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Graft Co-polymerization of N-Isopropyl acrylamide and Acrylic Acid on Bentonite Colloids for In-depth Fluid Diversion Abdelazim Abbas Ahmed, Ismail Mohamed Saaid, and Nur Asyraf Md Akhir Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b02507 • Publication Date (Web): 03 Mar 2017 Downloaded from http://pubs.acs.org on March 8, 2017
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Graft Co-polymerization of N-Isopropyl acrylamide and Acrylic Acid on Bentonite Colloids for In-depth Fluid Diversion Abdelazim Abbas Ahmed, *† Ismail Mohd Saaid † and Nur Ashraf Akhir† Petroleum Engineering Department, Universiti Technologi PETRONAS, Malaysia. Tel: +6053687044
Fax: +6053687139
Bentonite, Diverting agent, Graft copolymerization, Stability and Viscosity.
ABSTRACT: A new cost-effective in-depth fluid diversion has been developed and reported. In this paper, the diverting agent is prepared successfully from natural bentonite particles that were modified with N-isopropyl acrylamide (NIPAM) and acrylic acid (AA) co-polymers. First, Bentonite particles were intercalated with small precursor molecules that contained functional groups. These precursors were used to reduce bentonite particle size and introduce a vinyl group for subsequent polymerization. Then, Poly (NIPAM-co-AA) was grafted onto hydrophilic bentonite through a free radical polymerization process. The grafted bentonite morphology, microstructure and thermal stability was investigated using FTIR spectroscopy, dynamic light scattering (DLS), XRD and TGA measurements. The particle dispersion stability and rheological properties have been investigated by using Turbidimeter and Rheometer. Sand packs and core
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flooding tests were conducted to investigate the injectivity and determine permeability reductions. Experimental results obtained revealed that the grafted bentonite was easily injected and gradually built flow resistance by particle straining and physical-chemical attachment. A significant permeability reduction fraction was observed when the diverting agent was injected into a brine saturated sand pack column. Increasing flow rate resulted in increasing pressure drop across the sand pack and decrease in permeability reduction fraction. The results indicate that attached grafted bentonite particles deform by shear. Two-phase core flooding results show rock permeability reduced by 80% with oil recovery increment of 12% after injecting grafted bentonite.
These significant results highlighted new insights for successful applications of
modified bentonite to improve reservoir conformance problems.
INTRODUCTION
Most hydrocarbon reservoirs are characterized by complex geologic conditions and high permeability contrasts. High permeability contrasts as a result of inter-layer heterogeneity, geological layering and fractures limiting the successful performance of many water or chemical flooding projects [1]. As such heterogeneous reservoirs reach to maturity; they produce increasing quantities of water or chemicals. The large volume of producing water or chemicals are complicated issues prompting high operating cost and can even lead to early well abandonment and unrecoverable hydrocarbons [2]. Recently, in-depth fluid diversion (IFD) has received extensive consideration from oil and gas operating companies. The new soft solidparticle-like gels were developed and reported as an effective method for in-depth fluid diversion and/or relative permeability modification for water production control [3; 4; 5; 6; 7; 8 and 9]. The essential concept of in-depth fluid diversion is that particulate dispersion is formulated at
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surface facilities and then injected into formations to plug a water path and divert subsequent water to unswept low-permeability zones.
BACKGROUND
According to Bai, et al (2015), in-depth fluid diversion / preformed particle gel may be classified on the basis of their application to millimeter-sized particle gels and submicron/micrometer-sized gels. However application of preformed particle gels as a diverting agent is often limited to fractures or fracture-like channels due to poor injectivity in the rock matrix [10]. On the other hand, Micro-gels, however, due to their smaller particle size are often intended to be placed deep into more permeable ‘matrix rock’ reservoirs and stop fluid flow [11]. Temperature, salinity or pH changes, for the most part, are used as triggers to control microgel particle size [12]. As a general platform for such microgels, particles are made by the use of organic materials like monomers or polymer mixed with a cross-linker. The polymer-based structure imposes some upper-temperature limit above which microgels would not be useful for conformance treatment. The commonly used microgels are colloidal dispersed gels (CDG), softmicrogel and thermally activated polymer (TAP). Colloidal dispersed gels (CDG) are defined as dilute aqueous solutions of cross-linked polymer molecules. Mack, J. et al (1994), has reported that CDGs can be formed by cross-linking 100 to 1200 ppm high molecular weight hydrolyzedpolyacrylamide polymer with aluminum citrate at 10 to 100 ratio of polymer to cross-linker. CDGs have been employed in many oilfields in the Rocky Mountain Region and China, but little is known about its thermal stability with low resistance to high salinity [13]. Other softmicrogels were synthesized by using acrylamide polymer containing 2% acrylates and 2% sulfonated groups, and zirconium (IV) lactate as cross-linker at high shear rate. The sulfonate groups in the monomer were chosen to prevent long-term syneresis of the gel system [8]. The
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produced microgels were in size range of 1 to 3 micron. The cost of this product is relatively high, furthermore, the microgel will be delivered in the form of inverse emulsion with an active material concentration of 30% in weight [10]. Thermally activated polymers (TAP) or Bright Water are designed to pop/swell-in-size by a factor of roughly 10 after being placed deep in the reservoir and after experiencing some gel-particle-popping trigger, usually increased reservoir temperature [6,14]. The material is a highly cross-linked, sulfonate-containing polyacrylamide micro-particle in which the conformance is constrained by both labile and stable internal crosslinks [14]. When subjected to elevated temperatures, the rate of decross-linking of the labile cross-linker accelerates. This reduces the cross-link density of particle and allows the particle to expand by absorbing the surrounding water. The costs of these micro-gels are also relatively high with low thermal stability and limited application range [10]. Consequently, there is a great need to develop a low cost and thermally stable diverting agent especially for high-temperature applications. In accordance with a current study, grafted bentonite was synthesized and examined as possible in-depth diverting agent. For obvious reasons bentonite clay was chosen. It is an environmentally friendly and nontoxic alternative. Besides, it is thermally stable like other silicate-based materials. Bentonite also has a high tendency to provide different swelling ratio when it contacts with brines. Although, the applications of bentonite for underground earth sealing and grouting are not new, its application in the oil industry as an in-depth fluid diversion is in its infancy. Bentonite slurry mixed with high salt concentrations has been reported to plug the fractures and wormholes [15]. Unfortunately, due to low gel strength, bentonite is not widely used. From past investigations, bentonite has indicated distinctive swelling ratios when contacted with different brine systems. The free swelling of bentonite decreased with the increased of cation valence and
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concentration. The results confirmed that, bentonite swelling properties could be controlled and inhibited by varying solution salinities and/or altering interlayer exchangeable cations [16]. The particle size of the commercial API- grade bentonite that normally utilized as part of drilling mud (
