<p> Integrating Techlog, Petrel, Eclipse, and COMSOL is a game changer and led to a better understanding of a very complex undercompacted and overpressurized sand in Block 276. Different reservoir simulation sensitivity runs on P1-sand indicated that putting a new well in block (2,34) under pure depletion will yield the highest incremental oil recovery of about 38%. The sensitivity runs included dumpfloods, waterfloods, and artificial lift. COMSOL has also shown that formation overlying the salt dome is hotter than other portions of the reservoir and that planning a new well on the western flank of the accumulation was the right decision. COMSOL has also shown that overpressurization is driven by undercompaction but that heat conduction from the dome and underlying diapirs affected pore pressure by 3 to 15%.</p><p>

<p> Carbon sequestration is a promising solution to mitigate the accumulation of greenhouse gases. Depleted oil and gas reservoirs are desirable vessels for carbon sequestration. It is crucial to maintain the sealing ability of carbon sequestration fields with high concentrations of CO₂.</p><p> A systematic well integrity evaluation system has been developed and validated for carbon sequestration fields. The system constitutes 1) a newly developed analytical model for assessing cement sheath integrity under various operating conditions, 2) quantifications of well parameters contributing to the probability of well leakage, and 3) genetic-neural network algorithm for data analysis and well-leakage probability assessment.</p><p> A wellbore system consists of well casing, cement sheath, and formation rock. A new analytical stress model was developed. The new analytical model solves for the stresses in the casing-cement sheath formation system loaded by the isotropic and anisotropic horizontal in-situ stresses. Further analyses with the analytical model reveal that Young&rsquo;s modulus of cement sheath is a major factor that contributes to the sealing ability of the cement sheath, while Poisson&rsquo;s ratio and cohesion play less important roles in the cement sheath sealing ability. The cement sheath in the shale formation exhibits higher sealing ability than that in the sandstone formation. The sealing ability of weak cement is higher than that of strong cement.</p><p> Descriptive quantifications of well parameters were made in this study for analyzing their effect on the probability of well leakage. These parameters include well cement placement relative to aquifers and fluid reservoir zones, cement type, cement sheath integrity in operating conditions, well aging, and well plugging conditions. It is the combination of these parameters that controls the probability of well leakage. A significant proportion of wells were identified as risky wells in these two fields. It is concluded that the well trained neural network model can be used to predict the well leakage risk over the CO₂ sequestration lifespan, which can promote prevention activities and mitigations to the CO₂ leakage risky wells.</p>