Influencing factors and fracability of lacustrine shale oil reservoirs

Ma, Cunfei; Dong, Chunmei; Lin, Chengyan; Elsworth, Derek; Luan, Guoqiang; Sun, Xiaolong; Liu, Xiaocen

doi:10.1016/j.marpetgeo.2019.07.002

Cited by 20 publications

(6 citation statements)

References 23 publications

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“…Furthermore, the brittleness index (BI) could be calculated to assess the mechanical fracturing. Considering the abundant OM and plastic clays in lacustrine shales, this study calculates the BI by where V felsic is the felsic portion (%), V carbonate is the carbonate portion (%), V clay is the clay portion (%), and V organic is the organic portion (%). When BI is >40%, the rock will be brittle; when BI is >60%, the rock is predicted to be highly brittle .…”

Section: Resultsmentioning

confidence: 99%

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Shale Oil Potential and Mobility of Low-Maturity Lacustrine Shales: Implications from NMR Analysis in the Bohai Bay Basin

et al. 2021

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A vital factor influencing shale oil exploration in lacustrine shale reservoirs is oil mobility, which is closely associated with the shale pore structure and fluid properties, especially for the low-maturity lacustrine shales in China. In this study, the oil mobility and shale oil potential in the Middle Eocene Shahejie Formation lacustrine shales (MES shales) of the Nanpu Sag in the Bohai Bay Basin are evaluated by using nuclear magnetic resonance (NMR) experiments. The low-maturity MES shales have low porosity with NMR porosity ranging from 4.29–7.41%, and the oil saturation ranges from 9.35–36.09%. The pore types are various including intergranular and dissolution pores and fractures. The pore space size spans the range from nano- to microscale, and they are predominantly mesopres. The pore structure for fluid flow is complex and has good self-similarity with high fractal dimensions. The abundant brittle minerals with a relatively high brittleness index value benefit the fracturing of MES shales. Due to the high viscosity and heavy oil in low-maturity shales, bulk relaxation is proposed to analyze the oil properties in this study. The oil viscosity of MES shales mainly ranges from 2 to 70 cP. The movable oil with a viscosity lower than 10 cP accounts for 53.66% of the total oil-filling pore space. For the black mud-shales dominating MES shales, the thermal maturity influences the porosity, viscosity, free hydrocarbon content, and oil saturation in the rocks. Higher thermal maturity would facilitate pore space development with higher porosity, enhance the free hydrocarbon content and oil saturation, and reduce the oil viscosity to some extent. Moreover, MES shales have geological conditions similar to and better brittleness than those of other shale oil producing areas, which further supports the considerable and promising shale oil potential in this formation, especially for deposits located in deeper positions of the Nanpu Sag. The technologies of in situ conversion process and hydraulic fracturing make the resource potential of shale oil in the Nanpu Sag more attractive.

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Section: Resultsmentioning

confidence: 99%

“…BI comparison among main lacustrine shale oil reservoirs in China. I represents the Paleogene shale sediments in the Jiangsu Basin and Jiyang Depression . II and III represent the Eocene shale sediments in the Dongying Sag and the middle Jurassic Shimengou shales in the Qaidam Basin, respectively.…”

Section: Resultsmentioning

confidence: 99%

Shale Oil Potential and Mobility of Low-Maturity Lacustrine Shales: Implications from NMR Analysis in the Bohai Bay Basin

et al. 2021

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“…Generally, a reservoir with “better” fracability can easily form a complex fracture network and enhance the reconstruction effect (He et al, 2020; Holt et al, 2015). Therefore, the fracability evaluation of the reservoirs prior to hydraulic fracturing and reconstruction is important (Ma et al, 2019; Wu et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Novel triangle method for evaluation of fracability in transitional shale: Case study from well ZXY-1 in the southern North China Basin

Chen

Li³

et al. 2022

Energy Exploration & Exploitation

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Fracability is a property widely used to evaluate whether reservoirs can effectively fracture to increase production capacity. The brittleness index, which is used to evaluate reservoir fracability, is calculated via various methods, and the evaluation process of the brittleness index is complicated and not sufficiently intuitive. Thus, we used triangle method to evaluate reservoir fracability. The shale composition is classified into strong (quartz + pyrite), moderate (carbonate + plagioclase + siderite), and poor (clay + TOC + porosity) fracability based on the mechanical parameters of each shale component, which were integrated as the endpoints of the triangle method. Meanwhile, the triangle method is divided into four fracability evaluation grades: strong (I), moderate (II), weak (III) and poor (IV) fracability; each major evaluation grade has four sub-categories: best for fracturing (1), better for fracturing (2), poor for fracturing (3) and worst for fracturing (4). The triangle method is simpler and more convenient than the conventional method, dividing the fracability evaluation grades more specifically. The difference in fracability between samples can be shown intuitively, which enhances the accuracy and reliability of the evaluation of transitional shales and provides theoretical support for reservoir reconstruction.

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“…3 unit of Qianjiang formation was characterized , and three main rock types are identified: (1) silica-rich carbonate mudstone; (2) carbonate/siliceous mudstone; (3) salt. The influencing factors of lacustrine shale oil were studied, and one formula for calculating brittleness index based on mineral composition method is proposed (Ma et al 2019). The petrographic and geochemical characteristics of the salt-water lake shale were studied by organic geochemical analysis, X-ray diffraction, scanning electron microscopy, and low-pressure nitrogen adsorption analysis (Hou et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Study on the influence of mechanical characteristics of multi-rhythm inter-salt shale oil on fracture propagation in Qianjiang formation, China

Zeng

Guo²,

Zhang³

et al. 2022

J Petrol Explor Prod Technol

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There are many inter-salt rhythmic shale reservoirs in Qianjiang sag, and the mineral composition content with different rhythms is different. The thin interbedding characteristics of inter-salt shale oil reservoirs bring technical challenges to hydraulic fracturing. Taking one shale oil well in Qianjiang depression as an example, the mechanical properties and interface characteristics of rock under temperature and confining pressure are analyzed. The physical simulation test of fracture propagation under different fracturing fluid is completed, and the effects of four different factors on fracture propagation are analyzed by numerical analysis method. The results show that the mechanical characteristic and failure modes with different rhythms are obvious differences. Under uniaxial and triaxial compression, glauberite mudstone and shale have high strength, and salt rock shows obvious plastic deformation characteristics. The interbedded rock has clear interface characteristics. The cohesion of glauberite mudstone and shale bedding surface obtained from direct shear test is 0.60 MPa and 0.99 MPa. The fracture morphology of inter-salt shale is mainly affected by the development degree of rock bedding. The mechanical parameters, in situ stress difference, and the displacement have an important impact on the longitudinal propagation of fracturing fractures. The width and height of fracture propagation decrease, with the increase in the minimum horizontal principal stress in the salt layer, and the width of fracture in shale increases. The crack height decreases with the increase in tensile strength of the interlayer. With the increase in fracturing fluid injection rate from 3.0 to 7.0 ml/min, the propagation height of hydraulic fractures and the width of fractures in shale increase significantly. The research results can apply to understanding the mechanism of hydraulic fracture propagation in inter-salt shale formation.

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Influencing factors and fracability of lacustrine shale oil reservoirs

Cited by 20 publications

References 23 publications

Shale Oil Potential and Mobility of Low-Maturity Lacustrine Shales: Implications from NMR Analysis in the Bohai Bay Basin

Shale Oil Potential and Mobility of Low-Maturity Lacustrine Shales: Implications from NMR Analysis in the Bohai Bay Basin

Novel triangle method for evaluation of fracability in transitional shale: Case study from well ZXY-1 in the southern North China Basin

Study on the influence of mechanical characteristics of multi-rhythm inter-salt shale oil on fracture propagation in Qianjiang formation, China

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