Quantifying the Effect of Rock Strength Criteria on Minimum Drilling Mud Weight Prediction Using Polyaxial Rock Strength Test Data

Abstract

In engineering practice, a linear poroelasticity stress model in combination with a rock strength criterion is commonly used to determine a minimum mud weight for stable well drilling. Rock strength criterion therefore plays a key role in minimum mud weight prediction. There are a variety of rock strength criteria available in the literature. It is well known that all those criteria fall into two categories: intermediate principal stress dependent ( σ2 dependent) criteria and intermediate principal stress independent ( σ2 independent) criteria. To identify if a specific rock failure is σ2 dependent or σ2 independent, a polyaxial (true triaxial) rock strength test is essential. Similarly, to study the effect of rock strength criteria on wellbore stability and minimum drilling mud weight prediction, polyaxial rock strength test data are most useful. In this paper, we present a systematic approach to quantify the effect of three most commonly used rock strength criteria on minimum drilling mud weight predict...