GEOLOGIC CHARACTERIZATION OF THE DELAWARE MOUNTAIN GROUP IN THE DELAWARE BASIN FOR REGIONAL ASSESSMENT OF SALTWATER DISPOSAL CAPACITY AND INDUCED SEISMICITY

Development of the Permian Wolfcamp and Bone Spring Formations of the Delaware Basin has resulted in increased production of hydraulic fracturing flowback and produced water, six billion barrels (Bbbl) of which have been disposed into deepwater siliciclastics of the Delaware Mountain Group (DMG) as of the end of 2019. Some of the recent seismicity in the basin appears to follow shallow lineaments with earthquake hypocentral depths located in the DMG, and seismicity has been associated with wastewater disposal in the Delaware Basin and elsewhere. Understanding the static and dynamic storage capacity of the DMG is critical to mitigating potential risks such as induced seismicity.

Here we present a basin-wide geologic characterization of the DMG. The stratigraphic architecture, lithology, facies, and flow properties including porosity, permeability, amalgamation ratios and bedding trends, are interpreted and mapped. Primary facies include lowstand turbidite sandstone and transgressive to highstand siltstone and detrital carbonate. Porous and permeable channel sands of the DMG are oriented perpendicular to basin margins, and source rotates from NW to SE throughout Guadalupian time. Sandstones are fully amalgamated at the bed scale; however, at the channel scale, where net sand is less than 30% most channels are separated from one another by low-permeability siltstones or carbonates. Pore volume of the Brushy, Cherry and Bell Canyon Formations is 3600, 4800 and 4000 Bbbls, respectively, and its spatial distribution reflects net sand fraction. Rock strength estimates show fracture gradients on the order of 0.4 – 0.8 psi/ft. This geologic characterization can be used to assess the regional injection disposal resource of the DMG and as input for dynamic models to understand the limits of saltwater disposal storage capacity, addressing questions of pore pressure evolution, zonal containment, and induced seismicity with likely play development.