储层中蒙脱石碱溶相变缩膨实验研究

An Experimental Study on Phase Transformation of Montmorillonite in Reservoirs by Using Alkaline Treatment

蒙脱石作为常见的粘土矿物,广泛存在于含油气盆地中。针对由于蒙脱石具有强烈亲水性,遇水体积可膨胀至原体积的数倍甚至数十倍,从而造成油气储层的水敏损害这一实际问题,对蒙脱石在强碱条件下发生结构变化与物相转变,实现降低其亲水性进行了详细的实验研究。探讨了天然钙基蒙脱石与天然钠基蒙脱石在80℃,1 mol/L KOH溶液中所发生的相变过程;通过XRD、SEM、TEM等测试手段分析查明其碱溶相变最终产物主要是微米级纤维状、柱状、颗粒状的菱沸石和麦钾沸石,均为不具膨胀性的架状硅酸盐矿物;最后通过自由膨胀实验证实蒙脱石碱溶产物膨胀性较原矿物显著降低。研究成果为转化油气盆地中"水敏性"粘土矿物,降低油气储层水敏损害,保护储层与提高采收率,提供了新的思路。

Montmorillonite is a kind of widely distributed clay mineral in oil and gas basins.When encountered with water,its volume could expand to several or dozens times larger,which could be ascribed to the strong hydrophilic character.Consequently,oil and gas reservoirs might be damaged by its water-sensitive property.In this study,phase transformation and hydrophilic behavior of natural Ca-smectite and Na-smectite in alkaline solution were investigated.Natural smectite was put in 1 M KOH at 80 ℃ for 1,10,15,30,60,90,120,and 150 days,respectively.Solid products were analysed by X-ray Diffraction（XRD）,Scanning Electron Microscope（SEM） and Transmission Electron Microscope TEM.The XRD results indicated that,both Ca-smectite and Na-smectite were transformed into chabazite and merlinoite after 30 days.Concomitantly,new crystals with plate-like,fibrous and granular shapes were observed by SEM and TEM,and it’s revealed by EDX（Energy Dispersive X-ray Spectrometer） that the chemical composition of original mineral was also changed.Accompanied with phase transformation,the hydrophilicity and free swelling volume of minerals were reduced.This study provided a new method for transforming the water-sensitive clay mineral in oil and gas reservoirs,which protected oil and gas reserviors by reducing water-sensitive damage and enhenced oil recovery.