石油与天然气地质 ›› 2017, Vol. 38 ›› Issue (1): 49-61.doi: 10.11743/ogg20170106

• 油气地质 • 上一篇    下一篇

致密油储层微观特征及其形成机理——以鄂尔多斯盆地长6-长7段为例

钟大康1,2   

  1. 1. 中国石油大学(北京) 油气资源与探测国家重点实验室, 北京, 102249;
    2. 中国石油大学(北京) 地球科学学院, 北京, 102249
  • 收稿日期:2016-07-20 修回日期:2016-12-20 出版日期:2017-02-28 发布日期:2017-02-27
  • 作者简介:钟大康(1961-),男,教授,碎屑岩储层。E-mail:zhongdakang@263.net。
  • 基金资助:

    国家科技重大专项（2016ZX05002-004-009）；国家自然科学基金项目（41072104）。

Micro-petrology, pore throat characteristics and genetic mechanism of tight oil reservoirs-A case from the 6th and 7th members of Triassic Yanchang Formation in the Ordos Basin

Zhong Dakang1,2   

  1. 1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China;
    2. College of Geosciences, China University of Petroleum, Beijing 102249, China
  • Received:2016-07-20 Revised:2016-12-20 Online:2017-02-28 Published:2017-02-27

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摘要：

鄂尔多斯盆地陇东地区长（延长组）6段和长7段富含大量致密油，但由于对其微观特征与成因缺乏深入了解，阻碍了该区致密油的有效开采。为此，根据岩石孔隙铸体薄片、场发射扫描电镜等技术，对研究区长6段和长7段致密油储层微观特征及其成因进行了深入研究。结果表明：研究区致密油储层形成于三角洲前缘远端远砂坝-席状砂及半深湖-深湖重力流沉积环境，岩石粒度细（主要为极细砂岩、粉砂岩、泥质粉砂岩及粉砂质泥岩）、杂基含量高（8%~10%），几种储集岩的孔隙均极不发育，面孔率低，平均1.8%，孔径小（平均30 μm），喉道细（平均0.08 μm），平均孔隙度9%，渗透率基本上都低于0.3×10-3 μm2，物性差。孔隙类型主要为粒间杂基微孔、长石及岩屑溶孔、胶结物晶间微孔。不同岩石类型其微观特征存在差异。沉积环境决定了其粒度细、粘土杂基高，细粒高粘土杂基岩石抗压性差，强烈的压实作用导致大量的原生孔隙损失，孔喉变得更加细小；孔喉细小的岩石由于孔隙中各种流体离子的半渗透膜效应引起强烈的碳酸盐和粘土矿物胶结，尤其是伊利石搭桥状和丝网状胶结，使岩石孔隙度渗透率进一步变差，后期酸性流体也难以进入发生溶蚀作用；云母与水云母杂基及碳酸盐胶结物对石英的强烈交代导致岩石抗压性变差以及固体体积增加，最终导致岩石的致密化。

关键词: 微观特征, 形成机理, 储层, 致密油, 鄂尔多斯盆地

Abstract:

The 6th and 7th members of Yanchang Formation (Chang 6 and Chang 7) contain a large number of tight oil in the Longdong area of Ordos Basin. However,poor understanding of their microscopic characteristics and genesis has hindered the exploitation of tight oil. The current study attempts to investigate the pore throat characteristics and genesis of tight oil reservoirs of Chang 6 and Chang 7 members of Yanchang Formation on the basis of pore cast thin section,field emission electron microscopy (FE-SEM) and so on. The results show that the tight oil reservoirs were deposited in distal bar and sheet sand of delta front and gravity flow of semi-deep to deep lake,and the tight oil reservoir rocks with fine grain size and high matrix content (8%-10%) consist of very fine sandstones,siltstones,pelitic siltstones and silty mudstones. These reservoir rocks have very poorly developed pores,low thin section porosity averaging at 1.8%,small pore radius averaging at 30 μm,fine throat radius averaging at 0.08μm,low porosity averaging at 9% and low permeabi-lity of less than 0.3×10-3 μm2. The main pore types of the tight oil reservoirs are micropore of intergranular matrix,dissolution pore of feldspars and rock fragments and intercrystalline pore of cements. The microscopic characteristics of different oil reservoir rocks are different. The low-energy sedimentary environment is decisive in determining the fine grain size and high matrix content of the reservoir sandstones,which have weak resistance to compaction in early burial stage,hence,significant amount of original pore volume is lost,and the pore throat sizes become smaller. In the reservoir rocks with tiny pore throats,the strong carbonate and clay mineral cementation (especially the bridging and network-like cementation of illite),caused by semi-permeable membrane effects of ions,further reduce the porosity and permeability of the reservoir rocks,preventing the later acidic fluid dissolution and formation of secondary porosity. In addition,the strong replacement of quartz by detrital micas grain,hydromuscovite matrix and carbonate cement lowers the resistance of the reservoir rocks and increases the solid volume,finally leading to the tightening of the reservoir rocks.

Key words: microscopic characteristic, formation mechanism, reservoir, tight oil, Ordos Basin

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