Emulsion System With Nanoparticles Suitable for High-Temperature, High-Salinity Reservoirs
Authors: Carpenter Chris 
Published: December 2023

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 211167, “Selective and Reversible Water-Shutoff Agent Based on Emulsion System With Nanoparticles Suitable for Carbonate Reservoirs at High-Temperature and High-Salinity Conditions,” by Masashi Abe, SPE, Jumpei Furuno, and Satoru Murakami, Nissan Chemical Corporation, et al. The paper has not been peer reviewed.

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The complete paper presents the evaluation results of a water-shutoff (WSO) agent based on an emulsion-type chemical material with nanoparticles. The WSO agent, which the authors call an emulsion system with nanoparticles (ESN), has several advantages to existing polymer and gel materials, including high thermal stability, low sensitivity to mineralization, thixotropic characteristics, selectivity of blocking effects for oil and water, and reversibility of blocking effects. In WSO applications, these properties of ESN could be well-suited for improved oil recovery.

Introduction
ESN is recognized as a proven technology for carbonate reservoirs. However, the reservoir under study did not feature harsh conditions; therefore, this work evaluated ESN potential for carbonate reservoirs in the UAE typically having high-temperature and high-salinity conditions.
A primary purpose of the technology, aside from improved oil recovery, is contributing to greenhouse-gas emission reduction and building competitive low-CO2-intensity oil-brand value. In general, produced water volume dramatically increases in maturing oil fields. Reducing water production also can contribute to saving water injection from a reservoir-voidage-replacement viewpoint. Therefore, the functional chemical WSO concept has a significant effect on contributing to the International Energy Agency’s sustainable development scenario.

Materials and Physicochemical Property Tests
Oil, Water, and Carbonate Core. Dead oil is sampled from an offshore carbonate field in the Middle East containing light crude oil (32.3 °API). Brine and plug core properties are summarized in Tables 1 and 2 of the complete paper. For thermal-stability tests, both brines were used for making the ESN. The WSO coreflood tests used the ESN made with injection water.
Advanced Features of ESN. Rheology. The viscosity of ESN is controllable by changing the water/oil ratio; viscosity becomes lower with increasing oil content and higher with increasing water content. These components were stirred, and two ESN samples were prepared using Crude Oil A (from Oil Field A, UAE) or diesel oil. The samples are referred to as Crude Oil A-based ESN and Diesel Oil-based ESN in this paper.
Both ESN samples showed similar viscosity curves; such thixotropic characteristics are an important property of ESN. ESN is flowable at stirring conditions. In particular, the viscosity of ESN can be decreased to less than 50 cp at high shear rates, so it can be injected into the reservoir by pumping. On the other hand, ESN becomes highly viscous and less flowable when no energy is applied to it (the ESN surface looks semisolid in this condition). In field operations, the viscosity of ESN decreases depending on the pressure generated by injection pumps on the surface. However, the injection pressure also releases in a radial direction from the bottomhole zone. As a result, ESN recovers a high-viscosity state because of decreasing shear rate with pressure release.