煤岩微观结构分析及其与压裂液设计的关系研究

Study on coal-rock microstructure and it's relationship with fracturing fluid design

为了更直观和量化分析煤岩微观结构,以指导压裂液设计,提高压裂液效率和降低煤储层伤害,采用显微光度计、环境扫描电子显微镜和CT扫描等微观结构分析方法,得到了不同维度和角度的煤样裂隙结构图,并定量分析了煤样裂隙参数。结果表明:不同区块煤样的主裂隙长度、主裂隙宽度有很大不同;割理有明显的同向性,容易产生沟通的裂缝;裂缝的排布在微观尺寸上很复杂,使得裂缝对复杂的应力剖面和压裂过程中应力场的变化很敏感;裂缝具有各向异性和非均质性,提高了压裂液伤害的概率。通过定量分析可知:不同区块煤样的成分不同,其源于不同的地质作用,同时也导致了不同的压力液作用效果;CT软件可以通过统计计算受测样品的孔隙度和渗透率,试验样品的孔隙度为2.68%,渗透率为6.65×10^(-3)μm^2,与孔隙度-渗透率试验结果数值相近,印证了煤层低孔低渗的显著特点。润湿-吸附试验等数据证明不同的煤结构和成分是导致压裂液作用性能不同的原因,通过对煤岩微观结构分析能够指导压裂液的研究,为压裂液设计提供依据。

In order to more intuitively and quantitatively analyze the microstructure of coal-rock,the design of the fracturing fluid is guided through the understanding of the microstructure to improve the efficiency of the fracturing fluid and reduce the damage of coal reservoir.In this paper,microstructural analysis methods,such as microphotometer,scanning electron microscopy,and CT are used to establish coal structure fracture diagrams with different dimensions and angles,and to quantitatively analyze fracture parameters.Based on microscopic photometer,scanning electron microscope and CT： the main crack length and main crack width of different blocks of coal samples are very different; cleats have obvious isotropy and are prone to cracks in communication; the distribution of cracks is complex,making the cracks sensitive to complex stress profiles and changing stress field during fracturing; cracks have anisotropy and heterogeneity,increasing the chance of fracturing fluid damage.Quantitative analysis shows that： the coal samples in different blocks have different compositions.The different compositions of the coal samples come from different geological functions.At the same time,they also lead to different fluids effects.The CT software can calculate the porosity and permeability of the tested samples statistically.The porosity of sample is 2.68% and the permeability is 6.65×10（-3）μm2.It is similar to the porosity-permeability experimental structure and confirms the remarkable characteristics of low permeability and low permeability in coal seams.Wetting and sorption experiments and other data prove that different coal structures and components are the causes of different fracturing fluids＇ performance.Intuitive structural micrographs and quantitative data analysis can guide the research direction of fracturing fluids for fracturing fluids and provide the basis for fracturing fluid design.