An Injectivity Evaluation Model of Polymer Flooding in Offshore Multilayer Reservoir

Abstract

Good polymer flood performance evaluation requires an understanding of polymer injectivity. Offshore reservoirs are characterized by unfavorable water–oil mobility ratios, strong heterogeneity, and multilayer production, which collectively contribute to unique challenges. Accordingly, this article presents a semi-analytical model for the evaluation of commingled and zonal injectivity in the entire development phase, which consists of primary water flooding, secondary polymer flooding, and subsequent water flooding. First, we define four flow regions with unique saturation profiles in order to accurately describe the fluid dynamic characteristics between the injector and the producer. Second, the frontal advance equation of polymer flooding is built up based on the theory of polymer–oil fractional flow. The fluid saturation distribution and the injection–production pressure difference are determined with the method of equivalent seepage resistance. Then, the zonal flow rate is obtained by considering the interlayer heterogeneity, and the semi-analytical model for calculating polymer injectivity in a multilayer reservoir is established. The laboratory experiment data verify the reliability of the proposed model. The results indicate the following. (1) The commingled injectivity decreases significantly before polymer breakthrough and increases steadily after polymer breakthrough. The change law of zonal injectivity is consistent with that of commingled injectivity. Due to the influence of interlayer heterogeneity, the quantitative indexes of the zonal flow rate and injection performance are different. The injectivity of the high-permeability layer is better than that of the low-permeability layer. (2) The higher the injection rate and the lower the polymer concentration, the better the injectivity is before polymer breakthrough. An earlier injection time, lower injection rate, larger polymer injection volume, and lower polymer concentration will improve the injectivity after polymer breakthrough. The polymer breakthrough time is a significant indicator in polymer flooding optimization. This study has provided a quick and reasonable model of injectivity evaluation for offshore multilayer reservoirs.

Application of Fractional Flow Theory for Analytical Modeling of Surfactant Flooding, Polymer Flooding, and Surfactant/Polymer Flooding for Chemical Enhanced Oil Recovery

“…The non-Newtonian effect has also been incorporated in the fractional flow model [20,41]. This effect may not be neglected, especially when radial model is used [42].…”

“…The polymer front can be obtained by drawing a tangent line from (−D p , 0) to the polymer oil fractional flow curve, as shown in Figure 19a. The slope gives the specific velocity of the chemical front [42]. The intersection between the polymer tangent line and water oil fraction flow curve is the oil bank saturation, as illustrated in Figure 19b.…”

“…Rossen, 2011 [41] √ Sun, 2019 [42] √ Despite the many simplified assumptions (in Section 2.1), fractional flow theory still plays an important role in validation of numerical models, understanding of recovery mechanisms, and interpretation of transport behavior in porous media [3,31]. It is still capable of predicting trends and properties of displacement that still control behavior when the simplified assumptions are relaxed [31].…”

Overview of Methods for Enhanced Oil Recovery from Conventional and Unconventional Reservoirs

“…Over time, the amount of oil flowing from OR to WP decreases, and the sweep efficiency also decreases. However, it allows involving low-permeability differences in the effective thickness of the opened interval in the development [44]. Therefore, the thickness coverage ratio increases.…”

Viscosity Loss and Hydraulic Pressure Drop on Multilayer Separate Polymer Injection in Concentric Dual-Tubing

“…Despite the existing challenges, many researchers have studied the advances and technological method for polymer flooding in heavy oil reservoir [12][13][14] and the field application shows that the polymer flooding of heavy oils could result in incremental recoveries ranging from 7.5 to 25% OOIP [15]. Moreover, due to high demand for energy, polymer flooding has been successfully applied in offshore oil production in China [16][17][18][19]. As the development of the oil field, the main objectives of polymer flooding turns into type II formation, which has strong vertical heterogeneity between layers, and the physical properties between the high-permeability and low-permeability layer differ greatly [20][21][22].…”