基于γ射线宽束衰减模型的密度测井方法研究  

Study on density logging method based onγ-ray broad beam attenuation model

作　　者：杨宁宁 张宇昕 于华伟[2] YANG Ningning;ZHANG Yuxin;YU Huawei(Measurement and Control while Drilling Technology Center of Sinopec Oilfield Service Corporation,Dongying 257078,China;School of Geosciences,China University of Petroleum(East China),Qingdao 266580,China)

机构地区：[1]中石化胜利石油工程有限公司随钻测控技术中心,东营257078 [2]中国石油大学(华东)地球科学与技术学院,青岛266580

出　　处：《核技术》2020年第5期42-48,共7页Nuclear Techniques

基　　金：国家自然科学基金(No.41674129);国家科技重大专项(No.2016ZX05021-001);国家重点研发计划(No.2016YFC0302802)资助。

摘　　要：随着低密度天然气水合物地层的勘探越来越受重视,对密度测井的密度测量范围和精度提出了更高的要求。为了提高密度测井在低密度地层测量的精度,首先分析了密度测井传统使用的γ射线窄束衰减规律;然后结合了宽束γ射线的宽束衰减规律,推导出基于宽束γ射线的密度测井响应模型,并探讨出便于刻度的地层密度计算公式;最后利用蒙特卡罗方法模拟了低密度地层的密度测井响应,并对比分析了两种衰减规律在密度测井适用范围和精度。结果表明:在密度测井中,宽束衰减模型更好地描述了γ射线在地层的响应关系,而窄束响应关系只是宽束的一种特殊情况;基于宽束γ衰减模型提出的地层密度计算公式,使密度测井的密度测量范围扩至1.00~3.00 g?cm^?3,并且在密度范围为1.00~1.60 g?cm^?3的天然气水合物地层中,紧贴井壁测量,远探测器的测量密度平均误差从0.092 g?cm^?3降低到0.009 g?cm^?3,近探测器的测量密度平均误差从0.251 g?cm^?3降低到0.029 g?cm^?3,模拟测量精度有了大幅度的提升。为今后γ射线密度测井在低密度地层的精确测量提供了理论及方法基础。[Background]With more and more attention paid to low-density gas hydrate formation,higher requirements are raised for density measurement range and accuracy of density logging.[Purpose]This study aims to improve the accuracy of density logging in low-density formation by using board beam attenuation model.[Methods]Firstly,the attenuation law ofγ-ray narrow beam used for density logging was analyzed.Secondly,a response model based on broad-beam γ-ray density logging was derived by combining with the broad-beam γ-ray attenuation law,hence the calculation formula of formation density was obtained by scaling.Finally,the Monte Carlo N Particle Transport Code(MCNP)was used to simulate the density logging response in low-density formation,meanwhile,the application scope and accuracy of two attenuation laws in density logging were compared and analyzed.[Results]The response relationship of gamma rays in the formation can be better described by the broad beam attenuation model in density logging,while the narrow beam response relationship is only a special case of broad beam.By using the formation density formula based on the broad beam γ attenuation model,the density measurement range is expanded to 1.00~3.00 g?cm^?3.Furthermore,for gas hydrate formation with density ranging from 1.00 g?cm^?3 to 1.60 g?cm^?3,its average measurement error of the far detector is reduced from 0.092 g?cm^?3 to 0.009 g?cm^?3,and that of the near detector is reduced from 0.251 g?cm^?3 to 0.029 g?cm^?3.[Conclusions]The board beamγ-ray attenuation model can be used to greatly improve the accuracy and measuring range of density logging,and this provides theoretical and methodological basis for accurate measurement of gamma ray density logging in low-density formation in the future.

关 键 词：密度测井 宽束γ 衰减 蒙特卡罗模拟 低密度地层 

分 类 号：TL99[核科学技术—核技术及应用] P631.817[天文地球—地质矿产勘探]