湘西北下寒武统牛蹄塘组页岩气储集条件研究

Reservoir Conditions of Shale Gas in the Lower Cambrian Niutitang Formation,Northwestern Hunan

为客观评价湘西北地区下寒武统牛蹄塘组页岩气资源勘探潜力，本研究利用x射线衍射仪（XRD）、高倍扫描电镜、扫描探针显微镜等系统研究了其页岩气储集条件。XRD分析结果表明，泥页岩中脆性矿物含量为53．8％～98．1％，平均77．9％，脆性矿物含量丰富，其高值区主要分布在张家界柑子坪、三岔及其周边地区。高倍扫描电镜分析结果显示，湘西北下寒武统牛蹄塘组泥页岩中发育残余原生孔隙、有机质微孔隙、不稳定矿物溶蚀孔、矿物层间微裂隙和构造裂缝，其中构造裂缝、有机质微孔隙和不稳定矿物溶蚀孔是研究区页岩基质孔裂隙的主要组成部分。扫描探针显微镜分析结果显示，湘西北下寒武统牛蹄塘组泥页岩中蜂窝状的有机质丰富，主要呈分散状和条带状分布，其内部纳米级孔隙发育。Ultrapore-200A氦孔隙仪测试结果显示，湘西北下寒武统牛蹄塘组泥页岩孔隙度相对较低，为0．6％～11．7％，平均4．6％，其影响因素主要是构造裂缝，其次是泥页岩有机碳含量和长石含量。ULTRA—PERM200渗透率仪测试结果显示，湘西北下寒武统牛蹄塘组泥页岩渗透率度相对较低，为0．002-0．06mD，平均0．014mD，其影响因素主要是构造裂缝，其次是矿物层间微裂隙。等温吸附实验结果表明，湘西北下寒武统牛蹄塘组泥页岩具有较好的吸附气性能，其中有机碳含量可能是影响泥页岩吸附气含量的最主要因素。

To objectively evaluate shale gas exploration potential in the Lower Cambrian Niutitang Formation, northwestern Hunan, reservoir conditions of shale gas were investigated by means of X-ray diffraction （XRD）, scanning electron microscopy （SEM） and scanning probe microscopy （SPM） and so on. XRD analysis results suggest that brittle mineral contents range from 53.8 percent to 98. 1 percent, with an average content of 77.9 percent. High value zones of brittleness mineral contents are mainly distributed in the Zhangjiajie Ganziping, Sancha and the surrounding areas. High magnification SEM analysis results indicate that there exist five kinds of pores and fractures, including residual primary pores, organic micropores, dissolution pores in unstable minerals, interlayer microfracture in minerals, as well as tectonic fractures. Of which structural fractures, organic micropores, dissolution pores in unstable minerals are the main constituents. SPM analysis results suggest that honeycomb organic matters distributed mostly in strip-shaped and disperse states are rich in the mud-shale of Lower Cambrian Niutitang Formation, northwestern Hunan, with nanoscopic porosities well developed in organic matters. Test results of Ultrapore-200 helium porosimeter show that porosity of mud-shale is low, with a range from 0.6 percent to 11. 7 percent （an average content of 4. 6 percent） and the dominant factor of porosity is structural fractures, followed by TOC contents and feldspar contents. Test results of ULTRA-PERMTM200 permeameter show that permeability of mud-shale is relatively low, ranging from 0. 002mD to 0.06mD （an average content of 0. 014mD） and the dominant factor of permeability is structural fractures, followed by interlayer microfracture in minerals. Isothermal adsorption experimental results show that mud-shale of Lower Cambrian Niutitang Formation had good adsorbability and TOC content may be the dominant factor to affect the mud-shale.