DYNAMIC MODELING AND SIMULATION OF THE ANNULAR PRESSURE BUILDUP IN PRODUCING OIL WELLS

The present work aims to model the dynamic evolution of the “Annular Pressure Buildup” (APB) in oil wells to understand the effect of the operational parameters on this phenomenon as well as to propose an approach to model the fluid drainage to the rock formation, which is one of the possible mechanisms for annular pressure relief. To reach this goal, a detailed mathematical model of this process was developed considering design parameters such as oil well geometry, casings’ mechanical properties, rock formation’s geological characteristics, and physical-chemical factors related to the drilling fluid and its composition. The mathematical modeling of the APB phenomenon was based on the equations for the conservation of mass and energy, the equations of state for the thermodynamic properties of fluids, the mechanical properties of solid materials, and the PVT relations. Simulations were performed considering the worst scenario, i.e., the condition of complete sedimentation of solid contents of the drilling mud, aiming to verify under which conditions the fluid drainage would occur through the cake formed by the settled solids. Comparisons between different configurations of oil wells and rock formations with different geomechanical properties were also obtained for the APB calculation, considering the proposed model for pressure relief. The simulation results from the approach proposed in this work were compared to those obtained from WELLCAT™ software (Halliburton), a casing and tubing design computational package widely used for oil companies operating in heavy-oil drilling and production environments, showing deviations below 3%.