Performance evaluation of commingled production in a multilayer oil reservoir based on microscopic pore-throat structures

Abstract

Commingled production has typically been used to sustain fiscally viable oil production in a multilayer oil reservoir; nevertheless, the pore-throat properties have long been ignored, making efficient co-production difficult to achieve. To dynamically monitor and evaluate the co-production behavior of a multilayer reservoir, in this study, with consideration of complex seepage and pore-throat characteristics, an integrated and robust model has been developed and generalized. More specifically, pore-throat sizes and distributions were characterized using nuclear magnetic resonance (NMR) analysis and high-pressure mercury injection (HPMI) tests, while the seepage resistance during water displacement was estimated using a capillary bundle model. With mean relative errors of 1.62% and 3.94% for water-cut and oil recovery, respectively, a mathematical model was formulated and generalized to reproduce the experimental measurements by examining the effect of pore-throat alteration and coupling the boundary-layer contribution. In this way, the individual contributions of varying the throat diameter, advancing water front, and delaying water breakthrough can be distinguished. Subsequently, with overall deviations of 2.36% and 5.50% for oil production and water-cut, respectively, such a verified mathematical model has been upscaled and employed to precisely evaluate and forecast the dynamic co-production characteristics of a real multilayer reservoir.