基于黏土矿物分析的低电阻率油层识别

鄂尔多斯盆地镇北油田西部区块长8₁油层电阻率明显小于东部区块,且局部存在低电阻率油层,使得西部区块的油、水层难以识别,给油田开发带来一定难度。基于铸体薄片、X射线衍射、扫描电镜、压汞、测井解释等数据分析,对镇北油田长8₁油层黏土矿物特征及其对油层电阻率的影响进行了研究。结果表明,黏土矿物对镇北油田西部区块低电阻率油层的控制作用主要体现在3个方面：一是黏土矿物的附加导电作用,阳离子交换能力较强的伊利石和绿泥石含量高,其附加导电作用较强;二是黏土矿物对水分子的吸附作用,水分子吸附能力强的绿泥石含量高,容易形成水膜而增加导电能力;三是较高含量的黏土矿物使储集层孔隙结构更为复杂化,以致束缚水饱和度增高。对于此类高黏土矿物含量类型的低电阻率油层,通过测井曲线的响应特征,建立储集层黏土矿物含量的计算模型,结合生产情况拟合低电阻率油层的产水率,提高了低电阻率油层的识别精度。

Identification of Low Resistivity Oil Layers Based on Clay Mineral Analysis

There are distinct differences between the resistivity of Chang 81 reservoir of the western and eastern blocks in Zhenbei Oilfield,Ordos basin.The reservoir resistivity in the western block is significantly lower than that of the eastern block of Zhenbei oilfield and there are low resistivity oil layers in local areas.As a result,it is hard to identify oil and water layers in the western block,which brings difficul ties for oilfield development.Based on the data of cast thin section,X ray diffraction,SEM,mercury injection and logging interpretation,the characteristics of clay minerals and their effects on the resistivity of Chang 81 oil reservoir in Zhenbei oilfield are studied in this paper.The results show that the controls of clay minerals on low resistivity oil layer in western Zhenbei oilfield are mainly manifested in three as pects.The first is the additional conductivity of clay minerals—the contents of illite and chlorite with relatively strong cation exchange ca pacity are high in the reservoir of the western block,leading to stronger additional conductivity.The second is the adsorption of water mole cules to clay minerals—the content of chlorite with strong adsorption capacity is high,so it is easy to form water film and increase electric conductivity.Thirdly,the relatively high contents of clay minerals make the pore structures of the reservoir more complicated,which in creases irreducible water saturation.For this kind of low resistivity oil layers with high clay mineral content,a model is established to calcu late the clay mineral content in reservoir through analyzing the response characteristics of logging curves.Combining with production sta tus,the water productivity of low resistivity oil layer is eventually matched and finally the identification accuracy of low resistivity oil layer is improved.