四川盆地海相页岩储层微裂缝类型及其对储层物性影响

doi:10.11743/ogg20190105

摘要/Abstract

摘要：

为厘清地下页岩储层中微裂缝对页岩储层物性的影响，基于四川盆地涪陵页岩气田龙马溪组页岩岩心样品，以氩离子抛光-场发射扫描电镜观测、覆压孔、渗实验与CT扫描重构结合等手段为基础，利用图像拼接、图像灰度识别和阈值二值化分割技术，探讨裂缝类型及其对储渗的影响。结果显示：龙马溪组页岩样品中发育层理缝、贴粒缝、溶蚀缝、成岩收缩缝、异常压力缝及构造缝6种类型。在页岩储层中，微裂缝可以增加储层孔隙度，主要起增加储层导流能力的作用。微裂缝可以形成裂缝网络，连通页岩储层各个储集空间；贴粒缝是最主要纵向连通通道，页理缝是最主要横向连通通道，两者在空间上可以组合出最好的裂缝网络通道；贴粒缝本身可以组成以贴粒缝为主的微裂缝裂缝网络通道，溶蚀缝能在局部范围内组成裂缝网络，增加页岩储层连通性。有微裂缝样品渗透率均值是无微裂缝页岩样品渗透率均值的62.9倍，微裂缝对页岩储层渗透率具有很大影响。在地层条件下，页岩储层微裂缝在地下3 500 m以浅深度时，应为开启状态。考虑到页岩储层流体异常高压、沉积作用、构造作作用及其他岩石矿物特征，页岩微裂缝开启状态的深度可以适当增大。

关键词: 有效应力, 裂缝网络, 图像拼接, 图像灰度, 储层, 页岩, 龙马溪组, 四川盆地

Abstract:

The study analyzed the core samples from the Longmaxi Formation to investigate the types of fractures and their effects on reservoir properties by means of argon ion polishing-field emission scanning electron microscopy observation,experimental measurement of the porosity and permeability with overburden pressure,CT scanning and reconstruction,image mosaic,image grayscale recognition and threshold binarization,with a view to clarify the influence of microfractures on the physical properties of subsurface shale reservoir in Fuling shale gas field,Sichuan Basin.The results show that the microfractures for the shale samples can be divided into 6 types,including bedding fracture,particle edge fracture,dissolution fracture,diageneticcontraction fracture,abnormal pressure fracture and structural fracture.Microfractures can function to improve reservoir porosity and play an important role in increasing conductivity in shale reservoirs.Microfractures may form a net of fractures,connecting the various pores throughout the shale reservoir.Among them,particle edge fracturesare the main channels for vertical connection,while bedding fractures are mainly for lateral connection,both of which can be combined to form the best fracture network channels for shale reservoir.Effective fracture network can be composed by particle edge fractures in themselves,dissolution fractures can form fracture network in local area,improving the shale reservoir connectivity.The microfractures will exert a great influence on the permeability of shale reservoirs:the average permeability of microfracture samples is 62.9 times the mean permeability of microfracture-free shale samples.Under normal formation conditions,the microfractures in the shale reservoir should be open when they are shallow at a depth of 3,500 meters.Given the abnormal high pressure,sedimentation,tectonism and other rock mineral characteristics of shale reservoir fluid,the depth of the shale microfracture opening can be increased appropriately.

Key words: effective stress, image mosaic, fracture network, image grayscale, shale, reservoir, Longmaxi Formation, Sichaun Basin

中图分类号:

TE122.2

汪虎,何治亮,张永贵,等. 四川盆地海相页岩储层微裂缝类型及其对储层物性影响[J]. 石油与天然气地质, 2019, 40(1): 41-49. doi: 10.11743/ogg20190105 Wang Hu,He Zhiliang,Zhang Yonggui,et al. Microfracture types of marine shale reservoir of Sichuan Basin and its influence on reservoir property[J]. Oil & Gas Geology, 2019, 40(1): 41-49. doi: 10.11743/ogg20190105

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