Recent water disposal and pore pressure evolution in the Delaware Mountain Group, Delaware Basin, Southeast New Mexico and West Texas, USA
ABSTRACT
Study region: A flat, large, semi-arid plateau in the southwest United States (west Texas and southeast New Mexico) underlain by a deep Paleozoic sedimentary basin, the tectonic Delaware Basin, host of intensive hydrocarbon production. Study focus: Impacts of injection of large volumes of water produced from oil and gas wells and injected through 1000 + disposal wells, in particular, pressure buildup, induced seismicity and their potential consequences, in a formation underlying fresh-water aquifers but separated from them by thick layers of evaporites. The target formation is the Delaware Mountain Group (DMG) of Permian age and consisting of up to 4500 ft (~1400 m) of mostly fine-grained, deepwater siliciclastic slope and basin deposits (sandstones, siltstones, and minor limestones). A flow model was developed and calibrated from well log data, stratigraphic data, petrophysical analyses, and core data (123 ×170 mi2 - 1 ×1 mi2 grid size) complemented with dynamic injectivity information based on surface injection pressures and rates of the disposal wells. New hydrological insights for the region: Injection of 5.8 billion barrels (0.92 billion m3) of waste water has generated regional pressure increases in the DMG mostly in the 100–400 psi (0.7–2.8 MPa) range: (1) creating strong artesian conditions that, combined with the presence of numerous historical boreholes, could connect DMG and fresh-water aquifers; and (2) generating conditions leading to actually observed moderate induced seismicity.
