Zones In Wells Research Articles

Ocena skuteczności oczyszczania strefy przyodwiertowej

The article discusses issues related to methods of treatment of the bottomhole zone of wells and assessment of its effectiveness. Analyses of a large volume of field material have shown that the most effective treatments for oil fields at a late stage of operation include injection of solvents, the use of acid-containing micro-emulsions, acid treatment, and the use of foam systems. The study proposes a method for identifying the factors that have the greatest impact on the efficiency of geological and technical activities. This approach allows for the correct selection of wells for treatment and the evaluation of the effectiveness of the measures implemented, aiding in determining their potential for further use. For production wells selected for near-wellbore treatment, it is crucial to accurately assess the economic efficiency post-treatment. This requires evaluating changes in the permeability of the near-wellbore zone following treatment. Therefore, in these wells, the “pressure build-up curve” (PBC) is recorded both before and after treatment. The increase in current production due to acid treatment of the near-well zone is determined by comparing production levels before and after treatment. The overall increase in oil production is determined by comparing the well’s production curve prior to development with the actual curve following development. When treating the bottomhole zone, it is essential to consider the well as part of a larger system of interacting objects, where improving the characteristics of one object does not necessarily enhance the operation of the entire system. The effectiveness of treating the bottomhole zone with solvents is significantly influenced by factors such as the percentage of resins in the product, the specific gravity of oil before treatment, the specific gravity of the solvent, and the viscosity of the oil.

Prediction of technological indicators of selective water isolation of water-watered wells by nanostructured gel

In this work the composition forming nanostructured gel, which does not change phase permeability of oil, easily penetrating into water-saturated depth of the formation in watered wells, effectively closing the drainage channels, is established, the possibilities of its rapid heating up to formation temperature, gel formation within a certain time in contact with water depending on the concentration of the selected composition and with its use of involvement in the development of residual oil reserves, which are in watered wells, are investigated at injection of this composition into the well. As an optimal variant of well isolation in terrigenous reservoirs of oil fields it is suggested to use nanocomposite on the basis of silicate gel (with the content of liquid glass 4 % (modulus 3.1), 0.6 % of hydrochloric acid and 0.063 % of metal nanoparticles). The mechanism of selective isolation of water flow in production wells is based on the fact that when the composition is injected into the production well, part of its volume gets into the oil-saturated layer, and the rest – into the water-saturated layer. The composition is distributed in proportion to the permeability of the layers. In the process of well development the composition in the oil-saturated layer is removed, and in the water-saturated layer it retains its isolating properties. The greater the volume of injected fluid, the greater the isolation factor and pressure gradient. The isolation factor is directly proportional to the volume injected. Gel formed in the water-saturated layer corresponding to the volume of the injected composition reduces the phase conductivity on water at least 30 times. Practically does not change the phase conductivity by oil. On the basis of the calculation model including physical and chemical characteristics of selective isolation process taking into account real field conditions, the influence of possibility to isolate bottomhole zone of wells by gel on technological indicators of its operation was estimated. Thus, when putting into operation a well after isolation by water, the production of which was flooded with water, in the initial moments there was a sharp increase in oil flow rate (2–3 times), and at the subsequent stage – a slight decrease in the rate, compared to the flow rate before isolation, the effective time of development or flushing was about 150 days.

Prediction of Hydrodynamic Parameters of the State of the Bottomhole Zone of Wells Using Machine Learning Methods

The relevance of the development of a methodology for the operational assessment of the bottom-hole formation zone (the permeability of the bottom-hole formation zone and the skin factor) is primarily due to economic considerations, since existing approaches to its definition based on hydrodynamic studies lead to shortages and increased risks of failure to ensure the output of the well. In this regard, the use of modern methods of working with big data, such as deep learning of artificial neural networks, will ensure monitoring of the condition of the bottom-hole zone of the well formation without stopping them for hydrodynamic tests, which will reduce losses for oil production enterprises. It will allow for operational analysis for effective and timely application of intensification technologies, enhanced oil recovery. The authors analyzed the existing methods for determining the bottom-hole characteristics of the formation and machine learning approaches in the direction of solving this problem. The article presents a methodology for the operational assessment of the state of the bottom-hole formation zone: the permeability of the near bottomhole zone (NBHZ) and the skin factor using artificial neural network training approaches based on geological, operational data and the results of interpretation of hydrodynamic studies on the example of sandstones of oil fields in the Perm Region. A fully connected neural network was used to predict the NBHZ permeability. The article presents the results of testing various neural network architectures: the number of layers and neurons in layers with the choice of the best one. Some techniques were used to prevent over-training of models. The author’s methodology for assessing the skin factor of wells is proposed using a comprehensive analysis of the constructed statistical models and training models of artificial neural networks to solve the regression problem. In future studies, it is planned to use recurrent and convolutional neural networks to study the dynamic components of the formation of the bottom-hole formation zone and create an integrated approach to solve the problem.

SELECTION OF THE OPTIMAL METHOD OF INTENSIFICATION AND STABILIZATION OF OIL PRODUCTION IN THE FIELDS OF WESTERN KAZAKHSTAN

The article discusses research aimed at determining the effectiveness of measures to intensify oil production in the fields of Western Kazakhstan. Based on the results obtained, recommendations were developed for the further application of oil production intensification methods for the conditions of West Kazakhstan fields. The highest oil displacement coefficient (ODC) in the development of high-viscosity oils can be achieved using thermal production methods. To reduce viscosity, in practice, deep warming of the bottom-hole zone of the well is used, which can be carried out by electrothermal treatment of the bottom-hole zone of the formation, steam treatment of wells using downhole solid fuel heat generators, and so on. A combined heating method is proposed that allows heating the well products. Heating is provided by a solar panel all year round. In case of a decrease in solar activity, it automatically switches to a constant electric current. This method differs from others in that the solar panel continuously supplies electricity, reducing the consumption of electrical energy. In addition, the article presents the results of studies of the optimal heating temperature of the bottom-hole formation zone, potential well flow rates at this temperature and oil viscosity. Recommendations are given on the most rational way of heating the bottom-hole zone of wells in the fields of Western Kazakhstan.

METHODS FOR INCREASING THE CONDENSATE RECOVERY COEFFICIENT WHEN DEVELOPING GAS CONDENSATE FIELDS

This article will discuss methods for increasing the condensate recovery coefficient and the concept of condensate recovery. Gas condensate is a cold hydrocarbon reservoir that includes natural gas as well as liquid hydrocarbons, often in the form of liquid condensate. During reservoir extraction, liquids are mixed from mixtures of light hydrocarbons (eg methane, ethane, propane) and denser liquid hydrocarbons (known as condensates). Gas condensates are found in underground reservoirs, where temperature and pressure conditions allow the gas to condense into liquid form as it moves from the formation to the surface. Such situations are often observed in tanks where there is a combination of increased pressure, high temperatures and a specific gas composition. The condensate production indicator from the reservoir describes the level of gas condensate extraction from gas condensate and oil and gas condensate fields. A distinction is made between instantaneous condensate production (determined at a certain point in time) and final production (at the end of commercial exploitation of the field). To quantify condensate production, the condensate production indicator is used - this is the ratio between the given definition of condensate and the reserves taken from the reserves of the field based on its study (expressed as a percentage or fraction of units). This indicator is used to extract recoverable condensate reserves. In addition, it is taken into account when developing a project for a gas condensate or oil and gas condensate field, taking into account the efficiency of the technology used. The completeness of condensate removal in some cases determines the reasonableness of developing the selected system. The main features of the behavior of gas condensate systems are associated with the corresponding phenomena reflected in the phase diagrams of reverse condensation and evaporation. These features lead to the fact that when the pressure in the gas condensate system decreases to a level below the saturation pressure, condensation of heavier hydrocarbons (condensate) occurs. If the pressure in the gas condensate formation during development is maintained at the initial level (or the pressure at the beginning of condensation), then phase transitions occur only in the formation zones adjacent to the well. This requires taking into account changes over time, such as changes in filtration characteristics in the bottomhole zones of wells. When developing a gas condensate field to the point of depletion, condensate begins to fall out everywhere in the reservoir. However, the condensate that falls often has little effect on the gas saturation coefficient of the entire formation. Consequently, when developing a gas condensate field until depletion (with a low condensate content in the gas), filtration flows can be considered as single-phase, since the precipitated condensate remains motionless. Low condensate saturation of the formation leads to slight changes in its capacitive and filtration characteristics. In the zone of the bottomhole space of the formation, two-phase filtration occurs. Keywords: gas, gas condensate, heavier hydrocarbons, dew point, the condensate recovery coefficient.

Investigation of plugging materials for strengthening the bottomhole zone of wells in conditions of aggressive formation fluids

Investigation of plugging materials for strengthening the bottomhole zone of wells in conditions of aggressive formation fluids

Development and research of a new nanocomposition for elimination of asphaltene-tar-paraffin deposits

At long-operating fields, due to a drop in reservoir pressure and temperature in the bottom-hole zone of wells as a result of degassing, light oil fractions volatilize and heavy fractions deposit on the rock surface, which leads to weakened filtration and reduced productivity. On the other hand, these particles deposited in the pores hydrophobize the rock surface, and water passing through this surface mixes with the deposited hydrocarbons to form an emulsion. The emulsion formed reduces phase conductivity. For effective exploitation of this type of oil fields, compositions that have a stronger effect on the bottom-hole zone and are more economically feasible have been developed and their properties have been studied. As a result of these studies it was revealed that with the addition of small concentrations of metallic nanoparticles to compositions consisting of solvents and surfactants, the ability of the developed new composition to dissolve asphaltene-tar-paraffin deposits is significantly increased. Keywords: asphaltene-resin-paraffin deposits; metal nanoparticles; surfactants; solvents; new composition.

Revealing patterns in the influence of variable permeability of well bottomhole zones on the operational modes of underground gas storage facilities

The object of this study is underground gas storage facilities (UGSF). The main problem being solved is to ensure effective management of the operation process of underground gas storage facilities (UGSF) at operational and forecast time intervals. One of the main factors that affect the operating modes of UGSF is significantly non-stationary filtration processes that take place in the bottomhole zones of wells. The complexity of assessing the multifactorial impact on depression/repression around the wells affects both the speed and accuracy of calculating the mode parameters of UGSF operation. Analysis of the results of well studies revealed a significant area of uncertainty in the calculation of the filtration resistance coefficients of their bottomhole zones. A satisfactory accuracy of the result in the expected time was achieved by building a model of integrated consideration of the influence of the parameters of all the bottomhole zones of the wells on the mode of UGSF operation. It turned out that the integrated consideration of the impact on the parameters of the bottomhole zones of the wells neutralized the effect of significant changes in the filtration resistance coefficients of the wells and ensured a sufficient speed of calculation of UGSF operation modes. Simultaneous simulation of ten operating UGSFs under the peak mode of withdrawal the entire available volume of active gas takes no more than six minutes. The speed of simulation of filtration processes in the bottomhole zones of wells ensured finding the best of them according to one or another criterion of operation mode quality. As a result of the research, a model was built and implemented by software, which was tested under real operating conditions and provides optimal planning of UGSF operating modes for given time intervals. Its use is an effective tool for the operational calculation of current modes and technical capacity of UGSF for a given pressure distribution in the system of main gas pipelines. The performance of the constructed mathematical methods has been confirmed by the results of numerical experiments

Reducing the formation of asphaltene deposits and increasing the flow rates of oil wells

Purpose. Reducing the formation of asphaltene deposits in the bottom-hole zone of wells and increasing their flow rate. Methodology. The purpose of the work is achieved by conducting theoretical and experimental studies on the formation of asphaltene and paraffin deposits in the bottom-hole zone of the oil reservoir and identifying patterns of their dissolution by pumping heated low-boiling oil components containing carbon atoms C6–C9 in molecules into the well. Findings. The experimental studies conducted under laboratory conditions showed high solubility of asphalt-resin and paraffin compounds in low-boiling oil components. To prevent the deposition of asphaltene deposits in the bottom-hole zone of wells, the turbulent nature of oil movement is necessary, which is achieved by increasing reservoir pressure when water or gas is injected into the oil reservoir. It is also necessary to have a reservoir pressure above the saturation pressure of oil with gas. Effective methods are recommended to reduce the formation of asphaltene deposits in the oil reservoir in the bottom-hole zone and to restore the production rates of producing wells by pumping heated low-boiling oil components containing carbon atoms C6–C9 in molecules into the well. It has been experimentally established that when the temperature of the specified solvent changes from 20 to 800 °C, the time of complete dissolution of the asphalt-resin compound (bitumen) in the form of balls with a diameter of 5 mm is within 0.20–3.0 hours, and in reservoir conditions with a temperature of 60–80 °C – significantly less for 0.2–0.25 hours. This indicates that before pumping low-boiling oil components containing C6–C9 carbon atoms in the molecules, they must be preheated to reservoir temperature. A method is also proposed for treating the bottom-hole zone of an oil reservoir with a complex solution including low-boiling oil components containing carbon atoms C6–C9 in molecules, hydrochloric and fluoric acids. Originality. Effective methods are proposed to reduce the formation of asphaltene and paraffin deposits in the bottom-hole zone of the oil reservoir and to restore the production rates of producing wells by pumping heated low-boiling oil components into the well, as well as a complex solution with the inclusion of acids. Practical value. A technique has been developed to improve technological processes to reduce the formation of asphalt-resin-paraffin deposits and to establish rational parameters of the installation for producing low-boiling oil components containing carbon atoms C6–C9 in industrial conditions. Using the results of research in oil fields allows you to restore the initial permeability and thereby increase the flow rate of oil wells by 20–30 %.

SOME ASPECTS OF THE GAS WELL TESTING PROCEDURES

The article discusses the basic concepts of designing and testing gas wells. The need to increase the selection of hydrocarbons determines the relevance of creating an information array of data on the reservoir and the fluids that saturate it. To collect information, the results of studies of the bottomhole zone of wells, its drainage zone and the interwell space of the reservoir are analyzed. According to the status, the studied wells are divided into operating and stopped for the period of research. According to the type of wells, production and injection wells are distinguished. In the first, the inflow curve is taken for various well operation modes (IPR). Secondly, the dependence of pressure change during shutdown of a working well (PBU) is analyzed. These studies can be carried out both in production and injection wells. To study well clusters and evaluate the interwell space, the methods of interference testing and the method of pulse studies are used. Information on hydrodynamic studies is provided. Note that the studies carried out in wells can be divided into two large groups. The first one is hydrodynamic studies (well test) which involves carrying out various tests to establish the characteristics of the rock that makes up the reservoir, as well as the properties of the fluid that saturates the porous medium. As a result of the studies, such parameters as permeability, porosity, average reservoir pressure, and degree of reservoir heterogeneity (presence of a screening fault, degree of fracturing, and layering) are determined. The second group includes studies that are carried out in wells in order to determine the volume of potential production, that is, productivity studies. It should be noted that the quality of the results is influenced by a large number of factors that must be taken into account in the process in order to increase the degree of reliability of the information obtained about the reservoir system. Thus, this article provides an analysis and the degree of influence of one or another parameter on the reliability of well test results. Keywords: flow rate, test duration, well, reservoir properties, skin factor, permeability, bot-tomhole pressure.

Study of the Rheological Characteristics of Sediment-Gelling Compositions for Limiting Water Inflows

In view of the poor knowledge of the applicability of sediment-gelling compositions (SGCs) in waterproofing the bottom-hole zone of wells, work in this area of research is one of the most promising in waterproofing today. The key goal of this work is to study the prospect of using SGCs for waterproofing as well as to calculate the rheological characteristics of the proposed SGCs depending on variations in the components of their composition (alkali and polymer). In the course of our studies, it was found that the key factors influencing the rheological characteristics of SGCs are not only the variation in the ratio in the composition of alkali and polymer but also the degree of salinity of the formation water, which must be taken into account when developing waterproofing. During this research, it was found that due to the absence of calcium and magnesium ions in fresh water, the proposed polymers have good solubility (the exponent in the rheological model is equal to or close to unity), which leads to an increase in the viscosity of solutions. The dependence of changes in the rheological constants of SGCs on such parameters as temperature and alkali concentration have been established. It was determined that an increase in the solution temperature leads to an increase in the rheological constant n from 0.8 to 0.92 (at a polymer concentration of 0.05 and a NaOH concentration of 0.1), while a variation in the NaOH alkali concentration from 0.1 to 0.75 leads to similar changes in one measured temperature range. The results obtained can be used in the future to evaluate the use of SGCs to create barrier waterproofing in the bottom-hole zone of wells during oil production.

DEVELOPMENT OF ZEOLITE-CONTAINING LAYERS IN WESTERN SIBERIA DEPOSITS

Often, during the development of wells that have come out of drilling, these wells do not reach the design operating modes, since when the aqueous filtrate of the drilling fluid penetrates into the bottomhole formation zone (BFZ) and comes into direct contact with clay minerals, the pores narrow, the formation of insoluble sediments and creates insurmountable barriers. for the movement of reservoir fluids in the reservoir to the perforation interval, resulting in a decrease in the productivity of production wells. If the clayey cement of the reservoir rock contains zeolite, then its role in reducing the porosity and permeability properties (PPP) of rocks in the bottomhole zone of wells will be insignificant, since its presence does not lead to an increase in the water saturation of rocks in the bottomhole zone of wells and does not affect the reduction well flow rate. The article presents the results of experimental work on core samples of zeolite-containing rocks and geological and field studies in order to establish the effect of zeolites on obtaining potential well flow rates. Acid solutions are proposed for the development of wells when they exit from drilling.

EXPERIENCE OF USING ACID TREATMENTS IN THE OIL FIELD SUWAYDIYA (SYRIA)

Link for citation: Mohammad Almohammad Alnayef, Zain Alabidin Dalfi Abd Ali Khalaf, Gnidan E.V. Experience of using acid treatments in the oil field Suwaydiya (Syria). Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 7, рр. 50-58. In Rus. Relevance of the research is caused by the need to increase oil recovery from wells developed in the fields of Syria, in the carbonate reservoirs of the Massif and Shiranish formation, for which there is a natural drop in production rates due to decrease in reservoir pressure, water cut, opening of reservoirs with low reservoir properties and increase in the share of hard-to-recover reserves. The main aim of the study is to analyze the results of acid treatments to improve oil recovery in the field of Suwaydia, Syria. The object of study is the carbonate complexes in the Upper Cretaceous deposits of the Massif formation and the Shiranish formation, Syria. Methods: review of domestic and foreign experience in treating the bottomhole formation zone using acid compositions and analysis of production, technological, lithological, geological, geophysical, and field data of wells treated with acids. Results. The paper introduces the advantages of the acid treatments method, such as improving the reservoir permeability and decreasing the skin factor by increasing the pore space and fracture channels, as well as removing the filter cake and various inorganic sediments that prevent oil flow. The undesirable effects of acid treatments: corrosion, secondary sedimentation, water cut, are indicated. The geological and physical conditions of the well and reservoir for choosing a treatment technology are considered. They are: reservoir temperature, filtration, and reservoir properties of rocks, granulometric (fractional) and mineralogical composition of rocks, chemical composition of reservoir fluids. The main directions of measures for solving geological and technological complications that arise during acid treatments using inhibitors, new multicomponent compositions of acid agents, special additives, and multi-stage treatments are noted. The paper introduces the technology and results of the application of acid treatments: hydrochloric acid treatment and foam hydrochloric acid treatment of the bottomhole zone of wells located in the north-east of the Syrian Arab Republic, which belong to the two oil field – Suwaydia and Zarba – of the Al-Hasakah Oil Fields Administration. It was noted that the use of a simple hydrochloric acid treatment of several wells did not lead to the predicted increase in oil recovery, and the use of an acid mixture (HCL at a concentration of 15 %, HF at a concentration of 3 %) in well no. 462 of the Suwaydia oil field showed an increase in productivity of 1,5 times. Recommendations are given for improving acid treatments at the Suwaydia, Syria fields to intensify oil production.

Improvement of methods for combat with sand in production wells

Today, a large number of methods are used to combat the flow of sand along with the reservoir fluid, which must be divided into the following groups: improving the operating conditions of wells, under which sand rises along with the fluid from the well; creation of technology and equipment that allow retaining sand in the annulus. Methods that are used according to the first group are rarely used due to the fact that conditions arise for hydroabrasive wear of all equipment that comes into contact with sand, disturbance of the formation structure in the bottomhole formation zone, sand deposits in surface equipment and in the well sump when wells are shut down. The most promising method of combating these manifestations are technologies and equipment used according to the second group: injection of cement, foam-cement and cement-sand mixtures into the annulus of the well bottom zone; downhole filter application; injection of sand with a large fraction of grains and gravel into the bottomhole zone of wells; injection of synthetic resins into the annulus of the bottomhole zone of the well; combined methods, including the above. Titanium screens and gravel packs are the most effective means of preventing formation failure. Keywords: downhole reservoir; sand plug; well; steam-thermal impact.

Acid systems usage for inflow intensification technologies experimental justification

Purpose. Research and experimentally substantiate the use of acid systems for inflow intensification technologies. To study the peculiarities of the mechanisms and methods of restoration of the near-outbreak zone of the reservoir. The methods. 1. Diagnosis of the causes of deterioration. 2. Selection of appropriate reagents for processing. 3. Selection of the method of delivery of the agent into the reservoir (design). 4. Modeling (calculation). 5. Prediction of the final productivity of the well. Findings. There are some physical means of diverting the injected acid composition for selective treatment, which include: the use of rubber-coated balls added to the injected fluid composition to plug the receiving holes, and the use of packers that isolate the zone necessary for cleaning during operation from the rest of the wellbore. Mechanical methods of selective cleaning differ from others in that they completely cover non-target intervals, directing the entire flow of the reagent to the open area. The originality. Increasing the effectiveness of the influence of hydrochloric acid solutions on the near-cut zone of wells is one of the factors in the effective development of oil deposits in carbonate reservoirs. To solve this problem, geological and technological justification of the choice of wells and technological parameters of influence in specific geological conditions of the deposits is necessary. Practical implementation. A significant number of technologies proposed today for the intensification of the subsurface zone with hydrochloric acid indicate a great variety of productive layers in terms of their occurrence, geological-physical and physico-chemical properties of reservoir rocks and fluids that saturate them, differences in development technology that must be taken into account when influencing increasing its efficiency. Acid treatment is one of the traditional and generally accepted methods of restoring by dissolving the rock and the subsequent formation of highly permeable channels. In order to maximize the effect of the treatment, the active part of the composition (acid) should be redistributed to evenly treat all clogged areas, and the entire composition after working out should be easily removed at the stage of washing and development after the operation.

DEVELOPMENT OF TECHNOLOGY FOR CLEANING THE BOTTOM-HOLE ZONE OF THE FORMATION FROM ASPHALT-RESINOUS DEPOSITS

The article considered the process of operation of wells, paraffin oil, causing a serious problem during the operation of the well. Physico-chemical methods providing an increase in displacement and coverage coefficients simultaneously for the extraction of film and capillary–retained oil from flooded reservoirs. At the same time, by adding special chemicals to water, it is possible to create solutions that reduce: the interfacial surface tension of water, thereby changing the ratio of the displacing and displaced phase mobility. For this kind of issues, pilot field studies and testing of the optimal technology for cleaning the bottom-hole formation zone (BFZ) from deposits of asphaltene-resinous substances were carried out and 6 production wells were selected for this purpose. Further, the criteria of wells for conducting pilot field tests of the technology for cleaning bottom-hole zones of wells from asphaltene-resinous substances are recommended. A composite composition with a high solvent capacity in relation to asphaltene-resinous substances was selected, the results of laboratory studies to determine the effectiveness of hydrocarbon solvents were given. The volume of the solvent composition was calculated for all selected wells. It is recommended that for processing for each well, a "Plan for processing the bottom-hole zone of the well" was drawn up, and a recommendation was also given that the processing of the BFZ should be carried out without extracting the underground equipment of the well (tubing columns with a pump).

Decision Support System for Sustainable Exploitation of the Eocene Aquifer in the West Bank, Palestine

Groundwater is a crucial resource for water supply and irrigation in many parts of the world, especially in the Middle East. The Eocene aquifer, located in the northern part of the West Bank, Palestine, is threatened by unsustainable groundwater abstractions and on-ground pollution. Analysis and management of this aquifer are challenging because of limited data availability. This research contributes to the long-term sustainability of the aquifer by model-based design of future abstraction strategies considered within an uncertainty analysis framework. The methodology employed started with development of a single-layer steady-state MODFLOW groundwater model of the area, followed by uncertainty analysis of model parameters using Monte Carlo simulations. The same model was afterwards coupled with a Successive Linear Programming (SLP) optimization algorithm, implemented in the Groundwater Management tool (GWM) of the United States Geological Survey (USGS). The purpose of optimization was deriving five optimal abstraction strategies, each aiming to maximize groundwater abstraction, subject to different constraints regarding groundwater depletion. Given the uncertainty of model parameters, the sensitivity and reliability of these optimal strategies were then tested. Sensitivity was checked for two optimal strategies by performing re-optimization with different values of uncertain model parameters (one at a time). Reliability of the five strategies was tested by analyzing the extent of constraints’ violation for each strategy when varying the uncertain parameters using Monte Carlo simulations. Finally, the model was used for determining capture zones of wells for the five optimal abstraction strategies, land-use in these capture zones, and the associated estimates of on-ground nitrogen loading. The developed strategies were then deployed in a web-based decision support application (named Groundwater Decision Support System—GDSS), together with other relevant information. Users can analyze results of different optimal strategies in terms of groundwater level variations and total water balance results, and test consequences of uncertain parameters. Capture zones of wells for different abstraction strategies, together with land-use and on-ground nitrogen loading in these capture zones, are also presented. Results show that critical uncertain parameters are recharge, hydraulic conductivity, and conductance at key boundary condition locations. Optimal abstraction strategies results indicate that an increase in total abstractions could be between 5% and 20% from the current level (estimated at about 56 × 106 m3/year, which is about 74% of estimated annual recharge). The uncertain parameters, however, are impacting the sensitivity and the reliability of the optimal strategies to variable degrees. Recharge and hydraulic conductivity are the most critical uncertain parameters regarding sensitivity of the optimal strategies, while reliability is also impacted by the level of abstraction proposed in a given strategy (number, locations, and abstraction rates of new wells). The main novelty and contribution of this research is in combining modelling, uncertainty analysis, and optimization techniques in a comprehensive decision support system for the area of the Eocene aquifer, characterized with limited data availability.

Повышение выработки запасов конденсата методом периодических остановок скважин

Introduction. During the development of gas condensate deposits for depletion, with a decrease in reservoir pressure, condensate falls out in the bottomhole zone of wells (BWZ) and a zone with increased condensate saturation is formed. Materials and methods of research. The considered method of non-stationary operating mode was justified by the example of the development of the Achimov deposits of the Urengoyskoye field using the tNavigator software package. Research results and their discussion. The work studies a method of periodical shutting down a gas condensate well in order to increase the additional recovery of retrograde condensate from the reservoir. The optimal well shutdown period is substantiated through the use of hydrodynamic modeling. The paper also analyzes the factors aimed at maintaining the maximum effect from the periodic operation of the well, the main of which is the mode of operation after the well is launched. The considered method of non-stationary operating mode was justified by the example of the development of the Achimov deposits of the Urengoyskoye field using the tNavigator software package. The initial information for modeling was the following: monthly operational reports (MER); results of gas condensate studies; downhole and wellhead measurement data. Conclusion. Based on the studies performed to determine the optimal duration of well shutdown during the development of the Achimov deposits of the Urengoyskoye field, it was revealed that the shutdown duration (more than 183 days) will have a negative impact on the potential condensate content in the formation gas. It has been substantiated that the efficiency of periodic shutdowns is affected by the technological mode of well operation after start-up. Also, the drawdown reduction makes it possible to preserve the effect of the reverse dissolution of condensate through the use of the natural energy of the reservoir.

Особенности проведения ремонтновосстановительных работ в газовых скважинах месторождений Западной Сибири, находящихся на стадии падающей добычи

Introduction. The article discusses the features of carrying out repair and restoration work in gas wells of Western Siberian fields that are at the stage of declining production. The compositions of process fluids used to block the bottomhole formation zone during well killing, to isolate the inflow of formation waters in various mining and geological conditions are given. The compositions of process fluids used in repair and restoration work in certain fields of Western Siberia are presented. They are easily removed when inducing inflow from the formation, and allow providing the required pressure at the bottomhole, as well as maintaining the reservoir properties of the productive formation and preventing its destruction. Materials and research methods. Based on the generalization of field experience in killing wells, fields at the stage of declining production, the results of their own theoretical, laboratory and bench studies. Research results and their discussion. When killing wells with temporary blocking of the bottomhole formation zone, the choice of the composition of process fluids with high stability, low filtration, in a wide range of adjustable density and rheological properties, allows creating the necessary repression on the formation and carrying out various operations in the well without complications. Technological fluids for killing wells, which are direct-type emulsion systems based on a composite reagent, are pseudo-plastic systems in terms of rheological parameters, where the density range is 900-1000 kg/m3. The properties of the emulsion solution based on the kill fluid reagent are determined by the complex effect of the reagents included in its composition. Filler-based blocking fluids are used to temporarily block the bottomhole formation zone of wells, and are prepared by introducing the calculated amount of the reagent into the required volume of killing fluid based on the killing fluid reagent. As a water-insulating composition for creating an insulating barrier in the reservoir, a formulation of a gel-forming composition based on a reagent – a dry mixture for carrying out repair and restoration work and a gelforming reagent – is considered. Conclusions. Based on the study, it was determined that the most promising technology for killing wells under conditions of abnormally low formation pressures is the technology of preliminary blocking of the bottomhole formation zone using blocking fluids with filler. To ensure high efficiency of repair and restoration work, preliminary calculations of the process fluids used are necessary, taking into account the mining and geological conditions of the reservoir and the geometric parameters of the well.

Reservoir Characterization of Eocene Carbonates of Central Indus Basin, Pakistan

The present study is based on petrophysical analysis of the Eocene Sui Main Limestone (SML) penetrated in wells of Qadirpur Gas Field, Central Indus Basin, Pakistan. The analyzed petrophysical property of SML includes shale volume, total porosity, effective porosity, water saturation, hydrocarbon saturation and net pay thickness. The result from the study shows that the Sui Main Limestone reservoir is capable of yielding appreciable hydrocarbon. The petrophysical interpretation revealed that the studied SML has productive reservoir characteristics with average (total and effective) porosity is in K-1, 15% in K-2 15% and 17% in K-3, average saturated hydrocarbon in SML is (70-100%) indicating that zones in wells are purely saturated with hydrocarbon, and average volume of shale in the zone of K-1, 23% in K2, 27% and in K-3, 25% respectively delineating clean formation. Facies modeling revealed that the studied Eocene formation consist of clean limestone, shaly limestone and shals. The isopach thickness map and stratigraphic correlation helps to understand the thickness of Sui Main Limestone in the field.