Abstract
We present an analytical solution to estimate the minimum polymer slug size needed to ensure that viscous fingering of chase water does not cause its breakdown during secondary oil recovery. Polymer flooding is typically used to improve oil recovery from more viscous oil reservoirs. The polymer is injected as a slug followed by chase water to reduce costs; however, the water is less viscous than the oil. This can result in miscible viscous fingering of the water into the polymer, breaking down the slug and reducing recovery. The solution assumes that the average effect of fingering can be represented by the empirical Todd and Longstaff model. The analytical calculation of minimum slug size is compared against numerical solutions using the Todd and Longstaff model as well as high resolution first contact miscible simulation of the fingering. The ability to rapidly determine the minimum polymer slug size is potentially very useful during enhanced oil recovery (EOR) screening studies.
Highlights
Polymer flooding is the most widely used chemical enhanced oil recovery (EOR) technique in the world, with more incremental oil recovery attributed to this method than all other types of chemical EOR combined [21]
We evaluate the above analytical solution by comparing its predictions with results from detailed simulation of the viscous fingering of chase water into a polymer slug and black oil simulation in which the Todd and Longstaff model has been implemented in the polymer options
We have investigated the fingering of chase water into a polymer slug during secondary polymer flooding in the absence of adsorption using a mixture of numerical simulations and analytical approaches
Summary
Polymer flooding is the most widely used chemical enhanced oil recovery (EOR) technique in the world, with more incremental oil recovery attributed to this method than all other types of chemical EOR combined [21]. This has driven the development of empirical fingering models which capture the average behavior of a fingered front These were originally derived for application in miscible gas injection ([14, 16, 25]) but Bondor et al [7] proposed that the Todd and Longstaff model [25] could be used to describe the fingering of water into the rear of a polymer slug. We first briefly review the analytical solution of continuous polymer injection, following which the derivation describing the dynamics of a stable chase water front position as a function of time is made These solutions are combined and extended to capture the effect of miscible viscous fingering of the chase water into the polymer slug. The validity of the analytical technique is demonstrated by comparing it against its numerical equivalent as well as high resolution first contact miscibility simulation
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