A Micro-CT Based Study of Evolution of Fracture Expansion in Fuxing Continental Facies Shales Soaked in Drilling Fluid
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摘要: 通过微米CT扫描技术对复兴陆相页岩高温浸泡前后裂缝表征及演化进行量化分析，开展了膨润土浆、Nanodrill水基钻井液和白油基钻井液浸泡不同时间的CT扫描实验，并分析了不同钻井液对裂缝演化的影响。研究发现，凉高山组岩样中裂缝更为发育，不同钻井液对裂缝扩展的抑制效果有明显差异，随着浸泡时间的增加，膨润土浆浸泡10 d后岩样中最大层位裂隙占比为12.9%，明显高于白油基钻井液的6.13%，而水基介于两者之间。结合微观电镜实验研究了岩样浸泡前的裂缝开度分布，并对比得到浸泡10 d后的裂缝开度增长率，膨润土浆最大为61.6%，Nanodrill水基钻井液其次为52.1%，白油基钻井液最低为39.8%。进一步对裂缝长度分布进行量化统计得出，膨润土浆浸泡后，岩样中长度在50～100 μm的大尺度微裂缝数量明显增多，而Nanodrill水基钻井液与白油基钻井液浸泡后岩样中大尺度裂缝数量基本不变。白油基钻井液对页岩裂缝扩展的抑制效果最好，Nanodrill水基钻井液次之，膨润土浆效果最差。研究成果对复兴区块陆相页岩地层高效安全钻井作业提供参考。Abstract: Using micro-CT scanning technology, the characterization and evolution of the fractures in the Fuxing continental shales before and after high-temperature soaking are quantitatively analyzed. The continental shales are soaked in bentonite slurry, Nanodrill water based drilling fluid and white oil based drilling fluid, and are scanned with micro-CT at different soaking times. The effects of the different drilling fluids on the evolution of the fractures are analyzed. The study results show that the rock samples taken from the Liangshan Formation have more fractures than other rock samples, and different drilling fluids have different inhibitive capacities for the extension of the fractures. After soaking for 10 d in bentonite slurry, the percent layered fractures with the maximum width found in the rock samples is 12%, significantly higher than that of the rock samples in the white oil based drilling fluid, which is 6.13%, and the percent layered fractures with the maximum width of the rock samples in the water based drilling fluid lies in between the two. Using microscope, the distribution of the fracture widths of the rock samples before soaking is studied, and the percent increase of the fracture widths of the rock samples after soaking for 10 d is analyzed; the rock samples in the bentonite slurry have the highest percent increase in fracture width, which is 61.6%, the rock samples in the Nanodrill water based drilling fluid have the intermediate percent increase in fracture width, which is 52.1%, and the rock samples in the white oil based drilling fluid have the lowest percent increase in fracture width, which is 39.8%. Quantitative study on the distribution of the lengths of the fractures shows that the rock samples soaked in the bentonite slurry have the most fractures with lengths between 50 μm and 100 μm, and the numbers of the fractures with the same length distribution in the rock samples soaked in the Nanodrill water based drilling fluid and in the white oil based drilling fluid are basically remained unchanged. These data indicate that the white oil based drilling fluid has the best inhibitive capacity in inhibiting fracture extension in shales, with the Nanodrill water based drilling fluid inferior in inhibiting fracture extension to the oil based drilling fluid, and the bentonite slurry performs the poorest in this aspect. The results of this study can be used as a technical reference for efficient and safe drilling of the continental shale formations in the Fuxing area.
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Key words:
- Shale /
- Micro-CT /
- Drilling fluid immersion /
- Microfracture characterization /
- Wellbore stability
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表 1 不同钻井液浸泡下的裂缝平均开度变化
岩样 浸泡不同天数裂缝
平均开度/μm浸泡10 d后裂缝平均
开度增长率/%0 d 1 d 5 d 10 d Ⅰ号 5.446 5.729 6.185 8.856 62.6 Ⅱ号 3.857 3.908 5.561 5.867 52.1 Ⅲ号 6.205 7.536 8.084 8.678 39.8 
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