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Heavy oil and bitumen are making up approximately 70 percent of the remaining estimated hydrocarbon reserves. Many Enhanced Oil Recovery (EOR) methods such as chemical flooding, thermal recovery, gas injection, etc., were developed to make advances in the production of unconventional oil. Among all the variety of EOR methods, thermal recovery produces practically all of the heavy oil and bitumen among the various EOR methods. But at the same time, throughout its application, there are several disadvantages were revealed such as it is an expensive and not environmentally friendly process, heat loss in surface facilities and distribution lines, the efficiency is low after injection, increases in the extracted oil’s surface viscosity have caused polymerization reactions of free radicals created during the steam injection process, and the requirement for continuous steam injection is attempting to keep a hot oil-water interface at the front of the flow. For these reasons, the solvent-based non-thermal recovery method can be used to enhance heavy oil and bitumen recovery in unconventional reservoirs (thin or deep reservoirs) to prevent or reduce unwanted effects as described above. Toluene, carbon dioxide (CO2), ethane, propane, normal butane, and mixture solvents, among others, can be used as the injection solvent for the solvent-based non-thermal recovery method. That is why the researchers have concentrated on carbon dioxide as a solvent with Huff & Puff method to develop the production of heavy oil and bitumen to overcome all these negative issues because CO2 has several characteristics that make it an excellent option for this application. In this paper, the CO2 Huff and Puff method is reviewed. The CO2 Huff and Puff method’s viscosity reduction and oil swelling procedures have been the most significant factors in increasing heavy oil production. As a results, impacts of oil swelling at various temperatures and pressures as well as the viscosity reduction ratio with CO2 injection have been studied.

Petroleum is a mixture of many different hydrocarbon compounds, most of which primarily contain carbon and hydrogen in varying proportions. Monocyclic aromatic hydrocarbons, which are small, explosive, and volatile, to large, non-volatile, are all included in the mixture of hydrocarbons. Toxicological effects of a hydrocarbon depend on its molecular weight, family of hydrocarbons, creature exposed to it, and life-cycle stage of the exposed organism. Studies have shown that exposure to the toxic chemicals in crude oil, such as para-phenol compounds and volatile benzene, might have an adverse effect on human health. Furthermore, when there is an oil spill at sea, the wind and water currents disperse the oil, causing a thin slick to migrate across the ocean’s surface. There are numerous simultaneous chemical and physical changes. Reviewing the long-term effects of petroleum on the environment is the aim of this paper in terms of the impact on human health, plants, and marine life.

Any crude oil with an API gravity below 20 is considered heavy crude, and crude oil with an API gravity below 10 is considered extremely heavy. Conventional oil is lighter and less dense than unconventional oil resources such as heavy oil, extra-heavy oil, and bitumen. When the world’s conventional crude oil stocks are depleted, heavy oil resources will be well-positioned to continue satisfying demand for petroleum products. The economic viability of heavy oil depends on its quality being increased. The use of a catalytic steam injection in-situ upgrading technique to improve heavy oil recovery is discussed here. Previous research has shown that in-situ upgrading has a high catalytic ability to upgrade heavy crude oil by decreasing viscosity, increasing the amount of saturates (obviously low carbon number alkanes), and causing the thermal decomposition of high molecular weight substances such as asphaltenes and resin. There may be advantages to in-situ upgrading over more traditional methods of surface upgrading.

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