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 CO_(2)geological storage.Based on the published experimental results...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 CO_(2)geological storage.Based on the published experimental results,we present numerical simulations on CO_(2)breakthrough pressure in unsaturated low-permeability rock under 9 multiple P-T conditions(which can keep CO_(2)in gaseous,liquid and supercritical states)and thus,a numerical method which can be used to accurately predict CO_(2)breakthrough pressure on rock-core scale is proposed.The simulation results show that CO_(2)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 indexλ(0.6,0.7,0.8,and 0.9)in van Genuchten-Muale model.Results show that with the increase ofλ,CO_(2)breakthrough pressure and breakthrough time both show decreasing trends.In other words,the larger the value ofλis,the better the permeability of the caprock is,and the worse the CO_(2)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.展开更多
The pore structure of caprock plays an important role in underground gas storage security, as it significantly influences the sealing capacity of caprock. However, the pore structure evolution of caprock with the cycl...The pore structure of caprock plays an important role in underground gas storage security, as it significantly influences the sealing capacity of caprock. However, the pore structure evolution of caprock with the cyclic stress perturbations triggered by the cyclic gas injection or extraction remains unclear. In this study, the pore structure changes of mudstone caprock under cyclic loading and unloading were obtained by the nuclear magnetic resonance (NMR) tests system, then the influence of the changes on the breakthrough pressure of caprock was discussed. The results indicated that the pore structure changes are depending on the stress loading-unloading path and stress level. In the first cyclic, at the loading stage, with the increase of confining stress, the NMR T2 spectrum curve moved to the left, the NMR signal amplitude of the first peak increased, while the amplitude of the second peak decreased gradually. This indicated that the larger pores of mudstone are compressed and transformed into smaller pores, then the number of macropores decreased and the number of micro- and mesopores increased. For a certain loading-unloading cycle, the porosity curve of mudstone in the loading process is not coincide with that in the unloading process, the porosity curve in the loading process was located below that in the unloading process, which indicated that the pore structure change is stress path dependent. With the increase of cycle numbers, the total porosity shown an increasing trend, indicating that the damage of mudstone occurred under the cyclic stress load-unload effects. With the increase of porosity, the breakthrough pressure of mudstone decreased with the increase of the cyclic numbers, which may increase the gas leakage risk. The results can provide significant implication for the underground gas storage security evaluation.展开更多
Predicting the gas breakthrough pressure of saturated compacted bentonite is crucial for ensuring the long-term safe operation of deep geological repositories for the disposal of high-level radioactive nuclear wastes....Predicting the gas breakthrough pressure of saturated compacted bentonite is crucial for ensuring the long-term safe operation of deep geological repositories for the disposal of high-level radioactive nuclear wastes.In this work,the swelling pressure,water injection,gas injection and mercury intrusion porosimetry(MIP)tests on saturated compacted Gaomiaozi(GMZ)bentonite specimens with a dry density of 1.3 Mg/m^(3),1.4 Mg/m^(3),1.5 Mg/m^(3),1.6 Mg/m^(3) and 1.7 Mg/m^(3) were conducted.Subsequently,the relationships between the swelling pressure and average inter-particle distance,as well as between the gas entry pressure and the maximum effective pore size were analyzed and established.Considering that gas migration and breakthrough are all closely related to the pore structures of the tested geomaterials,a novel gas breakthrough pressure prediction model based on the pore size distribution(PSD)curve was constructed using an existing prediction model based on gas entry pressure and swelling pressure.Finally,based on the test results of the specimens 1.5 Mg/m^(3),1.6 Mg/m^(3) and 1.7 Mg/m^(3),gas breakthrough pressures of the specimens with dry densities of 1.3 Mg/m^(3) and 1.4 Mg/m^(3) were predicted.The results show that the calculated gas breakthrough pressures of 0.76 MPa and 1.28 MPa are very close to the measured values of 0.80 MPa and 1.30 MPa,validating the accuracy of the proposed model.展开更多
Water breakthrough in horizontal wells is now the main factor restricting the stable production of the Tainan Gas Field in the Qaidam Basin.In view of this problem,the distribution characteristics of irreducible water...Water breakthrough in horizontal wells is now the main factor restricting the stable production of the Tainan Gas Field in the Qaidam Basin.In view of this problem,the distribution characteristics of irreducible water saturation were investigated by using the nuclear magnetic resonance logging interpretation technology.And combined with the production situations of the horizontal wells in Tainan Gas Field in the initial stage of their production,the characteristic parameters of the reservoir which produced the intrastratal water as soon as it was put into production were determined.Then,the factors influencing the production of irreducible water were studied by means of gas drive water core experiments,and the factors influencing the sealing ability of the interbeds were researched by conducting mudstone breakdown tests.What's more,the effects on the bottomhole pressure by the length of horizontal section at different daily gas productions were investigated through numerical simulation.Finally,the prevention&control countermeasures for water breakthrough in horizontal wells were proposed.And the following research results were obtained.First,the horizontal well which drills into the reservoir with mobile water saturation higher than 7.2%and gas saturation lower than 63.5%produces formation water in its initial stage of production.Second,the lower the shale content is and the greater the production pressure difference is,the more favorable it is for the production of irreducible water.The production of irreducible water in the reservoirs with stronger areal heterogeneity is a continuous process.Third,the sealing capacity of the interbed increases with the decrease of its vertical permeability and water saturation and with the increase of its shale content and thickness.Fourth,the breakthrough pressure of type I mudstone(shale content>90%)is about 4 MPa,that of type II mudstone(80%<shale content<90%)is about 2 MPa,and that of type III mudstone(60%<shale content<80%)is about 1.5 MPa.In conclusion,the edge water encroachment can be delayed and the water-free gas production period of gas well can be extended by increasing the length of horizontal section and controlling the production pressure difference.It is recommended to carry out balanced gas production in horizontal wells in the initial stage of production,enhance dynamic monitoring in the process of production,and drain the water in time in the case of water breakthrough so as to increase its cumulative gas production.展开更多
Understanding the mechanisms of gas transport and the resulting preferential pathways formation through bentonite-based barriers is essential for their performance evaluation.In this experimental study,gas migration w...Understanding the mechanisms of gas transport and the resulting preferential pathways formation through bentonite-based barriers is essential for their performance evaluation.In this experimental study,gas migration within a heterogenous mixture of MX80 bentonite pellets and powder with a ratio of 80/20 in dry mass was investigated.A novel X-ray transparent constant volume cell has been developed to assess the effect of gas pressure,material heterogeneities,and water vapor gas saturation on breakthrough pressure and gas pathways.The new cell allows to perform high-resolution X-ray computed micro-tomography(X-ray μCT)scans to track microstructural changes during different phases of saturation and gas injection.Experimental results showed that the gas breakthrough occurred when the pressure was raised to 3 MPa.This is slightly higher than the expected swelling pressure(2.9 MPa)of the bentonite sample.Each gas injection was followed by a long resaturation phase restoring material homogeneity at μCT resolution scale(16 mm).However,the elapsed time needed for gas to breakthrough at 3 MPa diminished at each subsequent injection test.X-ray μCT results also revealed the opening of the specimen/cell wall interface during gas passage.This opening expanded as the injection pressure increased.The gas flow along the interface was associated with the development of dilatant pathways inside the sample,although they did not reach the outlet surface.It was observed that the water vapor gas saturation had no effect on the breakthrough pressure.These findings enhance the understanding of the complex mechanisms underlying microstructural evolution and gas pathway development within the highly heterogeneous mixture.The experimental outcomes highlight the effectiveness of X-ray μCT to improve quality protocols for engineering design and safety assessments of engineered barriers.展开更多
Self-sealing of fractures in the indurated Callovo-Oxfordian(COX)and Opalinus(OPA)claystones,which are considered as host rocks for disposal of radioactive waste,was investigated on artificially fractured samples.The ...Self-sealing of fractures in the indurated Callovo-Oxfordian(COX)and Opalinus(OPA)claystones,which are considered as host rocks for disposal of radioactive waste,was investigated on artificially fractured samples.The samples were extracted from four lithological facies relatively rich in clay mineral,carbonate and quartz,respectively.The self-sealing of fractures was measured by fracture closure,water permeability variation,gas penetration,and recovery of gas-induced pathways.Most of the fractured samples exhibited a dramatic reduction inwater permeability to low levels that is close to that of intact rock,depending on their mineralogical composition,fracture intensity,confining stress,and load duration.The self-sealing capacity of the clay-rich samples is higher than that of the carbonate-rich and sandy ones.Significant effects of sample size and fracture intensity were identified.The sealed fractures become gas-tight for certain in-jection pressures.However,the measured gas breakthrough pressures are still lower than the confining stresses.The gas-induced pathways can recover when contacting water.These important findings imply that fractures in such indurated claystones can effectively recover to hinder water transport but allow gas release under relatively low pressures without compromising the rock integrity.展开更多
Objective To reduce the risk of surgical resection of giant arteriovenous malformation (AVM) (>6.0 cm) and prevent normal perfusion pressure breakthrough (NPPB) for lowering the postoperative mortality. Methods ...Objective To reduce the risk of surgical resection of giant arteriovenous malformation (AVM) (>6.0 cm) and prevent normal perfusion pressure breakthrough (NPPB) for lowering the postoperative mortality. Methods During the operation under barbiturate anesthesia, the proximal end of the feeding arteries were ligated at first, and 0.5 ml isobutyl 12 cyanoacrylate (IBCA) with 0.5 ml 5% glucose was injected into the vessels towards the AVM, then the malformed vessels were resected totally. Postoperative digital subtraction angiography of the four vessels was performed in all patients. Results 50 patients with giant AVM survived after operation, only 6 (12.0%) had transient neurological dysfunction and 44 (88.0%) recovered after a follow up of 6-36 months. No patient suffered from normal perfusion pressure breakthrough (NPPB). Conclusions The embolization could block the arteriovenous shunts sufficiently to decrease the blood flow away from the normal areas of the brain so as to prevent the incidence of intra and postoperative rebleeding, especially in NPPB. Therefore, the combination of intraoperative embolization with surgical resection is an effective strategy in the treatment of giant cerebral AVMs, which make it operable for those used to be regarded as inoperable cases.展开更多
Calcified chronic subdural hematoma(CCSDH) is a rare disease that accounts for approximately 0.3%–2.7% of all chronic subdural hematomas(CSDHs). The clinical features of CCSDH are very similar to those of noncalcifie...Calcified chronic subdural hematoma(CCSDH) is a rare disease that accounts for approximately 0.3%–2.7% of all chronic subdural hematomas(CSDHs). The clinical features of CCSDH are very similar to those of noncalcified CSDH and include headache,decreased alertness,weakness,numbness,gait disturbance,seizures,memory impairment,confusion,and unconsciousness. All symptomatic CCSDH should be treated surgically. Majority of these patients recover well following surgery. In this report,we present the case of a patient with CCSDH who developed severe cerebral edema following its removal,necessitating decompressive craniectomy. Although there were no abnormal findings in laboratory blood tests,and no signs of brain herniation or epilepsy was found the following day after surgery,the patient's family refused all treatment and a post-operative brain computed tomography(CT) scan. The patient was discharged and died at home. Cerebral hematoma and normal perfusion pressure breakthrough(NPPB) may cause severe cerebral edema following the total removal of a CCSDH.展开更多
基金supported by Open Research Fund of State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences(Grant No.SKLGME021010)funded by the National Natural Science Foundation of China(Grant No.41702251 and 42141010)the MOE Key Laboratory of Groundwater Circulation and Environmental Evolution。
文摘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 CO_(2)geological storage.Based on the published experimental results,we present numerical simulations on CO_(2)breakthrough pressure in unsaturated low-permeability rock under 9 multiple P-T conditions(which can keep CO_(2)in gaseous,liquid and supercritical states)and thus,a numerical method which can be used to accurately predict CO_(2)breakthrough pressure on rock-core scale is proposed.The simulation results show that CO_(2)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 indexλ(0.6,0.7,0.8,and 0.9)in van Genuchten-Muale model.Results show that with the increase ofλ,CO_(2)breakthrough pressure and breakthrough time both show decreasing trends.In other words,the larger the value ofλis,the better the permeability of the caprock is,and the worse the CO_(2)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.
基金the National Natural Science Foundation of China(Grant No.52174107)the Basic Research and Frontier Exploration Projects in Chongqing(No.cstc2021 yszx-jcyjX0010).
文摘The pore structure of caprock plays an important role in underground gas storage security, as it significantly influences the sealing capacity of caprock. However, the pore structure evolution of caprock with the cyclic stress perturbations triggered by the cyclic gas injection or extraction remains unclear. In this study, the pore structure changes of mudstone caprock under cyclic loading and unloading were obtained by the nuclear magnetic resonance (NMR) tests system, then the influence of the changes on the breakthrough pressure of caprock was discussed. The results indicated that the pore structure changes are depending on the stress loading-unloading path and stress level. In the first cyclic, at the loading stage, with the increase of confining stress, the NMR T2 spectrum curve moved to the left, the NMR signal amplitude of the first peak increased, while the amplitude of the second peak decreased gradually. This indicated that the larger pores of mudstone are compressed and transformed into smaller pores, then the number of macropores decreased and the number of micro- and mesopores increased. For a certain loading-unloading cycle, the porosity curve of mudstone in the loading process is not coincide with that in the unloading process, the porosity curve in the loading process was located below that in the unloading process, which indicated that the pore structure change is stress path dependent. With the increase of cycle numbers, the total porosity shown an increasing trend, indicating that the damage of mudstone occurred under the cyclic stress load-unload effects. With the increase of porosity, the breakthrough pressure of mudstone decreased with the increase of the cyclic numbers, which may increase the gas leakage risk. The results can provide significant implication for the underground gas storage security evaluation.
基金the National Natural Science Foundationof China (Grant No. 42030714).
文摘Predicting the gas breakthrough pressure of saturated compacted bentonite is crucial for ensuring the long-term safe operation of deep geological repositories for the disposal of high-level radioactive nuclear wastes.In this work,the swelling pressure,water injection,gas injection and mercury intrusion porosimetry(MIP)tests on saturated compacted Gaomiaozi(GMZ)bentonite specimens with a dry density of 1.3 Mg/m^(3),1.4 Mg/m^(3),1.5 Mg/m^(3),1.6 Mg/m^(3) and 1.7 Mg/m^(3) were conducted.Subsequently,the relationships between the swelling pressure and average inter-particle distance,as well as between the gas entry pressure and the maximum effective pore size were analyzed and established.Considering that gas migration and breakthrough are all closely related to the pore structures of the tested geomaterials,a novel gas breakthrough pressure prediction model based on the pore size distribution(PSD)curve was constructed using an existing prediction model based on gas entry pressure and swelling pressure.Finally,based on the test results of the specimens 1.5 Mg/m^(3),1.6 Mg/m^(3) and 1.7 Mg/m^(3),gas breakthrough pressures of the specimens with dry densities of 1.3 Mg/m^(3) and 1.4 Mg/m^(3) were predicted.The results show that the calculated gas breakthrough pressures of 0.76 MPa and 1.28 MPa are very close to the measured values of 0.80 MPa and 1.30 MPa,validating the accuracy of the proposed model.
基金supported by the National Major Science and Technology Project“Technologies for maintain stable production of unconsolidated gas reservoir”(No.:2016ZX05015-004)PetroChina Major Science and Technology Project“Technologies for water control&gas stabilization in mature blocks and efficient development of new gas bocks in the Qaidam Basin”(No.:2016E-0106GE).
文摘Water breakthrough in horizontal wells is now the main factor restricting the stable production of the Tainan Gas Field in the Qaidam Basin.In view of this problem,the distribution characteristics of irreducible water saturation were investigated by using the nuclear magnetic resonance logging interpretation technology.And combined with the production situations of the horizontal wells in Tainan Gas Field in the initial stage of their production,the characteristic parameters of the reservoir which produced the intrastratal water as soon as it was put into production were determined.Then,the factors influencing the production of irreducible water were studied by means of gas drive water core experiments,and the factors influencing the sealing ability of the interbeds were researched by conducting mudstone breakdown tests.What's more,the effects on the bottomhole pressure by the length of horizontal section at different daily gas productions were investigated through numerical simulation.Finally,the prevention&control countermeasures for water breakthrough in horizontal wells were proposed.And the following research results were obtained.First,the horizontal well which drills into the reservoir with mobile water saturation higher than 7.2%and gas saturation lower than 63.5%produces formation water in its initial stage of production.Second,the lower the shale content is and the greater the production pressure difference is,the more favorable it is for the production of irreducible water.The production of irreducible water in the reservoirs with stronger areal heterogeneity is a continuous process.Third,the sealing capacity of the interbed increases with the decrease of its vertical permeability and water saturation and with the increase of its shale content and thickness.Fourth,the breakthrough pressure of type I mudstone(shale content>90%)is about 4 MPa,that of type II mudstone(80%<shale content<90%)is about 2 MPa,and that of type III mudstone(60%<shale content<80%)is about 1.5 MPa.In conclusion,the edge water encroachment can be delayed and the water-free gas production period of gas well can be extended by increasing the length of horizontal section and controlling the production pressure difference.It is recommended to carry out balanced gas production in horizontal wells in the initial stage of production,enhance dynamic monitoring in the process of production,and drain the water in time in the case of water breakthrough so as to increase its cumulative gas production.
基金funding from the European Union's Horizon 2020 research and innovation program European Joint Program on RadioactiveWaste Management(EURAD)(2019e2024)WP-Gas‘Mechanistic understanding of gas transport in clay materials’under Grant agreement No.847593.
文摘Understanding the mechanisms of gas transport and the resulting preferential pathways formation through bentonite-based barriers is essential for their performance evaluation.In this experimental study,gas migration within a heterogenous mixture of MX80 bentonite pellets and powder with a ratio of 80/20 in dry mass was investigated.A novel X-ray transparent constant volume cell has been developed to assess the effect of gas pressure,material heterogeneities,and water vapor gas saturation on breakthrough pressure and gas pathways.The new cell allows to perform high-resolution X-ray computed micro-tomography(X-ray μCT)scans to track microstructural changes during different phases of saturation and gas injection.Experimental results showed that the gas breakthrough occurred when the pressure was raised to 3 MPa.This is slightly higher than the expected swelling pressure(2.9 MPa)of the bentonite sample.Each gas injection was followed by a long resaturation phase restoring material homogeneity at μCT resolution scale(16 mm).However,the elapsed time needed for gas to breakthrough at 3 MPa diminished at each subsequent injection test.X-ray μCT results also revealed the opening of the specimen/cell wall interface during gas passage.This opening expanded as the injection pressure increased.The gas flow along the interface was associated with the development of dilatant pathways inside the sample,although they did not reach the outlet surface.It was observed that the water vapor gas saturation had no effect on the breakthrough pressure.These findings enhance the understanding of the complex mechanisms underlying microstructural evolution and gas pathway development within the highly heterogeneous mixture.The experimental outcomes highlight the effectiveness of X-ray μCT to improve quality protocols for engineering design and safety assessments of engineered barriers.
基金This work was co-funded by the German Federal Ministry for Economic Affairs and Energy(BMWi)under contract number 02E11627by the European Commission(EC)from the Euro-pean Union’s Horizon 2020 research and innovationprogram under Grant No.847593.
文摘Self-sealing of fractures in the indurated Callovo-Oxfordian(COX)and Opalinus(OPA)claystones,which are considered as host rocks for disposal of radioactive waste,was investigated on artificially fractured samples.The samples were extracted from four lithological facies relatively rich in clay mineral,carbonate and quartz,respectively.The self-sealing of fractures was measured by fracture closure,water permeability variation,gas penetration,and recovery of gas-induced pathways.Most of the fractured samples exhibited a dramatic reduction inwater permeability to low levels that is close to that of intact rock,depending on their mineralogical composition,fracture intensity,confining stress,and load duration.The self-sealing capacity of the clay-rich samples is higher than that of the carbonate-rich and sandy ones.Significant effects of sample size and fracture intensity were identified.The sealed fractures become gas-tight for certain in-jection pressures.However,the measured gas breakthrough pressures are still lower than the confining stresses.The gas-induced pathways can recover when contacting water.These important findings imply that fractures in such indurated claystones can effectively recover to hinder water transport but allow gas release under relatively low pressures without compromising the rock integrity.
文摘Objective To reduce the risk of surgical resection of giant arteriovenous malformation (AVM) (>6.0 cm) and prevent normal perfusion pressure breakthrough (NPPB) for lowering the postoperative mortality. Methods During the operation under barbiturate anesthesia, the proximal end of the feeding arteries were ligated at first, and 0.5 ml isobutyl 12 cyanoacrylate (IBCA) with 0.5 ml 5% glucose was injected into the vessels towards the AVM, then the malformed vessels were resected totally. Postoperative digital subtraction angiography of the four vessels was performed in all patients. Results 50 patients with giant AVM survived after operation, only 6 (12.0%) had transient neurological dysfunction and 44 (88.0%) recovered after a follow up of 6-36 months. No patient suffered from normal perfusion pressure breakthrough (NPPB). Conclusions The embolization could block the arteriovenous shunts sufficiently to decrease the blood flow away from the normal areas of the brain so as to prevent the incidence of intra and postoperative rebleeding, especially in NPPB. Therefore, the combination of intraoperative embolization with surgical resection is an effective strategy in the treatment of giant cerebral AVMs, which make it operable for those used to be regarded as inoperable cases.
文摘Calcified chronic subdural hematoma(CCSDH) is a rare disease that accounts for approximately 0.3%–2.7% of all chronic subdural hematomas(CSDHs). The clinical features of CCSDH are very similar to those of noncalcified CSDH and include headache,decreased alertness,weakness,numbness,gait disturbance,seizures,memory impairment,confusion,and unconsciousness. All symptomatic CCSDH should be treated surgically. Majority of these patients recover well following surgery. In this report,we present the case of a patient with CCSDH who developed severe cerebral edema following its removal,necessitating decompressive craniectomy. Although there were no abnormal findings in laboratory blood tests,and no signs of brain herniation or epilepsy was found the following day after surgery,the patient's family refused all treatment and a post-operative brain computed tomography(CT) scan. The patient was discharged and died at home. Cerebral hematoma and normal perfusion pressure breakthrough(NPPB) may cause severe cerebral edema following the total removal of a CCSDH.
