黔中隆起的油气勘探壁垒——兼论海相碳酸盐岩烃源岩

Barriers of Petroleum Exploration in Qianzhong Uplift, and on Hydrocarbon Source of Carbonate Source Rock

黔中隆起在地质构造上属于扬子地块的滇黔隆褶带,南华纪晚期初现雏形,震旦纪—奥陶纪为水下隆起,燕山运动使其整体抬高,喜马拉雅运动时急剧隆升,构造地貌长期相对隆起。地表油苗油样分析结果显示,在红外吸收谱图中缩合芳烃结构及含氧基团吸收明显,有机质热成熟度高,且遭受了氧化蚀变;震旦系以上地层大量暴露,地表水溶蚀下渗深度在黔西南地区可达3000～4000m;作为长期存在的古隆起,经历了多次抬升,直至挽近仍处于严重剥蚀阶段。地腹可能存在酸性岩浆热源使有机质过度热演化、保存条件不佳以及缺少勘探目的层,是黔中隆起油气勘探的三大壁垒。兼谈了碳酸盐岩烃源岩问题,认为形成大油气田的烃源岩主要是泥质岩系,“碳酸盐岩烃源岩”只是从属性的,分布在泥质烃源岩系的边缘或局部范围。

Qianzhong Uplift that is subordinate to Yunnan-Guizhou Bending Fold Belt of Yangzi Land Mass is a heavy denuded paleo-uplift that had been in sea during Sinian-Ordovieian period and rised rapidly during Himalayan movement. The overlying strata on Sinian rocks are all exposed and surface water has leaked down and solved into 3000-4000m of depth in southwestern Guizhou. The analysis of surface oil-seepage samples has shown a result of high organic maturation and oxidized alteration. Barriers of exploration in this area that will be faced are： （1） excessive heat evolution of organic matter brought from the heat of acidic magma that is likely to exist in deep; （2） not good condition of preservation; and （3） lack of exploration target beds. A problem, the source of hydrocarbon in carbonate rock, is discussed also. It is deemed that the source rocks in great oil and gas fields are dominantly argillaceous and subordinately carbonate.