Controls of hydrocarbon generation on the development of expulsion fractures in organic-rich shale: Based on the Paleogene Shahejie Formation in the Jiyang Depression, Bohai Bay Basin, East China

Ma, Cunfei; Elsworth, Derek; Dong, Changyin; Lin, Chengyan; Luan, Guoqiang; Chen, Bingyi; Liu, Xiaocen; Munawar, Muhammad Jawad; Muhammad, Aleem Zahid; Shen, Zhengchun; Tian, Fang

doi:10.1016/j.marpetgeo.2017.07.035

Cited by 29 publications

(8 citation statements)

References 39 publications

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“…3). This contrasts with catagenesis (Flores, 2014) which could induce volume swelling and produce fracture; though, such fractures would be expected to preferentially form in organic matter preserving shale layers (Ma et al, 2017). The theory of systematic joints in sedimentary rocks predicts that joint abundance is proportional to the inverse of the bed thickness (Hobbs, 1967).…”

Section: Discussionmentioning

confidence: 99%

Silica diagenesis-driven fracturing in limestone: an example from the Ordovician of Central Pennsylvania

Hoyt

Hooker

2020

Preprint

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Abstract. Fracture patterns, interactions, and crosscutting relationships are tools for interpretation of fractures as paleostress indicators for past tectonic events and as past or present-day fluid-flow networks. In the Appalachian Basin in Central Pennsylvania along Mount Nittany Expressway Route 322 lies a significantly stratified fracture set hosted in Ordovician age limestone. Tectonic strain is a problematic mechanism for these fractures because they are hosted in individual beds lacking apparent mechanical significance relative to other limestone beds in the outcrop. Many of the fractures are layer-parallel, a characteristic commonly observed in shales, due to shales' mechanical anisotropy and tendency to develop fluid overpressures; however, these fracture-hosting limestones lack obvious mechanical anisotropy. Fracture orientations vary, but desiccation, bentonite swelling, and dolomitization are eliminated by an interpreted transgressional paleoenvironment and a deficiency of the hypothesized minerals. X-ray diffraction determined the composition of samples collected, point-count quantification determined fracture intensity, and optical petrography recorded scaled petrographic photographs. Comparison between fracture intensity and host-rock minerals reveal that silica content is consistently depleted in fractured layers relative to unfractured layers. The diagenetic transition of biogenic silica to quartz is suggested to be the driving mechanism based on silica being present as biogenic grains, as well as cement and detrital grains, and fractures being filled with calcite cement. Silica migration explains the volume lost from fractured layers in a proposed horizontal fracturing mechanism whereby the host rock shrinks but is excluded from vertical contraction.

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Section: Discussionmentioning

confidence: 99%

Silica diagenesis-driven fracturing in limestone: an example from the Ordovician of Central Pennsylvania

Hoyt

Hooker

2020

Preprint

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“…Laboratory studies on immature shale samples have been performed and fracturing induced by kerogen maturation was visualized using either scanning electron microscopy (Allan et al, 2014; Ma et al, 2017) or time‐lapse synchrotron X‐ray microtomography (Kobchenko et al, 2011; Panahi et al, 2013). All these experiments were carried out without external stress applied and showed kerogen maturation‐induced fracture propagation along the bedding plane, which corresponds to the preferential direction of the penny‐shaped kerogen patches.…”

Section: Discussionmentioning

confidence: 99%

Layering in Shales Controls Microfracturing at the Onset of Primary Migration in Source Rocks

et al. 2020

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The process of primary migration, which controls the transfer of hydrocarbons from source to reservoir rocks, necessitates the existence of fluid pathways in low permeability sedimentary formations. Primary migration starts with the maturation of organic matter which produces fluids that increase the effective stress locally. The interactions between local fluid production, microfracturing, stress conditions, and transport remain difficult to apprehend in shale source rocks. Here, we analyze these interactions using a coupled hydro‐mechanical numerical model based on the discrete element method. The model is used to simulate the effects of fluid production emanating from kerogen patches contained within a shale rock alternating kerogen‐poor and kerogen‐rich layers. We identify two microfracturing mechanisms that control fluid migration: (i) propagation of hydraulically driven fractures induced by kerogen maturation in kerogen‐rich layers and (ii) compression‐induced fracturing in kerogen‐poor layers caused by fluid overpressurization of the surrounding kerogen‐rich layers. The relative importance of these two mechanisms is discussed considering different elastic properties contrasts between the shale layers, as well as various stress conditions encountered in sedimentary basins, from normal to reverse faulting regimes. The layering in shales causes local stress redistribution that controls the prevalence of each mechanism over the other and the onset of microfracturing during kerogen maturation. The approach is applied to the Draupne formation, a major source rock in the Norwegian continental shelf in the North Sea.

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“…Type I kerogen generates hydrocarbon primarily through depolymerization, which forms the internal OM pores. In contrast, type II kerogen generates hydrocarbon through depolymerization and parallel defunctionalization, which produces the internal OM pores and edge pores (Ma et al, 2017). The internal OM pores are mostly round, elliptical, bubble-like, and irregular, while the organic matter edge pores are mainly slit-like or mesh-like.…”

Section: Om Poresmentioning

confidence: 99%

Characteristics and Controlling Factors of Shale Oil Reservoir Spaces in the Bohai Bay Basin

Deng

Chen

et al. 2020

Acta Geologica Sinica (Eng)

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The Cenozoic continental strata of the Bohai Bay Basin are rich in shale oil resources, and they contain various types of reservoir spaces that are controlled by complex factors. Using field emission scanning electron microscopy (FE-SEM), automatic mineral identification and characterization system (AMICS), CO 2 and N 2 gas adsorption, and focused ion beam scanning electron microscopy (FIB-SEM), the types of shale reservoir spaces in the Bohai Bay Basin are summarized, the spatial distribution and connectivity of the various types of pores are described in detail, the microscopic pore structures are characterized, and the key geological mechanisms affecting the formation and evolution of the reservoir spaces are determined. Three conclusions can be drawn in the present study. First, the shale reservoir spaces in the Bohai Bay Basin can be divided into three broad categories, including mineral matrix pores, organic matter pores, and micro fractures. Those spaces can be subdivided into seven categories and fourteen sub-categories based on the distribution and formation mechanisms of the pores. Second, the complex pore-throat structures of the shale reservoir can be divided into two types based on the shape of the adsorption hysteresis loop. The pore structures mainly include wedge-shaped, flat slit-shaped, and ink bottle-shaped pores. The mesopores and micropores are the main contributors to pore volume and specific surface area, respectively. The macropores provide a portion of the pore volume, but they do not significantly contribute to the specific surface area. Third, the factors controlling the development of microscopic pores in the shale are complex. The sedimentary environment determines the composition and structure of the shale and provides the material basis for pore development. Diagenesis controls the types and characteristics of the pores. In addition, the thermal evolution of the organic matter is closely related to inorganic diagenesis and drives the formation and evolution of the pores.

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Controls of hydrocarbon generation on the development of expulsion fractures in organic-rich shale: Based on the Paleogene Shahejie Formation in the Jiyang Depression, Bohai Bay Basin, East China

Cited by 29 publications

References 39 publications

Silica diagenesis-driven fracturing in limestone: an example from the Ordovician of Central Pennsylvania

Silica diagenesis-driven fracturing in limestone: an example from the Ordovician of Central Pennsylvania

Layering in Shales Controls Microfracturing at the Onset of Primary Migration in Source Rocks

Characteristics and Controlling Factors of Shale Oil Reservoir Spaces in the Bohai Bay Basin

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