Review pubs.acs.org/EF
Polymer Gel Systems for Water Management in High-Temperature Petroleum Reservoirs: A Chemical Review Daoyi Zhu,*,†,§ Baojun Bai,*,†,‡,§ and Jirui Hou*,† †
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Enhanced Oil Recovery Institute, CNPC Tertiary Oil Recovery Key Laboratory, China University of Petroleum, Beijing 102249, China ‡ China University of Petroleum-Beijing at Karamay, Karamay, Xinjiang 834000, China § Department of Geosciences and Geological and Petroleum Engineering, Missouri University of Science and Technology, Rolla, Missouri 65401, United States ABSTRACT: Polymer gel systems as water management materials have been widely used in recent years for enhanced oil recovery applications. However, most polymer gel systems are limited in their ability to withstand the harsh environments of high temperature and high salinity. Those polymer gel systems that can handle high-temperature excessive water treatments are reviewed in this paper and categorized into three major types: in situ cross-linked polymer gels, preformed gels, and foamed gels. Future directions for the development of polymer gel systems for high-temperature conditions are recommended. For excessive water management with temperatures from 80 to 120 °C, current polymer systems are substantially adequate. Polymer gel systems composed of partially hydrolyzed polyacrylamide (HPAM)/chromium can be combined with nanoparticle technology to elongate their gelation time and reduce the adsorption of chromium ions in the formation. Phenolic resin cross-linker systems have reasonable gelation times and gel strengths; however, more environmentally friendly cross-linkers should be developed to meet the increasingly stringent environmental requirements. For particle gels, the addition of functional monomer(s) can improve the antitemperature performance. When the applied temperatures reach 120 °C, inorganic cross-linker systems are no longer applicable, and the gelation time of organic cross-linking polymer gel systems and gel thermal stability will decrease significantly due to fast cross-linking reactions. During this period, retarders can be used to elongate the gelation time, and gel strength enhancers (e.g., cement, silica) can also be applied to improve the gel strength at such extremely high temperatures. Most importantly, novel polymers (e.g., ter- or tetrapolymers), functional monomers, and environmentally friendly cross-linkers need to be discovered and developed for polymer gel applications. Second cross-linking systems can be applied to further enhance the strength of the particle gels in harsh conditions. On the basis of these developments, foamed gels can be wellimplemented in fractures and wormholes to save the amount of injected gels.
1. INTRODUCTION Excessive water production problems in petroleum reservoirs can be divided into two categories. The first and most common category (inconsistent or excessive fluid flow) is caused by the spatial diversifications in the fluid flow performance because of the unfavorable permeability heterogeneity and mobilityinduced viscous fingering in the formation. The second category (water leaks) mainly results from casing leaks, water coning through matrix, and water channeling behind pipes, all of which result in excessive water production.1−3 Excessive water production problems cause a lot of oil to remain in the unswept oil zones, which not only actively interferes with oil recovery but also substantially reduces the profitability of production.4 Comprehensive strategies have been introduced to address excessive water production problems and proper treatments.1,2 Polymer gel systems have become the most widely applied water management technology to address excessive water production problems and improve oil recovery,5 as shown in Figure 1. In production wells where excessive water problems exist, polymer gel systems can be used to plug offended zones or areas. This treatment not only improves oil recovery but also reduces the operating costs related to artificial lifting, oil and water separation, and treatment of produced water. Meanwhile, © 2017 American Chemical Society
injection well treatments via polymer gel systems are applied to change the direction of the flow, which displaces fluids to unswept layers where additional oils can be recovered. As the development of conventional petroleum reservoirs continues, more and more reservoirs with high-temperatures are being explored and developed.6,7 However, no uniform understanding has been put forth to establish a manageable concept of high-temperature reservoirs. In most cases of enhanced oil recovery (EOR) processes, the reservoir with a temperature less than 80 °C can be considered a hightemperature reservoir. If the reservoir temperature is higher than 120 °C, it can be regarded as an extremely hightemperature reservoir.8−10 This is mainly because conventional polymers, including polyacrylamide (PAM) and xanthan, are easily degraded or precipitated at temperatures higher than 80 °C.11,12 When the formation temperature is above between 60 and 80 °C, polymer gels cross-linked by an inorganic crosslinker (e.g., chromium and zirconium) become limited because of pumping problems caused by the short gelation time.13 Polymer gels formulated by organic cross-linkers (e.g., phenol/ Received: September 25, 2017 Revised: November 5, 2017 Published: November 7, 2017 13063
DOI: 10.1021/acs.energyfuels.7b02897 Energy Fuels 2017, 31, 13063−13087
Review
Energy & Fuels
Figure 1. Schematic of excessive water production problems and water management mechanisms used in gel systems.
Figure 2. Classifications of polymer gel systems.
focused on polymer gel systems used for high-temperature reservoirs. Moradi-Araghi19 considered the gel systems that can be applied to treat wells in high-temperature petroleum formations. Some available gel systems were summarized, and factors that influence the gel selection were briefly introduced. However, few papers, to the best of our knowledge, have provided a thorough review of the chemical systems and development of polymer gel systems for water management in high- or extremely high-temperature reservoirs, although various materials for high-temperature polymer gel systems have been reported. The objectives of this paper are to give a thorough review of available polymer gel systems used for hightemperature reservoirs from the perspective of chemistry and petroleum engineering and to try to provide directions for future studies of high-temperature polymer gel systems.
formaldehyde system and polyethylenimine) have been widely applied in high-temperature reservoirs (above 80 °C) because of the more thermally stable bonds (through dehydration condensation reactions) between polymer and cross-linker compared with that of the inorganic cross-linking polymer gel systems.2,14 Bai et al.15 gave a review of polyacrylamide gels for water management. On the basis of the compositions and application conditions, polyacrylamide polymer gels are classified into three types: in situ monomer-based gel, in situ polymer-based gels, and preformed particle gels (PPGs). They also compared the in situ gel systems with the preformed gels and reviewed their applications in in-depth emplacement. Vargas-Vasquez and Romero-Zerón16 presented the main factors that influence the gelation time: cross-linking reaction kinetics, rheology, and syneresis of the HPAM-Cr3+ polymer gels. Abdulbaki et al.17 provided a literature survey of various polymer microgel technologies for water management. Polymer microgels are divided into four different types in the paper: colloidal dispersion gels (CDGs), PPGs, temperature-sensitive microgels, and pH-sensitive polymer microgels. This review is mainly concerned with the various characteristics of the microgels, lab experiments, oilfield applications, and advantages and disadvantages of the microgels. El-Karsani et al.18 summarized the development of polymer gel systems for profile improvement and water shutoff from the years 2001 to 2011. Some detailed field application data and chemistry information on the gel treatment were described briefly; however, this review was not
2. CLASSIFICATION OF THE POLYMER GEL SYSTEMS Polymer gel systems are usually composed of a water-soluble polymer or monomer(s), cross-linkers, and other auxiliary reagents. In this paper, they are divided into three gel types, as shown in Figure 2. The first kind of polymer gel system is the in situ cross-linked polymer gels. The injected gelling solution or “gelant” is pumped into target zones and is sometimes called the immature gel.20,21 After a specific aging duration, it forms threedimensional (3D) network structures in porous media and acts as flow diverting or blocking agents. These in situ crosslinked polymer gels include the synthetic polymer-based 13064
DOI: 10.1021/acs.energyfuels.7b02897 Energy Fuels 2017, 31, 13063−13087
Review
Energy & Fuels
Figure 3. Chemical structures of different polymers.
Table 1. Gel Classifications by Gel Strength29−31 polymer concentration (mg/L) bulk gels weak gels CDGs
>4000 800−2000 100−1000
types of crosslinking intermolecular mainly intermolecular intramolecular
gel viscosity (mPa s)
applicable temperature
>30000
