Based on the study of the distribution of intra-platform shoals and the characteristics of dolomite reservoirs in the Middle Permian Qixia Formation in the Gaoshiti–Moxi area of the Sichuan Basin,SW China,the control...Based on the study of the distribution of intra-platform shoals and the characteristics of dolomite reservoirs in the Middle Permian Qixia Formation in the Gaoshiti–Moxi area of the Sichuan Basin,SW China,the controlling factors of reservoir development were analyzed,and the formation model of“intra-platform shoal thin-layer dolomite reservoir”was established.The Qixia Formation is a regressive cycle from bottom to top,in which the first member(Qi1 Member)develops low-energy open sea microfacies,and the second member(Qi2 Member)evolves into intra-platform shoal and inter-shoal sea with decreases in sea level.The intra-platform shoal is mainly distributed near the top of two secondary shallowing cycles of the Qi2 Member.The most important reservoir rock of the Qixia Formation is thin-layer fractured-vuggy dolomite,followed by vuggy dolomite.The semi-filled saddle dolomite is common in fracture-vug,and intercrystalline pores and residual dissolution pores combined with fractures to form the effective pore-fracture network.Based on the coupling analysis of sedimentary and diagenesis characteristics,the reservoir formation model of“pre-depositional micro-paleogeomorphology controlling shoal,sedimentary shoal controlling dolomite,penecontemporaneous dolomite benefiting preservation of pores,and late hydrothermal action effectively improving reservoir quality”was systematically established.The“first-order high zone”micro-paleogeomorphology before the deposition of the Qixia Formation controlled the development of large area of intra-platform shoals in Gaoshiti area during the deposition of the Qi2 Member.Shoal facies is the basic condition of early dolomitization,and the distribution range of intra-platform shoal and dolomite reservoir is highly consistent.The grain limestone of shoal facies is transformed by two stages of dolomitization.The penecontemporaneous dolomitization is conducive to the preservation of primary pores and secondary dissolved pores.The burial hydrothermal fluid enters the early dolomite body along the fractures associated with the Emeishan basalt event,makes it recrystallized into medium–coarse crystal dolomite.With the intercrystalline pores and the residual vugs after the hydrothermal dissolution along the fractures,the high-quality intra-platform shoal-type thin-layer dolomite reservoirs are formed.The establishment of this reservoir formation model can provide important theoretical support for the sustainable development of Permian gas reservoirs in the Sichuan Basin.展开更多
Given that dolomite is prone to strength degradation and susceptible to water-sand ingress under physicochemical actions,this study aims to investigate these phenomena,along with the sanding mechanism in the Xiaopu Tu...Given that dolomite is prone to strength degradation and susceptible to water-sand ingress under physicochemical actions,this study aims to investigate these phenomena,along with the sanding mechanism in the Xiaopu Tunnel of the Yunnan Dianzhong Water Diversion Project,using a combined experimental and modeling approach for systematic analysis.Triaxial cyclic loading-unloading tests were first conducted on dolomite samples soaked in sulfuric acid solutions of varying concentrations,with synchronous monitoring of their mechanical responses(e.g.,peak strength,deformation modulus,porosity changes).These tests,combined with observations of macroscopic morphology and mass changes during soaking,revealed a four-stage degradation pattern of dolomite in sulfuric acid:water absorption,dynamic equilibrium,dissolution,and stabilization.Key quantitative relationships established that as sulfuric acid concentration increased(from 0%to 15%),the peak strength of dolomite decreased significantly(by 7.49%to 24.99%),while porosity markedly increased(by 45%to 130%).Further post-failure analysis(fracture surface observation)and scanning electron microscopy(SEM)micro-characterization uncovered the intrinsic mechanisms of acid-induced damage:the acid solution not only promoted macroscopic crack propagation and increased fracture surface roughness but also triggered severe structural deterioration at the microscale,including enlarged crystal spacing,dissolution of gel-like substances,formation of intra-crystalline pores,weakened interparticle cementation,and development of macropores.The extent of this deterioration was positively correlated with acid concentration.Based on the experimentally revealed chemo-mechanical coupling damage mechanism between acid and rock,this study established,for the first time,a multi-scale predictive model capable of quantitatively correlating acid concentration,microstructural deterioration,and degradation of macroscopic mechanical properties.The development of this model not only deepens the quantitative understanding of the dolomite sanding mechanism but also provides a crucial theoretical tool for assessing surrounding rock stability and predicting risks in similar water diversion tunnel engineering.Addressing the specific risks of water and H^(+) erosion in the Xiaopu Tunnel,the research findings directly informed the engineering reinforcement strategy:concrete lining is recommended as the primary load-bearing structure,supplemented by surrounding rock surface protection measures,to effectively mitigate the acid-induced damage process and enhance the long-term stability of the surrounding rock.展开更多
Surface pretreatment can change the surface properties of minerals,placing them in either a favorable or an unfavorable state for flotation.To solve the separation problem associated with magnesite and dolomite,surfac...Surface pretreatment can change the surface properties of minerals,placing them in either a favorable or an unfavorable state for flotation.To solve the separation problem associated with magnesite and dolomite,surface pretreatment experiments with citric acid,tartaric acid,and tannic acid(TA)on magnesite and dolomite as well as flotation experiments on pretreated samples were performed in this study.Experimental results demonstrated that when citric acid and tartaric acid are used for surface pretreatment,the separation effect of magnesite and dolomite is poor.However,when TA is used,the separation effect of magnesite and dolomite improves.SEM and BET analysis indicated that surface pretreatment with TA changes the surface morphology of the two minerals,resulting in additional concave pores on the dolomite surface,and a significant increase in pore size and specific surface area.The adsorption quantity test and contact angle measurement demonstrated that after surface pretreatment with TA,the magnesite adsorption capacity on sodium oleate(NaOL)slightly decreases and the dolomite adsorption capacity on NaOL considerably decreases.XPS detection concluded that the surface pretreatment of TA on the magnesite surface mainly relies on physical adsorption with weak adsorption ability and poor ability to act on Mg sites.The TA surface pretreatment action on the dolomite surface is mainly through chemical adsorption,and it is strongly and selectively adsorbed on the Ca site of dolomite through O.Actual ore rough selection experiments reveal that TA pretreatment successfully removes dolomite from magnesite,resulting in a high-quality magnesite concentrate characterized by a MgO grade of 45.49%and a CaO grade of 0.75%.展开更多
To investigate the effects of water and cyclic loading on dolomite’s mechanical properties during deep mining,mechanical experiments on non-pressure water absorption and cyclic loading were conducted.The findings rev...To investigate the effects of water and cyclic loading on dolomite’s mechanical properties during deep mining,mechanical experiments on non-pressure water absorption and cyclic loading were conducted.The findings reveal that the elastic modulus and Poisson ratio of dolomite fluctuate with increasing water content.The mass of water absorption is positively correlated with time and the water absorption stage can be divided into three stages:accelerated,decelerated,and stabilized stages.During this process,the number of pores in dolomite increases,while the pore diameter initially decreases and then fluctuates.Microscopic analysis shows that the proportion of mesopores first increases and then decreases,while micropores exhibit the opposite trend,and the proportion of macropores fluctuates around 0%.A model diagram of structural evolution during water absorption has been developed.Additionally,the softening process of dolomite’s water absorption strength is categorized into three stages:a relatively stable stage,an accelerated softening stage dominated by mesopore water absorption,and a decelerated softening stage characterized by micropore water absorption.A uniaxial damage constitutive model for dolomite under water influence was established based on the Weibull distribution and Mohr-Coulomb strength criterion,and experimental validation indicates its strong applicability.展开更多
The widespread dolomite of the Sinian Dengying Formation in the Sichuan Basin(China)serves as one of the most important oil and gas reservoir rocks of the basin.Well WT1,as an exploration well,is recently drilled in t...The widespread dolomite of the Sinian Dengying Formation in the Sichuan Basin(China)serves as one of the most important oil and gas reservoir rocks of the basin.Well WT1,as an exploration well,is recently drilled in the Kaijiang County,northeastern Sichuan Basin(SW China),and it drills through the Dengying Formation dolomite at the depth interval of 7500–7580 m.In this study,samples are systematically collected from the cores of that interval,followed by new analyses of carbon-oxygen isotope,major elements,trace elements,rare earth elements(REEs)and EP-MA.The Dengying Formation dolomites of Well WT1 haveδ13C values of 0.37‰to 2.91‰andδ18O values of-5.72‰to-2.73‰,indicating that the dolomitization fluid is derived from contemporary seawater in the near-surface environment,rather than the burial environment.Based on the REE patterns of EPMA-based in-situ data,we recognized the seawater-sourced components,the mixedsourced components and the terrigenous-sourced components,indicating the marine origin of the dolomite with detrital contamination and diagenetic alteration.Moreover,high Al,Th,and Zr contents indicate significant detrital contamination derived from clay and quartz minerals,and high Sr/Ba and Sr/Cu ratios imply a relatively dry depositional environment with extremely high seawater salinity,intensive evaporation,and strong influences of terrigenous sediment.展开更多
[Objectives]To explore the methods for identifying pure honey.[Methods]Using 35 batches of Jiulongteng honey sourced from various production areas in Guangxi as the research subjects,this study investigated the chromo...[Objectives]To explore the methods for identifying pure honey.[Methods]Using 35 batches of Jiulongteng honey sourced from various production areas in Guangxi as the research subjects,this study investigated the chromogenic reactions of starch and dextrin,as well as the comparative study of thin-layer chromatography of oligosaccharides present in Jiulongteng honey.[Results]None of the 35 batches of Jiulongteng honey samples exhibited blue(indicating starch),green,or reddish-brown(indicating dextrin)coloration,suggesting that no adulterants such as artificially added starch,dextrin,or sugar were present in these samples.Furthermore,none of the 35 batches displayed additional spots below the corresponding positions of the control,indicating that the sugar composition was consistent with the oligosaccharide profile of natural honey.No components inconsistent with the oligosaccharide profile of natural honey were detected.Therefore,it can be concluded that the Jiulongteng honey samples in this experiment were pure and free from adulteration with starch,dextrin,or other sugar substances.[Conclusions]The method employed in this experiment is straightforward and quick to implement,effectively preventing adulterated honey from entering the market.It enhances the efficiency of quality control for Jiulongteng honey and promotes the healthy development of the Jiulongteng honey industry.展开更多
Lacustrine dolomite is paid increasing attention to uncover the diagenetic water condition of paleo-lake and“dolomite problem”.Here,a dolomite nodule from the Qingshankou Formation in the Songliao Basin was analyzed...Lacustrine dolomite is paid increasing attention to uncover the diagenetic water condition of paleo-lake and“dolomite problem”.Here,a dolomite nodule from the Qingshankou Formation in the Songliao Basin was analyzed to explore the salinity,alkalinity,and redox conditions of the diagenetic water.Multiple proxies,including bulk boron(B)content,B isotope composition(δ^(11)B_(bul)),boron to gallium weight ratio(B/Ga)and carbonate oxygen isotope composition(δ^(18)O_(carb)),were used to determine the diagenetic water to be brackish-fresh.Through numerical simulation,we calculated the B contents,δ^(11)B values and B/Ga in detritus(e.g.,clay,quartz and feldspar)and dolomite as two endmembers,confirming the intense interference of clay minerals onδ^(11)B_(bul).By using the fittedδ^(11)B of dolomite endmember(20.6‰),we calculated the p H value of the diagenetic water to be 8.2.The negativeδ^(11)B value of detritus endmember(-12.9‰)might be related to the terrestrial weathering.The indicative nature of strontium to barium weight ratio(Sr/Ba)was discussed to deny its applicability as a proxy of salinity in carbonate system.High Sr/Ba ratio in this dolomite nodule indicates a sulfate-poor water condition,consistent with the iron-manganese(Fe-Mn)reduction environments reflected by the Mn/Fe molar ratio.The positive carbonate carbon isotopes(δ^(13)C_(carb),4.5‰-9.4‰)indicate that methanogenesis dominated the formation of dolomite,coinciding with the weak sulfate reduction reaction in sulfate-poor water.The growth of dolomite nodule might be related to the microbial activities of methanogen and iron reducing bacteria,which had not only maintained the salinity,p H,and redox status of the diagenetic water,but also led to a ferricmethane transition zone(FMTZ).This research depicts a scenario about the diagenetic water environment of lacustrine dolomite formed in brackish-fresh water,which is different from that occurred in sulfate-rich condition.展开更多
The efficient recovery of fluorite is paid more and more attention with the increasing application especially in strategic emerging industries.In this study,acrylic acid-2-acrylamido-2-methylpropane sulfonic acid copo...The efficient recovery of fluorite is paid more and more attention with the increasing application especially in strategic emerging industries.In this study,acrylic acid-2-acrylamido-2-methylpropane sulfonic acid copolymer(AAAMPS)was first used as the depressant in fluorite flotation,and its effect on the flotation separation of fluorite and dolomite in sodium oleate(NaOL)system was investigated.The depression mechanism was analyzed by contact angle measurement,zeta potential test,FTIR and XPS analyses.The micro-flotation test results showed that dolomite can be inhibited in fluorite flotation system in the addition of 2 mg/L AA-AMPS and 20 mg/L NaOL at pH 10.The CaF_(2) grade increased from 49.85%in the artificial mixed mineral to 89.60%in the fluorite concentrate.The depression mechanism indicated that AA-AMPS could adsorb strongly on dolomite surface by the chelation with Ca and Mg active sites.Moreover,the further adsorption of NaOL on dolomite surface was prevented by the AA-AMPS adsorption,but that on fluorite surface was little affected,thereby increasing the difference in the hydrophobicity and floatability of the two minerals.展开更多
The Yingshan Formation of the Lower-Middle Ordovician in the Tarim Basin(NW China)was mainly deposited in a shallow platform,which was intensely bioturbated with burrows filled with both dolomites and calcites.This st...The Yingshan Formation of the Lower-Middle Ordovician in the Tarim Basin(NW China)was mainly deposited in a shallow platform,which was intensely bioturbated with burrows filled with both dolomites and calcites.This study aims to figure out the controls on the dolomitization of burrow infills and the effects on petroleum reservoir quality based on petrographic examination,fluid inclusion microthermometry,and isotopic(C-O-Sr)geochemical analyses.The differentiation of burrow-associated carbonates(dolomites and calcites)was likely controlled by the interactions of sea-level oscillations of variable orders and depositional environments.The burrow-associated dolomites(BADs)were precipitated in a relatively restricted(i.e.,lagoon)depositional environment during the lowstand of long-term sea level.In contrast,the burrow-associated calcites(BACs)were formed in a water circulation-improved lagoonal environment during the transgression of long-term sea level.Isotopic geochemical data indicate that the BADs in the Yingshan Formation were formed from slightly saline(i.e.,mesosaline to penesaline)seawater,whereas the BACs were precipitated from nearly normal seawater.In addition to the anoxic condition,the presence of marine-sourced organic matter and sulfate-reducing bacteria,and a sufficient supply of dolomitizing fluids enriched in magnesium ions(Mg^(2+))and their Mg^(2+)concentration may have played a critical role in the formation of BADs.In the more permeable and disturbed burrow sediments as a result of burrowing,penetrating fluids with higher salinities and higher Mg^(2+)concentration relative to seawater favored dolomite precipitation.The fluids with seawater-like Mg^(2+)concentration,however,would lead to calcite precipitation.The progressive dolomitization of these burrowed sediments could have propagated the dolomitizing fronts and extended into ambient limestones,leading to the development of extensive dolomites.This dolomitization process can improve the petrophysical properties(porosity and permeability)and the potential as hydrocarbon reservoirs during the emplacement of hydrocarbons from underlying source rocks of the Cambrian to Lower Ordovician.展开更多
Disintegrated dolomite slope and tunnel disasters occur frequently due to poor water stability of disintegrated dolomite,primarily in a form of seepage failure.For engineering purposes,it is critical to determine the ...Disintegrated dolomite slope and tunnel disasters occur frequently due to poor water stability of disintegrated dolomite,primarily in a form of seepage failure.For engineering purposes,it is critical to determine the seepage properties of disintegrated dolomite within the strata.However,conventional experimental methods are time-consuming and expensive and may not be effective in investigating seepage characteristics due to the heterogeneity of disintegrated dolomite.In this study,pore network model(PNM)was established by the computerized tomography(CT)scanning technology to characterize the pores.Meanwhile,the seepage and coefficient of permeability under different inlet stress conditions based on the accurate pore model were realized by linking the commercial image processing software Avizo with the commercial multi-physics modeling package Comsol.The results show that the porosities of severely and completely disintegrated dolomites are 29.17% and 45.37%,respectively.The grade of pore development increases with disintegration grade,which facilitates seepage failure.Severely and completely disintegrated dolomites have the coefficients of permeability of 9.67×10^(-7) m/s and 1.61×10^(-6) m/s,respectively.Under conventional conditions,severely and completely disintegrated dolomites undergo seepage failure above a pressure difference of 6×10^(3) Pa and 5×10^(3) Pa,respectively.These results are consistent with both in situ water pressure tests in the borehole and laboratory tests with the constant-head method,demonstrating that CT scanning is an effective method for observing fractures and pores in disintegrated dolomite for seepage evaluation.展开更多
The 10000-m ultradeep dolomite reservoir holds significant potential as a successor field for future oil and gas exploration in China's marine craton basin.However,major challenges such as the genesis of dolomite,...The 10000-m ultradeep dolomite reservoir holds significant potential as a successor field for future oil and gas exploration in China's marine craton basin.However,major challenges such as the genesis of dolomite,the formation time of high-quality reservoirs,and the preservation mechanism of reservoirs have always limited exploration decision-making.This research systematically elaborates on the genesis and reservoir-forming mechanisms of Sinian-Cambrian dolomite,discussing the ancient marine environment where microorganisms and dolomite develop,which controls the formation of large-scale Precambrian-Cambrian dolomite.The periodic changes inMg isotopes and sedimentary cycles show that the thick-layered dolomite is the result of different dolomitization processes superimposed on a spatiotemporal scale.Lattice defects and dolomite embryos can promote dolomitization.By simulating the dissolution of typical calcite and dolomite crystal faces in different solution systems and calculating their molecular weights,the essence of heterogeneous dissolution and pore formation on typical calcite and dolomite crystal faces was revealed,and the mechanism of dolomitization was also demonstrated.The properties of calcite and dolomite(104)/(110)grain boundaries and their dissolution mechanism in carbonate solution were revealed,showing the limiting factors of the dolomitization process and the preservation mechanism of deep buried dolomite reservoirs.The in situ laser U-Pb isotope dating technique has demonstrated the timing of dolomitization and pore formation in ancient carbonate rocks.This research also proposed that dolomitization occurred during the quasi-contemporaneous or shallow-burial periods within 50Ma after deposition and pores formed during the quasi-contemporaneous to the early diagenetic periods.And it was clear that the quasi-contemporaneous dolomitization was the key period for reservoir formation.The systematic characterization of the spatial distribution of the deepest dolomite reservoirs in multiple sets of the Sinian and the Cambrian in the Chinese craton basins provides an important basis for the distribution prediction of large-scale dolomite reservoirs.It clarifies the targets for oil and gas exploration at depths over 10000 m.The research on dolomite in this study will greatly promote China's ultradeep oil and gas exploration and lead the Chinese petroleum industry into a new era of 10000-m deep oil exploration.展开更多
This paper discusses the characteristics and formation mechanism of thin dolomite reservoirs in the lower submember of the second member of the Permian Maokou Formation(lower Mao 2 Member)in the Wusheng-Tongnan area o...This paper discusses the characteristics and formation mechanism of thin dolomite reservoirs in the lower submember of the second member of the Permian Maokou Formation(lower Mao 2 Member)in the Wusheng-Tongnan area of the Sichuan Basin,SW China,through comprehensive analysis of geological,geophysical and geochemical data.The reservoir rocks of the lower Mao 2 Member are dominated by porphyritic vuggy dolomite and calcareous dolomite or dolomitic limestone,which have typical karst characteristics of early diagenetic stage.The dolomites at the edge of the karst system and in the fillings have dissolved estuaries,and the dolomite breccia has micrite envelope and rim cement at the edge,indicating that dolomitization is earlier than the early diagenetic karstification.The shoal facies laminated dolomite is primarily formed by the seepage reflux dolomitization of moderate-salinity seawater.The key factors of reservoir formation are the bioclastic shoal deposition superimposed with seepgae reflux dolomitization and the karstification of early diagenetic stage,which are locally reformed by fractures and hydrothermal processes.The development of dolomite vuggy reservoir is closely related to the upward-shallowing sequence,and mainly occurs in the late highstand of the fourth-order cycle.Moreover,the size of dolomite is closely related to formation thickness,and it is concentrated in the formation thickness conversion area,followed by the thinner area.According to the understanding of insufficient accommodation space in the geomorphic highland and the migration of granular shoal to geomorphic lowland in the late highstand of the third-order cycle,it is proposed that the large-scale shoal-controlled dolomite reservoirs are distributed along structural highs and slopes,and the reservoir-forming model with shoal,dolomitization and karstification jointly controlled by the microgeomorphy and sea-level fluctuation in the sedimentary period is established.On this basis,the paleogeomorphology in the lower Mao 2 Member is restored using well-seismic data,and the reservoir distribution is predicted.The prediction results have been verified by the latest results of exploration wells and tests,which provide an important reference for the prediction of thin dolomite reservoirs under similar geological setting.展开更多
The process of aluminothermic reduction of a mixture of calcined dolomite and calcined magnesite had been developed. The mechanism of the process was studied by SEM and EDS. The reduction process was divided into thre...The process of aluminothermic reduction of a mixture of calcined dolomite and calcined magnesite had been developed. The mechanism of the process was studied by SEM and EDS. The reduction process was divided into three stages:0≤ηt/ηf≤0.43±0.06, 0.43±0.06≤ηt/ηf≤0.9±0.02 and 0.9±0.02≤ηt/ηf<1, whereηt andηf are the reduction ratio at time t and the final reduction ratio obtained in the experiment at temperature T, respectively. The first stage included the direct reaction between calcined dolomite or calcined magnesite and Al with 12CaO·7Al2O3 and MgO·Al2O3 as products. The reaction rate depended on the chemical reaction. The CA phase was mainly produced in the second stage and the overall reaction rate was determined by both the diffusion of Ca2+ with molten Al and the chemical reaction. The CA2 phase was mainly produced in the third stage and the reaction process was controlled by the diffusion of Ca2+.展开更多
The vacuum aluminothermic reduction of the mixture of calcined magnesite and calcined dolomite was studied. An isothermal reduction method satisfying the vacuum aluminothermic reduction was proposed. The experiments w...The vacuum aluminothermic reduction of the mixture of calcined magnesite and calcined dolomite was studied. An isothermal reduction method satisfying the vacuum aluminothermic reduction was proposed. The experiments were carried out at 4 Pa. The results indicate that the reduction rate is increased with increasing temperature, content of aluminum and pellet forming pressure. The XRD patterns of pellets at different reduction stages confirm that the reduction process can be roughly classified into three stages：the formation of MgAl2O4, and Ca12Al14O33 phases;the phase transformation from MgAl2O4 and C12A7 to CaAl2O4;the formation of CaAl4O7 phase. The experimental data were divided into three parts according to the kinetic models. The apparent activation energies of the three parts were determined to be 98.2, 133.0 and 223.3 kJ/mol, respectively.展开更多
REE fractionation during the weathering of dolomite has been recognized for decades.A regolith profile on dolomite in southwest Yunnan of China was selected to investigate the behaviors of REE during weathering.The we...REE fractionation during the weathering of dolomite has been recognized for decades.A regolith profile on dolomite in southwest Yunnan of China was selected to investigate the behaviors of REE during weathering.The weathering of dolomite is divided into two stages：the pedogenesis stage and soil evolution stage,corresponding to the saprolites and soils respectively in the regolith profile. SiO_2,TiO_2,P_2O_5,Zr,Hf,Nb and Ta were immobile components during the weathering by and large, while Al_2O_3,K_2O and Fe_2O_3 were lost during the soil evolution stage in the physical form（clay minerals probably）.REE were fractionated during the whole weathering of dolomite.The field weathering profile and the lab acid-leaching experiments on dolomite indicate that MREE were enriched clearly relative to other REE during the pedogenesis stage in a ＂capillary ascending-adsorption＂ mechanism, but they did not fractionate clearly in the soil evolution stage.REE were lost and accumulated in the weathering front of dolomite during the soil evolution stage in a ＂physical-chemical leaching＂ mechanism.展开更多
Study of dolomite texture can contribute to understanding the process of dolomitization.This research reports textures and homogenization temperatures of dolomites from the Permian-Triassic strata in the Sichuan Basin...Study of dolomite texture can contribute to understanding the process of dolomitization.This research reports textures and homogenization temperatures of dolomites from the Permian-Triassic strata in the Sichuan Basin and the Lower Paleozoic strata in the Tarim Basin,which provided insights into relationships between dolomite textures and their formation temperatures.Our results are summarized as follows：1） dolomites with well-preserved texture indicate low dolomitization temperature.However,in certain diagenetic environments,the hydrothermal dolomitization may completely or partially preserve the original texture of dolomites.2） The formation temperatures of non-planar dolomites are always higher than those of planar dolomites.3） The formation temperatures of dolomite cements are generally higher than those of replacive dolomites.4） Although the formation temperatures of saddle dolomite cements have a wide range,they show higher values than those of the planar subhedral to euhedral dolomite cements.Thus,saddle dolomites could generally be an indicator of high precipitation temperature.5） The fluid Mg/Ca ratio is another element controlling dolomite morphology.Micritic dolomites,which precipitate from hypersaline fluids with a high Mg/Ca ratio in a subaerial environment could also have features of non-planar anhedral crystal shape because of rapid nucleation and crystallization during dolomitization.展开更多
Hydrothermal mineral assemblages and related hydrothermally enhanced fracturing are common in the Precambrian Dengying Formation of Central Sichuan Basin. Petrographic and geochemical analyses of core samples show tha...Hydrothermal mineral assemblages and related hydrothermally enhanced fracturing are common in the Precambrian Dengying Formation of Central Sichuan Basin. Petrographic and geochemical analyses of core samples show that the hydrothermal dolomite reservoirs of Dengying Formation consist of four main types of pores in the reservoir facies. These include: 1) hydrothermal dissolution vug(or pore), 2) intercrystalline pore, 3) residual inter-breccia vug(or pore), and 4) enlarged dissolved-fracture. There are three different fabrics dolomite in hydrothermal dolomite reservoirs, namely, saddle dolomite, fine-medium dolomite and micritic dolomite. Micritic dolomite is the original lithology of host rock. Saddle dolomite with curved or irregular crystal faces was directly crystallized from hydrothermal fluids(average temperature 192°C). Fine-medium dolomites are the products of recrystallization of micritic dolomite, resulting in abnormal geochemical characteristics, such as slight depletion of δ^(18)O, significant enrichment of Mn-Fe and ^(87)Sr/^(86)Sr, and positive Eu anomaly. A model for the distribution of various hydrothermal dolomite reservoir facies is proposed here, which incorporates three fundamental geological controls: 1) extensional tectonics and tectono-hydrothermal events(i.e., the Xingkai Taphrogenesis of Late Sinian-Early Cambrian, and Emei Taphrogenesis of Late Permian), 2) hydrothermal fluid storage in clastic rocks with large thickness(e.g., Nanhua System of Chengjiang Formation and part of Doushantuo Formation), and 3) confining bed for hydrothermal fluids(such as, the shale in Qiongzhusi Formation). The supply of hydrothermal fluid is critical. Large basement-rooted faults and associated grid-like fracture system may function as the channels for upward migration of hydrothermal fluid flow. The intersection of the above-mentioned faults(including the conversion fault), especially transtensional sags above negative flower structures on wrench faults can serve as a key target for future hydrocarbon exploration.展开更多
The widespread Carboniferous KT-I dolomite in the eastern margin of the Pre-Caspian Basin is an important hydrocarbon reservoir. The dolomite lithology is dominated by crystalline dolomite. The δ18O values range from...The widespread Carboniferous KT-I dolomite in the eastern margin of the Pre-Caspian Basin is an important hydrocarbon reservoir. The dolomite lithology is dominated by crystalline dolomite. The δ18O values range from -6.71‰ to 2.45‰, and average 0.063‰, obviously larger than -2.5‰, indicating low-temperature dolomite of evaporation origin. Stable strontium isotope ratios （87Sr/86Sr） range from 0.70829 to 0.70875 and average 0.708365, very consistent with 87Sr/86Sr ratios in Carboniferous seawater. Chemical analysis of Ca and Mg elements shows that the dolomite has 9.1 mole% excess Ca or even higher before stabilization. The degree of order of dolomite is medium–slightly poor, varying in a range of 0.336-0.504 and averaging 0.417. It suggests that the dolomite formed under near-surface conditions. There are two models for the origin of the Carboniferous KT-I dolomite reservoir. These are 1） the evaporation concentration – weathering crust model and 2） the shoal facies – seepage reflux model. The former is mainly developed in restricted platforms – evaporate platforms of restricted marine deposition environments with a representation of dolomite associated with gypsum and mudstone. The latter mainly formed in platform edge shoals and intra-platform shoals and is controlled by dolomitization due to high salinity sea water influx from adjacent restricted sea or evaporate platform.展开更多
Carbonate rocks are important reservoirs for global petroleum exploration.The largest oilfield in the South China Sea,Liuhua 11-1,is distributed in the massive carbonate reef area of the Zhujiang(Pearl)River Mouth Bas...Carbonate rocks are important reservoirs for global petroleum exploration.The largest oilfield in the South China Sea,Liuhua 11-1,is distributed in the massive carbonate reef area of the Zhujiang(Pearl)River Mouth Basin.Previous studies showed that one 802.17-m-long core from well Xichen-1 in the South China Sea mainly consisted of white and light gray-white organic reefs.Recently,a Miocene whole core(161.9 m long)of well Xiyong-2,near well Xichen-1,was found to contain six layers of yellowish brown,light yellowish gray,iron black,or light yellowish gray-white organic reefs.Scanning electron microscope images of these layers reveal a typical ferroan dolomite rich in Fe(up to 29%),with the high concentrations of Mn,Cu,W,Zn,Cr,Ni,and Co.Systematic X-ray powder diffraction analysis yields a 1.9–6.1 match in phase ratio with ankerite,5.4–26.9 with dolomite,and zero with calcite,which indicate that the samples can be classified as ferroan dolomite.The iron and heavy metals are inferred to be originated from multiple volcanic eruptions of Gaojianshi Island in the Dongdao Atoll during the middle-late Miocene.These elements were dissolved in seawater,likely as a sol,and carried to Yongxing Island in the Xuande Atoll by sea currents and tides enhanced by prevailing winds,and deposited as a part of the sedimentation process in the study area.The ferroan dolomite has Sr content of (125–285)×10^(-6),which is lower than the accepted Sr boundary value of dolomite.This finding suggests that dolomitization occurred during large-scale global glacial regression in the late Miocene.The isolated Xisha carbonate platform,exposed to air,underwent freshwater leaching and dolomitization induced by mixed water,and caused the extensive Fe-Mg exchange along the organic reef profile to form ankerite and ferroan dolomite.These results may help to understand paleoceanographic environmental changes in the South China Sea during the Miocene.展开更多
The recent discovery of deep and ultra-deep gas reservoirs in the Permian Changxing Formation reefs, northeastern Sichuan Basin is a significant development in marine carbonate oil ＆ gas exploration in China. Reef do...The recent discovery of deep and ultra-deep gas reservoirs in the Permian Changxing Formation reefs, northeastern Sichuan Basin is a significant development in marine carbonate oil ＆ gas exploration in China. Reef dolomites and their origins have been major research topics for sedimentologists and oil ＆ gas geologists. The petrography, trace element and isotope geochemistry of the reef dolomites indicated that the dolomites are characterized by low Sr and Mn contents, relatively low Fe contents, very similar δ13C and 6180 values and very different 87Sr/86Sr ratios. Although the calculated results of the fluid mixing suggested that a mixture with 85%-95% meteoric water and 50/o- 15% seawater seemed to be the dolomitizing fluids of the reef dolomites, the low Mn contents, relatively low Fe contents, high δ13c values and high homogenization temperatures of the dolomites did not support that there were large proportions of meteoric water in the dolomitization process, and the 87Sr/86Sr ratios which were close to coeval seawater also did not support the possibility of the mixture of deep-burial circulated fluids from clastic rocks. High temperature deep-burial circulated seawater with low Mn and Fe contents, high Sr content and high δ13C values from the dissolution of widely distributed Triassic evaporites during the burial diagenetic processes （including dehydration of water-bearing evaporites） could have been the dolomitizing fluids of the reef dolomites.展开更多
基金Supported by the National Natural Science Foundation of China(42172177)CNPC Scientific Research and Technological Development Project(2021DJ05)PetroChina-Southwest University of Petroleum Innovation Consortium Project(2020CX020000).
文摘Based on the study of the distribution of intra-platform shoals and the characteristics of dolomite reservoirs in the Middle Permian Qixia Formation in the Gaoshiti–Moxi area of the Sichuan Basin,SW China,the controlling factors of reservoir development were analyzed,and the formation model of“intra-platform shoal thin-layer dolomite reservoir”was established.The Qixia Formation is a regressive cycle from bottom to top,in which the first member(Qi1 Member)develops low-energy open sea microfacies,and the second member(Qi2 Member)evolves into intra-platform shoal and inter-shoal sea with decreases in sea level.The intra-platform shoal is mainly distributed near the top of two secondary shallowing cycles of the Qi2 Member.The most important reservoir rock of the Qixia Formation is thin-layer fractured-vuggy dolomite,followed by vuggy dolomite.The semi-filled saddle dolomite is common in fracture-vug,and intercrystalline pores and residual dissolution pores combined with fractures to form the effective pore-fracture network.Based on the coupling analysis of sedimentary and diagenesis characteristics,the reservoir formation model of“pre-depositional micro-paleogeomorphology controlling shoal,sedimentary shoal controlling dolomite,penecontemporaneous dolomite benefiting preservation of pores,and late hydrothermal action effectively improving reservoir quality”was systematically established.The“first-order high zone”micro-paleogeomorphology before the deposition of the Qixia Formation controlled the development of large area of intra-platform shoals in Gaoshiti area during the deposition of the Qi2 Member.Shoal facies is the basic condition of early dolomitization,and the distribution range of intra-platform shoal and dolomite reservoir is highly consistent.The grain limestone of shoal facies is transformed by two stages of dolomitization.The penecontemporaneous dolomitization is conducive to the preservation of primary pores and secondary dissolved pores.The burial hydrothermal fluid enters the early dolomite body along the fractures associated with the Emeishan basalt event,makes it recrystallized into medium–coarse crystal dolomite.With the intercrystalline pores and the residual vugs after the hydrothermal dissolution along the fractures,the high-quality intra-platform shoal-type thin-layer dolomite reservoirs are formed.The establishment of this reservoir formation model can provide important theoretical support for the sustainable development of Permian gas reservoirs in the Sichuan Basin.
基金funded by Ordos Science and Technology Plan (Grant No. TD20240003)the National Natural Science Foundation of China (52174096, 52304110)+1 种基金Ordos Science and Technology Bureau (Grant No. IMRI23005)Ordos Science and Technology Plan (Grant No. YF20240021)
文摘Given that dolomite is prone to strength degradation and susceptible to water-sand ingress under physicochemical actions,this study aims to investigate these phenomena,along with the sanding mechanism in the Xiaopu Tunnel of the Yunnan Dianzhong Water Diversion Project,using a combined experimental and modeling approach for systematic analysis.Triaxial cyclic loading-unloading tests were first conducted on dolomite samples soaked in sulfuric acid solutions of varying concentrations,with synchronous monitoring of their mechanical responses(e.g.,peak strength,deformation modulus,porosity changes).These tests,combined with observations of macroscopic morphology and mass changes during soaking,revealed a four-stage degradation pattern of dolomite in sulfuric acid:water absorption,dynamic equilibrium,dissolution,and stabilization.Key quantitative relationships established that as sulfuric acid concentration increased(from 0%to 15%),the peak strength of dolomite decreased significantly(by 7.49%to 24.99%),while porosity markedly increased(by 45%to 130%).Further post-failure analysis(fracture surface observation)and scanning electron microscopy(SEM)micro-characterization uncovered the intrinsic mechanisms of acid-induced damage:the acid solution not only promoted macroscopic crack propagation and increased fracture surface roughness but also triggered severe structural deterioration at the microscale,including enlarged crystal spacing,dissolution of gel-like substances,formation of intra-crystalline pores,weakened interparticle cementation,and development of macropores.The extent of this deterioration was positively correlated with acid concentration.Based on the experimentally revealed chemo-mechanical coupling damage mechanism between acid and rock,this study established,for the first time,a multi-scale predictive model capable of quantitatively correlating acid concentration,microstructural deterioration,and degradation of macroscopic mechanical properties.The development of this model not only deepens the quantitative understanding of the dolomite sanding mechanism but also provides a crucial theoretical tool for assessing surrounding rock stability and predicting risks in similar water diversion tunnel engineering.Addressing the specific risks of water and H^(+) erosion in the Xiaopu Tunnel,the research findings directly informed the engineering reinforcement strategy:concrete lining is recommended as the primary load-bearing structure,supplemented by surrounding rock surface protection measures,to effectively mitigate the acid-induced damage process and enhance the long-term stability of the surrounding rock.
基金Project(BGRIMM-KJSKL-2024-07) supported by the Open Foundation of State Key Laboratory of Mineral Processing,ChinaProjects(52374259,52174239) supported by the National Natural Science Foundation of China。
文摘Surface pretreatment can change the surface properties of minerals,placing them in either a favorable or an unfavorable state for flotation.To solve the separation problem associated with magnesite and dolomite,surface pretreatment experiments with citric acid,tartaric acid,and tannic acid(TA)on magnesite and dolomite as well as flotation experiments on pretreated samples were performed in this study.Experimental results demonstrated that when citric acid and tartaric acid are used for surface pretreatment,the separation effect of magnesite and dolomite is poor.However,when TA is used,the separation effect of magnesite and dolomite improves.SEM and BET analysis indicated that surface pretreatment with TA changes the surface morphology of the two minerals,resulting in additional concave pores on the dolomite surface,and a significant increase in pore size and specific surface area.The adsorption quantity test and contact angle measurement demonstrated that after surface pretreatment with TA,the magnesite adsorption capacity on sodium oleate(NaOL)slightly decreases and the dolomite adsorption capacity on NaOL considerably decreases.XPS detection concluded that the surface pretreatment of TA on the magnesite surface mainly relies on physical adsorption with weak adsorption ability and poor ability to act on Mg sites.The TA surface pretreatment action on the dolomite surface is mainly through chemical adsorption,and it is strongly and selectively adsorbed on the Ca site of dolomite through O.Actual ore rough selection experiments reveal that TA pretreatment successfully removes dolomite from magnesite,resulting in a high-quality magnesite concentrate characterized by a MgO grade of 45.49%and a CaO grade of 0.75%.
基金Project(IMRI23005)supported by Ordos Science and Technology Bureau,ChinaProjects(52174096,52304110)supported by the National Natural Science Foundation of China。
文摘To investigate the effects of water and cyclic loading on dolomite’s mechanical properties during deep mining,mechanical experiments on non-pressure water absorption and cyclic loading were conducted.The findings reveal that the elastic modulus and Poisson ratio of dolomite fluctuate with increasing water content.The mass of water absorption is positively correlated with time and the water absorption stage can be divided into three stages:accelerated,decelerated,and stabilized stages.During this process,the number of pores in dolomite increases,while the pore diameter initially decreases and then fluctuates.Microscopic analysis shows that the proportion of mesopores first increases and then decreases,while micropores exhibit the opposite trend,and the proportion of macropores fluctuates around 0%.A model diagram of structural evolution during water absorption has been developed.Additionally,the softening process of dolomite’s water absorption strength is categorized into three stages:a relatively stable stage,an accelerated softening stage dominated by mesopore water absorption,and a decelerated softening stage characterized by micropore water absorption.A uniaxial damage constitutive model for dolomite under water influence was established based on the Weibull distribution and Mohr-Coulomb strength criterion,and experimental validation indicates its strong applicability.
基金financially supported by the Science Foundation of China University of Petroleum,Beijing(Nos.2462018YJRC030 and 2462020YXZZ020)the China Sponsorship Council(No.202306440071)。
文摘The widespread dolomite of the Sinian Dengying Formation in the Sichuan Basin(China)serves as one of the most important oil and gas reservoir rocks of the basin.Well WT1,as an exploration well,is recently drilled in the Kaijiang County,northeastern Sichuan Basin(SW China),and it drills through the Dengying Formation dolomite at the depth interval of 7500–7580 m.In this study,samples are systematically collected from the cores of that interval,followed by new analyses of carbon-oxygen isotope,major elements,trace elements,rare earth elements(REEs)and EP-MA.The Dengying Formation dolomites of Well WT1 haveδ13C values of 0.37‰to 2.91‰andδ18O values of-5.72‰to-2.73‰,indicating that the dolomitization fluid is derived from contemporary seawater in the near-surface environment,rather than the burial environment.Based on the REE patterns of EPMA-based in-situ data,we recognized the seawater-sourced components,the mixedsourced components and the terrigenous-sourced components,indicating the marine origin of the dolomite with detrital contamination and diagenetic alteration.Moreover,high Al,Th,and Zr contents indicate significant detrital contamination derived from clay and quartz minerals,and high Sr/Ba and Sr/Cu ratios imply a relatively dry depositional environment with extremely high seawater salinity,intensive evaporation,and strong influences of terrigenous sediment.
基金Supported by Enhancement Project of Basic Scientific Research Ability of Young and Middle-aged Teachers in Guangxi Universities(2020KY07040)School-level Scientific Research Project of Guangxi University of Chinese Medicine(2024QN022)Self-financed Scientific Research Project of Guangxi Zhuang Autonomous Region Administration of Traditional Chinese Medicine(GXZYL20240818).
文摘[Objectives]To explore the methods for identifying pure honey.[Methods]Using 35 batches of Jiulongteng honey sourced from various production areas in Guangxi as the research subjects,this study investigated the chromogenic reactions of starch and dextrin,as well as the comparative study of thin-layer chromatography of oligosaccharides present in Jiulongteng honey.[Results]None of the 35 batches of Jiulongteng honey samples exhibited blue(indicating starch),green,or reddish-brown(indicating dextrin)coloration,suggesting that no adulterants such as artificially added starch,dextrin,or sugar were present in these samples.Furthermore,none of the 35 batches displayed additional spots below the corresponding positions of the control,indicating that the sugar composition was consistent with the oligosaccharide profile of natural honey.No components inconsistent with the oligosaccharide profile of natural honey were detected.Therefore,it can be concluded that the Jiulongteng honey samples in this experiment were pure and free from adulteration with starch,dextrin,or other sugar substances.[Conclusions]The method employed in this experiment is straightforward and quick to implement,effectively preventing adulterated honey from entering the market.It enhances the efficiency of quality control for Jiulongteng honey and promotes the healthy development of the Jiulongteng honey industry.
基金financially supported by the National Natural Science Foundation of China(Nos.42372162,U22B6004)the Scientific Research and Technology Development Program of CNPC(Nos.2021DJ0102,2021DJ1808)。
文摘Lacustrine dolomite is paid increasing attention to uncover the diagenetic water condition of paleo-lake and“dolomite problem”.Here,a dolomite nodule from the Qingshankou Formation in the Songliao Basin was analyzed to explore the salinity,alkalinity,and redox conditions of the diagenetic water.Multiple proxies,including bulk boron(B)content,B isotope composition(δ^(11)B_(bul)),boron to gallium weight ratio(B/Ga)and carbonate oxygen isotope composition(δ^(18)O_(carb)),were used to determine the diagenetic water to be brackish-fresh.Through numerical simulation,we calculated the B contents,δ^(11)B values and B/Ga in detritus(e.g.,clay,quartz and feldspar)and dolomite as two endmembers,confirming the intense interference of clay minerals onδ^(11)B_(bul).By using the fittedδ^(11)B of dolomite endmember(20.6‰),we calculated the p H value of the diagenetic water to be 8.2.The negativeδ^(11)B value of detritus endmember(-12.9‰)might be related to the terrestrial weathering.The indicative nature of strontium to barium weight ratio(Sr/Ba)was discussed to deny its applicability as a proxy of salinity in carbonate system.High Sr/Ba ratio in this dolomite nodule indicates a sulfate-poor water condition,consistent with the iron-manganese(Fe-Mn)reduction environments reflected by the Mn/Fe molar ratio.The positive carbonate carbon isotopes(δ^(13)C_(carb),4.5‰-9.4‰)indicate that methanogenesis dominated the formation of dolomite,coinciding with the weak sulfate reduction reaction in sulfate-poor water.The growth of dolomite nodule might be related to the microbial activities of methanogen and iron reducing bacteria,which had not only maintained the salinity,p H,and redox status of the diagenetic water,but also led to a ferricmethane transition zone(FMTZ).This research depicts a scenario about the diagenetic water environment of lacustrine dolomite formed in brackish-fresh water,which is different from that occurred in sulfate-rich condition.
基金Project(52004333)supported by the National Science Foundation of ChinaProject(2021CB1002)supported by Hunan International Joint Research Center for Efficient and Clean Utilization of Critical Metal Mineral Resources,China。
文摘The efficient recovery of fluorite is paid more and more attention with the increasing application especially in strategic emerging industries.In this study,acrylic acid-2-acrylamido-2-methylpropane sulfonic acid copolymer(AAAMPS)was first used as the depressant in fluorite flotation,and its effect on the flotation separation of fluorite and dolomite in sodium oleate(NaOL)system was investigated.The depression mechanism was analyzed by contact angle measurement,zeta potential test,FTIR and XPS analyses.The micro-flotation test results showed that dolomite can be inhibited in fluorite flotation system in the addition of 2 mg/L AA-AMPS and 20 mg/L NaOL at pH 10.The CaF_(2) grade increased from 49.85%in the artificial mixed mineral to 89.60%in the fluorite concentrate.The depression mechanism indicated that AA-AMPS could adsorb strongly on dolomite surface by the chelation with Ca and Mg active sites.Moreover,the further adsorption of NaOL on dolomite surface was prevented by the AA-AMPS adsorption,but that on fluorite surface was little affected,thereby increasing the difference in the hydrophobicity and floatability of the two minerals.
基金supported by Guizhou Provincial Science and Technology Projects(No.ZK[2021]ordinary 199)the National Natural Science Foundation of China(Nos.42262019,92062221)the National Key R&D Program of China(No.2017YFC0603103)。
文摘The Yingshan Formation of the Lower-Middle Ordovician in the Tarim Basin(NW China)was mainly deposited in a shallow platform,which was intensely bioturbated with burrows filled with both dolomites and calcites.This study aims to figure out the controls on the dolomitization of burrow infills and the effects on petroleum reservoir quality based on petrographic examination,fluid inclusion microthermometry,and isotopic(C-O-Sr)geochemical analyses.The differentiation of burrow-associated carbonates(dolomites and calcites)was likely controlled by the interactions of sea-level oscillations of variable orders and depositional environments.The burrow-associated dolomites(BADs)were precipitated in a relatively restricted(i.e.,lagoon)depositional environment during the lowstand of long-term sea level.In contrast,the burrow-associated calcites(BACs)were formed in a water circulation-improved lagoonal environment during the transgression of long-term sea level.Isotopic geochemical data indicate that the BADs in the Yingshan Formation were formed from slightly saline(i.e.,mesosaline to penesaline)seawater,whereas the BACs were precipitated from nearly normal seawater.In addition to the anoxic condition,the presence of marine-sourced organic matter and sulfate-reducing bacteria,and a sufficient supply of dolomitizing fluids enriched in magnesium ions(Mg^(2+))and their Mg^(2+)concentration may have played a critical role in the formation of BADs.In the more permeable and disturbed burrow sediments as a result of burrowing,penetrating fluids with higher salinities and higher Mg^(2+)concentration relative to seawater favored dolomite precipitation.The fluids with seawater-like Mg^(2+)concentration,however,would lead to calcite precipitation.The progressive dolomitization of these burrowed sediments could have propagated the dolomitizing fronts and extended into ambient limestones,leading to the development of extensive dolomites.This dolomitization process can improve the petrophysical properties(porosity and permeability)and the potential as hydrocarbon reservoirs during the emplacement of hydrocarbons from underlying source rocks of the Cambrian to Lower Ordovician.
基金supported by the National Natural Science Foundation of China(Grant No.42162026)the Basic Research Program in Yunnan Province,China(Grant No.202401AT070328)the Young Talents Project of“Xingdian Talent Support Program"in Yunnan Province,China(Grant No.YNWR-QNBJ-2020-019).
文摘Disintegrated dolomite slope and tunnel disasters occur frequently due to poor water stability of disintegrated dolomite,primarily in a form of seepage failure.For engineering purposes,it is critical to determine the seepage properties of disintegrated dolomite within the strata.However,conventional experimental methods are time-consuming and expensive and may not be effective in investigating seepage characteristics due to the heterogeneity of disintegrated dolomite.In this study,pore network model(PNM)was established by the computerized tomography(CT)scanning technology to characterize the pores.Meanwhile,the seepage and coefficient of permeability under different inlet stress conditions based on the accurate pore model were realized by linking the commercial image processing software Avizo with the commercial multi-physics modeling package Comsol.The results show that the porosities of severely and completely disintegrated dolomites are 29.17% and 45.37%,respectively.The grade of pore development increases with disintegration grade,which facilitates seepage failure.Severely and completely disintegrated dolomites have the coefficients of permeability of 9.67×10^(-7) m/s and 1.61×10^(-6) m/s,respectively.Under conventional conditions,severely and completely disintegrated dolomites undergo seepage failure above a pressure difference of 6×10^(3) Pa and 5×10^(3) Pa,respectively.These results are consistent with both in situ water pressure tests in the borehole and laboratory tests with the constant-head method,demonstrating that CT scanning is an effective method for observing fractures and pores in disintegrated dolomite for seepage evaluation.
基金National Natural Science Foundation of China,Grant/Award Number:42230812。
文摘The 10000-m ultradeep dolomite reservoir holds significant potential as a successor field for future oil and gas exploration in China's marine craton basin.However,major challenges such as the genesis of dolomite,the formation time of high-quality reservoirs,and the preservation mechanism of reservoirs have always limited exploration decision-making.This research systematically elaborates on the genesis and reservoir-forming mechanisms of Sinian-Cambrian dolomite,discussing the ancient marine environment where microorganisms and dolomite develop,which controls the formation of large-scale Precambrian-Cambrian dolomite.The periodic changes inMg isotopes and sedimentary cycles show that the thick-layered dolomite is the result of different dolomitization processes superimposed on a spatiotemporal scale.Lattice defects and dolomite embryos can promote dolomitization.By simulating the dissolution of typical calcite and dolomite crystal faces in different solution systems and calculating their molecular weights,the essence of heterogeneous dissolution and pore formation on typical calcite and dolomite crystal faces was revealed,and the mechanism of dolomitization was also demonstrated.The properties of calcite and dolomite(104)/(110)grain boundaries and their dissolution mechanism in carbonate solution were revealed,showing the limiting factors of the dolomitization process and the preservation mechanism of deep buried dolomite reservoirs.The in situ laser U-Pb isotope dating technique has demonstrated the timing of dolomitization and pore formation in ancient carbonate rocks.This research also proposed that dolomitization occurred during the quasi-contemporaneous or shallow-burial periods within 50Ma after deposition and pores formed during the quasi-contemporaneous to the early diagenetic periods.And it was clear that the quasi-contemporaneous dolomitization was the key period for reservoir formation.The systematic characterization of the spatial distribution of the deepest dolomite reservoirs in multiple sets of the Sinian and the Cambrian in the Chinese craton basins provides an important basis for the distribution prediction of large-scale dolomite reservoirs.It clarifies the targets for oil and gas exploration at depths over 10000 m.The research on dolomite in this study will greatly promote China's ultradeep oil and gas exploration and lead the Chinese petroleum industry into a new era of 10000-m deep oil exploration.
基金Supported by the National Natural Science Foundation of China(42172166)National Natural Science Foundation and CNPC Joint Fund Project(U23B20154)CNPC-Southwest Petroleum University Science and Technology Cooperation Project(2020CX010000).
文摘This paper discusses the characteristics and formation mechanism of thin dolomite reservoirs in the lower submember of the second member of the Permian Maokou Formation(lower Mao 2 Member)in the Wusheng-Tongnan area of the Sichuan Basin,SW China,through comprehensive analysis of geological,geophysical and geochemical data.The reservoir rocks of the lower Mao 2 Member are dominated by porphyritic vuggy dolomite and calcareous dolomite or dolomitic limestone,which have typical karst characteristics of early diagenetic stage.The dolomites at the edge of the karst system and in the fillings have dissolved estuaries,and the dolomite breccia has micrite envelope and rim cement at the edge,indicating that dolomitization is earlier than the early diagenetic karstification.The shoal facies laminated dolomite is primarily formed by the seepage reflux dolomitization of moderate-salinity seawater.The key factors of reservoir formation are the bioclastic shoal deposition superimposed with seepgae reflux dolomitization and the karstification of early diagenetic stage,which are locally reformed by fractures and hydrothermal processes.The development of dolomite vuggy reservoir is closely related to the upward-shallowing sequence,and mainly occurs in the late highstand of the fourth-order cycle.Moreover,the size of dolomite is closely related to formation thickness,and it is concentrated in the formation thickness conversion area,followed by the thinner area.According to the understanding of insufficient accommodation space in the geomorphic highland and the migration of granular shoal to geomorphic lowland in the late highstand of the third-order cycle,it is proposed that the large-scale shoal-controlled dolomite reservoirs are distributed along structural highs and slopes,and the reservoir-forming model with shoal,dolomitization and karstification jointly controlled by the microgeomorphy and sea-level fluctuation in the sedimentary period is established.On this basis,the paleogeomorphology in the lower Mao 2 Member is restored using well-seismic data,and the reservoir distribution is predicted.The prediction results have been verified by the latest results of exploration wells and tests,which provide an important reference for the prediction of thin dolomite reservoirs under similar geological setting.
基金Project(MYF2011-34)supported by High-tech R&D Projects of Liaoning Province Magnesia Materials Industry,ChinaProject(2011221002)supported by Industrial Research Projects of Liaoning Province,ChinaProject(N100302009)supported by the Fundamental Research Funds for the Central Universities,China
文摘The process of aluminothermic reduction of a mixture of calcined dolomite and calcined magnesite had been developed. The mechanism of the process was studied by SEM and EDS. The reduction process was divided into three stages:0≤ηt/ηf≤0.43±0.06, 0.43±0.06≤ηt/ηf≤0.9±0.02 and 0.9±0.02≤ηt/ηf<1, whereηt andηf are the reduction ratio at time t and the final reduction ratio obtained in the experiment at temperature T, respectively. The first stage included the direct reaction between calcined dolomite or calcined magnesite and Al with 12CaO·7Al2O3 and MgO·Al2O3 as products. The reaction rate depended on the chemical reaction. The CA phase was mainly produced in the second stage and the overall reaction rate was determined by both the diffusion of Ca2+ with molten Al and the chemical reaction. The CA2 phase was mainly produced in the third stage and the reaction process was controlled by the diffusion of Ca2+.
基金Project(MYF2011-34)supported by High-tech R&D Plan of Liaoning Province,ChinaProject(2011221002)supported by Industrial Research Projects of Liaoning Province,ChinaProject(N100302009)supported by the Fundamental Research Funds for the Central Universities,China
文摘The vacuum aluminothermic reduction of the mixture of calcined magnesite and calcined dolomite was studied. An isothermal reduction method satisfying the vacuum aluminothermic reduction was proposed. The experiments were carried out at 4 Pa. The results indicate that the reduction rate is increased with increasing temperature, content of aluminum and pellet forming pressure. The XRD patterns of pellets at different reduction stages confirm that the reduction process can be roughly classified into three stages：the formation of MgAl2O4, and Ca12Al14O33 phases;the phase transformation from MgAl2O4 and C12A7 to CaAl2O4;the formation of CaAl4O7 phase. The experimental data were divided into three parts according to the kinetic models. The apparent activation energies of the three parts were determined to be 98.2, 133.0 and 223.3 kJ/mol, respectively.
基金supported by the National Basic Research Program of China(973 Program) (2009CB421006)the State Key Laboratory of Geological Processes and Mineral Resources (GPMR200843)
文摘REE fractionation during the weathering of dolomite has been recognized for decades.A regolith profile on dolomite in southwest Yunnan of China was selected to investigate the behaviors of REE during weathering.The weathering of dolomite is divided into two stages：the pedogenesis stage and soil evolution stage,corresponding to the saprolites and soils respectively in the regolith profile. SiO_2,TiO_2,P_2O_5,Zr,Hf,Nb and Ta were immobile components during the weathering by and large, while Al_2O_3,K_2O and Fe_2O_3 were lost during the soil evolution stage in the physical form（clay minerals probably）.REE were fractionated during the whole weathering of dolomite.The field weathering profile and the lab acid-leaching experiments on dolomite indicate that MREE were enriched clearly relative to other REE during the pedogenesis stage in a ＂capillary ascending-adsorption＂ mechanism, but they did not fractionate clearly in the soil evolution stage.REE were lost and accumulated in the weathering front of dolomite during the soil evolution stage in a ＂physical-chemical leaching＂ mechanism.
基金supported by the National Natural Science Foundation(Nos.41172099,41272130)
文摘Study of dolomite texture can contribute to understanding the process of dolomitization.This research reports textures and homogenization temperatures of dolomites from the Permian-Triassic strata in the Sichuan Basin and the Lower Paleozoic strata in the Tarim Basin,which provided insights into relationships between dolomite textures and their formation temperatures.Our results are summarized as follows：1） dolomites with well-preserved texture indicate low dolomitization temperature.However,in certain diagenetic environments,the hydrothermal dolomitization may completely or partially preserve the original texture of dolomites.2） The formation temperatures of non-planar dolomites are always higher than those of planar dolomites.3） The formation temperatures of dolomite cements are generally higher than those of replacive dolomites.4） Although the formation temperatures of saddle dolomite cements have a wide range,they show higher values than those of the planar subhedral to euhedral dolomite cements.Thus,saddle dolomites could generally be an indicator of high precipitation temperature.5） The fluid Mg/Ca ratio is another element controlling dolomite morphology.Micritic dolomites,which precipitate from hypersaline fluids with a high Mg/Ca ratio in a subaerial environment could also have features of non-planar anhedral crystal shape because of rapid nucleation and crystallization during dolomitization.
基金funded by the National Science and Technology Major Project(grant No.2016ZX05052)the National Natural Science Foundation of China(grant No.41072102)
文摘Hydrothermal mineral assemblages and related hydrothermally enhanced fracturing are common in the Precambrian Dengying Formation of Central Sichuan Basin. Petrographic and geochemical analyses of core samples show that the hydrothermal dolomite reservoirs of Dengying Formation consist of four main types of pores in the reservoir facies. These include: 1) hydrothermal dissolution vug(or pore), 2) intercrystalline pore, 3) residual inter-breccia vug(or pore), and 4) enlarged dissolved-fracture. There are three different fabrics dolomite in hydrothermal dolomite reservoirs, namely, saddle dolomite, fine-medium dolomite and micritic dolomite. Micritic dolomite is the original lithology of host rock. Saddle dolomite with curved or irregular crystal faces was directly crystallized from hydrothermal fluids(average temperature 192°C). Fine-medium dolomites are the products of recrystallization of micritic dolomite, resulting in abnormal geochemical characteristics, such as slight depletion of δ^(18)O, significant enrichment of Mn-Fe and ^(87)Sr/^(86)Sr, and positive Eu anomaly. A model for the distribution of various hydrothermal dolomite reservoir facies is proposed here, which incorporates three fundamental geological controls: 1) extensional tectonics and tectono-hydrothermal events(i.e., the Xingkai Taphrogenesis of Late Sinian-Early Cambrian, and Emei Taphrogenesis of Late Permian), 2) hydrothermal fluid storage in clastic rocks with large thickness(e.g., Nanhua System of Chengjiang Formation and part of Doushantuo Formation), and 3) confining bed for hydrothermal fluids(such as, the shale in Qiongzhusi Formation). The supply of hydrothermal fluid is critical. Large basement-rooted faults and associated grid-like fracture system may function as the channels for upward migration of hydrothermal fluid flow. The intersection of the above-mentioned faults(including the conversion fault), especially transtensional sags above negative flower structures on wrench faults can serve as a key target for future hydrocarbon exploration.
文摘The widespread Carboniferous KT-I dolomite in the eastern margin of the Pre-Caspian Basin is an important hydrocarbon reservoir. The dolomite lithology is dominated by crystalline dolomite. The δ18O values range from -6.71‰ to 2.45‰, and average 0.063‰, obviously larger than -2.5‰, indicating low-temperature dolomite of evaporation origin. Stable strontium isotope ratios （87Sr/86Sr） range from 0.70829 to 0.70875 and average 0.708365, very consistent with 87Sr/86Sr ratios in Carboniferous seawater. Chemical analysis of Ca and Mg elements shows that the dolomite has 9.1 mole% excess Ca or even higher before stabilization. The degree of order of dolomite is medium–slightly poor, varying in a range of 0.336-0.504 and averaging 0.417. It suggests that the dolomite formed under near-surface conditions. There are two models for the origin of the Carboniferous KT-I dolomite reservoir. These are 1） the evaporation concentration – weathering crust model and 2） the shoal facies – seepage reflux model. The former is mainly developed in restricted platforms – evaporate platforms of restricted marine deposition environments with a representation of dolomite associated with gypsum and mudstone. The latter mainly formed in platform edge shoals and intra-platform shoals and is controlled by dolomitization due to high salinity sea water influx from adjacent restricted sea or evaporate platform.
基金Supported by the National Basic Research Program of China(973 Program)(No.2012CB956004)the Science and Technology Basic Resources Investigation Program of China(No.2017FY201407)+1 种基金the National Oil and Gas Major Projects of China(No.2011ZX05025-002)the National Natural Science Foundation of China(NSFC)(No.41106064)
文摘Carbonate rocks are important reservoirs for global petroleum exploration.The largest oilfield in the South China Sea,Liuhua 11-1,is distributed in the massive carbonate reef area of the Zhujiang(Pearl)River Mouth Basin.Previous studies showed that one 802.17-m-long core from well Xichen-1 in the South China Sea mainly consisted of white and light gray-white organic reefs.Recently,a Miocene whole core(161.9 m long)of well Xiyong-2,near well Xichen-1,was found to contain six layers of yellowish brown,light yellowish gray,iron black,or light yellowish gray-white organic reefs.Scanning electron microscope images of these layers reveal a typical ferroan dolomite rich in Fe(up to 29%),with the high concentrations of Mn,Cu,W,Zn,Cr,Ni,and Co.Systematic X-ray powder diffraction analysis yields a 1.9–6.1 match in phase ratio with ankerite,5.4–26.9 with dolomite,and zero with calcite,which indicate that the samples can be classified as ferroan dolomite.The iron and heavy metals are inferred to be originated from multiple volcanic eruptions of Gaojianshi Island in the Dongdao Atoll during the middle-late Miocene.These elements were dissolved in seawater,likely as a sol,and carried to Yongxing Island in the Xuande Atoll by sea currents and tides enhanced by prevailing winds,and deposited as a part of the sedimentation process in the study area.The ferroan dolomite has Sr content of (125–285)×10^(-6),which is lower than the accepted Sr boundary value of dolomite.This finding suggests that dolomitization occurred during large-scale global glacial regression in the late Miocene.The isolated Xisha carbonate platform,exposed to air,underwent freshwater leaching and dolomitization induced by mixed water,and caused the extensive Fe-Mg exchange along the organic reef profile to form ankerite and ferroan dolomite.These results may help to understand paleoceanographic environmental changes in the South China Sea during the Miocene.
基金supported by the National Natural Science Foundation (41172099,40839908)Research Fund for the Doctoral Program of Higher Education of China(20050616005)
文摘The recent discovery of deep and ultra-deep gas reservoirs in the Permian Changxing Formation reefs, northeastern Sichuan Basin is a significant development in marine carbonate oil ＆ gas exploration in China. Reef dolomites and their origins have been major research topics for sedimentologists and oil ＆ gas geologists. The petrography, trace element and isotope geochemistry of the reef dolomites indicated that the dolomites are characterized by low Sr and Mn contents, relatively low Fe contents, very similar δ13C and 6180 values and very different 87Sr/86Sr ratios. Although the calculated results of the fluid mixing suggested that a mixture with 85%-95% meteoric water and 50/o- 15% seawater seemed to be the dolomitizing fluids of the reef dolomites, the low Mn contents, relatively low Fe contents, high δ13c values and high homogenization temperatures of the dolomites did not support that there were large proportions of meteoric water in the dolomitization process, and the 87Sr/86Sr ratios which were close to coeval seawater also did not support the possibility of the mixture of deep-burial circulated fluids from clastic rocks. High temperature deep-burial circulated seawater with low Mn and Fe contents, high Sr content and high δ13C values from the dissolution of widely distributed Triassic evaporites during the burial diagenetic processes （including dehydration of water-bearing evaporites） could have been the dolomitizing fluids of the reef dolomites.
