High Resolution Modeling of Pore Pressure Change, Fault Slip Potential and Induced Seismicity in the Fort Worth Basin

Abstract

Abstract The seismicity rate in the Fort-Worth Basin, north-central Texas, increased significantly from 2008. Previous studies attributed the seismic events to pore pressure increase caused by wastewater injection into the Ellenburger Formation. However, hydrocarbon production from the overlying Barnett Shale was not included in those previous studies. This study introduces a basin wide 10 year modeling and analysis of pore pressure change, fault slip potential and regional seismic events in the Fort-Worth Basin considering all production and injection activities. In order to better understand the controlling mechanisms of induced seismicity and its relationship to hydrocarbon production and water disposal, a 3D heterogeneous basin model, which incorporates all available well log data, stratigraphic data from more than 1200 wells and petrophysical analysis of 47 wells is constructed. The high resolution 90 million cell model is first upscaled using a combination of layer and areal coarsening scheme to improve simulation efficiency and then calibrated using a streamline-based inversion method with the bottom-hole pressure of 122 injection wells. The history matching period includes injection volume history and production history of more than 18000 producers for over 10 years. Next, we performed 3D fluid flow simulation on the calibrated upscaled model from which basin-wide pressure distribution was generated. Finally, fault slip potential of all the interpreted faults are calculated based on pore pressure results and fault framework model to analyze the controlling mechanisms of seismic events in the Fort Worth Basin. There are five main seismicity sequences in the Fort Worth area, which are DFW Airport Earthquake (2008), Cleburne Earthquake (2010), Azle Earthquake (2013), Irving Earthquake (2014) and Venus Earthquake (2015). Based on the pore pressure results from fluid flow simulation, all earthquake sequences, except for the Azle earthquakes, were found to be triggered by pore pressure increase. We previously proposed a different controlling mechanism for the phenomenon observed in Azle area, which is the unbalanced loading on two sides of a critically stressed fault. The results from this study are consistent with the previous findings. Fault slip potential calculations further validate the correlation between seismic events and pore pressure increase due to wastewater injection. By plotting the cumulative distribution of fault slip potential of all faults in the basin, we could identify the faults which are most likely to slip and trigger earthquakes. The novelty of this work is basin-wide identification of mechanisms of induced seismicity considering hydrocarbon production and fluid injection using basin scale high resolution fluid flow modeling and streamline-based inversion of pressure history.