CO_2 mobility control improvement using N_2-foam at high pressure and high temperature conditions

摘要

The high mobility of CO_2 in porous media is an issue in most subsurface CO_2 projects worldwide, demonstrated by uncontrolled and rapid migration through the reservoir, early well breakthroughs and poor sweep efficiency. Improved mobility control of CO_2 is needed to accelerate and improve the value-creation from subsurface CO_2 projects, both in terms of energy produced and volumes of CO_2 stored. Field-proven conformance and mobility control techniques, such as foam, provide a cost-effective and sustainable alternative to overcome geological and process constraints observed with CO_2 flow in reservoirs. In this laboratory study, we have investigated CO_2 mobility control by foam in sandstone core samples at typical North Sea reservoir conditions, 220 barg and 100°C, respectively. Two important aspects related to any field application of foam have been evaluated and discussed: Ⅰ) Can strong CO_2-foams be generated at reservoir conditions using AOS surfactant? If not, Ⅱ) can relatively simple modifications to the foam system be made to improve foam properties and CO_2 mobility control? Our results show that only high-mobility CO_2-foams with low degree of CO_2 mobility reduction are obtained at 220 barg and 100°C. An easy way to improve the foam properties at reservoir conditions is suggested by changing the gas-phase in foam to nitrogen (N_2). The N_2-foams display improved foam generation performance, larger mobility control in terms of mobility reduction factors (MRF) and ability to block subsequent CO_2 injection. An alternative strategy for applying foam for CO_2 conformance and mobility control in subsurface CO_2 projects, which emerges from this study, is to initiate the foam treatment with nitrogen followed by subsequent CO_2 injection to change the main direction of CO_2 flow to enhance the displacement area or reduce uncontrolled CO_2 production between the injecting and producing wells (as illustrated in the graphical abstract). The possible mechanisms explaining the observed differences in foam properties using CO_2 versus N_2, including implications that could be helpful for future studies and CO_2 field applications are discussed further in more detail. The efficiency and limitations of miscible CO_2 flooding to recover oil and simultaneously store CO_2 after extensive water flooding are also demonstrated in this article, which are relevant to enhanced oil recovery (EOR) and subsequent CO_2 storage applications, known as the Carbon Capture Utilization and Storage (CCUS).