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Subsurface Fluid Injection in Oil and Gas Reservoirs and Wastewater Disposal Zones of the Midcontinent

Abstract

Water and other fluids have been injected into oil and gas reservoirs for decades to allow for secondary recovery (i.e. enhanced oil recovery) of petroleum. In recent years, hydraulic fracturing and horizontal wells have allowed industry to access unconventional oil and gas reservoirs or to redevelop conventional resources. Intense leasing, drilling, and production from the Mississippian zone of southern Kansas and northern Oklahoma are prime examples of this. Because it is economic to produce at low oil-cuts, such as in the Mississippian, there is a disproportionate increase in the co-production of water. After separating water from oil & gas at the wellhead, producers are left with co-produced water having ∼150,000 ppm median concentrations of total dissolved solids (TDS) which is typically disposed of via saltwater disposal (SWD) wells. Recent research has suggested a link between fluid injection and seismicity in the mid-continent, but limited data are available for volumes of fluids injected, capacity of various injection zones, or pore pressure diffusion after injection. The objectives of this research were to conduct a data mining and analysis effort of fluid injection volumes (focused on the year 2011) and corresponding injection zones in Kansas and Oklahoma. Statewide fluid volume used for hydraulic fracturing was estimated to be > 2.0 Mm3 in Kansas and up to 12.4 Mm3 in Oklahoma during 2011. A large majority of hydraulically fractured completion zones were concentrated in the Mississippian and Woodford zones. EOR volumes totaled 42.2 Mm3 in Kansas and 177 Mm3 in Oklahoma with the Missourian and Desmoinesian zones receiving the highest EOR volumes. SWD volumes totaled 120 Mm3 in Kansas and 200 Mm3 in Oklahoma with the Arbuckle and Permian zones receiving the highest SWD volumes. The Arbuckle appears to be underpressured throughout most of the midcontinent; therefore, has an unwavering capacity to accept fluids. When relating fluid injection to seismicity we must carefully compare extraction/injection histories, characterize hydrogeologic parameters, identify critically-stressed faults, and explain mechanisms by which pore pressure diffuses or increases stress along a fault plane.