Session 20. Oral Presentation for: Mitigating the mud-loss challenge when drilling in a depleted field – a case study from New Zealand

Presented on 20 May 2026: Session 20 Unlike previous wells where losses were minimal, significant mud losses occurred unexpectedly while drilling a recent horizontal well in the Pohokura Field. To identify the root cause and develop preventive strategies in future wells, a geomechanical study was conducted. Analysis of conventional mechanisms, such as equivalent circulating density exceeding the fracture propagation gradient, did not account for the observed mud losses. The investigation then focused on fault stability. Traditional fault reactivation assessments in depleted reservoirs typically compare the reservoir stress path to faulting criteria. This study introduces a novel approach that incorporates borehole pressure into fault stability analysis, enabling evaluation of near-wellbore processes that can lead to fault-related mud losses. Results indicate that, under current and projected depletion, reservoir-scale fault reactivation is unlikely because the stress path does not intersect the fault stability line. However, borehole pressures in the recent horizontal well were sufficient to critically stress faults near the wellbore, correlating with observed mud losses. This work presents an industry-first methodology that integrates reservoir depletion and borehole pressure into a unified framework for assessing fault-related mud losses. The accompanying graphical representation enhances clarity and supports rapid planning and decision-making for drilling in depleted fields. To access the Oral Presentation click ‘Supplementary data’ below. To read the full paper click here