Dolomitization and Dolomite Pore Formation:Insights from experimentally simulated replacement
[Significance]Dolomite is a common carbonate rock and servers as an important reservoir for oil and gas.In the Sichuan Basin marine carbonate successions,for example,approximately 96%of the proved gas reserves are in dolomite reservoirs.Thus,studies of the dolomitization process,and how pores originate in dolomite,have made significant progress.However,how dolomitization affects the development of pores is still argued.[Methods]By sum-marizing the main theoretical viewpoints of pore origin,combined with the results of various replacement experimen-tal simulations,this study explains the formation and evolution of pores during dolomitization and suggests lines of fu-ture research on pore origin.[Progress]The pores in dolomite are either inherited from its precursor limestone,or they have resulted from the dissolution of calcite during or after dolomitization.Dolomitization might increase,main-tain or reduce reservoir porosity,depending on the environment,residence time and nature of the dolomitizing fluids.[Conclusions and Prospects]Replacement observations in experimental simulations imply that replacement is a micro-process of dissolution,migration and precipitation,accompanied by the formation of new pores that act as a channel for fluid and ion exchange to maintain the reaction.The molar volume of minerals does not influence the formation of pores.This is determined by relative solubility:that is,if the dissolution of reactants is greater than the precipitation of products,pore volume increases.The whole replacement process is accompanied by the formation of new pores,but they are mainly micropores,and their contribution to the effective porosity of a reservoir remains to be further evaluated.
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