云南喜山期断陷盆地特征与油气勘探方向——以保山盆地和曲靖盆地为例

在喜山期构造运动影响下,云南地区形成众多断陷盆地和拉分盆地。保山盆地和曲靖盆地是已经取得油气勘探突破的两个断陷盆地。两个盆地形态相似,均为受控盆断裂拉张、坳陷形成的一侧陡坡、一侧缓坡的箕状盆地。盆地演化均经历了拉张期、断陷期、坳陷期和抬升消亡期4个阶段。曲靖盆地受喜山运动二幕影响,缺失中新统地层沉积。烃源岩主要由盆地断陷和坳陷期半深湖-深湖相暗色泥岩和沼泽平原相煤系地层组成,有机碳含量1%~2%,有机质成熟度低。储层主要由盆地陡坡带冲洪积砂砾岩、三角洲前缘砂岩和三角洲平原水下分支河道砂体组成,具有高孔隙度低渗透率特点。鉴于断陷盆地烃源岩和储集层分布规律,在油气勘探过程中除了寻找有利的构造气藏外,应注重生烃坳陷内寻找有利的岩性气藏,有利相带为靠近陡坡带的冲洪积相和缓坡带的三角洲前缘相。

Characteristics and hydrocarbon exploration in the Himalayan faulted basins in Yunnan: Examples from the Baoshan and Qujing Basins in Yunnan

There are a lot of fault basins and pull-apart basins created by the Himalayan orogeny in Yunnan, among which the Baoshan and Qujing Basins have similar features and witnessed, without exception, four evolutionary stages of extension, rift faulting, downwarping and uplifting/collapse. Influenced by the second episode of the Himalayan orogeny, the Miocene deposits are absent in the Qujing Basin. The source rocks consist primarily of bathyal-abyssal dark mudstones and marshland plain coal measures generated during the rift faulting and downwarping stages of the basin. The organic carbon contents only range between 1% and 2%, and the organic carbon maturity is relatively low. The reservoir rocks are mainly made up of steep slope alluvial-pluvial sandstones and conglomerates, delta front sandstones and delta plain subaqueous distributary channel sandstones, with higher porosity and lower permeability. Except structural gas reservoirs, particular attention should be drawn to the favourable lithologic gas reservoirs in the alluvial-pluvial facies near the steep slope zones and delta front facies in the ramp zones.