桂中坳陷融水-融安地区下石炭统黑色泥页岩沉积特征及成藏潜力探讨

Sedimentary characteristics and reservoir-forming potential of Lower Carboniferous black shale in Rongshui-Rong’an area of Central Guangxi depression

为了进一步揭示研究区页岩气的成藏潜力与影响因素,通过野外地质调查、剖面资料、桂北下石炭统富有机质泥页岩层地质参数井(GRY1井)测录井资料、室内岩矿分析测试等,综合分析了桂中坳陷北部融水—融安地区下石炭统鹿寨组页岩气主要目的层系的沉积特征及黑色泥页岩有机地化特征、含气性和储集-保存条件,进而探讨了该区页岩气的成藏潜力。结果表明:①研究区融水和睦以东地区目的层系鹿寨组下段岩性为灰黑色泥质灰岩、钙质泥岩、炭质泥岩为主。融安地区目的层系下石炭统鹿寨组下段岩性以灰黑色、黑色含粉砂含钙泥岩、含碳泥岩夹黑色泥灰岩以及黑色炭质页岩为主;优质泥页岩段约40 m。②TOC值介于1.80%~2.96%之间,平均2.27%,Ro值介于1.80%~2.13%之间,平均值为2.00%,属于高—过成熟演化阶段,表明其已进入大量生干气期。储集层孔隙类型主要为矿物溶蚀孔、微裂缝、有机质孔隙等,经后期改造可形成较好的连通通道以及提高孔渗能力。且含气性最高可达2.61 m^(3)/t,不含残余气。③融水—融安地区下石炭统鹿寨组黑色泥页岩层系具有较好的页岩气成藏及勘探潜力,研究成果可为桂北乃至整个广西古隆起边缘页岩气的勘探提供参考。

In order to further reveal the reservoir-forming potential and influencing factor of shale gas in this area,through field survey and geological section data,analysis of test data and logging data of GRY1 well,which is the first complete drilling hole in the organic-richshale strata of Lower Carboniferous in North Guangxi,the sedimentary characteristics of the main target strata of shale gas such as Luzhai Formation of Lower Carboniferous and the organic geochemical characteristics,gas content and reservoir-preservation condition of black shale are comprehensively analyzed and studied.The research result is shown as follows.(1)The lithology of the lower member of Luzhai Formation is mainly gray-black argillaceous limestone,calcareous mudstone and carbonaceous mudstone in the east of Rongshui Hemu area.The lithology of the lower section of Luzhai Formation of Lower Carboniferous is mainly gray-black,black silt-bearing calcium mudstone,carbon mudstone with black marl and black carbonaceous shale in Rong’an area.The high quality shale section is about 40 m.(2)TOC value is between 1.80%-2.96%,with an average of 2.27%,Ro value is between 1.80%-2.13%,with an average of 2.00%,which belongs to the high-overmature evolution stage,indicating that it has entered a large number of dry gas generation period.The pore types of reservoir are mainly mineral dissolution pores,micro-fractures,organic pores,etc.,which can form better connectivity channels and improve porosity and permeability after later transformation.The highest gas content can reach 2.61 m^(3)/t without residual gas.(3)It is concluded that the black shale series of the Lower Carboniferous Luzhai Formation has a good shale gas accumulation and exploration potential in Rongshui-Rong'an area,indicating the direction for the exploration and development of shale gas in northern Guangxi and even the edge of the ancient uplift in Guangxi.