Pilot Deployment and Field Validation of Wellbore Strengthening Design Criteria and Enhanced Fracture Gradient in a Depleted Reservoir

Abstract

Fracture gradient enhancementtechnology has been developed for drilling mud compounds based on comprehensive large scale laboratory test data which can widen the stable mud weight window for safe and efficient drilling in depleted reservoirs. Based on the laboratory test data, correlations were developed between optimum compound particle size against Young's modulus of the rock and generated fracture width for maximising the wellbore strengthening performance of the compounds. In addition, Enhanced Fracture Gradient (EFG) concept and criteria were developed for the compounds to widen the stable mud weight window. The niche workflow developed for utilisation of the wellbore strengthening design criteria and guidelines was deployedand validated in the pilot deployment of the optimum compound particle size correlations and Enhanced Fracture Gradient criteria in two wellsfor drilling through a depleted reservoir in the Malay Basin.The enhanced fracture gradient was predicted and incorporated into the mud weight programme and mud loss contingency plan of the wells. The wells were drilled with 10 ppb of the optimum mud compounds and the concentration was monitored and maintained throughout the drilling. In the first well, the maximum ECD exceeded the in-situ fracture gradient of the depleted reservoir by 1 ppg without any losses. Following TD of the hole section, an openhole leak-off test was conducted which validated the predicted average EFG of 1.8 ppg above the in-situ fracture gradient. The predicted EFG was within 0.2-0.3 ppg from the openhole leak-off test value. In the second well, the depleted reservoir was exposed to 0.6 ppg above the in-situ fracture gradient and no losses was observed.