Application of the Vernik method for pore-pressure estimation in the Vaca Muerta Formation: Insights for geomechanical analysis and quantitative seismic interpretation in organic-rich mudrocks

In organic-rich mudrocks, intervals with the highest pore pressure are prime production targets due to their association with high hydrocarbon content and elevated productivity. However, these zones pose substantial operational risks. As pore pressure approaches the confining pressure, smaller differences between the maximum and minimum effective pressures are required for faulting to occur, regardless of the stress regime. Consequently, minor stress perturbations caused by hydraulic stimulation can trigger slippage in pre-existing cracks and faults. Assessing the spatial variability of pore pressure is essential, not only for selecting the most productive layers and mitigating induced seismicity events, but also for controlling influx in fractured zones during drilling and optimizing hydrocarbon recovery through effective choke management strategies. In this study, we apply the Vernik method (specifically designed to estimate pore pressure in organic-rich mudrocks) to analyze data from three wells within the maximum oil generation window in the Vaca Muerta Formation, Neuquén Basin, Argentina. Our analysis identified four dominant compaction trends, with the Lower Vaca Muerta section exhibiting the highest pore pressure, the greatest mechanical anisotropy, and the lowest stress anisotropy. Additionally, we quantified the effects of pore pressure on the elastic properties of the formation to enhance quantitative seismic interpretation. The robustness of the method is evidenced by its alignment with field observations and adherence to fundamental principles applicable to organic-rich mudrock reservoirs. This characterization improves our understanding of geomechanical behavior and production challenges in the Vaca Muerta Formation, offering valuable insights for reservoir management and optimization.