Hopanes and tricyclic terpanes were identified as the dominant terpanes in crude oils and source rock extracts many decades ago. The majority of terpane fingerprints consist of tricyclic terpanes ranging from C₁₉ to C₃₀ (higher members of the tricyclic terpanes are also present but typically not clearly evident due to the abundance of the hopanes) and hopanes ranging from C₂₇ to C₃₅. Within these two families of terpanes, variations will be observed resulting from factors such as source, depositional environments, maturity, biodegradation and migration. However, the most significant departure from a typical tricyclic and hopane type distribution is one entirely dominated by the tricyclic terpanes with the series extending to at least C₄₀ and in many cases, beyond. There are a few reported occurrences of such distributions in the literature, but satisfactory explanations are limited and speculative.

Characterization of numerous oils from Devonian-Mississippian age reservoirs in the STACK play in the Anadarko Basin, Oklahoma, has revealed that many of these oils have terpane fingerprints dominated by tricyclic terpanes with the virtual absence of hopanes. It is also of interest to note that there appear to be four additional series of tricyclic terpanes in many of these samples. While attempting to explain these distributions using previously published arguments, it appears there may be other factors at work leading to the dominance of the tricyclic terpanes in this region.

This paper discusses previous explanations put forward to explain these somewhat unusual terpane distributions, followed by a brief discussion of the terpane distributions in the STACK oils. Similar distributions of tricyclic terpanes have also been observed in a number of Mississippian rocks in the region, suggesting a possible source for the tricyclic terpanes in these oils. Results from these rock extracts are integrated into the discussion related to the oils.

In summary, it appears that maturity is probably the most significant driving force for these distributions, with preferential production of hopanes over the tricyclic terpanes at lower maturity levels. At the higher levels of maturity experienced by the unconventional reservoirs, only tricyclic precursors remain to generate oils dominated by the tricyclic terpanes. At the same time, potential source contributions cannot be ignored, as shown by the presence of extracts dominated by tricyclic terpanes in many of these core extracts.

几十年前，Hop烷和三环萜烯被确定为原油和烃源岩提取物中的主要萜烯。大多数萜烯指纹由C ₁₉至C ₃₀的三环萜烯组成（也存在较高的三环萜烯成员，但由于the烷的丰度，通常不明显）和C ₂₇至C _35的hop烷。在这两个萜族中，将观察到由于来源，沉积环境，成熟度，生物降解和迁移等因素而引起的变化。但是，与典型的三环和hop烷类型分布最显着的不同之处是，三环萜完全占据了主导地位，其系列至少延伸至C ₄₀，在许多情况下甚至超过了C ₄₀。文献中已经报道了这种分布的少数情况，但是令人满意的解释是有限的和推测性的。

在俄克拉荷马州的阿纳达科盆地的STACK层中，泥盆纪-密西西比时代油藏中的多种油的特征表明，这些油中有许多具有三环萜烯为主的萜烯指纹，而实际上没有s烷。还需要注意的是，在许多这些样品中似乎还有四个其他系列的三环萜烯。在尝试使用以前发表的论点解释这些分布时，似乎还有其他因素在起作用，导致该地区三环萜烯占主导地位。

本文讨论了先前提出的解释，以解释这些有些不同寻常的萜烯分布，然后简要讨论了STACK油中的萜烯分布。在该地区的许多密西西比岩石中也观察到了类似的三环萜烯分布，这表明这些油中三环萜烯的可能来源。这些岩石提取物的结果被整合到与油有关的讨论中。

总而言之，似乎成熟度可能是这些分布的最重要驱动力，在较低成熟度水平上，hop烷的生产优于三环萜烯。在非常规油藏经历的较高的成熟度水平下，仅三环前驱物仍然保留，以产生以三环萜烯为主的油。同时，正如许多此类核心提取物中以三环萜烯为主的提取物的存在所表明的那样，潜在的来源贡献不容忽视。