Perm Journal of Petroleum and Mining Engineering

Domestic standards for conducting laboratory studies on core samples of oil and gas formations provide for purification from hydrocarbons using extraction. Purification prepares core samples for the main types of research. A number of different solvents and special extraction and distillation apparatus are used. Core samples placed in the apparatus undergo purification cycles for a long time with high-temperature exposure. However, extraction leads to distorted ideas about the natural wettability of the rock surface, which is subject to change and, as a rule, hydrophilizes. In this regard, it is of scientific and practical interest to assess the wettability of the rock at various stages of sample preparation – before and after the extraction procedure. The purpose of the research is to analyze the wettability of core samples before extraction from hydrocarbons using statistical research methods. The work analyzes the effect of the porosity and permeability coefficient on the change in wettability. The results of the research showed that with the help of the conducted complex of laboratory studies using various statistical methods it was possible to create mathematical models for predicting the values of the wettability index for oil before extraction based on the filtration and capacity properties of core samples. The paper provides examples of the correlation fields analysis of various parameters before and after extraction. The multivariate statistical analysis conducted in the work made it possible to establish that it is most expedient to predict the wettability values after extraction differentially by wettability methods and by the studied formations. The multivariate models obtained in the work can be further used to predict changes in miscibility for some objects in the Timan-Pechora province.

One of the fundamental challenges in studying the properties of productive oil and gas reservoirs is the scale effect. Analysis of multi-scale research results often reveals discrepancies in data. For example, porosity and permeability properties determined from standard and full-size samples for the same depth interval can vary significantly. Similarly, these differences become even more pronounced when transitioning to the scale of the near-wellbore zone. At the same time, the type of reservoir significantly influences the scale effect. In porous reservoirs, the scale effect may not be pronounced, whereas in complex reservoirs, transitioning from one scale to another can result in properties changing by an order of magnitude. This is due to high heterogeneity caused by secondary processes such as leaching, dolomitization, and recrystallization. Neglecting the scale effect can adversely affect understanding reservoir structure. In this study, the scale effect of properties was examined using a complex carbonate reservoir as an example. A qualitative assessment of the scale effect was performed using mathematical statistics and petrotypification methods. To quantitatively evaluate the scale effect, a multiple regression model was developed to adjust porosity values from standard core samples to full-size samples for constructing a porosity cube. Several machine learning algorithms were used to predict the permeability values of full-size samples, including gradient boosting, random forest, multilayer perceptron, and k-nearest neighbors. It was found that the random forest-based model was the most accurate. The developed models enable highly reliable predictions of porosity and permeability when transitioning between scales (R2= 0.77–0.94).

The article presents an analysis of modern studies on the genesis of hydrocarbons. It is concluded that over the past decades, including in connection with the fundamental improvement of scientific equipment, new facts have appeared that cast doubt on the concept of exclusively biogenic genesis of hydrocarbons. By now, quite a lot of arguments have been accumulated in favor of oil and gas formation due to abiogenic synthesis reactions. For example, the presence of biomarkers in natural oil, which is one of the postulates of the organic theory, can be explained by filtration through layers containing organic matter. At the same time, the analysis of oil biomarkers in a number of superdeep deposits showed the abiogenic origin of oil. The organic hypothesis of the origin of oil is not able to adequately explain the existence of giant accumulations of oil and gas, for which the calculations of the generation potential of oil source suites are significantly inferior to the identified oil reserves. In recent years, extensive factual information has been obtained on the existence of degassing processes of the Earth and the replenishment of the sedimentary cover with hydrocarbons from the depths through fluid-drainage channels in the crystalline basement. This process is accompanied by deep fluids, which are an intermediate, connecting link between the internal and external factors of the oil and gas basin. Deep fluids affect the formation of oil source rocks, generation efficiency, formation of physical properties of reservoirs, as well as the migration and aggregation of oil and gas. For the South Caspian oil and gas basin, a special class of geological structures of complex shape in the form of subvertical and subhorizontal geological bodies has been identified, which can serve as migration paths (drainage zones) and hydrocarbon accumulation zones. The formation of such a structure of intracrustal migration paths is explained by the process of transformation of clay minerals in elisional deposits. The possibility of such a transformation in the South Caspian basin is substantiated by studying the influence of clay content on fluid transfer processes.

To determine the strength of rocks, experimental studies are carried out with loading of samples. It is not always possible to conduct a significant number of experimental studies on loading. It is possible to predict the strength parameters of rocks based on lithology, porosity, density of rocks, etc. The current study assessed the possibility of using known methods to predict the statistical Young's modulus of limestones of the Bashkir horizon of the Moskudinskoe deposit. Eight rock samples were selected from the field; density, porosity, and permeability before loading were determined for each sample. During the loading process, the static and dynamic Young's modulus and tensile strength were determined. It is noted that the known methods correctly reflect the direction of change in the statistical Young's modulus from the dynamic value, but for each geographical area it is necessary to introduce clarifying coefficients. The dependence of the static Young's modulus on the dynamic one is obtained. Based on the least squares method, it was revealed that the density and porosity of rocks have the most significant effect on the known parameters before loading on the static Young’s modulus, and the tensile strength is additionally affected by permeability. Low-permeability rocks have a greater tensile strength. With a decrease in permeability from 5223 to 0.002 mD and porosity from 22.9 to 0.54 %, the tensile strength in reservoir conditions increased from 44.1 to 166.2 MPa. Accordingly, in highly permeable porous rocks, lower pressures are required to create fractures during hydraulic fracturing.

The Russian Federation, as a country that is one of the largest centers of oil production, is currently increasingly puzzled by the threats of reducing its volumes. Despite the achieved level of the industry infrastructure development, serious problems arise with the development of new explored (primarily in oil source rocks and reservoirs of viscous oil) and the pre-processing of residual reserves, since most wells in them do not reach flow rates close to profitable. This is primarily due to the long-term intensive depletion of easily recoverable (active) oil in all explored areas. The increase in the share of unconventional oil in the total balance of its reserves, which is especially important for the “old” production regions, inevitably makes it necessary to search for and commercially introduce new ways of extracting it. Meanwhile, the geopolitical problems that have arisen in recent years in relation to the Russian Federation, actualize the issues of its technological sovereignty in this area of knowledge.Among the many methods of increasing oil recovery and inflow intensification, the method of influencing the bottom-hole formation zone with a high-frequency electromagnetic field is distinguished, which, despite many years of research, is still considered experimental in the Russian Federation and is limited to evaluating the production and technical characteristics of use. At the same time, financial and economic indicators are overlooked, the identification of which will make it possible to justify the relative low cost and high profitability of the innovative methods.The subject of the research is technological developments in the field of exposure of oil-containing rocks to a source of electromagnetic radiation. The purpose of the study is to determine the degree of technical and technological readiness of oil field development methods based on the use of electromagnetic field energy, in terms of the effectiveness of technology implementation and the possibility of commercialization of developments.The main research methods are the analysis of scientific literature and a review of available patents, systematization and generalization of specialized data, methods of economic analysis.The paper reveals the prospects of electromagnetic technologies and the degree of development of this topic in the scientific community of the Russian Federation and foreign countries: the process of electromagnetic influence on the bottom-hole zone, its thermohydrodynamic effects, directions of industrial use in the petroleum branch are described, the key problems of the technology's market positioning and limitations of its commercialization opportunities are outlined. In addition, an analysis of the effectiveness of electromagnetic treatment in comparison with other types of impact on the reservoir is presented, and additional effects and increased effectiveness of electromagnetic effects when combined with other types with the formation of combined methods are determined. Based on the calculation of the energy balance, the economic efficiency of technology implementation has been established.The results of the work can be used in the analysis of prospects for the completion of deposits with oil reserves, the extraction of which by other methods besides electromagnetic heating (or combined with it) is economically unprofitable.