敦煌盆地侏罗系致密油地质特征及其意义

敦煌盆地残留性质明显,侏罗纪成盆后改造变化大、油气地质条件复杂。为进一步加快勘探进程,在前期成果基础上,以非常规油气地质理论为指导,从盆地的演化入手,通过新钻探致密油藏的解剖和地质特征的系统研究,明确了侏罗系致密油藏形成条件和地质特征。中下侏罗统发育二套较好烃源岩,其中中间沟组一段的烃源岩有机质含量高、以I～II_1型为主,发育于还原性的湖相环境,为致密油形成提供了较好的物质基础。广泛分布的三角洲、扇三角洲前缘砂体,是致密油聚集的主要场所。近源聚集、保存条件较好的致密油藏是下步勘探的主攻方向,三危山北侧的清台、五墩凹陷烃源岩发育厚度大,其深洼带断层发育较少,后期改造以整体抬升为主,保存相对完整,发育的岩性和构造-岩性圈闭最为有利,特别是被大山口组和中间沟组烃源岩包裹的有利砂体是首选的钻探目标。对区内实现实质性的突破,推动整个河西走廊中小盆地群的油气勘探,均具有重要的现实意义。

Characteristics and Significance of Tight Oil Geology in Dunhuang Jurassic Basin

The residual nature of the Dunhuang basin is obvious. The Jurassic has great alteration after the basin forming, and the geological conditions of oil and gas are complex. In order to further accelerate the exploration process, the formation conditions and geological characteristics of the Jurassic tight reservoirs are clarified through the systematic study of the anatomy and geological characteristics of the newly drilled tight reservoirs, under the guidance of unconventional petroleum geology theory and under the guidance of fully digesting the previous achievements. There are two sets of good source rocks in the Middle-Lower Jurassic, among which the source rocks of the first member of Zhongjiangou Formation have high organic matter abundance, mainly of type I-II1, and developed in the original lacustrine environment, providing a good material basis for the formation of tight oil. Widely distributed Delta and fan delta front sandbodies are the main places for tight oil accumulation. Tight reservoirs with good near-source accumulation and preservation conditions are the main targets for next exploration. Source rocks in Qingtai and Wudun sags on the northern side of Sanweishan Mountain are thicker and have fewer faults in their deep depressions. In the later stage of reconstruction, the whole uplift is dominant and the preservation is relatively complete. The developed lithology and structural-lithologic traps are most favorable, especially. The favorable sand bodies wrapped by the source rocks of the dashantou formation and the middle trough formation are the preferred drilling targets. It is of great practical significance to realize a substantial breakthrough in the area and to promote the oil and gas exploration of small and medium-sized basin groups in the Hexi Corridor.