不同pH条件下长石和方解石矿物选择性溶蚀过程

Selective dissolution process of feldspar and calcite minerals under different pH conditions

为研究富含CO_(2)和有机酸两种地层流体对长石和方解石矿物溶蚀能力与特征的差异,模拟地层温压条件,在有机酸和CO_(2)体系中进行长石和方解石矿物溶蚀模拟实验,结合GWB(Geochemist's Workbench)12.0软件模拟结果,采用原子吸收、扫描电镜(SEM)、X线衍射(XRD)、能谱分析等方法,分析长石和方解石矿物的溶蚀过程。结果表明:pH是影响长石和方解石矿物选择性溶蚀的重要因素。在温度为200℃、乙酸溶液条件下,矿物溶蚀表现为长石强溶蚀—方解石弱溶蚀的选择性溶蚀,pH为3.0较pH为7.0溶蚀现象更明显。pH影响Si、Al在溶液中的存在形态,进而影响长石向高岭石等二次矿物的转化,从而影响矿物的溶蚀过程。长石和方解石矿物溶蚀过程主要分为方解石快速溶解—长石缓慢溶解阶段、层状硅酸盐矿物沉淀阶段、长石快速溶解—方解石缓慢溶解阶段。该结果为优质储层的预测提供数据支撑。

In order to explore the differences in the dissolution ability and characteristics of feldspar and calcite minerals by two different formation fluids rich in CO_(2) and organic acids,and to simulate the formation temperature and pressure conditions,the dissolution simulation experiment of feldspar and calcite minerals was carried out in the system of organic acid and CO_(2).Combined with Geochemist's Workbench(GWB)12.0 software simulation,the dissolution process of feldspar and calcite minerals is explored by atomic absorption,scanning electron microscope(SEM),X-ray diffraction(XRD),energy spectrum analysis and other technical means.The results show that pH is an important factor affecting the selective dissolution of feldspar and calcite.At 200℃,under acetic acid condition,the mineral dissolution showed a selective dissolution of strong feldspar dissolution and weak calcite mineral dissolution.The dissolution was more obvious pH=3.0 than pH=7.0.By influencing the form of Si and Al in solution,pH affects the transformation of feldspar to kaolinite and other secondary minerals,thus affecting the mineral dissolution process.The dissolution process of feldspar and calcite can be divided into three stages:rapid dissolution of calcite and slow dissolution of feldspar,deposition of layered silicate minerals,and rapid dissolution of feldspar and slow dissolution of calcite.The results provide data support for the prediction of high quality reservoirs.