Almost 60% of oil and 40% of gas reserves worldwide are contained in carbonate reservoirs where acidizing stimulation is more challenging compared to sandstone reservoirs. Utilization of emulsified acids in matrix acidizing operations has been the most effective technique for more than half a century. This is due to the colloidal system's ability to generate deep, narrow conduits toward production zones under controlled retarded reactivity with the rock surface, along with the excellent sweep efficiency and corrosion inhibition of the well equipment. This Review attempts to review the various kinds of emulsified acids that are used for matrix acidizing of carbonate formations. The Review is trying to trace the innovations that have, gradually, been applied for enhancing the performance of emulsified acids for a variety of conditions, their limitations, and the developmental solutions such hybrid emulsifiers and pickering emulsions. In addition, the Review also discusses the parameters, characteristics, and measuring techniques required for the successful synthesis of a stable and quality emulsion while considering the environmental concerns raised toward the application of an emulsified acid system. From the reviewed publications, it can be summarized that macroemulsions are best suited for matrix acidizing applications over microemulsions due to low emulsifier concentrations and high acid volume retention; similarly, water in oil emulsions provide better retardation in a comparison to oil in water emulsions. The small droplet size of the emulsion yields high viscosity and stability. The compositional balance between each component present in the acidizing system is a crucial factor for optimum performance. Moreover, for future practice, much focus is required to design emulsified acids as ecofriendly systems that can leave the least amount of toxicity during and after implementation.
Abstract Low sweep efficiency during water injection besets the oil production from matured Malaysian fields undergoing waterflood operations. The water conformance issue might cause premature breakthrough in heterogeneous reservoir leading to low oil recovery. In this study, we described comprehensive experimental work to evaluate emulsion stabilized by Pickering particles as conformance control agent considering the reservoir characteristics in offshore Malaysian fields. The Pickering emulsion offers better stability in terms of resistance against mechanical and thermal changes during propagation under reservoir conditions compared to surfactant-based emulsions. In addition, emulsion due to its rheology in comparison to foam and gel have low pumping requirements with minimum chances of formation damage, providing better selective placement and ability to maneuver to deep levels of the reservoir under high temperature, salinity, and pressure conditions. In the case of conformance control applications, the particle-based emulsions provide better pore throat plugging in the high permeability thief zones mostly due to the better adsorption of Pickering particles on to the rock surface. This study investigated an ecofriendly novel carbon nanocomposite-based Pickering emulsion designed for conformance control in harsh environments of high-temperature and salinity typical of reservoirs in Malaysian fields. The research evaluated the thermal stability, rheological behavior of the emulsion under different temperatures, and salinities. Adsorption behavior of the emulsion on sandstone rock surface was analyzed based on rock-fluid interaction via contact angle measurements. We performed core flooding test to evaluate plugging performance by determining permeability reduction stimulated by the emulsion closely mimicking reservoir conditions. A permeability reduction of 98.2% was observed showing promising plugging performance with single pill injection and maintaining colloidal stability under dynamic conditions. The insights from this study can be beneficial to optimize emulsion design during the development phase, leading to improved performance of the conformance control agent with the reservoir. Moreover, the newly developed, ecofriendly emulsion due to its low volume consumption and superior plugging performance can potentially enhance conformance control performance in Malaysian reservoirs by reduction excess water production and consumption, thereby reducing operational costs and increasing oil production from untapped low permeable zones.
The recent environmental concerns have raised the need for a green acidizing fluid, which is able to replace diesel oil as an oil phase in emulsion based acidizing fluids. In order to do so it must be able to provide not only retardation in acid reaction against the rock surface, but also provide suitable inhibition characteristic that can reduce the amount of corrosion which occurs due to acidizing. In this paper emulsified acids made from triglyceride oils namely; Jatropha curcas oil and Palm oil have been tested for corrosion inhibition in comparison with Diesel oil based emulsified acid and 15wt.% HCl. The emulsion made with Jatropha curcas oil showed capability to replace diesel oil as a viable and an environmental friendly substitute for oil phase in emulsified acids.
Matrix acidizing operations have been accounted to be the most hazardous and environmentally harmful among all the well stimulation techniques. In instance, diesel oil based emulsified acids have been prohibited from usage due to their high level of toxicity in the US Policy Act of 2005
Emulsions play a prominent role in the petroleum exploration and production fields. They act as working fluids for drilling exploration wells, cementing the completion assembly, and helping to enhance hydrocarbon production. Moreover, the liquid hydrocarbons produced are often in the form of emulsions. The rheological analysis is crucial for the effectiveness of emulsion-based working fluids as well as the optimization and refinement of water-engulfed crude oil produced. The chapter covers the vast role of emulsions in the petroleum upstream section and the rheological techniques applied (such as rotational, oscillatory, extensional rheometry, and microfluidics) to better understand the flow characteristics of the non-Newtonian fluid in multiple applications.
Matrix-acidizing operations have been accounted to be the most hazardous and environmentally harmful among all the well-stimulation techniques. For instance, diesel oil-based emulsified acids have been prohibited from usage due to their high level of toxicity. There is, therefore, a dire need for emulsified acids that are environmentally viable and technically competent to replace the diesel-based emulsified acids. In this study, a novel oil-based environmental friendly emulsified acid has been synthesized from Jatropha curcas oil and, then, compared against diesel and palm oil-based emulsified acids. The technical evaluation of the three acids has been done based on experimental results obtained from thermal stability, droplet size analysis, rheological study, acid solubility, and toxicity screening. In addition, core flooding experiments have been conducted to evaluate the performance of the three emulsified acids as well stimulants. The results revealed that Jatropha oil-based emulsified acid has the potential to replace diesel-based emulsified acid. Jatropha oil-based emulsified acid was found to perform better than the diesel-based emulsified acid as indicated by having greater thermal stability and more popular rheological properties at varying temperatures of ambient, 50 and 70 °C. Furthermore, it possessed a lower toxicity load and a higher retardation effect on acid solubility than that of the diesel oil-based emulsified acid. The core flooding results have also indicated better well-stimulation performance of Jatropha-based emulsified acid as compared with diesel-based emulsified acids.
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