| dc.description.abstract | The seismicity rate in Fort-Worth Basin, north-central Texas, where a lot of hydrocarbon production and disposal water injection activities happen, has increased dramatically from 2008 till now. There are five main seismicity sequences in this region, which are DFW Airport Earthquake (2008), Cleburne Earthquake (2010), Azle Earthquake (2013), Irving Earthquake (2014) and Venus Earthquake (2015). Previous studies attribute the seismicity events to pore pressure increase caused by wastewater injection into Ellenburger Formation. However, hydrocarbon production from the overlying Barnett Shale is not included in those previous studies. This study introduces a 10 year analysis comparing regional seismicity with Fort-Worth Basin wide production and injection activities.
In order to better understand the controlling mechanism of induced seismicity and its relationship to hydrocarbon production and disposal water injection, a 3D heterogeneous basin model, including monthly injection rate for 112 injectors and monthly production rate for more than 18000 producers is constructed. The model incorporates all available well log data, stratigraphic data from more than 1200 wells and petrophysical analysis of 47 wells. Moreover, fault permeability, which enhances the permeability of the carbonate system, is added to further adjust the model.
For the purpose of improving simulation efficiency during model calibration process, a combination of layer and areal coarsening is used to reduce the computational cost. The areal coarsening approach follows a regular structured upgridding, while for the layer upgridding we adopt the optimal layer coarsening approach. The coarsened model is then calibrated using a streamline-based inversion method, constrained by the bottom hole pressure (BHP) of 122 injection wells while honoring their injection volume history over 10 years.
Fluid flow simulation is then performed on the calibrated coarsened model to provide a basin-wide pore pressure distribution, serving as a fundamental step to find controlling mechanism for seismicity events and assess fault reactivation potential. Then, fault slip potential is calculated based on the time variant pore pressure and fault framework model to further analyze the controlling mechanism of seismic events in the Fort Worth Basin. All earthquake sequences, except for Azle earthquakes, were found to be triggered by pore pressure increase. We proposed a different controlling mechanism for the phenomenon we observed in Azle area, which is the unbalanced loading on two sides of a critically stressed fault. A site-specific study of Azle was conducted to further validate this mechanism. | en |
