Permeability, Compressibility and Pressure Prediction in Supercharged Wireline and FTWD Environments

Abstract

In conventional wireline and LWD/MWD formation testing, downhole predictions for rock and fluid properties are based on simplified Darcy flow models, but only for mathematical expediency. These require initially constant pressures that are uniform throughout the reservoir. This limitation precludes common applications in overbalanced drilling, so that supercharge or near-well invasion effects - associated with rapidly decreasing pressures at the sandface where pressures are measured - are completely ignored. Such 1990s math models are commonly used despite documented field results for overbalances as high as 2,000 psi. Incorrect modeling can produce incorrect predictions, leading to misleading formation evaluation results and economic analyses. Here, the conventionally accepted model (developed by the last author over two decades ago) is rigorously extended to allow general supercharge and also underbalanced drilling effects. The formulation and algorithm are explained and detailed pressure examples are offered showing essential differences between earlier and newer algorithms.