Gas Storage Reservoir Research Articles

Research on the Injection–Production Law and the Feasibility of Underground Natural Gas Storage in a Low-Permeability Acid-Containing Depleted Gas Reservoir

Depleted gas reservoirs are important places for the rebuilding of gas-storage reservoirs. In order to demonstrate the feasibility of constructing and operating such underground gas storage, a low-permeability gas-storage seepage model considering fracture development was developed and established. The model was solved using semi-analytical methods, and the pressure–response characteristics during natural gas injection were analyzed. The impact of gas injection volume on formation pressure has been clarified, and the calculation method for ultimate injection pressure has been determined. Additionally, through numerical simulation methods, the migration law of acidic gas during gas injection, the variation law of produced acidic gas concentration, and the main control factors affecting the concentration of the produced acidic gas were studied. Furthermore, measures to reduce the concentration of the acidic gas produced were proposed. Finally, injection and production plans were designed for typical depleted acidic gas reservoirs, simulating the operation of gas storage for 12 cycles. The results indicate that the quality of natural gas produced in the third cycle can meet the Class II standard for commercial natural gas. Through this study, the feasibility of constructing gas-storage facilities for acidic depleted gas reservoirs has been demonstrated, and injection and production strategies for this type of gas reservoir have been proposed.

A Study on the Breakthrough Pressure of Porous Rock Formations in Gas Storage Reservoirs

Breakthrough pressure of natural gas in rock is an important evaluation parameter in gas reservoir development. In this study, experimental measurements of porosity and permeability of the caprock core were carried out. A digital core model was obtained by body rendering of rock CT (Computed Tomography) slices using Avizo software. Then, the grid model was imported into Fluent software for a numerical simulation of natural gas breakthrough pressure in the core. The innovations of this paper include (1) an accurate calculation method of cap breakthrough pressure based on the VOF method; (2) the method performs a perceptual analysis of average pore radius, wettability, roughness height, and viscosity ratio.

Research Progress and Development Trend of Treatment Methods for Annular Pressure in Gas Storage Caverns

Abstract In recent years, pressure in the annulus of gas storage reservoir injection wells has become increasingly common. This presents a significant challenge to the safe and efficient operation of gas storage reservoirs and the integrity of injection wells. This paper presents a systematic introduction to the prevention and control measures of annular pressure. The introduction is based on research into the development status of prevention and control methods both domestically and internationally. The measures mainly include two aspects. Firstly, for the sealing failure of the tubular column, the differential pressure activated blocking agent is used for management. Secondly, for the sealing failure of the cement ring, the sealing agent is managed by extruding cement, resin, and other blocking agents. The text analyses the advantages and disadvantages of the treatment technology in depth, in combination with existing research. The repair methods for gas storage reservoir annulus with pressure have problems such as insufficient construction conditions, poor implementation effect, and limited types of blocking agents available. Additionally, the different working conditions and performances of the reservoir annulus are taken into account. To ensure high efficiency and cost-effectiveness, we propose a new method for treating annulus pressure. This involves repairing any damage to the cement ring, restoring the production packer’s seal, and rebuilding the integrity of the old wellbore. By doing so, we can guarantee the safety of gas storage reservoirs throughout the entire injection and production life cycle. It is important to maintain the integrity of the old wellbore to ensure the safety of gas storage during injection and extraction.

Study on the deformation and failure laws of surrounding rock under reduced roof thickness in Salt Cavern Gas Storage

Under the premise of guaranteeing the stability of the gas storage reservoir, reducing the thickness of the salt layer on the top plate of the gas storage reservoir can improve the utilization rate of the salt layer in the construction section and increase the vertical height of the gas storage reservoir cavity, creating a larger gas storage space. The mechanical planar model of the casing-cement sheath-surrounding rock in the top plate of the salt cavern gas storage reservoir yields the elastic–plastic theoretical solution for the stress and deformation of the well wall surrounding rock. Based on this, a three-dimensional mechanical numerical model of the top plate is constructed to compare the effects of various top plate thicknesses on the surrounding rocks of the gas storage reservoir and to analyze the stress and deformation behavior of the wall surrounding the rock of the top plate of the reservoir in the cementing section and bare wells under the long-term injection and extraction cycle. The results indicate that reducing the thickness of the roof salt layer primarily affects vertical displacement, radial displacement, equivalent strain, and principal stress changes in the cement sheath and surrounding rock. All other roof parameters, except for equivalent strain, show an increasing trend. Reducing the salt layer thickness in the cementing section has the least impact on the gas storage roof’s stability. In contrast, reducing the salt layer thickness in the cementing section and bare wells has a moderate impact, while reducing the thickness solely in the bare wells is the most detrimental. These findings provide valuable insights for optimizing the roof thickness of gas storage facilities and enhancing the utilization of the limited salt layer in the reservoir section.

Effects of H2S content on the corrosion behavior of gas storage reservoir injection and production pipeline steel in CO2-H2S environment

The effects of H2S content on the corrosion behavior of gas storage reservoir injection and extraction pipeline steel in a CO2-H2S environment were investigated by surface characterization and ultrasonic thickness measurement. The results show that the corrosion products of gas injection and extraction pipelines under real conditions are more complex. In the CO2-H2S environment, with the increase of H2S content, the corrosion rate of gas storage reservoir gas injection and extraction pipeline steel firstly increases and then decreases. At a partial pressure ratio of CO2 to H2S of 550, corrosion resulted mainly in the formation of FeCO3, FeS2, and Fe3O4, with limited generation of stabilizing protective films. This led to severe localized corrosion, mainly driven by CO2. In contrast, when the CO2 to H2S partial pressure ratio was reduced to 5.2, the corrosion mainly produced Fe7S8, FeS2, and BaSO4, which promoted the formation of a more stable protective film on the inner wall of the tube, while the presence of gums reduced the severity of the localized corrosion and shifted the corrosion control to H2S.

Investigation of the Upper Safety Operating Pressure Limit for Underground Gas Storage Using the Fault Activation Pressure Evaluation Method

As a crucial reserve for natural gas, the safe operation of underground gas storage facilities is paramount for seasonal peak shaving and emergency supply security. Focusing on the Lei X gas storage facility in the Liaohe Basin of China, this study delves into the mechanical integrity of gas storage facilities and assesses the upper limit pressure for safe operation. Leveraging seismic logging data, we conducted an analysis and statistical evaluation of boundary faults and top cover characteristics, integrating regional stress fields and rock mechanics to evaluate fault activation pressure and cover failure risk using a fault activation pressure assessment method. This research elucidates the maximum safe operating pressure for underground gas storage facilities. The research findings suggest that the sealing layer of the Lei X gas storage reservoir exhibits a predominant hydro-fracturing pattern. Under the existing stress field conditions, the sealing layer demonstrates favorable sealing properties, and the boundary faults remain relatively stable. Moreover, through data extraction and quantitative analysis, this study clearly determined the critical pressure at which each fault is activated and the pressure at which the sealing layer undergoes hydro-fracturing during cyclic injection and the production of gas storage. Considering the activation pressure and fracturing pressure data for the sealing layer, a secure operating pressure of 15.0 MPa was calculated for gas storage operations. This study offers crucial theoretical support for enhancing injection and production efficiency, as well as ensuring the safe operation of Lei X gas storage and providing technical guidance for future adjustments to injection and production schemes.

Experimental study on reservoir particle migration induced by the injection-production process of underground gas storage

Multi cycle injection and production of underground gas storage (UGS) promote continuous changes in reservoir characteristics, to clarify the impact of different injection and production characteristics on the reservoir, taking carbonate rock fracture-pore type gas storage reservoirs as the research object, established a set of experimental methods based on production characteristics, quantitative analysis of reservoir damage caused by particle migration caused by increasing, decreasing, fluctuating, and reverse changes in production pressure difference. And the following research results are obtained. First, established experimental methods based on production characteristics, the production method includes increasing, decreasing, fluctuating, and reverse changes, realized experimental evaluation of simulating actual production full features. Second, there is a critical pressure difference in the migration of reservoir particles, the fluctuation of production pressure difference induce further migration of particles, resulting in natural unblocking or new blockage. Third, the change in the direction of production pressure difference can cause large particle sizes break into small particle sizes and migrate out of the pore throat, thus the permeability of the reservoir can be improved to a certain extent. It is concluded that controlling a certain production pressure difference during the injection and production process of UGS, not only meets production needs, but also alleviate the damage of injection production to reservoir permeability to a certain extent.

Research and Application of Temporary Plugging Agent Technology for High-Pressure Wells in Gas Storage Facilities

Before various construction of gas storage well, in order to ensure safety, the reservoir must be temporarily blocked, degassed by circulation and no gas in the well can be operated. There are many temporary plugging methods for oil and gas wells. This paper studies the more advanced micro mesh gel temporary plugging technology in the industry and its application in gas storage wells, which mainly solves the problems of poor degradation backflow effect and difficult permeability recovery caused by weak formation stability after temporary plugging of gas storage wells. Research points: (1) On the basis of ordinary gel, through the fusion with cross-linking agent with special structure, a micron network polymer with significant steric hindrance effect on water molecules is finally formed, which improves the strength and stability of the gel system. (2) Add hexamethylene tetramine, bisphenol propane, delayed cross-linking agent and stabilizer into the polymer aqueous solution. It is verified by laboratory tests that the micron mesh gel can be formed after constant temperature coagulation for 3h~70h at ambient temperature of 90°C~170°C. (3) The temperature resistance, permeability and gel breaking of micron mesh gel are tested in the laboratory, and the results can meet the construction requirements. (4) After the temporary plugging operation of Well Su 49K-2X in the gas storage reservoir of Huabei Oilfield is completed, the degradation products of gel breaking will flow back smoothly to ensure that the well can be put into normal injection and production quickly. The test results show that: (1) Micron mesh gel has the advantages of long plugging validity, high temperature resistance, low viscosity after gel breaking, no residue, thorough gel breaking, no formation plugging pollution, and no impact on the original reservoir permeability. It is a new green plugging technology suitable for deep buried high-temperature depleted oil and gas reservoirs. (2) Before construction, the well temperature shall be measured to conduct test injection, so as to prevent gas invasion from affecting the construction effect. The pump injection displacement is designed to be redundant, so as to prevent the low molecular solution from not reaching the design position in the well on time, and the formation of solid rubber plugs at other positions in the well from affecting the construction.

Ab initio determination of melting and sound velocity of neon up to the deep interior of the Earth.

The thermophysical properties and elemental abundances of the noble gases in terrestrial materials can provide unique insights into the Earth's evolution and mantle dynamics. Here, we perform extensive abinitio molecular dynamics simulations to determine the melting temperature and sound velocity of neon up to 370GPa and 7500K to constrain its physical state and storage capacity, together with to reveal its implications for the deep interior of the Earth. It is found that solid neon can exist stably under the lower mantle and inner core conditions, and the abnormal melting of neon is not observed under the entire temperature (T) and pressure (P) region inside the Earth owing to its peculiar electronic structure, which is substantially distinct from other heavier noble gases. An inspection of the reduction for sound velocity along the Earth's geotherm evidences that neon can be used as a light element to account for the low-velocity anomaly and density deficit in the deep Earth. A comparison of the pair distribution functions and mean square displacements of MgSiO3-Ne and Fe-Ne alloys further reveals that MgSiO3 has a larger neon storage capacity than the liquid iron under the deep Earth condition, indicating that the lower mantle may be a natural deep noble gas storage reservoir. Our results provide valuable information for studying the fundamental behavior and phase transition of neon in a higher T-P regime, and further enhance our understanding for the interior structure and evolution processes inside the Earth.

Rock strength weakening subject to principal stress rotation: Experimental and numerical investigations

During the construction and operation of gas storage reservoirs, changes in the principal stress direction can induce fracture propagation under conditions of lower differential stress, potentially leading to failure in the surrounding rock. However, the weakening of strength due to pure stress rotation has not yet been investigated. Based on fracture mechanics, an enhanced Mohr-Coulomb strength criterion considering stress rotation is proposed and verified with experimental and numerical simulations. The micro-damage state and the evolution of the rock under the pure stress-rotation condition are analyzed. The findings indicate that differential stress exceeding the crack initiation stress is a prerequisite for stress rotation to promote the development of rock damage. As the differential stress increases, stress rotation is more likely to induce rock damage, leading to a transition from brittle to plastic failure, characterized by wider fractures and a more complex fracture network. Overall, a negative exponential relationship exists between the stress rotation angle required for rock failure and the differential stress. The feasibility of applying the enhanced criterion to practical engineering is discussed using monitoring data obtained from a mine-by tunnel. This study introduces new concepts for understanding the damage evolution of the surrounding rock under complex stress paths and offers a new theoretical basis for predicting the damage of gas storage reservoirs.

Experimental study on fatigue failure properties of mudstone interlayers under discontinuous loading in salt cavern gas storage

During the operation of an underground salt cavern gas storage, Fatigue failure occurs in the surrounding rock of gas storage reservoirs under non-continuous gas injection and extraction loading. Due to the special layered salt rock structure in China, the mudstone interlayer is the weak part of the gas storage. It is necessary to study the effect of stress magnitude and interval time on the fatigue mechanical properties of mudstone. Graded upper stress limit interval fatigue (GUIF) test and graded lower stress limit interval fatigue (GLIF) test were carried out on mudstone respectively. And different interval times were set to investigate the effect of interval time on the mechanical properties of mudstone. With the increase in the interval time, the fatigue life and peak strain of the mudstone increased. Under the same interval time, the lower-limit interval test result showed a significantly higher fatigue life than the upper-limit interval test result. The stress–strain curve exhibited three stages: scattered–dense–scattered. During the unloading phase, the modulus of elasticity increased with increasing stress levels, indicating that the internal structure of the mudstone is extremely sensitive to the stress. In the (GUIF) test, the average residual strain increased with the increase in the interval time, and the residual strain during the cycle after the time interval under different grades was lower than the residual strain before the time interval; the results of the (GLIF) test showed the opposite trend. In the (GUIF) test, the average creep strain increased with increasing interval time under the same stress level, and the average creep strain was greater than the average residual strain, and the creep stage had a greater effect on mudstone damage than the fatigue stage. The post-fatigue creep strain was significantly greater than the pre-fatigue creep strain. The research results can be useful in ensuring the stable operation of gas storage in salt caverns.

Underground Hydrogen Storage Safety: Experimental Study of Hydrogen Diffusion through Caprocks

Underground Hydrogen Storage (UHS) provides a large-scale and safe solution to balance the fluctuations in energy production from renewable sources and energy consumption but requires a proper and detailed characterization of the candidate reservoirs. The scope of this study was to estimate the hydrogen diffusion coefficient for real caprock samples from two natural gas storage reservoirs that are candidates for underground hydrogen storage. A significant number of adsorption/desorption tests were carried out using a Dynamic Gravimetric Vapor/Gas Sorption System. A total of 15 samples were tested at the reservoir temperature of 45 °C and using both hydrogen and methane. For each sample, two tests were performed with the same gas. Each test included four partial pressure steps of sorption alternated with desorption. After applying overshooting and buoyancy corrections, the data were then interpreted using the early time approximation of the solution to the diffusion equation. Each interpretable partial pressure step provided a value of the diffusion coefficient. In total, more than 90 estimations of the diffusion coefficient out of 120 partial pressure steps were available, allowing a thorough comparison between the diffusion of hydrogen and methane: hydrogen in the range of 1 × 10−10 m2/s to 6 × 10−8 m2/s and methane in the range of 9 × 10−10 m2/s to 2 × 10−8 m2/s. The diffusion coefficients measured on wet samples are 2 times lower compared to those measured on dry samples. Hysteresis in hydrogen adsorption/desorption was also observed.

Allowable Pillar Width for Salt Cavern Gas Storage Based on Triangular Well Layout: A Case Study in China

Salt rock, renowned for its remarkable energy storage capabilities, exists in deep underground environments characterized by high temperature and pressure. It possesses advantageous properties such as high deformability, low permeability, and self-healing from damage. When establishing a cluster of salt cavern gas storage facilities, the careful selection of ore column widths between these reservoirs is crucial for minimizing the risk of structural failure, optimizing salt rock resource utilization, and enhancing the construction and operation of gas storage reservoirs. In current practices, square triangular arrangements are commonly used in designing well layouts for reservoir groups to balance stability and economic considerations. This study, conducted in the context of the Jintan salt cavern gas storage project in Jiangsu Province, employed FLAC3D to create a finite element model for proposed gas storage configurations. A comprehensive analysis of the long-term operational safety of salt cavern gas storage with triangular well layouts was carried out. Various indices were examined, covering aspects such as cavern wall displacement, characteristics of the plastic zone, volume shrinkage, safety coefficients, seepage range, pore pressure fluctuations, and seepage volume. The study also considered the mechanical behavior of hexagonal columns within the surrounding rock during extended storage operations, leading to the optimization of allowable widths for these columns. The results indicate that, at operating pressures ranging from 6.5 to 17 MPa, the permissible column width should exceed 1.67 times the maximum cavern diameter to ensure compliance with criteria for long-term stability and containment within a square triangular layout. These findings provide valuable insights into determining the optimal allowable widths of salt cavern columns for positive triangular layouts.

Experimental study on the effect of confining pressure and interval time on the fatigue mechanical properties of mudstone

The mudstone interlayer experiences discontinuous cyclic loading during gas storage reservoir operation. To investigate the effects of intermittent action and confining pressure on the fatigue mechanical properties of mudstone. Continuous fatigue test and graded intermittent fatigue test were conducted respectively. The results show that: 1. the fatigue life of mudstone is enhanced by the intermittent effect during the fatigue process. The presence of confining pressure under the same experimental conditions also benefits the fatigue life of mudstone.2. the average modulus of elasticity of mudstone decreases with increasing stress level during cyclic loading, and both intermittency and confining pressure help to enhance the modulus of elasticity of mudstone.3. in graded intermittent fatigue tests. In both uniaxial and triaxial tests, the residual strains generated by the post-interval cycles are smaller than those generated before the intervals.4. In the 3MPa graded interval fatigue test, negative deformation occurs in the post-interval cycle due to the release of elastic energy.

Experimental and molecular dynamics studies on the multiscale permeability properties of various gases in salt rock

To respond to the challenges posed by the intermittent nature of renewable energy sources, salt caverns are considered as ideal storage sites for energy such as hydrogen, compressed air, etc., as well as various other gases such as methane, helium, CO2, etc., due to their unique properties. However, the microfractures of salt rock are characterized by multiscale features and the microscopic flow properties of different gases in them are not yet clear. Here, we combine experiments and molecular dynamics simulations to investigate the multiscale flow of the above gases in salt rocks. First, the permeability of six gases has been evaluated to elucidate the microscopic mechanisms underlying the Klinkenberg effect. Second, based on the adsorption and flow characteristics of the gas, a multiscale permeability curve (ranging from 10−9∼10−3 m) was obtained for the salt rock slit. Furthermore, a fast method for predicting the permeability of salt rock samples was proposed, with predictions in the same order of magnitude as the experimental results. Finally, the storage requirements for different gases in salt caverns were discussed. This work provides multiscale insights into gas storage in salt caverns, which can guide the construction of salt cavern gas storage reservoirs and the assessment of leakage risk.

Fracture identification and characteristics of carbonate underground gas storage: an example from the eastern area of Sulige gas field, ordos Basin, China

The carbonate rock formations have obvious dual media characteristics, fracture development and good physical conditions, which are the main seepage channels and storage spaces for gas after the reconstruction of underground gas storage. The carbonate strata of the Ordovician system are important natural gas reservoirs in the eastern area of Sulige Gas Field in the Ordos Basin, and the identification and characterization of their fractures are of great significance for the modeling of fractures in the later stage and the improvement of the operation scheme of the gas storage. At present, there is little research on fractures, which restricts exploration and development. Therefore, taking the 39–61 gas storage reservoir in the eastern area of Sulige Gas Field in the Ordos Basin as the research object, this paper identifies and studies the characteristics of the fractures by core, microscopic, conventional logging curves, and imaging logging identification. The results show that the fracture length ranges from 5 to 15 cm and the width ranges from 0.1 to 3 mm. The fracture angles are mostly between 75° and 90° and the main direction is NW–SE. In conventional logging curves, porosity logging has a good response to fractures, while resistivity logging has a general response to fractures; In layers with more developed fractures, natural gamma values are mostly higher than 40API, rock volume density is less than 2.8 g/cm3, neutron porosity is greater than 12.5%, and acoustic time difference is greater than 160 μ s/m. This study is of great significance for improving the identification of carbonate fractures, enriching the relevant theories, and providing guidance for the construction of carbonate gas storage.

In Situ Stress Evolution and Fault-Slip Tendency Assessment of an Underground Gas Storage Reservoir in the Turpan Basin (China): In Situ Stress Measurements and Coupled Simulations

In Situ Stress Evolution and Fault-Slip Tendency Assessment of an Underground Gas Storage Reservoir in the Turpan Basin (China): In Situ Stress Measurements and Coupled Simulations

Well Test Analysis for a Well in Gas Storage Reservoirs With the Formation Containing High Salinity Water

Abstract The production capacity of the gas wells is seriously affected by salt deposition during the injection and production process for underground gas storage with high salt content, so it is necessary to predict the production performance through well test technology. However, the existing well test analysis methods cannot be reliably used to interpret the well test data affected by salt deposition phase change and high-speed non-Darcy flow during the injection and production process. Therefore, this paper first determines the relationship between salt deposition and temperature and pressure through flash calculation of phase equilibrium of saltwater and hydrocarbon system, then establishes a porosity and permeability model considering the effect of salt deposition, and further establishes a high-speed injection-production well test analysis model considering the effect of salt deposition in combination with Forchheimer’s percolation law. Finally, the model is solved by numerical method, and the dynamic changes of reservoir pressure and salt deposition are simulated and calculated. The results show that the higher the salinity of formation water is, the greater the risk of salt deposition in the reservoir is, and the permeability of the reservoir will significantly decrease after salt deposition occurs; the non-Darcy flow effect will aggravate the risk of salt deposition in the reservoir. The research results provide a theoretical method for the evaluation of reservoir parameters and production performance prediction of salt gas storage reservoirs.

Gas Injection Capacity of Slotted Liner and Perforation Completion in Underground Natural Gas Storage Reservoirs

The use of Horizontal wells is a common method of underground natural gas storage (UGS), but there is still a need to discuss whether they are more suitable for slotted liner or perforation completions. To address this issue, a numerical model is developed to predict the gas injection rate of horizontal wells while considering the skin factor. Here, a novel uncoupled iteration method is employed to determine the skin factor deriving from turbulence in each time step when the bottom hole pressure is fixed. The uncoupled method begins with an estimate of the initial gas injection rate, which is then used to calculate a turbulent skin factor. This turbulent skin factor is then used to update the gas injection rate, iterating continuously until convergence is achieved. The effects of slotted liner and perforation design parameters, formation damage, and injection pressure on the skin factor are analyzed. The main findings suggest that the error in the gas injection rate calculated by the non-coupled model compared with the coupled model is only 0.6%, yet it can reduce the number of sub-iterations to 1/10 of that required by the coupled model. Moreover, the uncoupled model can provide results within four steps, even when the convergence condition is 10−14. The open area and perforation density play a significant role in determining the connection degree between the horizontal well and the reservoir, with a larger perforation density resulting in a negative skin factor. Perforations are more suitable than slotted liners for reservoirs with severe formation damage, and the difference in skin factor between the two can reach a value of 40.87 when the ratio of the damage zone’s permeability to that of the normal reservoir zone is 0.05. It is easier to reduce turbulence damage in slotted liner completions than perforation completions, with the turbulence damage of the slotted liner being only 15.9% of that of the perforation. However, to avoid damage it is crucial to prevent the screen tube from being plugged in, as it might otherwise rise to three to ten times the original level. This study provides a theoretical basis and practical reference for the application of slotted liner and perforation method in UGS horizontal wells.

Experimental study on uniaxial compression of granite under real-time loading at designated low-temperature conditions

A low temperature and the degree of saturation have important influence on the mechanical properties of rock surrounding cave-type underground liquefied natural gas storage. Uniaxial compression tests were carried out on dry and saturated granite under different real-time loadings at designated low-temperature conditions (25, 0, −20, −40, −50 and −60°C). The porosity and microstructure were then observed by nuclear magnetic resonance spectroscopy and scanning electron microscopy. The results show that with the decrease in temperature, the uniaxial compressive strength (UCS) and porosity of both dry and saturated granite monotonically increase, while the elastic modulus undergoes an increase–decrease transition and finally stabilises. At the same temperature, the UCS and elastic modulus of dry granite are generally greater than those of saturated granite. The reinforcement in the UCS and elastic modulus is caused by cold shrinkage, while the degradation in the elastic modulus, particularly for saturated granite, is attributed to freezing damage below 0°C. The results of this study can provide technical support for the long-term stability analysis and evaluation of underground cavernous liquefied-natural-gas-storage reservoirs.