Pore Shape Factors in Shale: Calculation and Impact Evaluation on Fluid Imbibition

Bin Yang, Lijun You, Yili Kang, Zhangxin Chen, Jian Yang, Han Huifen, Liang Wang
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引用次数: 2

Abstract

In shale gas reservoirs, the fluid imbibition was quite common during well drilling and stimulation, and it also related with engineering designs such as the borehole instability control and hydraulic fracturing operation, which fluid spontaneous imbibition into shales became a hot issues. In current fluid imbibition models, the pore shape was usually assumed to be circular tube, whereas scanning electron microscope (SEM) images analysis showed that the pore shapes in shale derived a lot from the ideal circular pores. One of the approaches to correct the deviation between the pore shapes and the ideal circular pores was to introduce a pore shape factor into the imbibition model. This paper provided a model to calculate the shape factors for specific geometric pores, and then based on the shape and proportion analyses of the inorganic and organic pores in shale, a comprehensive pore shape factor can be obtained. For tested two shale samples, the comprehensive pore shape factor was 0.54 and 0.61. Taking the values into the fluid imbibition model, it showed that the predicted curves accord quite well with the experimental data, and if the pore shape factors were ignored, there would present an overestimation of 37.0% and 27.9%, respectively. It seemed that calculating the pore shape factor accurately and involving it in the imbibition model would be very essential when dealing with the experimental fluid imbibition data or conducted field fluid imbibition volume predictions.
页岩孔隙形状因子的计算及对流体吸积的影响评价
在页岩气藏中,流体自吸现象在钻井和增产过程中十分普遍,也与井眼失稳控制和水力压裂等工程设计有关,其中流体自吸成为研究的热点问题。在现有流体吸胀模型中,孔隙形态通常被假设为圆管状,而扫描电镜(SEM)图像分析表明,页岩孔隙形态在很大程度上来源于理想的圆形孔隙。在吸胀模型中引入孔隙形状因子是修正孔隙形状与理想圆形孔隙之间偏差的方法之一。建立了计算特定几何孔隙形态因子的模型,在对页岩中无机孔隙和有机孔隙形态及比例分析的基础上,得到了综合孔隙形态因子。两种页岩样品的孔隙形状综合系数分别为0.54和0.61。将数值带入流体吸胀模型,结果表明,预测曲线与实验数据吻合较好,如果忽略孔隙形状因素,预测曲线分别高估了37.0%和27.9%。因此,在处理实验流体吸胀数据或进行现场流体吸胀体积预测时,准确计算孔隙形状因子并将其纳入吸胀模型是非常必要的。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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