It is well known that the development of unconventional reserves is quite complicated due to the poor reservoir porosity and permeability. The use of horizontal wells with multi-stage hydraulic fracturing remains one of the promising methods in use today for the development of such reserves. Subsequently, tertiary recovery methods popularly known as enhanced oil recovery (EOR) can then be carried out. In this paper, the compositions of anionic and non-ionic surfactants, potentially suitable for use in unconventional hydrocarbon deposits as EOR agents were investigated (on the example of one of the fields of Bazhenov formation). Also, attention was devoted to the assessment of the feasibility of co-injecting the surfactant solutions with a thermal agent (subcritical water) in a hybrid thermo-chemical EOR process. During the course of the study, 35 samples of industrial surfactants (individual and blends) were investigated. The compatibility of the surfactants with brine water, their stability under reservoir conditions (T>100 °C, P=25 MPa) for more than 14 days, and the effectiveness of the surfactants in reducing the interfacial tension (IFT) at the oil-brine boundary were the key factors in choosing the most appropriate compositions for use in the hybrid EOR. The ability of surfactants to decrease the IFT was investigated using a spinning drop tensiometer while the wettability alteration effect was estimated using a drop shape analyzer. Filtration experiment on oil-saturated core sample and evaluation of surfactant adsorption on rock surface were carried out with the best compositions. The results of the study show that the colloidal systems, represented by mixtures of anionic and non-ionic surfactants, have the best performance. The main components of these surfactant compositions are sodium salts of olefin sulfonates, derivatives of sulfonic acids C15-C20, and ethoxylated alcohols C6-C12. The results of measurements imply that certain compositions alter the initial rock wettability to become more water-wet and reduce the IFT between oil and water to a value of 0.051 mN/m. The adsorption of surfactant molecules on the rock was estimated to be 4 g/kg of rock, and the ultimate oil displacement rate increased due to surfactant injection from 8 % obtained during water flooding to 40.5 %. The possibility of using surfactants within the hybrid EOR technology was proven because the best surfactant mixture showed thermal stability at temperatures above 250 °C. Thus, we can conclude about the possibility of the use of some surfactant mixtures for the development of unconventional oil fields. Also, it is possible to combine the injection of surfactant solutions with the injection of thermal fluid, leading to the generation of synthetic oil in situ, thereby improving the reservoir properties of the rock and recovery of additional oil due to the effect of surfactants. This technology can be possibly applied for the development of unconventional reserves to increase the oil recovery ratio and make the process economically viable.

In situ shale or kerogen oil production is a promising approach to developing vast oil shale resources and increasing world energy demand. In this study, cyclic subcritical water injection in oil shale was investigated in laboratory conditions as a method for in situ oil shale retorting. Fifteen non-extracted oil shale samples from Bazhenov Formation in Russia (98 °C and 23.5 MPa reservoir conditions) were hydrothermally treated at 350 °C and in a 25 MPa semi-open system during 50 h in the cyclic regime. The influence of the artificial maturation on geochemical parameters, elastic and microstructural properties was studied. Rock-Eval pyrolysis of non-extracted and extracted oil shale samples before and after hydrothermal exposure and SARA analysis were employed to analyze bitumen and kerogen transformation to mobile hydrocarbons and immobile char. X-ray computed microtomography (XMT) was performed to characterize the microstructural properties of pore space. The results demonstrated significant porosity, specific pore surface area increase, and the appearance of microfractures in organic-rich layers. Acoustic measurements were carried out to estimate the alteration of elastic properties due to hydrothermal treatment. Both Young’s modulus and Poisson’s ratio decreased due to kerogen transformation to heavy oil and bitumen, which remain trapped before further oil and gas generation, and expulsion occurs. Ultimately, a developed kinetic model was applied to match kerogen and bitumen transformation with liquid and gas hydrocarbons production. The nonlinear least-squares optimization problem was solved during the integration of the system of differential equations to match produced hydrocarbons with pyrolysis derived kerogen and bitumen decomposition.

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