Underground Gas Storage Site Research Articles

The influence of an anticline structure on ambient noise spectral anomalies at an underground gas storage

SUMMARY The purpose of this study is to investigate the seismic ambient noise spectral anomalies that occur near gas reservoirs. These anomalies involve a significant spectral amplification of the vertical component for frequencies generally between 1.5 and 4 Hz and have been reported at various hydrocarbon sites worldwide. There are differing views on the mechanisms responsible for these anomalies. The guideline for this study is that many hydrocarbon reservoirs share a common geological feature: an anticline structure. It appears to cause site effects that influence the amplitude of the ambient noise wavefield. This research examines a dense real data set of ambient noise recorded at the Chémery underground gas storage site in France. The analysis identifies stable spectral anomalies between 1.2 and 2.4 Hz that are correlated to the position of the anticline structure, which also corresponds to the position of the gas bubble. We use a beamforming technique to study the composition and the origin of the ambient noise, and show that the variations of the spectral anomalies over time are correlated to changes in the source wavefield. Finally, we perform numerical simulations of Rayleigh wave propagation within a realistic 3-D velocity model of the Chémery site, while using source distributions directly extracted from real data analysis. The comparison of the simulated anomalies with real data yields a satisfactory qualitative fit. We conclude that the fundamental-mode Rayleigh wave site effect on the anticline is the main mechanism of the spectral anomaly.

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.

Sulfate reduction and homoacetogenesis at various hypersaline conditions: Implications for H2 underground gas storage

While interest in underground gas storage (UGS) of hydrogen (H2) in salt caverns is increasing in a growing H2 economy, knowledge of the microbial communities inhabiting those hypersaline environments is still scarce. High salt concentrations and limited availability of carbon (C) sources in cavern environments reduce microbial growth rates and metabolic activities. Growth conditions potentially change once H2 is stored in salt caverns. H2 is a universal electron donor that can facilitate autotrophic growth and subsequently growth of heterotrophs. In this study, a mixed culture enriched from hypersaline UGS sites was investigated in microcosm experiments with H2 atmosphere, testing the effect of different salt concentrations and C sources on methanogenesis, sulfate reduction and homoacetogenesis. Sulfate, acetate and lactate concentrations were quantified throughout a time span of 125 days of incubation and correlations with the microbial community structure and function were explored through 16S rRNA gene-based amplicon sequencing at the end of the experiment. Many of the amplicon sequence variants (ASVs) were only assigned to family or order level, reflecting that a large number of ASVs belong to previously undescribed taxa. At 4.4 M NaCl, close to cavern brine salinity, members of the Desulfovibrionales were absent when no C source other than CO2 was offered as the sole C source. This is in line with the finding that no sulfate reduction occurred at these conditions. Acetogenic Halanaerobiia dominated in these high salinity levels. Based on metagenome sequencing of four selected samples, we found that acetogenesis at autotrophic conditions relies on the activity of a halophilic homoacetogen, Acetohalobium sp. and that sulfate reduction can most likely be associated with a so far undescribed member of the Desulfonatronovibrionales. We further discuss the discrepancy between sulfate reduction at heterotrophic conditions, while no sulfate reduction was observed under autotrophic conditions although acetate was produced through the homoacetogenic activity of Acetohalobium. For the application of UGS of H2, this means that the presence and activity of the aforementioned microorganisms must be investigated, as they can eventually lead to the formation of acetate and allow sulfate reduction at relevant concentrations.

Improved method and practice for site selection of underground gas storage under complex geological conditions

Increasing attention has been paid to the site selection of Underground Gas Storage (UGS) due to the growing demand for natural gas peak shaving. Existing studies have made a practical contribution to this field based on the multidimensional geological exploration data and the multi-criteria decision-making method. However, previous studies mainly focused on screening or ranking technologies with different principles, which means only the attributes of UGS in the design period were considered while the performance in the operation period was ignored. The operation plan and economic performance are considerable concerns to the UGS investors especially when this type of storage facility was unbundling from other sectors in natural gas companies. To solve the UGS site selection problems more comprehensively and practically, the geological conditions and the injection & extraction plan in the operation period are considered Simultaneously. A case from the S-X area in China indicates that: 1. The improved multi-period optimization model of the natural gas (NG) supply chain can obtain the injection and production plan of UGS which are the basic parameters for the economic analysis. 2. The top potential UGS estimated by geological conditions may take inferior performance in the operation stage (less peak shaving amount, low economic profits, and high freight of NG supply chain), so the UGS investors should consider the potential profits when the finished UGS is put into operation. The proposed framework can be a new theoretical guideline for the site selection problems of UGSs and can help UGS investors judge their investment.

Study on thermodynamic behaviour of natural gas and thermo-mechanical response of salt caverns for underground gas storage

Using salt caverns for underground gas storage (UGS) is an important energy storage solution. A coupled aero-thermo-mechanical (ATM) model with an integrated wellbore–3D realistic cavern geometry was established to investigate the thermodynamic behaviour of natural gas and the thermo-mechanical response of rock salt for UGS caverns. Unlike classical thermo-gas-mechanical (TGM) models that assume the cavern gas is an ideal gas and in an isotropic thermodynamic state, the ATM model solved thermodynamic properties for the real gas, and revealed the tempo-spatial varying gas state and its mechanism. Predictions of gas temperature, pressure and flux by ATM modelling well captured the in-situ measurements obtained by the distributed optical cable monitoring system during a one-month field testing at Jintan UGS site. Effects of the tempo-spatial varying gas state on the mechanical response were unveiled by ATM modelling. Predictions of mechanical response by TGM modelling shared similar patterns as that by ATM modelling, however, the TGM model tended to underestimate the risk of creep failure, tensile failure, fatigue failure and plastic damage due to the isotropic gas state. The proposed model could be used to improve the thermodynamic and mechanical predictions that are pertinent to the optimal design and the stability of caverns.

Mechanical behavior of salt rocks: A geomechanical model

The geomechanical behavior of salt rocks is a significant concern during drilling and development operations in some hydrocarbon reservoirs and underground gas storage sites. In this study, the static and dynamic salt rock geomechanical properties from a field in southwest Iran were evaluated using experiments such as waves' velocities, and thermo-mechanical coupled uniaxial and triaxial compression tests. As a result and by considering both the petrophysical well logs and laboratory data of the waves’ velocities, it is observed that the elastic properties of the core samples are concentrated within a narrow range unless an abnormality causes scatter. The results of uniaxial compression tests showed that rock strength decreases with increasing temperature linearly. In addition, the reduction of rock strength was observed with increasing porosity of the core samples as expected. In the case of triaxial compression tests, applying confining pressure on the core sample caused an increment in rock strength, while temperature decreased rock strength. The temperature also increased cohesion and decreases friction angle. The ratio of changes in stress to strain was used to investigate the dynamic changes in the geomechanical state. The maximum 0.25 damage factor was observed for the core samples for different definitions of the damage factor. Finally, we propose a novel analytical model to predict the stress-strain behavior of salt rocks at different conditions. The model was validated using experimental results and indicated a satisfactory accuracy.

Subsidence above gas storage in salt caverns predicted with viscoelastic theory

Based on the on-site monitoring data, the surface subsidence in the Jintan underground gas storage site has occurred continuously since the construction and operation of gas storage engineering. Therefore, the prediction of surface subsidence above gas storage in salt caverns is important to ensure the long-term safety of gas storage. Based on the mechanics theory, the formulas of elastic deformation of spherical and cylindrical caverns are derived. The Burgers viscoelastic model is used to describe the creep of rock salt. The viscoelastic analytical solution of the cavern deformation is obtained by using the correspondence principle in viscoelastic theory. It is assumed that the volume of the surface subsidence basin is directly proportional to the shrinkage volume of the cavern. The surface subsidence distribution curve is described by a Gaussian function. The spatiotemporal prediction of surface subsidence above gas storage in salt caverns based on viscoelastic theory is thus developed. The proposed theoretical model is used to analyze the surface subsidence above a gas storage cavern in rock salt in Jintan. The calculated subsidence is compared with the monitoring data. The accuracy of the theoretical model is verified by numerical simulation. The theoretical model can be used to predict the surface subsidence considering the solution stage in which the internal pressure changes with time. Results of this paper can provide guidance and suggestions for engineering practice of gas storage in salt caverns.

Advanced monitoring and simulation for underground gas storage risk management

It is crucial to ensure the safety and integrity of underground gas storage (UGS) infrastructure for energy reliability in California, and many other places around the world. To address the risk management need in UGS industry, we take advantage of recent advances in downhole fiber optic monitoring and coupled well-reservoir simulation to provide unprecedented understanding of gas flow in wells at UGS sites. We have combined advanced monitoring and simulation of UGS operations into a decision-support system called the Integrated Risk Management and Decision Support System (IRMDSS). The IRMDSS framework includes three components: (i) mechanistic models, (ii) continuous and frequent monitoring data, and (iii) a supervisory interface for performing analyses using the models and monitoring data. The goal of the IRMDSS is to equip UGS operators with real-time monitoring data and simulation tools that can alert them to potential failures, detect early leakage, and support mitigation decision-making to prevent otherwise larger failures. We demonstrate an application of the IRMDSS by analyzing the temperature and pressure response to a hypothetical leak. Through a review of distributed temperature sensing (DTS) data collected at an operating UGS facility we show that DTS can uniquely and precisely identify the depth of the gas-water-contact in the well annulus, and that DTS can provide an early warning signal of upward gas flow as would occur in a well blowout scenario. When combined with modeling analysis, a rough leak rate can be roughly estimated to understand the severity of the leakage conditions and to support the mitigation decision needed. • Mechanistic models simulate system responses to UGS facility operations. • Advanced monitoring technologies provide continuous update status for UGS facilities. • DTS data can provide real-time well leakage detection and identify leaky location. • Combination of models and advanced monitoring benefits UGS risk management.

Poromechanical Properties of a Sandstone Under Different Stress States

Poromechanical properties of a sandstone from an underground gas storage site are investigated with the use of a neutral gas to control the pore pressure. The poroelastic theory of anisotropic medium is used to evaluate elastic properties and coupling coefficients under different stress states. In-situ CT observations have been made under uniaxial compression test and they are used to underline some effects due to the occurrence of damage and microcraks. Under hydrostatic loading, pores and micro-cracks are gradually compressed. The initial state of the sandstone is “slightly” transversely isotropic but in a first approach the Biot’s tensor reduces to a scalar. This coefficient decreases with the increase in confining pressure that can be attributed to the closure of micro-cracks. The effect of damage and cracking is investigated with two series of conventional triaxial tests conducted at different confining pressures, either with an increase in pore pressure (series 1) or with a decrease in pore pressure (series 2), to evaluate the coupling coefficients. The results, derived from these two test series, are consistent as regards the effects of cracking on the material behavior. There is an obvious damage due to the triaxial loading which induces a parallel decrease in the ratio E3/(1 − ν3) and in the modulus H3. Axial compaction results in the continual increase in the H1 modulus observed for every sample whatever the measurement technique was.

Key technologies and practice for gas field storage facility construction of complex geological conditions in China

Abstract In view of complex geological characteristics and alternating loading conditions associated with cyclic large amount of gas injection and withdrawal in underground gas storage (UGS) of China, a series of key gas storage construction technologies were established, mainly including UGS site selection and evaluation, key index design, well drilling and completion, surface engineering and operational risk warning and assessment, etc. The effect of field application was discussed and summarized. Firstly, trap dynamic sealing capacity evaluation technology for conversion of UGS from the fault depleted or partially depleted gas reservoirs. A key index design method mainly based on the effective gas storage capacity design for water flooded heterogeneous gas reservoirs was proposed. To effectively guide the engineering construction of UGS, the safe well drilling, high quality cementing and high pressure and large flow surface injection and production engineering optimization suitable for long-term alternate loading condition and ultra-deep and ultra-low temperature formation were developed. The core surface equipment like high pressure gas injection compressor can be manufactured by our own. Last, the full-system operational risk warning and assessment technology for UGS was set up. The above 5 key technologies have been utilized in site selection, development scheme design, engineering construction and annual operations of 6 UGS groups, e.g. the Hutubi UGS in Xinjiang. To date, designed main indexes are highly consistent with actural performance, the 6 UGS groups have the load capacity of over 7.5 billion cubic meters of working gas volume and all the storage facilities have been running efficiently and safely.

Crustal Deformation in the Hutubi Underground Gas Storage Site in China Observed by GPS and InSAR Measurements

Crustal Deformation in the Hutubi Underground Gas Storage Site in China Observed by GPS and InSAR Measurements

A new technology for estimating time shifts in seismic monitoring of the exploitation of oil and gas fields and underground gas storage sites

The process of exploitation of oil and gas fields and underground natural gas and CO 2 storage facilities is accompanied by time-dependent changes in the physical properties of both the reservoir itself and the overburden. The study of these changes via time lapse (4D) seismic allows controlling the efficiency of operation of oil and gas fields and underground gas storage facilities. A wide class of methods uses, as intermediate information, time shifts arising in time lapse seismic data when studying the changes in the geomechanical properties of a reservoir. In this paper, conditions are formulated under which the values of the reflection coefficients of boundaries when changing the properties of a medium are preserved, but shifted to a new position along the two-way traveltime axis. To assess the time shifts that arise in this way, a new technology is developed. It is based on the statistical properties of the cross-correlation function of two time-limited random processes one of which is a shifted and stretched or compressed in time variant of the other. The proposed technology allows the constant and linear components of the time shifts to be determined simultaneously when the number of accumulated cross-correlation functions of such processes is sufficient. The validity of the theoretical foundations of the method is confirmed by two numerical experiments. As a source of input data required for the application of this technology in practice, it is suggested to use a random component of seismic images generated by chaotic fluctuations in the acoustic impedance in the lower half-space. Some methods for approximating the regular component of seismic records are described. Subtracting this component from the record allows its random component, which is necessary for the implementation of the proposed technology in practice, to be obtained.

Finding a Balance between Accuracy and Effort For Modeling Biomineralization

Microbially induced calcite precipitation (MICP) is a technology aiming at the mitigation of potential leakage from underground gas storage sites. A numerical model for MICP was previously developed and validated. The model complexity leads to high computation times, prohibiting at the moment the use of the model for designing field-scale MICP applications. This study investigates savings of the computational time by well-chosen model simplifications. Additionally, this approach is motivated by the high uncertainty of relevant input-parameters. Excessively detailed equations are unnecessary burdens to the MICP model, whose reliability is influenced by the input-parameter uncertainty.

Concept for Investigating Mechanical and Thermal Impacts on Distributed Subsurface Gas Monitoring

A multifunctional sensor in line shape was developed and introduced in previous work for measuring of gas concentrations, temperature change, and strain. A current field study focuses on a spatially distributed monitoring of subsurface CO2 gas storage sites in near real time.Mechanical impacts, e.g., caused by construction work, denudation, and seismic activity, can affect the integrity of underground gas storage sites. Thermal or moisture impacts, e.g., caused by weather conditions, can influence the gas distribution behavior. In this paper, we briefly describe the setup of a CO2 injection soil test field. This setup contains actuating elements for the investigation of mechanical and thermal impacts on distributed subsurface gas monitoring. A concept is given for evaluating these impacts and first experimental results are presented.

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.

A risk-based method for the design of monitoring networks for surface gas emanations from abandoned underground coal mines

In this paper, a risk-based method implemented within a geographic information system is proposed to locate monitoring points near zones of lower hydraulic resistance for the detection of gas leaks from underground gas storage sites installed in former underground coal mines. Risk assessment is conducted considering (1) the location and extent of the mined areas and of the former underground mining infrastructures, (2) damage induced by the mining works on the upper geological formations and their associated increase in hydraulic conductivity, and (3) potential impacts on humans, based on a proxy for population density. A new physically based method is proposed to compute the damage induced by the mining activities on upper geological layers, based on a 3D reconstruction of the geometry of the voids of the upper part of the former mine and a computation of the associated ground movements using influence functions. A new type of influence function applicable to inclined coal seam is proposed. The whole methodology is applied to the former underground gas storage site of Peronnes-lez-Binche, in Belgium. Three locations are identified for the installation of new piezometers to complement the existing monitoring network.

Well integrity: An overlooked source of risk and liability for underground natural gas storage. Lessons learned from incidents in the USA

Abstract Safety is a primary concern at underground gas storage (UGS) sites. Thorough evaluation of all potential migration pathways is critical to ensure UGS containment and public safety. Substantial risk is directly associated with inaccurate technical evaluations, that may result in subsequent gas migration from a UGS facility. Existing wellbores, including abandoned oil and gas wells, old dry exploration wells and water wells represent primary potential vertical gas migration conduits, which are not always thoroughly analysed during UGS site evaluation studies. Most abandoned oil and gas wells develop leaks over time, even when plugged in accordance with current (US) government regulations. Leaking wells in urban areas represent significant health and safety hazards. Many cities including Los Angeles permit construction of new homes directly over abandoned wells, even though state agencies recommend against this practice, thus placing residents at risk. Explosions and fires, along with possible exposure to substances such as benzene and toluene, are possible when gas reaches the surface through leaking wells and accumulates inside building voids. These potential problems are amplified with UGS fields, where operating pressures, already raised above the declining pressures of the field, fluctuate when alternating gas injection and extraction induce cyclic stress on wellbores and caprock sequences.

A review of underground fuel storage events and putting risk into perspective with other areas of the energy supply chain

Abstract The UK became a net importer of gas during 2004 and faces an increasing dependency on imports, yet has very little gas storage capacity. The UKs capacity to import, transport and store gas and liquid natural gas (LNG) has to be improved, requiring greater investment in new gas supply infrastructure. Construction of appropriately sited onshore underground gas storage (UGS) facilities is needed. However, local groups oppose most proposed UGS sites on the grounds of safety, citing the dangers of gas migration and rare fatal events, mostly in America. This paper summarizes 228 reported events of widely varying cause, nature and severity at underground fuel storage (UFS) facilities; the majority at USA SPR facilities. Since UGS was first undertaken in 1915, reports of 13 fatalities, around 72 injured and the evacuation of at least 6700 people are found at UFS sites. Some communities have experienced multiple evacuations. In the context of the danger posed to the general public, three of those killed were staff at two UFS facilities. UGS (including LPG) has led to 10 civilian deaths, 25 injured and c. 1250 evacuated. In other areas of the energy supply chain, casualties are orders of magnitude greater, with at least 1525 dead, 6826 injured and the evacuation of over 7000 at incidents involving above ground fuel storage tanks since 1951. When considering UK UGS applications, the risk of UGS and wider UFS experiences should be put into context. Worldwide, over 90 years experience in UGS now exists, with around 630 facilities of different types currently operational. Technologies used are often those of, or derived from, a well-regulated oil and gas exploration industry. In contrast to public perception, industry and academia recognize that UGS has an excellent health, safety and environmental record. Although it should not be claimed that gas will never be found outside the intended well or storage facility area, UFS casualty figures appear to corroborate claims by supporters of the technologies that salt caverns provide one of the safest answers to the problem of storing large amounts of hydrocarbons and that even in urban areas underground gas storage, oil and gas production can be conducted safely if proper procedures are followed. If gas is found outside the intended system, then after recognition of the problem, mitigation and safe operating procedures can and have been developed.

Conditioning an Underground Gas Storage Site to Well Pressures

This paper is concerned with the integrated modelling of an underground gas storage (UGS) site, considering geological data as well as production data. The production history for this UGS, located in an aquifer close to Paris, France, consists of two periods. The first one is a 7-year filling period for which the cushion gas was injected. The second one is a 10-year cycling period for which gas was injected during the summer to replenish the reserves and withdrawn during the winter according to the demand. Gas storage was performed through a dozen wells. During these two periods, pressures were recorded in 11 observation wells located all around the site. The first period data only are used to constrain the reservoir model. The second period data are used for comparison purposes. An assisted history-matching process based on the gradual deformation method was implemented to integrate production history jointly with geological data into reservoir models. By use of this innovative technique, both stochastic and deterministic parameters were accounted for. We show that the most influential parameters are related to the petrophysical properties (porosity means, coefficients defining the relations between porosity and permeability). The stochastic parameters are of second order only: they did not impact the matching process. The optimal reservoir model deduced from the matching procedure reproduced the static data and the pressures recorded for almost all the wells. The assisted history-matching methodology developed is especially powerful for managing a workflow integrating every steps from fine grid model creation to fluid flow simulation, handling rapid preliminary history-matching tests, analyzing the influence of several deterministic and stochastic parameters, determining fine grid reservoir models consistent with all the available data, and lastly reducing uncertainty in predictions.

The effect of local distortions on time‐domain electromagnetic measurements

Based on the time‐domain integral equation, we derive expressions for the effect of an anomalous body close to the receiver or close to the transmitter on transient electromagnetic measurements. Similar to magnetotellurics, the distortion of electric fields at late times can be described by a constant distortion tensor relating the secondary electric field to the primary field components that would be obtained in the absence of the body. The distortion of a single electric field transient is a static shift only for particular configurations over a layered half‐space. In the general case, the perturbation is time dependent because the direction of the total electric field vector varies with time. The theory nicely explains spatial variations in electric field transients measured during a high‐redundancy long‐offset transient electromagnetics (LOTEM) survey over an underground gas storage site. An inversion example with synthetic data illustrates how distortion can be corrected. The elements of the distortion tensor are determined simultaneously with the model parameters. Ambiguity is reduced by a regularization of the distortion parameters. In the example, the background model is recovered well, even for the difficult case where only one transmitter is used. The distortion of the magnetic field time derivatives caused by bodies close to the receiver is proportional to the time derivative of the primary electric step response. The distortion is generally not limited to early times and cannot be neglected in general. Transmitter overprint effects resulting in static shifts of vertical magnetic field time derivatives may also be understood from the theory.