PRELIMINARY HYDROGEOLOGICAL MODELING OF PRODUCED WATER DEEP INJECTION IN THE DELAWARE BASIN FOR PORE PRESSURE CHARACTERIZATION

The Delaware Basin of west Texas and southeast New Mexico has become one of the top hydrocarbon producing provinces. However, seismic activity, which has been tentatively associated with deep injection of oilfield wastewater (SWD), have also increased in the same time interval. This study tentatively explores causation mechanisms by estimating pore pressure increase in the injection intervals. Although the main disposal strata in the Delaware Basin (Delaware Mountain Group) are relatively shallow and overlie the unconventional producing formations of lower Permian age (Wolfcamp and Bone Spring), some disposal activity also occurs in the deeper mostly carbonate section between the Precambrian basement and Pennsylvanian formations, particularly in New Mexico, and is the purpose of the study.

To constrain estimates of pore pressure increase, we have constructed a screening-level geological and hydrogeological model of the entire pre-Permian section of the northern Delaware Basin in Texas and New Mexico. It spans the formations used for SWD between the basement and the intervals targeted for petroleum development. The static geomodel was constructed using Petrel with geometric control from ~7,300 well logs. The thickness of the model varies from 1,000 to 11,000 ft and follows the basin structure from its center to its margins. The model is divided into 15 layers following generalized lithology (carbonate, clastics, shales). The hydrogeologic flow model is built with CMG STARS and incorporates 189 SWD wells, mainly in New Mexico, that were active from January 1989 to January 2020. The reservoir properties are adapted from data from the Fort Worth Basin of northcentral Texas which contains closely analogous strata (Ellenburger Formation) and better quantitative control. The model is calibrated using injection pressure constraints while honoring injection volume history.

Preliminary results indicate that the pore pressures have increased regionally by the low hundreds of psi in some areas. The impacted area is mainly in New Mexico. In addition, the model predicts a corridor of elevated pore pressure that possibly correlates with observed earthquakes in Texas, in an area with minimal injection volumes.