滨里海盆地盐下层系的碳酸盐岩储集层与油气特征

在晚泥盆世—石炭纪—早二叠世,滨里海盆地周缘广大地区普遍发育各类碳酸盐岩,在许多古隆起上还发育生物礁体.这些盐下层系的碳酸盐岩和生物礁厚度大,分布广,物性好,是盆地的主要储集层.在盆地南部和东部,盐下层系的产层以上泥盆统和石炭系为主,而西北及北部边缘带上则以下二叠统为主.盐下层系的深部储层温度总体上是从北向南提高,从东向西升高;地层压力是盆地南部和东部比西部和北部的要高.在同一地区,盐下层系地层中往往表现为在盐下顶部沉积层比深部地层有更高的地层压力值.盐下层系的大油气田均具有异常高压性质,可大大改善储层的储集性.盐下层系的碳酸盐岩储层可划分为3个油气远景层段,它们的厚度均较大,物性均好,是良好的油气储集体.

Reservoir characteristics and oil-bearing characters of the carbonate reservoir beds in the pre-salt sediments of Pre-Caspian Basin

In upper Devonian,Carboniferous and early Permian,a plenty of pre-salt carbonate rocks are formed along the marginal areas of Pre-Caspian Basin,and some bioherms develop on many palaeohighs.The pre-salt carbonate rocks and bioherms have great thickness,high porosity and high permeability.They widely distribute and are the main reservoir beds in the basin.The major reservoir beds in the southern and eastern parts of the basin are upper Devonian and Carboniferous,and in the northwestern and northern parts lower Permian is main reservoir bed.The formation temperature in the pre-salt deep reservoirs increases from north to south and from east to west.The formation pressure in the southern and eastern parts of the basin is higher than that in the northern and western parts.In the same area,the pressure of top strata is usually higher than that of the lower strata in the pre-salt sediments.The abnormal overpressure exists widely in the pre-salt large oilfields,which can greatly improve the reservoir property.The pre-salt carbonate reservoir beds can be divided into three prospect intervals,and they have great thickness and high porosity and permeability.They are all excellent reservoir beds.