Storage Reservoir Research Articles

Streamflow estimation using SWAT model including large storage reservoirs in Godavari River Basin, India

Streamflow estimation using SWAT model including large storage reservoirs in Godavari River Basin, India

The role of phase saturation in depressurization and CO2 storage in natural gas hydrate reservoirs: Insights from a pilot-scale study

The natural gas recovery and CO2 storage in natural gas hydrate (NGH) reservoirs is a promising integrated strategy for implementing clean energy production and CCUS. However, the fundamental characteristics (phase saturation) of NGH reservoirs on the feasibility and efficiency of the above-integrated processes remain unclear. In this study, we synthesized methane hydrate-bearing sediments (MHBS) with varying hydrate saturation (SH = 18–66 %) and aqueous saturation (SA = 7–92 %) at marine NGH conditions (T = 283.8 K, P = 11.0 MPa). The effect of phase saturation on depressurization-induced hydrate dissociation, and subsequent CO2 storage and hydrate restoration by CO2/N2 injection was investigated. The water-saturated MHBS with high SA can promote faster MH dissociation during the depressurization stage and prevent secondary hydrate formation, but a slower MH dissociation during the later stage due to slow heat transfer. A relatively high SH (> 63 %) results in sustained low temperatures due to insufficient heat supply slowing down MH dissociation. The CH4/CO2/N2 mixed hydrates (Mix-H) formation and CO2 storage in depleted MHBS after CO2/N2 injection initially increase and then decrease with post-mining SA (peak at SA = 54.5 %). The rate of Mix-H formation decreases as the post-mining SA increases. Higher pre-mining SH and CO2/N2 injection rate facilitates rapid gas phase mixing within the sediments, thereby improving the kinetics and homogeneity of Mix-H formation and hydrate-based CO2 storage efficiency. MHBS with relatively low SH and SA exhibit enhanced safety for the integrated process, offering reduced depressurization-induced sediment subsidence and increased hydrate restoration ratios (∼85 %) by Mix-H formation.

Software for CO2 Storage in Natural Gas Reservoirs

The paper presents a simulation-based approach for optimizing CO2 injection into depleted gas reservoirs, with the goal of enhancing underground CO2 storage. The research employs a two-dimensional dynamic reservoir model, developed using Darcy’s law, to describe gas flow in a pressure-homogeneous porous medium, along with real gas equations. The model integrates the Du Fort–Frenkel and finite-difference methods to accurately simulate the behavior of CO2 during injection and storage. Real data from an operational gas storage facility were used to calibrate the model. CO2sim v1 software, specifically developed for this purpose, simulates CO2 injection cycles and quiescence phases, enabling the optimization of storage capacity and energy efficiency. The reservoir model, based on the engineering of the geological structure, is discretized into approximately 16,000 cells and solved using the finite-difference method, allowing for rapid simulation of CO2 injection and quiescence processes. The average computation time for a 150-day cycle is approximately 5 min. Simulation results indicate that increasing the number of injection wells and carefully controlling the injection rates significantly improves the distribution of CO2 within the reservoir, thereby enhancing storage efficiency. Additionally, appropriate well placement and prolonged quiescence periods lead to better CO2 dispersion, increasing the storage potential while reducing energy costs. The study concludes that further development of the software, along with comprehensive technical and economic assessments, is required to fully optimize CO2 storage on a commercial scale.

Optimization of pressure management strategies for geological CO2 storage using surrogate model-based reinforcement learning

Injecting greenhouse gas (e.g. CO2) into deep underground reservoirs for permanent storage can inadvertently lead to fault reactivation, caprock fracturing and greenhouse gas leakage when the injection-induced stress exceeds the critical threshold. It is essential to monitor the evolution of pressure and the movement of the CO2 plume closely during the injection to allow for timely remediation actions or rapid adjustments to the storage design. Extraction of pre-existing fluids at various stages of the injection process, referred as pressure management, can mitigate associated risks and lessen environmental impact. However, identifying optimal pressure management strategies typically requires thousands of simulations, making the process computationally prohibitive. This paper introduces a novel surrogate model-based reinforcement learning method for devising optimal pressure management strategies for geological CO2 sequestration efficiently. Our approach comprises of two steps. The first step involves developing a surrogate model using the embed to control method, which employs an encoder-transition-decoder structure to learn dynamics in a latent or reduced space. The second step, leveraging this proxy model, utilizes reinforcement learning to find an optimal strategy that maximizes economic benefits while satisfying various control constraints. The reinforcement learning agent receives the latent state representation and immediate reward tailored for CO2 sequestration and choose real-time controls which are subject to predefined engineering constraints in order to maximize the long-term cumulative rewards. To demonstrate its effectiveness, this framework is applied to a compositional simulation model where CO2 is injected into saline aquifer. The results reveal that our surrogate model-based reinforcement learning approach significantly optimizes CO2 sequestration strategies, leading to notable economic gains compared to baseline scenarios.

Fine-tuning ocean energy storages for reservoir-integrated wave energy converters with dynamic activation of mechanical energy storage features

The proportion of renewable energy in the power supply has experienced substantial growth; however, its intermittent nature and inherent uncertainty present notable challenges in its integration. This study aims to explore the significance of energy flexibility in energy management by focusing on a hybrid renewable wave-wind zero-energy system implemented in a coastal building. Specifically, the study investigates various sources of flexibility within the system and introduces a novel energy storage mechanism utilising the in-built reservoir of the wave energy converter. The research provides new insights into the flexibility of control strategies from the generation and storage sides. The cost-responsive controls involved on/off-peak periods and monthly variations. Several attempts have been made to develop cost-responsive controls that depend upon the electricity tariffs; these include energy shift and peak shaving. The lower discharging limits and trigger lines were compared in the simulation environment to improve the cost-saving, energy-matching, and peak-shaving performances. In this study, the first group scheduled discharging; however, only limited improvements (0.5%) were achieved. Consequently, the second group shifted to varying the minimum fraction state of the reservoir under a lower discharging limit, which reduced operational cost by 4.5%. Using different discharging lines by considering the current month and the period, the third group achieved the expected peak shaving and correspondingly reduced the operational cost to 90.3 %. The final group showed that an additional battery could improve the peak-shaving and cost-saving performance but not the net present value, owing to high investment costs. Furthermore, annual savings increased for different battery capacities from 4.5 % to 6.8 % by conducting the energy shift. Peak shaving control with additional battery reduced maximum demand and substantially reduced costs from 6.4 % to 10.8 %. The study recommends focusing on peak shaving with extra batteries for further cost savings during the on-peak period. This research brings novelty by integrating flexibility control for both generation- and storage-sides in ocean renewable energy systems. It proposes using a wave energy converter as a mechanical energy storage reservoir, reducing costs and ensuring adequate capacity. The study emphasises dynamic storage control, adjusting in real time based on conditions and energy demands.

Implementation of Controlled Floods for Sediment Management on the Colorado River in Grand Canyon Under Aridification

ABSTRACTIn addition to supplying water for agriculture, cities, and industry, the Colorado River traverses the Colorado Plateau, including several of the most unique and valued National Parks and Recreation Areas in the United States. Although the water needs of these landscapes were not considered at the time water allocations were first negotiated, these needs were recognized in subsequent legislation and policy. Management goals address a range of aquatic and riparian resources, including fine sediment (sand, silt, and clay) which, in Grand Canyon, is important for ecological, cultural, and recreational resources. Over ~30 years, stakeholders, resource managers, and scientists collectively developed operational strategies for sediment management to meet goals outlined by an adaptive management program. However, prolonged drought, or “aridification,” resulting in declining runoff and the lowest reservoir storage elevations in decades has challenged those strategies. The paradigm for sustainable sediment management relies on (1) sand accumulation on the bed of the Colorado River during periods of sediment‐rich tributary floods from summer/fall thunderstorms, and (2) dam‐released controlled (artificial) floods, referred to as High‐Flow Experiments (HFEs), to redistribute the accumulated sand to rebuild eroded bar and floodplain deposits. The management protocol, which specifies narrowly defined sand accumulation periods and HFE implementation windows, is based on implementing HFEs in late fall during the period of greatest sediment enrichment, before higher winter releases for hydropower erode the accumulated sand from the riverbed. Low dam releases associated with drought, however, have changed the pattern of sand accumulation and low reservoir elevations have prevented HFE implementation in the defined window. An alternative strategy for HFE planning and implementation was tested opportunistically in April 2023 following lower‐than‐normal winter dam releases. We present findings from this HFE indicating that sand enrichment and sandbar building equaled or exceeded that of HFEs conducted under the established management protocol. These findings show that management goals for sediment under conditions of prolonged drought may be achievable but will likely require substantial changes in dam management strategies.

Mechanism of Minerals Action in Reservoir During CCS

Abstract The carbon capture and storage (CCS) is one of the most effective ways to control greenhouse gases emissions and mitigate greenhouse effects. There will be a series of effects on the physical properties and chemical composition of the reservoir after CO2 injection. It is of great significance to study the effect of CO2 injection on reservoir for better CO2 storage. In this paper, Through the mechanism model established by numerical simulation technology and the phase permeability hysteresis simulation method, the whole process of reservoir pH, mineral dissolution and precipitation and porosity change during CO2 storage was accurately described. The results indicate that CO2 firstly dissolves in water to form carbonic acid after injection into the reservoir, which will cause a drastic change acid-base properties of reservoir, manifesting as a significant decrease in pH value. Under the effect of H +, Partia mineral components(for example: anorthite) in the reservoir) are dissolved, however, some other minerals (for example: kaolinite and calcite) are precipitated, which significantly change the composition of underground aqueous solution. The reaction rate of CO2-water-rock is very slow. After stopping CO2 injection, the mineralization of all kinds of minerals still goes on for a long time. In addition, due to the effect of CO2-water-rock reaction, a certain increase of reservoir porosity is more conducive to CO2 migration in the reservoir.

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.

Characteristics of Effective Fractures in Deep Buried-Hill Basement Gas Reservoirs and Its Effects on Fluids: The Jianbei Slope, Qaidam Basin, China

Summary Buried hills are basement uplifts beneath sediment layers that possess significant exploration potential. Using the Jianbei Slope of the Qaidam Basin in China as a case study, we systematically investigated the types and origins of fractures in deep buried-hill gas reservoirs. In our study, we synthesized various data, including experimental results, production dynamics, and both conventional and special logging with the aim of clarifying the sequence and effectiveness of fracture formation in these gas reservoirs; analyzing the impact of effective fractures on fluid migration, accumulation, and preservation; and proposing a development plan to enhance stable production. Research reveals that since the Late Paleozoic, the region has been influenced by multiple phases of tectonic stress, deep fluid dissolution, and surface weathering leaching. This has resulted in a fracture system dominated by east-west trending deep major faults, with accompanying tectonic fractures, alongside dissolution, diagenetic, and weathering-collapse fractures. Smaller fractures oriented at an angle to the maximum principal stress and fractures with normal stress lower than the compressive strength are conducive to maintaining fracture effectiveness. Fracture widths range from 0.1 μm to 343.36 μm, with effective fractures comprising 63.49% of the total. Based on aperture and permeability, effective fractures are categorized into three levels: Level I fractures (>100 μm) serve as primary migration pathways; Level II fractures (10–100 μm) are well configured with dissolution pores, forming a foundation for favorable reservoir development; and Level III fractures (micron scale) enhance reservoir storage capacity by connecting fractures. The gas-water interface in the reservoir rises rapidly and unevenly. In the I + II + III fracture combination model, fluid exhibits high-conductivity channeling, leading to rapid declines in formation pressure, quick water breakthroughs in single wells, and severe water sealing. Conversely, in the II + III fracture combination model, fluid invasion is characterized by weak-to-strong finger-like intrusion, leading to prolonged stable production. Vertically, the 20-m to 60-m interval above the bedrock weathering crust has a favorable pore-fracture configuration, making it a high-quality reservoir zone in buried hills. In addition, local thick layers of Level II microfractures within the bedrock represent potential exploration targets. Considering the differential distribution of reservoir fractures, the optimal development plan is expected to achieve a recovery rate of 28.35% by 2030.

Numerical simulation on the prevention and control of landslide-induced wave disasters in Wangjiashan landslide area of Baihetan reservoir

The risk management of landslide surges after water storage in large reservoirs is a major challenge in reservoir management. The water storage in the reservoir area of the Baihetan hydropower station on the Jinsha River brings the potential of Wangjiashan landslide activation. This paper proposes a mitigation measurement based on slope cutting for the Wangjiashan landslide and evaluates the feasibility and effectiveness of the management scheme through numerical simulation. Results indicate that when water storage is in a normal level, after an earthquake, the landslide will impact the Baihetan Reservoir with a maximum velocity of 8.52 m/s, generating waves with a maximum wave height of 15.63 m. By removing the upper part of the landslide, the volume of the landslide is reduced from 611 × 10 4 m 3 to 369 × 10 4 m 3 , it will cut down the maximum wave height in the Xiangbiling residential area to 3.09 m, which significantly reduces the risk of landslide surge waves. It further establishes a disaster prevention and control plan for the landslide-induced wave disaster. Overall, this study provides important theoretical and practical references for the risk management of landslide surge waves and offers valuable insights for addressing similar issues in the future.

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.

Adaptive (re)operations facilitate environmental flow maintenance downstream of multi-purpose reservoirs

Multi-purpose reservoirs support socioeconomic development by providing irrigation, domestic water supply, hydropower, and other services. However, impoundment of water impacts instream aquatic ecosystems. Thus, the concept of minimum environmental flows (MEFs) was established to restore the benefits of naturally flowing rivers by specifying minimum flow rates to be maintained downstream of dams. But varying legislative contexts under which multi-purpose reservoirs operate may not always necessitate MEF releases. To what extent the release of MEF affects other sectoral benefits remains an open-ended and possibly a site-specific inquiry. A related issue is − how does the order in which releases are prioritized influences sectoral performances? We analyse these issues for the Nagarjuna Sagar reservoir, one of the largest multipurpose reservoirs in southern India. We formulate two versions of a multi-objective decision problem. PF_MEF formulation prioritizes MEF releases over releases for water demand satisfaction, followed by hydropower releases. PF_nMEF formulation follows the regional legislative rule releasing first for demand satisfaction, followed by hydropower and MEF releases. The objectives include: annual demand deficits (minimize), hydropower production (maximize), reliability of maintaining MEF (maximize), and reliability of non-exceedance of high flows downstream (maximize). A dynamic rule using radial basis functions (RBFs) specifies releases as a function of reservoir storage and the Borg multi-objective evolutionary algorithm is used to identify the Pareto approximate solutions. The reliability of MEF satisfaction, annual demand deficits, and hydropower production attained across the Pareto-optimal strategies obtained for PF_MEF (PF_nMEF) formulation is 86–99 % (63–80%), 47–1063 (17.6–340) Mm3, and 3452–3703 (3408–3650) GWh, respectively. Results thus indicate that prioritizing MEF releases improves can meet MEF requirements without significant compromises in other objectives. We hypothesize that similar investigations may reveal how simple modification of release order may improve ability of other reservoirs to meet environmental goals.

Application of pressure small signals extraction and amplification technology in abandoned well pattern for geothermal energy extraction and H2 storage: Numerical modeling and economic analysis

Using abandoned reservoirs for geothermal energy development and H2 storage is economical. The impact of complex fractures from long-term oil and gas extraction on geothermal energy and H2 storage is not yet clearly understood. Here, a pressure small signals extraction and amplification (PSEA) technology is developed to improve reservoir monitoring accuracy. This technology is capable of coupling many pressure transient analysis models to invert parameters for multiple scenarios. This work establishes numerical models to simulate the effects of geothermal energy extraction and H2 storage over 5000 days. Results show that this technology improves the accuracy of inverted parameters by 4–14 times. This technology adjusts the production temperature differences in a single injection-production system from 1.4K to 6.5K and the net heat power from 0.25 MW to 1.1 MW, and it can also identify an early low-rate H2 storage phase. The Non-Sorting Genetic Algorithm II calculates that the PSEA technology brings economic benefits of $704,000 and $352,000 for geothermal energy extraction and H2 storage in a single injection-production system. In conclusion, the developed monitoring technology and models improve accuracy in assessing geothermal energy development and H2 storage, preventing failures in residential heating or H2 storage projects.

Simulation of CO2 hydrate formation in porous medium and comparison with laboratory trial data

The storage of CO2 in gas hydrate form in the pore space in depleted natural gas reservoirs has been considered a method for greenhouse gas control. The formation of CO2 hydrate in porous medium is a strongly coupled Thermal-Hydraulic-Chemical (THC) problem under certain thermodynamic conditions. In this study, laboratory data on CO2 hydrate formation in silica sand, including the profiles of pressure, temperature, the amount of CO2, H2O, and CO2 hydrate, etc., were compared with results from numerical simulations. The minimized deviations between the simulation and experimental results, including the pressure drop, the significant temperature increase caused by hydrate formation, and the amount of CO2, water, and hydrate, were all less than 10 % in the numerical simulations. The sensitivities of the deviations between numerical simulations and experimental data to the domain discretization, thermal conductivity of the silica sand, absolute permeability, and kinetics of CO2 hydrate formation were analyzed. One of the major findings is that CO2 hydrate formation in the porous medium in this study is dominated by the kinetics of chemical reaction, rather than the heat or mass transfer. Another key finding of this study is the acquisition of the modeling parameters of the CO2 storage process in the laboratory-scale sand reservoir, including the thermal conductivity of the silica sand λs = 2.2 W/m/K, the absolute permeability k0 = 3.0 × 10−11 m2, and the kinetic constant Kf0 = 8.4 × 1011 kg/m2/Pa/s and the reduction exponent β = 5.3 in the kinetic model of CO2 hydrate formation. It is noteworthy that the mathematical models and the parameters faithfully fit three independent experiments of Run 1–3. The results of the experiments and corresponding numerical simulations provide a reliable method to evaluate the capacity, technical and commercial feasibility of CO2 storage in marine and permafrost reservoirs.

Forecasting solar irradiance for the strategic integration of hybrid hydro and solar photovoltaic systems in rural Indian regions

ABSTRACT Conversion of the conventional electrical grid into a smart and sustainable grid involves several considerations. The primary factors, however, are renewable energy penetration, associated storage systems, and energy generation costs. This research endeavors to conduct a thorough survey and analysis of the solar irradiance on various hydropower locations in India, including Run-of-River (RoR), Run-of-River with Pondage (RoRP), Reservoir Storage (S), Multi-Purpose Storage (MP) and Pumped Storage Systems (PSS). The hydroelectric projects in rural Indian regions have been the subject of the proposed case study. As a preliminary study, the probabilistic variables like minimum, maximum, and mean solar irradiance are calculated for 252 High-Scale Hydropower Plant locations (HSHPs) using the past 40 years day ahead solar radiation data to identify the high-irradiance hydropower plant location in each state of India. This study concludes that the maximum mean solar irradiance location in each state as these sites are well suited for hybrid PV-hydro systems. The identified high-irradiance locations 40 years day ahead data sets are analyzed employing 8 machine learning models and 2 deep learning models. This analysis aims to forecast solar irradiance, serving as a crucial foundation for the initial phase of the implementation of hybrid PV-hydro.

Status of planktonic community in the Kanewal Community reservoir in central Gujarat, India

A two-years study (March 2021 to February 2023) was carried out at the Kanewal Community Reservoir, an important water storage reservoir in central Gujarat, to assess the diversity and seasonal variation of the planktonic community. During the study period, a total of 60 phytoplankton species were recorded, belonging to 9 classes, 25 orders and 39 families. Class-wise percentage composition of phytoplankton showed a diverse array during the study period. The species gradient of phytoplankton was as follows: Bacillariophyceae (20) > Zygnematophyceae (14) > Cyanophyceae (10) > Chlorophyceae (9) > Euglenophyceae (2) > Trebouxiophyceae (2) > Dinophyceae (1) > Klebsormidiophyceae (1) > Ulvophyceae (1). Thirty (30) different zooplankton species were recorded during this study, belonging to 11 classes, 14 orders and 19 families. The number of abundant species remained constant throughout the study period. The recorded number of common zooplanktonic species also remained steady (14). However, the number of rare species slightly increased to two (2), which indicates a slight increase in the occurrence of less prevalent species. The highest density of zooplankton was observed during the summer, and the lowest in the monsoon season. Overall, it was found that KCR (Kanewal Community Reservoir) contains a higher number of phytoplankton species (60) compared to zooplankton (30), which could be a consequence of the voluminous hydrological regime with abundant occurrence of macrophyte elements.

Investigation of cabin heating in electric vehicles with integrating solar cells and heat storage systems

In recent years, the production and usage of electric vehicles have been encouraged due to zero emissions, efficiency, and economic factors. Efficient cabin heating and thermal management in electric vehicles are crucial for enhancing passenger comfort, extending battery life, and optimizing overall energy usage, thus contributing to the sustainability and practicality of electric transportation. Heating the cabin of electric vehicles in winter has a negative effect on range. Therefore, methods are being researched to use energy efficiently without sacrificing passenger comfort and minimizing the effect on the vehicle's range. This study presents an innovative radiator design specifically crafted for Electric Vehicles (EVs), leveraging solar panels to heat water for the radiator. This system enables the vehicle to harness solar energy for heating a water tank while stationary, effectively serving as an energy storage reservoir. Upon vehicle movement, the radiator system activates to disperse the stored thermal energy throughout the cabin, ensuring superior thermal comfort. Consequently, optimizing battery range is achieved as the heating load typically leads to significant range reductions. From the obtained results in experiment 2, the results indicated that the cabin temperature rose from 3 °C to around 15 °C within a few minutes, reflecting an increase of approximately 12 °C. According to the results, this indicates that there will be a reduction in energy consumption of between 1.9 % and 3 % for a one-hour travel range in this electric vehicle. The findings of this investigation demonstrate that utilizing warm water energy storage effectively enhances cabin thermal management.

CO2-EOR and storage in a low-permeability oil reservoir: Optimization of CO2 balanced displacement from lab experiment to numerical simulation

CO2 flooding can enhance oil recovery associated with CO2 storage, but its performance is often damaged by the gas channeling due to reservoir heterogeneity and the large CO2 mobility. Most current research focuses on chemical agents to prevent CO2 channeling, while there is less attention to reservoir engineering methods. In this study, a concept of balanced displacement was introduced to delay the gas channeling and achieve balanced development in a multi-layer and low-permeability block Y21. A series of lab experiments and numerical simulations were conducted to explore the best CO2 flooding scheme by considering three aspects of optimization. Layer grouping and well pattern and spacing adjustment were applied to seek for balanced utilization of geological reserves; gas channeling plugging and mobility control measures were taken to increase the CO2 swept volume; and the pressure control and injection-production optimization were carried out to improve the oil displacement efficiency. The results show that CO2 can reach miscible with crude oil in block Y21 under the original formation pressure, but gas breakthrough quickly occurs along the hydraulic fractures to the top of the structure. To obtain a balanced displacement, the layers of block Y21 should be divided into two groups for separate development. The current well pattern and spacing are suitable for CO2 flooding, which need not be adjusted. WAG injection with acid-resistant gel particles and foaming agents can be used to inhibit gas channeling. These measures can significantly improve the CO2 displacement profile in block Y21. The oil recovery factor can be increased by 10.01%, and 5.41 × 104 tons of CO2 can be stored. This study can provide valuable guidance for CO2-EOR and storage in low-permeability oil reservoirs.

A numerical model for evaluating the long-term migration and phase transition behavior of foam-assisted injection of CO2 in saline aquifers

Geological Carbon Storage (GCS) is a rapidly developing technology with the potential to mitigate the environmental impact of excessive greenhouse gas emissions. Foam-assisted injection of CO2 can effectively alter fluid rheological properties, thereby enhancing sweep efficiency. In this paper, a numerical model to evaluate the long-term migration behavior of foam-assisted injected CO2 in saline aquifers is developed. It is found that foam-assisted injection improves storage efficiency and reduces the plume migration distance compared to direct CO2 injection. This creates higher demands on the injection pressure but minimizes the risk of leakage. The effects of injection strategy, volume fraction of foam, and reservoir heterogeneity were investigated. Modeling results show that the injection strategy with a high foam volume fraction enhances the sweep efficiency and improves the transition rate of injected CO2 to the dissolved state. This can effectively enhance the long-term security of the sequestration. Simulations of layered formations indicates that foams can potentially inhibit the rapid migration of plumes along high-permeability zones. Our study provides insights for foam-assisted injection to enhance reservoir storage efficiency and long-term safety for GCS.

Geochemical influences of hydrogen storage in depleted gas reservoirs with N2 cushion gas

Geochemical investigation of hydrogen (H2), brine, rock formations, and residual gases (nitrogen – N2, methane – CH4, and carbon dioxide – CO2) is crucial for understanding H2 storage processes in depleted gas reservoirs. This study examines the effects of injecting a gas mixture (60% H2 + 30% N2 + 5% CH4 + 5% CO2) into Bandera Grey sandstone with notable clay mineral content. The experiment lasted 50 days at 42 °C, 1350 psi, and 5 wt% NaCl brine, with detailed analytical characterization before and after aging. Results show minimal sample reactivity, causing slight alterations in petrophysical characteristics. Dissolution primarily affected dolomite and barite minerals, while illite and kaolinite caused pore blockage. Gas chromatography data indicate only 0.45% of injected H2 is lost (via dissolution in brine and reaction with CO2), CH4 increased by 6.22%, N2 remained stable, and CO2 decreased by 1%. These results provide valuable insights into the feasibility and safety of utilizing depleted gas reservoirs for H2 storage.