三塘湖盆地侏罗系西山窑组褐煤储层孔隙结构特征及脱水演化规律  

Pore structure characteristics and dehydration evolution of lignite reservoirs of Jurassic Xishanyao Formation in Santanghu Basin

作　　者：孔令峰 徐加放[1] 刘丁 KONG Lingfeng;XU Jiafang;LIU Ding(School of Petroleum Engineering,China University of Petroleum(East China),Qingdao 266580,Shandong,China;Development Planning Department,China National Petroleum Corporation,Beijing 100007,China;School of Energy Resources,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国石油大学(华东)石油工程学院,山东青岛266580 [2]中国石油天然气集团有限公司发展计划部,北京100007 [3]中国地质大学(北京)能源学院,北京100083

出　　处：《岩性油气藏》2024年第5期15-24,共10页Lithologic Reservoirs

基　　金：中石油股份公司科技重大专项“煤炭地下气化地质评价与选址研究”(编号:2019E-25)资助。

摘　　要：查明干燥前后煤孔隙结构差异及演化规律有助于准确预测煤炭地下气化炉运行效果。通过选择水、煤油作为饱和流体进行低场核磁共振实验,测试并对比同一样品分别在饱水和干燥状态下的孔隙结构差异;通过X-CT技术观察了煤样孔隙结构的脱水演化过程并建立了演化模式;通过脉冲衰减渗透率测试与低温液氮吸附实验评估了煤样的传质能力变化。研究结果表明:(1)褐煤干燥发生孔隙收缩的同时会产生裂缝,总孔容由0.630 cm^(3)/g降至0.481 cm^(3)/g,而大孔体积显著增加,由0.070 cm^(3)/g增加至0.420 cm^(3)/g,脱水导致孔隙集中,大孔体积占比达88%。(2)褐煤干燥时的孔隙收缩受基质收缩程度控制,不同煤岩组分脱水的孔隙结构演化模式不同,易收缩的基质煤脱水时,其组分边缘或内部产生大量裂隙,而木质煤或丝质煤脱水收缩较弱,保留大量原生孔隙,裂隙发育较少。(3)褐煤干燥后,水分脱除、空孔体积增加,渗流状态由单相水向气水两相、单相气流转变的同时形成了良好的连通孔隙网络,煤层渗流能力显著改善,渗透率由0.248 mD增加至48.080 mD,扩散传质贡献增大,干燥褐煤在温度为200℃、压力为0.5 MPa时中孔及大孔的扩散系数约为0.09 cm^(2)/s。It is helpful to accurately predict the operation effect of underground coal gasifier to find out the difference and evolution law of pore structure of coal before and after drying.By selecting water and kerosene as saturated fluids to carry out low-field NMR experiment,the pore structure of the same sample under saturated and dry conditions was tested and compared.The dehydration evolution process of pore structure of coal samples was observed through X-CT technology and an evolution model was established,and pulse attenuation permeability test and low-temperature liquid nitrogen adsorption experiments were conducted to evaluate the mass transfer ability of coal samples.The results show that:(1)During the drying of lignite,pore shrinkage occurs while cracks are produced,and the total pore volume decreases from 0.630 cm^(3)/g to 0.481 cm^(3)/g,while the large pore volume significantly increases from 0.070 cm^(3)/g to 0.420 cm^(3)/g.Dehydration leads to pore concentration,with the large pore volume accounting for 88%.(2)The pore shrinkage during the drying of lignite is controlled by the degree of matrix shrinkage.The dehydration of different coal rock components can be summarized into two types of pore structure evolution models:the dehydration of matrix coal that is prone to shrink develops a large number of cracks at the edges or inside of the components,while the dehydration shrinkage of xylite-rich and charcoal-rich coal is weak,retaining a large number of primary pores and developing fewer cracks.(3)After the drying of the lignite,water is removed and the number of empty pores increases.The seepage state changes from single-phase water to gas-water two-phase and single-phase airflow,forming a good interconnected pore network.The seepage ability of the coal is significantly improved,and the permeability increases from 0.248 to 48.080 mD.The contribution of diffusive mass transfer is increased,with diffusion coefficient of medium and large pores in dry lignite being about 0.09 cm^(2)/s at a temperature of 200�

关 键 词：褐煤储层 孔隙结构 脱水演化规律 弛豫谱 X射线断层扫描 渗流能力 煤炭地下气化 西山窑组 侏罗系 三塘湖盆地 

分 类 号：TE122[石油与天然气工程—油气勘探] P618.11[天文地球—矿床学]