Article pubs.acs.org/EF
Gelation Study on a Hydrophobically Associating Polymer/ Polyethylenimine Gel System for Water Shut-off Treatment Yingrui Bai,† Chunming Xiong,† Falin Wei,† Junjian Li,*,‡ Yong Shu,† and Dexin Liu§ †
Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, P. R. China China University of Petroleum (Beijing), Beijing 102249, P. R. China § China University of Petroleum (East China), Qingdao, Shandong 266580, P. R. China ‡
ABSTRACT: A gel system has been widely used in many mature oilfields for water shut-off treatment. In the present study, the hydrophobically associating polymer (HAP) was cross-linked with the polyethylenimine (PEI) to form a HAP/PEI gel system which contains 0.35 wt % HAP and 0.60 wt % PEI. Gelation behaviors of the HAP/PEI gel formed in bottle and in core were studied, respectively. Results show that the gelation behaviors of the gel system were greatly affected by the concentration of HAP and that of PEI. The addition of the sodium chloride or calcium chloride generally resulted in a decrease of the apparent viscosity and an extension of the gelation time. However, a low concentration of sodium chloride led to a slight increase of the gel viscosity in bottle due to the intensification of the hydrophobic association. The rock skeleton of the core had a great effect on the gelation behavior. Compared with the results obtained in bottle, the apparent viscosity of the HAP/PEI gel system in core was obviously reduced, and the gelation time in core was extended two times or even longer. Both the gelation times achieved in bottle and in core decreased with the increase of temperature following the relationship of Arrhenius-type. The activation energy of the HAP/PEI gel system was 41.57 kJ/mol in bottle but increased to 60.95 kJ/mol in core. Data collected from the core flowing tests present a favorable shut-off performance and a strong wash-out resistance of the HAP/PEI gel system. In addition, the in-depth flow diversion and water permeability reduction were two main mechanisms of this gel system for water shut-off treatment.
1. INTRODUCTION With the wide application of water flooding for enhancing oil recovery in oilfields for decades, many mature oilfields have stepped into the development stage of high water-cut and low oil production.1,2 Large quantities of useless water break through via high permeability zones or fractures into oil wells and make the watered out well become common. Excessive water production not only burdens the subsequent water disposal but also shortens the development life of an oilfield because of the decreasing economic value.3,4 Therefore, much work should be done to control the excessive water production in mature oilfields, especially in oilfields of China. Mechanical and chemical water shut-off treatments are two main methods for controlling water production in oil wells.5 One or more packers are required to run in the wellhole to seal the water production interval(s) when using the mechanical method. It works when the water production interval is definite and can be separated from the oil production interval but may be helpless when oil and water are produced from the same interval or when water breakthrough occurs in the in-depth formation.6 Chemical water shut-off treatment has proved its feasibility and practicality in oilfields for decades. The gel system, which is formed after the cross-linking reaction between polymer and cross-linker, is one of the most favorable water shut-off agents because of its low cost and easy preparation.7 Polyacrylamide can cross-link with the cross-linker, which is ether metallic or organic, to form the polyacrylamide-based gel system that has been widely applied in oilfields.8 The metallic cross-linker, such as Cr3+ and Al3+, reacts with the carboxyl group of the polymer chain to generate the ionic bond; the © XXXX American Chemical Society
organic cross-linker, such as phenol/formaldehyde and polyethylenimine, reacts with the amide group to generate the covalent bond.9 The cross-linking reaction rate between metallic cross-linker and polymer is relatively fast; sometimes the gelation time is too short (90 °C) to satisfy the field application.10 Therefore, a retarding agent is always required during the application of the metallic cross-linker/ polymer system.11 Moreover, the metallic cross-linking reaction may result in the gel syneresis in the presence of multivalent cations because of the excessive cross-linking reaction.12 Despite some disadvantages, the metallic cross-linker, such as chromium(III) acetate, is still commonly used with polymer for water shut-off because of its low cost and relatively well performance.13 In contrast, the covalent bond generated by the organic cross-linker and polymer is relatively stable at high temperature and then contributes to stable gels.10 Moradi-Araghi et al.14 reported a stable phenol-formaldehyde gel which survived over 9 months at 149 °C in seawater containing 3.4% TDS and 1,700 mg/L hardness. Jia et al.15 found that the resorcinol/phenol-formaldehyde formaldehyde/polyacrylamide gel system presented a perfect thermostability at 90 °C after 30 days, and this kind of gel system has been applied in Shengli and Daqing oilfields of China. However, due to the toxicity of the phenol and formaldehyde, the application of these crosslinkers has been restrained in some oilfields.16 Polyethylenimine Received: June 2, 2014 Revised: January 18, 2015
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DOI: 10.1021/ef502505k Energy Fuels XXXX, XXX, XXX−XXX
Article
Energy & Fuels
2. EXPERIMENTAL SECTION
(PEI), which is environmentally friendly, is one of the hot topics of cross-linkers nowadays. Although PEI belongs to a kind of polymer with a low molecular weight, it is also used as a kind of cross-linker for water shut-off treatment. Among PEI-based gel systems, the polyacrylamide and t-butyl acrylate (PAtBA)/PEI system is popular and has been reported in some literature.17 Al-Muntasheri et al.18 and Jia et al.19 obtained stable PAtBA/PEI gels at 130 and 40 °C, respectively, proving that PEI could form stable gels with PAtBA within a wide range of temperature. Al-Muntasheri reported the favorable efficiency of the PAtBA/PEI gel system, which has been performed in more than 450 field jobs around the world to deal with water production problems, such as water coning/cresting, highpermeability streaks, and gravel pack isolation. The main shortcoming of the PAtBA/PEI gel system for water shut-off is the high cost because the required polymer concentration is too high (as much as 7 wt %). Except for the PAtBA, PEI can also cross-link with the hydrolyzed polyacrylamide (HPAM) to form stable gels at relatively low temperature (
