Abstract

Water and other fluids have been injected into the subsurface for decades in enhanced oil recovery (EOR) operations and for saltwater disposal (SWD). In recent years, hydraulic fracturing and horizontal wells have allowed development of 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 and gas at the wellhead, producers are left with co-produced water having ~150,000 ppm median concentrations of total dissolved solids which is typically disposed of in SWD wells.

Research has cited an increasing number of seismic events in the midcontinent, some of which are potentially induced by fluid injection. Unfortunately, limited data are published for volumes and pressures of fluids injected or distribution of those fluids into subsurface zones. The objectives of this research were to compile Class II underground injection control (UIC) data for the year 2011 and inventory injection data by geologic zone in Kansas and Oklahoma. EOR injected (EORI) fluid volumes totaled 265.5 million barrels (MMbbl) in Kansas and 1093 MMbbl in Oklahoma with the Desmoinesian and Atokan-Morrowan zones receiving the highest EORI fluid volumes. SWD volumes totaled 754.0 MMbbl in Kansas and 891.9 MMbbl in Oklahoma with the Arbuckle and Devonian to Middle Ordovician zones receiving the highest SWD volumes. The Arbuckle Group is underpressured throughout most of the midcontinent and has an unwavering capacity to accept fluids without any observed increases in pressure. Future studies of relationships between fluid injection and seismicity 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.