Ocean alkalinity enhancement(OAE)via carbonate dissolution has emerged as a promising approach for marine carbon dioxide removal(mCDR).However,the properties of oversaturated seawater in the upper ocean with respect t...Ocean alkalinity enhancement(OAE)via carbonate dissolution has emerged as a promising approach for marine carbon dioxide removal(mCDR).However,the properties of oversaturated seawater in the upper ocean with respect to calcium carbonate(CaCO_(3))minerals are unfavorable for their dissolution,and mediation strategies are thus required to improve the efficiency of OAE-mCDR.In this study,we conducted laboratory incubation experiments using nearshore surface seawater to examine the dissolution dynamics of natural(Iceland spar)and biogenic(Emiliania huxleyi coccolith)calcite minerals.In the experimental group with added bacteria,total alkalinity(TA)and dissolved inorganic carbon(DIC)concentrations markedly increased over the incubation period,corresponding to a notable decline in pH and dissolved organic carbon concentrations.Moreover,the concentration of dissolved calcium ions increased in the coccolith dissolution experiment.However,in the control group without bacteria,all the parameters were nearly constant or changed only slightly over time in both the Iceland spar and coccolith dissolution experiments.Therefore,microbial mediation clearly enhanced calcite mineral dissolution in oversaturated seawater,which likely occurred in the acidic microenvironments produced by bacterial metabolic activity.Linear regression analyses of the DIC and TA revealed that the relative contribution of CaCO_(3)dissolution to organic matter decomposition was 0.18±0.13 and 0.22±0.01,respectively,in the Iceland spar and coccolith experimental groups.The linear regression slope,defined as the OAE-mCDR efficiency indicating the amount of atmospheric CO_(2)absorbed per unit increase in TA,was 3.53±1.87 and 4.36±0.05 for the two groups.Both values exceed a theoretical value of 0.81 under the incubation seawater conditions,primarily driven by DIC increases from organic matter decomposition in the substrate medium.However,microbe-mineral interactions might also improve OAE performance and capabilities.We propose that microbial mediation plays an important role in promoting carbonate mineral dissolution,even in calcite-oversaturated seawater,and can be incorporated into future mCDR implementation strategies.展开更多
Reservoirs in the Xing＇anling Group in the Suderte Oil Field,Hailar Basin exhibit ultra-low to low permeability and high tuffaceous material content.This study comprehensively analyzed diagenesis and quality evolutio...Reservoirs in the Xing＇anling Group in the Suderte Oil Field,Hailar Basin exhibit ultra-low to low permeability and high tuffaceous material content.This study comprehensively analyzed diagenesis and quality evolution of these low-permeability reservoirs using thin sections,SEM samples,rock physical properties,pore water data,as well as geochemical numerical simulations.Calcite and analcite are the two main types of cements precipitated in the eodiagenetic stage at shallow burial depths in the reservoirs.These two cements occupied significant primary intergranular pores and effectively retarded deep burial compaction.Petrography textures suggest selective dissolution of massive analcite and little dissolution of calcite in the mesodiagenetic stage.Chemical calculations utilizing the Geochemist＇s Workbench 9.0indicated that the equilibrium constant of the calcite leaching reaction is significantly smaller than that of the analcite leaching reaction,resulting in extensive dissolution of analcite rather than calcite in the geochemical system with both minerals present.Numerical simulations with constraints of kinetics and pore water chemistry demonstrated that the pore water in the Xing＇anling group is saturated with respect to calcite,but undersaturated with analcite,leading to dissolution of large amounts of analcite and no dissolution of calcite.Significant secondary intergranular pores have formed in analcite-cemented reservoirs from selective dissolution of analcite in the mesodiagenetic stage;the analcite dissolution formed preferential flow paths in the reservoirs,which promoted feldspar dissolution;and dissolution of such minerals led to the present reservoirs with medium porosity and low permeability.Calcite-cemented tight reservoirs have not experienced extensive dissolution of cements,so they exhibit ultra-low porosity and permeability.展开更多
基金The National Natural Science Foundation of China under contract No.42421004.
文摘Ocean alkalinity enhancement(OAE)via carbonate dissolution has emerged as a promising approach for marine carbon dioxide removal(mCDR).However,the properties of oversaturated seawater in the upper ocean with respect to calcium carbonate(CaCO_(3))minerals are unfavorable for their dissolution,and mediation strategies are thus required to improve the efficiency of OAE-mCDR.In this study,we conducted laboratory incubation experiments using nearshore surface seawater to examine the dissolution dynamics of natural(Iceland spar)and biogenic(Emiliania huxleyi coccolith)calcite minerals.In the experimental group with added bacteria,total alkalinity(TA)and dissolved inorganic carbon(DIC)concentrations markedly increased over the incubation period,corresponding to a notable decline in pH and dissolved organic carbon concentrations.Moreover,the concentration of dissolved calcium ions increased in the coccolith dissolution experiment.However,in the control group without bacteria,all the parameters were nearly constant or changed only slightly over time in both the Iceland spar and coccolith dissolution experiments.Therefore,microbial mediation clearly enhanced calcite mineral dissolution in oversaturated seawater,which likely occurred in the acidic microenvironments produced by bacterial metabolic activity.Linear regression analyses of the DIC and TA revealed that the relative contribution of CaCO_(3)dissolution to organic matter decomposition was 0.18±0.13 and 0.22±0.01,respectively,in the Iceland spar and coccolith experimental groups.The linear regression slope,defined as the OAE-mCDR efficiency indicating the amount of atmospheric CO_(2)absorbed per unit increase in TA,was 3.53±1.87 and 4.36±0.05 for the two groups.Both values exceed a theoretical value of 0.81 under the incubation seawater conditions,primarily driven by DIC increases from organic matter decomposition in the substrate medium.However,microbe-mineral interactions might also improve OAE performance and capabilities.We propose that microbial mediation plays an important role in promoting carbonate mineral dissolution,even in calcite-oversaturated seawater,and can be incorporated into future mCDR implementation strategies.
基金financially supported by the National Science and Technology Special Grant (No. 2011ZX05009003)China Postdoctoral Science Fund (2015M580617)+1 种基金Shandong Postdoctoral Innovation Fund (201502028)2014 Innovation Project of China University of Petroleum (YCX2014002)
文摘Reservoirs in the Xing＇anling Group in the Suderte Oil Field,Hailar Basin exhibit ultra-low to low permeability and high tuffaceous material content.This study comprehensively analyzed diagenesis and quality evolution of these low-permeability reservoirs using thin sections,SEM samples,rock physical properties,pore water data,as well as geochemical numerical simulations.Calcite and analcite are the two main types of cements precipitated in the eodiagenetic stage at shallow burial depths in the reservoirs.These two cements occupied significant primary intergranular pores and effectively retarded deep burial compaction.Petrography textures suggest selective dissolution of massive analcite and little dissolution of calcite in the mesodiagenetic stage.Chemical calculations utilizing the Geochemist＇s Workbench 9.0indicated that the equilibrium constant of the calcite leaching reaction is significantly smaller than that of the analcite leaching reaction,resulting in extensive dissolution of analcite rather than calcite in the geochemical system with both minerals present.Numerical simulations with constraints of kinetics and pore water chemistry demonstrated that the pore water in the Xing＇anling group is saturated with respect to calcite,but undersaturated with analcite,leading to dissolution of large amounts of analcite and no dissolution of calcite.Significant secondary intergranular pores have formed in analcite-cemented reservoirs from selective dissolution of analcite in the mesodiagenetic stage;the analcite dissolution formed preferential flow paths in the reservoirs,which promoted feldspar dissolution;and dissolution of such minerals led to the present reservoirs with medium porosity and low permeability.Calcite-cemented tight reservoirs have not experienced extensive dissolution of cements,so they exhibit ultra-low porosity and permeability.
