五墩凹陷北部斜坡带储层沉积特征及油气勘探意义

Sedimentary Characteristics of Reservoir in Northern Slope Zone of Wudun Sag and its Significance for Oil and Gas Exploration

摘要: 研究结果表明，敦煌盆地五墩凹陷侏罗纪时期为山前断–坳陷盆地，发育有南部、北部、东北部三个方向物源体系，中间沟组一段(J₂z¹)是凹陷内主要的烃源岩及储层发育组段，油气藏多为自生自储。中间沟组一段(J₂z¹)沉积期，湖盆整体较浅，受北山物源体系控制，凹陷北部斜坡带坡度较缓，但随沉积水体逐渐扩大、加深，发育有退积型浅水辨状河三角洲沉积，地震剖面具有S型前积和斜交型前积地震反射。储层物性受沉积微相、砂岩组分及填隙物的影响，泥质杂基含量高是导致储层物性差的主要原因，寻找有利储集相带是该区下步主要的勘探方向。

Abstract: The result of exploration in Wudun sag of Dunhuang Basin shows that the Wudun sag is a pied-mont fault-depression basin with three source systems in the south, north and northeast in Jurassic period. The middle gully formation (J₂z¹) is the main source rock and reservoir formation in the sag, where the self-generated and self-stored reservoir developed. During the deposition period of the middle gully formation (J₂z¹), the lake basin is shallow overall, controlled by the Beishan provenance system. The slope of the northern slope of the depression is relatively slow. As the sedimentary water body gradually expands and deepens, there is a degraded shallow water-discriminating river delta deposit. The seismic profiles have S-type progradation and oblique progradation seismic reflection. The physical properties of reservoir are affected by sedimentary microfacies, sandstone composition and interstitial materials. The physical properties of underwater distributary channel and estuarine sand bar are better than that of the interchannel. The physical properties of the reservoir tend to be better with the increase of quartz content, and the content of the rock cuttings is inversely proportional to the physical properties of the reservoir. The high content of muddy heterogeneity is the main cause of poor physical properties of the reservoir. Finding a favorable reservoir phase belt is the main exploration direction of the next step in the area.