Geochemistry for Unconventional: Hydrocarbon Phase (e.g., API Gravity, GOR) Prediction, Production Allocation, and Reservoir Monitoring
Wahid Rahman, PhD
Research Geochemist, Geoscience and Petroleum Research Inc., Houston, Texas
Geochemistry data (source rock maturity, maturity equivalent from oil, bulk molecular compositions (GC) and biomarker (GCMS) ratios) from the extracts of cored or cutting samples vs produced oil from well head have been compared to predict oil family types, migration, mixing of hydrocarbon between various reservoired oils, GOR (gas-to-oil ratio), and allocate production contribution to different reservoirs from different US on shore basins (e.g., Anadarko, Permian, Eagle Ford and Rockies basins). Furthermore, the predicted GOR (gas-to-oil ratio) values from the same oil chemistry data are well matched with the produced GOR and estimated GOR from the recombined fluid samples.
Molecular geochemistry data of rock cuttings collected during drilling can be a cost-effective way to provide a better understanding of hydrocarbon composition and production contribution within a lateral well. Studies have shown that molecular chemistry data can be used via many statistical techniques to identify the end member contribution from different wells or from whole basin. But molecular chemistry (GC, GCMS) from a single well application to allocate production contribution is relatively less understood because of failure to pinpoint the end members hydrocarbon from different horizon. A system of machine learning methods is used to evaluate each feature’s ability to discriminate samples and determine representative features showing variation between different formations or sublayers. Deep learning regression methods are used to quantify end member contributions to the commingled produced oil.
These case studies highlight many important ways in which geochemistry can be used to better evaluate unconventional reservoirs: 1) by identifying the existence and extent of hydrocarbon migration, 2) by predicting and understanding the quality and type of petroleum fluids stored in tight, unconventional source rocks, 3) by explaining high GOR anomalies as the result of multiple charging episodes in certain areas in tight reservoirs and 4) finally to properly identify the host rock end members and allocate the production accordingly.
Dr. Wahid Rahman is currently working as a Petroleum Geochemist at Geoscience and Petroleum Research Inc, Houston, Texas, USA. Dr. Rahman has previously worked as Chief Geochemist at Paladin Geological Services, Edmond, OK, Geological Adviser at Ossidiana Energy, Denver, CO, Staff Geochemist at Pioneer Natural Resources, Irving, Texas and as Sr Geochemist at Devon Energy, Oklahoma City, OK. Dr Rahman has 19+ years of industry, academic, and research experience in the field of geochemistry, basin modeling, petrophysics, reservoir engineering, and geology; worked on the most of the North American onshore unconventional and conventional petroleum plays/basins. Dr Rahman’s research interest include organic geochemistry, production allocation, reservoir geochemistry, basin modeling, conventional and unconventional resource play evaluation, HC migration pathway analysis, thermal maturity of organic matter (OM) and hydrocarbons (oil and gas), and application of geochemistry to calibrate petrophysical and reservoir PVT properties (e.g., GOR, pressure gradient, kerogen/OM density, LOM, Bo etc). He also uses water geochemistry to figure out reservoir continuity, formation evaluation, water resistivity (Rw), water saturation (Sw), and production allocation. Dr Rahman has over 35 published
conference papers, and peer-reviewed journals (with more than 600 citations) in the field of geochemistry, environmental geochemistry, geology and petroleum engineering. He received his Ph.D. in Geochemistry from Southern Illinois University, Carbondale, IL; Masters in Geology from Auburn University, Auburn, AL; another M.S. and B.S. in Geology from University of Dhaka, Dhaka, Bangladesh.
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