Application of Geochemistry on Assessment of Petroleum Fluid Phase Behavior, Migration, Production Allocation, Reservoir Monitoring, and Petroleum Systems Analysis: Case Studies from a US On-shore Unconventional Shale and Tight Reservoir

Mohammad "Wahid" Rahman, Ph.D. 

Petroleum Geochemist| Director, Geoscience and Petroleum Research. Inc

Irving, Texas, USA

Abstract

It is hypothesized that oils migrate in an up-dip direction, but the extent of the migration has not been well documented. This study provides new insights as to the extent of this self-sourced petroleum and its characteristic phase behavior. Source rock maturity, carbon isotopes, produced oil chemistry, and biomarker ratios were all analyzed and compared to better understand migration and self-sourcing in the study area. In the paper, major emphasis is given to the Woodford Shale, which is one of the most prolific unconventional petroleum reservoirs in the United States. Within the study area, the petroleum produced from this reservoir is self-sourced with a significant component having migrated in from deeper in the basin.

This geochemical work was performed on well cuttings, cores and oils extracted from source rocks; as well as produced oils from the reservoir. Sampled Woodford organic-rich shales contain very little vitrinite; however, they contain abundant solid bitumen. Thermal maturity data from solid bitumen were converted to a vitrinite reflectance equivalent (Jacob, 1989) and compared with pyrolysis data (e.g. Tmax and Hydrogen Index). Both methods were found to be in excellent agreement. Source rock maturities vary across the area of study from early oil (~0.70 % Ro) to gas windows (~>1.35 % Ro) and approximately follow the present-day structural depth of the Woodford source rock.

Produced oil geochemistry data (specifically bulk molecular compositions, isoprenoid distributions, saturate and aromatic carbon isotopes, and biomarker ratios) from several wells suggest a common Woodford source; however, the oil maturities (e.g. Ro  equivalent from biomarkers) are significantly higher than the Woodford source rock in many locations. 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. These findings support the interpretation (Peryum et al., 2018; Peryum et al., 2017; Rahman et al., 2017a; 2017b) that production from several Woodford wells includes migrated hydrocarbons from a deeper source. This study highlights 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, and 3) by explaining high GOR anomalies as the result of multiple charging episodes in certain areas in tight reservoirs (e.g. Meramec). The approaches described in this paper can be utilized to predict, understand, and more accurately classify unconventional reservoirs all over the world.

References:

• Peryum, T., Parks, S., Veach, D., and Rahman, M.W., 2018, Multiple Generations of Hydrocarbon Charge in the Mississippian Reservoirs of the Stack Play, Central Oklahoma: Evidence from Structural, Production and Geochemical Data: AAPG Datapages/Search and Discovery Article ©2018 AAPG ACE 2018 Meeting, Salt Lake, Utah, USA, July 23-25, 2018
• Rahman, M.W., Veach, D., Jayakumar, R., and Esmaili, S., 2017a, Application of Organic Geochemistry on Assessment of Fluid Behavior and Oil Migration within the Woodford Shale in the Anadarko Basin: In Unconventional Resources Technology Conference, Austin, Texas, 24-26 July 2017. Society of Exploration Geophysicists, American Association of Petroleum Geologists, Society of Petroleum Engineers. (DOI 15530-urtec-2017-2688342).
• Rahman, M.W., Peryum, T., Veach, D., Homan, M., Anderson, J., and Price, B., 2017b, Geochemical Fingerprinting and Fluid Phase behavior of Produced oils from Meramec and Woodford Reservoirs from the STACK Play, Anadarko Basin: AAPG Datapages/Search and Discovery Article #90309 ©2017 AAPG Mid-Continent Section Meeting, Oklahoma City, Oklahoma, September 30 – October 3, 2017.
• Peryum, T., Rahman, M.W., Anderson, J., Parks, S., and Veach, D., Woodford-Sourced Oil in the Mississippian STACK Play: A Two-Phase Migration Model: AAPG Datapages/Search and Discovery Article #90309 ©2017 AAPG Mid-Continent Section Meeting, Oklahoma City, Oklahoma, September 30 – October 3, 2017.
• Jacob, H., 1989, Classification, structure, genesis and practical importance of natural solid oil bitumen (“migrabitumen”): International Journal of Coal Geology 11, 65-79.

Speaker Dr. Mohammad Rahman​​​​​​​

Dr. Mohammad “Wahid” Rahman is currently working as a Petroleum Geochemist| Director at Geoscience and Petroleum Research Inc, Irving, Texas, USA. Dr. Rahman has years of industry (Devon Energy, Pioneer Natural Resources and working for many US/international E&P and environmental companies as adviser), academic, and research experience in the field of geochemistry and geology; provided geochemistry services for most of the North American onshore unconventional plays/basins, and conventional petroleum plays, basin modeling, behavior of reservoir fluids, petrophysical data calibration, and reservoir characterization. Wahid’s research interest include organic geochemistry, isotope geochemistry, onsite geochemistry, conventional and unconventional resource play evaluation, HC migration pathway analysis, thermal maturity of organic matter (OM) and hydrocarbons (oil and gas), relationship between OM maturity versus Gas Oil Ratio (GOR), pressure gradient, kerogen/OM density, formation water geochemistry to figure out reservoir continuity, water resistivity (Rw), water saturation (Sw), inorganic geochemistry, well completion geochemistry, stable isotope geochemistry, production allocation, production prediction, and reservoir geochemistry. Wahid has over 40 conference presentations, papers, and peer-reviewed journals in the field of geochemistry and geology. He received his Ph.D. in Organic Geochemistry from Southern Illinois University, Carbondale, IL; M.S. in Geology from Auburn University, Auburn, AL; and M.S. and B.S. in Geology from University of Dhaka, Dhaka, Bangladesh.