Hydrogen,a genuinely clean energy,is a promising alternative to fossil fuels.Inspired by underground gas storage of methane,establishing underground hydrogen storage(UHS)in depleted oil and gas reservoirs has emerged ...Hydrogen,a genuinely clean energy,is a promising alternative to fossil fuels.Inspired by underground gas storage of methane,establishing underground hydrogen storage(UHS)in depleted oil and gas reservoirs has emerged as a significant research focus.Carbonate reservoirs,where widely-presented fractures can facilitate the high-speed injection and production of gases,are hence ideal candidates for building underground hydrogen storage facilities.During the cyclic injection and extraction processes of UHS,the formation is subjected to stress disturbances,leading to stress sensitivity.Understanding the stress sensitivity patterns of carbonate rocks is crucial for optimizing injection and production strategies.This study reconstructed three-dimensional digital models of fractured carbonate rocks from the L gas field using micro-CT scanning technology.Utilizing the finite element method,we investigated the microscopic permeability characteristics of carbonate rocks and analyzed the impact of stress loading direction and confining stress on stress sensitivity.The findings reveal that the stress loading direction significantly influences the stress sensitivity of fractured carbonate rocks.When a stress of 60 MPa is applied perpendicular to the fracture direction,the permeability reduction ratio can reach 17.32%.In contrast,when the same stress is applied parallel to the fracture direction,the permeability reduction ratio is only 4.82%.Furthermore,a simulation of UHS with cyclic injection and production of H2 in the target block was conducted.When both permeability and porosity stress sensitivity were considered,the working gas volume for UHS decreased by only 3.4%,demonstrating that fractured carbonate reservoirs are feasible candidates for constructing underground hydrogen storage.展开更多
With a more complex pore structure system compared with clastic rocks, carbonate rocks have not yet been well described by existing conventional rock physical models concerning the pore structure vagary as well as the...With a more complex pore structure system compared with clastic rocks, carbonate rocks have not yet been well described by existing conventional rock physical models concerning the pore structure vagary as well as the influence on elastic rock properties. We start with a discussion and an analysis about carbonate rock pore structure utilizing rock slices. Then, given appropriate assumptions, we introduce a new approach to modeling carbonate rocks and construct a pore structure algorithm to identify pore structure mutation with a basis on the Gassmann equation and the Eshelby-Walsh ellipsoid inclusion crack theory. Finally, we compute a single well＇s porosity using this new approach with full wave log data and make a comparison with the predicted result of traditional method and simultaneously invert for reservoir parameters. The study results reveal that the rock pore structure can significantly influence the rocks＇ elastic properties and the predicted porosity error of the new modeling approach is merely 0.74%. Therefore, the approach we introduce can effectively decrease the predicted error of reservoir parameters.展开更多
Fine-grained carbonate rocks, which extensively occur in the Eocene strata in the Shulu sag, Bohai Bay Basin, North China, represent an unconventional, fine-grained carbonate reservoir. However, previous studies have ...Fine-grained carbonate rocks, which extensively occur in the Eocene strata in the Shulu sag, Bohai Bay Basin, North China, represent an unconventional, fine-grained carbonate reservoir. However, previous studies have ignored the complexity of the lithofacies components and their formation mechanisms. Fine-grained carbonate rocks are typical reservoirs in which hydrocarbons form and gather. A better understanding of the nature of these rocks is extremely important for evaluating the quality of unconventional, fine-grained carbonate reservoirs. Various lithofacies components were discriminated in this study with a combination of petrographic observations and carbon isotope analyses. These finegrained carbonate rocks comprise terrigenous, biogenic and diagenetic materials. Terrigenous input and biologically induced precipitation are the main sources of the materials in the lake. Five lithofacies were identified based on the observations of sedimentary features（core and thin section） and mineralogical data：（1） varve-like laminated calcilutite,（2） graded laminated calcilutite,（3） interlaminated calcisiltitecalcilutite,（4） massive calcilutite, and（5） massive calcisiltite-calcarenite. Their origins were recorded by various lithofacies components, which are controlled by the interactions of physical, chemical and biological processes. This study indicated that the lithology of the bedrocks was the key factor controlling carbonate accumulation. The tectonics and climate can influence the weathering and types of lithofacies. Primary productivity controlled the precipitation of the endogenic calcite. These factors jointly determined the abundant fine-grained carbonate rocks that have accumulated in the Shulu sag.展开更多
We investigated the weathering-pedogenesis of carbonate rocks and its environmental effects in subtropical regions of China. The investigation demonstrated that the weathering- pedogenesis of carbonate rocks is the pr...We investigated the weathering-pedogenesis of carbonate rocks and its environmental effects in subtropical regions of China. The investigation demonstrated that the weathering- pedogenesis of carbonate rocks is the process of a joint action of corrosion and illuviation and metasomatism in subtropical region. It is characterized by multi-stage, multi-path and multi-style. With the persisting development of weathering-pedogenesis of carbonate rocks, metasomatic pedogenesis progressively became the main process of the weathering-pedogenesis and the dominant style of formation of minerals. And it proceeds through the whole process of evolution of the weathering-pedogenesis of carbonate rocks. The stage evolution of weathering-pedogenesis of carbonate rocks and the fractionation evolution of newly produced minerals are characterized by obvious vertically zoning structures and the rules of gradation of elements geochemical characteristics in the carbonate rocks weathering profiles. The geochemical process of weathering-pedogenesis of carbonate rocks can be divided into three geochemical evolution stages, i.e., the Ca, Mg-depletion and Si, Al-enrichment stage; the Fe, Mn enrichment stage and the Si-depletion and Al-enrichment stage in the subtropical regions. Consistent with the three geochemical evolution stages, the sequence of formation and evolution of minerals can be divided into the clay mineral stage; the Fe, Mn oxide and the gibbsite stage. The influence of weathering-pedogenesis of carbonate rocks on the chemical forms of heavy elements is mainly affected via newly produced components and minerals in the process of weathering-pedogenesis, e.g., iron oxide minerals and organic matters. The important mechanism for the mobilization, transport and pollution of F and As is affected the selective adsorption and desorption of F and As on the surface of iron oxide minerals in the subtropical karst zones, i.e., the selective adsorption and desorption on mineral surfaces of newly produced minerals in the process of weathering-pedogenesis control the geochemical behavior of elements on the Earth＇s surface and environmental quality in subtropical regions.展开更多
Objective The Ordovician–Silurian transitional period is a special time when the global paleo-environment changed greatly.It witnessed the first mass extinction as of Phanerozoic period and glaciations that occurred ...Objective The Ordovician–Silurian transitional period is a special time when the global paleo-environment changed greatly.It witnessed the first mass extinction as of Phanerozoic period and glaciations that occurred frequently at a large scale in a very short time,which has thus attracted much attention among geoscientists at home and abroad.展开更多
Objective The dissolution and precipitation of carbonate during burial diagenetic process controls the reservoir property in deep buried strata. The geological process related with it has become a research focus durin...Objective The dissolution and precipitation of carbonate during burial diagenetic process controls the reservoir property in deep buried strata. The geological process related with it has become a research focus during recent years. The most important dissolution fluids to carbonates are probably H2S and CO2 as byproducts of sulfate reduction in deep-buried setting with sulfate minerals, but carbonates are more soluble in relatively low temperature, which is the so-called retrograde solubility. Several geological processes can result in the decrease of temperature, including the upward migration of thermal fluids and tectonic uplift.展开更多
Rock typing is an important tool in evaluation and performance prediction of reservoirs.Different techniques such as flow zone indicator(FZI),FZI~*and Winland methods are used to categorize reservoir rocks into distin...Rock typing is an important tool in evaluation and performance prediction of reservoirs.Different techniques such as flow zone indicator(FZI),FZI~*and Winland methods are used to categorize reservoir rocks into distinct rock types.Generally,these methods are applied to petrophysical data that are measured at a pressure other than reservoir pressure.Since the pressure changes the pore structure of rock,the effect of overburden pressure on rock typing should be considered.In this study,porosity and permeability of 113 core samples were measured at five different pressures.To investigate the effect of pressure on determination of rock types,FZI,FZI~*and Winland methods were applied.Results indicated that although most of the samples remain in the same rock type when pressure changes,some of them show different trends.These are related to the mineralogy and changes in pore system of the samples due to pressure change.Additionally,the number of rock types increases with increasing pressure.Furthermore,the effect of overburden pressure on determination of rock types is more clearly observed in the Winland and FZI~*methods.Also,results revealed that a more precise reservoir dynamic simulation can be obtained by considering the reservoir rock typing process at reservoir conditions.展开更多
Thermochemical sulfate reduction （TSR） is the reaction between anhydrite and petroleum fluids at elevated temperatures to produce H2S and CO2. TSR has been studied in many sedimentary basins such as China＇s Sichuan...Thermochemical sulfate reduction （TSR） is the reaction between anhydrite and petroleum fluids at elevated temperatures to produce H2S and CO2. TSR has been studied in many sedimentary basins such as China＇s Sichuan and Tarim basins because it has a profound impact on the commercial viability of petroleum resources, with HzS typically being undesirable.展开更多
Nowadays, isotope environmental technique tends to be used as a reconnaissance tool , both qualitative and quantitative, to calculate the aquifer parameters particularly in carbonate rock aquifers. But, the hetero...Nowadays, isotope environmental technique tends to be used as a reconnaissance tool , both qualitative and quantitative, to calculate the aquifer parameters particularly in carbonate rock aquifers. But, the heterogeneous flow is still problematic when Lumped parameter Models are usually used to calculate the residence times and hydraulic parameters. However, Discrete State Compartment Model can provide a powerful model to heterogeneous medium. One such study was carried on in Dazha valley, where the environmental tritium was used as a tracer for determining hydrogeological parameters based on a discrete state compartment model展开更多
Deep marine carbonate rocks have become one of the key targets of onshore oil and gas exploration and development for reserves replacement in China.Further geological researches of such rocks may practically facilitat...Deep marine carbonate rocks have become one of the key targets of onshore oil and gas exploration and development for reserves replacement in China.Further geological researches of such rocks may practically facilitate the sustainable,steady and smooth development of the petroleum industry in the country.Therefore,through a deep investigation into the fundamental geological conditions of deep marine carbonate reservoirs,we found higher-than-expected resource potential therein,which may uncover large oil or gas fields.The findings were reflected in four aspects.Firstly,there are two kinds of hydrocarbon kitchens which were respectively formed by conventional source rocks and liquid hydrocarbons cracking that were detained in source rocks,and both of them can provide large-scale hydrocarbons.Secondly,as controlled by the bedding and interstratal karstification,as well as the burial and hydrothermal dolomitization,effective carbonate reservoirs may be extensively developed in the deep and ultra-deep strata.Thirdly,under the coupling action of progressive burial and annealing heating,some marine source rocks could form hydrocarbon accumulations spanning important tectonic phases,and large quantity of liquid hydrocarbons could be kept in late stage,contributing to rich oil and gas in such deep marine strata.Fourthly,large-scale uplifts were formed by the stacking of multi-episodic tectonism and oil and gas could be accumulated in three modes(i.e.,stratoid large-area reservoir-forming mode of karst reservoirs in the slope area of uplift,back-flow type large-area reservoir-forming mode of buried hill weathered crust karst reservoirs,and wide-range reservoir-forming mode of reef-shoal reservoirs);groups of stratigraphic and lithologic traps were widely developed in the areas of periclinal structures of paleohighs and continental margins.In conclusion,deep marine carbonate strata in China onshore contain the conditions for widely and intensively preserving hydrocarbons,so large oil or gas fields are expected.展开更多
Nigeria has an abundance of valuable solid minerals and rocks which can generate revenue for the government if they are fully exploited. Carbonate rock is one of such rocks that occur prominently in Igwe Igarra area o...Nigeria has an abundance of valuable solid minerals and rocks which can generate revenue for the government if they are fully exploited. Carbonate rock is one of such rocks that occur prominently in Igwe Igarra area of Edo State. Five (5) carbonate rock samples (Four marble and One Calcsilicate) were subjected to geochemical analyses. A petrographic study reveals that marble and calcsilicate contain calcite, quartz, microcline, plagioclase, biotite and opaque minerals. Geochemical data shows that carbonate rocks have variable geochemical characteristics: Igwe marble is highly Calcitic (96% - 98%) and very low in dolomite Mg(CO<sub>3</sub>). Calcsilicate rock is low in CaO (27.5%) and higher in marble. The Igwe marble is pure and contains fewer impurities compared to calcsilicate rock which makes it unideal for usage. Based on these characteristics the marble from Igwe is suitable as raw materials for the productions of glass, papers, beet sugar, aggregates, lubricants and fillers.展开更多
A number of geotechnical analyses were carried out on selected carbonate rock samples from eight sites located in Egypt. This analysis was to assess the suitability of these rocks for building construction aggregate. ...A number of geotechnical analyses were carried out on selected carbonate rock samples from eight sites located in Egypt. This analysis was to assess the suitability of these rocks for building construction aggregate. The analyses included properties of uniaxial compressive strength, tensile strength, porosity, water absorption, and dynamic fragmentation. The success of building construction depends to a large extent on the availability of raw materials at affordable prices. Raw materials commonly used in the building industry include sands, gravels, clays and clay-derived products. Despite the widespread occurrence of carbonate rocks throughout Egypt, the low premium placed on their direct application in the building sector may be explained in two ways: firstly, the lack of awareness of the potential uses of carbonate rocks in the building construction industry(beyond the production of asbestos, ceiling boards, roof sheets and Portland cement); and secondly, the aesthetic application of carbonate rocks in the building construction depends mainly on their physical attributes, a knowledge of which is generally restricted to within the confines of research laboratories and industries. Thus this paper addresses the physical and mechanical characteristics of some Egyptian carbonate rocks, evaluating them for their suitability as building construction aggregates.展开更多
In view of the characteristics of deep marine carbonate reservoirs in the Sichuan Basin,such as a deep burial depth(5000-8120 m),high temperatures(150℃-180℃),a large inclination toward wells,and large acid-rock reac...In view of the characteristics of deep marine carbonate reservoirs in the Sichuan Basin,such as a deep burial depth(5000-8120 m),high temperatures(150℃-180℃),a large inclination toward wells,and large acid-rock reaction rate,a high-temperature gelled acid and a preflush containing a self-generating acid that matched with the high-temperature gelled acid were developed.The results of laboratory evaluation showed that the viscosity of the high-temperature gelled acid at 180℃ was 30 mPa·s,with a corrosion rate lower than 70 g/m^(2)·h.The drag reduction and acid-rock reaction rates reached 64%-71% and 1.569×10^(-4) mol/cm^(2)·s respectively,demonstrating obvious retarding performance.In addition,the viscosity of the preflush containing a self-generating acid(after shearing at 160℃ for 1 h)remained at 200 mPa·s.Compared with a full injection of the high-temperature gelled acid,the acid-etched fracture conductivity after an alternate injection of the preflush containing self-generating and high-temperature gelled acids increased by more than 50%.Field application showed that the hightemperature gelled acid played a vital role in connecting fractures where as the preflush containing self-generating acid demonstrated an outstanding fracture-formation ability.After a three-stage alternate injection(a preflush containing self-generating and gelled acids),a remarkable stimulation effect was achieved for increase natural gas production.展开更多
The Cenozoic evolution history of Guizhou Province, which is located on the southeastern flank of the Qinghai-Tibet Plateau, is unclear because of the lack of sedimentation records. The red weathering crusts widesprea...The Cenozoic evolution history of Guizhou Province, which is located on the southeastern flank of the Qinghai-Tibet Plateau, is unclear because of the lack of sedimentation records. The red weathering crusts widespread on the Yunnan-Guizhou Plateau may bear critical information about their evolution history. This work firstly determined the ages of four red weathering crusts in eastern, central and northern Guizhou. The material used in fission track dating is well-crystallized quartz occurring in many in-situ weathering crusts of carbonate rocks. The results showed that the fission track ages of quartz vary over a wide range from 1 to 25 Ma in the four profiles, significantly younger than the ages of the Triassic and Cambrian parent rocks. In combination with the evolution history of the regional geology during the period from 25 to 1 Ma, the ages of quartz can exclude the possibility that the origin of quartz has nothing to do with primary clastic minerals in parent rocks, authigenesis during diagenesis and hydrothermal precipitation or roplacement by volcanic activities. It is deduced that the well-crystallized quartz was precipitated from Si-rich weathering fluids during the weathering process of carbonate rocks. The recorded ages of quartz from the four profiles are consistent with the episodes of the planation surfaces on the Qinghai-Tibet Plateau, the forming stages of red soil in the tropics of South China, the tectonically stable periods in Guizhou, and the ages of weathering in other parts of the world during the Cenozoic era. That is to say, the ages of authigenic quartz dated by the fission track method are well feasible and credible.展开更多
Owing to the low contents of their acid-insoluble components, carbonate rocks tend to decrease sharply in volume in association with the formation of weathering crust. The formation of a 1 m-thick weathering crust wou...Owing to the low contents of their acid-insoluble components, carbonate rocks tend to decrease sharply in volume in association with the formation of weathering crust. The formation of a 1 m-thick weathering crust would usually consume more than ten meters to several tens of meters of thickness of parent rocks. The knowledge of how to identify the homogeneity of parent rocks is essential to understand the formation mechanism of weathering crust in karst regions, especially that of thick-layered red weathering crust. In this work the grain-size analyses have demonstrated that the three profiles studied are the residual weathering crust of carbonate rocks and further showed that there objectively exists the heterogeneity of parent rocks in the three studied weathering crusts. The heterogeneity of parent rocks can also be reflected m geochemical parameters of major elements, just as the characteristics of frequency plot of grain-size distribution. Conservative trace element ratios Zr/Hf and Nb/Ta are proven to be unsuitable for tracing the heterogeneity of parent rocks of weathering crust, but its geochemical mechanism is unclear. The authors strongly suggest in this paper that the identification of the homogeneity of parent rocks of weathering crust in karst regions is of prime necessity.展开更多
Taking the mixed pre-salt carbonate rocks in the upper member of Eocene Xiaganchaigou Formation(E_(3)^(2))of Yingxi area in the Qaidam Basin as an example,the lithofacies and controlling mechanisms of reservoir format...Taking the mixed pre-salt carbonate rocks in the upper member of Eocene Xiaganchaigou Formation(E_(3)^(2))of Yingxi area in the Qaidam Basin as an example,the lithofacies and controlling mechanisms of reservoir formation are analyzed based on a large dataset of cores,thin sections and geochemical analysis.The reservoirs in E_(3)^(2)pre-salt layers have five types of lithofacies,of them,mixed granular calcareous dolostone,massive calcareous dolostone,plaque calcareous dolostone,and laminated dolomtic limestone are of sedimentary origin,and breccia calcareous dolostone is of tectonic origin.The four types of sedimentary lithofacies are divided into two types of saline sedimentary sequence lithofacies combinations,low-energy type in the sag area and low to high-energy type in the slope and paleo-uplift zone in the depression.Affected by high-frequency supply of continental clastic material,the two types of salty sedimentary sequences are mostly incomplete subtypes of lithofacies.Lithofacies have strong impacts on pre-salt reservoirs in E_(3)^(2):(1)Lithofacies type and sedimentary sequence controlled the formation and distribution of dolomite intercrystalline pores and dissolved pores during the pene-sedimentary period.(2)The structure of laminated dolomitic limestone controlled the formation of large-scale laminated fractures and high permeability channels during the diagenetic period.(3)Granular,massive,plaque calcareous dolostones have low mud content and strong brittleness,in the late tectonic reactivation period,the distribution of the three types of lithofacies,together with their distance from the top large slip faults and secondary faults,controlled the formation and distribution of high-efficiency fracture-cave brecciaed calcareous dolostone reservoirs.The above research led to the composite lithofacies-tectonic formation model of pre-salt reservoir in E_(3)^(2)of Yingxi area.The tempo-spatial distribution of tectonic breccia calcareous dolostone reservoirs,laminated dolomitic limestone shale oil reservoirs and granular,massive calcareous dolostone dissolved-intercrystalline pore tight reservoirs in various structural belts of the studied area have been figured out.These findings gave new insights into tight-shale oil accumulation theory in mixed carbonate successions from saline lacustrine basins,aiding in high efficient exploration and development of petroleum in the studied area.展开更多
The mechanism for development of littoral karst differs from that of inland karst, and the mixture corrosion effects are one of the most important factors that control the development of littoral karst. Through seven ...The mechanism for development of littoral karst differs from that of inland karst, and the mixture corrosion effects are one of the most important factors that control the development of littoral karst. Through seven groups of static experiments carried out in a closed CO2-H2O system, basic conclusions can be drawn as follows: (1) the basic law of corrosion process in a transitional zone of seawater-freshwater in littoral karst areas is identical with that in the fresh water, i.e., the lithologic characteristics and rock structure are the main factors which control the development of littoral karst; (2) the mixture corrosion rate of the carbonate rock in the above transitional zone is faster than that in fresh water or seawater; (3) the mechanism for development of carbonate rocks differs at various pressures of CO2 in a transitional zone in littoral karst areas.展开更多
Carbonate outcrops were taken from Ma 51 sub-member in the Lower Paleozoic in the Yan’an gas field to conduct true tri-axial hydraulic fracturing experiments with water, liquid CO_(2) and supercritical CO_(2). CT sca...Carbonate outcrops were taken from Ma 51 sub-member in the Lower Paleozoic in the Yan’an gas field to conduct true tri-axial hydraulic fracturing experiments with water, liquid CO_(2) and supercritical CO_(2). CT scan was applied to analyze initiation and propagation laws of hydraulic fractures in carbonate rocks. The experiments show that supercritical CO_(2) has low viscosity, strong diffusivity and large filtration during fracturing, which is more liable to increase pore pressure of rocks around wellbore and decrease breakdown pressure of carbonate rocks. However, it would cost much more volume of supercritical CO_(2) than water to fracture rocks since the former increases the wellbore pressure more slowly during fracturing. For carbonate rocks with few natural fractures, tensional fractures are generated by fracturing with water and liquid CO_(2), and these fractures propagate along the maximum horizontal principal stress direction;while fracturing with supercritical CO_(2) can form shear fractures, whose morphology is rarely influenced by horizontal stress difference. Besides, the angle between propagation direction of these shear fractures near the wellbore and the maximum horizontal principal stress is 45°, and the fractures would gradually turn to propagate along the maximum horizontal principal stress when they extend to a certain distance from the wellbore, leading to an increase of fracture tortuosity compared with the former. For carbonate rocks with well-developed natural fractures, fracturing with fresh water is conducive to connect natural fractures with low approaching angle and form stepped fractures with simple morphology. The key to forming complex fractures after fracturing carbonate rocks is to connect the natural fractures with high approaching angle. It is easier for liquid CO_(2) with low viscosity to realize such connection. Multi-directional fractures with relatively complex morphology would be formed after fracturing with liquid CO_(2).展开更多
This paper discusses the reservoir space in carbonate rocks in terms of types,combination features,distribution regularity,and controlling factors,based on core observations and tests of the North Truva Oilfield,Caspi...This paper discusses the reservoir space in carbonate rocks in terms of types,combination features,distribution regularity,and controlling factors,based on core observations and tests of the North Truva Oilfield,Caspian Basin.According to the reservoir space combinations,carbonate reservoirs can be divided into four types,i.e.,pore,fracture-pore,pore-cavity-fracture,and pore-cavity.Formation and distribution of these reservoirs is strongly controlled by deposition,diagenesis,and tectonism.In evaporated platform and restricted platform facies,the reservoirs are predominately affected by meteoric fresh water leaching in the supergene-para-syngenetic period and by uplifting and erosion in the late stage,making both platform facies contain all the above-mentioned four types of reservoirs,with various pores,such as dissolved cavities and dissolved fractures,or structural fractures occasionally in favorable structural locations.In open platform facies,the reservoirs deposited continuously in deeper water,in an environment of alternative high-energy shoals（where pore-fracture-type reservoirs are dominant） and low-energy shoals（where pore reservoirs are dominant）.展开更多
Many euhedral dolomite crystals and related pores are found in the microbial siliceous stromatolite dolomite and siliceous oolitic dolomite in the Fengjiawan Formation of the Mesoproterozoic Jixian System in the south...Many euhedral dolomite crystals and related pores are found in the microbial siliceous stromatolite dolomite and siliceous oolitic dolomite in the Fengjiawan Formation of the Mesoproterozoic Jixian System in the southern Ordos Basin.With the application of the microscope,scanning electron microscope,cathodoluminescence and in-situ trace element imaging,it can be seen that different from the phase I dolomite that was damaged by silicification,the intact euhedral phase II dolomite occurred through dolomitization after silicification,concentrated mainly in the organic-rich dark laminae of the stromatolite and the dark spheres and cores of the ooids.A considerable number of phase II dolomite crystals were dissolved,giving rise to mold pores and vugs which constituted the matrix pores and also the major pore space of the Fengjiawan Formation.The formation and dissolution of the dolomite were controlled by the microenvironment favorable,respectively,for carbonate precipitation and dissolution under the influence of microbial biological activities and related biochemical reactions.The driving force and material supply of dolomitization and dissolution were confined to the fabrics enriched with microorganisms,which are highly autochthonous.This mechanism may be a key factor for the development of Precambrian dolomite and related reservoirs,in the context of the domination of microbial rocks.展开更多
基金National Natural Science Foundation of China,52304048Ye Tian,China Postdoctoral Science Foundation,2022M722637,Ye Tian。
文摘Hydrogen,a genuinely clean energy,is a promising alternative to fossil fuels.Inspired by underground gas storage of methane,establishing underground hydrogen storage(UHS)in depleted oil and gas reservoirs has emerged as a significant research focus.Carbonate reservoirs,where widely-presented fractures can facilitate the high-speed injection and production of gases,are hence ideal candidates for building underground hydrogen storage facilities.During the cyclic injection and extraction processes of UHS,the formation is subjected to stress disturbances,leading to stress sensitivity.Understanding the stress sensitivity patterns of carbonate rocks is crucial for optimizing injection and production strategies.This study reconstructed three-dimensional digital models of fractured carbonate rocks from the L gas field using micro-CT scanning technology.Utilizing the finite element method,we investigated the microscopic permeability characteristics of carbonate rocks and analyzed the impact of stress loading direction and confining stress on stress sensitivity.The findings reveal that the stress loading direction significantly influences the stress sensitivity of fractured carbonate rocks.When a stress of 60 MPa is applied perpendicular to the fracture direction,the permeability reduction ratio can reach 17.32%.In contrast,when the same stress is applied parallel to the fracture direction,the permeability reduction ratio is only 4.82%.Furthermore,a simulation of UHS with cyclic injection and production of H2 in the target block was conducted.When both permeability and porosity stress sensitivity were considered,the working gas volume for UHS decreased by only 3.4%,demonstrating that fractured carbonate reservoirs are feasible candidates for constructing underground hydrogen storage.
基金sponsored by the National Nature Science Foundation of China (Grant No.40904034 and 40839905)
文摘With a more complex pore structure system compared with clastic rocks, carbonate rocks have not yet been well described by existing conventional rock physical models concerning the pore structure vagary as well as the influence on elastic rock properties. We start with a discussion and an analysis about carbonate rock pore structure utilizing rock slices. Then, given appropriate assumptions, we introduce a new approach to modeling carbonate rocks and construct a pore structure algorithm to identify pore structure mutation with a basis on the Gassmann equation and the Eshelby-Walsh ellipsoid inclusion crack theory. Finally, we compute a single well＇s porosity using this new approach with full wave log data and make a comparison with the predicted result of traditional method and simultaneously invert for reservoir parameters. The study results reveal that the rock pore structure can significantly influence the rocks＇ elastic properties and the predicted porosity error of the new modeling approach is merely 0.74%. Therefore, the approach we introduce can effectively decrease the predicted error of reservoir parameters.
基金provided by the National Major Research Program for Science and Technology of China (No. 2017ZX05009-002)the National Natural Science Fund (No. 41772090)
文摘Fine-grained carbonate rocks, which extensively occur in the Eocene strata in the Shulu sag, Bohai Bay Basin, North China, represent an unconventional, fine-grained carbonate reservoir. However, previous studies have ignored the complexity of the lithofacies components and their formation mechanisms. Fine-grained carbonate rocks are typical reservoirs in which hydrocarbons form and gather. A better understanding of the nature of these rocks is extremely important for evaluating the quality of unconventional, fine-grained carbonate reservoirs. Various lithofacies components were discriminated in this study with a combination of petrographic observations and carbon isotope analyses. These finegrained carbonate rocks comprise terrigenous, biogenic and diagenetic materials. Terrigenous input and biologically induced precipitation are the main sources of the materials in the lake. Five lithofacies were identified based on the observations of sedimentary features（core and thin section） and mineralogical data：（1） varve-like laminated calcilutite,（2） graded laminated calcilutite,（3） interlaminated calcisiltitecalcilutite,（4） massive calcilutite, and（5） massive calcisiltite-calcarenite. Their origins were recorded by various lithofacies components, which are controlled by the interactions of physical, chemical and biological processes. This study indicated that the lithology of the bedrocks was the key factor controlling carbonate accumulation. The tectonics and climate can influence the weathering and types of lithofacies. Primary productivity controlled the precipitation of the endogenic calcite. These factors jointly determined the abundant fine-grained carbonate rocks that have accumulated in the Shulu sag.
基金the Ministry of Science and Technology of China（Grant No.2006CB403200）National Natural Science Foundation of China（Grant No.49463011,49833002 and 49962002）+2 种基金the open foundation projects of the State Key Laboratory of Environmental Geochemistry（in the years of 1993 and 1995）Engineering Project for Cross-century Qualified Scientific and Technological Personnel of Guizhou Province （2000-2004）Science Foundation of Guizhou Province.
文摘We investigated the weathering-pedogenesis of carbonate rocks and its environmental effects in subtropical regions of China. The investigation demonstrated that the weathering- pedogenesis of carbonate rocks is the process of a joint action of corrosion and illuviation and metasomatism in subtropical region. It is characterized by multi-stage, multi-path and multi-style. With the persisting development of weathering-pedogenesis of carbonate rocks, metasomatic pedogenesis progressively became the main process of the weathering-pedogenesis and the dominant style of formation of minerals. And it proceeds through the whole process of evolution of the weathering-pedogenesis of carbonate rocks. The stage evolution of weathering-pedogenesis of carbonate rocks and the fractionation evolution of newly produced minerals are characterized by obvious vertically zoning structures and the rules of gradation of elements geochemical characteristics in the carbonate rocks weathering profiles. The geochemical process of weathering-pedogenesis of carbonate rocks can be divided into three geochemical evolution stages, i.e., the Ca, Mg-depletion and Si, Al-enrichment stage; the Fe, Mn enrichment stage and the Si-depletion and Al-enrichment stage in the subtropical regions. Consistent with the three geochemical evolution stages, the sequence of formation and evolution of minerals can be divided into the clay mineral stage; the Fe, Mn oxide and the gibbsite stage. The influence of weathering-pedogenesis of carbonate rocks on the chemical forms of heavy elements is mainly affected via newly produced components and minerals in the process of weathering-pedogenesis, e.g., iron oxide minerals and organic matters. The important mechanism for the mobilization, transport and pollution of F and As is affected the selective adsorption and desorption of F and As on the surface of iron oxide minerals in the subtropical karst zones, i.e., the selective adsorption and desorption on mineral surfaces of newly produced minerals in the process of weathering-pedogenesis control the geochemical behavior of elements on the Earth＇s surface and environmental quality in subtropical regions.
基金financially supported by the National Natural Science Foundation of China(grant No.4157020610)Science and Technology Program of Guizhou Province,China(No.[2017]1407)
文摘Objective The Ordovician–Silurian transitional period is a special time when the global paleo-environment changed greatly.It witnessed the first mass extinction as of Phanerozoic period and glaciations that occurred frequently at a large scale in a very short time,which has thus attracted much attention among geoscientists at home and abroad.
基金financially supported by the NationalScience Foundation of China(grants No.41402293 and 41502089)the China Geological Survey Program (grant No.121201021000150009)
文摘Objective The dissolution and precipitation of carbonate during burial diagenetic process controls the reservoir property in deep buried strata. The geological process related with it has become a research focus during recent years. The most important dissolution fluids to carbonates are probably H2S and CO2 as byproducts of sulfate reduction in deep-buried setting with sulfate minerals, but carbonates are more soluble in relatively low temperature, which is the so-called retrograde solubility. Several geological processes can result in the decrease of temperature, including the upward migration of thermal fluids and tectonic uplift.
文摘Rock typing is an important tool in evaluation and performance prediction of reservoirs.Different techniques such as flow zone indicator(FZI),FZI~*and Winland methods are used to categorize reservoir rocks into distinct rock types.Generally,these methods are applied to petrophysical data that are measured at a pressure other than reservoir pressure.Since the pressure changes the pore structure of rock,the effect of overburden pressure on rock typing should be considered.In this study,porosity and permeability of 113 core samples were measured at five different pressures.To investigate the effect of pressure on determination of rock types,FZI,FZI~*and Winland methods were applied.Results indicated that although most of the samples remain in the same rock type when pressure changes,some of them show different trends.These are related to the mineralogy and changes in pore system of the samples due to pressure change.Additionally,the number of rock types increases with increasing pressure.Furthermore,the effect of overburden pressure on determination of rock types is more clearly observed in the Winland and FZI~*methods.Also,results revealed that a more precise reservoir dynamic simulation can be obtained by considering the reservoir rock typing process at reservoir conditions.
基金supported by the National Natural Science Foundation of China(grant No.41530314)Geological Survey Program(grant No.1212291313016001)
文摘Thermochemical sulfate reduction （TSR） is the reaction between anhydrite and petroleum fluids at elevated temperatures to produce H2S and CO2. TSR has been studied in many sedimentary basins such as China＇s Sichuan and Tarim basins because it has a profound impact on the commercial viability of petroleum resources, with HzS typically being undesirable.
文摘Nowadays, isotope environmental technique tends to be used as a reconnaissance tool , both qualitative and quantitative, to calculate the aquifer parameters particularly in carbonate rock aquifers. But, the heterogeneous flow is still problematic when Lumped parameter Models are usually used to calculate the residence times and hydraulic parameters. However, Discrete State Compartment Model can provide a powerful model to heterogeneous medium. One such study was carried on in Dazha valley, where the environmental tritium was used as a tracer for determining hydrogeological parameters based on a discrete state compartment model
基金Special and Significant Project of National Science and Technology“Development of Large Oil/gas Fields and Coalbed Methane”(No.2011ZX05004-001).
文摘Deep marine carbonate rocks have become one of the key targets of onshore oil and gas exploration and development for reserves replacement in China.Further geological researches of such rocks may practically facilitate the sustainable,steady and smooth development of the petroleum industry in the country.Therefore,through a deep investigation into the fundamental geological conditions of deep marine carbonate reservoirs,we found higher-than-expected resource potential therein,which may uncover large oil or gas fields.The findings were reflected in four aspects.Firstly,there are two kinds of hydrocarbon kitchens which were respectively formed by conventional source rocks and liquid hydrocarbons cracking that were detained in source rocks,and both of them can provide large-scale hydrocarbons.Secondly,as controlled by the bedding and interstratal karstification,as well as the burial and hydrothermal dolomitization,effective carbonate reservoirs may be extensively developed in the deep and ultra-deep strata.Thirdly,under the coupling action of progressive burial and annealing heating,some marine source rocks could form hydrocarbon accumulations spanning important tectonic phases,and large quantity of liquid hydrocarbons could be kept in late stage,contributing to rich oil and gas in such deep marine strata.Fourthly,large-scale uplifts were formed by the stacking of multi-episodic tectonism and oil and gas could be accumulated in three modes(i.e.,stratoid large-area reservoir-forming mode of karst reservoirs in the slope area of uplift,back-flow type large-area reservoir-forming mode of buried hill weathered crust karst reservoirs,and wide-range reservoir-forming mode of reef-shoal reservoirs);groups of stratigraphic and lithologic traps were widely developed in the areas of periclinal structures of paleohighs and continental margins.In conclusion,deep marine carbonate strata in China onshore contain the conditions for widely and intensively preserving hydrocarbons,so large oil or gas fields are expected.
文摘Nigeria has an abundance of valuable solid minerals and rocks which can generate revenue for the government if they are fully exploited. Carbonate rock is one of such rocks that occur prominently in Igwe Igarra area of Edo State. Five (5) carbonate rock samples (Four marble and One Calcsilicate) were subjected to geochemical analyses. A petrographic study reveals that marble and calcsilicate contain calcite, quartz, microcline, plagioclase, biotite and opaque minerals. Geochemical data shows that carbonate rocks have variable geochemical characteristics: Igwe marble is highly Calcitic (96% - 98%) and very low in dolomite Mg(CO<sub>3</sub>). Calcsilicate rock is low in CaO (27.5%) and higher in marble. The Igwe marble is pure and contains fewer impurities compared to calcsilicate rock which makes it unideal for usage. Based on these characteristics the marble from Igwe is suitable as raw materials for the productions of glass, papers, beet sugar, aggregates, lubricants and fillers.
文摘A number of geotechnical analyses were carried out on selected carbonate rock samples from eight sites located in Egypt. This analysis was to assess the suitability of these rocks for building construction aggregate. The analyses included properties of uniaxial compressive strength, tensile strength, porosity, water absorption, and dynamic fragmentation. The success of building construction depends to a large extent on the availability of raw materials at affordable prices. Raw materials commonly used in the building industry include sands, gravels, clays and clay-derived products. Despite the widespread occurrence of carbonate rocks throughout Egypt, the low premium placed on their direct application in the building sector may be explained in two ways: firstly, the lack of awareness of the potential uses of carbonate rocks in the building construction industry(beyond the production of asbestos, ceiling boards, roof sheets and Portland cement); and secondly, the aesthetic application of carbonate rocks in the building construction depends mainly on their physical attributes, a knowledge of which is generally restricted to within the confines of research laboratories and industries. Thus this paper addresses the physical and mechanical characteristics of some Egyptian carbonate rocks, evaluating them for their suitability as building construction aggregates.
基金supported by the Science and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance(No.2020CX010501).
文摘In view of the characteristics of deep marine carbonate reservoirs in the Sichuan Basin,such as a deep burial depth(5000-8120 m),high temperatures(150℃-180℃),a large inclination toward wells,and large acid-rock reaction rate,a high-temperature gelled acid and a preflush containing a self-generating acid that matched with the high-temperature gelled acid were developed.The results of laboratory evaluation showed that the viscosity of the high-temperature gelled acid at 180℃ was 30 mPa·s,with a corrosion rate lower than 70 g/m^(2)·h.The drag reduction and acid-rock reaction rates reached 64%-71% and 1.569×10^(-4) mol/cm^(2)·s respectively,demonstrating obvious retarding performance.In addition,the viscosity of the preflush containing a self-generating acid(after shearing at 160℃ for 1 h)remained at 200 mPa·s.Compared with a full injection of the high-temperature gelled acid,the acid-etched fracture conductivity after an alternate injection of the preflush containing self-generating and high-temperature gelled acids increased by more than 50%.Field application showed that the hightemperature gelled acid played a vital role in connecting fractures where as the preflush containing self-generating acid demonstrated an outstanding fracture-formation ability.After a three-stage alternate injection(a preflush containing self-generating and gelled acids),a remarkable stimulation effect was achieved for increase natural gas production.
基金This work was granted by the National Natural Science Foundation of China(Nos.40371012 and 49833002).
文摘The Cenozoic evolution history of Guizhou Province, which is located on the southeastern flank of the Qinghai-Tibet Plateau, is unclear because of the lack of sedimentation records. The red weathering crusts widespread on the Yunnan-Guizhou Plateau may bear critical information about their evolution history. This work firstly determined the ages of four red weathering crusts in eastern, central and northern Guizhou. The material used in fission track dating is well-crystallized quartz occurring in many in-situ weathering crusts of carbonate rocks. The results showed that the fission track ages of quartz vary over a wide range from 1 to 25 Ma in the four profiles, significantly younger than the ages of the Triassic and Cambrian parent rocks. In combination with the evolution history of the regional geology during the period from 25 to 1 Ma, the ages of quartz can exclude the possibility that the origin of quartz has nothing to do with primary clastic minerals in parent rocks, authigenesis during diagenesis and hydrothermal precipitation or roplacement by volcanic activities. It is deduced that the well-crystallized quartz was precipitated from Si-rich weathering fluids during the weathering process of carbonate rocks. The recorded ages of quartz from the four profiles are consistent with the episodes of the planation surfaces on the Qinghai-Tibet Plateau, the forming stages of red soil in the tropics of South China, the tectonically stable periods in Guizhou, and the ages of weathering in other parts of the world during the Cenozoic era. That is to say, the ages of authigenic quartz dated by the fission track method are well feasible and credible.
基金This work was jointly supported by the Knowledge-Innovation Project of the Institute of Geochemistry,the“Westerm Light”Program sponsored by the Chinese Academy of Sciencesthe National Natural Science Foundation of China grants 49833002,40273015 and 40371012.
文摘Owing to the low contents of their acid-insoluble components, carbonate rocks tend to decrease sharply in volume in association with the formation of weathering crust. The formation of a 1 m-thick weathering crust would usually consume more than ten meters to several tens of meters of thickness of parent rocks. The knowledge of how to identify the homogeneity of parent rocks is essential to understand the formation mechanism of weathering crust in karst regions, especially that of thick-layered red weathering crust. In this work the grain-size analyses have demonstrated that the three profiles studied are the residual weathering crust of carbonate rocks and further showed that there objectively exists the heterogeneity of parent rocks in the three studied weathering crusts. The heterogeneity of parent rocks can also be reflected m geochemical parameters of major elements, just as the characteristics of frequency plot of grain-size distribution. Conservative trace element ratios Zr/Hf and Nb/Ta are proven to be unsuitable for tracing the heterogeneity of parent rocks of weathering crust, but its geochemical mechanism is unclear. The authors strongly suggest in this paper that the identification of the homogeneity of parent rocks of weathering crust in karst regions is of prime necessity.
基金Supported by the China National Science and Technology Major Project(2017ZX05001-002,2016ZX05046-006)Petro China Science and Technology Major Project(2019B-0309)。
文摘Taking the mixed pre-salt carbonate rocks in the upper member of Eocene Xiaganchaigou Formation(E_(3)^(2))of Yingxi area in the Qaidam Basin as an example,the lithofacies and controlling mechanisms of reservoir formation are analyzed based on a large dataset of cores,thin sections and geochemical analysis.The reservoirs in E_(3)^(2)pre-salt layers have five types of lithofacies,of them,mixed granular calcareous dolostone,massive calcareous dolostone,plaque calcareous dolostone,and laminated dolomtic limestone are of sedimentary origin,and breccia calcareous dolostone is of tectonic origin.The four types of sedimentary lithofacies are divided into two types of saline sedimentary sequence lithofacies combinations,low-energy type in the sag area and low to high-energy type in the slope and paleo-uplift zone in the depression.Affected by high-frequency supply of continental clastic material,the two types of salty sedimentary sequences are mostly incomplete subtypes of lithofacies.Lithofacies have strong impacts on pre-salt reservoirs in E_(3)^(2):(1)Lithofacies type and sedimentary sequence controlled the formation and distribution of dolomite intercrystalline pores and dissolved pores during the pene-sedimentary period.(2)The structure of laminated dolomitic limestone controlled the formation of large-scale laminated fractures and high permeability channels during the diagenetic period.(3)Granular,massive,plaque calcareous dolostones have low mud content and strong brittleness,in the late tectonic reactivation period,the distribution of the three types of lithofacies,together with their distance from the top large slip faults and secondary faults,controlled the formation and distribution of high-efficiency fracture-cave brecciaed calcareous dolostone reservoirs.The above research led to the composite lithofacies-tectonic formation model of pre-salt reservoir in E_(3)^(2)of Yingxi area.The tempo-spatial distribution of tectonic breccia calcareous dolostone reservoirs,laminated dolomitic limestone shale oil reservoirs and granular,massive calcareous dolostone dissolved-intercrystalline pore tight reservoirs in various structural belts of the studied area have been figured out.These findings gave new insights into tight-shale oil accumulation theory in mixed carbonate successions from saline lacustrine basins,aiding in high efficient exploration and development of petroleum in the studied area.
基金supported by the National Natural Science Foundation of China(grant 49832005)IGCP443 Magnesite and Talc Geological and Environmental Correlations.
文摘The mechanism for development of littoral karst differs from that of inland karst, and the mixture corrosion effects are one of the most important factors that control the development of littoral karst. Through seven groups of static experiments carried out in a closed CO2-H2O system, basic conclusions can be drawn as follows: (1) the basic law of corrosion process in a transitional zone of seawater-freshwater in littoral karst areas is identical with that in the fresh water, i.e., the lithologic characteristics and rock structure are the main factors which control the development of littoral karst; (2) the mixture corrosion rate of the carbonate rock in the above transitional zone is faster than that in fresh water or seawater; (3) the mechanism for development of carbonate rocks differs at various pressures of CO2 in a transitional zone in littoral karst areas.
基金Supported by National Natural Science Foundation of China Project(51704249)The Open Fund Project of the State Key Laboratory Oil and Gas Reservoir Geology and Exploitation(PLN2020-1)。
文摘Carbonate outcrops were taken from Ma 51 sub-member in the Lower Paleozoic in the Yan’an gas field to conduct true tri-axial hydraulic fracturing experiments with water, liquid CO_(2) and supercritical CO_(2). CT scan was applied to analyze initiation and propagation laws of hydraulic fractures in carbonate rocks. The experiments show that supercritical CO_(2) has low viscosity, strong diffusivity and large filtration during fracturing, which is more liable to increase pore pressure of rocks around wellbore and decrease breakdown pressure of carbonate rocks. However, it would cost much more volume of supercritical CO_(2) than water to fracture rocks since the former increases the wellbore pressure more slowly during fracturing. For carbonate rocks with few natural fractures, tensional fractures are generated by fracturing with water and liquid CO_(2), and these fractures propagate along the maximum horizontal principal stress direction;while fracturing with supercritical CO_(2) can form shear fractures, whose morphology is rarely influenced by horizontal stress difference. Besides, the angle between propagation direction of these shear fractures near the wellbore and the maximum horizontal principal stress is 45°, and the fractures would gradually turn to propagate along the maximum horizontal principal stress when they extend to a certain distance from the wellbore, leading to an increase of fracture tortuosity compared with the former. For carbonate rocks with well-developed natural fractures, fracturing with fresh water is conducive to connect natural fractures with low approaching angle and form stepped fractures with simple morphology. The key to forming complex fractures after fracturing carbonate rocks is to connect the natural fractures with high approaching angle. It is easier for liquid CO_(2) with low viscosity to realize such connection. Multi-directional fractures with relatively complex morphology would be formed after fracturing with liquid CO_(2).
基金supported by the National Major Science and Technology Project (No.2016ZX05030002)
文摘This paper discusses the reservoir space in carbonate rocks in terms of types,combination features,distribution regularity,and controlling factors,based on core observations and tests of the North Truva Oilfield,Caspian Basin.According to the reservoir space combinations,carbonate reservoirs can be divided into four types,i.e.,pore,fracture-pore,pore-cavity-fracture,and pore-cavity.Formation and distribution of these reservoirs is strongly controlled by deposition,diagenesis,and tectonism.In evaporated platform and restricted platform facies,the reservoirs are predominately affected by meteoric fresh water leaching in the supergene-para-syngenetic period and by uplifting and erosion in the late stage,making both platform facies contain all the above-mentioned four types of reservoirs,with various pores,such as dissolved cavities and dissolved fractures,or structural fractures occasionally in favorable structural locations.In open platform facies,the reservoirs deposited continuously in deeper water,in an environment of alternative high-energy shoals（where pore-fracture-type reservoirs are dominant） and low-energy shoals（where pore reservoirs are dominant）.
基金funded by the National Key Research&Development Plan‘The Formation and Distribution of Ultra-deep and Meso-Neoproterozoic Hydrocarbon Resources’(Grant No.2017YFC0603104)the CNPC upstream prospective and fundamental research program of‘Study on formation mechanism and effectiveness evaluation of a large-scale reservoir in the lower assemblage of the foreland thrust belt’(Grant No.2021DJ0302)。
文摘Many euhedral dolomite crystals and related pores are found in the microbial siliceous stromatolite dolomite and siliceous oolitic dolomite in the Fengjiawan Formation of the Mesoproterozoic Jixian System in the southern Ordos Basin.With the application of the microscope,scanning electron microscope,cathodoluminescence and in-situ trace element imaging,it can be seen that different from the phase I dolomite that was damaged by silicification,the intact euhedral phase II dolomite occurred through dolomitization after silicification,concentrated mainly in the organic-rich dark laminae of the stromatolite and the dark spheres and cores of the ooids.A considerable number of phase II dolomite crystals were dissolved,giving rise to mold pores and vugs which constituted the matrix pores and also the major pore space of the Fengjiawan Formation.The formation and dissolution of the dolomite were controlled by the microenvironment favorable,respectively,for carbonate precipitation and dissolution under the influence of microbial biological activities and related biochemical reactions.The driving force and material supply of dolomitization and dissolution were confined to the fabrics enriched with microorganisms,which are highly autochthonous.This mechanism may be a key factor for the development of Precambrian dolomite and related reservoirs,in the context of the domination of microbial rocks.
