摘要
煤层气钻井时,钻井液会对煤层孔–裂隙造成污染堵塞。为了查明钻井液对煤中不同尺度孔–裂隙的污染程度差异及不同尺度孔–裂隙对渗透率的贡献率,以晋城矿区长平矿井的煤为研究对象,应用扫描电镜(SEM)与Image Pro Plus(IPP)图像处理技术,定量表征煤中不同尺度裂隙污染前后的平均长度、平均宽度、总面积、总周长等参数;基于分形理论构建了污染前后不同尺度孔裂隙的渗透率数学模型,定量评价了污染前后渗透率变化,并与实验测试的渗透率结果进行对比,验证计算方法的可行性。结果表明:污染后不同尺度裂隙的平均长度和平均宽度均有所减小。减少程度从大到小依次为:毫米级>纳米级>微米级。不同尺度裂隙被污染程度不同,从大到小依次为:毫米级>微米级>纳米级;不同尺度裂隙对渗透率的贡献不同,一般情况下,毫米级裂隙是压裂液优先渗流通道,对渗透率的贡献最大,所占比例为46%~72%;微米级次之,所占比例为27%~53%;纳米级的贡献微乎其微,一般不超过2%。当煤中毫米级和微米级裂隙较多,且弯曲度、宽度非均质性较强时,可能存在大尺度向小尺度转化、小尺度裂隙增加现象。不同注入条件(如注入压力、注入时间)及钻井液类型对煤中不同尺度裂隙污染程度需要进一步深入研究。
During coalbed methane well drilling,the drilling fluid contaminates and blocks the pores and fractures of coal seam.In order to find out the difference of pollution degree of drilling fluid coal and the contribution rate of the pores and fractures of different scale to permeability,the coal of Changping mine was taken as the research object,the scanning electron microscopy(SEM)and the Image Pro Plus(IPP)processing technology were used,the parameters such as the average length,the average width,the total area and the total perimeter of the fractures of different scales in coal before and after contamination were quantitatively characterized.Based on the fractal theory,the mathematical model of the permeability of the fractures of different scales before and after contamination was established,the change of the permeability before and after contamination was evaluated quantitatively,and was compared with the results of the experimentally tested permeability to verify the feasibility of the calculation method.The results show that after contamination,the average length and the width of fractures of different sizes were reduced,and the decreasing degree was:millimeter scale>nanometer scale>micron scale.The degree of contamination was different in different scales,millimeter scale>micron scale>nanometer scale.The contribution rate of different scales to permeability was different,and the millimeter fracture was the preferential flow channel of fracturing fluid,contributed the most to the permeability,accounting for 46%-72%;the contribution of micron level was the second,accounting for 27%-53%;the contribution of nano scale to permeability was negligible,generally less than 2%.When there are many millimeter and micron scale fractures in coal,and the curvature and width heterogeneity are strong,there may be large-scale to small-scale transformation and small-scale fractures increase.Different injection conditions(such as injection pressure,injection time)and drilling fluid types need to be further studied.
作者
张径硕
倪小明
李阳
李宗源
曹运兴
ZHANG Jingshuo;NI Xiaoming;LI Yang;LI Zongyuan;CAO Yunxing(School of Energy Science and Engineering,Henan Polytechnic University,Jiaozuo 454003,China;The CBM Exploration and Development Pilot Test Base of CNPC,Renqiu 062550,China;School of Resources&Environment,Henan Polytechnic University,Jiaozuo 454003,China)
出处
《煤田地质与勘探》
CAS
CSCD
北大核心
2020年第5期64-72,共9页
Coal Geology & Exploration
基金
国家科技重大专项课题(2017ZX05064-002)
国家自然科学基金项目(41872174)。
