In extreme cases, depletion might result in production induced faulting, casing damage/shearing, wellbore instability and solid production (Santarelli et al., 1998 Zoback and Zinke, 2002 Agbasi et al., 2021 Baouche et al., 2021a Leila et al., 2021 Radwan and Sen, 2021b). These are very critical for producing fields as well, where production induced depletion can significantly change the pore pressure and horizontal stress magnitudes.
Rock-mechanical properties, pore pressure and principal stress magnitudes are the primary parameters of a geomechanical model. Geomechanic s have become an integral part of hydrocarbon exploration program contributing to safe mud window, drilling mud and casing program, wellbore stability, hydraulic fracturing and production optimization. Deformation analysis in reservoir space indicates stress path in depleted Mishrif formation of Zubair oil field is less than the normal faulting limit (0.71) and depletion-induced faulting is therefore unlikely to occur. Stress path, interpreted from the reduction of pore pressure ( Δpp) and minimum horizontal stress ( ΔS h ), yields average values of 0.65 and 0.62 for upper and lower Mishrif, respectively. Recent downhole measurements indicate that the primary producer Mishrif limestone is in depleted condition. C-quality wellbore breakouts, interpreted from the oriented four arm caliper data infer a mean N60☎ S H orientation, which is parallel to the movement direction of the Arabian plate towards the Eurasian plate. Relative stress magnitudes ( S H ≥ S v > S h) indicate a normal to strike-slip faulting transitional tectonic state in the study area.
In absence of image log-based breakout widths, maximum horizontal stress ( S H) is estimated from three approaches, which provided a gradient range of 0.89–1.21 psi/feet. Minimum horizontal stress ( S h) estimated from effective stress ratio and Poisson's ratio-based approaches yielded an about 0.58–0.76 psi/ft gradient and validated with C-category fracture closure pressure data available from mini-frac tests.
Vertical stress ( S v) has 0.97–0.99 psi/ft gradient. This work presents the first reservoir geomechanical modeling from the supergiant Zubair oil field, southern Iraq to decipher the pore pressure, in-situ stresses and depletion stress path of the middle Cretaceous Mishrif limestone reservoir. Accurate understanding of the reservoir pore pressure and in-situ stress behaviour in response to depletion has critical effects in production optimization and field redevelopment while ensuring reservoir integrity.
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