埋藏条件下碳酸盐岩储层溶蚀作用实验模拟——以鄂尔多斯盆地西缘奥陶系碳为例

通过模拟在埋藏条件下不同流体(0.2%的乙酸和分压2 MPa的CO2)与碳酸盐岩的溶蚀环境，对鄂尔多斯盆地奥陶系碳酸盐岩的溶蚀特性和微观特征进行研究。结果表明：在不同流体中白云岩溶蚀速率增加的幅度均高于石灰岩，在深埋藏环境下，二者的增加量差距更大，白云岩比石灰岩更易溶蚀形成溶蚀孔洞；乙酸中石灰岩和白云岩的溶蚀速率随温度压力的升高而升高，CO2中岩石的溶蚀速率先增后降；相同温度压力下，乙酸中岩石的溶蚀速率高于CO2中；岩石在CO2和乙酸溶液溶蚀后微观特征具有相似性，泥晶灰岩整体溶蚀降低，形成溶蚀坑；颗粒灰岩在原始的孔隙较发育的颗粒内部形成溶蚀坑；白云岩溶蚀后常形成晶间溶孔；白云质灰岩溶蚀后方解石整体溶蚀降低；硬石膏白云岩常形成膏模孔。实验证明埋藏条件下流体介质的差异对岩石溶蚀孔洞的发育具有重要影响。白云岩溶蚀能力大于石灰岩，溶蚀后孔隙发育，是马家沟组下组合值得关注的储集空间。

Dissolution Simulation Experiment of Buried Carbonate Reservoir: A Casefrom the Ordovician Carbonate Rock ofthe Western Ordos Basin

The corrosion and microscopic characteristics of the Ordovician carbonate rocks in the Ordos Basin were studied by simulation of the carbonate dissolution in different fluids (0.2% acetic acid and CO2 under partial pressure of 2 MPa respectively) under buried conditions. It is found that the dissolution rates of dolomite in above fluids are obviously higher than those of limestone. In a deeply buried environment, the difference in dissolution rates of the two increases with depth. Dolomite is more likely to dissolve than limestone to form dissolved pores; The dissolution rates for both limestone and dolomite in acetic acid increase with temperature and pressure, while the dissolution rate of the two rocks increases first and then decreases afterwards in CO2. Under the same temperature and pressure, the dissolution rate of either dolomite or limestone is higher in acetic acid rather than in CO2; The microscopic characteristics of the rock after the dissolution in either CO2 or acetic acid are similar. For micritic limestone, dissolution is usually weak and easy to form corrosion pits; In granular limestone, however, corrosion pits are always found in the inner part of the grains; Intergranular pores are often formed by dissolution of dolomite; After dissolution of dolomite, the dissolution of calcite will slow down in general; Dissolved anhydrite mold pores are often observed in anhydritic limestone. The experiment results confirm that the fluid medium under burial conditions play important roles on the development of rock dissolution pores. The dissolution ability of dolomite is greater than that of limestone. The reservoir space developed by dissolution is worthy for attention in oil and gas exploration in the Majiagou Formation of the Ordos Basin.