Underground Gas Storage Construction 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.

Evaluation of fault-sealing: a case study on Xiangguosi underground gas storage, SW China

China vigorously implements the dual carbon strategy, and natural gas consumption continues to grow rapidly. It is urgent to improve the natural gas “production, supply, storage, and sales” system and accelerate the construction of underground gas storage (UGS). UGS requires “storage, injection, and extraction”. Faults are the primary factor of “storage”, the evaluation of fault-sealing is crucial for the safe construction and operation of UGS. Existing researches start from the perspective of the hydrocarbon reservoir, develop an evaluation of the basic characteristics of faults, lithological configuration of the fault’s two blocks, analysis of production performance, Shale Smear Factor (SSF), Shale Gouge Ratio (SGR), properties of fault-filling materials, 3D tectonic model, normal pressure on the fault plane, fault shear index, and fault plugging coefficient. This paper systematically analyzes the adaptability of existing methods and proposes an index to evaluate the fault-sealing capability of UGS. Taking the first UGS in SW China—Xiangguosi UGS as a case, using this workflow to evaluate the fault-sealing capability of 5 major faults. It is believed that the evaluation of fault-sealing on Xiangguosi UGS is good. This conclusion supports the design of construction key indicators and is the important basis point of the construction of the “signpost” UGS. It is of guiding significance and provides a reference for the evaluation of fault-sealing for the rebuilding of depleted gas reservoirs to UGSs.

Development, challenges and strategies of natural gas industry under carbon neutral target in China

In the mid-21st century, natural gas will enter its golden age, and the era of natural gas is arriving. This paper reviews the development stages of global natural gas industry and the enlightenment of American shale gas revolution, summarizes the development history and achievements of the natural gas industry in China, analyzes the status and challenges of natural gas in the green and low-carbon energy transition, and puts forward the natural gas industry development strategies under carbon neutral target in China. The natural gas industry in China has experienced three periods: start, growth, and leap forward. At present, China has become the fourth largest natural gas producer and third largest natural gas consumer in the world, and has made great achievements in natural gas exploration and development theory and technology, providing important support for the growth of production and reserves. China has set its goal of carbon neutrality to promote green and sustainable development, which brings opportunities and challenges for natural gas industry. Natural gas has significant low-carbon advantages, and gas-electric peak shaving boosts new energy development; the difficulty and cost of development are more prominent. For the national energy security and harmonious development between economy and ecology under the carbon neutral goal, based on the principle of “comprehensive planning, technological innovation, multi-energy complementarity, diversified integration, flexibility and efficiency, optimization and upgrading”, the construction of the production-supply- storage-marketing system has to be improved so as to boost the development of the natural gas industry. First, it is necessary to strengthen efforts in the exploration and development of natural gas, making projects and arrangement in key exploration and development areas, meanwhile, it is urgent to make breakthroughs in key science theories and technologies, so as to increase reserve and production. Second, it should promote green and innovative development of the natural gas by developing new techniques, expanding new fields and integrating with new energy. Third, there is a demand to realize transformation and upgrading of the supply and demand structure of natural gas by strengthening the layout of pipeline gas, liquefied natural gas and the construction of underground gas storage, establishing reserve system for improving abilities of emergency response and adjustment, raising the proportion of natural gas in the primary energy consumption and contributing to the transformation of energy consumption structure, realizing low-carbon resources utilization and clean energy consumption.

A quantitative approach for sealing capacity evaluation of caprock in candidate of aquifer gas storage.

The gas sealing capacity of caprock (SCC) is one of the key factors that determine whether aquifer trap can be constructed into underground gas storage (UGS). However, no standard protocol for evaluating SCC of candidate aquifers has been proposed. Based on the core observation, laboratory experiment, and well logging data, the sealing capacity of the target aquifer caprock of Permian mudstone in D5 block of Litan sag, China, is quantitatively evaluated. The important parameters of mineral brittleness, permeability, breakthrough pressure (BP), mechanical brittleness, thickness, and areal extent that affect the SCC are determined. The results of specific tests and data statistics show that the caprock of D5 block is a low permeability rock with a permeability of 10-4 mD, and the BP of undisturbed rock is greater than 38MPa. Although the brittle mineral quartz is abundant with an average of 38.38%, the mechanical brittleness is not strong under formation conditions. The direct caprock has a thickness of greater than 50m, and on the top of it is a high-quality indirect caprock that complements the physical closure. The results of a mathematical evaluation model show that except for the sealing index of sample 2, all the other samples have optimal sealing capacity. The field interference test shows that the optimal sealing capacity of the caprock meets the requirements of the construction of underground gas storage (UGS). The rationality of the comprehensive evaluation model can provide a reference for similar evaluation projects in the future.

Implications of the European gas market for the long‐term construction of underground gas storage in China

AbstractUnderground gas storage (UGS) is an important part of the natural gas industry. Its peaking characteristics and storage capacity are critical to national energy supply and energy security. Compared with the mature gas market in Europe, the construction of UGSs in China faces many challenges. This study is expected to provide references for China UGS through a detailed analysis and calculations of the European natural gas market and underground storage. First, the current status and development of the European gas market were summarized. And the situation of primary energy structure, gas utilization, and UGSs construction was compared between the EU and China. Second, the working gas volume of UGSs in Europe was analyzed from the perspective of its relationship with total consumption and peak‐shaving volume. Finally, the simulation and prediction of the working curve of the energy storage facilities and the reasonable ratio of the energy storage to load were solved by the numerical fitting method. Meanwhile, the recommendations for China's natural gas market and UGSs were provided. It is appropriate to set the planning target of China UGS capacity to load at 5% of total consumption and the actual peaking gas volume will be 14.4 billion cubic meters by 2030.

Study on simulation of cement plug—formation interface stripping failure and main influencing factors

Among the existing gas storage facilities, salt cavern gas storage has the advantages of high injection production efficiency, low gas cushion volume, safety, flexibility, etc. It is of great significance to speed up the construction of underground gas storage by transforming abandoned salt caverns of salt industry into underground gas storage. However, old salt cavern wells cannot be directly converted into gas storage injection and production wells, so the old wellbore must be plugged to ensure the effectiveness of plugging. Therefore, a set of plugging optimization technology for salt cavern gas storage wells is urgently needed. In this paper, a 3D finite element model of the cement plug-formation system based on cohesive element method is established for the milling and plugging of the old well in the salt cavern gas storage section. The results show that under the condition of constant gas storage pressure, a certain degree of small deformation will occur at the bottom of the cement plug after compression, resulting in the shear direction deformation of the cement plug formation cementation interface, and peeling will occur after accumulation to a certain extent. With the increase of simulation time, the length of stripping section gradually increases and tends to be stable, and reaches the limit of stripping failure length. In the process of research, the factors and laws affecting the stripping failure length were also analyzed. It was found that the stripping failure length of cement plug formation cementation interface was related to the maximum operating pressure of gas storage, cement plug length, cement plug diameter, elastic modulus, Poisson’s ratio and other factors. The research results are helpful to judge whether the milling and plugging length of the old well section is sufficient, and provide theoretical guidance for ensuring the long-term safe operation of the gas storage.

Geomechanical Feasibility Analysis of Salt Cavern Gas Storage Construction in Sanshui Basin, Guangdong Province

Salt cavern gas storage has become the key project of current and future underground gas storage (UGS) facilities construction due to their efficient peak-shaving and supply assurance capacities. The Sanshui Basin in Guangdong Province, China, is rich in salt resources and has high-purity salt rock, which is a potential area for the construction of salt cavern underground gas storage. To speed up the large-scale construction of underground gas storage in China and promote the sustainable development of the natural gas market, it is very necessary to analyze the geomechanics of the target salt layer and study the feasibility of gas storage construction. Based on comprehensive experiments of rock mechanics and thermodynamics, the strength, creep and temperature-sensitive mechanical properties of the target rock in Sanshui Basin were studied. Then, according to the geological conditions of Sanshui salt formation, a three-dimensional geological model was established to analyze the stability of salt cavern gas storage under the injection-production operation. The results show that the average tensile strength and uniaxial compressive strength of salt rock are 1.51 MPa and 26.04 MPa, respectively, showing lower strength. However, under triaxial compression, the compressive strength of salt rock increases significantly, and there is no obvious shear failure phenomenon observed. Moreover, after the peak strength, the salt rock still has a large bearing capacity. In addition, under the confining pressure of 30 MPa, the strength of salt rock decreases by 8.3% at a temperature of 60 °C compared with that at room temperature, indicating that the temperature has a low, modest effect on the mechanical properties of salt rock. The stability analysis shows that, under an injection-production operating pressure of 10–23 MPa, the displacement, plastic zone range and volume convergence rate of single cavity and cavity group are small, and the cavity shows good stability. Overall, the target salt formation in Sanshui Basin, Guangdong Province, presents a good geomechanical condition suitable for the construction of underground salt cavern gas storage. This study can provide a reference for the development and design of salt cavern UGS.

Discussion on the Reconstruction of Medium/Low-Permeability Gas Reservoirs Based on Seepage Characteristics

The construction of underground gas storage mostly focuses on depleted gas reservoirs. However, the depleted gas reservoir used to build underground gas storage in China is located far from the main gas consumption economic zone. It is necessary to reconstruct underground gas storage using nearby reservoirs in order to meet the needs of economic development. The complex three-phase seepage characteristics encountered in the process of reconstruction of underground gas storage reservoirs seriously affect their storage and injection production capacities. Combined with the mechanism of multiphase seepage and the multicycle injection production mode during the process of gas storage construction, the feasibility of rebuilding gas storage in medium- and low-permeability reservoirs was evaluated through relative permeability experiments and core injection production experiments. The results showed that the mutual driving of two-phase oil–water systems will affect the storage space and seepage capacity, that the adverse effect will be weakened after multiple cycles, and that increasing the gas injection cycle can enhance the gas-phase seepage capacity and improve the crude oil recovery. Therefore, we found that it is feasible to reconstruct underground gas storage in medium- and low-permeability reservoirs, which lays a foundation for the development of underground gas storage in China.

Subsurface Characterization, Monitoring Play Role in Development of Gas-Storage Facilities

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 204787, “The Importance of Subsurface Characterization and Monitoring During Development and Operation of Underground Gas-Storage Facilities,” by Romain Guises, Emmanuel Auger, and Sanjeev Bordoloi, SPE, Baker Hughes, et al. The paper has not been peer reviewed. The complete paper describes an integrated subsurface characterization and monitoring approach not only for the construction of underground gas storage (UGS) but also for safe and efficient operation over many decades. Close integration of subsurface understanding with optimization of surface facilities is a critical factor in ensuring optimal UGS performance and deliverability. Another important task of the final phase of UGS facilities design involves enablement of sustainable operation through an asset-integrity-management plan. Importance of Integrated Subsurface Characterization and Monitoring The work flows developed to aid integrated subsurface characterization and monitoring play a critical role. These work flows can be grouped as follows: - Capacity (the potential of the storage site to ensure optimal working capacity) - Deliverability (the ability of the wells and associated infrastructure to ensure the delivery of the gas from the surface into the reservoir and vice versa) - Integrity (including reservoir and well integrity with overall asset safety and surface infrastructures) The element that connects these work flows and ensures collaboration between different work groups and technical disciplines is the 4D dynamic geomechanical model.

Underground Gas Storage Construction in Gas Fields with Oil Ring and Edge and Bottom Water: A Case Study

ABSTRACT Most underground gas storages (UGSs) are constructed in gas fields, but there are few UGS examples constructed in a gas field with an oil ring and edge/bottom water (OR-EBW-gas field). In areas where suitable gas fields are not available for USG development, existing gas fields with oil ring and edge and bottom water have to be used to construct UGS to balance the seasonal natural gas consumption and supply. Compared with conventional gas reservoirs, fluid distribution is much more complicated in OR-EBW-gas fields and there exist different modes for storage space plan, which brings up more uncertainty for the UGS construction. In this work, an active UGS construction in an OR-EBW-gas field is studied using a comprehensive compositional numerical model. The operation parameters are firstly determined through detailed sensitivity studies. UGS construction schemes employing different porous medium spaces are then investigated to determine the optimal one. The results indicate that UGS constructed using gas cap area is the optimal scheme. After 20 I/W cycles, the predicted working load of the UGS is 1.726 × 108 m3, which reaches the designed value of 1.7 × 108 m3. The incremental cumulative water production and oil production are 0.21 × 104m3 and 0.42 × 104m3 respectively. The study shows that it is crucial to prevent the intrusion of edge water for UGS construction in an OR-EBW-gas field. The oil ring is not suitable for UGS construction due to its poor petrophysical property, but can be used as a natural barrier to separate gas cap and edge water. The formation pressure needs to be improved when the gas cap, oil ring and edge water are selected as USG construction zones. However, it will also lead to a significant increase in the formation pressure near the main control fault, which leads to a high risk of fault failure.

Effect of Nanomagnetite on Properties of Medium- and High-Rank Coals

Coal seams are natural gas reservoirs that provide potential for future CO2 capture and storage. Many problems must be resolved for CO2 storage in coal seams. To target problems of gas percolation, adsorption, and “stagnation” in gas reservoirs, the specific surface area, pore volume, permeability, and adsorption–desorption curves of three coal types with nanometer magnetite powder (NMP) mass fractions of 0%, 2%, 4%, and 6% were measured in dry state. The coal’s adsorption potential, specific surface area, and pore volume increased with an increase of NMP mass fraction. The specific surface area of coal mixed with NMP differed significantly from data that were calculated from the coal and NMP specific surface area, and the permeability was higher than for core without NMP, which indicates that the surface properties of coal can be changed by NMP addition. Although the permeability of coal core mixed with NMP exceeded that of the original coal core, an increase of NMP mass fraction resulted in an initial increase and then a decrease of coal core permeability from Pingdingshan and Anyang in China. NMP coverage of the coal surface increases the permeability for a coverage below 27%, and the permeability decreases when coverage exceeded 27%. Gas “stagnation” was affected by the ratio of equilibrium pressure to the saturated vapor pressure (p/p0) and by the coverage ratio. This research is significant for coal-bed methane exploration and underground gas storage construction.

Impurity Effects on the Mechanical Properties and Permeability Characteristics of Salt Rock

Impure salt rock strata are extensively distributed in China, giving them great significance in the study of the physical properties of impure salt rock for the construction of underground gas storage in salt mines. To investigate the confining pressure and impurity effects on the mechanical properties and gas permeability characteristics of salt rock, permeability tests under hydrostatic confining pressure and conventional triaxial compression (CTC), on salt rock samples with different impurity contents, were carried out. The results demonstrate that the confining pressure effects cause an increase in triaxial compression strength, but a decrease in permeability. However, impurity enhances the bearing capacity and permeability of the salt rock; both rock strength and permeability increase with an increase in impurity content. Moreover, the broken salt rock specimens were analyzed after the CTC test using Computed Tomography (CT) equipment. To understand the relationships between pore volume and permeability, considering the confining pressure and impurity effects, the cracks were divided into four groups according to different crack diameter ranges: ~0.05 mm, 0.05–1 mm, 1–10 mm and ~10 mm. The CT analysis results show that while the pore volume of smaller cracks shows an “increasing–decreasing” trend by increasing confining pressure, the pore volume of large cracks gradually decreases, indicating that the rock permeability is highly related to macro-cracks. However, impurity has more complicated implications on rock permeability and cracks, and needs further investigation.

Key technologies for salt-cavern underground gas storage construction and evaluation and their application

Salt-cavern underground gas storage is technically faced with non-uniform distribution of stratified salt rocks, complex solution mining mechanism, difficult control of solution mining process, less operation safety and stability of caverns and difficult reconstruction and utilization of old caverns. In view of these technical difficulties, the design concept was fully updated based on the design experience and field practice of Jintan gas storage in Jiangsu, for purpose of maximizing salt layer utilization ratio, improving solution mining efficiency, shortening construction time and ensuring cavity safety. Based on the updated design concept, five series of key technologies were proposed in site evaluation, cavern design and control, stability assessment and storage capacity parameter design, old cavern screening and utilization, and gas storage operation and monitoring. The following results were obtained from the actual application of these key technologies to the Jintan gas storage. First, the actual drilling coincidence rate of geological program is high. Second, the cavern is morphologically coincident with the design. Third, the cavern deformation retract rate is in line with the stability evaluation result. Fourth, old caverns are successfully reconstructed and utilized. Fifth, the arrangement of the monitoring network ensures the operation safety of salt-cavern underground gas storage and makes an important contribution to the peak shaving and supply guarantee of natural gas in the Yangtze River Delta region. In conclusion, the research results provide guidance for the design and engineering implementation of salt-cavern underground gas storage construction program, as well as a theoretical and technical support for the construction of similar gas storages.

A Method for Evaluating the Dynamic Sealing Efficiency of Underground Gas Storage Reconstructed by Aquifer

There are very few living examples of engineering test cases in domestic aquifer underground gas storage construction, however, engineering test analysis can greatly reduce the risk of evaluation. This paper systematically introduced interference well test method application of aquifer gas storage construction in Huabei oilfield, and take the target of the D5 aquifer construction in Jizhong depression as an example to analyze the reasonable water injection, excited period and interference test results. Interference well test result shows that the target cap rock of D5 aquifer is sealed, the fault vertical sealing ability is good, the sealing condition of the reservoir is provided, and also the horizontal connectivity of the reservoir is good. The research results are directive and with reference value for the construction of aquifer underground gas storage in China.

A fatigue damage model for rock salt considering the effects of loading frequency and amplitude

With the large-scale construction of underground gas storage in salt deposit, much more efforts have been made to assess the fatigue properties of rock salt. The fatigue damage processes the primary, steady, and accelerated phases, which is similar to the axial irrecoverable deformation compiled from the loci of the loading cycles of rock salt. The cumulative fatigue damage increases with a decrease in the loading frequency and with an increase in the stress amplitude within the range tested. To take into account the effects of loading frequency and amplitude on the fatigue behavior of rock salt subjected to cyclic loading, a low cycle fatigue damage model was exclusively established combined with the Manson–Coffin formula. The proposed damage evolution equation was validated with experimental results and proved to be efficient in the prediction of fatigue damage tendency of rock salt under different loading frequencies and amplitudes.

The status quo and technical development direction of underground gas storages in China

UGS (underground gas storage) construction in China has stepped into a new development stage after years of exploration. The eleven UGSs that have been put into production play an important role in domestic natural gas peak shaving safety and supply guarantee, with designed working gas volume of 180 × 108 m3, but there are still various difficulties in UGS construction in China. Firstly, the increasing speed of working gas volume is slower than that of peak shaving demand volume. Secondly, the UGS building engineering is difficult in technologies and high in investment costs. Thirdly, safe operation is under high pressure and it is hard to identify and control risks. Fourthly, there are fewer candidate UGS sites in China and UGS building conditions are complicated. And fifthly, it is difficult for those UGSs to realize economic benefits only based on their own operation under the existing natural gas price systems. To sum up, the currently available UGS operation modes and building technologies in China are not sufficient to cope with the challenges resulted from markets and complex geologic conditions. Facing all these challenges, it is necessary not only to explore market driven operation modes, but also to strengthen technology tackling and carry out core technological research and development, including geologic evaluation, gas reservoir engineering, drilling and completion engineering, UGS injection and gas recovery engineering, surface auxiliary technologies and UGS integrity evaluation, so that UGS building efficiency can be increased greatly.