套管及环形水泥对自然伽马测井曲线的影响

陈晓芬　盖建宾　高文明

摘 要：自然伽马测井是通过测量地层的自然伽马值，从而划分岩性，进行地层对比。自然伽马测井的优点是可以在裸眼井、套管井和高矿化度钻井液以及干孔中进行测量。在已下入套管的井内进行自然伽马测井时，影响地层自然伽马测井曲线的主要因素有套管、环形水泥等。通过套管段及套管加环形水泥段分别与裸眼段自然伽马测井曲线进行对比分析，发现套管对地层放射性的影响比较均匀，与裸眼段相比幅值降低36%左右，不影响地层放射性曲线的整体形态;套管加上环形水泥后，由于受到第四纪地层的稳定性、分选性以及固井质量等因素的影响，难以确定裸眼自然伽马测井曲线的整体形态，因此能否利用下套管井測量的自然伽马测井数据恢复地层信息，要综合考虑地层情况、井径变化、固井质量等要素。

关键词：自然伽马;裸眼;套管;环形水泥;测井

Influence of casing and annular cement on gamma ray logging curve

CHEN Xiaofen，GAI Jianbin，GAO Wenming

（Beijing Institute of Geological and Prospecting Engineering，Beijing 100048， China）

Abstract： Natural gamma logging divides lithology by measuring the natural gamma value of formation， carry out stratigraphic correlation. The advantage of natural gamma logging is to measure in open hole， cased well and high salinity drilling fluid and dry hole. When natural gamma logging is carried out in the wells that have been put into the casing， the main factors that affect the formation gamma ray logging curve are casing， annular cement casing packing and so on. This paper compares and analyzes the natural gamma logging curves between casing section and casing plus annular cement section and open hole section. It is found that the casing has a uniform influence on the formation radioactivity， and the amplitude of the casing decreases by 36% compared with the open hole section， which does not affect the overall form of the formation radioactivity curve.  Because of the influence of Quaternary formation stability， formation sorting and cementing quality， it is difficult to determine the overall shape of the open hole natural gamma ray logging curve after casing and annular cement are added. Therefore， whether the formation information can be recovered by using the natural gamma ray logging data measured in cased wells should comprehensively consider the formation condition， well diameter change and cementing quality.

Keywords： natural gamma; open hole; casing; annular cement; logging

自然伽马测井是以地层自然放射性为基础，测井时自然伽马射线探测器沿井眼进行测量，记录伽马射线强度（徐保庆等，2002）。不同的岩层，放射性物质含量不同，因而不同岩层在自然伽马曲线上就有不同的反映，这是用自然伽马测井的地质地球物理基础（陆勇，2018;尉中良等，2005）。自然伽马测井的优点是可以在裸眼井、套管井和高矿化度钻井液以及干孔中进行测量（王新杰等，2019）。测量和获取测井曲线的方法技术简单、成本低廉（宋子齐等，2011）。有些钻孔在当时环境下不具备测井的条件或地层不稳定不具备裸眼探测的条件。……