Carbonate rocks have a wide variety of pore shapes and different types of grains, which greatly affect the elastic properties and characteristics of the reservoir. This causes certain difficulties in petroelastic modeling. One of the problems is the scale of the input data, which is then used to build the rock physics model. The paper presents the results of studying three core samples of carbonate rocks of the Upper Devonian and Lower Carboniferous age, which are located in the South Tatar arch (Volga-Ural oil and gas basin (Russia)). To evaluate the structural characteristics of the pore space, the effective medium theory is used. The input data are the results of laboratory studies that include measurements of the velocities of longitudinal and transverse waves, porosity, and thin section and computed tomography analysis. When using the computed tomography, the core samples are analyzed at different resolution (12–37 µm/voxel). The tomography studies of pore space at different scales provide rather different values of porosity and pore aspect ratio. The tomography-based porosity estimations also differ from the experimentally measured porosity (up to 10%). The pore space characteristics provided by different datasets are used to build a rock physics model for the studied rocks that helps to estimate the elastic wave velocities with three different methods of effective medium theory (self-consistent approximation, differential effective medium (DEM), and the Kuster–Toksöz method). A comparison of the velocity estimations with their experimental analogs for dry rocks may indicate the presence of microcracks whose size is beyond the tomography resolution. Improved rock physics models incorporating both pores and microcracks are then used to predict the elastic wave velocities of fluid-saturated rock in a wide porosity range. It is demonstrated that the predicted values significantly differ (up to 30%) from those provided by the rock physics (RP) models constructed without the support of the tomography results. Moreover, other types of models are considered in which the difference in experimental and theoretical velocities is attributed to changes in the host matrix properties as compared to the calcite polycrystal, which are caused by various reasons.

Every year, the percentage of development of complex and unconventional hydrocarbon reservoirs is increasing, which is associated with the depletion of traditional oil and gas reserves. Carbonate reservoirs are hard-to-recover reservoir rocks due to the high degree of heterogeneity. A more detailed study of the lithological features and physical properties of carbonate rocks is an important and integral part of the complex reservoirs development. In the present work has done a comprehensive analysis of the lithological and geomechanical properties of the Middle Carboniferous strata deposits of the Dachnoye oil field, located in the southeast of the Republic of Tatarstan. The main attention in the research was focused on the estimation of the britleness of rocks. Britleness index is necessary for correct prediction of hydraulic fracturing. The result of the research is the identification of carbonate facies and their geomechanical characteristics, as well as the estimation of the britleness of rocks by various methods.

This work is devoted to investigate the ability of thermal shocking to create fractures in rock samples and thermal cracking of heavy crude oil structure. In order to study the thermobaric characterizations of catalytic and thermal decomposition reaction of binary mixture (BM), a series of experiments was designed in high-temperature and high-pressure reactor (HTHP) and the time to reach the maximum temperature and pressure were monitored. Before and after the experiments, core samples were scanned by 4D tomography. In addition, SARA analysis was done to study the effect of thermal shocking on heavy oil composition. The results showed that using BiMTheCh, the temperature in the reaction zone was increased up to 273 °C during very short time (2 seconds) after activation of the reaction. Either, the pressure was increased up to 129 atm. As results showed, the simultaneous sudden increase in temperature and pressure creates a thermal shock which reduces breakdown pressure from 235 to 12 atm. Computed scanning tomography results confirmed formation of new fractures on the surface of core samples. Results of the SARA analysis also confirmed that the molecular structure of heavy oil due to the binary mixture's reaction was changed. Sharp increase in pressure and temperature induced transformation of heavy components of crude oil such as asphaltenes into lighter components such as saturates. Generally, the binary mixture technology can be used as a new high-efficient and eco-friendly technology for enhanced heavy oil recovery from tight heavy oil reservoirs.

The paper presents an algorithm for reconstruction of stress state parameters of rock massif based on data on natural fractures. For one well developing an oil field, the directions of the principal in-situ stresses, their relative magnitudes, and the strength of the rocks in the near-wellbore space were reconstructed. Stress inversion results are in agreement with other methods of stress estimation, in particular, with the results of the mini-hydraulic fracture test. The inverse problem of stress state estimation is solved using the Monte Carlo method. An algorithm of applying the apparatus of mathematical statistics – the method of moments for determining distribution parameters from the Pearson distribution family – to quantify the ambiguity of the estimation of the directions of the principal stresses and their relative magnitudes is presented. The proposed algorithm can be used for independent reconstruction of stresses for carbonate rocks, provided that there is information about the conductivity of fractures in the rocks of the near-wellbore space to further improve the quality of one-dimensional and three-dimensional geomechanical modelling.

The paper examines the geochemical method's effectiveness for assessing the gas potential of territories and prospecting for natural gas fields in combination with data on a territory's neotectonic activity obtained from the digital elevation model analysis in the Eastern Siberia area. Geochemical data include the content of methane and its homologues (C1 – C6), determined by gas chromatography in subsoil samples, as well as the carbon isotope ratio (δ 13C) of the detected methane, measured on an isotope mass spectrometer. The reconstruction of neotectonic activity areas was carried out using a modified morphometric method of digital elevation model analysis. Estimates of the macroscopic fracturing of the sedimentary cover, also caused by neotectonic activity, were obtained from the digital elevation model as the density of lines – primary linear objects expressed in relief, identified using the method of A. A. Zlatopolsky. The information obtained from the digital elevation model allows to identify areas where the probability of gas fields destruction is the highest. A joint analysis of isotope-geochemical data and information on the probable hydrocarbon deposits destruction makes it possible to assess the prospects for the territory's gas content, as well as identify promising areas.

The paper presents the results of laboratory studies of the physical and mechanical properties of carbonate rock cores from one of the oil fields in the Republic of Tatarstan. The experimental data obtained, together with the results of geophysical studies of wells and fracture data, were used to calculate the stress-strain state of the rocks. Horizontal stresses were calculated using the Eaton poroelastic model. The deformation coefficients at the depth of hydraulic fracturing were preliminarily determined. The minimum horizontal stress was determined as the fracture closure pressure, and the maximum horizontal stress was calculated from the stress diagram (combining the rock failure criterion and the classification of tectonic states). The elastic moduli obtained from laboratory studies were used in the stress reconstruction. As a result, the values of the stress along the borehole section were calculated and the tectonic regime was determined. The dependence equations for the strength properties of the rocks composing the section were obtained and the strength values along the entire borehole were calculated. The geomechanical model was used to calculate the dependence of fracture pressure on fracture length and to assess the conditions of uncontrolled fracture growth.