Three-dimensional simulation of oil distribution during waterflooding in a micrometer-sized pore network system of tight sandstone
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摘要: 致密油储层孔隙度和渗透率均较低,其微米级孔隙网络系统内石油赋存状态是致密油成藏地质研究中亟待解决的核心问题之一。采用油气驱替系统与X射线微米CT扫描系统联用,通过对3 mm和5 mm直径致密砂岩干岩心、饱和碘化钾(KI)溶液及油驱替KI溶液后致密砂岩岩心在线CT扫描及数据重构,三维展示了致密砂岩微米级孔隙网络系统中石油的赋存状态。研究发现孔隙半径10 μm以上孔隙的连通性较好,是石油聚集的优势孔隙网络系统,致密砂岩62.9%~84.1%的石油聚集于半径在10~60 μm之间的孔隙内;孔隙半径小于10 μm的孔隙数量多,但其在空间上多呈孤立状分布,该部分孔隙的石油充满度较低,只聚集了致密砂岩内6.8%~20.0%的石油。致密砂岩含油饱和度随孔径呈阶梯状增长,半径小于10 μm、10~60 μm和60~80 μm的孔隙的含油饱和度分别为10%~40%,30%~75%,40%~75%。致密砂岩微米级孔隙网络系统石油的赋存与孔隙的尺寸、成因类型及空间分布特征有关。Abstract: The porosity and permeability of tight oil reservoirs are quite low. The occurrence of oil in tight oil reservoirs, which are composed of a micrometer-sized pore network system, is one of the most important scientific issues to be solved in tight oil research. Oil was removed from two tight sandstone core samples (with diameter 3 mm and 5 mm) which were saturated with KI and oil and monitored by core flooding system using X-ray Micro-CT, to display the occurrence and accumulation characteristics of oil in the micrometer-sized pore network. Pores with radius larger than 10 μm have good connectivity and comprise the dominant pore network system for oil accumulation, while 62.9%-84.1% of the oil accumulates in pores with radius from 10-60 μm. Pores with radius smaller than 10 μm are huge in number; however, most of them are isolated in space, the oil saturation of these pores is low and they only gathered 6.8%-20.0% of oil in tight sandstone. The oil saturation of tight sandstone increases in three steps with pore radius in the range of 10%-40% for pores with radius smaller than 10 μm, 30%-75% for pores with radius 10-60 μm, 40%-75% for pores with radius 60-80 μm. The occurrence of oil in micrometer-sized pore network systems in tight sandstones is controlled by the size, origin and spatial distribution of pores.
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Key words:
- tight oil /
- oil charging /
- pore network /
- oil occurrence /
- Micro-CT /
- three-dimensional reconstruction
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图 2 直径3 mm干岩心、饱和KI溶液岩心和油充注后相同视域致密砂岩岩心X射线CT扫描
XY切片方向:a.干岩心;b.饱和KI溶液岩心,孔隙内充填白色发亮KI溶液(红色箭头指示部位);c.油驱替饱和KI溶液后图像。XZ切片方向:d.干岩心;e.饱和KI溶液岩心,孔隙内充填白色发亮KI溶液;f.油驱替饱和KI溶液后图像
Figure 2. X-ray CT images showing the structure of tight sandstone (core plug with diameter of 3 mm) before and after saturated with KI and oil in the same view
表 1 两块致密砂岩样品基本信息及基于CT扫描重构获得的岩石孔隙度参数
Table 1. Basic information of two tight sandstone samples and porosity parameters calculated from CT reconstruction
样品编号 样品直径/mm CT扫描图像分辨率/μm 据CT重构数据计算 绝对孔隙度/% 含油体积分数/% 含油饱和度/% 1号 3 2.0 12.7 5.6 44.2 2号 5 3.3 16.0 6.3 39.4 表 2 CT扫描重构获取的2块致密砂岩孔隙、油及含油饱和度分布特征
Table 2. Pore and oil distributions and oil saturation of two tight sandstone samples calculated from CT reconstruction
孔隙半径区间/μm 孔隙分布体积分数/% 油分布体积分数/% 含油饱和度/% 3 mm岩心 5 mm岩心 3 mm岩心 5 mm岩心 < 10 31.4 16.5 20.0 6.8 (10~40)/25.7 10~60 57.7 77.1 62.9 84.1 (30~75)/46.1 60~80 10.9 6.4 17.1 9.2 (40~75)/59.3 注:含油饱和度为:(最小值~最大值)/平均值。 -
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