页岩油储层核磁有效孔隙度起算时间的确定——以吉木萨尔凹陷二叠系芦草沟组页岩油储层为例

准噶尔盆地吉木萨尔凹陷芦草沟组页岩油储层岩性细,孔喉结构复杂,常规测井评价方法难以准确计算有效孔隙度。为此,选取5种粘土类型共30块砂岩样品,分别测量了氦气孔隙度、不同状态下的核磁T2谱、粘土类型以及含量。通过对配套实验数据的分析,明确了粘土类型对储层核磁T2信号短横向弛豫分量的影响机制。在此基础上,结合实验测量结果以及不同类型粘土束缚水的核磁共振弛豫时间,利用迭代法实现了研究区页岩油储层有效孔隙度的准确计算,并确定起算核磁时间为1. 7 ms。该方法的计算结果得到了岩心分析数据以及实际测井资料的验证,应用效果较好,为页岩油储层有效孔隙度评价提供了一种新的技术思路和解决办法。

Determination of the starting time for measurement of NMR effective porosity in shale oil reservoir: A case study of the Permian Lucaogou shale oil reservoir,Jimusaer sag

Due to the fine-grained lithology and complex pore throat structure of the Lucaogou shale oil reservoir in Jimusaer sag,Junggar Basin,it is difficult to accurately calculate the effective porosity by conventional logging interpretation methods.To solve this difficulty,30 sandstone samples of five clay types were selected for measurements such as porosity under helium expansion,nuclear magnetic resonance (NMR) T₂ spectrum under different conditions,type and content of clay.The mechanism of clay type effect on short lateral relaxation component of reservoir NMR T₂ signal was revealed through the analysis of matching experimental data.Subsequently,combined with the experimental results and the NMR relaxation time of bound water in various clay types,the effective porosity of shale oil reservoirs in the study area was calculated accurately by iteration method.The initial NMR time was determined to be 1.7 ms,which have been verified well by core analysis and actual logging.The study serves as a new technical solution for effective porosity evaluation of shale oil reservoir.