Underground Gas Storage Operations Research Articles

Experimental investigation and predictive modeling of dry-out and salt precipitation effects during underground gas storage operations

Formation damage poses the greatest threat to underground gas storage (UGS) operations, with permeability reduction being a key cause of injectivity and productivity losses. To better understand the mechanisms behind dry-out and salt precipitation (DSP) and predict the resulting near-wellbore damage, this study experimentally and quantitatively evaluates key factors affecting rock properties before and after salt precipitation. We conducted long-term gas-brine core flooding experiments, obtained salt-contaminated samples, and supplemented them with core permeability-porosity parameter tests, high-pressure mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) experiments to better evaluate the salt clogging behavior of the samples. In addition, we discussed the applicability of the key parameter prediction model in modeling the DSP effects, including the water content of natural gas (WCNG), the porosity-permeability clogging model (PPC), and relative permeability (RP) function, providing usage recommendations. Based on our findings, we introduced a model to predict water saturation, salt saturation, and the salt-induced skin factor near the wellbore, particularly after viscous displacement ends, when liquid becomes immobile and evaporation dominates.The results show that salt precipitation has a significant impact on core porosity and permeability. Notably, lower flow rates subtly promote salt precipitation by enhancing the role of evaporation, resulting in greater salt accumulation. In addition, elevated salinity and higher initial water saturation are key contributors to the precipitation process, further exacerbating salt buildup within the reservoir. MIP experiments further confirm the aforementioned impacts. SEM observations reveal NaCl crystals, either clustered or isolated, extensively distributed within the pores and filling the pore spaces from micro to nanometer scale, highlighting their substantial role in altering pore structure and impacting porosity and permeability due to DSP effects. Our developed model confirms that high temperature, low pressure, high flow rates, low initial porosity and permeability, and strong near-well inertia effects lead to DSP effects manifesting sooner near the wellbore during the post-viscous displacement stage. Model validation with core-scale predictions closely matches experimental data in terms of trend.By laying the groundwork for analyzing the mechanisms of flow-through drying and salt precipitation, our findings can be directly applied to identifying the key controlling factors influencing DSP effects, mitigating formation damage, improving injectivity and productivity, and enhancing the efficiency of UGS operations under various operational conditions.

Compositional simulation of coupled transport mechanisms in fractured-vuggy underground gas storage: A case study of LWC in the Sichuan Basin

Compositional models were built to simulate the underground gas storage (UGS) operation, which is characterized by multiple cycles of rapid injection and production. Based on the validated model of the fractured-vuggy underground gas storage Lao Weng-Chang (LWC), this study evaluated the individual and coupling effects of stress sensitivity, relative permeability hysteresis, and high-speed non-Darcy flow on UGS operation. It was found that stress sensitivity is the main controlling factor behind the reduced working gas volume, and it led to a 6.07% decline in working gas volume. Relative permeability hysteresis is the determining factor for the storage capacity, and it led to a 9.05% decline in storage capacity. The high-speed non-Darcy flow only led to a 0.16% reduction in storage capacity but led to a 4.19% decline in working gas volume. A higher stress sensitivity coefficient and increased residual gas saturation both lead to greater losses in both storage capacity and working gas volume. Coupling stress sensitivity and relative permeability hysteresis would have a more pronounced effect on working gas volume than when considered individually. Considering the high-speed non-Darcy flow further decreases working gas volume. The gas production per unit pressure drop will also decrease with the increasing Reynolds number, and there exists a critical value of Re where the decrease significantly accelerates.

The Inversion Location of Microleakage Source and Diffusion Backward Tracing Method Based on 3D Visual Information Model of Salt-Cavern Gas Storage

Summary The safe and stable operation of underground gas storage makes a positive contribution to national energy security. To improve the efficiency of real-time monitoring and early warning of gas leakage accidents at the wellsite of salt-cavern gas storage, an inversion location of the gas microleakage source and a backward tracing method of leakage diffusion are proposed. Through building a 3D visual information model of the salt-cavern gas storage based on building information modeling (BIM) technology and combining it with the advantages of the gas sensors, the real-time inversion location of the microleakage source and diffusion backward tracing in the wellsite can be realized. First, multiple point-type laser methane sensors were used to monitor the leakage of some key zones in real time, and a pan/tilt/zoom (PTZ) scanning laser methane telemeter was used to realize the real-time multidimensional space monitoring on-site from horizontal 360° to vertical 180°. Second, a 3D integrated monitoring platform is established to analyze the gas leakage source by combining the monitoring data and improving the mesh interpolation points. Finally, the whole data and wellsite information are imported into the 3D integrated monitoring platform to realize the inversion location of the microleakage source and the real-time monitoring of the leakage and diffusion state in the whole region. The monitoring precision of gas leakage concentration can be up to 1.0 ppm, and the location distance is within 0.1 m based on the numerical simulation of the 3D model and actual detected data from sensors in the platform. Compared with the technical means of manual assisted leak location, this method effectively solves the difficult problem of leakage monitoring and location accurately in the gas storage and can timely reduce the expansion and impact of leakage accidents.

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.

Determination of internal gas losses during cyclic operation of an underground gas storage using identification modeling

An identification modeling method is proposed that makes it possible to determine of in-situ gas losses during the cyclic operation of underground gas storages (UGS) facilities and, on its basis, a preliminary estimate of in-situ gas losses during the cyclic operation of a particular tectonic block of the Galmaz UGS facility is predicted. It has been established that the main part of in-situ gas losses is the volume of gas that has diffused into the formation waters.

Piston rod fracture in natural gas process compressors for underground gas storage: A comprehensive case study

The reliable operation of process gas compressors is critical in the operation of underground gas storage (UGS). The piston rod is a critical moving part of the compressor, whose fracture can lead to serious consequences, including gas leakage or explosion. In this study, simulation and experimental investigations are carried out to analyse the factors contributing to the fracture failure of the piston rod in an actual engineering case in a UGS. Firstly, a three-dimensional computational fluid dynamics model is developed to elucidate the mechanism by which liquid-carry compression imposes significant piston rod overload. It is also established to capture the dynamic pressure changes in the compression cylinder during gas–liquid two-phase compression. A finite element model is then constructed, allowing analysis of the stress distribution of the piston rod in conjunction with the liquid-carry load patterns. Next, the crack propagation of the piston rod is analysed to unveil its effect on the service life during liquid-carry overload conditions. Finally, fracture analysis is performed on the actual fractured components to conclusively determine the root cause of this accident. The objective of this investigation was to enhance the comprehension of potential risks and causative factors leading to the fracture of compressor piston rods, which hope to contribute valuable insights and theoretical fundamentals towards the safety and maintenance of UGS.

Sealing capacity evaluation of underground gas storage under intricate geological conditions

Evaluating underground gas storage (UGS) sealing capacity is essential for its safe construction and operational efficiency. This involves evaluating both the static sealing capacity of traps during hydrocarbon accumulation and the dynamic sealing capacity of UGS under intensive gas injection and withdrawal, and alternating loads. This study detailed the methodology developed by Sinopec. The approach merges disciplines like geology, geomechanics, and hydrodynamics, employing both dynamic-static and qualitative-quantitative analyses. Sinopec's evaluation methods, grounded in the in situ stress analysis, include mechanistic studies, laboratory tests, geological surveys, stress analysis, and fluid-solid interactions. Through tests on the static and dynamic sealing capacity of UGS, alongside investigations into sealing mechanisms and the geological and geomechanical properties of cap rocks and faults, A geomechanics - rock damage - seepage mechanics dynamic coupling analysis method has been developed to predict in situ stress variations relative to pore pressure changes during UGS operations and evaluate fault sealing capacity and cap rock integrity, thereby setting the maximum operational pressures. Utilizing this evaluation technique, Sinopec has defined performance metrics and criteria for evaluating the sealing capacity of depleted gas reservoirs, enabling preliminary sealing capacity evaluations at UGS sites. These evaluations have significantly informed the design of UGS construction schemes and the evaluation of fault sealing capacity and cap rock integrity during UGS operations.

Failure Mechanism of Integrity of Cement Sheath under the Coupling Effect of Formation Creep and Temperature during the Operation of Salt Rock Gas Storage

Maintaining the integrity of the cement sheath is essential for the sealing of underground gas storage. The formation creep, temperature changes, and operating pressure changes during the operation of underground gas storage can cause changes in the stress of the cement sheath, which probably induces the failure of the cement sheath’s integrity. A creep model taking the effects of stress and temperature into account is developed to study the cement sheath’s integrity in creep formation, and the feasibility of creep simulation via finite element method is verified. The finite element method is used to analyze the effects of formation creep, temperature, operating pressure, and the cement sheath’s elastic modulus on the cement sheath’s integrity. The result shows that the coupling effect of formation creep and temperature increases the cement sheath’s failure risk; both the formation creep and the decrease in cement sheath temperature increase the Von Mises stress on the cement sheath, increasing the risk of the cement sheath’s shear failure. The decrease in cement sheath temperature decreases the circumferential compressive stress on the cement sheath and raises the risk of the cement sheath’s tensile failure. Shear failure of the cement sheath occurs at high operating pressure upper limits. The operating pressure is less than 70 MPa, or the cement sheath’s elastic modulus is less than 3 GPa, which can prevent the failure of the cement sheath’s integrity during the operation of underground gas storage.

Hydrodynamic Modeling of Cyclic Operation of Underground Gas Storages

Hydrodynamic Modeling of Cyclic Operation of Underground Gas Storages

Spillovers of underground gas storage facilities and their role in the sustainable energy markets: assessment and policy recommendations

PurposeThe purpose of this study is to investigate the impact of the construction and operation of underground gas storage (UGS) facilities, under the prism of the recent rise in energy prices. The focus is on developing energy markets interconnected with gas producers through pipelines and has access to liquefied natural gas (LNG) facilities in parallel.Design/methodology/approachThrough a focal market in Europe, the authors estimate the economic value for both stakeholders and consumers by introducing a methodology, appropriately adjusted to the specificities of the domestic energy market. The Transmission System Operator, the Energy Market Regulator, the Energy Exchange and Eurostat are the main data sources for our calculations and conclusions.FindingsThe authors investigate the perspectives of UGS facilities, identifying financial challenges considering specific energy market conditions which are barriers to new storage facilities. Nevertheless, the energy price rocketing coupled with the security of gas supply issues, which arose in autumn 2021 and were continuing in 2022 due to the Russia–Ukraine crisis, highlight that gas storage remains, at least for the midterm, at the core of European priorities.Originality/valueThe paper emphasizes on developing markets toward green transition, proposing tangible policy recommendations regarding gas storage. A new methodological approach is proposed, appropriate to quantify the economic value of UGSs in such markets. Last, a mix of energy policy options is suggested which include regulatory reforms, support schemes and new energy infrastructures that could make the gas storage investments economically viable.

Viscoelastic analysis of surface deformation above salt caverns for gas storage based on semi-infinite space

The construction of salt caverns for energy storage is of strategic significance, but the operation of underground gas storages in salt formations will cause surface deformation. The research and analysis of surface deformation is an important part of the stability evaluation of salt caverns for gas storage. From the perspective of classical mechanics theory, the analytical solution of surface deformation above salt caverns for gas storage is deduced. The surface displacement caused by the contraction of a salt cavern is regarded as the boundary displacement caused by the surface force acting on a spherical cavern in a semi-infinite space. The equivalent conversion of load form is carried out based on the mirror principle. The vertical subsidence and horizontal displacement of the surface of the elastic semi-infinite space is obtained. According to the elastic-viscoelastic correspondence principle, the viscoelastic solution of the surface displacement of the semi-infinite body, regarded as Maxwell body, can be obtained. A numerical model of a salt cavern for gas storage is established based on the engineering practice. The results of the analytical solution and the numerical simulation are compared and analyzed to verify the accuracy of the analytical solution. The analytical solution was applied to predict the surface displacement above a group of caverns, and the influence of the layout of salt caverns and cavern center spacing on the surface displacement is analyzed. The research results show that the regular triangular layout is slightly better than the square layout. The larger the cavern center spacing, the smaller the maximum surface subsidence. The proposed theoretical prediction model can provide a theoretical basis for controlling surface deformation for the construction of gas storage caverns.

Study on Critical Drawdown Pressure of Sanding for Wellbore of Underground Gas Storage in a Depleted Gas Reservoir

Accurately predicting the critical differential pressure (CDP) of sand production contributes to improving the peak-shaving capacity and ensuring safe operation of underground gas storage (UGS). The CDP of sanding production in the target wells of the UGS was predicted coupling laboratory tests, inversed analysis with well logging data and numerical simulations. The in-situ mechanical properties of rock were estimated by coupling the laboratory test results and well-logging data. The in-situ stress field of the target formation was then deduced through inversed analysis coupled finite element method (FEM) and genetic algorithm (GA), based on the existing known stress data and the seismic data of the measured points. Using the critical strain limit (CSL) of 5‰ as the sanding criterion of the wellbore, the CDPs of the gas production in the UGS were predicted, which was 5.59 MPa, 3.98 MPa, and 4.01 MPa for well #1, well #2 and well #3, when the pressure of the gas storage was 30 MPa, respectively. The simulation results showed good agreements with the field-measured benchmark data of well #2 and well #3. The effects of moisture contents (ranging from 10 to ~40%), and cycling times of gas injection and withdrawal (ranging from 40 to ~200 cycling times) on the critical differential pressure were simulated and analyzed. The results indicated that the CDP decreased with an increase of the moisture content and the cycling times. This study provides a reliable tool for the sanding prediction of the wellbore in the UGS.

Change mechanism of pore structure and filling efficiency during injection production of sandstone underground gas storage

Ten sandstone samples were chosen to conduct rock pore structure change law experiment before and after injection and production and the NMR fluid test experiment, the changes of pore size, permeability, and space filling degree were compared and analyzed. According to the findings, certain authigenic minerals (authigenic quartz and feldspar) in sandstone pores may come off after repeated rounds of high-intensity fluid erosion, obstructing the seepage channel. The composition and amount of clay minerals vary little due to gas–water interaction displacement, although some banded clay particles readily break off (polyhydrate kaolinite). The cracks produced by certain brittle rock particles can enhance the rock's porosity and permeability by about 20% and 10%, respectively. The fluid wettability of the rock changes as the operating cycle of subterranean gas storage rises, the gas saturation degree in the pores gradually increases, and the water gradually declines. Gas injection and production tended to attain equilibrium after 10 injection production cycles, and gas loss steadily decreased. It can be considered the node for the stable operation of subterranean gas storage at the present moment. As a result, high-intensity and numerous cycles of injection and production for sandstone underground gas storage may expand storage space, improve permeability, and progressively improve the gas-water ratio, all of which are beneficial to the stable and efficient operation of underground gas storage.

Optimization of injection-withdrawal schedules for underground gas storage in a multi-block depleted gas reservoir considering operation stability

ABSTRACT Underground gas storage (UGS) is an important facility to overcome the imbalance between natural gas supply and demand. In this paper, an optimization model of injection-withdrawal scheduling for UGS in a depleted gas reservoir is established to find the optimal operating state of the gas storage facility. Faults are widely developed in reservoir, which can divide a full reservoir into several pressure disconnected reservoir blocks (RB). Considering that the unbalanced pressure distribution of reservoir will significantly affect the stable operation of UGS, the optimization model aims to minimize the deviation degree of pressure between RBs under the condition of satisfying the gas injection-withdrawal requirements. The decision variables are the number of operating wells and the flow rate of a single well of each RB. A series of equality and inequality constraints are developed, including maximum inventory of RB, maximum pressure of RB and maximum flow rate of a single well. To verify the validity of the proposed method, the optimization model is applied to an actual UGS in a depleted gas reservoir in China. The GAMS modeling system and DICOPT solver are adopted to solve the optimization problem. The results show that the deviation degree of pressure between RBs of the optimized scheme is about 75% lower than that of the empirical scheme. In the empirical scheme, there is an extremely high-pressure RB with a maximum pressure of 43.98 MPa, which exceeds the pressure limit of 5.38 MPa. However, all RBs meet the pressure requirement in the optimized scheme. Overall, the optimized scheme can effectively reduce the deviation degree of pressure between RBs and avoid the occurrence of extremely high-pressure RB.

Effects of in-situ stress and elastic parameters of cement sheath in salt rock formation of underground gas storage on seal integrity of cement sheath

The cement sheath seal integrity is crucial for a safe operation of underground gas storage. Owing to its creep characteristics, the salt formation squeezes the cement sheath, which may cause failure of the cement sheath’s seal integrity and pose risks to the safe operation of underground gas storage. In this study, the experimentally obtained salt rock creep law and finite-element software ABAQUS were used to verify the adaptability of the salt rock creep in ABAQUS. In addition, a model of casing–cement sheath formation combination under creep formation conditions was developed. The effects of the in-situ stress (ISS) and cement sheath’s elastic parameters on the seal integrity of the cement sheath were studied in the salt rock layer. The creep of the salt rock increased the stress acting on the cement sheath over time and caused shear failure of the cement sheath. A larger uniform horizontal ISS led to a shorter time period for shear failure of the cement sheath, larger equivalent plastic strain (PEEQ), and larger yield area. A larger maximum horizontal ISS led to a shorter time period for shear failure of the cement sheath, larger PEEQ, and larger yield area. The yield area was concentrated in the direction of the maximum and minimum horizontal ISSs. Uniform and non-uniform horizontal ISS creeps did not cause tensile failure of the cement sheath. The reduction in the elastic modulus of the cement sheath and increase in the Poisson’s ratio of the cement sheath could reduce the shear failure risk of the cement sheath in salt rock formation. The influences of the ISS and cement sheath elastic parameters in the salt rock layer on the seal integrity of the cement sheath obtained in this study can provide references for the seal integrity failure of the cement sheath in the creep formation.

Optimization and utilization of peak-shaving capability for water drive gas storage

To determine the reasonable gas injection and production quantity and to minimize the influence of water invasion on the operation of underground gas storage is one of the key factors to decide whether the water drive gas storage can fully exert its peak shaving ability. At present, gas reservoir engineering method is mainly used in China, which mainly reflects the operation of underground gas storage under the condition of less water invasion at the end of gas production, it cannot really reflect the influence of water invasion on the operation of underground gas storage under the condition of large injection-production volume. Through the numerical simulation and the research of the injection-production performance, it is clear that the main geological factors affecting the reasonable injection-production rate of the gas storage are the pressure of the gas storage, the properties of the reservoir, the distribution of gas and water and the radius of well control. Based on the reservoir changes of pressure, water yield, gas-water ratio, gas-water interface and saturation, and according to the influence of multi-period water invasion on the operation of gas storage, the optimization technology of peak shaving capacity of water drive gas reservoir is established, which successfully guides the optimization of injection-production operation of an underground gas storage in China. The result shows that after 5 cycles of operation, the gas injection displacement effect is successful, the gas production capacity is improved gradually, and the peak shaving capacity is 6.85 X 108m3 in 2019. The conclusion is that the optimization technology of peak shaving capacity is applicable to some extent, which provides theoretical basis and operating experience for the design of injection-production operation of the same type gas storage in China.

Environmental problems of sustainable development of oil-producing regions of the North

There is a relationship between the economic requirements for the development of oil and gas facilities in the oil-producing regions of the North and the environmental problems of sustainable development. One of the ways to solve this problem is the wider use of underground gas storage facilities both for reducing peak loads in the Unified Gas Supply System by collecting and storing previously flared associated petroleum gas, and for burying a large volume of industrial emissions that are harmful to the environment. We have considered a mathematical model of an automated control system for the creation and operation of underground gas storage in the horizons of a depleted oil and gas condensate field with its subsequent use for disposal of industrial emissions. To ensure the stability of the functioning of objects of accumulation and consumption, it is necessary to calculate the depth of feedback for each component of the component: proportional, integral, differential.

Research deformation caused by hydraulic fracturing

The paper discusses problems of tensile loadings affecting a soil layer when conducting hydraulic fracturing. The effect of tensile stress on rocks in a bottomhole formation zone during hydraulic fracturing is studied using numerical methods. A special analysis of the processes of cores deformation under reservoir conditions is carried out in the paper. The article provides formulas to calculate stress-strain state of rocks in bottomhole formation zone. Along with an exact numerical study of the distribution of stresses in bottomhole formation zone, some approximate analytical dependencies reflecting features of the stress-strain state of bottomhole formation zone are obtained with the aim of solving optimization problems. The paper presents the scheme of production layer vertical deformation which shows layer’s roof and bottom displacement caused by increased pressure inrepression cone. Formulas describing the influence of deformation processes in bottomhole formation zone can also be used to study cyclic operation of underground gas storages.

Research on Injection-Production Capability and Seepage Characteristics of Multi-Cycle Operation of Underground Gas Storage in Gas Field—Case Study of the Wen 23 Gas Storage

With the increasing energy demands of current modern society, underground gas storage (UGS) in gas fields is the most popular type of UGS used to meet the seasonal variation of gas consumption. However, compared with gas fields, UGS in gas fields has the characteristics of periodic high-speed injection and production of exploitation modes and operation rules, which causes the rules of gas-water seepage and utilization of reserves to be more particular and complicated. In this paper, based on Wen 23 gas storage, the rules of multicycle injection and production flow and the utilization of UGS pore volume were investigated. The experimental results showed that variation in porosity and permeability caused by injection and production pressure changes in Wen 23 gas storage can be neglected. The pore volume of gas storage and the degree of gas recovery increased gradually in the pre-UGS gas zone, which was higher than that of reservoirs. In the initial stage of UGS operation, the pore volume of gas storage and the degree of gas recovery were low in the gas-drive-water gas zone as a result of water invasion during the process of reservoir exploitation. During operation of multicycle high-speed injection and production, the seepage conditions in the gas-drive-water gas zone gradually improved. The higher the reservoir permeability, the greater increases in pore volume and degree of gas recovery. In the gas-water transition zone, gas and water were reciprocated and displaced with the multicycle injection-production of UGS, resulting in the gradual deterioration of pore volume and gas recovery, which remained stable at a low value. The negative effects of reservoir heterogeneity on the effective utilization of UGS occurred in the gas-water transition zone. These findings may contribute to a better understanding of the rules of multicycle injection and production flow and utilization of UGS to optimize the injection-production efficiency of Wen 23 gas storage.

Influence of hysteretic stress path behavior on seal integrity during gas storage operation in a depleted reservoir

In this study, we numerically investigate the influence of hysteretic stress path behavior on the seal integrity during underground gas storage operations in a depleted reservoir. Our study area is the Honor Rancho Underground Storage Facility in Los Angeles County (California, USA), which was converted into an underground gas storage facility in 1975 after 20 years of oil and gas production. In our simulations, the geomechanical behavior of the sand reservoir is modeled using two models: (1) a linear elastic model (non-hysteretic stress path) that does not take into consideration irreversible deformation, and (2) a plastic cap mechanical model which considers changes in rock elastic properties due to irreversible deformations caused by plastic reservoir compaction (hysteretic stress path). It shows that the irreversible compaction of the geological layer over geologic time and during the reservoir depletion can have important consequences on stress tensor orientation and magnitude. Ignoring depletion-induced irreversible compaction can lead to an over-estimation of the calculation of the maximum working reservoir pressure. Moreover, this irreversible compaction may bring the nearby faults closer to reactivation. However, regardless of the two models applied, the geomechanical analysis shows that for the estimated stress conditions applied in this study, the Honor Rancho Underground Storage Facility is being safely operated at pressures much below what would be required to compromise the seal integrity.