Perm Journal of Petroleum and Mining Engineering

This study investigates the construction of a probabilistic-statistical model using two reference areas of field X, drilled with horizontal and deviated wells. The model involves discriminant analysis combined with the development of both linear and multivariate regression relationships to predict well locations within the undrilled area and potentially forecast initial oil production rates. The impact of geological structure on well placement is analyzed using a t-test for comparing means. Based on identified differences in the geological structure at well locations, discriminant analysis was conducted to determine the factors influencing well type selection. The analysis revealed that the areas differ in geological structure, and porosity, permeability, and sand content of the formation influence the placement of horizontal and deviated wells. Linear and multivariate regression analysis was performed to classify the territory into zones with distinct geological structures. Linear regression analysis indicated that oil production rates in low-permeability reservoirs are differentiated into three classes with varying parameter influences within each production rate range. Multivariate regression analysis enabled the assessment of the combined influence of the most statistically significant formation characteristics on oil production rates and provided multivariate regression equations for predicting oil production rates of horizontal and deviated wells.

Assessing the hydrodynamic state of bottomhole zones is a key task to be solved when conducting and interpreting hydrodynamic well studies. The most widely used indicator of the condition of bottomhole zones in practice is the skin factor. However, its definition for the conditions of complex carbonate reservoirs is often accompanied by difficulties. Under conditions of incomplete pressure recovery, typical for the conditions under consideration, the value of the skin factor often takes on an unreliable value, in some cases leading to an incorrect interpretation of the state of the bottomhole zone, regardless of the approaches used to interpretation. Using actual data as an example, the article demonstrates that a reduction in the pressure recovery curve leads to false negative skin factor values both when implementing the tangent graph-analytical method and when processing in accordance with Bourdais's theory. In such conditions, it is recommended to use fundamentally different indicators of the state of the bottomhole zones, for example, a dimensionless diagnostic feature determined when implementing the method of deterministic moments of pressure. However, the lack of experience in the widespread practical application of this method necessitates an assessment of its reliability. For this purpose, this article uses an effective tool of mathematical statistics - multiple regression analysis, which, in this case, was reduced to the construction of multidimensional models of well flow rates. The geological and technological indicators of well operation were used as independent variables, including parameters characterizing the bottomhole formation zone (skin factor determined in the KAPPA Workstation software product (Saphir module), skin factor calculated using the tangent method, as well as a dimensionless diagnostic feature). According to the theory of regression analysis, the parameter that is included in the constructed model at the earliest possible step is reliable. The procedure for constructing and analyzing multidimensional statistical models performed in this work demonstrated the reliability of a dimensionless diagnostic feature in assessing the state of bottomhole zones of productive formations represented by complex carbonate reservoirs.

Rock permeability is not a constant value, it depends on many factors, including the presence of small particles in the fluids and porous medium - colloids that can clog pore channels and reduce permeability. The effect of natural colloids migration, as a rule, is not taken into account when determining the dependencies of permeability on effective pressure, this phenomenon is often ignored by many authors and interpreted as a result of the influence of other factors. The reason for insufficient attention to the fact of mobilization and migration of natural colloids is the difficulty of identifying this phenomenon. It was found that with a change in the effective pressure in the initial period of oil production in real conditions, permeability can decrease more than according to laboratory studies. With a small change in effective pressure, when the probability of a decrease and hysteresis of permeability due to deformation of the porous reservoir is extremely small, the dependencies of permeability on the amount of oil produced were established. This fact confirms the probability of the influence of migration of natural colloids on the decrease in permeability and emphasizes the need to study it. The aim of the work is to study the effect of colloid migration on the permeability of porous sandstones with changes in the fluid injection rate and pore pressure. The article presents the methodology and results of core filtration tests taking into account the decrease in the permeability of the porous medium caused by the migration of natural colloids during fluid injection. The conditions of filtration tests exclude other permeability factors, such as creep and chemical mobilization of colloids. The results obtained demonstrate the dependence of permeability on colloid migration with changes in the fluid injection rate and pore pressure. Filtration studies of core samples using the proposed technique showed that the permeability of the cores decreases only with fluid movement inside the samples, which is direct evidence of pore clogging due to the migration of natural colloids. It was found that a decrease in pore pressure leads to a more intense decrease in permeability during injection, which indicates additional mobilization of colloids. Porous media with higher permeability are less sensitive to colloid migration and changes in pore pressure.

Climate change and the reduction of sea ice in the Arctic Ocean allow scientists and engineers to think about the development of undiscovered hydrocarbon reserves, most of which are currently located in the Arctic. Underwater storage tanks are an important element of the infrastructure that can provide strategic storage of hydrocarbons in emergency situations or supply disruptions, as well as develop oil and gas reserves. The paper considers underwater oil storage tanks as one of the stages that will allow the exploitation of offshore fields underwater. The use of underwater storage tanks can contribute to a more sustainable and safe development of the oil and gas industry, reduce environmental risks and increase economic efficiency. In the course of the study, a numerical finite element model of the underwater storage tank was developed in accordance with the patent of M.S. Sonin. A numerical analysis of the stress-strain state of the storage tank with a capacity of 120,000 m3 was carried out and the distribution of stresses in the dome and foundation of the tank was estimated taking into account the features of the underwater structure. The main reasons leading to the loss of stability, destruction of the tank and foundation were identified. The most vulnerable part of the tank was the junction of the bottom and the wall, made with welded seams. For the foundation, the most dangerous sector is where the tank wall is monolithic into the foundation slab - here, maximum stresses of both compression and tension are observed. There are two possible approaches to leveling this problem: reduce the immersion depth of the storage facility, increase the thickness of the dome part of the body and add stiffeners to increase the rigidity and stability of the structure. However, both of these technical solutions will lead to additional costs and technological difficulties during the implementation of the project.

In the course of the research, a geological model of the mechanism of formation of gas-dynamic hazard centers in the rocks of the sylvinite-carnallite zone at the Verkhnekamskoye potassium salt deposit was developed. During the formation of gas-dynamic hazard centers in the rocks of the sylvinite-carnallite zone, the sources of gas-saturated fluids were gas-bearing aqueous solutions, including fluids from oil-bearing deposits located in the thickness of rocks underlying the salt deposit. The paths of ascending migration of gas-saturated fluids could be: rupture tectonic faults, thrusts, through zones of increased fracturing and permeability zones above the slopes of reef structures. Migration of gas-saturated fluids into the salt thickness from the underlying rocks occurred in a subvertical direction (from the bottom up). In the rocks of the sylvinite-carnallite zone, the lateral direction of migration of gas-saturated aqueous solutions prevailed over the vertical one due to the pronounced anisotropy of filtration properties. Fluids moved laterally along numerous clay layers, interlayers and intergranular space. During the migration of gas-saturated fluids in the rocks of the sylvinite-carnallite zone, epigenetic transformations of salt rocks occurred: replacement of sylvinites with rock salt, sylvinization of carnallites, formation of rocks of mixed composition (sylvinite + carnallite). During sylvinization of carnallites, the migration of aggressive gas-saturated fluids occurred in the direction from the zones of replacement of sylvinites with rock salt and variegated sylvinites in the direction of development of carnallite rocks. Variegated sylvinite as a product of epigenetic processes in rocks of the sylvinite-carnallite zone near the contact with carnallite rock has increased porosity and decreased strength. The patterns of free gas distribution in the layers of the sylvinite-carnallite zone are determined by the work of the three-zone functional system of halogen metasomatism. The decomposition of carnallite was accompanied by the formation of a deficit of the solid phase, the value of which could vary in a wide range of values and reach almost 70%. In areas of complete decomposition of carnallite in rocks of the sylvinite-carnallite zone, voids were formed due to the deficit of the solid phase. These voids, by analogy, can be considered a process of natural “undermining” of the overlying layers and “overmining” of the underlying ones. The effect of natural “undermining” was accompanied by the formation of crack systems in the undermining part of the sylvinite-carnallite zone due to unloading from rock pressure and rock displacement, through which free gases migrated into the undermining layers. As a result, in the rocks of the sylvinite-carnallite zone, under the influence of natural “undermining”, in the zone of unloading from vertical stresses due to destruction and stratification at the contacts of layers and layers, as well as along clay interlayers, favorable conditions are created for the filtration of free gases into it.