New Approach to Alternating Thickened–Unthickened Gas Flooding for Enhanced Oil Recovery

Abstract

Direct gas thickening is a conventional mobility control method to improve volumetric sweep efficiency for miscible gas injection (MGI) projects. However, the viability of this approach with technically feasible thickeners has not been verified at the field-scale due to a combination of high costs and/or environmental issues. One approach to make this technique economically more attractive is the implementation of an alternating injection scheme (similar to water-alternating-gas (WAG)) that would require less of the thickened gas compared with a continuous injection scheme. In this study, the effectiveness of this approach where a miscible alternating injection of thickened associated gas (TAG) or thickened CO2 (TCO2) with unthickened AG is explored in both nonfractured and fractured composite carbonate cores. Twelve core-flooding experiments were conducted using different injection schemes (i.e., continuous unthickened, continuous thickened, and alternating thickened–unthickened). These tests demonstrate that overall the experimental results indicate that the alternating injection of TAG or TCO2 with unthickened AG mixture as an enhanced recovery technique may produce results similar to those with continuous thickened gas injection. This reduces the consumption of thickening agents noticeably resulting in reduced operational costs and improved economic viability for this method.

Thickening CO2 with Direct Thickeners, CO2-in-Oil Emulsions, or Nanoparticle Dispersions: Literature Review and Experimental Validation

“…One would expect a greater increase because the PVEE molecular weight is greater than the PMO molecular weight, but a 3-fold viscosity increase at the same dilute mass concentration is unexpectedly high given typical dilute solution viscosity results. Further, in earlier work 23,24 Al Hinai and coworkers reported that CO 2 was thickened by 50% using 1.5 wt % P1D oligomer (MW 544). The same group conducted core studies that demonstrated how the alternating injection of thickened CO 2 with unthickened natural gas gave comparable results to the continuous injection of thickened natural gas.…”

“…For example, 2 wt % CO 2 -soluble poly­(vinyl acetate) (PVAc; MW 11,000) was able to induce only a several percent increase in CO 2 viscosity at very high pressure . Al Hinai and colleagues examined the CO 2 -thickening ability of four low molecular weight polymers (P1D; MW 900; PVEE, MW 3800; poly­(isobutyl vinyl ether) (PIVE), MW 4000; PDMS, MW 5180), some of which Heller had previously found to be poor thickeners. They accurately portrayed the controversy regarding the viscous changes associated with these oligomers and low molecular weight polymers and reported viscosity increases significantly higher than those reported by Heller, yet much smaller than those shown in Zhang’s report .…”

“…A very recent paper reported CO 2 viscosity increases of 20–400% for P1D in CO 2 at 2–8 wt %; however, no details of the falling ball viscometer were reported and the molecular weight of the P1D was extremely high (MW 600,000). No explanation was offered as to how such a high molecular weight P1D sample could be solubilized in CO 2 without a cosolvent when prior investigators ,,,, were only able to dissolve very low molecular weight (∼500–1,000) P1D in CO 2 . Another recent work attempted to shed insight on the intermolecular interactions responsible for the purported thickening of CO 2 by PVEE (MW 3822) and P1D (MW 910) using molecular dynamics simulations .…”

“…22 Al Hinai and colleagues examined the CO 2thickening ability of four low molecular weight polymers (P1D; MW 900; PVEE, MW 3800; poly(isobutyl vinyl ether) (PIVE), MW 4000; PDMS, MW 5180), 23 some of which Heller had previously found to be poor thickeners. They 23 accurately portrayed the controversy regarding the viscous changes associated with these oligomers and low molecular weight polymers and reported viscosity increases significantly higher than those reported by Heller, yet much smaller than those shown in Zhang's report. 17 For example, the Al Hinai team reported a 70% increase in CO 2 viscosity using 1.2 wt % PVEE at 330 K, nearly three times greater than that reported by Heller for the same mass concentration of a lower molecular weight PMO.…”

Quantification and Evaluation of Thermodynamic Miscibility in Nanoconfined Space

“…Thermodynamic miscibility is a critical state that has attracted a great deal of attention in many practical applications, such as pharmaceutical dosage forms, macromolecule materials, oil and gas production, etc. In practice, the miscibility state is defined as a stable homogeneous mixture that exhibits macroscopic physicochemical properties of a single-phase fluid .…”