Enhancing heavy oil recovery is attracting a considerable interest due to the depletion of conventional oil resources. In fact, thermal enhanced oil recovery methods are presenting a potential impact on improving heavy oil recovery especially for terrigenous reservoirs, where they are able to increase oil mobility due to heating (steam and thermal exposure) or due to its in-situ conversion to light fractions during ignition of the reservoir. At the same time, it is worthy to note that steam-thermal methods are accompanied by a significant heat loss when injecting steam into great depths heat. Moreover, oil deposits in heterogeneous low-permeability reservoirs (for example, carbonate) are among the potential unconventional oil resources. Along with geological heterogeneity, low porosity and permeability, fracturing, these reservoirs contain, in most cases, heavy oils with a high content of resins, asphaltenes and hard paraffins, characterized by a non-Newtonian fluid property. All this taken together makes the extraction of oil from such reservoirs a hard task to implement.
Heavy oil and natural bitumen resources in carbonate formations are huge and considered as the promising alternative energy resource to the conventional crude oils. However, the production of such resources is challenging due to the low permeability, high viscosity and significant content of resins and asphaltenes in the composition of heavy oil and natural bitumen. The combination of thermal, chemical and gas enhanced oil recoveries can be a promising method to unlock and upgrade heavy oil and natural bitumen in carbonate reservoirs. In this paper, we propose a novel in-situ liquid-phase oxidation of light hydrocarbons for a revolutionary thermo-gas-chemical enhanced oil recovery method, which can be applied in carbonate heavy oil reservoir formations. It is assumed that the oxidation process is carried out in a downhole well reactor, the products of which are a high temperature mixture of organic carboxylic acids and organic solvents. Here, we present the results of laboratory investigations of liquid-phase oxidation of n-hexane as a model compound imitating associated petroleum gases in the presence of Fe, Cr and Ni catalysts, which were introduced in the form of oil-soluble catalyst precursors. It was revealed that the oxidation process yields hydro peroxides, organic carboxylic acids (acetic, propionic and valeric acids), alcohols and ethers. The products of the oxidation process were justified by the results of FT-IR and GC-MS analysis methods. According to the results, Cr-based catalyst leads to the increase of CH3-groups in the products. The oxidation process in the presence of nickel-based catalyst is compared with a control sample. The naphthalene was detected in the oxidation products of all experiments, the formation of which is explained by polymerization of benzene rings. In its turn, benzene is obtained due to dehydrocyclization of n-hexane on the surface of nanoparticles. However, iron-based catalyst showed the best catalytic performance in low-temperature oxidation of n-hexane in autocatalysis mode as the yield of acetic acid prevailed 52%. The given approach provides prolonged thermal and acid treatment of carbonate formations, where the evolved CO2 gas will further assist in increasing the mobility of crude oil. Moreover, the produced alcohols, ethers and other hydrocarbons play the role of solvents, which dissolves polar and non-polar components of crude oil.
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