ASSESSING SLIP POTENTIAL OF INFERRED FAULTS IN THE PALEOZOIC BEDROCK AND CRYSTALLINE BASEMENT IN KANSAS: AN APPLICATION OF THE OPEN-SOURCE SOFTWARE PYFAULTSLIP

Induced slip from elevated pore fluid pressures remains a large driver of seismicity within the US midcontinent. Preexisting faults are loaded by the prevailing regional stress field, and if there is a sufficient drop in effective normal stress from increased pore fluid pressure, slip occurs. To balance the societal needs and detriments related to deep fluid injection, it is necessary to assess the slip potential of subsurface faults within an area of operation. To this end, we developed the open-source software package PyFaultSlip, which can calculate a probabilistic or deterministic estimate of the slip potential of 2D lineaments or 3D fault surfaces. Since there is generally a large element of uncertainty regarding the principal horizontal stress magnitudes and other influential factors, PyFaultSlip can fully propagate uncertainty values for all variables in its calculations for a probabilistic solution.

To assess the likelihood of induced slip from pore fluid pressure increases across Kansas, we generated a map of lineaments based on surfaces interpolated from well tops for key horizons in the Paleozoic and Precambrian for the entire state. Since the data is derived from well data, data quality is highest in areas with large oil and gas operations. Stress orientations and magnitudes were estimated using borehole breakouts, induced fractures, borehole bulk density logs, and a ‘stress polygon’ approach for different stress scenarios following observed focal mechanisms. These lineaments can be analyzed following a number of different scenarios that sufficiently characterize the range of possible configurations from variations in stress field orientation, fault plane properties, and pore fluid pressure perturbations. These results show the likelihood of slip occurring on these mapped lineaments from a pore fluid pressure perturbation up to 6 MPa. The likelihood of induced slip is greatly controlled by the orientation of each lineament relative to the prevailing stress field. These results also show the changes in likelihood of slip for increasing depth / deeper stratigraphic horizons. These results demonstrate how PyFaultSlip is a straightforward tool to assess and mitigate the hazards posed by fluid injection operations.