Evaluation method for resource potential of shale oil in the Triassic Yanchang Formation of the Ordos Basin, China

Abstract

<jats:p> The widely distributed, thick Chang 7 Shale is the richest shale oil formation in China. A calculation method for the evaporative hydrocarbon recovery coefficient based on formation volume factor is proposed considering the correction of heterogeneity-based total organic carbon differences to improve the adsorbed oil calculation method, and light hydrocarbon evaporative sampling losses, which can make mobile and total oil calculations more accurate. The adsorbed oil, S1 evaporative loss, total oil yield, and movable oil yield of 200 shale samples from the Chang 7 Member were calculated using the new methods. Results show that S1 evaporative loss accounts for 29% of S1, total oil yield is 3.5 times S1, and movable oil yield accounts for 37% of total oil yield. Based on the calculated total oil yield and movable oil yield results, the relationships among total oil yield, movable oil yield, and total organic carbon of the Chang 7 were established yielding total oil yield and movable oil yield estimates of 11.12 × 10<jats:sup>9</jats:sup> t and 4.01 × 10<jats:sup>9</jats:sup> t, respectively, revealing its tremendous shale exploration potential. </jats:p>

Occurrence Space and State of Petroleum in Lacustrine Shale: Insights from Two-Step Pyrolysis and the N2 Adsorption Experiment

“…Through pyrolysis methods, Li et al calculated the shale resource amount of Shahejie Formation in Dongying Sag (Bohai Bay Basin) and obtained the proportion of free oil that varies between 44.70 and 55.80%. Guo et al used similar methods to evaluate shale oil in Chang 7 member of Ordos Basin and obtained that the ratio of MOY to TOY is 37.00%. In this study, the average proportion of free oil in the Fengcheng shale of the Junggar Basin is high (57.17%), indicating that shale oil has great exploitation potential.…”

“…Through pyrolysis methods, Li et al 50 calculated the shale resource amount of Shahejie Formation in Dongying Sag (Bohai Bay Basin) and obtained the proportion of free oil that varies between 44.70 and 55.80%. Guo et al 49 used similar methods to evaluate shale oil in Chang 7 member of Ordos Basin and obtained that the ratio of MOY to TOY is 37.00%.…”

“…Previous studies have shown that the oil mainly occurs in two states in shale: free and adsorbed. ,− Therefore, characterizing the quantity of shale oil accurately and quantitatively in different physical states has always been a divergent scientific issue. At present, solvent extraction and pyrolysis methods are widely used to predict the physical state and the amount of hydrocarbons in liquid-rich unconventional systems. ,− Compared with solvent extraction, pyrolysis is an efficient and fast screening tool to evaluate the in-situ hydrocarbon characteristics in shale plays. ,,− However, because of the carry-over effect, the standard pyrolysis S 1 value cannot be directly regarded as an indicator of shale oil content. ,, Its use may lead to an erroneous estimation of the quantities of hydrocarbons. , Therefore, the article that cites Jarvie's method proposed the two-step pyrolysis method, which can distinguish and evaluate oil in different physical states and has been widely cited in subsequent studies. ,,− …”

Characteristics of Oil and Gas Produced by In Situ Heating of Shale: A Case Study of the Chang 7 Member, Ordos Basin, China

“…The Triassic Yanchang Formation in the basin comprises continental clastic deposits and is divided into 10 members. Organic-rich shale occurs mainly in the Chang 7 member, which covers an area of (5–10) × 10 4 km 2 with a thickness of 70–130 m. , The maturity of the Yanchang Formation shale is low at <1.1%, and the organic matter comprises type II kerogen . Although it is not an optimal source rock, its organic matter content is high with total organic carbon (TOC) contents up to 35 wt %, averaging at 14 wt % .…”

Organic matter heterogeneity and shale oil significance in Triassic Zhangjiatan shale, Ordos Basin, China

“…Shale oil is abundant throughout the world, and it is considered to be a strategic alternative resource to solve the energy crisis in China (Guo et al, 2020; Zhao et al, 2020; Zou, 2017). There are abundant unconventional oil resources in the Chang 7 member of the Triassic Yanchang Formation in the Ordos Basin.…”