HISTORY MATCHING PRESSURE IN THE ARBUCKLE GROUP AQUIFER TO MANAGE MIDCONTINENT SEISMICITY

Seismicity has increased markedly across the US midcontinent due to large-volume wastewater injection into deep aquifers. The primary disposal zone in Oklahoma and Kansas is the Arbuckle Group aquifer, an intercommunicating system of carbonate reservoirs. Although numerous studies have demonstrated a link between increases in injection volumes and seismicity, generalized relations that can be used by industry and the regulatory community to mitigate earthquakes have not has been established. The increase in the Arbuckle pressure is considered the primary factor inducing the earthquakes. Newly compiled legacy pressure data, obtained from annual well tests, offer a remarkable opportunity to understand pressure increases in the Arbuckle and their relationship with injection volumes. The collected data come from 49 Class I injection wells in Kansas that show that pressure increases are ubiquitous across much of the state and have accelerated in recent years across south-central and central Kansas, parallel with the surge in seismicity. Here, we link observed pressure increases in the Arbuckle Group aquifer to the injection volumes using simple semi-analytical solutions and superposition principles. The resulting history-matched models use injection volumes as the input for predicted pressures. With simplicity and ease of use for operators and regulators in mind, the models incorporate the physical processes involved while minimizing complexity, paving the path for development of decision-support tools for management of formation and well pressure for seismicity mitigation. The work also quantifies scale-dependent properties of the Arbuckle such as permeability, transmissivity, and diffusivity, filling a critical gap in data-availability for the Arbuckle.