页岩孔隙整合化表征方法——以四川盆地下志留统龙马溪组为例

页岩低孔隙度、强非均质性及纳米级孔隙发育等特征给其孔隙表征带来了诸多困难,而现今的孔隙表征方法各有其优缺点,且不同的表征方法往往适用干特定的孔隙尺寸范围,单独使用准确性往往不高。为此,基于前人的研究成果,通过开展实验并对各种表征方法进行针对性分析与比较,总结出了一套集气体吸附法、核磁共振法、高压压汞法、气体孔隙度法等多种孔隙表征方法优点于一体的"整合化"表征方法,并据该方法对四川盆地下志留统龙马溪组页岩孔隙进行了表征。结果表明:①该表征方法以核磁共振法测试结果作为基准孔径分布尺度,采用优化选取、分段及加权等措施,设置不同尺度区段及其比例系数以优化表征准确度,得到的数据其衔接部分契合度较为良好,孔隙分布结果符合相关规律;②四川盆地龙马溪组页岩"整合化"后的孔隙特征与其地质性质相符,证明该表征方法能够得到在全孔隙尺度上更具有代表性的数据,可对页岩孔隙的准确表征起到一定的技术支撑作用。

An integrated shale pore characterization method : A case study of the Lower Silurian Longmaxi Formation in the Sichuan Basin

The characterization of shale is much more difficult because of its characteristics of low porosity, strong heterogeneity and existence of the nano-scale pores. Current pore characterization methods have their own advantages and disadvantages, and they are applicable to specific ranges of pore sizes, so only one single method cannot realize accurate characterization of pores in shale. Based on the previous research results, therefore, an integrated pore characterization method was established through the integration of gas adsorption, nuclear magnetic resonance, high-pressure mercury intrusion and gas porosity after experiments were performed and all characterization methods were analyzed and compared. This method was used to characterize the pores in the Lower Silurian Longmaxi shale in the Sichuan Basin. The conclusions are reached as follows. First, the measurement result by nuclear magnetic resonance is used as the datum pore diameter distribution scale for this integrated method. Scale sections and their ratio coefficients are set by means of optimization selection, segmentations and weights, so as to optimize characterization accuracy. The obtained data are better accordant at the linking parts and pore distribution is in accordance with the related rules. Second, the integrated pore characteristics of the Longmaxi shale in the Sichuan Basin fit the geologic properties. This indicates that this method can provide not only more representative data in full pore scales, but technical support for the accurate characterization of shale pores.