The degree of certainty in pore pressure estimates from resistivity data is examined through a case study interpreted by eight trained analysts. The relevant data included resistivity, gamma ray, density, and mud weight as a function of depth. A shallow kick pressure and several deeper MDTs were provided for calibration.
While the models and tools are quite simple, the shale pressures are derived from several measurements and decisions. The results from each analyst's interpretation were compiled and combined with some theoretical analysis to estimate the uncertainty attached to components used to estimate shale pore pressure. Two sources of variation dominate the uncertainty in estimating pore pressure from resistivity:
trust that sand pressure calibration points are representative of shale pressures, and
choice of the normal compaction trend.
