Borehole Stability Model in Presence of Intrussive-Igneous Body, Highly Challenging for Drilling, Yuralpa Field, Oriente Basin, Ecuador

Abstract

This paper presents three cases of wellbore instability in presence of igneous intrusive bodies but also a successful borehole stability model applied to a wellbore in the Yuralpa Field, Oriente Basin, Ecuador. The borehole stability model was integrated with petrophysics analysis from conventional logs to estimate presence of open or partially-open fractures and its impact on borehole stability. In addition, mechanical behavior response analysis during drilling of intrusive body was combined with morphology of caving analysis in real time for diagnose of failure mechanisms and to apply necessary corrective actions. Severe instability problems were observed at the level of the Napo shale, when wells are drilled at an oblique angle to the bedding planes. This condition has an effect on wellbore stability, so that the weak bedding planes of Napo shale can slip, due to having a low rock strength, thus jeopardizing the borehole stability. On the other hand, a significant mud weight can destabilize the wellbore wall due to that mud filtrate and mud itself inject between permeable bedding planes, reducing the already low existing cohesion, and inducing slip on weak bedding planes in wellbore walls. The instability problems have generated significant no production time or investment loss.