黔西北地区下古生界盖层条件研究

RESEARCH OF LOWER PALAEOZOIC CAP FORMATION IN THE NORTHWEST OF GUIZHOU PROVINCE

黔西北地区与四川盆地同为刚性稳定基底,对比四川盆地钻探实践,黔西北地区仅保留中、下含油气系统,对黔中地区而言,有现实意义的只有下含油气系统。下组合盖层中以娄山关群膏质岩和金顶山组、牛蹄塘组泥岩最为重要,它们是保持勘探潜力的关键因素,构成整体封盖。特别是晚期经历了多期、多次构造运动,娄山关群膏质岩仍能完好保存,对下含油气系统构成整体封盖,发挥压力封闭作用;泥岩盖层亦具有较强的封闭性能,突破压力大于15.97 MPa,属Ⅰ类盖层。研究表明,黔西北地区压力封盖仍存在可能性,这是因为黔中隆起晚期抬升幅度虽较大,但-C1—-C2-3整体封盖系统未被破坏,与威远气田类似,仍具有效封盖功能。在封存有效的前提下,成藏最有利部位是黔中隆起主轴大方—金沙构造带及其南北两翼斜坡部位。

Similar to the Sichuan Basin,the northwest region of Guizhou Province is of stiff and stable basement.Only middle and lower petroleum systems have been preserved in the northwest of Guizhou.In the middle of Guizhou,only lower petroleum system is accessible.As to cap formation of lower system,gypsiferous rock of Loushanguan Formation as well as mudstone of Jindingshan and Niutitang Formations play important roles.They are the keys for exploration potential preservation and serve as overall seal.Though multi-stages of tectonic movements take place during the late stage,gypsiferous rock of Loushanguan Formation is still preserved and seals the lower system.Mudstone cap formation also has strong seal ability with breakthrough pressure over 15.97 MPa and belongs to type I cap formation.Pressure seal may exist in the northwest of Guizhou because that,though the Middle Guizhou Uplift up rises greatly during the late stage,Cambrian seal system is not yet destroyed and can work as effective seal.The most favorable place for accumulation is the Dafang-Jinsha tectonic belt and its northern and southern slopes.