TY - JOUR
T1 - Controls of hydrocarbon generation on the development of expulsion fractures in organic-rich shale
T2 - Based on the Paleogene Shahejie Formation in the Jiyang Depression, Bohai Bay Basin, East China
AU - Ma, Cunfei
AU - Elsworth, Derek
AU - Dong, Chunmei
AU - Lin, Chengyan
AU - Luan, Guoqiang
AU - Chen, Bingyi
AU - Liu, Xiaocen
AU - Muhammad, Jawad Munawar
AU - Muhammad, Aleem Zahid
AU - Shen, Zhengchun
AU - Tian, Fuchun
N1 - Funding Information:
This work was funded by China Scholarship Council (Grant No. 201506450031) and National Science and Technology Major Project, P.R. China (Grant No. 2011ZX05009-003, 2017ZX05009-001). We thank Professor Qiang Jin from China University of Petroleum (East China) for his constructive suggestions on the design of thermal simulation experiments. We thank Professor Terry Engelder and Professor Michael Arthur from the Pennsylvania State University for their beneficial discussion on the origin of expulsion fractures in shale.
Publisher Copyright:
© 2017
PY - 2017/9
Y1 - 2017/9
N2 - The development of expulsion fractures in organic-rich shale is closely related to hydrocarbon generation and expulsion from kerogen. Organic-rich shales from the upper part of the fourth member and the lower part of the third member of the Paleogene Shahejie Formation in the Jiyang Depression, Bohai Bay Basin, East China, are used as an example. Based on thin sections, SEM and thermal simulation experiments, the characteristics of hydrocarbon generation and the conditions supporting the development of expulsion fractures were explored. The key factors influencing these fractures include the presence of kerogens, their distribution along laminae and around particle boundaries, their exposure to heat and the build-up in pressure due to confinement by low permeability. The development of excess pore fluid pressures and intrinsic low rock fracture strength are the main influencing factors. Pressurization by rapid generation of hydrocarbon provides impetus for fracture initiation and cause bitumen to migrate quickly. The shale laminae results in distinctly lower fracture strength laminae-parallel than laminae-normal and this directs the formation of new fractures in the direction of weakness. When pore fluid pressure increases, maximum and minimum principal effective stresses decrease by different proportions with a larger reduction in the maximum principal effective stress. This increases the deviatoric stress and reduces the mean stress, thus driving the rock towards failure. Moreover, the tabular shape of the kerogen aids the generation of hydrocarbon and the initiation of expulsion fractures from the tip and edge. The resulting fractures extend along the laminae when the tensile strength is lower in the vertical direction than in the horizontal direction. Particle contact boundaries are weak and allow fractures to expand around particles and to curve as the stress/strength regime changes. When pore fluid pressure fields at different fracture tips overlap, fractures will propagate and interconnect, forming a network. This paper could provide us more detailed understanding of the forming processes of expulsion fractures and better comprehension about hydrocarbon expulsion (primary migration) in source rocks.
AB - The development of expulsion fractures in organic-rich shale is closely related to hydrocarbon generation and expulsion from kerogen. Organic-rich shales from the upper part of the fourth member and the lower part of the third member of the Paleogene Shahejie Formation in the Jiyang Depression, Bohai Bay Basin, East China, are used as an example. Based on thin sections, SEM and thermal simulation experiments, the characteristics of hydrocarbon generation and the conditions supporting the development of expulsion fractures were explored. The key factors influencing these fractures include the presence of kerogens, their distribution along laminae and around particle boundaries, their exposure to heat and the build-up in pressure due to confinement by low permeability. The development of excess pore fluid pressures and intrinsic low rock fracture strength are the main influencing factors. Pressurization by rapid generation of hydrocarbon provides impetus for fracture initiation and cause bitumen to migrate quickly. The shale laminae results in distinctly lower fracture strength laminae-parallel than laminae-normal and this directs the formation of new fractures in the direction of weakness. When pore fluid pressure increases, maximum and minimum principal effective stresses decrease by different proportions with a larger reduction in the maximum principal effective stress. This increases the deviatoric stress and reduces the mean stress, thus driving the rock towards failure. Moreover, the tabular shape of the kerogen aids the generation of hydrocarbon and the initiation of expulsion fractures from the tip and edge. The resulting fractures extend along the laminae when the tensile strength is lower in the vertical direction than in the horizontal direction. Particle contact boundaries are weak and allow fractures to expand around particles and to curve as the stress/strength regime changes. When pore fluid pressure fields at different fracture tips overlap, fractures will propagate and interconnect, forming a network. This paper could provide us more detailed understanding of the forming processes of expulsion fractures and better comprehension about hydrocarbon expulsion (primary migration) in source rocks.
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U2 - 10.1016/j.marpetgeo.2017.07.035
DO - 10.1016/j.marpetgeo.2017.07.035
M3 - Article
AN - SCOPUS:85026682362
SN - 0264-8172
VL - 86
SP - 1406
EP - 1416
JO - Marine and Petroleum Geology
JF - Marine and Petroleum Geology
ER -