Factors affecting shale microscopic pore structure variation during interaction with supercritical CO2

Dai, Xiaogan; Meng, Weiyi; Wei, Chongtao; Zhang, Junjian; Wang, Xiaoqi; Zou, Mingjun

doi:10.1016/j.jcou.2020.01.021

Cited by 40 publications

(22 citation statements)

References 54 publications

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“…However, for Type II kerogen (TOC < 3%), the change is governed by pore framework reorganization due to dissolution of minerals. 203 Thus, because of their different chemistries and structure, different kerogens behave differently when studied in different environments, 227,228 and it is likely that, depending on the degree of aromatization, aliphatic content, and stability, the kerogens would respond uniquely when exposed to SC-CO 2 .…”

Section: Changes In Porosity and Mineralogymentioning

confidence: 99%

Impact of Supercritical CO₂ on Shale Reservoirs and Its Implication for CO₂ Sequestration

et al. 2022

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Hydraulic fracturing has transformed the international energy landscape by becoming the go-to method for the exploitation of natural gas from unconventional shale reservoirs. However, in the recent years, the search for an alternative method of shale-gas exploration has intensified, because of various problems (e.g., contamination of ground and surface water, overexploitation of precious water resources, air pollution, etc.) associated with the usage of water-based fracturing techniques. The use of CO2 for shale gas exploitation has emerged as a better alternative to aqueous-based gas exploration techniques. CO2 when injected into deep shale reservoirs, transitions into supercritical CO2 (SC-CO2) when temperature and pressure condition exceeds the critical point, i.e., 31.1 °C and 7.38 MPa. In this paper, we comprehensively review the impact of SC-CO2 on shale gas reservoirs during the different stages of shale-gas exploration, i.e., (i) drilling, which involves the superiority of SC-CO2 over water-based drilling fluids, in terms of achieving under-balanced well condition, higher rates of penetration, and resistance to formation damage; (ii) fracturing, which involves factors affecting the tortuosity of fractures created by SC-CO2 fracturing, breakdown pressure, and proppant-carrying capacity; and (iii) injection, which involves the twin-headed benefit of enhanced recovery due to CO2/CH4 competitive adsorption and geological sequestration, CO2 vs CH4 excess sorption as a function of pressure, etc. Several research works have indicated discrepancies on how SC-CO2 impacts different shale properties. Some studies show low-pressure N2-gas-adsorption-derived surface area and total pore volume to be increasing with SC-CO2 imbibition, while others show a decreasing trend for the same. Similarly, for some shales, the quartz content, along with the clay mineral contents, decreased as the exposure to SC-CO2 increased, while in some other studies, with similar long-term exposure to SC-CO2, the quartz content was observed to increase along with the decrease in clay content and vice versa. Essentially, the increased exposure to SC-CO2 results in the dissolution of primary porous structures and fractures, and reformation of newer porous structure and conduits in shales. Nonetheless, these changes in the mineralogy weaken the microstructure of the rock bringing significant changes in the mechanical properties of the shales with implications on the wellbore stability and fracturing efficiency. The mechanical properties such as uniaxial compressive strength (UCS), Young’s modulus, and tensile strength decrease as the SC-CO2 saturation period increases. However, some studies have shown factors like bedding angle and phase-state of CO2 having varying effect on the strength behavior of the shales. Moreover, changes in the structure of shales caused by the creation of fractures and the reduction of their strength can also pose major risks, because of potential leakage of CO2 through these created pathways. How these processes would i...

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Section: Changes In Porosity and Mineralogymentioning

confidence: 99%

Impact of Supercritical CO₂ on Shale Reservoirs and Its Implication for CO₂ Sequestration

et al. 2022

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“…Micropore volume exhibits a general increase as the k value is <1, whereas a decrease becomes obvious when k is >1. The calcite dissolution effect during the scCO 2 –H 2 O–shale experiments is interpreted to account for these, reflecting that calcite dissolution mainly influences the micropores, and this has been partially demonstrated in previous works . Sufficient calcite will result in enlarged micropores during the scCO 2 reaction.…”

Section: Discussionmentioning

confidence: 63%

“…The calcite dissolution effect during the scCO 2 −H 2 O− shale experiments is interpreted to account for these, reflecting that calcite dissolution mainly influences the micropores, and this has been partially demonstrated in previous works. 79 Sufficient calcite will result in enlarged micropores during the scCO 2 reaction. Mesopore and macropore volumes show a remarkable decline, along with the scCO 2 reaction, suggesting that precipitation dominates the mesopore and macropore variations.…”

Section: Mineralogical Variation Mechanism and The Effect Of Dissolut...mentioning

confidence: 99%

Alteration of Potential Storage Space of Shale Gas Reservoirs Induced by Mineral Dissolution and Precipitation during scCO₂–H₂O Shale Reactions

et al. 2022

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Long-term storage of CO2 in geological reservoirs can be achieved by mineral trapping through the formation of carbonate minerals. Hence, investigating the precipitation and dissolution processes of carbonate minerals and their effects on the storage space of the target reservoir are of great significance. In this study, a suite of shale samples collected from the southern Sichuan Basin were selected for supercritical carbon dioxide (scCO2)–H2O–shale experiments. Mineralogical composition, surface morphology, and gas adsorption feature variations before and after scCO2–H2O–shale reaction were studied. The results reveal that the carbonate, clay, and feldspar mineral contents in the samples decrease, while the concentrations of Ca2+, Mg2+, and K+ cations in the reacted filtrate increase, indicating the dissolution process. The elevated concentrations of K+ and Na+ cations in the flushed filtrate are ascribed to the redissolution of the precipitated carbonates. The precipitation process has a tendency to decrease the mesopore volume. However, this influence on micropores merely occurs in samples with lower calcite content. After flushing, mesopore volume exhibits an increasing trend, because of the redissolution of soluble precipitates. Precipitation and redissolution also affect pore geometrical characteristics, characterized by increased hysteresis coefficient, initiating blocked pore structure and greater pore heterogeneity. This mainly develops in ink bottle pores, uneven capillary pores, and parallel plate pores. In summary, mineral dissolution, precipitation, and redissolution during scCO2–H2O-shale experiments can significantly alter the storage space of reservoirs. Understanding these dynamic variations and their underlying mineralization mechanism during CO2 storage is a matter of considerable concern for “Carbon Neutrality”.

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“…Two reactions may occur during the CO 2 –water–caprock system, i.e., the dissolution of feldspars, micas, and pyrite and the precipitation of kaolinite, which has a different impact on the caprock structure. − Some scholars considered that the CO 2 –water–rock reaction can promote the development of the pore-fracture structure and thus improve the permeability; for example, Foroutan et al stated that the porosity of sandstone specimens after CO 2 -saturated brine injection is increased by 2.87–3.60% . Dai et al found that the CO 2 aqueous solution causes the dissolution of clay and carbonate in shale and increases the micropore volume and mesopore specific surface area. Zou et al reported that CO 2 –brine–rock interactions eventually not only cause a significant increase in porosity and permeability (up to 1 order of magnitude) but also influence the extension of the natural fracture .…”

Section: Introductionmentioning

confidence: 99%

Changes of Multiscale Surface Morphology and Pore Structure of Mudstone Associated with Supercritical CO₂-Water Exposure at Different Times

et al. 2021

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CO2 enhanced coalbed methane recovery (CO2-ECBM) has been confirmed as an effective technology to improve coalbed methane (CBM) production; however, the injected CO2 and the reservoir water can react with the caprock of the coal seam, which changes its internal structure and increases the risk of CO2 leakage. To clarify the CO2–water–rock reaction process and the structural responses of the caprock, the roof mudstone samples of coal seams from Qinshui Basin were first selected to conduct the geochemical reaction experiment; then, scanning electron microscopy (SEM), N2 adsorption, and mercury intrusion porosimetry were adopted to monitor the multiscale structure alteration of the samples. The results show that the rock sample has progressively deteriorated during the CO2–water–rock reaction process, and this effect is aggravated with the increase of the reaction time. The dissolution process consists of three stages: (1) lots of isolated and shallow holes are developed; (2) holes are connected and formed to the dissolution grooves; (3) dissolution grooves are widened, and the dissolution zone is expanded until all the soluble minerals immerse into the reaction solution. The pore volume (PV) and specific surface area (SSA) of small pores are reduced, while those of large pores are increased, which can be attributed to the pore-blocking effect caused by clay mineral swelling and mineral precipitation and the pore-enlarging effect caused by mineral dissolution, respectively. Additionally, the ScCO2–water–rock reaction varies the pore structure distribution and makes the PV distribution more heterogeneous and the SSA distribution more homogeneous. The changes in the internal structure of the roof mudstone promote gas diffusion and seepage, which may increase the potential threat of CO2 leakage during the long-term CO2-ECBM process to a certain degree. This study will provide an essential basis for the investigation and evaluation of the security of CO2-ECBM in Qinshui Basin, China.

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Factors affecting shale microscopic pore structure variation during interaction with supercritical CO2

Cited by 40 publications

References 54 publications

Impact of Supercritical CO₂ on Shale Reservoirs and Its Implication for CO₂ Sequestration

Impact of Supercritical CO₂ on Shale Reservoirs and Its Implication for CO₂ Sequestration

Alteration of Potential Storage Space of Shale Gas Reservoirs Induced by Mineral Dissolution and Precipitation during scCO₂–H₂O Shale Reactions

Changes of Multiscale Surface Morphology and Pore Structure of Mudstone Associated with Supercritical CO₂-Water Exposure at Different Times

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Factors affecting shale microscopic pore structure variation during interaction with supercritical CO2

Cited by 40 publications

References 54 publications

Impact of Supercritical CO2 on Shale Reservoirs and Its Implication for CO2 Sequestration

Impact of Supercritical CO2 on Shale Reservoirs and Its Implication for CO2 Sequestration

Alteration of Potential Storage Space of Shale Gas Reservoirs Induced by Mineral Dissolution and Precipitation during scCO2–H2O Shale Reactions

Changes of Multiscale Surface Morphology and Pore Structure of Mudstone Associated with Supercritical CO2-Water Exposure at Different Times

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Product

Resources

About

Impact of Supercritical CO₂ on Shale Reservoirs and Its Implication for CO₂ Sequestration

Impact of Supercritical CO₂ on Shale Reservoirs and Its Implication for CO₂ Sequestration

Alteration of Potential Storage Space of Shale Gas Reservoirs Induced by Mineral Dissolution and Precipitation during scCO₂–H₂O Shale Reactions

Changes of Multiscale Surface Morphology and Pore Structure of Mudstone Associated with Supercritical CO₂-Water Exposure at Different Times