顺磁性物质含量对火山岩核磁孔隙度的影响及校正——以准噶尔盆地中拐凸起石炭系火山岩为例

Influence of paramagnetic material content on nuclear magnetic porosity of volcanic rocks and its correction:Taking Carboniferous volcanic rocks in Zhongguai uplift of Junggar Basin as an example

当火山岩中含有一定量的顺磁性物质时,核磁共振测井在火山岩中的应用会受到限制,应考虑顺磁性物质含量对核磁共振测井的影响,并对核磁孔隙度进行校正。针对准噶尔盆地中拐凸起石炭系火山岩含顺磁性物质导致玄武安山岩(中基性火山岩)核磁孔隙度解释精度低的问题,利用常规测井、物性分析、核磁试验及ECS(地层元素)测井资料,开展了火山岩顺磁性物质含量对核磁孔隙度的影响分析及孔隙度校正研究。结果显示,火山角砾岩和英安岩(酸性火山岩)核磁孔隙度与岩心分析孔隙度较为一致,而玄武安山岩核磁孔隙度与岩心分析孔隙度误差较大;确定了中基性火山岩核磁孔隙度校正Fe含量下限为0.057%,当ECS测井中的Fe含量高于该值时,需要对核磁孔隙度进行校正;建立了Fe、Al、Ca、Ti等多种顺磁性矿物元素与核磁孔隙度误差的校正公式,经实际资料验证,校正后的核磁孔隙度解释精度大幅提高,应用效果较好。

When the volcanic rocks contain a certain amount of paramagnetic materials,the application of NMR logging in volcanic rocks will be limited.Therefore,the effect of paramagnetic material content on NMR logging should be considered and the porosity of NMR should be corrected.Aiming at the problem that the lithology of Carboniferous volcanic rocks in Zhongguai uplift of Junggar Basin contains paramagnetic materials,resulting in the low accuracy of nuclear magnetic porosity interpretation of medium basic volcanic rocks,the influence of magnetic substance content of volcanic rocks on nuclear magnetic porosity and porosity correction was studied by using conventional logging,physical property analysis,nuclear magnetic experiment and ECS logging data.The results show that the nuclear magnetic porosity of volcanic breccia and dacite(acidic volcanic rocks)is consistent with the porosity of core analysis,while the nuclear magnetic porosity of basaltic andesite has large error with that of core analysis.The lower limit of nuclear magnetic porosity correction for Fe content in intermediate basic volcanic rocks is determined to be 0.057%.When the Fe content in ECS logging is higher than this value,the nuclear magnetic porosity should becorrected.The calibration formula between paramagnetic mineral elements such as Fe,Al,Ca and Ti and magnetic porosity errors has been established.Through the verification of practical data,the accuracy of nuclear magneticporosity interpretation has been greatly improved and the application effect is good.