Intelligent representation method of shale pore structure based on semantic segmentation
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摘要:
页岩孔隙类型和结构参数影响储层流体的富集和运移,是页岩储层评价的重要内容。现有评价方法存在主观性强、效率低及定量化程度低等问题,难以满足快速、精准分析页岩样品的迫切需求。基于此,提出一种基于语义分割的页岩孔隙结构智能表征方法。利用扫描电子显微镜(SEM)和多尺度采集与处理软件(MAPS)获取页岩二维灰度图像;由岩矿鉴定专家进行数据标注,分为有机孔、无机孔、裂缝和有机质;提出一种面向页岩孔隙结构分析任务的组合网络ShaleSeger及其训练范式,建立基于深度学习的页岩孔隙智能识别模型,形成基于多视域拼接的超大尺寸图像孔隙识别方案,从而实现基于MAPS图像的孔隙提取;利用图像处理技术实现孔隙结构特征智能表征。目前已实现古龙页岩孔隙结构定量分析,能够在孔隙边缘提取和类型识别的基础上自动计算各类型孔隙的面积占比,统计诸如孔径、视孔隙比表面、形状因子等孔隙结构参数。所提方法可以拓展应用于CO2复合压裂效果评估,对CO2复合压裂前后的微观结构特征改变进行定量比较。
Abstract:The enrichment and migration of reservoir fluids are affected by the types and structural parameters of shale pores, which are significant components of shale reservoir evaluation. Due to issues with current assessment methods, including high subjectivity, low efficiency, and low degree of quantification, it is challenging to address the urgent needs of quick and accurate examination of shale samples. Based on this, an intelligent characterization method for shale pore structure based on semantic segmentation is proposed. Firstly, the two-dimensional gray images of shale are obtained by scanning electron microscopy (SEM) and multi-scale acquisition and processing software (MAPS). Secondly, these images are annotated by the rock mineral identification experts, and divided into organic pores, inorganic pores, fractures and organic matter. Then, a combination network Shale Seger and its training paradigm for shale pore structure analysis tasks is innovatively proposed, an intelligent recognition model of shale pores based on deep learning is constructed, as well as, a pore recognition scheme of super large image based on multi-view mosaicisis established to extract pore from MAPS images. Lastly, intelligent characterisation of pore structural features is achieved by applying image processing techniques. As of right now, this study has produced a quantitative analysis of the Gulong shale's pore structure that can statistically compute pore structure parameters like pore diameter, apparent pore ratio surface, shape factor, and so forth, as well as automatically determine the area proportion of each type of pore based on pore edge extraction and type recognition. In addition, the technique described in this article can also be extended to the evaluation of CO2 composite fracturing, through which the change of microstructure characteristics before and after CO2 composite fracturing can be quantitatively compared.
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Key words:
- tight shale oil /
- micro nano /
- pore structure /
- scanning electron microscopy /
- Gulong shale
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表 1 分割效果定量对比
Table 1. Quantitative comparison of segmentation effects
模型 半监督训练 像素准确率/% 平均交并比/% 平均准确率/% 平均F1分数/% 平均精确率/% 平均召回率/% SegFormer[25] 否 99.25 66.70 75.57 77.82 80.64 75.57 OCRNet[19] 否 98.99 61.59 71.94 73.48 75.47 71.94 DeepLabv3[21] 否 98.57 52.43 59.49 64.11 71.37 59.49 PSPNet[22] 否 98.54 53.95 62.67 65.94 70.04 62.67 SegFormer+边缘特征增强 否 99.25 66.84 75.49 77.84 81.06 75.49 ShaleSeger 是 99.50 72.28 79.67 82.06 85.03 79.67 表 2 各类型孔隙、有机质面积占比
Table 2. Area proportion of various types pores and organic matter
样本名称 无机孔
占比/%有机孔
占比/%裂缝
占比/%有机质
占比/%其他
占比/%样本a 0.400 0.014 1.997 0.213 97.377 样本b 2.953 0 5.93×10−3 0 97.041 表 3 每个孔隙的特征参数
Table 3. Characteristic parameters of each pore
面积/mm2 直径/$ \mathrm{nm} $ 周长/$ \mathrm{nm} $ 视孔隙比
表面/nm−1形状因子 214.577 16.529 246.510 1.463 0.044 643.728 28.629 153.593 0.304 0.343 5257.087 81.814 367.252 0.089 0.490 1823.911 48.190 208.632 0.146 0.527 858.308 33.058 146.484 0.217 0.503 751.023 30.923 150.039 0.254 0.419 2253.051 53.560 208.632 0.118 0.650 $\vdots $ $\vdots $ $\vdots $ $\vdots $ $\vdots $ 4184.242 72.990 403.657 0.123 0.323 表 4 基于MAPS图像的各类型孔隙、有机质面积占比
Table 4. Area proportion of various types pores and organic matter based on MAPS
无机孔占比/% 有机孔占比/% 裂缝占比/% 有机质占比/% 面孔率/% 0.529 0.016 0.305 0.353 0.849 表 5 CO2复合压裂前后孔隙结构变化
Table 5. Changes in pore structure before and after CO2 composite fracturing
状态 无机孔占比/% 有机孔占比/% 裂缝占比/% 其他占比/% 复合压裂前 1.107 0.541 2.751 95.601 复合压裂后 1.019 0.561 3.211 95.209 -
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