天峨-南丹地区泥盆系罗富组页岩气成藏条件及有利区预测

Geological conditions for shale gas accumulation and favorable area prediction of Luofu formation of Devonian in Tian'e-Nandan area

通过野外地质调查、钻测井资料分析、有机地化分析及现场含气量解析等工作手段,对桂西北天峨–南丹地区中泥盆统罗富组页岩气的烃源岩特征、储集条件、富集规律及保存条件进行了深入分析。结果表明:研究区罗富组沉积期为半深‐深水台盆相沉积环境,具有明显的垂直分带性,罗富组上段岩性为硅质泥岩、泥页岩,暗色泥页岩有效厚度40~80 m,下段以灰岩、泥灰岩为主;罗富组泥页岩TOC平均值为2.36%;有机质类型属典型的混合型干酪根,上段为Ⅱ_1腐殖腐泥型,下段为Ⅱ_2腐泥腐殖型;烃源岩整体成熟度较高,R_o大于2.0%;泥页岩石英平均含量为30.5%,碳酸盐矿物平均含量为24.6,黏土矿物含量42.2%,储集空间以泥页岩粒间孔、溶蚀孔和有机质孔为主;区域具备良好的页岩气形成与富集条件。推断保存条件是天峨–南丹区页岩气富集的关键,预测更亮‐困里一带为页岩气有利勘探区带。

Based on field geological survey analysis, drilling data analysis, organic geochemical analysis and field gas content analysis, the study on accumulation conditions, reservoir conditions, enrichment regularity and preserving conditions of shale gas in Luofu formation of Devonian in Tian'e-Nandan area of northwestern Guangxi was carried out. The results indicated the depositional period of Luofu formation in this area was semi-deep-water interplatform basin of depositional environment and it had obvious vertical zoning. The upper lithology of Luofu formation was siliceous mudstone, shale and dark shale were 40~80 m, mainly of limestone construction. The overall maturity of Luofu formation was high, the average maturity(Ro) was greater than 2.0%, and the average TOC was 2.36%. The organic type was a typical mixed kerogen, the upper part of Ⅱ1 was humic saprophy and the lower section of Ⅱ2 was sap humus. The average content of shale quartz was 30.5% and the carbonate mineral content was 24.6%. The clay mineral content was 42.2% and the reservoir space was mainly composed of interglacial pores, dissolution holes and organic matter holes. Therefore, the region was qualified with good shale gas accumulation and enrichment conditions. It was concluded the preserving condition was the key to the shale gas enrichment in the Tian'e-Nandan region, and the Gengliang-Kunli region was predicted to be favorable exploration area.