甘肃敦煌盆地五墩凹陷致密油成藏地质条件

甘肃敦煌盆地五墩凹陷勘探程度极低，基底埋深大，中、下侏罗统较厚，是一个生油潜力较好、储层致密的自生自储式油藏类型，为中国一个油气勘探新区。全面分析了五墩凹陷侏罗系致密油储集层的成藏地质条件，并对其勘探潜力进行了评价。结果表明:五墩凹陷中侏罗统中间沟组—下侏罗统大山口组湖相泥岩、砂砾岩碎屑储集层构成了对致密油形成非常有利的源储共生关系；中侏罗统中间沟组—下侏罗统大山口组总有机碳平均为3.26%，有机质类型以Ⅱ型为主，处于成熟阶段，具有较好的生油潜力；碎屑岩储集层以原生孔隙为主，为超低孔—低孔、超低渗储集层；五墩凹陷发育构造、岩性、地层及构造-岩性等圈闭类型；油气成藏受烃源岩与构造双重控制；中央洼陷带及其周边储集层发育的具有有利构造条件的圈闭是进一步进行致密油勘探的首选目标。

Geological Conditions of Tight Oil Reservoirs in Wudun Sag of Dunhuang Basin,Gansu, China

The exploration in Wudun sag of Dunhuang Basin, Gansu is poor. The basement is buried deeply; the thickness of Middle and Lower Jurassic is large; the potential for generating hydrocarbon is better; the reservoir is tight. The accumulation model of Wudun sag is self-generating and self-bearing, so that it is a new oil-gas exploration area. The accumulation geological conditions of Jurassic tight oil reservoirs in Wudun sag were analyzed, and the exploration potential was evaluated. The results show that the lacustrine mudstone and glutenite clastic reservoir are very favorable for forming the tight oil reservoirs in Middle Jurassic Zhongjiankou Formation-Lower Jurassic Dashankou Formation in Wudun sag; the average of total organic carbon is 3.26%, and the organic matter is mainly type Ⅱ in mature stage with better potential for generating hydrocarbon; for the clastic reservoir, there is mainly primary pore with ultra-low to low porosity and ultra-low permeability; the traps include structural, lithologic, stratigraphic and structural-lithologic in Wudun sag; hydrocarbon accumulation is both controlled by source rocks and structural settings; the further advantageous exploration targets are the traps with abundant reservoir growth and beneficial structural condition in the central sub-sag belts and reservoir nearby.