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早泥盆世埃姆斯期至早石炭世杜内期,南丹-河池一线为独特的台间盆地环境,位于桂中坳陷西部边缘,自下而上发育塘丁组、罗富组、榴江组、五指山组和鹿寨组含磷、锰的泥质、硅质和扁豆状的灰岩沉积。其中罗富组发育有连续的,具有一定沉积厚度的黑色、深灰色、灰黑色泥页岩沉积,具有页岩气开发潜力。针对南丹地区泥盆纪剖面罗富组进行的实测和沉积学分析能够更进一步的评价其中罗富组沉积的页岩气前景,研究共采集样品120件,采样间距为2m~3m。泥页岩层位选择其中10件含有机质样品进行有机质特征、矿物成分、孔隙度、孔隙结构等测试,20件样品用于电镜分析,80件样品进行薄片鉴定分析。综合野外露头剖面测量和样品地球化学测试及微孔结构观察结果,确定南丹地区罗富组下段具备形成页岩气的资源基础和优越的成藏条件。罗富组厚约330m,以富硅质泥页岩的首现,将之划为上、下两段。罗富组下段有机质丰度高(TOC分布于1.64%~3.69%之间),成熟度小于3.6%(Ro值介于3.14%~4.19%),泥页岩厚度大(大于100m),储层微孔隙发育,脆性矿物含量合适(介于48%~58%),黏土矿物之中不含蒙皂石。将研究剖面页岩气储层的地化、物性特征及沉积厚度与北美及四川页岩气对比,判断研究区中泥盆统罗富组下段具有较好的页岩气勘探潜力。
The Early Devonian Ames period to early Carboniferous Dunes period and the Nandan-Hechi frontier are unique platform environments in the Taiwan Strait. They are located on the western margin of the central Guangxi Zhuang Autonomous Region and develop the Tongding Formation, Luo Fu Formation, The Liujiang Formation, Wuzhishan Formation and Luzhai Formation contain phosphorous and manganese argillaceous, siliceous and lenticular limestone sediments. Among them, the Luofu Formation developed continuous, shale deposits of black, dark gray and gray-black muddy shale with a certain depositional thickness, which has the potential for exploitation of shale gas. According to the measured and sedimentological analysis of the Lo Phub Member of the Devonian Section in Nandan area, the prospect of shale gas deposition in the Lo Fu Formation can be further evaluated. A total of 120 samples were collected and the sampling interval was 2m ~ 3m. In the shale formation, 10 samples containing organic matter were selected to test the characteristics of organic matter, mineral composition, porosity and pore structure, 20 samples for electron microscopy and 80 samples for identification. Based on the results of field outcrop profile measurement, geochemical test of samples and observation of micropore structure, the resource base and superior reservoir forming conditions of shale gas formation in the lower part of Lo Fu Formation in Nandan area are determined. The Lo Fu Formation is about 330m thick and was first classified as upper and lower sections with siliceous shale. The lower abundance of organic matter in the Loess Formation (TOC distribution ranged from 1.64% to 3.69%), maturity less than 3.6% (Ro between 3.14% and 4.19%), shale thickness (over 100 m) Micro-pore development, suitable for brittle minerals (between 48% and 58%), smectite-free clay minerals. Comparing the geochemistry, physical properties and sedimentary thickness of shale gas reservoirs in the study area with shale gas in North America and Sichuan Province, it is concluded that shale gas exploration potential in the lower part of the LoPo Formation in the study area is good.