Recent Advances in Pore Pressure Prediction In Complex Geologic Environments

Abstract

In recent years, methods have been developed to enable robust pressure prediction in the presence of multiple pressure mechanisms including undercompaction, unloading processes (secondary pressure mechanisms) and at great depth, the onset of secondary chemical compaction. These models utilize geological and geophysical information to constrain the calibration models and the depths at which they must be applied to develop a multilayer pressure calibration model that will accurately predict pressures for prospect-level analysis and pre-drill prediction. These models are then integrated with the velocity field and the geological and geophysical information to predict pore pressures and fracture pressures at greater depths than have been previously feasible. This methodology has been tested in multiple basins and has been proven to be effective in helping drilling engineers improve well performance through more effective mud and casing program designs that significantly reduces well costs and rig time. Recent application of elastic and acoustic inversion in complex carbonate environments have also proven effective in predicting pressures in environments where the shales can be separated from the carbonates. The approach requires that the inverted data be separated into the shale and carbonate velocity trends to allow the shales to be used for effective stress prediction while the complete velocity field is used for time-depth conversion. These studies have revealed that pore pressure prediction from mixed lithology (carbonate and shale) environments is feasible using advanced inversion methods. Successful pressure prediction in this type of geology requires seismic data that is of sufficient quality to enable a robust acoustic and/or elastic inversion to be performed that can separate the shale velocities for effective stress calculation, and perform time-depth conversion from the complete velocity field. As the amount of shale present in the geologic section becomes smaller, the ability to predict pressures decreases. The presence of marls also presents a problem because the carbonate material within the shale suppresses the sensitivity of the shale velocity to pore pressure.

Well-Seismic Integration to Pore Pressure Prediction using Multivariate Geostatistics: a Case Study in a Brazilian Equatorial Margin Basin

“…Predicting pore pressure is a key tool to assist drilling engineers regarding operational safety and dimensioning of drilling and completion engineering projects, and consequently, improving well performance, reducing operational cost, and rig time (Huffman et al, 2011) as well as reducing safety operational risks. Drilling events such as kicks, blowouts, well collapse, stuck pipes and elevated torques are the most common problems resulting from pore pressure anomalies due to misestimating the pore pressure and poorly predicting its behavior.…”

“…These logs show the relationship between compaction, porosity, density, and the electrical and acoustic properties of sediments (Chopra & Huffman, 2006). Taking into account the thick carbonate package overlaid and knowing that carbonates suppress the sensitivity of the shale velocity to pore pressure (Huffman et al, 2011), a 3D pore pressure volume using multivariate geostatistics was adopted as a solution to predict the pore pressure in this area. Multivariate geostatistics techniques are promising tools to achieve high-quality pore pressure distribution and reservoir characterization maps integrating well and seismic data.…”