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Gas reservoirs have significant engineering characteristics of injection and extraction. The reservoir cap rock is subjected to cyclic alternating loading and has the potential risk of seal failure. Therefore, it is necessary to study the stress−percolation−damage mechanism of the reservoir cap rock in depleted gas reservoirs. The rock Mechanics Test System (MTS) was used to study the permeability characteristics of a typical mud shale cap layer under different loading and unloading rates, analyze the deformation characteristics and permeability performance evolution law of the rock under the confining pressure alternation, and study the effects of loading and unloading rate, confining pressure and number of cycles on the permeability of the cap rock. The test results show that with the increase in the number of cycles, the hysteresis loop moves in the direction of axial strain increase offset. The overall morphology is presented as an elongated type, and the damage of the specimen is small in the cyclic confining pressure; At the beginning of the cycling period, the permeability decreases with the increase in the confining pressure in the form of a negative exponential. At the later stage of the cycling period, the permeability basically stays unchanged, and is maintained at a low level; At low confining pressure, permeability also decreases in a negative exponential form with the increase in the number of confining pressure cycles; The greater the loading and unloading rate at the beginning of the cycle, the more the permeability decreases; There is a tendency of sealing improvement under cyclic loading in the gas storage of depleted reservoirs with mud shale as the cap layer. The results of the study can provide technical parameters for the evaluation of the cap sealing of gas storage of depleted reservoirs. [ABSTRACT FROM AUTHOR]

Low-permeability sandstone reservoirs have been widely used as a gas storage medium worldwide. Compared with the high porosity and high permeability of sandstone, low-permeability sandstone may present different mechanical (deformation, damage or failure) and acoustic responses under cyclic loading-unloading processes caused by the high-rate injection–production of underground gas storage. In this paper, multistage triaxial loading–unloading tests with a continuously increased upper limit of stress were carried out on low-permeability sandstone under six different confining pressures. The results showed that the superposition of stress–strain curves become much denser in the process of each level of stress. Based on the variation of the elastic modulus of low-permeability sandstone under alternating loads, the mechanical behavior of low-permeability sandstone under cyclic loading is divided into three stages: cyclic hardening, stability and cyclic softening. According to the evolution of acoustic emission (AE) signal parameters, AE counts appear intensively at the initial stage of each level of stress and then gradually stabilize. The peak frequency presents the zonal distribution, which is divided into low-frequency, intermediate-frequency and high-frequency zones. Low confining pressure leads to a small b-value. The RA–AF distribution implies that the mixed tensile–shear cracks are continuously generated in low-permeability sandstone during the cyclic loading process, and the shear cracks are more obviously developed. [ABSTRACT FROM AUTHOR]

The good sealing caprocks are significant for the integrity of underground gas storage (UGS) in depleted natural gas reservoirs. The screening of parameters, weight assignment, and evaluation method are important for evaluating the sealing performance of caprocks. Many factors can affect the sealing performance of caprocks, including caprock thickness, lithology, brittleness, porosity and permeability, breakthrough pressure, etc. In this paper, the dominant factors in the sealing performance of caprocks in UGSs are systematically analyzed, and the weights of these factors are analyzed by the analytic hierarchy process (AHP). The fuzzy comprehensive evaluation method (FCEM) is applied in the sealing evaluation of caprocks in three typical underground gas reservoirs (i.e., Zhujiadun, Xu-2, and Xing-9) in China. The sandstone reservoir in the Zhujiadun gas field is only about 20 m, and the thickness of the overlying mudstone is about 600 m. The caprock of the Xu-2 gas reservoir in Zhongba gas field is well distributed and developed, and the breakthrough pressure is relatively large. The caprock of Xing-9 gas field is mudstone with a thickness of over 400 m. The results show that the breakthrough pressure and permeability are the key parameters affecting the sealing ability of caprocks, with weights of 0.4291 and 0.2157, respectively. Among these three examples of gas fields, the sealing performance of caprocks in Zhujiadun gas storage is the best. The evaluation procedure and methods proposed in this paper are valuable for the evaluation of the tightness of caprocks in depleted gas reservoirs. [ABSTRACT FROM AUTHOR]

The structure of caprocks is often greatly altered by different scales of faults or fissures in long-term geological tectonic evolution, and the sealing performance may be deteriorated. In this paper, a simplified geological model characterized as multilayered sandstone and fault-bearing caprocks extracted from the Shuang 6 underground gas storage located in the Liaohe oilfield was established. Different fault geometry (e.g., fault length, fault dip angle, and fault type) and seepage attributes (porosity and permeability) were considered to illustrate their impacts on natural gas migration during the cyclic high rate of injection and production of natural gas. The results showed that the seepage anisotropy and the natural gas front are strongly affected by the formation properties and, especially, are hindered by the low permeability sandstone layers. The difference in the lateral migration distance of natural gas in different layers can reach 110 m at the end of the injection period, with an annual injection volume of 108 m3. The migration of natural gas along the fault zone is mainly controlled by the permeability of faults, followed by fault scale, fault dip angle, and fault type. The sealing failure of caprocks in the fault zone does not occur based on the simulated gas migration distribution, showing that a very limited amount of natural gas migrates into the caprocks. [ABSTRACT FROM AUTHOR]

The utilization of geothermal energy can reduce CO2 emissions into the atmosphere. The reinjection of cooled return water from a geothermal field by a closed loop system is an important strategy for maintaining the reservoir pressure and prolonging the depletion of the geothermal reservoir by avoiding problems, e.g., water level drawdown, ground subsidence, and thermal pollution. However, the drawdown of water injectivity affected by physical and chemical clogging may occur in sandstone aquifers, and the reservoir temperature may be strongly affected by the reinjection of large amounts of cooled geothermal water, thus resulting in early thermal breakthrough at production wells and a decrease in production efficiency. In addition to the injection of cooled geothermal water, the injection of CO2 can be used to maintain the reservoir pressure and increase the injectivity of the reservoir by enhancing water–rock interactions. However, the thermal breakthrough and cooling effect of the geothermal reservoir may become complex when both CO2 and cooled geothermal water are injected into aquifers. In this paper, a simplified small-scale multilayered geological model is established based on a low-medium geothermal reservoir in Binhai district, Tianjin. The ECO2N module of the TOUGH2MP simulator is used to numerically simulate temperature and pressure responses in the geothermal reservoir while considering different treatment strategies (e.g., injection rates, temperatures, well locations, etc.). The simulation results show that a high injection pressure of CO2 greatly shortens the CO2 and thermal breakthrough at the production well. A much lower CO2 injection pressure is helpful for prolonging hot water production by maintaining the reservoir pressure and eliminating the cooling effect surrounding the production wells. Both pilot-scale and commercial-scale cooled water reinjection rates are considered. When the water production rate is low (2 kg/s), the temperature decrease at the production well is negligible at a distance of 500 m between two wells. However, when both the production and reinjection rates of cooled return water are increased to 100 m3/h, the temperature decrease in the production well exceeds 10 °C after 50 years of operation.

Gas breakthrough pressure is a key parameter to evaluate the sealing capacity of caprock, and it also plays important roles in safety and capacity of CO2 geological storage. Based on the published experimental results, we present numerical simulations on CO2 breakthrough pressure in unsaturated low‐permeability rock under 9 multiple P‐T conditions (which can keep CO2 in gaseous, liquid and supercritical states) and thus, a numerical method which can be used to accurately predict CO2 breakthrough pressure on rock‐core scale is proposed. The simulation results show that CO2 breakthrough pressure and breakthrough time are exponential correlated with P‐T conditions. Meanwhile, pressure has stronger effects on experimental results than that of temperature. Moreover, we performed sensitivity studies on the pore distribution index λ (0.6, 0.7, 0.8, and 0.9) in van Genuchten‐Muale model. Results show that with the increase of λ, CO2 breakthrough pressure and breakthrough time both show decreasing trends. In other words, the larger the value of λ is, the better the permeability of the caprock is, and the worse the CO2 sealing capacity is. The numerical method established in this study can provide an important reference for the prediction of gas breakthrough pressure on rock‐core scale and for related numerical studies. [ABSTRACT FROM AUTHOR]

In the current international situation, energy storage is an important means for countries to stabilize their energy supply, of which underground storage of natural gas is an important part. Depleted gas reservoir type underground gas storage (UGS) has become the key type of gas storage to be built by virtue of safety and environmental protection and low cost. The multi-cycle high injection and production rate of natural gas in the depleted gas reservoir type UGS will cause the in-situ stress disturbance. The slip risk of fault in the geological system increases greatly compared with that before the construction of the storage engineering, which becomes a great threat to the sealing of the gas storage. Reasonable injection and production strategy depend on the reliable assessment of the shear behavior of the fault belt, which can guarantee the sealing characteristics of the UGS geological system and the efficient operation of the UGS. Therefore, the shear behavior of the fault is studied by carrying out experiments, which can provide important parameters for the evaluation of fault stability. However, there is a large gap between the rock samples used in the previous experimental study and the natural faults, and it is difficult to reflect the shear failure characteristics of natural faults. In this paper, similar fault models based on high-precision three-dimensional scanners and engraving machines, filled with three types of fault gouge, are prepared for a batch of representative direct shear tests. The results show that the peak shear strength of the fault rocks with a shear surface is higher than that of the fault rocks with a tensile surface. Compared with the clay mineral content, the roughness of the fault surface is much more significant for the shear strength of the fault rock. For the fault rocks with similar fault surface morphology, the higher the clay content in the fault gouge, the greater the shear strength of the fault rocks. For the fault rocks with different fault surface morphology and the same fault gouge, the cohesion and internal friction angle of the tensile type is generally smaller than that of the shear type. [ABSTRACT FROM AUTHOR]

The underground gas storage (UGS) in depleted sandstone reservoirs forms the largest proportion of the UGS market in China. Multiple cycles of natural gas injection and production in the sandstone cause the rapid increase and drawdown of pore pressure, which may induce damage to the rock skeleton structure, and cause complex fluid flow paths in the sandstone reservoir. In this paper, transverse relaxation time (T2), nuclear magnetism resonance imaging, and high-pressure mercury intrusion analysis are combined to evaluate the variation in pore structure of medium-grained sandstone. The results show that cyclic injection and production of fluid leads to a slight increase in total pore volume, indicating that weak damage to rocks occurs. The T2 spectrum at the low pore pressure (10 MPa) and high pore pressure (25 MPa) both show that the shrinkage of the medium-size pores occurs after multiple cycles of injection and production. The pore volume of large-size pores was not highly correlated with the number of cycles. With the increase in pore pressure, the pore volume ratio under high pore pressure increased with the number of cycles, while it fluctuated strongly under low pore pressure. [ABSTRACT FROM AUTHOR]

With the increasing scale and depth of underground engineering, the geological environment that engineering is faced with is becoming more complex. As the weak position of rock mass, the structural surface has a particularly great influence on the mechanical characteristics of the rock mass. In order to obtain the shear strength characteristic of the structural plane and analyze the influence of morphological parameters such as the undulating angle and bulge degree on shearing, taking medium-low permeability tight sandstone as the research object, four kinds of structural plane samples with different undulating angles (10, 20, 30 and 40°) were prepared with a Python and high-precision engraving machine. Direct shear tests under different normal stresses (2, 4, 6 and 8 MPa) and shear rates (0.6, 1.2 and 2.4 mm/min) were performed, and the shear mechanical properties were analyzed. The structural surfaces before and after shearing were scanned using a high-precision three-dimensional scanner, so as to evaluate the roughness of the structural surface and determine the influence from various factors on the shear characteristics. The test results showed that for the structural plane with the same undulating angle, the peak shear stress increased approximately linearly with an increase in normal stress at a 0.6 mm/min shear rate and an increment speed of approximately 0.82, while the peak shear stress negatively correlated with the shear rate at a value of 4 MPa for normal stress. The larger the undulating angle was, the greater the influence of the shear rate (the shear stress decreased by 2.31 MPa at a 40° angle). When the normal stress and the shear rate were fixed, the peak shear stress corresponding to the structural surface gradually increased with the increase in the undulating angle, and the maximum increment was 5.04 MPa at 4 MPa normal stress and a 0.6 mm/min shear rate. An analysis of the morphological characteristics of the structural plane showed that when the undulating angle (40°) and the normal stress (6 and 8 MPa) were larger, the damage of the structural plane became more obvious, the shear point was closer to the tooth valley position, and the mechanical bite force and friction force of the structural plane were better utilized. When the shear rate was lower (0.6 mm/min), the friction characteristics of the shear surface were more visible, the shear was increasingly sufficient, and the corresponding shear strength was also greater. [ABSTRACT FROM AUTHOR]

In a casing-cement sheath-formation system, the cement–formation interface is usually weakly cemented for the residual of drilling mud, in which a leakage path would easily form, threatening the safe operation of underground energy exploitation and storage. To evaluate the compressive and shear mechanical behavior of the cement–formation interface, cement–rock composite cylindrical specimens were prepared. Uniaxial and triaxial compression and direct shear tests were implemented. The flushing efficiency of the rock surface, compressive strength, interface incompatible deformation, parameters of shear strength, and morphology of shear failure surface were acquired and analyzed. Results show that the flushing efficiency of shale surface decreases from 76.7% to 64.2% with the surface roughness increasing from 0 to 2 mm. The flushing efficiency of sandstone is only 44.7%, remarkably lower than that of shale. With the stress condition transforming from uniaxial to triaxial compression, the feature of the stress–strain curves changes from elastic-brittle to elastoplastic, and the compressive strength increases from 20.6~60.1 MPa to 110~120 MPa. The cement part presents noteworthy plastic deformation and several micro shear fractures develop. There is incompatible deformation between cement and rock, which induces interface debonding for almost all the composite specimens. The internal friction angle and cohesive strength both decrease with the increase in pollution degree of drilling mud, and increase with the rise in surface roughness. The shear facture surface is not exactly the rock–cement interface, but usually manifests as a shear zone, in which the rock, cement, and interface all contribute to the final shear failure. The above findings would be valuable for the revealing of cement–formation interface failure mechanism. [ABSTRACT FROM AUTHOR]

Frequent micro-seismic events or even the severely destructive earthquakes can be induced by the subsurface fluid injection or production. In this paper, the induced seismicity related with four types of classical subsurface fluid injection or production engineering projects (i.e., wastewater injection into deep wells, CO2 geological storage, oil and gas exploitation, deep geothermal energy production) was reviewed to understand the position, occurrence time of induced seismicity, range of influence and the trigger mechanism. Furthermore, targeting at the deep geothermal energy production, the determination methods of the maximum earthquake magnitude, and the challenges in reducing the induced earthquake risks were reviewed. China is rich in deep geothermal energy, especially the reserves of hot dry rocks is considerable. Multiple geophysical observation methods, e.g., seismic, electrical and magnetic methods, can be applied to obtain the multi-scale geophysical and geological information. Laboratory experiments and numerical simulations should be combined to obtain a clear understanding on the triggering mechanism of seismicity. Identification technologies of faults or concealed faults can be widely applied to reduce the destructive earthquake risks associated with the production of deep geothermal energy. For the development of high-efficiency connection control technology between injection and production wells, it is possible to develop an integrated reservoir stimulation method, i.e., alternative thermal stimulation of hot and cold water-chemical corrosion-hydraulic fracturing technology. The microseismic monitoring technology should be used to adjust the reservoir stimulation scheme in time in the field. Through the development of a series of enhanced geothermal system (EGS) pilot projects, key exploitation technologies can be obtained to ensure the safety and efficiency of the EGS project in China. [ABSTRACT FROM AUTHOR]

Purpose. To study the effect of osthole extract on proliferation, migration, invasion, and apoptosis of human cervical carcinoma HeLa cells and investigate its underlying mechanism. Methods. HeLa cells were exposed to osthole at various concentrations. Cell viability, migration, and invasion were detected by MTT assay, scratch wound-healing assay, and invasion assay, respectively. The proportion of cells undergoing apoptosis was analyzed by flow cytometry. Western blot and RT-qPCR were performed to determine changes in the expression of key factors in the Wnt/β-catenin signaling pathway. Results. The osthole extract effectively inhibited the proliferation, migration, and invasion potential of HeLa cells in a dose-dependent manner. The rate of apoptosis induction in HeLa cells treated with the osthole extract for 48 h was significantly higher than that of the untreated controls. Outcomes of the western blotting analysis and RT-qPCR showed that the expression of β-catenin, c-Myc, cyclin D1, survivin, and MMP-9 was significantly inhibited. Conclusion. Osthole could significantly inhibit the malignant behavior of HeLa cells and induce cellular apoptosis. Inactivation of the Wnt/β-catenin signaling pathway by osthole may be a mechanism to control cancer metastasis. [ABSTRACT FROM AUTHOR]

The global warming induced by the emission of greenhouse gases, especially the carbon dioxide, has become the global climate and environmental issues. China has been working in the CO2 emission reduction and carbon sinks with the purpose of becoming the carbon-neutral country by 2060. The CO2 capture, utilization and storage (CCUS) technologies and the reforestation technology represented by the Conversion of Cropland to Forestland Program (CCFP) have great potential for sinking CO2 emission. However, the trade-off among CCFP, CCS/CCUS and Water-Energy-Food (WEF) nexus are not well evaluated. In this paper, the remote-sensing data are collected and used to evaluate the sustainability of CCFP by analyzing the variation of land use and land cover (LULC), crop production, etc. The results show that 13.29% of the cropland in 2001 vanished and converted to grassland (8.3%), mosaic cropland (3%) and urban land (0.98%) in 2019, demonstrating that the CCFP is successful in both WEF nexus and carbon sink. The total crop production has increased around 50% between 2001 and 2019, implying that the CCFP will not lead to the food risk during the conversion of croplands into other types of land in China. A sustainable implementation of CCFP and other environmental Payments for Ecosystem Services (PES) policies in 2019–2060 could reach an estimated total growth of 7.462 billion m3 in comparison of that in 2018 and the total plantation forest stock of about 10.852 billion m3 in 2060, with a corresponding minimum CO2 sink of 2.90 billion tons in 2060. The estimated peak of net equivalent CO2 emissions before 2030 is about 11.0 billion tons and could not be reduced to zero by 2060 without the large-scale application of the CCS/CCUS technologies as geological sequestration of CO2. Besides, the application of CCS/CCUS can be beneficial for WEF, e.g., through replacing the water by CO2 during energy production, especially in the shale gas production in the regions with high water risks in China. In one word, CCS/CCUS and CCFP are two decided pathways of carbon sequestration and should be systematically applied to achieve China's carbon neutrality by 2060. [ABSTRACT FROM AUTHOR]

Salt rock has been regarded as the optimal surrounding rock for underground gas storage (UGS), and it is occasionally subjected to cyclic tension because of the gas injection and production of salt cavern, which leads to the change in mechanical properties of salt rock. In this paper, a laboratory study is conducted to investigate the energy dissipation and damage evolution characteristics of salt rock under uniaxial cyclic tension monitored by acoustic emission (AE) machine. Compared to monotonic tension, both tensile strength and deformation capacity of salt rock are enhanced under cyclic tension. The fracture crack is approximately a single linear crack with large elliptical plastic deformation zone, which is consistent with the spatial distribution of AE events. In yield stage, the proportion of dissipative energy increases first but decreases subsequently. The relationship between AE energy-based damage variable and displacement is established. It is concluded that the damage variable is a piecewise power correlation with displacement while the growth rate of damage variable increases in the pre-peak stage but decreases in post-peak stage. [ABSTRACT FROM AUTHOR]

Considering that fractures arising from fracturing systems have bifurcation characteristics, mathematical models for single- and two-phase flow in porous media with a bifurcated fracture (BFPM) were established. The phase-field method was adopted to trace the oil–water interface, and the influence of fracture morphology, boundary conditions, gravity, and wettability on imbibition in BFPM was discussed. The results are as follows: (1) during single-phase flow in BFPM, the velocity in the bifurcated fracture was several orders of magnitude greater than that in the matrix. (2) Imbibition in BFPM includes countercurrent imbibition and the combination of co-current and countercurrent imbibition. The bifurcated fracture produces an increase in matrix pores that participate in imbibition, thus increasing the oil recovery factor by approximately 30% during simulation. (3) Closing an outlet of the bifurcated fracture has minimal effect on imbibition during the early stage (approximately the first 6 s) and an inhibitory effect during the middle and late stages (after 6 s), which leads to a decrease in oil recovery factor. (4) When the surface tension value is low (0.1 and 1 mN/m), disregarding the effect of gravity during imbibition results in an overestimated oil recovery factor value, while a large surface tension value (20 and 25 mN/m) produces the opposite effect. (5) Similar to the laws followed in porous media with pure pores and a single fracture, improving BFPM wettability increases the oil recovery factor value. This study can provide guidance for the production of low-permeability reservoirs. [ABSTRACT FROM AUTHOR]

CO sequestration in deep saline formations has been proved to be an effective method for reducing greenhouse emissions into the atmosphere. However, pure sequestration of CO will add to the costs incurred by both industries and governments. A win-win method of CO injection and hot brine (water) extraction can become attractive to the investors, as it will not only increase the storage capacity of the injected CO, but also offset the costs by selling and using the produced hot water for industrial, agricultural or household purposes. For instance, water from very hot geothermal reservoirs ( T ≥ 150 °C) can be used for electricity generation in power plants and water from low-medium temperature reservoirs, the most predominant in natural systems, are more popular for direct use, e.g., in heating systems, household hot water, baths, aquaculture, etc. In this paper, low-medium geothermal reservoirs widely distributed in China, especially those in the Ordos Basin, were selected for the numerical case studies using TOUGH2MP with the ECO2N module for the simulations. Generally, simulation parameters were taken from the Ordos Basin, where the first full-integration CO sequestration project had been operated since 2010. The simulations in the base case study lasted 35 years, based on the lifespan of a normal geothermal project. Shallow re-injection systems were also considered to investigate the influence of thermal breakthrough, pressure perturbation, etc. Results show that injection of cold CO causes sharp decrease in temperature in the reservoir region near the injection well, which is enlarged with continuous injection. The region near the production well is dominated by different fluid phases during the CO driven process, including a single water phase, a two-phase fluid (water and CO) and a phase of almost pure CO. Results also show that the CO breakthrough lags far behind the pressure response in the geothermal production system. Before breakthrough, the injected CO pressurizes the reservoir, improving the overall performance of the geothermal reservoir. Furthermore, the heat extraction efficiency of CO-based system is obviously higher than HO-based system. [ABSTRACT FROM AUTHOR]

Because of the high costs involved in CO sequestration in deep saline formations, it has been difficult for its widespread application in the short term. Recently, however, a new technology called 'combined geothermal production-CO sequestration technology' has made the technique more attractive not only by increasing the CO storage capacity, but also by decreasing the operational costs, through the utilization of geothermal energy, either directly or for the purpose of producing electricity. A CO-aided (or CO-involved) geothermal extraction system (CO-AGES) is presented, based on existing technologies and the new ideas of 'combined geothermal production-CO sequestration' introduced in this paper. This system can be used to extract geothermal energy from sedimentary aquifer formations (low-medium temperature) at different stages. The purpose of this paper is to set up an evaluation system for selecting a suitable site for this CO-AGES system. There are both similarities and differences in the procedure needed for selecting a site for a conventional pure CO sequestration and for this CO-AGES system. Both are carried out at different scales, including basin, region and target formation scales. The biggest difference is the temperature gradient, which plays an opposite role in the two systems. By using the preliminary ranking and screening method presented in this paper, it can be shown that the Bohaiwan, Songliao and Qiangtang basins have the highest potential for the application of this CO-AGES technology. However, if CO sequestration is considered alone, the Ordos, Tarim and Bohaiwan basins should be selected as the best three operational sites in China. While preliminary evaluation methods can provide some useful information on the selection of the best sites for the 'combined geothermal production-CO sequestration technology', more detailed work is still required because of the strong uncertainties that exist in the determination of the upper and lower boundaries for each indicator. [ABSTRACT FROM AUTHOR]

Subsurface immobilization and conversion of CO into solid mineral phases in deep siliciclastic saline formations containing silicate minerals, commonly known as 'mineral trapping', is gaining research attention as a significant option to reduce CO emissions in the atmosphere. Although mineral trapping of CO is a long-term process, a combination of short-term results from both laboratory experiments and numerical simulations can lead to some general understanding of the required long-term CO sequestration mechanisms. This is a 100 year preliminary batch simulation study of four sandstone samples, under CO saturated water at 75 °C from the Upper Permian formations in the Ordos Basin, using the TOUGHREACT/ECO2N module to simulate the CO-brine-rock interaction processes in deep siliciclastic multilayered saline aquifers. The samples approximately correspond to the four target saline formations selected by the Shenhua Group for a CO sequestration field demonstration project in the Ordos Basin, PR China. Preliminary simulation results show that the initial salinity of formation brine plays a significant role in determining the amount of CO that will be sequestered by solubility or mineral trapping in a deep saline aquifer. Minimal differences between experimental results and numerical calculation occur in low salinity waters, and significantly larger differences in high salinity waters, which is still under the maximum acceptable difference between experimental and computed data (10 %). The upper Liujiagou formation, with the highest level of salinity (ca. 88.7 g/L TDS) and lowest level of CO solubility, offers the highest mineral trapping capacity, with a maximum carbonate mineral storage of ca. 0.7 kg/m of bulk rock over a 100 year period. Regardless of the initial acidity or alkalinity of the aquifer brine, injection of CO will inflict a sudden drop in pH of the brine to acidity levels in a range of 3.0-4.6. The subsequent amount of dissolved and precipitated minerals, arising from the CO-brine-rock interaction, is site specific and mainly dependent on initial aquifer mineralogy and brine composition. [ABSTRACT FROM AUTHOR]