塔北隆起西部地区白垩系碎屑岩油气成藏规律及成藏模式

Hydrocarbon accumulation law and model of Cretaceous clastic rocks in western Tabei uplift

以岩心观察、物性分析、地球化学分析和三维地震资料为基础,通过单井、连井沉积相分析、地震精细解释及优势砂体识别等方法,从油气来源、油气充注特征、输导体系及储盖组合等4个方面对塔北隆起西部地区白垩系碎屑岩油气成藏规律及模式进行了研究。研究结果表明:(1)研究区白垩系油气具有“陆源”特征,石油主要来自库车坳陷三叠系湖相烃源岩,天然气主要来自库车坳陷侏罗系煤系烃源岩,区内深部三叠系海相烃源岩贡献极小。(2)研究区白垩系油气充注持续时间长,成藏时期晚,早期生油,晚期生气,油成藏于中新世(4.0~22.0 Ma),气成藏于晚中新世—中上新世(3.5~11.0 Ma),受2.6~3.5 Ma构造隆升影响,气藏成熟度较低。(3)研究区油气输导体系较发育,天山南地区以断裂和不整合面作为主要运移通道;顺北地区以不整合面和巴西改组薄层砂体为运移通道。(4)研究区储层主要发育在舒善河组和巴西改组,含砂率一般高于60%,与其上部发育的连续泥岩构成良好的储盖组合;优质储层的分布受沉积相控制,天山南地区优质储层主要分布在扇三角洲前缘砂坝及滩坝,顺北地区优质储层主要分布在辫状河三角洲前缘朵体,目前探井未钻遇朵体最高部位,油气显示相对较差;顺北地区储层物性更佳。(5)研究区天山南与顺北地区因断裂活动强度及储盖组合特征存在差异造成了二者的油气藏类型不同,前者以低幅度构造、构造-岩性复合油气藏为主,后者以规模较小的岩性油气藏为主。

Based on core observation and physical property,geochemical analysis and 3D seismic data,through sedimentary facies analysis of single well and well-tie profile,fine seismic interpretation and identification of dominant sand bodies,the hydrocarbon accumulation law and model of Cretaceous clastic rocks in western Tabei uplift were studied from the aspects of oil source,oil and gas charging characteristics,transport system and reservoircap assemblage.The results show that:(1)The Cretaceous oil and gas in the study area has the characteristics of terrigenous origin.The oil mainly comes from Triassic lacustrine source rocks in Kuqa Depression,the gas mainly comes from Jurassic coal-measure source rocks in Kuqa Sag,while the deep Triassic marine source rocks contribute a little to oil and gas.(2)The Cretaceous oil and gas charging in the study area lasted for a long time,and the accumulation period was late.The accumulation can be divided into two phases:oil generation in the early period and gas accumulation in the late period.Oil accumulation occurred in the Miocene(4.0-22.0 Ma),and gas accumulation occurred in the early Pleistocene(3.5-11.0 Ma).Affected by the structural uplift of 2.6-3.5 Ma,the gas reservoir maturity was low.(3)The oil and gas transport system in the study area is well developed.Faults and unconformities are used as the main migration channels in southern Tianshan Mountains.The unconformity surface and thin sand bodies of Baxigai Formation are the migration channels in Shunbei area.(4)The reservoirs in the study area are mainly developed in Shushanhe Formation and Baxigai Formation,with sand content generally higher than 60%,which constitute a good reservoir-cap assemblage with the continuous mudstone developed in the upper part.The distribution of high-quality reservoirs is controlled by sedimentary facies.The high-quality reservoirs in southern Tianshan Mountains are mainly distributed in the front sand bar and beach-bar of fan delta,while the high-quality reservoirs in Shunbei area are mainly distributed in front lobe of braided river delta.At present,the exploration wells are not at the highest part of the lobe,and the oil and gas shows are relatively poor.the reservoir properties in Shunbei area are better.(5)Due to different fault activities and reservoir-cap assemblages,there are obvious differences in the types of oil and gas reservoirs between southern Tianshan Mountains and Shunbei area.The oil and gas reservoirs in southern Tianshan Mountains are mainly low-amplitude structural and structural-lithologic composite reservoirs.The oil and gas reservoirs in Shunbei area are mainly lithologic reservoirs with small scale.