地学前缘 ›› 2021, Vol. 28 ›› Issue (1): 214-224.DOI: 10.13745/j.esf.sf.2020.5.20

• 致密/页岩储层 • 上一篇    下一篇

二连盆地额仁淖尔凹陷下白垩统湖相云质岩优质储层特征及控制因素

魏巍1,2(), 朱筱敏1,2,*(), 朱世发1,2, 何明薇3, 孙书洋4, 王名巍5   

  1. 1. 中国石油大学(北京) 地球科学学院, 北京 102249
    2. 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
    3. 中海油研究总院有限责任公司, 北京 100027
    4. 弗吉尼亚州立理工大学, 美国 布莱克斯堡 24060
    5. 中国石油华北油田分公司 勘探开发研究院, 河北 任丘 062550
  • 收稿日期:2019-12-05 修回日期:2020-05-19 出版日期:2021-01-25 发布日期:2021-01-28
  • 通讯作者: 朱筱敏
  • 作者简介:魏巍(1988—),女,博士,地质学专业,主要从事储层沉积和成岩研究。E-mail: hunqiu8854@163.com
  • 基金资助:
    国家自然科学基金项目(41802176)

Characteristics and control mechanism of high quality reservoir of lacustrine dolomitic rocks from the Lower Cretaceous of the Erennaoer Sag, Erlian Basin, northeastern China

WEI Wei1,2(), ZHU Xiaomin1,2,*(), ZHU Shifa1,2, HE Mingwei3, SUN Shuyang4, WANG Mingwei5   

  1. 1. College of Geosciences, China University of Petroleum(Beijing), Beijing 102249, China
    2. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum(Beijing), Beijing 102249, China
    3. Research Institute of CNOOC Co. Ltd, Beijing 100027, China
    4. Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24060, USA
    5. Research Institute of Petroleum Exploration and Development, Huabei Oilfield Company, CNPC, Renqiu 062550, China
  • Received:2019-12-05 Revised:2020-05-19 Online:2021-01-25 Published:2021-01-28
  • Contact: ZHU Xiaomin

RichHTML

2

PDF (PC)

326

摘要：

二连盆地多个凹陷的下白垩统均发育一套湖相白云岩。它不仅是一个重要的地层对比标志层,还是一套有效的储集层。这套储层孔隙结构复杂,非均质性强。寻找优质储层是油气勘探的关键。研究以二连额仁淖尔凹陷的下白垩统湖相云质岩为研究对象,研究了云质岩储层的储层特征和成因。本次研究采用岩心观察、岩石学、扫描电镜(SEM)、X射线衍射、稳定碳氧同位素地球化学等多种方法,进而了解储层的岩石学、成岩特征及其对储层物性的影响。为了深入分析云质岩的储层特征,将云质岩分为三种类型:云质粉砂岩、云质沉凝灰岩和云质泥岩。云质粉砂岩常与云质/钙质泥岩相邻。白云石的主要特征是微晶结构、填充粒间孔隙或取代基质或方解石胶结物。云质粉砂岩物性较好,平均孔隙度为10.2%,渗透率为1.03 mD,属于低-超低孔特低渗储层。除了白云石化外,方解石胶结作用是降低储层孔隙度和渗透率的主要因素。有机酸的溶蚀作用主要发生在凝灰质矿物中,常见于与云质沉凝灰岩相邻的云质粉砂岩,形成粒内和粒间溶孔。云质沉凝灰岩常与泥岩、粉砂岩互层,主要发育前扇三角洲亚相。白云石以微晶为主,方解石以细晶粗晶为主。它们以团块的形式分布在凝灰质基质中。云质沉凝灰岩的平均孔隙度和渗透率分别为9.85%和0.34 mD,属于特低孔特低渗储层。储层孔隙度和渗透率降低的主要因素与火山物质有关。火山物质的蚀变作用释放出大量的离子进入地层水,不仅加强了早期碳酸盐胶结作用,而且导致了黏土矿物充填孔隙。另外,溶蚀作用是改善储层物性的主要因素,主要溶蚀云质沉凝灰岩中的碳酸盐团块,形成粒内和粒间溶孔。白云石化作用在云质泥岩中较弱,白云石沿纹层以泥晶形式出现。云质泥岩物性差,平均孔隙度为2.5%,渗透率为0.01 mD,储层物性差主要是原始物性差造成的。此外,成岩晚期的强碳酸盐胶结作用导致云质泥岩形成致密储层。该类岩石主要依靠微裂缝来改善储层物性,在断裂带附近的云质泥岩易发育微裂缝,微裂缝富集程度随离主断层距离的增大而减小。

关键词: 优质储层成因, 成岩作用, 云质岩, 白垩系阿尔善组, 额仁淖尔凹陷, 二连盆地

Abstract:

The Lower Cretaceous layer of most sags in the Erlian Basin develops a set of lacustrine dolomitic rocks. The dolomitic layer not only serves as an important stratigraphic correlation marker, but also is an effective hydrocarbon reservoir with a highly heterogeneous complex pore structure. The key of hydrocarbon exploration is finding high quality reservoir. In this study, we took lacustrine dolomitic rocks from the Lower Cretaceous of the Erennaoer Sag as an example to investigate the characteristics and genesis of high quality reservoir of dolomitic rocks. We utilized a multifaceted approach including core observation, petrography, scanning electron microscope (SEM), X-ray diffraction and stable carbon/oxygen isotope geochemistry to better understand the rocks’ petrologic and diagenetic characteristics and their influence on reservoir quality. In order to analyze their reservoir characteristics in-depth, we divided the dolomitic rocks into three types: dolomitic siltstone, dolomitic tuffacecous rocks and dolomitic mudstone. The results are summarized below. Dolomitic siltstone often occurs adjacent to dolomitic/calcareous mudstone. It shows relatively good physical properties with an average porosity of 10.2% and permeability of 1.03 mD, and belongs to low-ultra low porosity and extra-ultra low permeability reservoir. While microcrystalline dolomite can fill intergranular pores or replace matrix or calcite cement, calcite cementation was the major factor for decreasing reservoir porosity and permeability. On the other hand, organic acid dissolution of tuffacecous rich minerals or dolomitic siltstone (adjacent to dolomitic tuffacecous rocks) resulted in intra and intergranular pores. Dolomitic tuffacecous rocks are often interbedded with mudstone and siltstone, occurring mainly in the fore-fan delta subfacies as microcrystalline dolomite or fine-coarse crystalline calcite. They mostly distribute in the tuffaceous matrix as aggregates, with an average porosity of 9.85% and permeability of 0.34 mD, and belong to ultra-low porosity and extra low permeability reservoir. The decreasing reservoir porosity and permeability were primarily attributed to the tuffaceous materials, whose alteration released abundant ionic species into the formation water, resulting in not only early carbonate cementation enhancement but also clay mineral pore filling. In contrast, dissolution contributed the most to reservoir quality improvement as dissolution of carbonate aggregates led to intra and intergranular pores. In dolomitic mudstone, dolomitization is weak and dolomite occurs mainly as micritic crystal along the laminae. The physical properties of dolomitic mudstone are rather poor with an average porosity of 2.5% and permeability of 0.01 mD, resulting in poor reservoir quality. Furthermore, strong carbonate cementation in the late diagenetic stage resulted in the dense reservoir which relies mainly on microfractures for improvements. Although microstructures are prone to develop near the fault zone, their likelihood decreases with increasing distance from the main fault.

Key words: genesis of high-quality reservoir, diagenesis, dolomitic rocks, Cretaceous Arshan Formation, Erennaoer Sag, Erlian Basin

中图分类号: