Porosity and storage capacity of Middle Devonian shale

Significance 

Shale reservoirs comprise of pore systems whose porosity and pore size distribution are used to characterize the pore structure. Despite the efforts to determine the influence of pore structure on the performance of the shale reservoirs, reliable shale reservoir evaluation has remained a challenge due to wide pore size distribution and heterogeneity of the fine-grained strata. On the other hand, the evolution of organic matter hosted porosity has not been effectively understood. However, incorporating the effects of various geological factors in controlling the generation and modification of organic matter hosted pores, a deep understanding of the porosity and storage capacity evolution by thermal maturation is highly recommended.

To this note, West Virginia University-based research team: Dr. Liaosha Song (currently an assistant professor at California State University Bakersfield), Keithan Martin (PhD candidate), Professor Timothy Carr and Dr. Payam Kavousi investigated the porosity and storage capacity of middle Devonian shale. Specifically, they studied the effect of presence of the organic matter on the most critical reservoir parameter: porosity and pore structure. Their work is currently published in the research journal, Fuel.

Briefly, the authors started their work by measuring the specific surface area, porosity, pore size and pore volume for four different wells in West Virginia and Pennsylvania: CS1, SW1, G55, and A1 wells. This was done using subcritical nitrogen adsorption and helium porosimetry technique. Next, samples were collected from the four wells and used to analyze the evolution of porosity with an increase in the thermal maturity that covered a wide range of hydrocarbon generation sequence from the wet gas zone to post mature zone.

The shale samples had a total organic carbon content ranging from 0.41-7.88wt%. From the analysis, the research team noticed that the porosity and pore structure were highly affected by the total organic carbon of the samples. For instance, an increase in the total organic carbon level resulted in a corresponding decrease in the average and median pore sizes. Additionally, the presence of organic matter in shale increased the specific surface area and pore volume thus enhancing the storage capacity. This represented both the free-gas storage capacity and the sorption storage capacity. Furthermore, carbonate and quartz showed no correlations with the pore volume, porosity, and specific surface area.

To actualize their study, they investigated the relationship between the geological factors like mineralogy and thermal maturity, porosity and pore structure. The complex relationship observed, however, raised the question on the accessibility of the pore space within the clay minerals which proved difficult. It was worth noting that thermal maturation was the main reason for altering the development of organic pores. For example, the highest specific surface area and pore volume were observed in samples in the dry gas zone as compared to those in the post-mature zone for similar total organic carbon level. The study by Dr. Liaosha Song and colleagues is hoped to improve the performance of shale reservoirs.

Porosity and storage capacity of Middle Devonian shale: A function of thermal maturity, total organic carbon, and clay content - Advances in Engineering

About the author

Dr. Liaosha Song is an assistant professor at California State University, Bakersfield. He received his Ph.D. degree in geology from West Virginia University in 2018. He also holds a Master of Science degree in marine geology (2013) and a Bachelor of Science degree in geology (2010) from China University of Petroleum. Prior to Joining CSU Bakersfield, he worked in EQT Corporation and US-China Clean Energy Research Center. He had conducted research on multiple shales in the Appalachian Basin, including the Marcellus Shale, Utica Shale, and a Cambrian shale. His work has been published in AAPG Bulletin, Fuel, Interpretation, etc. His current research focuses on petrophysics, reservoir characterization, CO2 sequestration, and unconventional reservoirs.

About the author

Keithan Martin is a PhD Candidate in Geology in the Department of Geology and Geography at West Virginia University. He holds both a B.S. and M.S. degree from Kansas State University, where he studied Mississippian-age carbonate depositional environments and facies prediction via artificial neural networks in mature fields. His current research focuses on X-ray fluorescence applications in reservoir characterization, natural fractures in unconventional reservoirs, and inorganic geochemistry of mudrock.

About the author

Timothy R Carr

Research and outreach efforts focus on energy production in the United States and globally. Current projects include the Marcellus Shale Energy and Environment Laboratory (MSEEL), a public-private multi-institutional 25-million-dollar project that involves more than 80 researchers from WVU, other academic institutions, national labs and the private sector. The objective of MSEEL is to provide a long-term collaborative field site to develop and validate new knowledge and technology to improve recovery efficiency and minimize environmental implications of shale resource development. MSEEL has developed approaches to reduce impacts and created innovative technology that is having an impact in improving hydrocarbon recovery. We have undertaken international outreach and education in numerous countries seeking sustainable development of unconventional gas resources. I continue to publish papers and developed new patented software.

About the author

Payam Kavousi is a research assistant professor in the Department of Geology at West Virginia University. His current research focus on fiber-optic application for hydraulic fracturing diagnostics and reservoir monitoring. Payam holds a PhD in geology from West Virginia University.

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Reference

Song, L., Martin, K., Carr, T., & Ghahfarokhi, P. (2019). Porosity and storage capacity of Middle Devonian shale: A function of thermal maturity, total organic carbon, and clay content. Fuel, 241, 1036-1044.

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