Wellbore strengthening for drilling through depleted reservoirs in offshore Vietnam oil fields
Abstract
Long-term hydrocarbon production significantly reduces reservoir pressure, which in turn lowers the minimum horizontal stress and fracture gradient, narrows the drilling window, and increases the risks of lost circulation, stuck pipe and wellbore collapse.
This paper reviews and analyses the geomechanical fundamentals, drilling fluid technology and additive systems used for wellbore strengthening (WBS), covering the stress cage, fracture closure stress (FCS) and fracture propagation resistance (FPR) models. The material systems, including conventional lost circulation materials (LCM), deformable foam, nanoparticles, mixed metal hydroxide (MMH) and fluid loss control (FLC) additives, are analysed in terms of their action mechanism and application range.
Experimental results demonstrate that a 0.05% polymer system maintains surface friction resistance better than an 8% bentonite drilling fluid, with reductions of 11.1% and 23.4%, respectively. Based on these findings, the study proposes a depletion-based reservoir classification, a seven-step wellbore strengthening design workflow and a framework for selecting wellbore strengthening materials, applicable to the Bach Ho, Su Tu Den and Dai Hung fields on the Vietnamese continental shelf.
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