准噶尔盆地上二叠统上乌尔禾组大面积岩性-地层油气藏形成条件及勘探方向

近年来,准噶尔盆地在玛湖、沙湾、阜康、东道海子等凹陷的上二叠统发现大面积岩性-地层油气藏(群),形成了全盆地整体突破的良好勘探局面。基于大面积岩性-地层油气藏形成的构造背景、供烃基础、储集性能、圈闭与保存条件等地质因素的综合分析,认为盆地断坳转换期不整合之上发育的低位体系域砂砾岩体、扇三角洲前缘相带及优质甜点储层是全盆地源上它源型油气大面积聚集成藏、局部高产富集的物质基础。明确了准噶尔盆地上二叠统大面积岩性-地层油气藏3大成藏主控因素:中-下二叠统规模优质咸化湖相烃源岩提供了坚实的油气资源基础;断裂-不整合立体输导体系为油气运移、大面积聚集成藏提供了重要保障;环凹大型斜坡区发育的不整合为大面积岩性-地层油气藏提供了良好的圈闭与保存条件。在此基础上,建立了盆地西部上二叠统的"源储分离型——超覆-削截复合"油气成藏模式和盆地东部上二叠统的"源储紧邻型——低位超覆"油气成藏模式。以该研究认识为指导,指出玛湖凹陷南斜坡、沙湾凹陷西斜坡、盆1井西凹陷东北斜坡、东道海子凹陷北斜坡和阜康凹陷东斜坡是准噶尔盆地上二叠统大面积岩性-地层油气藏的有利勘探方向。

Hydrocarbon accumulation conditions and exploration directions of large-scale lithologic-stratigraphic oil and gas reservoirs in Upper Wuerhe Formation of Upper Permian in Junggar Basin

In recent years, large-scale lithologic-stratigraphic oil and gas reservoirs (groups) have been discovered in the Upper Permian in Mahu, Shawan, Fukang and Dongdaohaizi sags in Junggar Basin, thus making an overall breakthrough in exploration of the whole basin. Based on the comprehensive analysis of geological factors, such as tectonic setting, material basis for hydrocarbon supply, reservoir properties as well as trap and preservation conditions of large-scale lithologic-stratigraphic oil and gas reservoirs, it is considered that the development of low-level sandy conglomerates above unconformity in the transformation period of basin fault depression, fan delta front belt and high-quality sweet spot reservoirs provides a material basis for the large-scale accumulation and local enrichment of above-source allochthonous oil and gas in the whole basin. On this basis, the paper clarifies three main controlling factors for the development of large-scale lithologic-stratigraphic oil and gas reservoirs in the Upper Permian in Junggar Basin. The Middle and Lower Permian high-quality salinized lacustrine source rocks provide abundant oil and gas resources as a solid material basis; the three-dimensional pathway system of fault and unconformity provides an important guarantee for the large-scale accumulation and migration of oil and gas; the unconformity developed in the large slope zone around the sag provides favorable trap and preservation conditions for large-scale lithologic-stratigraphic oil and gas reservoirs. Based on this, two oil and gas accumulation models of "source-reservoir separation type and composite overlap-truncation combination" in the Upper Permian series of western Junggar Basin and "source-reservoir adjacent type and low-level overlap" in the Upper Permian series of eastern Junggar Basin have been established. Guided by the understandings, it is pointed out that the south slope of Mahu sag, west slope of Shawan sag, northeast slope of Pen 1 Well West sag, north slope of Dongdaohaizi sag and east slope of Fukang sag are the favorable exploration directions for large-scale lithologic-stratigraphic oil and gas reservoirs in the Upper Permian in Junggar Basin.