泥页岩热演化所排有机酸对长石的溶蚀作用——以大民屯凹陷沙四段为例

Experimental study on the effect of organic acid on feldspar dissolution by thermal evolution of shale:a case from the fourth member of Shahejie formation in Damintun depression

针对泥页岩热演化生成的有机酸对储层改造的问题,以Ⅱ1型干酪根所排有机酸和长石为研究对象,通过水岩模拟实验,从有机酸对长石的溶蚀特征及其对储层的贡献的角度进行研究。通过分析实验前后长石质量变化、长石表面形态特征以及反应后溶液中离子浓度变化,明确有机酸对长石溶蚀的特征,并结合工区泥页岩储层矿物组成分析有机酸对长石的溶蚀作用和对次生孔隙的贡献。结果表明,长石的溶蚀首先沿着晶面溶蚀,而后沿着矿物解理面溶蚀,最后沿矿物边缘溶蚀,并且斜长石的溶蚀强度要大于钾长石,虽然在长石与有机酸的反应过程中会生成水铝矿、绿泥石及伊利石等新矿物并充填于孔隙之间,但长石溶蚀能够形成大量次生孔隙,改善储层物性,提高孔隙率,经计算,长石溶蚀最高可以增加12.87%的面孔率。

Aiming at the problem of reservoir reformation caused by the thermal evolution of mud shale, taking the feldspar and organic acid discharged by type Ⅱ 1 kerogen as the study object through the water rock simulation experiment to study the dissolution characteristics of feldspar which caused by organic acid and its contribution to the reservoir. By analyzing the mass change of feldspar before and after the experiment and the surface morphology of the feldspar and the change of ion concentration in the solution after the reaction to understanding the characteristics of the dissolution of feldspar which caused by organic acids. And combined with the mineral composition of mud shale reservoirs to analysis the dissolution of feldspar by organic acids and its contribution to secondary pores in the work area. The results show that the feldspar first dissolves along its crystal plane, and then the feldspar will dissolve along the mineral cleavage surface. Finally, the feldspar will dissolve along the mineral edge, and the dissolution strength of plagioclase is greater than that of potassium feldspar. Although new minerals such as gibbsite, chlorite and illite are formed during the reaction of feldspar with organic acids and filled between pores but feldspar dissolution can form a large number of secondary pores to improve reservoir properties and increase porosity. After calculation, feldspar dissolution can increase a maximum of 12.87% of the face rate.