川西北下二叠统栖霞组斑马状白云岩地球化学特征及形成过程——以ST18井为例

王利超; 周杨; 胡林辉; 张亚; 王柏智; 乔艳萍

doi:10.11781/sysydz202204647

川西北下二叠统栖霞组斑马状白云岩地球化学特征及形成过程——以ST18井为例

doi: 10.11781/sysydz202204647

1.
西南石油大学地球科学与技术学院, 成都 610500
2.
中国石油东方地球物理公司西南物探分公司, 成都 610213
3.
中国石油西南油气田分公司勘探开发研究院, 成都 610041

基金项目:

中国石油—西南石油大学创新联合体科技合作项目“深层碳酸盐岩成烃—成储—成藏理论及目标区块优选技术” 2020CX010301

详细信息

作者简介:
王利超(1988—), 女, 博士, 讲师, 从事碳酸盐岩储层地质学相关研究。E-mail: wanglichaohappy@126.com

中图分类号: TE122.2
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出版历程
- 收稿日期: 2022-01-19
- 修回日期: 2022-04-26
- 刊出日期: 2022-07-28

Geochemical characteristics and formation process of zebra dolomites in Lower Permian Qixia Formation, northwestern Sichuan Basin: a case study of well ST 18

1.
School of Geoscience and Technology, Southwest Petroleum University, Chengdu, Sichuan 610500, China
2.
Southwest Geophysical Prospecting Branch of PetroChina Eastern Geophysical Exploration Company, Chengdu, Sichuan 610213, China
3.
Exploration and Development Research Institute, PetroChina Southwest Oil & Gasfield Company, Chengdu, Sichuan 610041, China

摘要

摘要: 四川盆地下二叠统栖霞组具有丰富的天然气资源。近年来，川西北地区在栖霞组取得了重大的油气勘探突破，其中优质储层主要位于白云岩层位。然而，有关该区栖霞组白云岩的成因至今仍有争议。ST18井钻遇栖霞组，岩心观察发现特殊的斑马状白云岩。针对斑马结构中的亮带和暗带，系统开展了岩石学和地球化学的对比研究。斑马结构中亮带由中粗晶—鞍形白云石组成，阴极发光呈亮红色；而暗带则由中—细晶白云石组成，阴极发光呈暗红色。亮带和暗带白云石的δ¹³C值均在同时期海水δ¹³C值范围内，而δ¹⁸O值较同时期海水偏负，表明白云石化流体来源于海水，且受到较高温度的影响，使得氧同位素发生分馏。亮、暗带白云石有序度均较高，推测是在后期埋藏作用下发生了调整，使得有序度增加到同一水平。此外，热液矿物黄铁矿的发现进一步证实了白云岩形成过程中热液流体的参与。研究表明，ST18井栖霞组斑马状白云岩的形成过程主要经历了以下三个阶段：(1)流体沿着构造裂缝溶蚀—交代原始灰岩，形成暗带白云石；(2)热流体沉淀形成亮带白云石；(3)深埋藏环境下亮暗带白云石均发生调整，形成有序度较高的斑马状白云岩。
- 热液白云岩 /
- 白云石有序度 /
- 斑马结构 /
- 栖霞组 /
- 下二叠统 /
- 川西北
Abstract: Abundant natural gas resources are stored in the Lower Permian Qixia Formation of the Sichuan Basin. In recent years, great breakthrough for oil and gas exploration has been achieved in the Qixia Formation in the NW Sichuan Basin, and high-quality reservoirs mainly locate in dolomite strata. However, the origin of dolomites in the Qixia Formation is still unclear. Special zebra-textured dolomites were observed in the Qixia Formation from the cores of well ST 18. In this paper, a comparative study of the light and dark belts in the zebra texture was systematically carried out with petrological and geochemical methods. Results show that the light belt is mainly composed of medium to coarse crystalline saddle dolomites and its cathodoluminescence is bright red, while the dark zone is composed of medium to fine crystalline dolomites and its cathodoluminescence is dark red. The δ¹³C values in light and dark zones are within the δ¹³C range of contemporary seawater, while the δ¹⁸O values are more negative than those of contemporary seawater. It is then indicated that the dolomitization fluid was derived from seawater and the oxygen isotopes were fractionated by the affection of high temperature. The order degrees of dolomites in the light and dark zones are consistently high. It was speculated that the order degrees of dolomites in the light and dark zones had been matured to the same degree during the later burial stage. In addition, the occurrence of pyrite confirmed the involvement of hydrothermal fluids in the formation of dolomites. Therefore, the formation of zebra dolomites in well ST 18 mainly went through the following three stages: (1) Fluids dissolved and dolomitized primary limestones along tectonic fractures to form medium to fine crystalline dolomites in the dark zone; (2) Hot fluids precipitated to form medium to coarse crystalline saddle dolomites in the light zone; (3) The order degrees of dolomites in the dark and light zones had adjusted to the same degree in the later deep burial stage.
- hydrothermal dolomite /
- order degree of dolomite /
- zebra texture /
- Qixia Formation /
- Lower Permian /
- northwestern Sichuan Basin

HTML全文

图 1 川西北ST18井区域地质简图及地层柱状图

a.ST18井大地构造位置(据参考文献[15]修改)；b.ST18井构造带位置(据参考文献[16]修改)；c.ST18井地层柱状图

Figure 1. Regional geological sketch and stratigraphic histogram of well ST 18, northwestern Sichuan Basin

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图 2 川西北ST18井栖霞组斑马状白云岩的岩石学特征

a.斑马状白云岩岩心，斑马结构，ST18井，7 638.93~7 639.01 m；b.斑马状白云岩薄片镜下特征，靠近开放空间的亮带白云石有晶粒增大的趋势(红色箭头方向)，ST18-04，单偏光；c.斑马状白云岩岩心，鞍形白云石胶结物(蓝色箭头所指)充填在溶孔中，ST18井，7 637.77~7 637.97 m；d.沿裂缝发育的鞍形白云石，弯曲晶面(蓝色箭头所指)，ST18-07，单偏光；e.斑马状白云岩中亮暗带界限处白云石波状消光特征，ST18-04，正交偏光；f.斑马状白云石晶体被缝合线切穿(黄色箭头所指)，ST18-03，单偏光

Figure 2. Petrological characteristics of zebra dolomites in Qixia Formation, well ST 18, northwestern Sichuan Basin

下载: 全尺寸图片幻灯片

图 3 川西北ST18井栖霞组斑马状白云岩薄片观察及阴极发光特征

a.斑马状白云岩，亮带为中—粗晶白云岩，暗带为中—细晶白云石，表面附着有机质，ST18-06，单偏光；b.视域a的阴极发光，亮带发亮红色光，暗带发暗红色光；c.鞍形白云石，发育在溶蚀孔洞中，具有溶蚀残余结构，ST18-03，单偏光；d.视域c的阴极发光，可见鞍形白云石核部发暗红色光，边缘为亮红色环带结构(蓝色箭头)

Figure 3. Thin section observation and cathodoluminescence characteristics of zebra dolomites in Qixia Formation, well ST 18, northwestern Sichuan Basin

下载: 全尺寸图片幻灯片

图 4 川西北ST18井栖霞组热液矿物特征

a.斑马状白云岩光面，黄铁矿沿裂缝分布(黄色箭头所指)，ST18-05；b.粗晶鞍形白云石与黄铁矿伴生，鞍形白云石表面洁净，晶间溶孔充填黄铁矿，ST18-11，单偏光；c.视域b的反射光观察，黄铁矿发亮黄色金属光；d.视域c中①和②位置处的能谱分析图

Figure 4. Characteristics of hydrothermal minerals in Qixia Formation, well ST 18, northwestern Sichuan Basin

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图 5 川西北ST18井栖霞组斑马状白云岩地球化学特征

Figure 5. Geochemical characteristics of zebra dolomites in Qixia Formation, well ST 18, northwestern Sichuan Basin

下载: 全尺寸图片幻灯片

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