optimization and New Technology Improves Carbonate Reservoir Evaluation

Abstract

Abstract Wireline formation testing in low permeability carbonate reservoirs of the U.A.E. has been challenging with frequent tool plugging, extended pumping time, and multiple trips out of the hole. A recent well, drilled offshore Abu Dhabi for ADMA-OPCO, penetrated the main three reservoirs and presented a rare opportunity to address these challenges. The tested intervals contain multiple thin zones, which make it difficult to predict reservoir fluid types from open-hole logs or pressure gradients alone. An extensive Downhole Fluid Analysis (DFA) program was needed for fluid types and contacts determination. A multidisciplinary team between the operator and the service company was organized to carefully consider the challenges mentioned above, identify the source problems and recommend a solution. The solution involved the economically viable replacement of the drilling fluid with a low solid content fluid prior to the wireline formation testing operations. A new wireline formation tester technology, the Extra Large Diameter module (XLD), was also recommended to replace the dual-packer at a broad permeability range. The combination of drilling fluid displacement, XLD utilization and the addition of two pumps proved to be major factors in reducing the overall job duration, rig time, and smoothly achieving the required objectives. As the results, a record job including 27 DFA stations (16 with samples), 2 mini-frac stations and in access of 90 pressure points were achieved. The DFA and samples provided significant answers and clues to a broad range of reservoir issues including compartmentalization, fluid compositional variation, the unexpected identification of oil, oil reserve assessment, and gas compositional analysis to understand its origin and potential contact migration. The wireline formation testing results have added direct values to reservoir evaluation and development. In this work, a best operating practice for similar reservoirs is demonstrated.