Recent water disposal and pore pressure evolution in the Delaware Mountain Group, Delaware Basin, Southeast New Mexico and West Texas, USA
Jun Ge, Jean‐Philippe Nicot, Peter Hennings, Katie Smye, Seyyed A. Hosseini, Shuang Gao, Caroline Breton
Abstract
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. 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. 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.