Underground Gas Storage Wells Research Articles

Wellbore salt-deposition risk prediction of underground gas storage combining numerical modeling and machine learning methodology

Strengthening the construction of underground gas storage (UGS) is significant for securing national energy and achieving carbon neutrality. However, salt deposition occurs in the wellbore affecting the safety of UGS seriously. How to predict the salt-deposition risk in UGS wells accurately and quickly is still challenging. This work aims at establishing a fast and convenient framework of wellbore salt-deposition risk prediction in UGS wells. Firstly, the influence of the production parameters on wellbore salt-deposition is analyzed by an in-house simulator. Further, an intelligent diagnostic model of salt-deposition risk is proposed based on the machine learning algorithm. The effect of salt deposition on reservoir is analyzed by reservoir salt-deposition simulation model. Finally, downhole video survey is used to validate the modeling accuracy of diagnostic model. Results indicate that the contribution ratio of daily gas production and water-gas-ratio to wellbore salt deposition is 3:2. After the salt deposition, the reduction in water saturation and the permeability of near wellbore areas are 77.14 % and 98.91 %. The modeling accuracy of diagnostic model is 97 %, which is applied in the Y UGS successfully. The proposed framework can predict the salt-deposition risk of UGS wells in real time to help engineers control salt clogging issues.

Mathematical Modeling of Gas Filtration in the Bottomhole Zone of Underground Gas Storage Wells Using Fractional Derivatives

Mathematical Modeling of Gas Filtration in the Bottomhole Zone of Underground Gas Storage Wells Using Fractional Derivatives

Developing an electronic archive of geophysical survey results from underground gas storage wells

The study aims to analyse and systematise the data from geophysical surveys of wells (GSW) of underground gas storage (UGS) facilities. In order to minimise the time required for a detailed analysis of the paper-based GSW data for the entire period of gas storage facility operation, it is advisable to transfer it to electronic form as much as possible.

Evaluation and treatment of casing pressure in injection/production wells of SQ underground gas storage

The evaluation and management of sustaining casing pressure (SCP) in injection/production wells of underground gas storage(UGS) is an important part of the wellbore integrity. SQ underground gas storage has experienced ten complete injection/production cycles, which puts forward high requirements on management of well integrity. At present, there are different degrees of SCP of injection/production wells of SQ UGS, which seriously threatens the safety of the UGS. This paper analyzes casing pressure in different injection/ production stages and working conditions of injection/production wells, combined with API RP 90-2, NORSOK, ISO/TS 16530-2, SY/T5724-2008 standards. We established an SCP evaluation process and a static and dynamic SCP risk evaluation system, and then proposed a four-level risk control mode for UGS injection/production wells. We formulated a production management method for wells with SCP, constantly improved the operating environment of UGS wells. We managed the injection /production wells with SCP higher than the MAWOP, especially the annular leak problem of well S7. The SCP treatment achieves effective plugging, guarantees the integrity of the injection /production wells, and achieves good repair effect, which has certain guiding significance for the evaluation of the integrity of the injection/production wells of the UGS and the management of the SCP.

Case Study of the Use of a Digital Twin for Leak Detection and Quantification in Underground Gas Storage Wells

Summary Underground gas storage (UGS) wells are essential components in energy security. However, UGS wells present a complicated and delicate combination of elements where ensuring safe and secure functionality over long periods is paramount. This paper showcases how a digital twin is used to evaluate and forecast the link between leaks and temperature and pressure trends in a UGS well, allowing the identification and quantification of defects and, subsequently, well barrier integrity. The digital twin used for this application presents advantages compared with other solutions present on the market with regard to the simplified configuration; that is, with minimal input data, the system can produce an accurate and useful output, which is then used in the well integrity decision-making process. UGS wells present additional criticalities with respect to normal production wells due to their longer life span and the repetitive production and injection cycles. This makes early and accurate leak detection essential for the safe management of the well barriers. The proposed digital twin simulates the trends of pressure and temperature within each annulus and compares results with data from the field, allowing the identification of the position and size of leaks. A genetic algorithm is applied to optimize the placement of leaks on their specific barriers. Once a leak is identified, a risk assessment is conducted to evaluate the overall integrity of the well. If the status of the well is found to be critical enough, an intervention may be planned. The studies presented show how the digital twin has been used on two wells with similar problems. At first, it has confirmed the necessity to put the well out of service as opposed to planning maintenance, thereby saving both time and cost. In the second case, it allowed the validation of a solution that led to a 60% reduction in failure consequence, allowing the well to continue operating without major costs or risks. The errors of the resulting simulations were always confined within the 0.5 bar limit highlighting its accuracy. The system has been in use for over a year and has shown great potential in accurate and efficient identification of leaks. This has accelerated the process of well integrity evaluation and allowed timely interventions on wells that required it. On the other hand, the process has highlighted cases where previous assumptions about leak location and size were corrected using the digital twin, therefore reducing the costs of interventions. Finally, the model showcases a clear readiness for predictive capabilities aimed to select, plan, and design fit for purpose mitigating actions.

The Application of Breakthrough Pressure in the Evaluation of the Sealing Ability of Cement–Casing Interface and Cement Matrix in Underground Gas-Storage Wells

This paper proposes an evaluation system for the sealing ability of cement–casing interface and cement matrix, which was developed based on a permeability testing device and a model that predicts the breakthrough pressure of cement sheath matrix and interfacial transition zone (ITZ). It was found that the breakthrough pressure of ITZ was much smaller than that of cement matrix. Moreover, compared with water-based drilling fluid, oil-based one led to lower breakthrough pressure of ITZ even after the flushing treatment. Meanwhile, latex, resin and elastic materials enabled a substantial rise in the breakthrough pressure of cement matrix. However, compared with the latex, resin and elastic cement, the expansive cement had higher breakthrough pressure of ITZ, indicating an improvement on the interface sealing ability. Additionally, a small enlargement rate of the hole diameter and long effective bond were able to prevent gas storage wells from leakage.

Анализ эффективности кислотных обработок скважин ПХГ

Introduction. In the world practice of using technologies for increasing of production one of the most widely used method for bottom-hole zone treatment for increasing or restoration of wells productivity is acid treatment of productive formation. Acid treatments of productive formation is the essential one in a group of methods for bottom-hole zone treatment directed on maintenance of project well production of gas fields and underground gas storages. Essential aim of acid treatment of gas fields and underground gas storages wells is restoration of reservoir properties in near wellbore zone of productive formation by destruction, transfer to the solution and removing to the bore hole wasting solid particles of natural and technogenic origin, as well as by improvement of filtration characteristics of bottom-hole zone of productive formation by means of expansion of existing and creating of new channels for fluid migration by all length of perforated interval. Materials and research methods. As the base reagents, used for acid treatment, could be declared hydrochloric (HCl) and hydrofluoric (HF) acids. In the article discussed questions of different factors influence to efficiency of acid treatment. Described mechanism of reaction of acid compound with rock of productive formation, essential principles for choosing of acid compound for terrigenous reservoir. Research results and their discussion. It is shown analysis of field data about results of acid treatments, done during of workover in wells of one of underground gas storage from 2014 to 2021, information about number of acid treatments, used acid compounds, technological and economic parameters, which allows to estimate efficiency for done activities. Conclusions. Basing on the results of analysis it is down conclusions about possible directions for increasing efficiency of terrigenous reservoir acid treatments in underground gas storage wells.

Mathematical modeling of the gas-filtration in the bottomhole zone of underground gas-storage wells using fractional derivatives

Mathematical modeling of the gas-filtration in the bottomhole zone of underground gas-storage wells using fractional derivatives

Uncertainty analysis framework for tubular connection sealability of underground gas storage wells

The seal failure of tubing and casing connections compromises underground gas storage well safety. This work proposes a systematic uncertainty analysis framework for connection sealability assessment. The framework covers reliability analysis and reliability sensitivity analysis and attempts to provide more effective support for the reliability design of connection seals. The reliability analysis introduces an adaptive Kriging with stopping criterion P-Monte Carlo simulation (AKP-MCS) method, which can provide a satisfactory estimate of failure probability with a small number of performance function evaluations. This metamodeling technology can effectively reduce the numerical efforts required for the reliability assessment of connection sealability. In the reliability sensitivity analysis, the refined metamodel obtained from the reliability analysis is coupled into a single-loop Monte Carlo simulation (MCS) method. The classifier attribute of this metamodel can meet the requirement of the single-loop MCS method to classify the signs of sampling points. This attribute enables sample matrices to be evaluated on this metamodel instead of the performance function, making the reliability sensitivity assessment more feasible. The proposed method is first demonstrated with four academic examples with promising results. Next, an illustrative tubular connection case is provided. The proposed scheme gives estimates of the failure probability and reliability sensitivity close to the classical model but requires less computational cost. The results of the analysis can provide useful information for the scheme decision-making and reliability optimization of connection seal design.

Analysis of the effectiveness of ways to improve the performance in underground gas storage wells

The article provides an assessment of the effectiveness of various ways to improve the productivity of wells in underground gas storage facilities. We conducted comparisons of the performance of wells of increased diameter in the interval of the productive reservoir with wells in which hydraulic fracturing or horizontal ending was carried out.

Внедрение инновационного программно-аппаратного комплекса пассивной акустики для диагностики технического состояния скважин

To ensure operational stability of the unified gas supply system depending on the seasonal gas demand fluctuations, the underground gas storage facilities are effectively used. Well integrity diagnostics using the advanced logging techniques facilitate timely identification of potential problems (pinpointing cross-flows behind casing, detecting leaks in production casing and other well construction components, locating sustained annulus pressure sources etc.), and, thereby extension of the safe operation life of functioning of the underground gas storage facilities. The results of the complex of field and geophysical studies in several underground gas storage wells are given in this article. Different types of the underground gas storages are reviewed: the ones located in an aquifer, salt dome, and mature field. The diagnostics was carried out based on the complex of downhole logging including a passive acoustic tool. The passive acoustics hardware and software technology can capture and interpret acoustic signals generated by the wellbore or reservoir flows. To recognise and interpret the captured signals, the temporal coherence algorithms, data wavelet filtration, and neural networks are used. The use of this technology allows to significantly improve the safety of well operation. The information obtained is used both in the preparation of industrial safety expert reports and for the development of effective programs for major repairs of the underground gas storage wells located in the depleted gas and water fields, as well as in the salt caverns. Hardware and software technology of passive acoustics is being used in almost all the major oil and gas provinces in the world, receiving recognition from the largest domestic and foreign companies, however, this is the first time that underground gas storage facilities are used to check the technical condition of the wells.

Analysis of growth drive breakdown by the increase of the Dashav UGS fountain pipes

Scientists who were analyzing the results of the underground gas storage (UGS) complex of Ukraine, say that for modern conditions the maximum daily productivity should be increased by 30-35%. Since the beginning of the creation of gas storage facilities passed than 40 years, work is carried on outdated and physically worn out equipment. Work of the wells (which were build based on the old technologies at low reservoir pressure) are characterized by low productivity because their bottomhole zone is partially occluded by the mud filtrate, partially contaminated with compressor oil; due to the selective placement of wells in the underground storage area, some of them were formed so-called "stagnant" zones; extraction of all active gas volume which takes 100-180 days. Need for Ukraine to further develop underground gas storage should be aimed at increasing both the active volume of gas and the daily productivity of gas storage facilities. The main directions of increasing the productivity of gas storage are the drilling of horizontal shafts in both new wells and old ones in experience [9], the formation of open holes in the drilling of new wells and the milling of operational columns in the "old" drilled holes, filters, hydraulic fracturing, construction of large diameter wells, additional perforation of gas-saturated intervals. Nowadays, the most important problem is the reconstruction and modernization of existing underground storage facilities through replacement of equipment. This will not only save the achieved performance, but also can improve it. Due to the reconstruction of the equipment, gas preparation will be improved, gas storage capacity will be increased and operating costs will be reduced. Therefore, an increase in the daily productivity of UGS can be achieved, first of all, due to the improvement of the main element in the gas storage facility - the operational well. In order to analyze this issue, the paper analyzes the efficiency of replacing the fountain pipes of the Dashavsky UGS wells with a larger diameter, and presents the results of the hydraulic, technical and economic calculation of the implementation of this UGS reconstruction.

Геолого-технологические исследования при строительстве скважин на подземных хранилищах газа (опыт применения и перспективы развития)

Геолого-технологические исследования при строительстве скважин на подземных хранилищах газа (опыт применения и перспективы развития)

Cement sheath integrity analysis of underground gas storage well based on elastoplastic theory

For injection & production well built in underground gas storage (UGS), sealing failure of cement sheath is one of the major factors threatening wellbore integrity due to continuous varied casing pressure and temperature. Cement sheath may deform plastically in the process of gas injection and lose airtightness if unloading casing pressure. In view of this, an analytical model of the stress, displacement and interaction of casing-cement sheath-surrounding rocks subjected to inner casing pressure and outer radial far-field in-situ stress and debonding of cementing surfaces were derived with due consideration of varied casing pressure, temperature and pore pressure due to cyclic injection and production. In this model, casing, cement sheath and surrounding rocks were seen as multi-layer cylinders and were analyzed based on thermoelastic, elastoplastic and poroelastic theory, respectively. A demonstration calculation is performed to reveal the stress and displacement of cement sheath under conditions of cyclic loading and unloading. The model was compared and validated by finite element simulations. Factors affecting the interaction of cement-casing and cement-rocks and the formation of micro-annulus were analyzed. As a result, when loading casing pressure, the radial contact stress on the bonding surfaces increases nonlinearly and cement sheath may deform plastically. In the process of unloading casing pressure, if low far-field in-situ stress exists, the radial contact stress tends to transform from compression to tension leading to the separation of bonding surfaces. The variation of temperature, pore pressure and far-field in-situ stress are key factors affecting the stress & deformation of cement sheath and micro-annulus. For cement with large elasticity modulus and small Poisson's ratio, plastic deformation and micro-annulus are prone to forming. Thus, the reasonability of the application of ultra-high toughness cement in UGS well has been verified. The results are of guiding significance to the operating optimization, micro-annulus prevention and wellbore integrity improvement of UGS wells.

Developing a Method of Calculating the Operational Flow of Methanol to Prevent the Formation of Crystalline Hydrates in the Operation of Underground Gas Storage Facilities

When operating underground storage (UGS) of gas hydrates liquidation formed untimely could lead to serious consequences - a complete shut-in and elimination of its process. With a small fund operating wells with high daily output storage operation would entail a violation of technological regime, the failure of gas sales plans, increased hours of downtime operational fund. Therefore, ensuring the smooth and reliable operation of underground gas storage wells fund is an urgent task. The authors of the article developed a methodology for calculating the operational flow of methanol to prevent the formation of gas hydrates in UGS operation. On the basis of the developed technique using industrial operating data Punginskoye UGS made the study of technological modes of its work and recommendations to prevent hydrate formation in the underground gas storage wells.

Finite Element Optimised Back Analysis of In Situ Stress Field and Stability Analysis of Shaft Wall in the Underground Gas Storage

A novel optimised back analysis method is proposed in this paper. The in situ stress field of an underground gas storage (UGS) reservoir in a Turkey salt cavern is analysed by the basic theory of elastic mechanics. A finite element method is implemented to optimise and approximate the objective function by systematically adjusting boundary loads. Optimising calculation is performed based on a novel method to reduce the error between measurement and calculation as much as possible. Compared with common back analysis methods such as regression method, the method proposed can further improve the calculation precision. By constructing a large circular geometric model, the effect of stress concentration is eliminated and a minimum difference between computed and measured stress can be guaranteed in the rectangular objective region. The efficiency of the proposed method is investigated and confirmed by its capability on restoring in situ stress field, which agrees well with experimental results. The characteristics of stress distribution of chosen UGS wells are obtained based on the back analysis results and by applying the corresponding fracture criterion, the shaft walls are proven safe.

Mechanical properties of EVA-modified cement for underground gas storage

Underground gas storage (UGS) is an artificial gas reservoir used for balancing the supply-demand chain throughout the year. During its operation cycle, the cement sheath experiences cyclic mechanical stress, and thermal and may crack due to its low elasticity, hard brittleness, and porosity. These cracks could lead to the transmission of stored gas through the cement behind the casing and before the formation and can even be a source of micro-cracks. Therefore, the mechanical properties of the cement sheath have higher requirements. In this work, a new material was used to prevent cement cracking, improve cement elasticity at low stress and deformability at high stress, reduce the number of pores and reduce the crack propagation in the cement used for completion of UGS wells. The experimental results showed that mixing EVA into cement decreases the compressive strength, but significantly improves the toughness and deformability at high stress and the elasticity deformation restorability at low stress. Moreover, the addition of EVA results in the remarkable reduces reduction of macropores.

Cement design for underground gas storage well completion

In order to shave the peak demands during the cold seasons, underground gas storage (UGS), balancing the supply-demand chain throughout the year, has been accepted as a strategic method. During the successive UGS cycles, the well cement experiences cyclic mechanical, thermal, and hydraulic stress and may crack due to its low elasticity and ductility. This could lead to the transmission of stored gas through cementing behind casing, one of the major challenges experienced in UGS operations, so posing high workover costs on UGS wells. In addition to workover costs, the loss of inventory due to gas transmission makes the reservoir insufficient in proper gas supply during the high-demand season. In this work, a new formulation has been invented in order to prevent cement cracking, improve cement elasticity and ductility, and reduce the crack propagation in the cement used for completion of UGS well. The new formulation adds a polymer and an elastomer to cement composition. Results showed that addition of latex to cement decreases the density, hydration and fluid loss of cement; also, the rate of cement bonding decreases. On the other hand, addition of polypropylene fibers results in dramatic improvement of compressive strength and stress strain properties of the cement. In comparison with elastomer, this additive provides a higher threshold elasticity of cement. Also, the combined cohesive effect of latex and flexibility of microfibers brings about the best resistance against excessive pressures.

Lifetime of a Natural Gas Storage Well Assessment of Well-Field Maintenance Cost

Gaz de France has been operating underground gas storage wells since more than 50 years. These wells have been drilled with the current available technologies in oil and gas industry. These technologies had improved a lot in the last decades (slurry compositions, drilling and cementing techniques, etc.) and the lifetime of a well therefore has to be estimated with reference to the techniques in use at the date it was built. These uncertainties and the inaccurate data of the oldest wells (drilling logs and casings specifications) led GDF to investigate the wells lifetime. Two approaches are presented here: - assessing a theoretical lifetime of a well; - calculating the average lifetime of each well using essentially corrosion scenarios and kinetics. Combining the two different approaches, one can better assess well aging and remaining well lifetime in order to schedule the best action (work-over, abandonment) at the proper time. A better knowledge of well's lifetime enables good control of underground storage operational expenditures (OPEX).

Improved treatment of acrylamide co- and terpolymers for water control in gas-producing and storage wells

The main objective of this study was to determine the optimal conditions for application of acrylamide co- and terpolymers for water control in gas wells under various environmental conditions. Starting in February 1992, the limits of application of acrylamide co- and terpolymers were first defined in the laboratory through extensive tests. Based on the results of the comparative feasibility study, four field tests were performed in both gas reservoir and underground gas storage wells. This paper presents the latest results of field tests. Using a partially sulfonated acrylamide terpolymer, the first field test was performed in January 1993 on an abandoned gas-producing well with a BHT of about 130°C, an average matrix permeability of 0.01 μm 2 and a produced brine salinity of more than 300 g/l TDS. The second test was performed in a well from a gas storage field with a temperature of about 87°C, an average permeability of 0.06 μm 2 and a produced brine salinity of more than 270 g/l. Based on the information provided from the first field test and the feasibility study performed for this well, a lower molecular weight partially sulfonated acrylamide terpolymer was finally used for this test. Using a cationic acrylamide copolymer, the third field test was performed in a low-temperature, high-brine-salinity gas storage well with BHT of 30°C and brine salinity of 218 g/l. Based on the excellent results of the third field test, the same polymer was selected for the last water shut-off treatment in a low-temperature gas storage well with a matrix permeability ranging from 0.04 to 3.6 μm 2. Since the treatment, the gas well and the gas storage wells have exhibited improved production performances.