深埋砂岩储层长石溶孔率定量计算的新方法及应用——以鄂尔多斯盆地陇东地区长8_1储层为例

A new method for the calculation of secondary porosity originating from the dissolution of feldspars in deeply buried formations and its application:A case study of the Chang 8_1 Formation in Longdong area,Ordos Basin

次生孔隙是砂岩储层中重要的油气储集空间,而长石溶蚀产生的次生孔隙(即长石溶孔)往往是最重要的次生孔隙类型之一。基于热力学原理,提出了依据溶蚀产物自生黏土矿物的含量定量计算深埋条件下长石溶蚀产生的次生孔隙率的新方法,即:钾长石次生孔隙率=0.28×高岭石含量或0.36×伊利石含量;钠长石次生孔隙率=0.10×高岭石含量或0.17×伊利石含量;钙长石次生孔隙率=0.014×高岭石含量或0.08×伊利石含量。在对鄂尔多斯盆地陇东地区长8_1储层的矿物岩石学特征进行详细研究的基础上,依据新方法对陇东地区长8_1储层深埋条件下长石溶蚀产生的次生孔隙率进行了计算,并与实测面孔率和溶蚀模拟实验结果进行了对比。结果表明,长8_1储层51块样品长石溶蚀产生的次生孔隙率的计算平均值为1.32%,与长石溶孔率的实测值(平均1.44%)比较接近;与溶蚀模拟实验产生的溶孔率相比,新方法的计算结果也是合理的。

Secondary porosity is an important accumulation space in clastic reservoirs. Among secondary pores,those pores originating from the dissolution of feldspars are dominant. A new method to calculate the volumes of secondary porosity from the dissolution of feldspars in deeply buried formations based on thermodynamic principle is proposed. The calculation method is as follows. The volume of secondary porosity originating from the dissolution of potassium feldspars = 0.28×kaolinite content or 0.36×illite content. The volume of secondary porosity originating from the dissolution of albite feldspars = 0. 10 × kaolinite content or 0. 17 × illite content. The volume of secondary porosity originating from the dissolution of anorthite feldspars = 0.014 ×kaolinite content or 0.08 ×illite content. After a thorough investigation of petrologic characteristics,the new calculation method was applied to the Chang 8_1 Formation in Longdong area,Ordos Basin. The volumes of secondary porosity originating from the dissolution of feldspars in deeply buried formations in the Chang 8_1 Formation in the study area were calculated with the new method,and were compared with measured and simulated porosities. The average value of calculated secondary porosity from the dissolution of feldspars of 51 core samples from the Chang 8_1 Formation is 1. 32%,which is close to the average measured value（ 1.44%） for those samples. The comparison between calculated and simulated results also confirms the reliability of this new method.