石英溶解型次生孔隙的成因及其对储层的影响——以大牛地气田上古生界致密砂岩储层为例

以鄂尔多斯盆地大牛地气田上古生界致密砂岩储层中的石英溶解为研究对象，借助偏光显微镜、扫描电镜、阴极发光显微镜、激光共聚焦显微镜的观察及统计，结合X-衍射分析数据及水-岩反应实验，总结了石英溶解的典型形貌特征、成因及其对致密砂岩储层的影响。研究结果显示：1）大牛地气田石英溶解现象普遍发育，且具有典型的电镜形貌特征，常呈“雨痕状”与“蜂窝状”的溶蚀坑洞。2）大牛地气田的石英溶解发生于碱性环境下，具体证据为①水热实验证实石英溶解于碱性环境下更易发生，在致密砂岩储层中很难发生酸性溶蚀；②与石英溶解共生的方解石胶结交代现象普遍；③部分层位富伊利石贫高岭石，并发育数量不等的绿泥石包壳。3）石英的碱性溶解作用形成粒间溶蚀孔、扩大孔等次生孔隙，平均増孔近6％，是大牛地气田致密砂岩储层部分层位优质储层的成因。

Genesis of secondary pore of quartz dissolution type and its influences on reservoir:Taking the tight sandstone reservoir in the Upper Paleozoic of Daniudi gas field as an example

By virtue of polarizing microscope,scanning electron microscope,cathode luminescence microscope,laser scan confocal microscope in combination with X-ray diffraction data and water rock interaction experiment,we studied quartz dissolution in tight sandstone reservoirs in the Upper Paleozoic of Daniudi gas field in Ordos Basin,and summarized the typical morphology features,genesis and its influences on tight sandstone reservoir.Results show that:(1)Quartz dissolution is common and has typical SEM morphology features as “rain print” and “honey comb” solution pits and/or vugs.(2)Quartz dissolution in Daniudigas field develops in alkaline environment,and the detailed evidences are as follows:①hydrothermal experiments verify that quartz dissolves more easily in alkaline environments than in acid conditions;②calcite cementation and metasomatism associated with quartz dissolution are common;③some horizons are rich in illite but poor in kaolinite,with some chlorite coatings occurring sporadically.(3)Quartz alkaline dissolution results in secondary pores such as intergranular dissolution pores and enlarged pores,leading to an average incremental porosity of about 6%.This is the cause of quality reservoirs in some tight sandstone intervals of Daniudi gas field.