Hackley Paul C, Scott Clint, Birdwell Justin E, Nedzweckas Jennifer L, Valentine Brett J, Zhang Tongwei, Nesheim Timothy O
U.S. Geological Survey, Reston, Virginia 20192, United States.
U.S. Geological Survey, Lakewood, Colorado 80225, United States.
ACS Omega. 2024 Jul 26;9(31):33983-33997. doi: 10.1021/acsomega.4c04547. eCollection 2024 Aug 6.
To further refine the use of solid bitumen reflectance (BR in %) as a measurement of thermal maturity in source-rock reservoirs, we examined its relationship to other thermal proxies in the Bakken Formation. Comparisons included criteria from programmed temperature pyrolysis, gas chromatography (GC), and Fourier transform infrared (FTIR) spectroscopy. Thirty-two organic-rich samples from the lower and upper shale members of the Devonian-Lower Carboniferous Bakken Formation were collected from eight cores across the Williston Basin, USA, at depths (∼7575-11,330 ft) representing immature through post peak oil/early condensate thermal maturity conditions based on proximity to current hydrocarbon production. Unmodified BR values were correlated to programmed temperature pyrolysis parameters (hydrogen index, production index, and ), normal hydrocarbon and isoprenoid analysis of extractable organic matter (pristane/-C and phytane/-C) from GC analysis, and peak ratios from FTIR spectroscopy (branching ratio and -factor). Strong correlations between unmodified BR values (not corrected to a vitrinite reflectance equivalent, VR) and other thermal proxies suggest that BR can be used as a direct thermal proxy in marine Paleozoic source-rock reservoirs where vitrinite is rare or absent. Moreover, an apparent overestimation of VR at the lowest thermal maturity investigated herein may argue against the application of BR conversion to VR in the Bakken Formation. Solvent extraction caused a consistent decrease in BR when average post-extraction values from a given well were compared to BR prior to extraction, although the decrease in mean value was not statistically significant. These results are discussed in the context of advocating for the use of unmodified BR values as a best practice for thermal maturity determination in Paleozoic marine source-rock reservoirs.
为了进一步优化将固体沥青反射率（以%计的BR）用作烃源岩储层热成熟度的测量指标，我们研究了它与巴肯组中其他热指标的关系。对比包括程序升温热解、气相色谱（GC）和傅里叶变换红外（FTIR）光谱的标准。从美国威利斯顿盆地的8个岩芯中采集了32个来自泥盆纪-下石炭统巴肯组下部和上部富有机质页岩段的样品，深度约为7575 - 11330英尺，这些深度代表了从不成熟到油峰后/早期凝析油热成熟度条件，依据与当前油气生产的距离来确定。未修正的BR值与程序升温热解参数（氢指数、产率指数和）、GC分析中可提取有机质的正构烃和类异戊二烯分析（姥鲛烷/C和植烷/C）以及FTIR光谱的峰面积比（支化比和因子）相关。未修正的BR值（未校正为镜质体反射率当量，VR）与其他热指标之间的强相关性表明，在镜质体稀少或缺失的海相古生代烃源岩储层中，BR可作为直接的热指标。此外，本文研究的最低热成熟度下VR明显被高估，这可能反对在巴肯组中将BR转换为VR的应用。当将给定井的萃取后平均值与萃取前的BR进行比较时，溶剂萃取导致BR持续下降，尽管平均值的下降在统计学上不显著。在倡导将未修正的BR值用作古生代海相烃源岩储层热成熟度测定的最佳实践的背景下，对这些结果进行了讨论。
