Assessment of shale oil potential using a new free hydrocarbon index

Li, Shuifu; Hu, Shouzhi; Xie, Xinong; Lv, Qian; Huang, Xin; Ye, Jiaren

doi:10.1016/j.coal.2016.02.005

“…S 1 is the remaining hydrocarbon content in shale, which is generally used to characterize the shale oil content [3]. The OSI (oil saturation index, S 1 /TOC × 100 mg/g) is widely used to characterize the mobility of shale oil [39]. In this paper, the relationships between these two parameters and pore structure and fractal dimensions were investigated (as shown in Figure 12).…”

Section: Oil Contents Controlled By Pore Structure and Fractalmentioning

confidence: 99%

Pore Structure and Fractal Character of Lacustrine Oil-Bearing Shale from the Dongying Sag, Bohai Bay Basin, China

Zhang

¹

,

Lu

²

,

Zeng³

et al. 2021

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To better understand the pore structure and fractal character of lacustrine shales and their influence on liquid hydrocarbon occurrences, in this study, a total of 29 lacustrine oil-bearing shale samples collected from the Shahejie Formation in the Dongying Sag, Bohai Bay Basin, were investigated based on nitrogen adsorption (NGA) analysis combined with TOC, Rock-Eval pyrolysis, X-ray diffraction (XRD), and field emission-scanning electron microscopy (FE-SEM) experiments. The relationships among the compositions (TOC, minerals, and oil content), pore structures, and fractal dimensions of the lacustrine shale samples were discussed. The results showed that the adsorption and fractal characteristics of lacustrine oil-bearing shales differ at relative pressures of 0-0.1 and 0.5-1. Two corresponding fractal dimensions D 1 and D 2 were determined by the FHH model according to the nitrogen adsorption branches. Specifically, D 1 varies from 2.4292 to 2.6109 (mean 2.5245), and D 2 varies between 2.4680 and 2.8535 (mean 2.6889). The specific surface area (SSA) ranges from 1.512 m2/g to 34.002 m2/g, with an average of 13.656 m2/g, the total pore volume is between 6.0 × 10-3 cm3/g and 48.4 × 10-3 cm3/g (mean 24.5 × 10-3 cm3/g), and the average pore diameter is in the range of 4.22 nm to 19.57 nm (mean 9.35 nm). Both D 1 and D 2 increase with increasing SSA and increase with decreasing average pore diameters but have no correlation with pore volume. Moreover, D 1 and D 2 exhibit positive relationships with clay minerals and negative correlations with carbonate minerals (calcite and dolomite). The relationship between fractal dimensions ( D 1 and D 2 ) and TOC contents is expressed as a U-shaped curve, characterized by the minimum D values at approximately 3% TOC. The shale oil content is controlled by the pore structures and fractal dimensions, and lacustrine shales with lower SSAs and smaller fractal dimensions would have more free oil. Therefore, lacustrine shales in the oil window with TOC contents ranging from 2% to 4% are probably the preferred shale oil exploration target in the Shahejie Formation, Dongying Sag, Bohai Bay Basin. The results indicate that fractal analysis can provide insight into the pore structure characteristics and oil storage capacity of lacustrine shales.

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“…While the different change trends of S 1 rising slowly with the increase of TOC value and rising rapidly with low TOC (samples in circles of Fig. 5c) may be due to relatively high hydrocarbon expulsion efficiency and the external migrated hydrocarbon impact, respectively (Li et al 2016). By applying method of multivariate regression analysis, the thickness and average TOC contents of ORI 5 in 30 wells are predicted (Shang et al 2016).…”

Section: Sources and Contents Of Organic Mattermentioning

confidence: 99%

“…Higher TOC content and maturity, and better type of organic matter are beneficial to generate much hydrocarbon, and volume expansion causes overpressure in source rock, especially in sections with low hydrocarbon expulsion efficiency due to less fractures. The ORI 5 is dominated by types I and II 1 kerogen (Li et al 2016) and has maturities ranging from lowly to oil mature, kerogen being converted to oil tends to form overpressure. interlayers are well developed with better porosity and effective reservoir spaces.…”

Section: Advantageous Shale Lithofacies and Effective Reservoirsmentioning

confidence: 99%

Enrichment conditions of Hetaoyuan Formation shale oil in Biyang Depression, China

Shang

¹

,

Xie

²

,

Li

³

2018

J Petrol Explor Prod Technol

Self Cite

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In this paper, the data of thin section, organic petrology, geochemistry, lithology and porosity were used to investigate enrichment conditions of Hetaoyuan Formation shale oil in the Biyang Depression. The results show the shale oil is a kind of low-maturity oil with medium density and low viscosity, and main factors controlling shale oil enrichment include total organic content (TOC), formation pressure, lithofacies and effective reservoirs. Shales in the fifth organic-rich interval are developed widely with large thickness (reach up to 150 m), high TOC content (2.0-4.68%), better organic matter types (type I and II 1 ) and appropriate thermal maturity (usually larger than 0.5%), which are beneficial to generate much hydrocarbon, and volume expansion causes overpressure in source rock, especially in sections with low hydrocarbon expulsion efficiency due to less fractures. Free hydrocarbons S 1 values increase with TOC contents, and significant overpressure correlates with the larger OSI (S 1 /TOC × 100) values and porosity. Well-developed calcareous shales and argillaceous shales with silty shale interlayers have better porosity, and effective pores (throat diameters greater than 10 nm) contribute to 47.5% of the total volume.

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“…25 ΔS 1 represents the difference between the oil production and free oil (S 1 ) amounts of these units, and different ΔS 1 values indicate varying enrichment degrees. 25,26 However, this method cannot quantitatively evaluate the shale oil enrichment degree. Liu et al proposed a new enrichment evaluation method, namely, the oil content evaluation index (OCEI).…”

Section: Introductionmentioning

confidence: 99%

“…This value is not suitable for enrichment evaluation of lacustrine shale oil in China. Li et al divided shale into small hydrocarbon generation and expulsion units . Δ S 1 represents the difference between the oil production and free oil ( S 1 ) amounts of these units, and different Δ S 1 values indicate varying enrichment degrees. , However, this method cannot quantitatively evaluate the shale oil enrichment degree.…”

Section: Introductionmentioning

confidence: 99%

Innovative Standard for Graded Evaluation of Oil Enrichment of Lacustrine Shale: A Case Study of the Lower Third Member of the Shahejie Formation, Zhanhua Sag, Eastern China

Gong

¹

,

Jiang

²

,

Gao

³

et al. 2021

Energy Fuels

2

0

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The exploration and production results of lacustrine shale oil are closely related to shale oil enrichment evaluation. However, there exists a lack of rapid and accurate oil enrichment evaluation methods for strongly heterogeneous lacustrine shale. In this study, an innovative standard for graded evaluation of shale oil enrichment is proposed. In the innovative standard, considering the light hydrocarbon loss of shale oil, the free oil (S 1) content is corrected for light hydrocarbons. Moreover, on the basis of the hydrocarbon expulsion threshold theory, and combined with the specific geochemical characteristics of the shale in the study area, the lacustrine shale oil mobility threshold OSI (the oil saturation index) is determined to replace the fixed empirical shale oil mobility threshold (100 mg/g). By combining the absolute oil content (S 1) with the relative oil content (OSI), we are able to divide the shale oil resources into four categories: enriched resources, moderately enriched resources, low-efficient resources, and ineffective resources. This standard is successfully applied to evaluate the oil enrichment degree of the lower third member (Es3 L) of the Shahejie Formation in well Luo 69 of the Zhanhua Sag, Bohai Bay Basin. The oil enrichment degrees of shales with varying kerogen compositions and distinct lithofacies are highly diverse. Shale comprising type I kerogen is the most conducive to shale oil enrichment. However, more than 15% of the tested shales composed of type II1 kerogen include enriched and moderately enriched resources, which should be considered. Organic-fair laminated calcareous shale (OFLCS) is the most favorable lithofacies type for shale oil enrichment. The development of bedding structures and a moderate organic matter content are beneficial for shale oil enrichment. This standard is suitable for graded evaluation of the oil enrichment degree of strongly heterogeneous lacustrine shale worldwide.

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Assessment of shale oil potential using a new free hydrocarbon index

Cited by 51 publications

References 28 publications

Pore Structure and Fractal Character of Lacustrine Oil-Bearing Shale from the Dongying Sag, Bohai Bay Basin, China

Pore Structure and Fractal Character of Lacustrine Oil-Bearing Shale from the Dongying Sag, Bohai Bay Basin, China

Enrichment conditions of Hetaoyuan Formation shale oil in Biyang Depression, China

Innovative Standard for Graded Evaluation of Oil Enrichment of Lacustrine Shale: A Case Study of the Lower Third Member of the Shahejie Formation, Zhanhua Sag, Eastern China

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