Gypsum caprocks'sealing ability is affected by temperature-pressure coupling.Due to the limitations of experimental conditions,there is still a lack of triaxial stress-strain experiments that simultaneously consid...Gypsum caprocks'sealing ability is affected by temperature-pressure coupling.Due to the limitations of experimental conditions,there is still a lack of triaxial stress-strain experiments that simultaneously consider changes in temperature and pressure conditions,which limits the accuracy of the comprehensive evaluation of the brittle plastic evolution and sealing ability of gypsum rocks using temperature pressure coupling.Triaxial stress-strain tests were utilized to investigate the differences in the evolution of the confinement capacity of gypsum rocks under coupled temperaturepressure action and isothermal-variable pressure action on the basis of sample feasibility analysis.According to research,the gypsum rock's peak and residual strengths decrease under simultaneous increases in temperature and pressure over isothermal pressurization experimental conditions,and it becomes more ductile.This reduces the amount of time it takes for the rock to transition from brittle to plastic.When temperature is taken into account,both the brittle–plastic transformation's depth limit and the lithological transformation of gypsum rocks become shallower,and the evolution of gypsum rocks under variable temperature and pressure conditions is more complicated than that under isothermal pressurization.The sealing ability under the temperature-pressure coupling is more in line with the actual geological context when the application results of the Well#ZS5 are compared.This provides a theoretical basis for precisely determining the process of hydrocarbon accumulation and explains why the early hydrocarbon were not well preserved.展开更多
The Meso-Neoproterozoic is a new play in the Ordos Basin.A deeper understanding about the dynamic relationship between the caprocks and the source rocks is needed.Based on the comprehensive analysis of hydrocarbon sou...The Meso-Neoproterozoic is a new play in the Ordos Basin.A deeper understanding about the dynamic relationship between the caprocks and the source rocks is needed.Based on the comprehensive analysis of hydrocarbon source development characteristics of the Meso-Neoproterozoic and its overlying strata,as well as the formation contact relationships,lithology characteristics and exploratory drilling data,it is recognized that the Meso-Neoproterozoic contains two types of petroleum accumulation assemblage,that is,the“self-sourced indigenous”and“upper source rock-lower reservoir”assemblages.The former is mainly controlled by the development and distribution of source rocks of the Changcheng System,with the Lower Cambrian shale sequence as its caprock.The later is controlled by the superposition between the Meso-Neoproterozoic and its overlying source rocks and this assemblage is mainly distributed in Hangjinqi and Pingliang areas with the Carboniferous-Permian shale sequence as its caprock.The dynamic evaluation on the displacement pressure serves to reconstruct the displacement pressure history of the caprock.The results show that the shale sequence of the Cambrian Maozhuang Formation in well XY 1 in the southern Ordos Basin has possibly acquired the ability of sealing natural gas since the early of Late Triassic.Its displacement pressure increased rapidly up to 20 MPa during the Late Triassic-Jurassic and keeps at 9.2 MPa at present,indicating fair sealing ability.The Carboniferous-Permian caprocks in Hangjinqi area could have acquired the ability to seal natural gas in the Late Jurassic-Early Cretaceous,and the present-day displacement pressure is 9e12 MPa,indicating good sealing ability.The upper Paleozoic caprock in Pingliang area has been able to seal natural gas since the Early Jurassic,with a maximum displacement pressure of 23 MPa during the Cretaceous period and a current value of 17 e20 MPa,indicative of strong ability to seal natural gas.The sealing ability of caprocks of both the“selfsourced indigenous”and“upper source rock-lower reservoir”assemblages has come into being earlier than or at least no later than the peak gas generation of the source rocks and therefore the caprocks are dynamically effective in geohistory.The Meso-Neoproterozoic reservoirs in the Ordos Basin are well preserved and probabally of better potential for exploration in terms of the caprock-source rock combination.展开更多
The caprock is one of the key factors for a reservoir, especially for a gas reservoir. Whether the caprocks can block off the gas is of significance for the accumulation and preservation of the gas reservoir. In this ...The caprock is one of the key factors for a reservoir, especially for a gas reservoir. Whether the caprocks can block off the gas is of significance for the accumulation and preservation of the gas reservoir. In this paper, we use the Amplitude versus offset （AVO） seismic technique to determine the lateral extension of the hydrocarbon concentration sealing caprocks. The essence of this technique is to detect the variations of the reservoir bed physical properties by monitoring the variations of the reflection coefficient of seismic waves upon the interfaces between different lithologies. Generally it is used to indicate hydrocarbon directly. For the hydrocarbon concentration sealing caprocks, the change of hydrocarbon concentration may cause the change of physical properties of the caprocks. Therefore it is possible to evaluate the hydrocarbon concentration sealing ability of the caprocks by AVO. This paper presents a case study using AVO to determine the lateral extension of the hydrocarbon concentration sealing caprocks. The result shows that this method is helpful for the exploration of the region.展开更多
Super-large natural gasfields have been discovered in the deep and ultra-deep layers of onshore and offshore petroliferous basins in China since the beginning of the 21st century,and the geological conditions for the ...Super-large natural gasfields have been discovered in the deep and ultra-deep layers of onshore and offshore petroliferous basins in China since the beginning of the 21st century,and the geological conditions for the formation of these gasfields and their development laws have already been discussed in a large number of literatures,but the relationship between over pressure and the formation of this kind of gasfields is still less researched.In this regard,this paperfirstly analyzed the gas reservoir development law,sealing conditions and over pressure char-acteristics of deep and ultra-deep super-large gasfields.Then,the formation mechanisms of deep and ultra-deep over pressure caprocks were investigated and the development law of deep and ultra-deep super-large gasfields and their relationship with over pressure caprocks were discussed.Finally,the favorable areas for the next exploration of deep and ultra-deep natural gas were pointed out.And the following research results were obtained.First,the formation of deep and ultra-deep super-large gasfields is closely related to the development of over pressure caprocks.Over pressure caprock is a necessary condition for the formation of deep and ultra-deep super-large gasfields,and there are three over pressure formation mechanisms,including pressure seal of salt-gypsum layer,pressure seal of residual uplift and pressure seal of hydrocarbon-generating pressurization.Second,as for deep and ultra-deep over pressure caprocks and super-large gasfields,there are four reservoirecaprock assemblage modes under different pressure environments,i.e.,over pressure salt-gypsum seal and over pressure super-large gasfield(Type I),internal over pressure compartment and over pressure super-large gasfield(Type II),high-pressure argillaceous shale seal at the bottom of over pressure compartment and normal-pressure super-larger gasfield(Type III),and over pressure source rock seal and normal-pressure super-larger gasfield(Type IV).In conclusion,there are Type I super-large gasfields in the Kuqa Depression of the Tarim Basin,types II and III in the Junggar Basin,types IeIV in the Sichuan Basin and Type IV in the Bohai Bay Basin.展开更多
In the process of oil and gas production,reservoir pressure depletion leads to changes in pore pressure and in-situ stress in caprock,which may reactivate closed faults in caprock,break the sealing of caprock,and make...In the process of oil and gas production,reservoir pressure depletion leads to changes in pore pressure and in-situ stress in caprock,which may reactivate closed faults in caprock,break the sealing of caprock,and make depleted oil and gas reservoirs unsuitable for gas storage.In order to effectively evaluate the sealing of faults in caprock above depleted reservoir and provide a basis for a reasonable selection of injection time and location for gas storage,this paper comprehensively considers fault slip potential(FSP)and fault tensile potential(FTP),and establishes a fault sealing evaluation model in caprock above depleted reservoir.The influences of distance of fault from reservoir top,reservoir pressure depletion degree,cap mechanical property,fault occurrence,fault frictional property and in-situ stress anisotropy in caprock on different types of FSP and FTP are analyzed.The results show that for normal faults,reverse faults,and strike-slip faults,FTP increases with reservoir depletion and does not cause tensile failure,among which FTP is the smallest for normal faults.FSP is the key to controlling fault sealing in caprock above depleted reservoir.For reverse faults and strike-slip faults,in the early stage of reservoir depletion,the FsP is larger when the fault is farther away from the top of the reservoir,while normal faults are the opposite.When the normal fault is closer to the top of the reservoir,the cap poisson ratio is smaller,the Biot's coefficient is larger,the internal friction coefficient of the fault is smaller,the inherent shear strength of the fault is smaller,σH/σv is smaller,σh/σv is smaller,45°<β<75°,α=0° or α=180°,the FSP is larger with the reservoir depletion,and the shear failure of the fault is the most likely.At this time,the reservoir pressure should be strictly controlled not to be too small,so that it can be suitable for the construction of gas storage.Under other conditions,the possibility of shear failure of the caprock is less.For reverse faults and strike-slip faults,when is smaller,the FSP decreases first and then increases with reservoir depletion.Although the possibility of shear failure decreases in the initial stage of reservoir depletion,it increases in the later stage.The research results can provide a theoretical basis for the reconstruction of underground gas storage.展开更多
Based on the achievements and research advances in oil and gas exploration in the Persian Gulf Basin,this study analyzes the orderliness of oil and gas distribution and main controlling factors of hydrocarbon accumula...Based on the achievements and research advances in oil and gas exploration in the Persian Gulf Basin,this study analyzes the orderliness of oil and gas distribution and main controlling factors of hydrocarbon accumulation with reservoir-forming assemblage as the unit.In the Persian Gulf Basin,the hydrocarbon-generating centers of source rocks of different geological ages and the hydrocarbon rich zones migrate in a clockwise direction around the Ghawar Oilfield in the Central Arabian Subbasin.Horizontally,the overall distribution pattern is orderly,showing“oil in the west and gas in the east”,and“large oil and gas fields dense in the basin center and sparse at the basin edges”.Vertically,the extents of petroleum system compounding and sources mixing increase from west to east,the pattern of tectonic strength(weak in the west and strong in the east)forming the distribution characteristics of“gas rich in the Paleozoic,oil rich in the Mesozoic,and both oil and gas rich in the Cenozoic”.The large scale accumulation and orderly distribution of oil and gas in the Persian Gulf Basin are controlled by three factors:(1)Multiple sets of giant hydrocarbon kitchens provide a resource base for near-source reservoir-forming assemblages.The short-distance lateral migration determines the oil and gas enrichment in and around the distribution area of effective source rocks.(2)The anhydrite caprocks in the platform area are thin but have experienced weak late-stage tectonic activities.Their good sealing performance makes it difficult for oil and gas to migrate vertically to shallow layers through them.The thrust faults and high-angle fractures formed by intense tectonic activities of the Zagros Orogenic Belt connect multiple source-reservoir assemblages.However,the Neogene Gachsaran Formation gypsum-salt rocks are thick and highly plastic,generally with good sealing performance,so large-scale oil and gas accumulations are still formed beneath the salt;(3)Each set of reservoir-forming assemblages is well matched in time and space in terms of the development of source rocks and reservoir-caprock assemblages,the maturation and hydrocarbon generation of source rocks,and the formation of traps,thus resulting in abundant multi layer hydrocarbon accumulations.At present,the Persian Gulf Basin is still in the stage of structural trap exploration.The pre-salt prospective traps in effective hydrocarbon kitchens remain the first choice.The areas with significant changes in Mesozoic sedimentary facies have the conditions to form large scale lithologic oil and gas reservoirs.The deep Paleozoic conventional oil and gas reservoirs and the Lower Silurian Qusaiba Member shale gas have great exploration potential and are expected to become important reserve growth areas in the future.展开更多
Understanding the mechanical and transport behavior of thin(i.e.small aperture)cracks slipping under supercritical carbon dioxide(sc-CO_(2))conditions is essential to evaluate the integrity of sealing formations with ...Understanding the mechanical and transport behavior of thin(i.e.small aperture)cracks slipping under supercritical carbon dioxide(sc-CO_(2))conditions is essential to evaluate the integrity of sealing formations with buoyant sc-CO_(2)below and the success of waterless fracturing.The two major items of interest in this work are frictional strength and permeability change of the crack.We used a triaxial cell that permits in situ visualization to conduct and monitor slippage along the faces of narrow cracks subjected to triaxial stresses.Such cracks are analogs to small geological faults.We tested carbonate-rich,1-inch diameter Wolfcamp shale samples that are saw cut 30to vertical to create a thin crack.Friction coefficients ranged from about 0.6 to 0.8 consistent with expectations for brittle rocks.The sc-CO_(2)generally did not alter friction coefficient over the time scale of experiments.From a transport perspective,saturating cracks with sc-CO_(2)substantially decreased permeability of the crack by 26%e52%,while slip resulted in a variety of permeability responses.Overall,the combined impact of sc-CO_(2)saturation and slip reduced fault permeability for all tests.Our observations support the notion that the sealing capacity of some caprocks improves when saturated with sc-CO_(2)and that some slip of small fractures is not necessarily detrimental to caprock integrity.展开更多
Under the joint action of gypsum-salt rocks and faults,fluid evolution process is complicated in the northern Tuzimazha,Kuqa Depression,Tarim Basin.In the past,however,the oil and gas distribution rules in this area w...Under the joint action of gypsum-salt rocks and faults,fluid evolution process is complicated in the northern Tuzimazha,Kuqa Depression,Tarim Basin.In the past,however,the oil and gas distribution rules in this area were less studied,so the related understanding was insufficient.In this paper,the reservoirs in Well Block Tubei 1 were analyzed by means of fluid inclusion and quantitative grain fluorescence(QGF)techniques.Based on tectonic evolution history,burial history,thermal history and hydrocarbon generation history,the paleofluid evolution process in this area was reproduced.It is shown that the well block experienced hydrocarbon charge in two periods.The first period is the earlyemiddle stage(16-9 Ma)of Miocene Kangcun Fm(N_(1-2)k),when it was charged with oil,with the corresponding characteristics of yellow and whiteeyellow fluid inclusion fluorescence and the QGF Index higher than 4,indicating that there were paleo-oil reservoirs at the early stage of the reservoirs.And at the late stage,the fluids that were accumulated at the early stage escaped because the gypsum-salt rocks were cut by faults,and bitumen remained in the reservoirs.It is also the evidence for the escaping of the early charged oil that the total scanning fluorescence(TSF)of the hydrocarbon adsorbed to the surface of the current reservoirs is generally unimodal.The second period is the late stage(about 3 Ma)of Pliocene Kuqa Fm(N_(2)k),when the natural gas and light oil charging occurred.Correspondingly,there are two inclusions,i.e.black gaseous hydrocarbon inclusion and blue fluorescence inclusion located along the edge of the quartz grains.At this stage,the gypsum-salt caprocks deepened and their sealing capacity was recovered due to a strong plastic flow.Moreover,the trap was uplifted violently under the effect of Himalaya orogeny,and a large amount of natural gas and a little light oil were accumulated.展开更多
Carbon dioxide(CO2) capture and storage(CCS) is considered widely as one of promising options for CO2emissions reduction,especially for those countries with coal-dominant energy mix like China.Injecting and storing a ...Carbon dioxide(CO2) capture and storage(CCS) is considered widely as one of promising options for CO2emissions reduction,especially for those countries with coal-dominant energy mix like China.Injecting and storing a huge volume of CO2in deep formations are likely to cause a series of geomechanical issues,including ground surface uplift,damage of caprock integrity,and fault reactivation.The Shenhua CCS demonstration project in Ordos Basin,China,is the first and the largest full-chain saline aquifer storage project of CO2in Asia.The injection started in 2010 and ended in 2015.during which totally 0.3 million tonnes(Mt) CO2was injected.The project is unique in which CO2was injected into 18 sandstone formations simultaneously and the overlying coal seams will be mined after the injection stopped in 2015.Hence,intense geomechanical studies and monitoring works have been conducted in recent years,including possible damage resulting from the temperature difference between injected CO2and formations,injection induced stress and deformation change,potential failure mode and safety factor,interaction between coal mining and CO2geological storage,determination of injection pressure limit,and surface monitoring by the interferometric synthetic aperture radar(InSAR) technology.In this paper,we first described the background and its geological conditions of the Shenhua CCS demonstration project.Then,we gave an introduction to the coupled thermo-hydro-mechano-chemical(THMC) processes in CO2geological storage,and mapped the key geomechanical issues into the THMC processes accordingly.Next,we proposed a generalized geomechanical research flowchart for CO2geological storage projects.After that,we addressed and discussed some typical geomechanical issues,including design of injection pressure limit.CO2injection induced near-field damage,and interaction between CO2geological storage and coal mining,in the Shenhua CCS demonstration project.Finally,we concluded some insights to this CCS project.展开更多
In this study,we numerically investigate the influence of hysteretic stress path behavior on the seal integrity during underground gas storage operations in a depleted reservoir.Our study area is the Honor Rancho Unde...In this study,we numerically investigate the influence of hysteretic stress path behavior on the seal integrity during underground gas storage operations in a depleted reservoir.Our study area is the Honor Rancho Underground Storage Facility in Los Angeles County(California,USA),which was converted into an underground gas storage facility in 1975 after 20 years of oil and gas production.In our simulations,the geomechanical behavior of the sand reservoir is modeled using two models:(1)a linear elastic model(non-hysteretic stress path)that does not take into consideration irreversible deformation,and(2)a plastic cap mechanical model which considers changes in rock elastic properties due to irreversible deformations caused by plastic reservoir compaction(hysteretic stress path).It shows that the irreversible compaction of the geological layer over geologic time and during the reservoir depletion can have important consequences on stress tensor orientation and magnitude.Ignoring depletion-induced irreversible compaction can lead to an over-estimation of the calculation of the maximum working reservoir pressure.Moreover,this irreversible compaction may bring the nearby faults closer to reactivation.However,regardless of the two models applied,the geomechanical analysis shows that for the estimated stress conditions applied in this study,the Honor Rancho Underground Storage Facility is being safely operated at pressures much below what would be required to compromise the seal integrity.展开更多
Maintaining caprock integrity is prerequisite for hydrocarbon accumulation. And gypsolyte caprock integrity is mainly affected by fracturing. Composition, damage behavior and mechanical strength of Paleocene Artashi F...Maintaining caprock integrity is prerequisite for hydrocarbon accumulation. And gypsolyte caprock integrity is mainly affected by fracturing. Composition, damage behavior and mechanical strength of Paleocene Artashi Formation gypsolyte rock that seals significant petroleum in the Kashi Sag of Tarim Basin had been revealed via X-ray diffraction and triaxial compression test. The results indicate the Artashi Formation can be lithologically divided into the lower and upper lithologic members. The lower member comprises gypsum as the dominant mineral, and the cohesion and friction coefficient are 8 MPa and 0.315, respectively. Similarly, the upper lithologic member consists mainly of anhydrite at the cohesion and coefficient of internal friction values of 18 MPa and 0.296. Given that the failure criterion and brittle-ductile transition factors during burial, the sealing integrity of Artashi Formation can be quantized for seven different stages. The reservoirs at the bottom of Artashi Formation caprock buried from 2285 m to 3301 m are expected to be the most favorable exploration target in the Kashi Sag.展开更多
Caprocks play an important role in the trapping of coalbed methane(CBM)reservoirs.To study the sealing capacities of caprocks,five samples with different lithologies of Neogene clayrock,Paleogene redbeds,Permian sands...Caprocks play an important role in the trapping of coalbed methane(CBM)reservoirs.To study the sealing capacities of caprocks,five samples with different lithologies of Neogene clayrock,Paleogene redbeds,Permian sandstone,Permian mudstone and Permian siltstone were collected and tested using experimental methods of microstructure observation,pore structure measurement and diffusion properties determination.Results indicate that with denser structures,lower porosities,much more developed micropores/transition pores and higher pore/throat ratios,mudstone and siltstone have the more ideal sealing capacities for CBM preservation when comparing to other kinds of caprocks;the methane diffusion coefficients of mudstone/siltstone are about 6 times higher than sandstone and almost 90 times higher than clayrock/redbeds.To further estimate the CBM escape through caprocks,a one-dimensional CBM diffusion model is derived.Modeling calculation result demonstrates that under the same thickness,the CBM sealing abilities of mudstone/siltstone are almost 100 times higher than those of clayrock/redbeds,and nearly 17 times higher than sandstone,which indicates that the coal seam below caprocks like clayrock,redbeds or sandstone may suffer stronger CBM diffusion effect than that below mudstone or siltstone.Such conclusion is verified by the case study from III3 District,Xutuan Colliery,where the coal seam capped by Paleogene redbeds has a much lower CBM content than that capped by the Permian strata like mudstone,siltstone and sandstone.展开更多
Caprock is a water-saturated formation with a sufficient entry capillary pressure to prevent the upward migration of a buoyant fluid. When the entry capillary pressure of caprock is smaller than the pressure exerted b...Caprock is a water-saturated formation with a sufficient entry capillary pressure to prevent the upward migration of a buoyant fluid. When the entry capillary pressure of caprock is smaller than the pressure exerted by the buoyant CO2plume, CO2gradually penetrates into the caprock. The CO2penetration depth into a caprock layer can be used to measure the caprock sealing efficiency and becomes the key issue to the assessment of caprock sealing efficiency. On the other hand, our numerical simulations on a caprock layer have revealed that a square root law for time and pore pressure exists for the CO2penetration into the caprock layer. Based on this finding, this study proposes a simple approach to estimate the CO2penetration depth into a caprock layer. This simple approach is initially developed to consider the speed of CO2invading front. It explicitly expresses the penetration depth with pressuring time, pressure difference and pressure magnitude. This simple approach is then used to fit three sets of experimental data and good fittings are observed regardless of pressures, strengths of porous media, and pore fluids(water,hydrochloric acid, and carbonic acid). Finally, theoretical analyses are conducted to explore those factors affecting CO2penetration depth. The effects of capillary pressure, gas sorption induced swelling, and fluid property are then included in this simple approach. These results show that this simple approach can predict the penetration depth into a caprock layer with sufficient accuracy, even if complicated interactions in penetration process are not explicitly expressed in this simple formula.展开更多
Based on the compilation and analysis of the lithofacies and paleogeography distribution maps at present and paleoplate locations during six key geological periods of the Mesozoic and Cenozoic,the lithofacies and pale...Based on the compilation and analysis of the lithofacies and paleogeography distribution maps at present and paleoplate locations during six key geological periods of the Mesozoic and Cenozoic,the lithofacies and paleogeography features and their development laws were expounded.Based on our previous research results on lithofacies and paleogeography from Precambrian to Paleozoic,we systematically studied the features and evolution laws of global lithofacies and paleogeography from the Precambrian and their effects on the formation of source rocks,reservoirs,cap rocks and the distribution of oil and gas worldwide.The results show that since Precambrian,the distribution areas of uplift erosion and terrestrial clastic deposition tended to increase gradually,and increased significantly during the period of continental growth.The scale of coastal and shallow marine facies area had three distinct cycles,namely,from Precambrian to Devonian,from Carboniferous to Triassic,and from Jurassic to Neogene.Correspondingly,the development of shallow carbonate platform also showed three cycles;the lacustrine facies onshore was relatively developed in Mesozoic and Cenozoic;the sabkha was mainly developed in the Devonian,Permian and Triassic.The Cretaceous is the most important source rock layers in the world,followed by the Jurassic and Paleogene source rocks;the clastic reservoirs have more oil and gas than the carbonate reservoirs;the basins with shale caprocks have the widest distribution,the most abundant reserves of oil and gas,and the evaporite caprocks have the strongest sealing capacity,which can seal some huge oil and gas fields.展开更多
The study of each part of petroleum system is necessary.However,recently,petroleum geologists focused their attention on the study of source rock, migration and accumulation with use of different geochemical methods.O...The study of each part of petroleum system is necessary.However,recently,petroleum geologists focused their attention on the study of source rock, migration and accumulation with use of different geochemical methods.Of these,carbon isotope and biomarkers or chemical fossils are new scopes in petroleum geology especially in correlation.The member 1 of Gachsaran formation can be divided into 6 keybeds,among them the B keybed is展开更多
Marine strata in the Jianghan Plain area are widely distributed with a total depth of more than 8,000 m from the Upper Sinian to the Middle Triassic. Six reservoir caprock units, named Z-C2, C2-O, S, D--C, P and T1, c...Marine strata in the Jianghan Plain area are widely distributed with a total depth of more than 8,000 m from the Upper Sinian to the Middle Triassic. Six reservoir caprock units, named Z-C2, C2-O, S, D--C, P and T1, can be identified with each epoch. The geology, stratigraphy, drilling, oil testing and other basic data as well as the measured inclusion and strontium isotope data in the study area are used in the analysis of the formation and evolution process of marine petroliferous reservoirs in the Jianghan Plain area. This study aims to provide a scientific basis for the further exploration of hydrocarbons in the Jianghan Plain and reduce the risks by analyzing the key factors for hydrocarbon accumulation in the marine strata. Our findings show that in the Lower Palaeozoic hydrocarbon reservoir, oil/gas migration and accumulation chiefly occurred in the early period of the Early Yanshanian, and the hydrocarbon reservoir was destroyed in the middle-late period of the Early Yanshanian. In the Lower Triassic-Carboniferous hydrocarbon reservoir, oil/gas migration and accumulation chiefly occurred in the Early Yanshanian, and the hydrocarbon reservoir suffered destruction from the Late Yanshanian to the Early Himalayanian. The preservation conditions of the marine strata in the Jianghan Plain area have been improved since the Late Himalayanian. However, because all source beds have missed the oil/gas generation fastigium and lost the capacity to generate secondary hydrocarbon, no reaccumulation of hydrocarbons can be detected in the study area＇s marine strata. No industrially exploitable oil/gas reservoir has been discovered in the marine strata of Jianghan Plain area since exploration began in 1958. This study confirms that petroliferous reservoirs in the marine strata have been completely destroyed, and that poor preservation conditions are the primary factor leading to unsuccessful hydrocarbon exploration. It is safely concluded that hydrocarbon exploration in the marine strata of the study area is quite risky.展开更多
The surface karst of the Bakony Region is described. VES measurements were applied to study the cover and the morphology of the bedrock. A karstmorphological mapping was also performed. A relation was established betw...The surface karst of the Bakony Region is described. VES measurements were applied to study the cover and the morphology of the bedrock. A karstmorphological mapping was also performed. A relation was established between the karst types and block types in the mountains. The karstification of the mountains was affected by the block structure of the mountains, the mounds of the uneven bedrock, the presence of superficial deposits and their young denudation. As a result of the above mentioned facts, the karst of the mountains is varied. Soil-covered karst is wide spread in the mountains, but the specific features of this type (solution dolines) only occur on threshold surfaces at the margin of the mountains and on dolomite. The concealed karst was mainly formed on horsts elevated to summit position, but it can also be found on threshold surfaces and on horsts in summit position. Its features are subsidence dolines and depressions of superficial deposit. Cryptokarst and buried karst can be created by gravelly cover or basalt. Where the cover is gravel, epigenetic valleys develop with opened-up phreatic cavities. Where the cover is basalt, ponors develop at its margin, while inside, where the basalt thins out, caprock dolines are formed.展开更多
In the South Yellow Sea Basin,Mesozoic-Paleozoic marine strata are generally well developed with large thickness,and they are characterized by multi-source and multi-stage hydrocarbon accumulation,providing a material...In the South Yellow Sea Basin,Mesozoic-Paleozoic marine strata are generally well developed with large thickness,and they are characterized by multi-source and multi-stage hydrocarbon accumulation,providing a material basis for the formation of large-scale oil and gas fields.However,no substantial breakthrough has been made in this area.Based on previous research results,the complex tectonic pattern of this superimposed basin was formed by multi-stage tectonic movements and the favorable static conditions for hydrocarbon preservation were reworked or destroyed by later superimposition.Therefore,hydrocarbon preservation conditions are the key factors for restricting the breakthrough of marine oil and gas exploration in this area.In this paper,hydrocarbon preservation conditions of marine strata in the South Yellow Sea Basin were comprehensively analyzed from many aspects,such as tectonic movement,source conditions,caprock characteristics,magmatic activities,and hydrogeological and hydrogeochemical characteristics.It is indicated that the complex tectonic pattern of the South Yellow Sea Basin is resulted from tectonic events in multiple stages,and the development and evolution of regional source rocks are mainly controlled by two stages(i.e.,the stable evolution stage of Mesozoic-Paleozoic marine basin and the Mesozoic-Cenozoic tectonic pattern transformation and basin formation stage),so the characteristics of differential oil and gas preservation are presented.Besides,better marine hydrocarbon preservation preconditions in this area are weaker tectonic reworking,development of high-quality thick source rocks,good vertical sealing capacity of caprocks,weaker magmatic activity and confined hydrogeological conditions.It is concluded that the Laoshan Uplift in the central part of the South Yellow Sea Basin is structurally stable with weaker faulting and magmatic activities,so it is better in oil and gas preservation conditions.Besides,several large-scale structural traps with good petroleum geological conditions and complete source-reservoir-caprock assemblages are developed in this area.Therefore,this area is the most promising region for Paleozoic marine oil and gas exploration in this basin.展开更多
The concentration of CO_(2)in the global atmosphere,which is increasingly annually with continued industrial development,affects both the global climate and the ecological environment.To control the concentration of a...The concentration of CO_(2)in the global atmosphere,which is increasingly annually with continued industrial development,affects both the global climate and the ecological environment.To control the concentration of atmospheric CO_(2),various methods of carbon capture and sequestration have been proposed and continue to be developed.Among them,CO_(2)sequestration in saline aquifers has potential for effective high-capacity carbon storage.This work reviews both the research status of structural,residual,solubility,and mineral CO_(2)sequestration in saline aquifers,and the research progress associated with the integrity of cement sheaths and caprocks.The findings indicate that structural sequestration research must comprehensively consider the influence of various factors,and that the capacity of structural sequestration must be evaluated based on the actual geological conditions of the saline aquifer,caprock properties,and CO_(2)injection rate.The heterogeneity of the caprock and dynamic changes of CO_(2)concentration are not considered in current simulations of the effect of chemical interaction between CO_(2)-rich brine and the caprock.Residual sequestration and solubility sequestration are mutually interactive;therefore,exploration of the residual sequestration mechanism must consider the impact of solubility sequestration.Models for simulation of CO_(2)solubility sequestration in an entire saline aquifer should be developed to reservoir scale and must consider reservoir heterogeneity.展开更多
基金funded by the National Natural Science Foundation of China(Grant No.42172147)PetroChina Major Science and Technology Project(Grant No.ZD2019-183-002).
文摘Gypsum caprocks'sealing ability is affected by temperature-pressure coupling.Due to the limitations of experimental conditions,there is still a lack of triaxial stress-strain experiments that simultaneously consider changes in temperature and pressure conditions,which limits the accuracy of the comprehensive evaluation of the brittle plastic evolution and sealing ability of gypsum rocks using temperature pressure coupling.Triaxial stress-strain tests were utilized to investigate the differences in the evolution of the confinement capacity of gypsum rocks under coupled temperaturepressure action and isothermal-variable pressure action on the basis of sample feasibility analysis.According to research,the gypsum rock's peak and residual strengths decrease under simultaneous increases in temperature and pressure over isothermal pressurization experimental conditions,and it becomes more ductile.This reduces the amount of time it takes for the rock to transition from brittle to plastic.When temperature is taken into account,both the brittle–plastic transformation's depth limit and the lithological transformation of gypsum rocks become shallower,and the evolution of gypsum rocks under variable temperature and pressure conditions is more complicated than that under isothermal pressurization.The sealing ability under the temperature-pressure coupling is more in line with the actual geological context when the application results of the Well#ZS5 are compared.This provides a theoretical basis for precisely determining the process of hydrocarbon accumulation and explains why the early hydrocarbon were not well preserved.
基金supported by the National Key R&D Program of China grant(2017YFC0603105).
文摘The Meso-Neoproterozoic is a new play in the Ordos Basin.A deeper understanding about the dynamic relationship between the caprocks and the source rocks is needed.Based on the comprehensive analysis of hydrocarbon source development characteristics of the Meso-Neoproterozoic and its overlying strata,as well as the formation contact relationships,lithology characteristics and exploratory drilling data,it is recognized that the Meso-Neoproterozoic contains two types of petroleum accumulation assemblage,that is,the“self-sourced indigenous”and“upper source rock-lower reservoir”assemblages.The former is mainly controlled by the development and distribution of source rocks of the Changcheng System,with the Lower Cambrian shale sequence as its caprock.The later is controlled by the superposition between the Meso-Neoproterozoic and its overlying source rocks and this assemblage is mainly distributed in Hangjinqi and Pingliang areas with the Carboniferous-Permian shale sequence as its caprock.The dynamic evaluation on the displacement pressure serves to reconstruct the displacement pressure history of the caprock.The results show that the shale sequence of the Cambrian Maozhuang Formation in well XY 1 in the southern Ordos Basin has possibly acquired the ability of sealing natural gas since the early of Late Triassic.Its displacement pressure increased rapidly up to 20 MPa during the Late Triassic-Jurassic and keeps at 9.2 MPa at present,indicating fair sealing ability.The Carboniferous-Permian caprocks in Hangjinqi area could have acquired the ability to seal natural gas in the Late Jurassic-Early Cretaceous,and the present-day displacement pressure is 9e12 MPa,indicating good sealing ability.The upper Paleozoic caprock in Pingliang area has been able to seal natural gas since the Early Jurassic,with a maximum displacement pressure of 23 MPa during the Cretaceous period and a current value of 17 e20 MPa,indicative of strong ability to seal natural gas.The sealing ability of caprocks of both the“selfsourced indigenous”and“upper source rock-lower reservoir”assemblages has come into being earlier than or at least no later than the peak gas generation of the source rocks and therefore the caprocks are dynamically effective in geohistory.The Meso-Neoproterozoic reservoirs in the Ordos Basin are well preserved and probabally of better potential for exploration in terms of the caprock-source rock combination.
文摘The caprock is one of the key factors for a reservoir, especially for a gas reservoir. Whether the caprocks can block off the gas is of significance for the accumulation and preservation of the gas reservoir. In this paper, we use the Amplitude versus offset （AVO） seismic technique to determine the lateral extension of the hydrocarbon concentration sealing caprocks. The essence of this technique is to detect the variations of the reservoir bed physical properties by monitoring the variations of the reflection coefficient of seismic waves upon the interfaces between different lithologies. Generally it is used to indicate hydrocarbon directly. For the hydrocarbon concentration sealing caprocks, the change of hydrocarbon concentration may cause the change of physical properties of the caprocks. Therefore it is possible to evaluate the hydrocarbon concentration sealing ability of the caprocks by AVO. This paper presents a case study using AVO to determine the lateral extension of the hydrocarbon concentration sealing caprocks. The result shows that this method is helpful for the exploration of the region.
基金supported by the Special and Significant Project of National Research Council of Science and Technology"Evaluation of Hydrocarbon Accumulation,Distribution Law and Favorable Areas in the Foreland Thrust Belt and Complex Structure Area"(No.:2016ZX05003-002).
文摘Super-large natural gasfields have been discovered in the deep and ultra-deep layers of onshore and offshore petroliferous basins in China since the beginning of the 21st century,and the geological conditions for the formation of these gasfields and their development laws have already been discussed in a large number of literatures,but the relationship between over pressure and the formation of this kind of gasfields is still less researched.In this regard,this paperfirstly analyzed the gas reservoir development law,sealing conditions and over pressure char-acteristics of deep and ultra-deep super-large gasfields.Then,the formation mechanisms of deep and ultra-deep over pressure caprocks were investigated and the development law of deep and ultra-deep super-large gasfields and their relationship with over pressure caprocks were discussed.Finally,the favorable areas for the next exploration of deep and ultra-deep natural gas were pointed out.And the following research results were obtained.First,the formation of deep and ultra-deep super-large gasfields is closely related to the development of over pressure caprocks.Over pressure caprock is a necessary condition for the formation of deep and ultra-deep super-large gasfields,and there are three over pressure formation mechanisms,including pressure seal of salt-gypsum layer,pressure seal of residual uplift and pressure seal of hydrocarbon-generating pressurization.Second,as for deep and ultra-deep over pressure caprocks and super-large gasfields,there are four reservoirecaprock assemblage modes under different pressure environments,i.e.,over pressure salt-gypsum seal and over pressure super-large gasfield(Type I),internal over pressure compartment and over pressure super-large gasfield(Type II),high-pressure argillaceous shale seal at the bottom of over pressure compartment and normal-pressure super-larger gasfield(Type III),and over pressure source rock seal and normal-pressure super-larger gasfield(Type IV).In conclusion,there are Type I super-large gasfields in the Kuqa Depression of the Tarim Basin,types II and III in the Junggar Basin,types IeIV in the Sichuan Basin and Type IV in the Bohai Bay Basin.
基金National Natural Science Foundation of China(52074224)Key Research and Development Program of Shaanxi Province(2023-YBGY-312).
文摘In the process of oil and gas production,reservoir pressure depletion leads to changes in pore pressure and in-situ stress in caprock,which may reactivate closed faults in caprock,break the sealing of caprock,and make depleted oil and gas reservoirs unsuitable for gas storage.In order to effectively evaluate the sealing of faults in caprock above depleted reservoir and provide a basis for a reasonable selection of injection time and location for gas storage,this paper comprehensively considers fault slip potential(FSP)and fault tensile potential(FTP),and establishes a fault sealing evaluation model in caprock above depleted reservoir.The influences of distance of fault from reservoir top,reservoir pressure depletion degree,cap mechanical property,fault occurrence,fault frictional property and in-situ stress anisotropy in caprock on different types of FSP and FTP are analyzed.The results show that for normal faults,reverse faults,and strike-slip faults,FTP increases with reservoir depletion and does not cause tensile failure,among which FTP is the smallest for normal faults.FSP is the key to controlling fault sealing in caprock above depleted reservoir.For reverse faults and strike-slip faults,in the early stage of reservoir depletion,the FsP is larger when the fault is farther away from the top of the reservoir,while normal faults are the opposite.When the normal fault is closer to the top of the reservoir,the cap poisson ratio is smaller,the Biot's coefficient is larger,the internal friction coefficient of the fault is smaller,the inherent shear strength of the fault is smaller,σH/σv is smaller,σh/σv is smaller,45°<β<75°,α=0° or α=180°,the FSP is larger with the reservoir depletion,and the shear failure of the fault is the most likely.At this time,the reservoir pressure should be strictly controlled not to be too small,so that it can be suitable for the construction of gas storage.Under other conditions,the possibility of shear failure of the caprock is less.For reverse faults and strike-slip faults,when is smaller,the FSP decreases first and then increases with reservoir depletion.Although the possibility of shear failure decreases in the initial stage of reservoir depletion,it increases in the later stage.The research results can provide a theoretical basis for the reconstruction of underground gas storage.
基金Supported by the CNPC Major Science and Technology Project(2023ZZ07).
文摘Based on the achievements and research advances in oil and gas exploration in the Persian Gulf Basin,this study analyzes the orderliness of oil and gas distribution and main controlling factors of hydrocarbon accumulation with reservoir-forming assemblage as the unit.In the Persian Gulf Basin,the hydrocarbon-generating centers of source rocks of different geological ages and the hydrocarbon rich zones migrate in a clockwise direction around the Ghawar Oilfield in the Central Arabian Subbasin.Horizontally,the overall distribution pattern is orderly,showing“oil in the west and gas in the east”,and“large oil and gas fields dense in the basin center and sparse at the basin edges”.Vertically,the extents of petroleum system compounding and sources mixing increase from west to east,the pattern of tectonic strength(weak in the west and strong in the east)forming the distribution characteristics of“gas rich in the Paleozoic,oil rich in the Mesozoic,and both oil and gas rich in the Cenozoic”.The large scale accumulation and orderly distribution of oil and gas in the Persian Gulf Basin are controlled by three factors:(1)Multiple sets of giant hydrocarbon kitchens provide a resource base for near-source reservoir-forming assemblages.The short-distance lateral migration determines the oil and gas enrichment in and around the distribution area of effective source rocks.(2)The anhydrite caprocks in the platform area are thin but have experienced weak late-stage tectonic activities.Their good sealing performance makes it difficult for oil and gas to migrate vertically to shallow layers through them.The thrust faults and high-angle fractures formed by intense tectonic activities of the Zagros Orogenic Belt connect multiple source-reservoir assemblages.However,the Neogene Gachsaran Formation gypsum-salt rocks are thick and highly plastic,generally with good sealing performance,so large-scale oil and gas accumulations are still formed beneath the salt;(3)Each set of reservoir-forming assemblages is well matched in time and space in terms of the development of source rocks and reservoir-caprock assemblages,the maturation and hydrocarbon generation of source rocks,and the formation of traps,thus resulting in abundant multi layer hydrocarbon accumulations.At present,the Persian Gulf Basin is still in the stage of structural trap exploration.The pre-salt prospective traps in effective hydrocarbon kitchens remain the first choice.The areas with significant changes in Mesozoic sedimentary facies have the conditions to form large scale lithologic oil and gas reservoirs.The deep Paleozoic conventional oil and gas reservoirs and the Lower Silurian Qusaiba Member shale gas have great exploration potential and are expected to become important reserve growth areas in the future.
基金supported as part of the Center for Mechanistic Control of Unconventional Formations(CMC-UF),an Energy Frontier Research Center funded by the U.S.Department of Energy,Of-fice of Science under DOE(BES)Award DE-SC0019165Stanford Nano Shared Facilities(SNSF)with support from NSF under award CMMI-1532224SNSF is additionally supported by the NSF as part of the National Nanotechnology Coordinated Infrastructure under award ECCS-1542152.
文摘Understanding the mechanical and transport behavior of thin(i.e.small aperture)cracks slipping under supercritical carbon dioxide(sc-CO_(2))conditions is essential to evaluate the integrity of sealing formations with buoyant sc-CO_(2)below and the success of waterless fracturing.The two major items of interest in this work are frictional strength and permeability change of the crack.We used a triaxial cell that permits in situ visualization to conduct and monitor slippage along the faces of narrow cracks subjected to triaxial stresses.Such cracks are analogs to small geological faults.We tested carbonate-rich,1-inch diameter Wolfcamp shale samples that are saw cut 30to vertical to create a thin crack.Friction coefficients ranged from about 0.6 to 0.8 consistent with expectations for brittle rocks.The sc-CO_(2)generally did not alter friction coefficient over the time scale of experiments.From a transport perspective,saturating cracks with sc-CO_(2)substantially decreased permeability of the crack by 26%e52%,while slip resulted in a variety of permeability responses.Overall,the combined impact of sc-CO_(2)saturation and slip reduced fault permeability for all tests.Our observations support the notion that the sealing capacity of some caprocks improves when saturated with sc-CO_(2)and that some slip of small fractures is not necessarily detrimental to caprock integrity.
基金Project supported by National Major Oil and Gas Project(Grant No.2011ZX05003)CNPC Technological Development Project(Grant No.2014B-04)。
文摘Under the joint action of gypsum-salt rocks and faults,fluid evolution process is complicated in the northern Tuzimazha,Kuqa Depression,Tarim Basin.In the past,however,the oil and gas distribution rules in this area were less studied,so the related understanding was insufficient.In this paper,the reservoirs in Well Block Tubei 1 were analyzed by means of fluid inclusion and quantitative grain fluorescence(QGF)techniques.Based on tectonic evolution history,burial history,thermal history and hydrocarbon generation history,the paleofluid evolution process in this area was reproduced.It is shown that the well block experienced hydrocarbon charge in two periods.The first period is the earlyemiddle stage(16-9 Ma)of Miocene Kangcun Fm(N_(1-2)k),when it was charged with oil,with the corresponding characteristics of yellow and whiteeyellow fluid inclusion fluorescence and the QGF Index higher than 4,indicating that there were paleo-oil reservoirs at the early stage of the reservoirs.And at the late stage,the fluids that were accumulated at the early stage escaped because the gypsum-salt rocks were cut by faults,and bitumen remained in the reservoirs.It is also the evidence for the escaping of the early charged oil that the total scanning fluorescence(TSF)of the hydrocarbon adsorbed to the surface of the current reservoirs is generally unimodal.The second period is the late stage(about 3 Ma)of Pliocene Kuqa Fm(N_(2)k),when the natural gas and light oil charging occurred.Correspondingly,there are two inclusions,i.e.black gaseous hydrocarbon inclusion and blue fluorescence inclusion located along the edge of the quartz grains.At this stage,the gypsum-salt caprocks deepened and their sealing capacity was recovered due to a strong plastic flow.Moreover,the trap was uplifted violently under the effect of Himalaya orogeny,and a large amount of natural gas and a little light oil were accumulated.
基金the National Natural Science Foundation of China(Grant No.41274111)the Shenhua Group(Grant No.CSCLC-03-JS-2014-08)the National Department Public Benefit Research Foundation of MLR,China(Grant No.201211063-4-1)
文摘Carbon dioxide(CO2) capture and storage(CCS) is considered widely as one of promising options for CO2emissions reduction,especially for those countries with coal-dominant energy mix like China.Injecting and storing a huge volume of CO2in deep formations are likely to cause a series of geomechanical issues,including ground surface uplift,damage of caprock integrity,and fault reactivation.The Shenhua CCS demonstration project in Ordos Basin,China,is the first and the largest full-chain saline aquifer storage project of CO2in Asia.The injection started in 2010 and ended in 2015.during which totally 0.3 million tonnes(Mt) CO2was injected.The project is unique in which CO2was injected into 18 sandstone formations simultaneously and the overlying coal seams will be mined after the injection stopped in 2015.Hence,intense geomechanical studies and monitoring works have been conducted in recent years,including possible damage resulting from the temperature difference between injected CO2and formations,injection induced stress and deformation change,potential failure mode and safety factor,interaction between coal mining and CO2geological storage,determination of injection pressure limit,and surface monitoring by the interferometric synthetic aperture radar(InSAR) technology.In this paper,we first described the background and its geological conditions of the Shenhua CCS demonstration project.Then,we gave an introduction to the coupled thermo-hydro-mechano-chemical(THMC) processes in CO2geological storage,and mapped the key geomechanical issues into the THMC processes accordingly.Next,we proposed a generalized geomechanical research flowchart for CO2geological storage projects.After that,we addressed and discussed some typical geomechanical issues,including design of injection pressure limit.CO2injection induced near-field damage,and interaction between CO2geological storage and coal mining,in the Shenhua CCS demonstration project.Finally,we concluded some insights to this CCS project.
基金conducted with funding provided by the California Energy Commission under the contract PIR-16-027 for Research on Risk Management Framework for Underground Natural Gas infrastructure in California。
文摘In this study,we numerically investigate the influence of hysteretic stress path behavior on the seal integrity during underground gas storage operations in a depleted reservoir.Our study area is the Honor Rancho Underground Storage Facility in Los Angeles County(California,USA),which was converted into an underground gas storage facility in 1975 after 20 years of oil and gas production.In our simulations,the geomechanical behavior of the sand reservoir is modeled using two models:(1)a linear elastic model(non-hysteretic stress path)that does not take into consideration irreversible deformation,and(2)a plastic cap mechanical model which considers changes in rock elastic properties due to irreversible deformations caused by plastic reservoir compaction(hysteretic stress path).It shows that the irreversible compaction of the geological layer over geologic time and during the reservoir depletion can have important consequences on stress tensor orientation and magnitude.Ignoring depletion-induced irreversible compaction can lead to an over-estimation of the calculation of the maximum working reservoir pressure.Moreover,this irreversible compaction may bring the nearby faults closer to reactivation.However,regardless of the two models applied,the geomechanical analysis shows that for the estimated stress conditions applied in this study,the Honor Rancho Underground Storage Facility is being safely operated at pressures much below what would be required to compromise the seal integrity.
基金Project(41672121)supported by the National Natural Science Foundation of ChinaProject(D1438)supported by the China Geological Survey
文摘Maintaining caprock integrity is prerequisite for hydrocarbon accumulation. And gypsolyte caprock integrity is mainly affected by fracturing. Composition, damage behavior and mechanical strength of Paleocene Artashi Formation gypsolyte rock that seals significant petroleum in the Kashi Sag of Tarim Basin had been revealed via X-ray diffraction and triaxial compression test. The results indicate the Artashi Formation can be lithologically divided into the lower and upper lithologic members. The lower member comprises gypsum as the dominant mineral, and the cohesion and friction coefficient are 8 MPa and 0.315, respectively. Similarly, the upper lithologic member consists mainly of anhydrite at the cohesion and coefficient of internal friction values of 18 MPa and 0.296. Given that the failure criterion and brittle-ductile transition factors during burial, the sealing integrity of Artashi Formation can be quantized for seven different stages. The reservoirs at the bottom of Artashi Formation caprock buried from 2285 m to 3301 m are expected to be the most favorable exploration target in the Kashi Sag.
基金Project(2016YFC0801608) supported by the National Key Research and Development Plan,ChinaProject(51574148) supported by the National Natural Science Foundation of China
文摘Caprocks play an important role in the trapping of coalbed methane(CBM)reservoirs.To study the sealing capacities of caprocks,five samples with different lithologies of Neogene clayrock,Paleogene redbeds,Permian sandstone,Permian mudstone and Permian siltstone were collected and tested using experimental methods of microstructure observation,pore structure measurement and diffusion properties determination.Results indicate that with denser structures,lower porosities,much more developed micropores/transition pores and higher pore/throat ratios,mudstone and siltstone have the more ideal sealing capacities for CBM preservation when comparing to other kinds of caprocks;the methane diffusion coefficients of mudstone/siltstone are about 6 times higher than sandstone and almost 90 times higher than clayrock/redbeds.To further estimate the CBM escape through caprocks,a one-dimensional CBM diffusion model is derived.Modeling calculation result demonstrates that under the same thickness,the CBM sealing abilities of mudstone/siltstone are almost 100 times higher than those of clayrock/redbeds,and nearly 17 times higher than sandstone,which indicates that the coal seam below caprocks like clayrock,redbeds or sandstone may suffer stronger CBM diffusion effect than that below mudstone or siltstone.Such conclusion is verified by the case study from III3 District,Xutuan Colliery,where the coal seam capped by Paleogene redbeds has a much lower CBM content than that capped by the Permian strata like mudstone,siltstone and sandstone.
基金the financial support from the Creative Research and Development Group Program of Jiangsu Province(2014-27)the National Science Fund for Distinguished Young Scholars(Grant No.51125017)the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD2014)
文摘Caprock is a water-saturated formation with a sufficient entry capillary pressure to prevent the upward migration of a buoyant fluid. When the entry capillary pressure of caprock is smaller than the pressure exerted by the buoyant CO2plume, CO2gradually penetrates into the caprock. The CO2penetration depth into a caprock layer can be used to measure the caprock sealing efficiency and becomes the key issue to the assessment of caprock sealing efficiency. On the other hand, our numerical simulations on a caprock layer have revealed that a square root law for time and pore pressure exists for the CO2penetration into the caprock layer. Based on this finding, this study proposes a simple approach to estimate the CO2penetration depth into a caprock layer. This simple approach is initially developed to consider the speed of CO2invading front. It explicitly expresses the penetration depth with pressuring time, pressure difference and pressure magnitude. This simple approach is then used to fit three sets of experimental data and good fittings are observed regardless of pressures, strengths of porous media, and pore fluids(water,hydrochloric acid, and carbonic acid). Finally, theoretical analyses are conducted to explore those factors affecting CO2penetration depth. The effects of capillary pressure, gas sorption induced swelling, and fluid property are then included in this simple approach. These results show that this simple approach can predict the penetration depth into a caprock layer with sufficient accuracy, even if complicated interactions in penetration process are not explicitly expressed in this simple formula.
基金Supported by the China National Science and Technology Major Project(2011ZX05028-003,2016ZX05029-001).
文摘Based on the compilation and analysis of the lithofacies and paleogeography distribution maps at present and paleoplate locations during six key geological periods of the Mesozoic and Cenozoic,the lithofacies and paleogeography features and their development laws were expounded.Based on our previous research results on lithofacies and paleogeography from Precambrian to Paleozoic,we systematically studied the features and evolution laws of global lithofacies and paleogeography from the Precambrian and their effects on the formation of source rocks,reservoirs,cap rocks and the distribution of oil and gas worldwide.The results show that since Precambrian,the distribution areas of uplift erosion and terrestrial clastic deposition tended to increase gradually,and increased significantly during the period of continental growth.The scale of coastal and shallow marine facies area had three distinct cycles,namely,from Precambrian to Devonian,from Carboniferous to Triassic,and from Jurassic to Neogene.Correspondingly,the development of shallow carbonate platform also showed three cycles;the lacustrine facies onshore was relatively developed in Mesozoic and Cenozoic;the sabkha was mainly developed in the Devonian,Permian and Triassic.The Cretaceous is the most important source rock layers in the world,followed by the Jurassic and Paleogene source rocks;the clastic reservoirs have more oil and gas than the carbonate reservoirs;the basins with shale caprocks have the widest distribution,the most abundant reserves of oil and gas,and the evaporite caprocks have the strongest sealing capacity,which can seal some huge oil and gas fields.
文摘The study of each part of petroleum system is necessary.However,recently,petroleum geologists focused their attention on the study of source rock, migration and accumulation with use of different geochemical methods.Of these,carbon isotope and biomarkers or chemical fossils are new scopes in petroleum geology especially in correlation.The member 1 of Gachsaran formation can be divided into 6 keybeds,among them the B keybed is
基金the subsidization of a Major Project of Chinese National Programs for Fundamental Research and Development (973 Program, No. 2012CB214805)supported by the Chinese National Natural Science Foundation (No. 41372141)
文摘Marine strata in the Jianghan Plain area are widely distributed with a total depth of more than 8,000 m from the Upper Sinian to the Middle Triassic. Six reservoir caprock units, named Z-C2, C2-O, S, D--C, P and T1, can be identified with each epoch. The geology, stratigraphy, drilling, oil testing and other basic data as well as the measured inclusion and strontium isotope data in the study area are used in the analysis of the formation and evolution process of marine petroliferous reservoirs in the Jianghan Plain area. This study aims to provide a scientific basis for the further exploration of hydrocarbons in the Jianghan Plain and reduce the risks by analyzing the key factors for hydrocarbon accumulation in the marine strata. Our findings show that in the Lower Palaeozoic hydrocarbon reservoir, oil/gas migration and accumulation chiefly occurred in the early period of the Early Yanshanian, and the hydrocarbon reservoir was destroyed in the middle-late period of the Early Yanshanian. In the Lower Triassic-Carboniferous hydrocarbon reservoir, oil/gas migration and accumulation chiefly occurred in the Early Yanshanian, and the hydrocarbon reservoir suffered destruction from the Late Yanshanian to the Early Himalayanian. The preservation conditions of the marine strata in the Jianghan Plain area have been improved since the Late Himalayanian. However, because all source beds have missed the oil/gas generation fastigium and lost the capacity to generate secondary hydrocarbon, no reaccumulation of hydrocarbons can be detected in the study area＇s marine strata. No industrially exploitable oil/gas reservoir has been discovered in the marine strata of Jianghan Plain area since exploration began in 1958. This study confirms that petroliferous reservoirs in the marine strata have been completely destroyed, and that poor preservation conditions are the primary factor leading to unsuccessful hydrocarbon exploration. It is safely concluded that hydrocarbon exploration in the marine strata of the study area is quite risky.
文摘The surface karst of the Bakony Region is described. VES measurements were applied to study the cover and the morphology of the bedrock. A karstmorphological mapping was also performed. A relation was established between the karst types and block types in the mountains. The karstification of the mountains was affected by the block structure of the mountains, the mounds of the uneven bedrock, the presence of superficial deposits and their young denudation. As a result of the above mentioned facts, the karst of the mountains is varied. Soil-covered karst is wide spread in the mountains, but the specific features of this type (solution dolines) only occur on threshold surfaces at the margin of the mountains and on dolomite. The concealed karst was mainly formed on horsts elevated to summit position, but it can also be found on threshold surfaces and on horsts in summit position. Its features are subsidence dolines and depressions of superficial deposit. Cryptokarst and buried karst can be created by gravelly cover or basalt. Where the cover is gravel, epigenetic valleys develop with opened-up phreatic cavities. Where the cover is basalt, ponors develop at its margin, while inside, where the basalt thins out, caprock dolines are formed.
文摘In the South Yellow Sea Basin,Mesozoic-Paleozoic marine strata are generally well developed with large thickness,and they are characterized by multi-source and multi-stage hydrocarbon accumulation,providing a material basis for the formation of large-scale oil and gas fields.However,no substantial breakthrough has been made in this area.Based on previous research results,the complex tectonic pattern of this superimposed basin was formed by multi-stage tectonic movements and the favorable static conditions for hydrocarbon preservation were reworked or destroyed by later superimposition.Therefore,hydrocarbon preservation conditions are the key factors for restricting the breakthrough of marine oil and gas exploration in this area.In this paper,hydrocarbon preservation conditions of marine strata in the South Yellow Sea Basin were comprehensively analyzed from many aspects,such as tectonic movement,source conditions,caprock characteristics,magmatic activities,and hydrogeological and hydrogeochemical characteristics.It is indicated that the complex tectonic pattern of the South Yellow Sea Basin is resulted from tectonic events in multiple stages,and the development and evolution of regional source rocks are mainly controlled by two stages(i.e.,the stable evolution stage of Mesozoic-Paleozoic marine basin and the Mesozoic-Cenozoic tectonic pattern transformation and basin formation stage),so the characteristics of differential oil and gas preservation are presented.Besides,better marine hydrocarbon preservation preconditions in this area are weaker tectonic reworking,development of high-quality thick source rocks,good vertical sealing capacity of caprocks,weaker magmatic activity and confined hydrogeological conditions.It is concluded that the Laoshan Uplift in the central part of the South Yellow Sea Basin is structurally stable with weaker faulting and magmatic activities,so it is better in oil and gas preservation conditions.Besides,several large-scale structural traps with good petroleum geological conditions and complete source-reservoir-caprock assemblages are developed in this area.Therefore,this area is the most promising region for Paleozoic marine oil and gas exploration in this basin.
基金the financial support of the Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance,the National Natural Science Foundation of China(Grant no.U19A2043)the National Natural Science Foundation of China(Grant no.52174033).
文摘The concentration of CO_(2)in the global atmosphere,which is increasingly annually with continued industrial development,affects both the global climate and the ecological environment.To control the concentration of atmospheric CO_(2),various methods of carbon capture and sequestration have been proposed and continue to be developed.Among them,CO_(2)sequestration in saline aquifers has potential for effective high-capacity carbon storage.This work reviews both the research status of structural,residual,solubility,and mineral CO_(2)sequestration in saline aquifers,and the research progress associated with the integrity of cement sheaths and caprocks.The findings indicate that structural sequestration research must comprehensively consider the influence of various factors,and that the capacity of structural sequestration must be evaluated based on the actual geological conditions of the saline aquifer,caprock properties,and CO_(2)injection rate.The heterogeneity of the caprock and dynamic changes of CO_(2)concentration are not considered in current simulations of the effect of chemical interaction between CO_(2)-rich brine and the caprock.Residual sequestration and solubility sequestration are mutually interactive;therefore,exploration of the residual sequestration mechanism must consider the impact of solubility sequestration.Models for simulation of CO_(2)solubility sequestration in an entire saline aquifer should be developed to reservoir scale and must consider reservoir heterogeneity.
