高电阻率地层自然电位异常分析与对策

Spontaneous potential abnormality analysis and countermeasures for high resistivity zone

针对胜利油田部分井在东营组、沙一段、沙三段和沙四段等高电阻率地层中出现明显自然电位异常,造成岩电不统一与解释失误的情况,结合现场实例对高电阻率地层自然电位异常进行了分析。结果表明,高电阻率地层的自然电位异常不能同砂岩渗透性地层那样利用曲线半幅点确定地层顶底界面,其形成的自然电位异常相对于渗透性地层的异常来说是一种“非正规异常”。为此提出了高电阻率地层的综合解释方法应考虑复查落实岩性、分析测井曲线、确定分层界线和评价储集层4个解释对策,指出评价高电阻率地层的储集性时,必须结合岩性、其他测井曲线以及分析化验资料综合分析才能作出合理评价。

In view of the situation that the spontaneous potential (SP) abnormality in some wells of Shengli Oilfield at high resistivity zones, such as Dongying group and membersⅠ,Ⅱ and Ⅲ of Shahejie group resulted in disunity of rock feature with wireline logging data and errors in interpretation, combining with on-site samples, the paper made analysis of SP abnormality of high resistivity pay zones. The results indicated that SP abnormality for high resistivity zones couldn′t be used to determine formation top & bottom interfaces with the half amplitude point of the curve as sandstone permeable formations could. Comparing with the permeable formation abnormality, the formed SP abnormality is different from sandstone permeable formation. Therefore, the paper put forward 4 interpretation countermeasures should be considered for high resisitivity zone comprehensive interpretation methods, that is, reexamining and deciding lithology, analyzing wireline logging curves, determining stratification boundary and evaluating reservoirs. It also pointed out that evaluating reservoir characteristics must be combined with lithology, the other wireline logging curves and analysis & test data, only through these comprehensive analyses, can the reasonable evaluation be made out.