New approach for compaction prediction in oil reservoirs
Abstract
As reservoir fluids are produced, pore pressure decreases and compacting rock loses capacity to support the overburden pressure, while the effective stress increases rapidly leading to pore collapse. Reservoir can elastically compact itself until pore pressure drops to the elastic limit, then initiates a plastic deformation known as mechanical compaction. Using numerical models is a good tool for compaction prediction; as they can predict reservoir behavior. This paper is purported by some models that allow providing for an approximate representation and prediction of the compaction magnitude at the wellbore developed in oil reservoirs during production (another model could be used to amplify the range until reservoir limits), integrating a uniaxial compaction mathematical model with pressure drawdown equation in formation face, and then a numerical model is built aimed reproducing the phenomenon and its changes over time. The mathematical model is built with the uniaxial compaction model and the drawdown pressure equation. The model is not complex but integrates the mean variables and rock properties involved in compaction phenomenon, like rock compressibility, elastic modulus, porosity, permeability and fluid pressure. This paper develops new numerical model based on the foundations of the Geertsma (1973) model, adding a step-by-step procedure to calculate the new rock properties over time, in order to have a more realistic compaction magnitude result.
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