Pore pressure and fracture gradient predictions are the most critical part of every well plan. Calculating these properly defines the drilling window needed for safe drilling operations. Uncertainties in these models arise from (i) the input data, (ii) assumptions used in the workflow and, (iii) the complexity/uncertainty of the geological conditions and rock properties.
A conventional workflow to plan wells includes derivation of a hydrostatic gradient and overburden gradient, correct interpretation of measured pore pressures (RFT/MDT-type data) and fracture pressure (LOT and FITs) data, shale discrimination and the definition of normal compaction trend lines and the application of the most suitable prediction method. All of these parameters make a precise prediction almost impossible and it is therefore normally more appropriate to describe High, Expected and Low-Case ranges.
In order to mitigate and reduce as much as possible these uncertainties, adherence to a best practice workflow for pore pressure and fracture pressure prediction is recommended and proposed here in this paper. This paper provides a method to enable any well to be drilled safely and efficiently. An important message is that for a robust model to be built, geological information and knowledge must be reconciled when completing pore pressure and fracture gradient predictions. Furthermore, understanding the uncertainties involved in the pressure models and ability to high grade data sets (direct and indirect data) are essential. In the current climate, optimising drilling time with as much confidence as possible is vital.