CO<sub>2</sub>驱替对致密砂岩孔隙结构的影响：以鄂尔多斯盆地三叠系延长组长7段为例

吴小斌; 强小龙; 张晓燕; 李刚; 解强旺; 王伟

doi:10.19509/j.cnki.dzkq.tb20240452

CO₂驱替对致密砂岩孔隙结构的影响：以鄂尔多斯盆地三叠系延长组长7段为例

doi: 10.19509/j.cnki.dzkq.tb20240452

1.
延安大学石油工程与环境工程学院，陕西延安 716099
2.
中国石油长庆油田分公司第二采气厂，陕西榆林 719000
3.
榆林学院化学与化工学院，陕西榆林 719000

基金项目: 国家自然科学基金项目（42362023）; 陕西省教育厅青年创新团队项目（24JP217; 22RCYPJB0103）; 榆林市青年科技新星项目（2024-KJZG-QNXX-007）; 陕西省科技厅项目（2025JC-YBQN-456; 2025JC-YBMS-452）; 中国科学院洁净能源创新研究院-榆林学院联合基金项目（YLU-DNL Fund 2022012）

详细信息

作者简介:
吴小斌：E-mail：wxblcq@163.com

通讯作者:
E-mail：283465227@qq.com

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出版历程
- 网络出版日期: 2025-12-18

The effect of CO₂ displacement on the pore structure of tight sandstones: a case study of the Chang7 member of the Yanchang formation of the Triassic in the Ordos Basin

1.
School of Petroleum Engineering and Environmental Engineering, Yan'an University, Yan'an Shaanxi 716099, China
2.
No.2 Gas Production Plant, Changqing Oilfield Company of PetroChina, Yulin Shaanxi 719000, China
3.
College of Chemistry and Chemical Engineering, Yulin University, Yulin Shaanxi 719000, China

More Information

Author Bio:
E-mail：wxblcq@163.com

Corresponding author: E-mail：283465227@qq.com

摘要

摘要:
CO₂驱替是提高致密油藏采收率的重要方法。CO₂注入地层与原位矿物发生反应，改变岩石的孔隙结构。但致密砂岩成岩作用复杂，需要明确不同填隙物特征的致密砂岩在CO₂驱替过程中的微观结构变化机制。利用CO₂驱替、铸体薄片、扫描电镜、核磁共振、X衍射等方法，研究CO₂驱替前后致密砂岩矿物成分和孔隙结构的变化。结果表明，致密填隙物复杂多样，以黏土矿物和碳酸盐为主，不同填隙物分布差异明显。填隙物会影响致密砂岩的矿物结构和孔隙形态。CO₂驱替后致密砂岩孔隙度增加0.55%、渗透率增加率为21.5%、相对分选系数仅减少0.01，表明CO₂驱替会增加储集层的孔隙度和渗透率，但对孔隙结构非均质性影响微弱。CO₂驱替过程中长石和碳酸盐被溶蚀，生成石英和黏土矿物沉淀。在黏土含量高的致密砂岩中，CO₂溶蚀作用分散，新沉淀的矿物和从骨架颗粒剥落的黏土会堵塞孔隙，物性变化幅度小。在方解石含量高的致密砂岩中，碳酸会溶蚀大量方解石，形成新的储集空间和流动路径，显著改善致密砂岩物性。因此，CO₂驱替对不同填隙物特征致密砂岩的孔隙结构影响不同，CO₂驱替对碳酸盐含量高致密砂岩的物性增加明显好于黏土含量高致密砂岩。研究成果可为致密砂岩油藏开发评价提供了新的思路。
- CO₂驱替 /
- 孔隙结构 /
- 致密砂岩 /
- 矿物成分
Abstract: Objective
CO₂ flooding is an important method to improve the recovery efficiency of tight oil reservoirs. However, the diagenesis of tight sandstones is complex, and it is necessary to clarify the mechanisms behind the microstructural changes in tight sandstones with different cement characteristics during the CO₂ flooding process.
Methods
In this study, CO₂ flooding, casting thin sections, scanning electron microscopy, nuclear magnetic resonance, and X-ray diffraction were used to investigate the changes in pore structure and mineral composition of tight sandstone before and after CO₂ flooding.
Results
The results show that the cementation of tight sandstone is complex and diverse. Clay minerals and carbonates are the main filling materials, with significant distribution differences. Cements can affect the mineralogical structure of tight sandstone and its structural impact on pore morphology. After CO₂ flooding, the increase in porosity of the tight sandstone is 0.55%, the increase in permeability is 21.5%, and the relative selectivity coefficient decreases by only 0.01, indicating that CO₂ flooding can increase the porosity and permeability of the reservoir, but has a weak impact on the heterogeneity of the pore structure. During CO₂ flooding, feldspar and carbonates are dissolved, resulting in the precipitation of quartz and clay minerals. In tight sandstone with high clay content, CO₂ dissolution is dispersed, and the newly precipitated minerals and exfoliation of skeleton particles during CO₂ flooding can block pores, leading to a slight improvement in properties. In tight sandstone with high calcite content, extensive dissolution of calcite can create new storage spaces and flow paths, significantly improving the properties of tight sandstone after CO₂ flooding.
Conclusion
Therefore, CO₂ flooding has different effects on the pore structure of tight sandstones with varying types of cement. CO₂ flooding leads to a more significant improvement in the physical properties of tight sandstones with high carbonate content compared to those with high clay content. These results provide new insights for the development and evaluation of tight sandstone reservoirs.
- CO₂ flooding /
- pore structure /
- tight sandstone /
- mineral composition

HTML全文

图 1 CO₂驱替实验示意图

Figure 1. Schematic diagram of the CO₂ flooding apparatus

下载: 全尺寸图片幻灯片

图 2 致密砂岩微观特征

a. 样品X1，压实作用强烈，矿物颗粒镶嵌状接触；b. 样品X5，溶蚀孔隙发育；c. 样品X3，高岭石填充孔隙；d. 样品X7，方解石镶嵌状填充孔隙

Figure 2. Microscopic characteristics of the tight sandstone samples

下载: 全尺寸图片幻灯片

图 3 长7段致密砂岩样品孔隙度与渗透率相关性

Figure 3. The Permeability versus porosity in the Chang7 tight sandstone samples

下载: 全尺寸图片幻灯片

图 4 CO₂驱替前后T₂谱分布曲线比较

Figure 4. Comparisons of T₂ distribution curves before and after CO₂ flooding

下载: 全尺寸图片幻灯片

图 5 致密砂岩溶蚀率与矿物含量关系

Figure 5. Relationship between dissolution rates and mineral contents of the tight sandstone

下载: 全尺寸图片幻灯片

图 6 CO₂驱替前后T₂谱孔隙结构参数变化（T_2gm. T₂谱的振幅加权平均值）

Figure 6. Changes in T₂ spectrum pore structure parameters before and after CO₂ flooding

下载: 全尺寸图片幻灯片

图 7 物性增量与黏土含量关系

Figure 7. Relationships between clay contents and physical property increments

下载: 全尺寸图片幻灯片

图 8 CO₂驱替前后矿物含量变化

Figure 8. Changes in mineral content before and after CO₂ flooding

下载: 全尺寸图片幻灯片

图 9 CO²驱替前后致密矿岩矿物变化示意图

a. CO₂驱替前黏土矿物分布；b. CO₂驱替后形成的矿物填充孔隙；c. CO₂驱替前方解石充填孔隙；d. CO₂驱替后方解石溶蚀形成新的孔隙

Figure 9. Schematic diagram of mineral changes in tight sandstone before and ater CO₂ flooding

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图 10 物性增量与易溶矿物含量关系

Figure 10. Relationships between soluble mineral content and physical property increments

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表 1 长7段致密砂岩矿物组成

Table 1. Mineral Composition of Chang 7 Member tight sandstone

样品	干重/g	孔隙度/%	渗透率/ 10⁻³ μm²	钠长石	钾长石	石英	黏土	方解石
样品	干重/g	孔隙度/%	渗透率/ 10⁻³ μm²	w_B/%
X1	59.64	8.32	0.24	30.6	7.3	38.6	18.2	5.3
X2	58.93	9.62	0.32	32.2	6.3	37.2	17.1	7.2
X3	59.12	9.45	0.23	27.1	7.6	38.3	19.6	7.4
X4	57.36	10.33	0.32	28.2	8.1	33.2	17.7	12.8
X5	58.88	11.52	0.31	27.1	7.8	33.4	15.2	16.5
X6	59.13	8.20	0.31	25.4	7.2	34.6	12.6	20.2
X7	58.31	9.15	0.25	26.1	9.6	34.5	13.7	16.1
X8	58.67	7.82	0.18	26.3	5.7	32.6	14.1	21.3

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表 2 CO₂驱替后致密砂岩物性变化

Table 2. Petrophysical properties changes of Chang 7 member tight sandstone after CO₂ flooding

样品	干重/g	孔隙度/%	渗透率/ 10⁻³μm	溶蚀率/%	孔隙度增量/%	渗透率增加率/%
X1	58.89	8.75	0.28	1.25	0.43	15.6
X2	58.09	9.98	0.36	1.42	0.36	13.2
X3	58.31	9.71	0.27	1.37	0.26	16.1
X4	56.48	10.86	0.38	1.53	0.53	18.6
X5	57.91	12.11	0.39	1.64	0.59	24.5
X6	58.11	8.87	0.39	1.72	0.67	28.3
X7	57.07	9.97	0.32	2.13	0.82	29.8
X8	57.78	8.53	0.23	1.51	0.71	26.2

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