Zhuoyan Zhu1
Qi Gao- 1Research Institute of Petroleum Exploration and Development, Beijing, China
- 2PetroChina Ji Dong Oilfield Company, Tangshan, China
- 3Key Laboratory of Theory and Technology of Petroleum Exploration and Development in Hubei Province, China University of Geosciences, Wuhan, China
Introduction
According to the statistics, about 38% of oil and gas fields in the world and 46% in China are contributed by low-permeability reservoirs. The effective development of low permeability oil and gas fields has important strategic significance to ensure the sustainable development and exploitation of oil and gas resources in China. Due to lack of natural energy in the formation and the difficulty of water injection, the oil recovery rate and factor of these reservoirs are fairly low (WANG, et al. 2007; LI, 2020).
CO2 flooding is often used as a EOR technology to improve oil recovery in low permeability reservoirs due to its good solubility and strong extraction ability. It is mainly used to facilitate oil displacement by reducing the viscosity of crude oil, improving the mobility ratio, expanding the volume of crude oil, and reducing the interfacial tension (ZHAO, et al. 2017). However, due to the strong heterogeneity and the existence of natural and induced fractures, as well as the influence of injection-production well parameters and fluid properties, CO2 is prone to channeling along the high seepage zone (LI, 2018; WANG, 2019). Avoiding gas channeling during the process of gas flooding has become a major issue. It is vital to increase the sweep volume and improve the performance of CO2 flooding to reduce the heterogeneity of reservoir and plug the breakthrough channels such as fractures, throats and pores (LIU, et al. 2022).
Water-alternate-gas (WAG) injection, gas thickening, foam plugging and polymer gel plugging are common methods to address gas channeling (PENG, 2013; YUN, 2013; WEN, 2019; ZHAO, et al. 2020). However, these measures are generally one-time plugging, which limits the effectiveness on gas channeling. In this work, a variety of CO2 responsive plugging systems are summarized and analyzed, including CO2 responsive foams, surfactant solutions and gels. The main mechanism of these systems is that in saturated CO2 solution, amine-containing compounds spontaneously or combine with surfactant molecules to form worm-like micelles (WLMs) after deprotonation, so as to improve the viscosity of the solution and achieve precise and efficient blocking of gas channeling.
Types of plugging agent
CO2-responsive foam
A formula of CO2 responsive foam system was proposed previously by (LV, et at. 2021). The system had obvious shear-thinning characteristics and was more viscoelastic than the conventional foam system. The FCI value of the foam system could be more than 11 times than that of the conventional foam system, which could effectively inhibit gas channeling in strongly heterogeneous reservoir, and improve the CO2 flooding development efficiency. Li et al. screened the surfactant with the best performance from five surfactants (ODPTA, AC-1810, AC-1815, SDS, OTAC) and constructed a CO2 sensitive and self-enhanced foam system for mobility control (LI, et al. 2017). ODPTA had a carbon chain consisting of an amine group and 18 carbon atoms, which could not be ionized in water. However, in the acidic environment caused by CO2, the amine group was protonated and ion pairs (C18H37-NH-(CH2)3-NH2+-(CH2)3-NH3+ and C18H37-NH-(CH2)3-NH-(CH2)3-NH2-CO2-) are formed. The results showed that the CO2 foam prepared by ODPTA is sensitive to CO2 and had good plugging and mobility control performance at low concentration. Even under the harsh conditions of 7.8 MPa and 160°C, the resistance factor could still reach 274.
CO2-responsive surfactant
Some studies showed that the use of CO2 as an external stimulus to transform surfactant micelles was currently a simple and environmentally friendly way to prepare micelles. (SU, et al. 2013; ZHENG, et al. 2015; ZHANG, et al. 2016). Su et al. prepared an anionic worm-like micellar system with CO2 response using sodium octadecyl sulfate (C18H37SO4Na) and N, n-dimethylethanolamine (DMAE) at 60°C. DMAE was positively charged by protonation under CO2 stimulation and then self-assembles with the anionic surfactant C18H37SO4Na under electrostatic attraction to form worm-like micelles. When N2 was injected, the high viscosity system returned to the initial viscosity state. And this process could be repeated more than three times, and the maximum viscosity formed without a big deviation (SU, et al. 2013). Shen et al. screened ten compounds containing tertiary amine groups, and finally determined N, N-Dimethyl Erucamide tertiary amine (DMETA) as the research object. The results showed that the DMETA solution forms WLMs in saturated CO2 solution, and the viscoelastic fluid could effectively reduce gas flow during CO2 gas flooding in low-permeability fractured cores, and had a strong ability to withstand high temperature. WLMs had the ability of self-repair and had high residual resistance even after gas channeling (SHEN, et al. 2021).
CO2-responsive gel
The mechanism of gel-blocking gas channeling was discussed in detail, and the future development direction of CO2 trapping and interpenetrating gel system was prospected. CO2 responsive intelligent gel can solve the problem of poor acid resistance of HPAM. The cross-linking formed a three-dimensional network structure after CO2 treatment, with increased viscosity and volume, and remained stable for a long time under acidic CO2 conditions (LIU, et al. 2022). A CO2 responsive gel system mainly using small molecule amine (DMTA) and a modified long chain alkyl anionic surfactant (NADS) was prepared (DAI, et al. 2020). The experimental results showed that the DMTA-NADS system exhibited viscoelastic properties and shear thinning properties at high shear rates. The environment scanning electron microscope (ESEM) visually showed that the connection mode of its internal structure changed from lamellar to three-dimensional network structure. It was confirmed by NMR that amine molecules can bridge two anionic surfactant molecules by non-covalent electrostatic attraction after protonation. The core physical simulation experiment proved that the system could effectively block the CO2 channeling channel, and the blocking efficiency was more than 90%, which increased the sweep volume of the subsequent CO2 gas flooding and improved the recovery efficiency. It provided effective guidance for solving the practical problem of gas channeling and plugging in low permeability CO2 gas flooding development reservoir.
Comparative analysis of different materials
The mainly mechanism of CO2 responsive materials involved in this paper is shown in Figure 1.
FIGURE 1. Schematic diagram of structure change of surfactant—amine system stimulated by CO2 (LI, et al., 2015).
It is shown that CRMs are effective measures to prevent gas channeling during gas flooding. When the CRMs encounters CO2, its structure changes and the viscosity of the solution increases, which can be observed in both bulk and porous media. The three CRMs mentioned in this paper have essentially the same mechanism, but different plugging systems can be obtained by changing the type and concentration of surfactants, amines, and volume and rate of CO2 injection according to different purposes of using.
Compared with other plugging agents, CRMs has a better application prospect in tight fractured reservoirs. Before CRMs gelling, the solution viscosity is low (1–2 mPa s), resulting in easy injecting. It can quickly form high viscosity gel after CO2 injection and has strong blocking ability. Using suitable surfactants and amines, CRMs can maintain high stability under high temperature and high salt conditions.
Conclusion
1) The mechanism of CO2 responsive plugging system is that the molecular structure in aqueous solution changes upon CO2 stimulation, forming worm-like micelles. The macroscopic behavior is that the viscosity of the system changes, which is reversible and controllable.
2) By using different materials to interact with amine compounds, CRMs are low viscosity solutions before injection and can be formed as CO2 responsive blocking systems after reaction with CO2 in porous media such as CO2 responsive foam, CO2 responsive surfactant solution and CO2 responsive gel. With good injection ability, CRMs can effectively block the gas channeling, force the gas to turn to the unswept zone, and improve the degree of reservoir production. At present, it is necessary to develop a low cost and high tolerance CO2 responsive plugging system for the development of fractured tight oil reservoirs, so as to improve the production capacity and benefit of oil fields. (LIU AND LIU, 2022), (LV et al., 2021).
Author contributions
ZZ: investigation and research, writing manuscript draft; YS: resources and conceptualization; QG: modify analysis; CW: typesetting and supervision.
Funding
This work is supported by PetroChina “Fourteenth Five Year” Significant Programs (No. 2021DJ3203).
Conflict of interest
Author YS was employed by the company PetroChina Ji Dong Oilfield Company.
The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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Keywords: CO2-responsive, foam, worm-like micelle, gel, enhanced oil and gas recovery (EOR and EGR), fractured oil reservoir
Citation: Zhu Z, Song Y, Gao Q and Wang C (2023) The application of CO2-responsive materials on enhanced oil recovery for fractured tight oil reservoirs. Front. Earth Sci. 10:1053307. doi: 10.3389/feart.2022.1053307
Received: 25 September 2022; Accepted: 20 October 2022;
Published: 16 January 2023.
Edited by:
Zhilin Cheng, Xi’an Shiyou University, ChinaReviewed by:
Yang Yang, Chengdu University of Technology, ChinaKun Xie, Northeast Petroleum University, China
Copyright © 2023 Zhu, Song, Gao and Wang. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Qi Gao, eHV4aW5nZ3VhbmcxMjNAMTI2LmNvbQ==