北部湾盆地涠西南凹陷涠洲组黏土矿物异常转化对储层质量的影响

Influence of abnormal transformation of clay minerals on reservoir quality in Weizhou Formation, Weixinan Sag, Beibuwan Basin

为寻找北部湾盆地涠西南凹陷优质储层发育区带,指明后期油气勘探开发方向,本文基于实验分析和热力学计算相结合的方法,深入研究了涠西南凹陷渐新统涠洲组储层中黏土矿物异常转化层段及类型,明确了异常高孔高渗带成因。结果表明:受热流体活动影响,研究区在埋深2300~2900 m存在明显的黏土矿物异常转化现象,且可分为绿泥石化和高岭石化两种类型,热力学计算结果也证实高岭石绿泥石化和伊利石高岭石化在涠西南凹陷具有热力学优先性,是涠西南凹陷涠洲组优质储层的重要成因。异常高孔高渗带集中分布于绿泥石含量(质量分数)大于35%(高岭石含量在30%~35%之间)和高岭石含量大于45%(绿泥石含量在10%~20%之间)两个层段。其中,在2300~2400 m和2500~2700 m深度范围内储层主要发育异常高岭石化;在2400~2500 m和2700~2900 m深度范围内储层主要发育异常绿泥石化。

In order to find the development position of high quality reservoir and determine the direction of later exploration and development in Weixinan Sag of Beibuwan Basin,this paper studied the location and type of abnormal clay mineral transformation in Weizhou Formation,Weixinan Sag,and identified the cause of abnormally high porosity and permeability zones based on the method of combining experimental analysis and thermodynamic calculation.The results show that,under the influence of thermal fluid activity,abnormal transformation of clay minerals is developed in the study area at the burial depth of 2300~2900 m,which can be divided into two types:chloritization and kaolinization.Thermodynamic calculation results also confirm that the chloritization of kaolinite and kaolinization of illite have thermal mechanical priority in Weixinan Sag,which is the important cause of high quality reservoir of the Weizhou Formation in Weixinan Sag.The abnormally high porosity and permeability zones are concentrated in two layers,where the the proportion of chlorite mass is more than 35%(the proportion of kaolinite mass is between 30%and 35%)and the proportion of kaolinite mass is more than 45%(the proportion of chlorite mass is between 10%and 20%).Among them,abnormal kaolinization is mainly developed within the depth range of 2300~2400 m and 2500~2700 m,abnormal chloritization is mainly developed within the depth range of 2400~2500 m and 2700~2900 m.