埋藏过程中泥页岩非构造裂缝的形成演化模式

doi:10.11743/ogg20150514

摘要/Abstract

摘要： 通过归纳总结前人研究成果，同时考虑到泥页岩普遍具有层理发育、非均质性、力学性质各向异性、欠压实作用和烃类生成等本身固有的特殊性质，划分了泥页岩非构造裂缝的主要类型，分析了泥页岩非构造裂缝分布的深度区间。依据覆压条件下的孔隙度、渗透率测试数据，获得了泥页岩裂缝覆压闭合的临界围压和对应的深度范围。综合分析认为：泥页岩非构造裂缝主要有干裂裂缝、水下收缩裂缝、成岩层理裂缝、超压裂缝（欠压实超压裂缝和生烃超压裂缝）和现代表生裂缝5种类型。泥页岩覆压渗透率测试数据揭示，当上覆岩层的垂直有效压力达到15 MPa时，常压泥页岩的天然缝裂缝（水平方向）将发生闭合。裂缝覆压闭合门限深度为870～1 138 m，平均为1 000 m。超压泥页岩底界深度与泥页岩裂缝（水平方向）覆压闭合深度一致，超压带底界之下的泥页岩裂缝通常不再保持开启状态。埋藏过程中泥页岩非构造裂缝形成演化具有时序性/阶段性，即从沉积开始到最大埋藏深度的不同阶段，泥质沉积物或泥页岩形成不同类型的非构造裂缝，由浅至深依次形成表层干裂裂缝—浅层水下收缩裂缝—中深层欠压实超压裂缝—深层生烃超压裂缝—超深层闭合裂缝。

关键词: 裂缝闭合, 非构造裂缝, 超压裂缝, 泥页岩

Abstract: The main types of non-tectonic fractures and their depth distribution range are discussed based on the previous research and considering the inherent special properties of shale such as bedding,heterogeneity,anisotropy in mechanical properties,under-compaction and hydrocarbon generation.The critical confining pressure of shale fracture closing and its corresponding depth range are calculated by making use of porosity and permeability data measured under overburden pressure.A comprehensive analysis reveals that the non-tectonic fractures of shale can be categorized into five types,including suncrack,underwater shrinkage crack,bedding crack,overpressure fracture and modern hypergenetic fracture.The permeability data measured under confining pressure reveals that shale fracture should be closed under a vertical effective stress of about 15 MPa.The depth threshold of shale fracture closing is in the range of 870-1 138 m,averaging at 1 000 m.The depth of bottom boundary of overdressed shale is consistent with the depth of fracture(in horizontal direction)closing under overlying pressure and the fractures in shale under the bottom boundary of overpressure zone are no longer open.The formation and evolution of non-tectonic fractures of shale in burial history feature in time sequence/episode,i.e.different types of non-tectonic fractures develop in different stages from the deposition to maximum buried depth.Surface weather-shack,shallow subaqueous shrinkage cracks,mid-deep under-compaction overpressure fractures,deep hydrocarbon-generating overpressure cracks and super-deep closed fracture occur successively from shallow to deep.

Key words: non-tectonic fracture, overpressure fracture, closed fracture, shale

中图分类号:

TE122.1

袁玉松,周雁,邱登峰,等. 埋藏过程中泥页岩非构造裂缝的形成演化模式[J]. 石油与天然气地质, 2015, 36(5): 822-827. doi: 10.11743/ogg20150514 Yuan Yusong,Zhou Yan,Qiu Dengfeng,et al. Evolutionary patterns of non-tectonic fractures in shale during burial[J]. Oil & Gas Geology, 2015, 36(5): 822-827. doi: 10.11743/ogg20150514

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