WATER-ROCK INTERACTION IN THE DEEP RIVER BASIN, NC, A CANDIDATE BASIN FOR SHALE GAS DEVELOPMENT

Interest in unconventional shale gas is growing as a result of advances in technology such as directional drilling and hydraulic fracturing. In shale gas production, significant quantities of produced water are expected. As production continues, the produced water is primarily natural formation water that records fluid sources and geological events in the basin's history. Produced water may contain high naturally-occurring salinity, organic constituents, and radioactivity, making disposal a challenge throughout the production history of a well. Wastewater management has emerged as a critical issue in the development of these resources. This study aims to simulate the formation water that may be brought to the surface during shale gas development in North Carolina (NC), and to examine geochemical fingerprints that could be used to identify this formation water in the environment. An improved understanding of the possible characteristics of formation water could allow industry and regulatory agencies to have a more accurate picture of the possible disposal and recycling options prior to beginning operations. Currently, little is known about the composition of formation water in the Deep River Basin, NC. The present study, into distinctive chemical signatures in simulated formation water, will generate not only a better understanding of the nature of the produced water resulting from hydraulic fracturing, but also a better understanding of the geologic evolution of the basin. The study focuses on rock-water interactions that likely influence formation water composition in the Deep River Basin. X-ray diffraction and petrographic analysis were used to characterize the mineralogy of the basin’s clastic rocks. Sequential rock-water leaching experiments were used to (1) investigate signatures of rock-water interaction, and (2) compare the shale-water signatures to those produced by water interacting with other lithologies in the basin. Preliminary data suggest fine-grained lithologies leach trace elements (e.g strontium (Sr)) more readily than coarse-grained lithologies. Sr release from siltstones and shales occurs to some degree in ammonium acetate, acetic acid, and HCl extraction, which suggests that the fine-grained rocks are a source of Sr to the extent that they could be leached by groundwater flow.