埋藏有机酸性流体对四川盆地东北部飞仙关组储层的溶蚀改造作用:溶解动力学实验研究

Dissolution and alteration of Feixianguan Formation in the Sichuan Basin by organic acid fluids under burial condition: Kinetic dissolution experiments

通过白云岩化鲕粒灰岩与0.1 mol/L乙酸的旋转盘溶解动力学实验,研究了深埋藏中有机质热演化过程中伴生的有机酸对鲕粒灰岩储层的改造作用机理。结果显示,白云岩化鲕粒灰岩溶解反应的速率在3.26×10–7～6.66×10–7 mol/(cm2.s)之间,并且溶蚀速率随温度和转速的增加而增大。反应前后样品表面的扫描电子显微镜分析结果表明,相对白云石鲕粒,方解石基质溶蚀程度更大,并沿方解石填充脉溶蚀程度最大,并且在温度≥80℃时鲕粒表面出现Fe(OH)3覆盖层,可能抑制了溶蚀反应的进行。计算得到该反应过程的表观活化能(7.89～9.32 kJ/mol)以及反应后的表面形貌特征均指示该条件下的溶解反应受扩散过程控制。总的来说,埋藏条件下有机酸溶解作用是飞仙关组优质储层中次生孔隙形成不可忽略的改造过程,鲕粒间的方解石胶结物被溶蚀后形成的粒间溶孔,白云岩化鲕粒内部易容的组分溶解形成的粒内溶孔、铸模孔是主要储集空间。

In order to study the control factors and mechanism of oolitic limestone reservoir corrosion by organic acid produced in burial stage. The reactions of acetic acid （initial 0.1 mol/L） with oolitic limestone were investigated using the rotating-disk corrosion reactor system （CRS）. The results indicate that dissolution rates of dolomitic oolite limestone are between 3.26× 10^-7 and 6.66×10^-7 mol/（cm2 . s）, and dissolution rates increase as temperature or disk rotation speed increasing. The values of Ea decrease with disk rotation speed from 7.89 to 9.64 kJ/mol, it demonstrates that these reactions are controlled by mass-transfer process. Scanning Electron Microscope images and EDX spectrum data also indicate the same view. Besides, SEM images and EDX spectrum data show the dissolution of calcite matrix is more intense than ooids comprise with dolomite. Dissolution at higher temperature was even more pronounced, generating the interooid pore space and oomolds. The surface of ooids reacted at temperature exceed 80 ~C was found to be covered with rufous layers. These are identified as ferric hydroxide using EDX spectrum, which might inhibit the formation of secondary pores in ooids. In summary, dissolution and alteration of Feixianguan Formation by organic acid fluids under burial condition should not be neglected during the process of the secondary pore formation. The intergranular pores which formed after the calcite cement between ooids had been dissolved, the intragranular dissolved pores and mould pore in dolomitic ooids are primary reservoir space in Feixianguan Formation of the Sichuan Basin.