Optimum Logging Suite Design for Characterization of Shaly Sandstones as a Part of Brown Field Exploration Campaign in West Kazakhstan

Abstract

Re-exploration of the existing oil fields is one of the main projects for many oil and gas companies operating in West Kazakhstan. As a part of one of such campaign carried out in 2015, the optimum logging suite was designed to acquire more detailed information about static and dynamic properties of the clastic shaly sand reservoir. It included standard logging suite, nuclear-magnetic tool and wireline formation tester. The studies were conducted in the exploration wells drilled in three different fields with different reservoir properties in order to obtain the most complete information about the formation and locate bypassed reservoirs. Wireline formation tester, in addition to standard solutions such as formation pressure and mobility profiling, downhole fluid sampling, allowed to clearly identify the reservoir saturation in the zones, where it was not possible to do with standard logging suite. Fluid analyzers integrated into the formation tester toolstring helped to clearly identify fluid type, hydrocarbon composition and vital physical and chemical properties of the formation fluid. All measurements were carried out in real-time; the decisions about acquiring downhole samples were taken situationally, not prescriptively. Study mainly focuses on thinly laminated complex clastic reservoirs with high shale content that have high uncertainty in formation water salinity estimates. As the result of this work: new oil reservoir was discovered in Middle Jurassic deposits in first field, heavy oil downhole samples were acquired in unconsolidated Lower Cretaceous sands and highly depleted gas reservoir was discovered at a depth of 400 m in the second field. In the third field, a few oil bearing intervals discovered in sub-salt low permeability Permian-Triassic formation and the most promising intervals were tested with wireline formation tester, based on this information the decision was made to drill another wells in this area to better characterize the reservoir. The integration of wireline formation tester, standard and nuclear-magnetic logging suite data, and the results of formation fluid laboratory analysis allowed to create 3-d single well simulation model to estimate the well productivity and optimize well completion design. The results of this analysis were compared with real well test data. The study shows a modern approach to the planning of additional exploration activities in producing fields fined-tuned to locate and evaluate bypassed hydrocarbon intervals, and confirm their productivity. Integrating the results of different logging suites with single well predictive modeling allowed to understand better the total well productivity. Moreover, it can further be used to optimize the completion of future wells.