基于CPMG和FID核磁共振实验的页岩有机质定量评价方法  

A Quantitative Evaluation Method for Organic Matter in Shale Based on CPMG and FID NMR Experiments

作　　者：徐陈昱 谢然红[1] 王翔宇 郭江峰[1] XU Chenyu;XIE Ranhong;WANG Xiangyu;GUO Jiangfeng(College of Geophsics,China University of Petroleum(Beijing),Beijing 102249,China)

机构地区：[1]中国石油大学(北京)地球物理学院,北京102249

出　　处：《测井技术》2024年第5期574-585,601,共13页Well Logging Technology

基　　金：国家自然科学基金项目“页岩有机质核磁共振探测理论与评价方法研究”(42304118)。

摘　　要：中国陆相页岩油中未转化的有机质占比高,有机质的定量评价对于页岩油勘探开发至关重要。核磁共振是一种快速、无损的探测技术,已广泛用于油气勘探开发领域。然而现有Carr-Purcell-Meiboom-Gill(CPMG)采集模式受仪器最短回波间隔的限制,难以有效探测有机质等超短弛豫组分信号。引入了自由感应衰减(Free-Induction-Decay,FID)采集模式,通过数值模拟和实验测量比较了CPMG与FID采集模式在页岩有机质评价方面的差异,提出了一种基于CPMG和FID的页岩有机质定量评价方法。研究表明,有效信号的起始采集时间对页岩有机质评价至关重要,核磁共振仪器死区时间为17μs,采集时间步长为1μs的FID测量能够提供页岩有机质和流体组分含量,而回波间隔为0.6 ms的CPMG测量只能够提供流体组分含量。这两种测量结果的差值与总有机碳含量(TOC)、裂解烃含量(S_2和(S_(2-1)+S_(2-2)))等多项地球化学特征参数之间具有强相关性,其中,与TOC和(S_(2-1)+S_(2-2))的决定系数分别高达0.910和0.837,证明该方法可以用于有机质的定量评价。Unconverted organic matter accounts for a high proportion in lacustrine shale oil reservoirs in China,making the quantitative evaluation of organic matter crucial for the exploration and development of shale oil.Nuclear magnetic resonance(NMR)is a rapid and non-destructive detection technique that has been widely utilized in the field of oil and gas exploration.However,the Carr-Purcell-Meiboom-Gill(CPMG)acquisition mode is limited by the shortest echo time of the instrument,making it difficult to effectively detect signals from short relaxation components such as organic matter.To address this,this paper introduces the Free-Induction-Decay(FID)acquisition mode and compares the differences between the CPMG and FID acquisition modes in shale organic matter evaluation through numerical simulations and experimental measurements.A quantitative evaluation method is proposed for shale organic matter based on both CPMG and FID measurements.The study indicates that the initial acquisition time of effective signals is crucial for evaluating shale organic matter.The FID measurement with a dwell time of 1μs and a NMR instrument dead time of 17μs can accurately provide the content of organic matter and fluid cpmponents,in shale,while the CPMG measurement with an echo time of 0.6 ms can only provide the content of fluid components.The difference between these two measurements shows a strong correlation with several geochemical characteristic parameters such as total organic content(TOC),cracking hydrocarbon content(S_(2)) and(S_(2-1)+S_(2-2)),S_(2),and(S_(2-1)+S_(2-2)),with correlation coefficients of 0.910 and 0.837 for TOC and(S_(2-1)+S_(2-2)),respectively.This proves that the method can be used for quantitative evaluation of organic matter.

关 键 词：陆相页岩油 有机质定量评价 核磁共振实验 自由感应衰减 总有机碳含量 

分 类 号：P631.84[天文地球—地质矿产勘探]