黔北地区牛蹄塘组富有机质泥岩储层特征

Reservoir Characteristics of Organic-rich Mudstone of Niutitang Formation in Northern Guizhou

为全面研究黔北地区牛蹄塘组富有机质泥岩储层特征,对该组7口页岩气调查井和4口地质浅钻的岩芯进行了系统采样,并做了矿物学分析、地球化学分析、孔隙度和渗透率测定、含气性分析等实验。结果表明,牛蹄塘组富有机质泥岩主要发育于深水陆棚相带,岩性以含粉砂炭质泥岩、粉砂质炭质泥岩为主,脆性矿物以石英+长石组合为主,方解石、白云石、黄铁矿等自生脆性矿物含量总体较低;黏土矿物含量较低,变化范围较大,成分以伊利石为主。有机碳含量普遍较高,在1.5%~15.7%,有机质成熟度174%~3.40%,总体演化程度较高;平均岩石密度2.52g/cm^3,BET比表面积0.33~33.76m^2/g;微观储集空间以粒间(晶间)孔为主,其次为粒内孔,有机质孔发育较差,微裂缝总体不发育,具有低孔低渗—低孔超低渗的储层特征;总含气量0.02~2.05m^3/t,现场解析气中N_2、H_2含量异常,CH_4等烃类气体含量较低。

A complete analysis was conducted of the reservoir characteristics of the organic-rich mudstone of the Niutitang Formation in Northern Guizhou,China.The rock core of seven shale-gas survey wells and four geology shallow wells was sampled and various experimental tests,such as mineral and geochemical analyses,porosity and permeability measurements,and hydrocarbon content analysis were carried out.The results show that the organic-rich mudstone of the Niutitang Formation develops mainly in a deep-water shelf facies.The rocks are mainly silty carboniferous and silty carbonaceous mudstone.The brittle minerals are mainly quartz-feldspar combinations.The content of other authigenic brittle minerals,such as calcite,dolomite,and pyrite is generally low.The clay mineral content,mainly illite,is low but the variation range is large.The overall organic carbon content is high(1.5%_15.7%),and the organic matter has a high level of maturity(1.74%_3.40%),with a higher evolution level.The average density of the reservoir rock is2.52g/cm3,and the BET specific surface area is0.33_33.76m2/g.The main reservoir spaces are interparticle pores and intraparticle pores.The development of the organic holes is inferior and there is a lack of micro-fractures.The characteristics of the reservoir point to low porosity and low permeability,as well as low porosity and ultra-low permeability.The total gas content is0.02_2.05m3/t.Field gas-component analysis shows the N2and H2content is higher than is the CH4content.