FAR-FIELD RESERVOIR PRESSURE INCREASES AND SEISMICITY IN SOUTH-CENTRAL KANSAS

Kansas resides within the stable intraplate where strain rates and historical seismicity are low. Despite this position, the state has experienced an exceptionally high number of earthquakes since 2013, with more than 2000 earthquakes occurring in a two-county area in the south-central part of the state. Although the seismicity is linked to large-scale brine disposal in the Cambro-Ordovician Arbuckle Group, questions remain regarding the underlying processes responsible the earthquakes and their expansion into areas with negligible disposal. Here, we explore these issues by constructing a geologic model of the Arbuckle that incorporates data from ~18 wells, covering a 5500 km² area. Core, well log, and well test data were analyzed using a range of techniques in order to establish porosities, horizontal and vertical permeabilities, water saturations, and geologic flow units within the model. The resulting 20 layer geologic model was simulated using dynamic data from 103 saltwater disposal wells and shows an increase in reservoir pressure across the model area after 26 years of injection, with most of the change occurring in the past few years. The largest change in reservoir pressure occurs near the highest rate injection wells; however, the simulations also show that there is a broader pressure response across the model area. Our modeling results are confirmed by data acquired from an installed pressure transducer in the Berexco Wellington KGS #1-28 well in north-central Sumner County. Static buttonhole pressures in this well have increased 31.4 psig over the past five years, similar to the pressure increase estimated from our model. Continuous pressure monitoring in this well also shows that the reservoir pressure is steadily increasing by ~0.6 psi per month. Although the cause has not been firmly established, our current hypothesis is that this trend of increasing pressure will continue with active disposal in the region, as will the expansion of seismicity.