A critical review of concept and methods related to accessible pore volume during polymer-enhanced oil recovery

摘要

Polymer flooding is an enhanced oil recovery (EOR) technique that improves frontal stability problems associated with waterflooding. It has two primary mechanisms, the reduction of mobility ratio and improvement of conformance in heterogeneous reservoirs with a high coefficient of permeability variation (V). The former mechanism is more pertinent to heavy oil whereas later is to light oil reservoir. It is imperative to estimate the adsorption/retention losses for designing a slug that maintains integrity until the target destination. The optimum polymer slug is determined using reservoir simulators such as CMG & ECLIPSE, which require adsorption loss data per unit of the accessible pore volume. Unlike water, polymer molecules are not able to penetrate the entire pore volume due to size and wall exclusion. The fraction of total pore volume, which is not available for polymer invasion is called IPV (Inaccessible Pore Volume). This paper reviews and critically evaluates IPV whose determination is essential for finding polymer losses to the accessible pore volume. The five methods available for IPV determination fall into either tracer-laden or tracer-free category. For tracer-laden, the analysis is based on separation area between the tracer and polymer profiles or breakthrough time gap. It was observed that estimation based on the separation between the tracer profile of the first injected polymer slug and a polymer profile of the second injected slug is likely to provide the most accurate IPV value. It is hoped that this critical review could guide researchers in selecting a suitable IPV estimation method for their polymer flooding studies depending upon the complexity & time required and the availability of equipment in their laboratory.