Development of a Deterministic Seismicity Potential Assessment of the Fort Worth Basin
Abstract
As an part of the Texas Bureau of Economic Geology’s TexNet and CISR Research portfolio on induced seismicity we have constructed a 3D geological model of the Fort Worth Basin (FWB) where we have integrated, from the Barnett producing level down into the crystalline basement, all production and injection wells in the basin, pore pressure, injection intervals with time-stamped allocated volumes, petrophysical analysis of the injection intervals, faults from all possible sources including outcrops, controls on permeability anisotropy from outcrops, seismicity, and a new model of basin stress state.
We are using our integrated geological model, and its derivative fluid flow and geomechanical models, to predict the evolution of pore pressure in the basin and apply it to deterministic populations and stochastic realizations of the faults to assess: (1) the spatiotemporal likelihood of fault reactivation, (2) variation in the mean distance to the nearest fault of concern, and (3) assessment of basin seismogenic potential.
The 3D fault interpretation and measures of its confidence is critical in this analysis. We have assembled data on faults in the basin from published sources, 2D and 3D seismic data, seismicity, and interpretations provided from petroleum operators to yield a 3D model with 291 faults ranging in strike-length from 116 to 0.4 km for which we have moderate to strong confidence. The faults have mostly normal geometries, cut the disposal intervals, and are presumed to cut into the underlying crystalline and metamorphic basement. Analysis of outcrops along the SW flank of the basin assist with geometric characterization of the fault systems.
With these deterministic inputs and appropriate ranges of uncertainty, we assess the conditional probability that faults in our 3D model might slip via Mohr-Coulomb reactivation in response to increases in injected-related pore pressure. A key component of the analysis is constraining the uncertainties associated with each of the principal parameters. A significant majority of faults in the model are critically-stressed within reasonable ranges of uncertainty.
AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018