Development and application of a double action acidic emulsion for improved oil well performance : laboratory tests and field trials

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Effects of microfractures on permeability in carbonate rocks based on digital core technology

Carbonate reservoirs develop many different types of microfractures that play an important role in increasing the effective reservoir space and permeability. Thus, the qualitative and quantitative characterisation of the effect of microfractures on permeability in rocks is essential. In this study, a quantitative method for evaluating the impact of different microfracture parameters on carbonate rock permeability was proposed. Lattice Boltzmann simulations were carried on two carbonate digital cores with different types of artificially added microfractures. Based on the simulation results, a partial least squares regression analysis was used to investigate the impact of microfractures on the permeability of the cores. Increases in the fracture length, aperture, and density were found to linearly increase the permeability of the carbonate rocks, and as the fracture length increased to penetrate the whole core, an exponential increase in permeability was observed. Additionally, the effect of microfractures on the digital core permeability was more significant in cores with high permeability compared to that in low-permeability cores. Although both fractures and matrix permeability contribute to the permeability of the digital cores, the former were found to have a greater effect on the permeability.Cited as: Liu, C., Zhang, L., Li, Y., Liu, F., Martyushev, D. A., Yang, Y. Effects of microfractures on permeability in carbonate rocks based on digital core technology. Advances in Geo-Energy Research, 2022, 6(1): 86-90. https://doi.org/10.46690/ager.2022.01.0

Conditions for Effective Application of the Decline Curve Analysis Method

Determining the reliable values of the filtration parameters of productive reservoirs is the most important task in monitoring the processes of reserve production. Hydrodynamic studies of wells by the pressure build-up method, as well as a modern method based on production curve analysis (Decline Curve Analysis (DCA)), are some of the effective methods for solving this problem. This paper is devoted to assessing the reliability of these two methods in determining the filtration parameters of terrigenous and carbonaceous productive deposits of oil fields in the Perm Krai. The materials of 150 conditioned and highly informative (obtained using high-precision depth instruments) studies of wells were used to solve this problem, including 100 studies conducted in terrigenous reservoirs (C1v) and 50 carried out in carbonate reservoirs (C2b). To solve the problem, an effective tool was used—multivariate regression analysis. This approach is new and has not been previously used to assess the reliability of determining the filtration parameters of reservoir systems by different research methods. With its use, a series of statistical models with varying degrees of detail was built. A series of multivariate mathematical models of well flow rates using the filtration parameters determined for each of the methods is constructed. The inclusion or non-inclusion of these filtration parameters in the resulting flow rate models allows us to give a reasonable assessment of the possibility of using the pressure build-up method and the DCA method. All the constructed models are characterized by high statistical estimates: in all cases, a high value of the determination coefficient was obtained, and the probability of an error in all cases was significantly less than 5%. As applied to the fields under consideration, it was found that both methods demonstrate stable results in terrigenous reservoirs. The permeability determined by the DCA method and the pressure build-up curve does not control the flow of the fluid in carbonate reservoirs, which proves the complexity of the filtration processes occurring in them. The DCA method is recommended for use to determine the permeability and skin factor in the conditions of terrigenous reservoirs

Evaluation of opening of fractures in the Logovskoye carbonate reservoir, Perm Krai, Russia

The development of naturally fractured carbonate reservoirs is extremely challenging. Such reservoirs have a dual pore structure consisting of low-permeable matrix with large pore volume and high-permeable fractures constituting main paths for fluid flow. Productivity of wells drilled in such formations tends to decrease rapidly due to the drop in the reservoir pressure and closure of fractures. Therefore, it is crucial to monitor opening of fractures for the effective development of carbonate reservoirs. Three methods for monitoring of opening of fractures including tracer indicators method, Warren and Root method and Victorin’s empirical relation, are applied in the Logovskoye oil reservoir, a carbonate Tournaisian-Famennian formation in Upper Kama Region, Perm Krai, Russia. The three methods provide reliable estimation of the opening of fractures, which match the reported laboratory data obtained on thin sections of core samples. The limitations of each method are also discussed. The tracer indicator method is time-consuming, the Warren and Root method includes hydrodynamic studies and requires shutdown of wells influencing the oil production, and the application of Victorin’s relation requires estimation of initial opening and current compressibility of fractures, which can be done using analysis of cores or tracer indicators studies. The appropriate method for monitoring of opening of fractures should be chosen according to available resources, time, and economic targets of the development project

Justification of the optimal type of well completion profile based on a retrospective assessment of the technical and economic performance indicators

To date, significant foreign and domestic experience has been accumulated in the construction and operation of horizontal, multilateral and multilateral wells, as well as the restoration of an idle well stock by drilling sidetracks and sidetracks into various productive formations: low-permeability and highly dissected, with low values of effective oil-saturated thicknesses, degraded hydrodynamic connection with the contour area, etc. In this regard, it becomes extremely important to make a decision on choosing the optimal well profile in specific geological and physical conditions. The relevance of the work is also confirmed by the fact that at some development sites there is a decrease in the oil production rate of horizontal wells to the level of directional wells in the initial period of operation. Based on a significant difference in the reservoir properties of oil fields in the Perm Territory, all the analyzed objects operated by horizontal wells are combined into several groups: “northern” (N) and two “southern” (S1 and S2). The main parameter in the selection of groups was the coefficient of mobility of oil. The well-by-well technical and economic assessment performed in the article, based on the actual values of production over a long period, made it possible to identify the optimal well profile depending on the geological and physical characteristics of the reservoir. Combining the main geological characteristics that affect the technological parameters of well operation, with an economic assessment, the dependences of the net present value on the formation hydraulic conductivity were built. Dependences built for the first time make it possible to reasonably select the well profile in specific geological and physical conditions. Also in the work for a variety of geological and physical conditions, the value of the minimum profitable oil production for various well profiles is determined. Thus, the basis has been created, which is necessary for determining the profile of wells when planning production drilling

Paleoenvironmental Evaluation Using an Integrated Microfacies Evidence and Triangle Model Diagram: A Case Study from Khurmala Formation, Northeastern Iraq

The sequence of the Khurmala Formation located in northeastern Iraq was measured and sampled to evaluate its paleoenvironmental features, including sedimentological and microfacies analyses. The studied formation was analyzed under an optical microscope and was dominated by three main types of microfacies: coralligenous–algal wackestone, foraminiferal–peloidal packstone, and foraminiferal–peloidal grainstone. These hosted microfacies in the Khurmala Formation rarely contain a non-geniculate algae that insufficient for complete reef-building as a crest, but among the common algae, there are calcareous geniculate and green algae associated with benthic foraminifera and a minor component of planktonic foraminifera in the basin due to high-energetic open shallow-water environmental conditions during the deposition of the Khurmala Formation. The relative percentages of foraminifera, including both benthic and planktonic, plotted on triangular diagrams revealed a graphic indicator of paleoenvironment analyses. Detailed examination and analyses for microfacies, new findings of calcareous green algae (Acicularia and Clypeina), and microfacies analyses based on the triangle method and standard facies zones, denote that the upper part of the Khurmala Formation was richer in fined grain and Acicularia green algae, reflecting lower energy conditions than during deposition in the lower part of the formation, which was represented by algal wackestone microfacies and dominated by Clypeina green algae. In summary, these fluctuations in facies/microfacies changes, the appearance of new green algae, and different percentages of foraminiferal content are linked to the global sea level fluctuation that occurred during the Paleocene–Eocene interval

STUDY OF THE FORMATION OF A WELL BOREHOLE ZONE WHEN OPENING CARBONATE RESERVOIRS TAKING INTO ACCOUNT THEIR MINERAL COMPOSITION

The relevance of the research is caused by the significant influence of the permeability of bottomhole zones of productive formations on well productivity. In practice, a decrease in reservoir permeability in bottomhole zones is often caused by the effects accompanying the interaction of the filtrate of process fluids used in the construction and workover of wells. In turn, the study of the features of the interaction of various process fluids and rocks will allow you to effectively plan operations for the construction and repair of wells. The main aim of the research is to study the features of the interaction of process fluids and rocks based on the integrated use of modern laboratory studies of core and field data. Object: bottomhole zones of wells operating a carbonate object of oil field development. The methods: hydrodynamic studies of wells, processed in the KAPPA Workstation software (Saphir module), using the methods of tangential and deterministic pressure moments with an assessment of the state of bottomhole zones; modern methods of laboratory core research, including electron microscopy, X-ray phase analysis, micro-X-ray tomography. The results. When processing the materials of hydrodynamic studies, it was found that the state of the bottomhole zone in 70 % of the wells of the fund is characterized as degraded, and in some wells – to a large extent, which is not typical for carbonate reservoirs. Water-based drilling fluid was used in all wells during formation opening. Studies of core samples from this deposit (at the micro level) made it possible to establish the complex structure of the void space, including the presence of cracks partially healed by clay material. The interaction of clay material with the water base of the drilling fluid is one of the common reasons for the decrease in the permeability of the reservoir in the zone of its contact with the drilling fluid. Similar studies performed in another field with no clay material in the voids demonstrated the effectiveness of the same water-based drilling fluids, which is confirmed by the almost unchanged state of the bottomhole zone after the wells were put into production

A Comprehensive Review of the Oil Flow Mechanism and Numerical Simulations in Shale Oil Reservoirs

The pore structure of shale oil reservoirs is complex, and the microscale and nanoscale effect is obvious in the development of shale oil reservoirs. Understanding the oil flow mechanism in shale reservoirs is essential for optimizing the development plan and enhancing the recovery rate of shale oil reservoirs. In this review, we briefly introduce the occurrence status of shale oil and shale oil flow in the inorganic matrix and the organic matrix (including the shrinkage of kerogen, oil diffusion in kerogen, oil transport in the organic pore channels, coupling of diffusion, and fluid transport in the organic matrix). Then, the shale oil microflow simulation and a coupling model of double-porous media for microflow and macroflow in the production process of shale oil are discussed. Finally, we summarize the main conclusions and perspectives on the oil flow mechanism and numerical simulations in shale oil reservoirs. An accurate description of shale oil occurrence status and shale oil flow in the inorganic and organic matrices is crucial for the numerical simulation of shale oil reservoirs. It can provide a basis and reference for the future directions of shale oil flow and numerical simulations during the development of shale oil reservoirs

FEATURES OF DETERMINING FILTRATION PARAMETERS OF COMPLEX CARBONATE RESERVOIRS AT THEIR OPERATION BY HORIZONTAL WELLS

Link for citation: Salnikova O.L., Chernykh I.A., Martyushev D.A., Ponomareva I.N. Features of determining filtration parameters of complex carbonate reservoirs at their operation by horizontal wells. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 5, рр.137-147 In Rus. The relevance of the research is caused by the fact that in the conditions of continuous deterioration in the structure of hydrocarbon reserves, complex technologies for their development are being implemented, based, among other things, on the use of wells of complex design (horizontal wells). The increase in the share of horizontal wells in the total operating stock determines the relevance of the scientific and methodological justification of research technologies that comprehensively take into account the structural features of the reservoir and the geometry of the fluid flow. The most complete volume of geological and field information can be obtained by combining two main types of research – geophysical and hydrodynamic. The problem of data, in fact, of the indirect research methods, should be considered the need to assess the reliability of their results and the lack of approaches to reduce interpretation uncertainties, which is especially important in the conditions of the impossibility of coring in horizontal wells. This article proposes possible directions for solving these problems. The main aim of the study is the scientific substantiation of approaches to research and interpretation of their results, allowing reliably determining the filtration parameters of productive formations during their operation with horizontal wells. Object: complex Tournaisian-Famenian carbonate reservoirs in Perm region, operated by horizontal wells. Methods: geophysical and hydrodynamic studies of wells, laboratory core studies, multivariate statistical modeling. Results. It has been established that geophysical studies (interpretation was made in accordance with the algorithms for vertical wells) do not allow reliably estimating the length of the horizontal section of the wellbore and the filtration properties of the reservoir. It is recommended to determine the filtration properties when interpreting the data of hydrodynamic studies of wells. Algorithms of modern methods of interpretation of hydrodynamic studies, implemented in common software products, allow you to determine a large amount of geological and field data, including a number of parameters specific to horizontal wells. However, this procedure is accompanied by uncertainties, for example, in terms of the choice of interpretation models. The performed multivariate statistical modeling made it possible to substantiate the methodology for reliably determining the filtration properties of the reservoirs under consideration and the approach to reduce uncertainties when choosing interpretation models

A Multi-Criteria Decision Intelligence Framework to Predict Fire Danger Ratings in Underground Engineering Structures

A wide variety of natural catastrophes are induced by coal mining, with fire hazard being one of the most significant threats to underground engineering structures. In recent years, there has been an alarming rise in mine fire accidents due to the abundance of coal deposits around the world. Underground fires and explosions have continuously been the primary reason for a significant proportion of deaths and the destruction of infrastructure over the last few decades. Underground mining fires deplete natural coal resources, have an adverse impact on the environment by releasing hazardous chemicals and greenhouse gases into the atmosphere, and cause subsidence due to coal depletion during the combustion process. This study aims to predict fire danger rating of underground mining production processes by using the application of state-of-the-art unsupervised and supervised machine learning techniques. The developed k-nearest-neighbors-based isometric feature mapping and fuzzy c-means clustering algorithm has shown its dependability and superiority with a higher accuracy and has been advantageous to the monitoring and prevention of fire danger in underground mining production processes. The proposed multi-criteria decision intelligence framework permits early fire detection, providing the emergency response team extra time to respond the critical situations in order to prevent the fire from spreading, hence promoting sustainable, green, climate-smart, environmentally friendly and safe mining engineering operations