不同类型鲕粒灰岩储集层溶解动力学特征

Dissolution kinetics of different types of oolitic limestones in northeastern Sichuan Basin

采用溶解动力学实验方法研究四川盆地东北部鲕粒灰岩储集层中孔-洞-缝等油气储集空间的发育、演化规律。不同温度和CO2分压(pCO2)条件下鲕粒灰岩的溶解动力学实验和微观形貌观察发现:温度为50℃、pCO2由1 MPa升高至4 MPa时,鲕粒灰岩的溶解速率增大,并且鲕粒灰岩的溶解速率大于白云石化鲕粒灰岩的溶解速率;pCO2为3 MPa、温度由25℃升高至150℃,鲕粒灰岩溶蚀呈弱—强—弱的变化趋势,最大溶蚀速率在100℃左右,但白云石化鲕粒灰岩溶解速率随着温度的升高而增大,并且高于非白云石化鲕粒灰岩的溶解速率。扫描电镜图像显示,除原生构造裂隙外,白云石化鲕粒灰岩比非白云石化鲕粒灰岩更容易形成粒间孔、粒内孔等微观孔隙,说明溶蚀作用不是深埋环境下鲕滩优质储集层形成的单一控制因素,白云石化和溶蚀的共同作用更利于形成优质储集层。

The oolitic limestone is the target oil and gas reservoir in the northeastern Sichuan Basin,China.The dissolution kinetics experiment method was applied to study the development and evolution rule of hydrocarbon accumulation spaces such as pores,caves and fractures in oolitic limestones.The experiments and micro-morphology observations under different temperatures and pCO2 show that,when pCO2 increases from 1 MPa to 4 MPa,at constant temperature of 50 ℃,oolitic limestone dissolution rate increases with pressure increasing,and oolitic limestone dissolution rate is greater than dolomitized oolitic limestone;when temperature increases from 25℃ to 150 ℃ and pCO2 is 3 MPa,there is a weak-strong-weak trend for oolitic limestone dissolution,and the maximum rate occurs at 100 ℃ or so,but dolomitized oolitic limestone’s dissolution rate increases with temperature increasing,higher than non-dolomite oolitic limestone;SEM images show,in addition to the primary structure cracks,the dolomitized oolitic limestone is easier to form micropores such as intergranular pores and intragranular pores than the non-dolomite limestone,indicating that dissolution is not the only controlling factor for the oolitic reservoir formation in the deep burial environment,and the combination of dolomitization and dissolution is favorable to form high-quality reservoirs.