Predicting Pore Pressure from Onshore Seismic Data in the Delaware Basin

Written by: Sam Green and Jeremy Meyer of Ikon Science, and Marianne Rauch-Davies, Bob Schmicker and Steven W. Smith of Devon Energy

Based on wireline logs, core data and pressure information obtained directly during drilling, the various shale units within the Wolfcamp Formation in the Delaware Basin are known to be variably pressured with depth, and the pressure can change laterally within the same rock formation. Zones with anomalous high pressure can generally be linked to better producing wells. Unknown overpressured areas are also considered a drilling hazard and being able to predict these cells is of high interest. Pore pressure prediction from onshore seismic data is not trivial as the relationship between porosity and overpressure is complicated by a relatively complex geological history. A prestack facies-based seismic inversion process, capable of producing physical estimates of impedances and density, was used to invert the seismic dataset for facies and elastic properties. This paper discusses this methodology and the results.

In on-shore areas where the overpressure is complicated by relative complex geology, low permeability and the presence of TOC in the reservoir rocks, pressure variations can be difficult to measure, making calibration difficult. Pore pressure is a critical input to a geomechanical model and can impact the mechanical behavior of the well. Consequently, comparing the predictions of different geomechanical models can be used to help calibrate the pore pressure model. A well-based workflow was developed which was able to predict the pore pressure and construct a geomechanical model that matched the wellbore measurements. This model was then tested on wells with the requisite log dataset and was able to replicate the observed mechanical wellbore behavior, highlighting the accuracy of the pore pressure prediction.