鄂尔多斯盆地奥陶系不同组构碳酸盐岩埋藏溶蚀实验

鄂尔多斯盆地奥陶系碳酸盐岩储层受埋藏溶蚀作用控制明显，而地层深部复杂的水-岩反应造成埋藏溶蚀研究难度较大，并进而影响了储层的评价与预测。分别利用CO₂溶液和乙酸溶液为流体介质进行溶蚀模拟实验，探讨埋藏条件下温度、压力、流体等因素对不同矿物及组构碳酸盐岩溶蚀作用的影响。结果表明:1）随着温度与压力升高，碳酸盐岩样品在乙酸溶液中的溶解速率均相应提高，在CO₂溶液中的溶解速率则先增加后减小，且在110℃~130℃区间内溶蚀速率最大；深埋藏环境下，各岩类溶蚀速率差异减小，并趋于一致；2）岩石矿物成分和组构，原岩初始孔隙度的大小及其连通关系，以及晶体的产状对成岩后期的埋藏溶蚀作用也具有重要的影响。不溶组分含量低、颗粒/灰泥比高、矿物成分复杂的碳酸盐岩由于组构选择性溶蚀作用而更易被溶蚀；碳酸盐岩的溶蚀速率随方解石含量的增加而增加，但深埋藏环境下，矿物成分含量差异对溶蚀速率的影响作用减弱；硬石膏与白云岩相伴生时，可优先溶蚀形成膏模孔，并促进白云石的溶解，改善储层效果。不同岩性，总体上灰岩较白云岩及过渡岩类更易发生埋藏溶蚀作用。结合研究区实际地质条件分析，砂屑灰岩、膏质白云岩等埋藏溶蚀强度较大，通过对原岩早期组构选择性溶蚀形成孔隙的继承和调整，叠加埋藏期岩溶作用后，可形成规模优质储层。

Simulation Experiment for the Burial Dissolution of Different Petrofabric Carbonate Rocks of Ordovician in the Ordos Basin

The development of Ordovician carbonate reservoir in Ordos Basin was obviously controlled by burial dissolution,while the condition and environment of fluid-rock interaction in the deep stratum were much more complicated than the epigenic karstification,which increased the difficulty of burial dissolution study,reservoir evaluation and prediction.This contribution aimed to study the dissolution effects on carbonate rocks with different mineralogical compositions and petrofabric in acetic acid and CO2 solution,under burial environment with simultaneously changing temperature (30℃ ～ 180℃) and pressure (5～50 Mpa) by equipment of water-rock interaction.For this simulation experiment,the typical six carbonates samples were collected from the Kelimoli and Majiagou Formation of Ordovician in Ordos Basin.The results showed that:1) The dissolution rates of carbonate rocks all increased in acetic acid,while tended to increase firstly when the temperature reached from 30℃ to 120℃ and pressure reached from 5 Mpa to 30 Mpa,then decreased gradually in CO2solution with increasing temperature and pressure.The dissolution peak scope were between 110℃ to 130℃ under the condition where CO2 solution acted as dissolution fluid.However,when exceeded the peak,the differentiation of corrosion rates gradually decreased and kept the same in the deep burial settings.2) Burial dissolution was not only controlled by petrofabric and mineralogical composition,the size and connectivity of pre-existing pores also palyed an important role,except for the condition of temperature,pressure and fluids,the occurrence of crystal could also have significant impact on the dissolution of post diagenesis.As the selective solution of petrofabric,the rocks with lower content of insoluble mineral such as clay mineral and quartz,high grain micrite ratio and complex components were likely more easier to dissolve.With the increase of the calcite content,dissolution rates of carbonate rocks increased as well,but mineral composition content differences contributed little in the deep buried digenetic environments.Anhydrite was prior to dissolution and further developped as gypsum mould pores,at the same time promoted dolomite to dissolve and improve reservoir,when it developed along with dolomite.In terms of different lithology,limestones were more likely to occur burial dissolution than dolomite and transitional rock types.The burial dissolution rates and intensity of calcarenite and gypsodolomite were superior compared with other rock,thus when they inherited the pre-existing pores conducted by the early selective corrosion pore and modulated,superposed with late burial karstification,they were able to become high quality reservoirs based on the analysis in combination with the actual geological conditions.