Monitoring and re-evaluation of petrophysical attributes in a mature field under production for many decades is crucial for optimizing production and further development planning. In this case study, a multidisciplinary approach is deployed for formation evaluation and reservoir characterization using logging-while-drilling (LWD) sensors spanning formation volumetrics, fluid analysis, high-resolution image interpretation, and geomechanics to confirm remaining oil saturations and help identify recompletion intervals.

LWD technologies were used in four wells in Sahmah field of Oman to provide an integrated petrophysical and geomechanical field study using a bottomhole assembly (BHA) including gamma ray, resistivity, formation bulk density, thermal neutron, acoustic, high-resolution imaging, and formation pressure testing sensors. A deterministic multimineral petrophysical model was used to derive formation volumetrics and fluid analysis. Geomechanical interpretation used high-resolution microresistivity imaging, acoustic slownesses, and formation pressure data to verify principal stress orientations and to quantify pore pressure and horizontal minimum and maximum stress magnitudes. These data were then correlated with historical data to evaluate sweep efficiency and residual fluid saturations.

LWD sensors have proven to provide robust geological, petrophysical, and geomechanical data compared to previous traditional wireline data acquisition. High-resolution images facilitated fracture evaluation and the determination of the rock facies. Formation pressures were used to fine-tune the geomechanical parameters and depletion profile.

With the integration of historical data, remaining oil saturations were estimated, which enabled new completions intervals. Well test results and the production profiles further facilitated re-evaluation of the original petrophysical cutoffs for the calculation of the oil in place and remaining oil saturations. Reservoir petrophysical attributes were then updated, taking into account the pressure depletion intervals while honoring history matching to help design future well construction and development drilling.

The pilot case study helped better understand the flow units in this mature field and facilitated benchmarking future petrophysical data gathering requirements and optimization of the overall reservoir management strategy, including well-construction options to help minimize field development costs.

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