Nanopore structure comparison between shale oil and shale gas:examples from the Bakken and Longmaxi Formations

In order to analyze and compare the differences in pore structures between shale gas and shale oil formations, a few samples from the Longmaxi and Bakken Formations were collected and studied using X-ray diffraction, LECO TOC measurement, gas adsorption and field-emission scanning electron microscope. The results show that samples from the Bakken Formation have a higher TOC than those from the Longmaxi Formation. The Longmaxi Formation has higher micropore volume and larger micropore surface area and exhibited a smaller average distribution of microsize pores compared to the Bakken Formation. Both formations have similar meso-macropore volume. The Longmaxi Formation has a much larger meso-macropore surface area, which is corresponding to a smaller average meso-macropore size. CO_2 adsorption data processing shows that the pore size of the majority of the micropores in the samples from the Longmaxi Formation is less than 1 nm, while the pore size of the most of the micropores in the samples from the Bakken Formation is larger than 1 nm. Both formations have the same number of pore clusters in the 2–20 nm range, but the Bakken Formation has two additional pore size groups with mean pore size diameters larger than 20 nm. Multifractal analysis of pore size distribution curves that was derived from gas adsorption indicates that the samples from the Longmaxi Formation have more significant micropore heterogeneity and less meso-macropore heterogeneity. Abundant micropores as well as mesomacropores exist in the organic matter in the Longmaxi Formation, while the organic matter of the Bakken Formation hosts mainly micropores.

美国北达科他州巴肯烃源岩的热成熟度测井预测

利用页岩的岩石物理和岩石力学特征结合地球化学特征构建预测模型的研究已广泛开展。本研究将利用一系列测井资料预测巴肯泥岩的热成熟度。首先,利用横波和纵波速度以及密度获取动态模量(Ed),然后利用己有的Ed和Ei的实验关系获取Ei(基于纳米压痕的杨氏模量)。之后,利用测井曲线得到的泥岩E和实测TOC建立经验公式,解释单井TOC曲线。三口井实测TOC和计算值的差值在合理误差范围内。在缺乏镜质组成分时,采用固体沥青的反射率(BRo%)作为反映成熟度的指标,并建立了12口井GR/NPHI/RHOZ和BR0%的关系。根据不同测井曲线与BR0%的相关性,重新定义了“■”反映成熟度,结果发现■与BR0%在整个泥岩段均有较好的相关性。最终,可以利用BR0%与实测Tmax计算巴肯泥岩的Tmax曲线。使用重构的GR/NPHI/RHOZ曲线,可以构建BR0%和Tmax的三维地质模型,进而开展含油气系统的评价。