武威盆地上石炭统羊虎沟组页岩气成藏条件

Shale Gas Accumulation Condition of the Upper Carboniferous Yanghugou Formation in Wuwei Basin

武威盆地上石炭统羊虎沟组是中小盆地海陆过渡相泥页岩层系的典型代表,分析其页岩气成藏条件对揭示该区页岩气潜力和勘探方向具有重要意义。对野外露头和钻井样品进行了采集,并分析了泥页岩的发育特征、有机地球化学、储层物性和含气性。结果表明,羊虎沟组泥页岩单层厚度薄、累计厚度大、连续性差;有机质丰度高、热成熟度适中、类型以Ⅱ_1～Ⅱ_2型为主。Pr/nC_(17)和Ph/nC_(18)相关性揭示羊虎沟组泥页岩形成于还原性较强的沉积环境。矿物组成以黏土矿物为主,质量分数为28.5%～73.4%,平均为53.07%,其次是石英和少量的菱铁矿。孔隙类型主要为有机质孔和微裂缝,钻井样品的平均孔隙度为4.89%,渗透率主要分布在0.001×10^(-3)～0.1×10^(-3)μm^2,比表面积介于4.74～22.29 m^2/g。2个钻井样品的解析气含量分别为2.19 cm^3/g和2.39 cm^3/g,气体组成以CH_4为主;泥页岩甲烷等温吸附量为0.68～8.57 cm^3/g。TOC和R_o是武威地区海陆过渡相泥页岩物性和含气能力的主控因素,伊蒙混层含量的增加也可使泥页岩孔隙度和含气能力轻微增加。

The Upper Carboniferous Yanghugou Formation shale gas in the Wuwei Basin is a representative shale gas of the marine-continental transitional shale in small and medium basins, and analyzing the shale gas accumulation conditions is of great significance to reveal the shale gas potential and exploration direction in this area. This paper analyses the shale distribution, organic geochemistry, reservoir characteristics and gas-bearing properties of the Yanghugou Formation through field geology, drilling sample collection and analytical testing. The results show that the shale of the Yanghugou Formation is thin and the cumulative thickness is large with a poor continuity. The organic matter abundance is relatively high, showing the shale has already entered a high maturity stage. The organic matter is mainly type Ⅱ1-Ⅱ2. The correlation between Pr/nC17 and Ph/nC18 reveals that the Yanghugou Formation shale formed in a relatively reductive sedimentary environment. The mineral composition is dominated by clay mineral with a mass fraction of 28.5%-73.4%,with an average of 53.07%,followed by quartz and a small amount of siderite.Organic pores and micro-fractures are dominated pore types in the Yanghugou Formation shale,with averaged porosity of 4.89% for the drilling shale samples, and permeability mainly distributed within 0.001×10^-3-0.1×10^-3μm^2, and a specific surface area of 4.74-22.29 m^2/g.Two drilling samples have desorbed gas content of 2.19 and 2.39 cm^3/g, with main composition being CH4.The methane adsorption capacity ranges from 0.68 to 8.57 cm^3/g. TOC and Ro are the main controlling factors of the physical property and gas-bearing capacity of the marine-continental transitional shale in Wuwei Basin,and the porosity and gas-bearing capacity of the shale could also slightly increase with increasing of the content of I/S content.