Assessment of Factors Influencing Effective CO₂ Storage Capacity and Injectivity in Eastern Gas Shales

Building upon advances in technology, production of natural gas from organic-rich shales is rapidly developing as a major hydrocarbon supply option in North America and around the world. The same technology advances that have facilitated this revolution - dense well spacing, horizontal drilling, and hydraulic fracturing - may help to facilitate enhanced gas recovery (EGR) and carbon dioxide (CO{sub 2}) storage in these formations. The potential storage of CO {sub 2} in shales is attracting increasing interest, especially in Appalachian Basin states that have extensive shale deposits, but limited CO{sub 2} storage capacity in conventional reservoirs. The goal of this cooperative research project was to build upon previous and on-going work to assess key factors that could influence effective EGR, CO{sub 2} storage capacity, and injectivity in selected Eastern gas shales, including the Devonian Marcellus Shale, the Devonian Ohio Shale, the Ordovician Utica and Point Pleasant shale and equivalent formations, and the late Devonian-age Antrim Shale. The project had the following objectives: (1) Analyze and synthesize geologic information and reservoir data through collaboration with selected State geological surveys, universities, and oil and gas operators; (2) improve reservoir models to perform reservoir simulations to better understand the shale characteristics that impact EGR, storage capacity and CO{sub 2} injectivity in the targeted shales; (3) Analyze results of a targeted, highly monitored, small-scale CO{sub 2} injection test and incorporate into ongoing characterization and simulation work; (4) Test and model a smart particle early warning concept that can potentially be used to inject water with uniquely labeled particles before the start of CO{sub 2} injection; (5) Identify and evaluate potential constraints to economic CO{sub 2} storage in gas shales, and propose development approaches that overcome these constraints; and (6) Complete new basin-level characterizations for the CO{sub 2} storage capacity and injectivity potential of the targeted eastern shales. In total, these Eastern gas shales cover an area of over 116 million acres, may contain an estimated 6,000 trillion cubic feet (Tcf) of gas in place, and have a maximum theoretical storage capacity of over 600 million metric tons. Not all of this gas in-place will be recoverable, and economics will further limit how much will be economic to produce using EGR techniques with CO{sub 2} injection. Reservoir models were developed and simulations were conducted to characterize the potential for both CO{sub 2} storage and EGR for the target gas shale formations. Based on that, engineering costing and cash flow analyses were used to estimate economic potential based on future natural gas prices and possible financial incentives. The objective was to assume that EGR and CO{sub 2} storage activities would commence consistent with the historical development practices. Alternative CO{sub 2} injection/EGR scenarios were considered and compared to well production without CO{sub 2} injection. These simulations were conducted for specific, defined model areas in each shale gas play. The resulting outputs were estimated recovery per typical well (per 80 acres), and the estimated CO{sub 2} that would be injected and remain in the reservoir (i.e., not produced), and thus ultimately assumed to be stored. The application of this approach aggregated to the entire area of the four shale gas plays concluded that they contain nearly 1,300 Tcf of both primary production and EGR potential, of which an estimated 460 Tcf could be economic to produce with reasonable gas prices and/or modest incentives. This could facilitate the storage of nearly 50 Gt of CO{sub 2} in the Marcellus, Utica, Antrim, and Devonian Ohio shales