Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production

Abstract Brittleness and ductility of shale are closely related to shale gas exploration and production. How to predict brittleness and ductility of shale is one of the key issues in the study of shale gas preservation and hydraulic fracturing treatments. The magnitude of shale brittleness was often...

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Autores principales:	Yu-Song Yuan, Zhi-Jun Jin, Yan Zhou, Jun-Xin Liu, Shuang-Jian Li, Quan-You Liu
Formato:	article
Lenguaje:	EN
Publicado:	KeAi Communications Co., Ltd. 2017
Materias:	Shale Brittleness Fracture Over-consolidation ratio (OCR) Confining pressure Science Q Petrology QE420-499
Acceso en línea:	https://doaj.org/article/5366a1a465ce4571a6005dc471a2282e
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spelling	oai:doaj.org-article:5366a1a465ce4571a6005dc471a2282e2021-12-02T06:02:49ZBurial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production10.1007/s12182-017-0189-71672-51071995-8226https://doaj.org/article/5366a1a465ce4571a6005dc471a2282e2017-10-01T00:00:00Zhttp://link.springer.com/article/10.1007/s12182-017-0189-7https://doaj.org/toc/1672-5107https://doaj.org/toc/1995-8226Abstract Brittleness and ductility of shale are closely related to shale gas exploration and production. How to predict brittleness and ductility of shale is one of the key issues in the study of shale gas preservation and hydraulic fracturing treatments. The magnitude of shale brittleness was often determined by brittle mineral content (for example, quartz and feldspars) in shale gas exploration. However, the shale brittleness is also controlled by burial depth. Shale brittle/ductile properties such as brittle, semi-brittle and ductile can mutually transform with burial depth variation. We established a work flow of determining the burial depth interval of brittle–ductile transition zone for a given shale. Two boundaries were employed to divide the burial depth interval of shale brittle/ductile properties. One is the bottom boundary of the brittle zone (BZ), and the other is the top boundary of the ductile zone (DZ). The brittle–ductile transition zone (BDTZ) is between them. The bottom boundary of BZ was determined by the over-consolidation ratio (OCR) threshold value combined with pre-consolidation stress which the shale experienced over geological time. The top boundary of DZ was determined based on the critical confining pressure of brittle–ductile transition. The OCR threshold value and the critical confining pressure were obtained from uniaxial strain and triaxial compression tests. The BZ, DZ and BDTZ of the Lower Silurian Longmaxi shale in some representative shale gas exploration wells in eastern Sichuan and western Hubei areas were determined according to the above work flow. The results show that the BZ varies with the maximum burial depth and the DZ varies with the density of the overlying rocks except for the critical confining pressure. Moreover, the BDTZ determined by the above work flow is probably the best burial depth interval for marine shale gas exploration and production in Southern China. Shale located in the BDTZ is semi-brittle and is not prone to be severely naturally fractured but likely to respond well to hydraulic fracturing. The depth interval of BDTZ determined by our work flow could be a valuable parameter of shale gas estimation in geology and engineering.Yu-Song YuanZhi-Jun JinYan ZhouJun-Xin LiuShuang-Jian LiQuan-You LiuKeAi Communications Co., Ltd.articleShaleBrittlenessFractureOver-consolidation ratio (OCR)Confining pressureScienceQPetrologyQE420-499ENPetroleum Science, Vol 14, Iss 4, Pp 637-647 (2017)
institution	DOAJ
collection	DOAJ
language	EN
topic	Shale Brittleness Fracture Over-consolidation ratio (OCR) Confining pressure Science Q Petrology QE420-499
spellingShingle	Shale Brittleness Fracture Over-consolidation ratio (OCR) Confining pressure Science Q Petrology QE420-499 Yu-Song Yuan Zhi-Jun Jin Yan Zhou Jun-Xin Liu Shuang-Jian Li Quan-You Liu Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production
description	Abstract Brittleness and ductility of shale are closely related to shale gas exploration and production. How to predict brittleness and ductility of shale is one of the key issues in the study of shale gas preservation and hydraulic fracturing treatments. The magnitude of shale brittleness was often determined by brittle mineral content (for example, quartz and feldspars) in shale gas exploration. However, the shale brittleness is also controlled by burial depth. Shale brittle/ductile properties such as brittle, semi-brittle and ductile can mutually transform with burial depth variation. We established a work flow of determining the burial depth interval of brittle–ductile transition zone for a given shale. Two boundaries were employed to divide the burial depth interval of shale brittle/ductile properties. One is the bottom boundary of the brittle zone (BZ), and the other is the top boundary of the ductile zone (DZ). The brittle–ductile transition zone (BDTZ) is between them. The bottom boundary of BZ was determined by the over-consolidation ratio (OCR) threshold value combined with pre-consolidation stress which the shale experienced over geological time. The top boundary of DZ was determined based on the critical confining pressure of brittle–ductile transition. The OCR threshold value and the critical confining pressure were obtained from uniaxial strain and triaxial compression tests. The BZ, DZ and BDTZ of the Lower Silurian Longmaxi shale in some representative shale gas exploration wells in eastern Sichuan and western Hubei areas were determined according to the above work flow. The results show that the BZ varies with the maximum burial depth and the DZ varies with the density of the overlying rocks except for the critical confining pressure. Moreover, the BDTZ determined by the above work flow is probably the best burial depth interval for marine shale gas exploration and production in Southern China. Shale located in the BDTZ is semi-brittle and is not prone to be severely naturally fractured but likely to respond well to hydraulic fracturing. The depth interval of BDTZ determined by our work flow could be a valuable parameter of shale gas estimation in geology and engineering.
format	article
author	Yu-Song Yuan Zhi-Jun Jin Yan Zhou Jun-Xin Liu Shuang-Jian Li Quan-You Liu
author_facet	Yu-Song Yuan Zhi-Jun Jin Yan Zhou Jun-Xin Liu Shuang-Jian Li Quan-You Liu
author_sort	Yu-Song Yuan
title	Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production
title_short	Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production
title_full	Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production
title_fullStr	Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production
title_full_unstemmed	Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production
title_sort	burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production
publisher	KeAi Communications Co., Ltd.
publishDate	2017
url	https://doaj.org/article/5366a1a465ce4571a6005dc471a2282e
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Burial depth interval of the shale brittle–ductile transition zone and its implications in shale gas exploration and production

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