Laboratory Study on the Oil Displacement Process in Low-Permeability Cores with Different Injection Fluids

Abstract

Although flooding technology has found wide application in low-permeability reservoir development practices, the oil recovery enhancement mechanisms for different injection fluids still lack specific focus based on comprehensive investigations. Therefore, in this paper, supercritical CO2 (ScCO2), N2, and water injection processes in oil-saturated low-permeability tight cores were comparatively studied. To reveal the effect of physicochemical properties of the injection fluid on the oil recovery efficiency, the Berea sandstones with three permeability levels and kerosene were employed in this study to exclude other parameter influences. The flooding processes employing various injection media were investigated based on quantitative comparisons of the oil recovery factor and the displacement pressure difference at two system pressures. The experimental results show recovery efficiencies of 59–91 and 84–92% with the increasing permeability for the ScCO2 injection process at system pressures of 15 and 25 MPa, respectively, which are much higher than 26–40 and 21–52% in the N2 case and 43–46 and 45–49% in the water cases. Interfacial tension (IFT) measurement results indicate that miscibility conditions have been achieved for the ScCO2/oil system, thus leading to much higher oil recovery. On the other hand, the pressure difference results show a similar magnitude of 10 MPa/m for both ScCO2 and N2 processes, which is much lower than the 100 MPa/m for the water flooding cases. Comprehensive comparison shows that ScCO2 shows great advantages in the application of unconventional reservoirs. It is expected that our research work could enrich the investigations of CO2 flooding and the in-depth understanding of the mechanisms and better guide the utilization of CO2.

CO2-Controlled Water Injection in Carbonate Gas Reservoirs: An Effective Approach to Improve Production

“…Izdec et al used experiments and numerical Mimics to study the trend of changes in rock porosity and permeability after CO 2 injection . Overall, there is less research on water control by injecting CO 2 , but CO 2 injection can effectively avoid some of the problems mentioned above. − In this study, we investigated the movement and gas production patterns of edge water after CO 2 injection based on a series-connected core flooding experiment. By varying different injection pressure conditions, we explored the dynamic characteristics of marginal water seepage and gas production as well as the effects of different CO 2 injections on suppressing water breakthrough and increasing the extent of natural gas extraction from the core.…”

Microscopic Production Characteristics of Huff-n-Puff after CO2 Flooding in Tight Oil Sandstone Reservoirs

“…Consequently, the implementation of supercritical CO 2 can significantly enhance oil recovery. 28,29 Currently, CO 2 injection development technologies primarily encompass CO 2 flooding and CO 2 huff-n-puff. CO 2 flooding can be classified into different categories, including immiscible flooding, near-miscible flooding, miscible flooding, and carbonated water flooding.…”

“…Moreover, carbon capture, utilization, and storage (CCUS) have garnered substantial attention all over the word. − CO 2 injection, owing to its distinctive physical and chemical properties and relatively cost-effective implementation, has found widespread application in oil reservoirs. − Notably, CO 2 injection serves not only to enhance oil recovery but also to facilitate CO 2 geological storage. , The mechanisms underlying CO 2 -enhanced oil recovery predominantly encompass viscosity reduction, light oil extraction, and alteration of oil–gas interfacial tension. − When pressure surpasses 7.4 MPa and temperature exceeds 31.26 °C, CO 2 transitions into a supercritical state, exhibiting low viscosity, high density, remarkable swelling capacity, and diffusion capabilities. Consequently, the implementation of supercritical CO 2 can significantly enhance oil recovery. , …”

Feasibility of Advanced CO2 Injection and Well Pattern Adjustment to Improve Oil Recovery and CO2 Storage in Tight-Oil Reservoirs

“…Global tight-oil reserves are abundant [1,2], but numerous tight reservoirs still face the difficulty of efficient development, which is characterized by rapid production decline and low oil recovery [3,4]. CO 2 injection development is an important method of reservoir development, and the main mechanism is to supplement the formation energy [5][6][7][8], volume expansion [9][10][11], interfacial tension reduction [12,13], and viscosity reduction of the crude oil caused by the oil-gas interaction [14,15]. During CO 2 flooding development, injected gas can form the miscible phase with crude oil (exceeding the miscible pressure), reduce the interfacial tension between the oil and gas, and improve the oil displacement efficiency [16][17][18][19].…”