Sanei Hamed, Ardakani Omid H, Akai Takashi, Akihisa Kunio, Jiang Chunqing, Wood James M
Lithospheric Organic Carbon Group (LOC), Department of Geoscience, Aarhus University, Aarhus, Denmark.
Natural Resources Canada, Geological Survey of Canada, Calgary, Alberta, Canada.
Sci Rep. 2020 May 13;10(1):7920. doi: 10.1038/s41598-020-64936-y.
Core samples from petroleum wells are costly to obtain, hence drill cuttings are commonly used as an alternative source of rock measurements for reservoir, basin modelling, and sedimentology studies. However, serious issues such as contamination from drilling mud, geological representativeness, and physical alteration can cast uncertainty on the results of studies based on cuttings samples. This paper provides a unique comparative study of core and cuttings samples obtained from both vertical and horizontal sections of a petroleum well drilled in the Canadian Montney tight gas siltstone reservoir to investigate the suitability of cuttings for a wide range of geochemical and petrophysical analyses. The results show that, on average, the bulk quantity of kerogen or solid bitumen measured in cuttings is comparable to that of the core samples. However, total organic carbon (TOC) measurements are influenced by oil-based drilling mud (OBM) contamination. Solvent-cleaning of cuttings has been shown to effectively remove OBM contamination in light, medium, and heavy range hydrocarbons and to produce similar kerogen/solid bitumen measurements to that of core samples. Similarly, pyrolysis methods provide an alternative to the solvent-cleaning procedure for analysis of kerogen/solid bitumen in as-received cuttings. Microscopic study substantiates the presence of significant contamination by OBM and caved organic and inorganic matter in the cuttings, which potentially influence the bulk geochemistry of the samples. Furthermore, minerals in the cuttings display induced micro-fractures due to physical impacts of the drilling process. These drilling-induced micro-fractures affect petrophysical properties by artificially enhancing the measured porosity and permeability.
获取石油井的岩芯样本成本高昂，因此钻屑通常被用作储层、盆地建模和沉积学研究中岩石测量的替代来源。然而，诸如钻井泥浆污染、地质代表性和物理改变等严重问题可能会使基于钻屑样本的研究结果产生不确定性。本文对从加拿大蒙特尼致密气粉砂岩储层的一口石油井的垂直和水平段获取的岩芯和钻屑样本进行了独特的对比研究，以调查钻屑在广泛的地球化学和岩石物理分析中的适用性。结果表明，平均而言，钻屑中测得的干酪根或固体沥青的总量与岩芯样本相当。然而，总有机碳（TOC）测量受油基钻井泥浆（OBM）污染的影响。已证明对钻屑进行溶剂清洗可有效去除轻、中、重质烃类中的OBM污染，并产生与岩芯样本类似的干酪根/固体沥青测量结果。同样，热解方法为分析原样钻屑中的干酪根/固体沥青提供了一种替代溶剂清洗程序的方法。显微镜研究证实了钻屑中存在大量OBM以及坍塌的有机和无机物质污染，这可能会影响样本的整体地球化学。此外，钻屑中的矿物由于钻井过程的物理冲击而显示出诱导微裂缝。这些钻井诱导的微裂缝通过人为提高测量的孔隙度和渗透率来影响岩石物理性质。
