Subscriber access provided by READING UNIV
Review
Polymer Gel Systems for Water Management in HighTemperature Petroleum Reservoirs: A Chemical Review Daoyi Zhu, Baojun Bai, and Jirui Hou Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02897 • Publication Date (Web): 07 Nov 2017 Downloaded from http://pubs.acs.org on November 7, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Energy & Fuels is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 83
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
Polymer Gel Systems for Water Management in High-Temperature Petroleum Reservoirs: A Chemical Review Daoyi Zhu*,†,§, Baojun Bai*,†,‡,§, Jirui Hou*,† † 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, MO 65401, United States * E-mail:
[email protected] (B. B.);
[email protected] (D. Z.);
[email protected] (J. H.)
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 its gelation time and reduce the adsorption of chromium ions in the formation. Phenolic resin cross-linking 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 anti-temperature 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
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 2 of 83
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 tetra- polymers), functional monomers and environmentally friendly cross-linkers need to 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. Based on the above developments, foamed gels can be well implemented 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 the mobility-induced 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 to 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, 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.
ACS Paragon Plus Environment
Page 3 of 83
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
Figure 1. Schematic of excessive water production problems and water management mechanisms used in gel systems. 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 high-temperature reservoir. If the reservoir temperature is higher than 120 °C, it can be regarded as an extremely high-temperature 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-linking by an inorganic cross-linker (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/formaldehyde system and polyethylene imine) have been widely applied in high-temperature reservoirs (above 80°C) because of the more thermal stable bond (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. Based on 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, ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 4 of 83
oilfield applications, 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 year 2001 to 2011. Some detailed field application data and chemistry information of the gel treatment were described briefly; however, this review was not 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 high-temperature reservoirs from the perspective of chemistry and petroleum engineering and to try to provide directions for future studies of high-temperature polymer gel systems.
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.
ACS Paragon Plus Environment
Page 5 of 83
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
Figure 2. Classifications of polymer gel systems The first kind of polymer gel systems 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 three-dimensional (3D) network structures in porous media
and acts as flow diverting or blocking agents. These in situ cross-linked polymer gels include the synthetic polymer-based polymer gels and the natural polymer based gels. Synthetic polymers mainly include polyacrylamides (PAM) or partially hydrolyzed polyacrylamide (HPAM), polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polyvinylamine (PVAm) and copolymers based on acrylamide (AM) monomers. Chemical structures of the conventional synthetic polymers used in oilfields are shown in Figure 3. Natural polymers include guar, lignin, tannin and so on. These polymers can be cross-linked by inorganic cross-linker systems (e.g., aluminum, Al3+, chromium, Cr3+, and zirconium, Zr4+) or organic cross-linker systems (e.g., aldehydes and polyethyleneimine).
ACS Paragon Plus Environment
Energy & Fuels
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 6 of 83
Figure 3. Chemical structures of different polymers The second kind of polymer gel system is the preformed gels or mature gels.22, 23 They can be classified into four types, including preformed bulk gels (BGs), PPGs, microgels and dispersed particle gels (DPGs). These gels are cross-linked on the surface and then injected into the formation in the form of bulk gels or weak gels, massive particles (size from micrometer to centimeter) or microparticles (size from nanometer to micrometer) suspensions.24 For preformed particle gels and microgels, the water-absorbent groups, such as carboxyl groups (–COOH) and amide groups (– CONH2) in their chemical structures make these preformed gels swellable in aqueous solutions. After swelling, these particles can obtain a degree of elasticity and strength, which can block the water channeling in the petroleum reservoirs and control the water production.25 The last kind of polymer gel system is called foamed gels. It is a further updated technology of the foam EOR method. In this approach, the gelant or mature gel can be used to stabilize the lamella of foams under harsh conditions. Foamed gels can combine the advantages of foams and polymer gels that are commonly used in excessive water treatments, particularly for those far-wellbore oil formations with relatively low differential pressures.26, 27 The low density of foamed gels can also provide a displacing force when the foamed gels propagate throughout the formation to seek out low permeable and, sometimes, more preferential flow paths than the conventional gelants. Such selective displacing capacity of the foamed gels could be particularly effective to mitigate the problems of the gas override. Moreover, foamed gels also reduce the unit-volume cost of the polymer gel treatment through substituting the relatively expensive gelant for lower price gas or foams. Foamed gels are reported to be successfully used as a water management technology at a CO2 flooding project in Rangely Field.28 ACS Paragon Plus Environment
Page 7 of 83
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Energy & Fuels
3. In situ cross-linked polymer gels In the design of in situ cross-linked polymer gels, two important factors should be considered. First, the gels must be thermally stable; they should maintain flexible physical structures over extended periods of time (from 6 months to two years).19 At elevated temperatures, molecular activities of polymer and cross-linkers will increase significantly, and thus increase the cross-linking reaction rate and shorten the time of gelation. Second, the gelation time should be suitable for oilfield operations. In formation matrix treatments, the gelation time should be long enough so that the gel systems can penetrate into the reservoir to ensure sufficient deep placement. Various factors can influence the gelation time, such as temperature, salinity, the pH of mixing water and surrounding brine, concentrations of polymers and cross-linkers.
3.1. Gelation of polyacrylamides (PAM) 3.1.1. Classifications of the PAM gels by gel strength Polymer gel systems prepared by polyacrylamides (PAM) have been extensively used in water management. They can provide better viscosity and gel strength than the polymer solutions to plug the high permeability features, fractures or fracture-like channels. The chemical structure of PAM is shown in Figure 3a, which is a non-ionic polymer in its purest state, and it cannot be cross-linked via the process of ionic bonding. However, when it is mixed with alkaline solutions or subjected to elevated temperature conditions, some of the –CONH2 groups can hydrolyze to –COOH groups, as shown in Figure 3b. They become susceptible to ionic cross-linking. PAM is a cost-effective polymer, which is approximately 2-4 dollars per kilogram. To better understand the benefits of the polymer gel system prepared by PAM, we first classified them by their gel strength in this section. Specifically, they are divided into bulk gels (BGs), weak gels (WGs), and colloidal dispersion gels (CDGs), as shown in Table 1. Table 1. Gel classifications by gel strengths 29-31
Bulk gels
Weak gels
Polymer concentration (mg/L)
Types of cross-linking
Gel viscosity (mPa·s)
Applicable temperature
Pilot application
>4,000
Intermolecular
>30,000
