The Use of Modeling to Enhance the Analysis of Formation Pressure Integrity Tests

Abstract

Abstract Formation pressure integrity tests (FPIT) are used to verify the integrity of cement at a casing shoe, measure the stress state of the exposed formations for well planning and operations, and determine the maximum equivalent circulating density (ECD) to which a shoe can be safely exposed. Critical decisions on operations are made directly from the results and include decisions about the need for remedial cement operations, maximum mud weights that can be used to drill the next well section, minimum mud weights that can be used to prevent hole collapse, calibration factors for predicting fracture gradients, and the potential need for lost circulation mitigation strategies. The interpretation techniques of the result most frequently focus upon the point at which a fracture first initiates, the point where unstable fracture growth begins, or the closure pressure of the fracture when pumping ceases. However, the early pressure build-up behavior is often overlooked and can provide much insight on the integrity of cement, the point of initiation of a fracture, the permeability of the formation being tested, the need for cement remediation, and the potential to increase fracture resistance using wellbore strengthening techniques. This paper presents a model for predicting early pressure build-up behavior, discusses how the model can be used to improve the interpretation of FPIT tests significantly, and provides examples of the application in select wells.