Near-Wellbore Formation Damage by Polyacrylates: Effects of pH and Salinity

Denys, K.; Zitha, Pacelli L.J.; Hensens, H.C.; Nijenhuis, K. te

doi:10.2118/39465-ms

Cited by 4 publications

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“…the dependency in α in this expression is the same as the sinusoidal cylinder previously described by Denys et al18 . The hydraulic conductivity is defined by an analogy with the electric conductivity by…”

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confidence: 92%

Modification of Two Phase Flow Properties by Adsorbed Polymers and Gels

Zitha

Vermolen

Bruining

1999

Proceedings of SPE European Formation Damage Conference

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA model for the flow of water and oil in granular porous media treated with polymer and gels is presented. The pore geometry is represented by a triangular duct with a periodically varying section while the topological features are modeled by a statistical network. The mathematical treatment consists of the solution of the hydrodynamic equations in the duct and the upscaling by a percolation type of approach.The relative permeabilities of a wetting (water) and nonwetting phases (water and oil or gas respectively) are derived both (a) in the absence and (b) in the presence of the an adsorbed polymer or gels. The preliminary results show that both the flow restrictions at the pore level and the topological changes resulting from polymer adsorption or gel retention contribute to the disproportionate permeability reduction (DPR) for water and oil.A more systematic study of the effects of the parameters and the comparison of the model with the experiments are required for a full validation of the model.

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confidence: 92%

Modification of Two Phase Flow Properties by Adsorbed Polymers and Gels

Zitha

Vermolen

Bruining

1999

Proceedings of SPE European Formation Damage Conference

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“…This pH trigger is simpler than chemical cross-linking and thus offers operational advantages. Denys et al (1998) studied the effect of pH and salinity on permeability reduction caused by polyacrylate retention in a porous medium. According to them, two mechanisms are involved in such a process: pore plugging and adsorption.…”

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Application of pH-Triggered Polymers in Fractured Reservoirs to Increase Sweep Efficiency

Lalehrokh¹,

Bryant

Huh

et al. 2008

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Water and gas shutoff in naturally fractured reservoirs is traditionally achieved with cross-linked gels. Low sweep efficiency is also an important problem in waterflooding such reservoirs which can be treated with gel. In-depth placement of gels is the key to success, and this requires careful control of the cross-linking chemistry. This work examines the feasibility of an alternative gelation mechanism in fractured rock: pH-triggered polymer microgels. The microgel particles are small enough to pass through fractures but not pore throats in a matrix. The pH change occurs naturally and inevitably; it thus offers a simpler means of obtaining deep placement.When an acidic polymer solution is injected into the formation, several factors affect the pH: rock mineralogy, reactive surface area of the minerals, temperature and dilution due to mixing with residual water. The viscosity of the solution depends strongly on pH and upon polymer concentration and salinity of the polymer solution. The rate of pH increase relative to the rate of fluid advance determines the depth of placement.We used commercially available polymers which exhibit low viscosity at a pH below 3 but transform to gels at pH > 4. Polymer solutions were injected through artificial fractures in outcrop cores. Both sandstone and carbonate rocks raise the polymer solution pH. The presence of acid-soluble minerals containing cations such as calcium can independently trigger viscosification by precipitating the polymer. After polymer injection, a shut-in time allows further reaction to increase the pH and thus affects the Permeability Reduction Factor (PRF), the ratio of original fractured core permeability to treated core permeability. The PRF was measured to be in the range of 200 to 5 during the various experiments. The gelation is faster and PRF is higher in carbonates than in sandstones. Because the neutralization capacity of a core is large, it is possible to approximate reactive transport in a reservoir by continuously re-circulating the polymer effluent. Experiments showed gellike characteristics after 30 pore volumes of recirculation in Berea sandstone. IntroductionThere are large reserves of mobile oil in reservoirs around the world that cannot be produced due to problems such as low reservoir pressure and thief zones. Water injection is commonly employed to increase the average reservoir pressure and push out the oil. However, water flooding is not always successful. The most important problem is channeling of the injected water into high permeability zones which occur in heterogeneous reservoirs. In this situation, the water breakthrough time decreases, and significant portions of the reservoir remain untouched by the injected water. This reduces the sweep efficiency and oil recovery. In addition, the water oil ratio (WOR) increase which increases the cost of the water flood process.One of the methods to overcome the channeling problem is to block the high permeability zones with a specific kind of polymer or gel. By blocking the areas already s...

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Application of pH-Triggered Polymers for Deep Conformance Control in Fractured Reservoirs

Lalehrokh

Bryant

2009

All Days

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Water injection is commonly employed to increase the average reservoir pressure and displace the oil. However, water flooding is not always successful. The most important problem is channeling of the injected water into high permeability zones which occur in heterogeneous reservoirs. This is particularly true in naturally fractured reservoirs. Injecting low viscosity pH-triggered polymers into the reservoir to block the already swept fractures and high permeability zones is a promising solution. No injection of high viscosity gels or triggering agents is needed is this process. Polyacrylic acid microgels can swell a thousand fold as the pH of the surrounding solution changes, with an accompanying large increase in viscosity. In this paper we studied the factors affecting the feasibility and the placement of pH-triggered polymers into fractured reservoirs by performing several coreflood experiments in fractured cores. Polymer treatment reduced the overall core permeability in all cases in contact with different minerals in various sandstone and carbonate fractured cores. At polymer concentrations of 1% or greater, the permeability reduction was more than a factor of ten. The polymer microgels showed excellent consistency after being one month in reservoir condition at 58°C and resisted flow at pressure gradients up to 80 psi/ft. The selection of polymer and salt concentration in polymer solution depends on the application and desired PRF value. However, the 1% polymer concentration and 3% NaCl concentration is recommended due to the ease of polymer preparation, injectivity, reasonable geochemical buffering time and PRF values. Introduction A persistent problem in waterflooding is channeling of the injected water into high permeability zones which occur in heterogeneous reservoirs. This is particularly true in naturally fractured reservoirs. In this situation, the water breakthrough time decreases, and significant portions of the reservoir remain untouched by the injected water. This reduces the sweep efficiency and oil recovery. In addition, the water oil ratio (WOR) increases which increases the cost of the water flood process. To produce the remaining oil trapped in matrix or in low permeability sections of a highly heterogeneous reservoir, operators can apply selective perforation (Yildiz, 2002; and Yildiz and Cinar 1998), deep profile modification (Nasr-El-Din et al., 2002) and infill drilling (Gould and Sam, 1989; Wu et al., 1989). Wasnik et al. (2005) presented a method to use a system comprising a resin and a hardener for repairing channels and for controlling mud loss in fractured reservoirs. Another method to overcome the channeling problem is to block the high permeability zones with a specific kind of polymer or gel. By blocking the areas already swept by the water, subsequently injected water can sweep an unswept area of the reservoir and thereby increase the oil recovery. The polymer should be very viscous to be able to block the high permeability zones and ideally, these polymers should be economical and easy to prepare. However, injecting a viscous polymer into the reservoir at reasonable rates requires high injection pressures. The limitation imposed by the local fracture gradient greatly restricts the depth to which such a solution can be placed. Therefore, we are looking for a polymer that can be injected easily to the reservoir, yet offers large resistance to flow once placed in the reservoir.

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Near-Wellbore Formation Damage by Polyacrylates: Effects of pH and Salinity

Cited by 4 publications

References 0 publications

Modification of Two Phase Flow Properties by Adsorbed Polymers and Gels

Modification of Two Phase Flow Properties by Adsorbed Polymers and Gels

Application of pH-Triggered Polymers in Fractured Reservoirs to Increase Sweep Efficiency

Application of pH-Triggered Polymers for Deep Conformance Control in Fractured Reservoirs

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