Openhole Stability and Sanding Predictions by 3D Extrapolation from Hole-Collapse Tests

Abstract

Summary Wellbore failure is best simulated in the laboratory by subjecting a model hole to simulated in-situ stresses. A jacketed, thick-walled, hollow cylinder is subjected to increasing pressure on the outer surface until hole collapse occurs. This provides a direct measure of the stress required to cause hole failure in that particular formation interval. To extrapolate to the downhole situation, a 3D analytic model is presented that is applicable to both stability and sanding of open wellbores. This model uses a Modified Lade failure criterion that properly accounts for the effect of the intermediate principal stress on rock failure. The Modified Lade rock-strength parameters are extracted from the measured hole-collapse strength (HCS) and are then combined with the in-situ stresses and formation pore pressure to determine the required mud weight for stability while drilling and the allowable drawdown pressure for prevention of sand production.