东道海子凹陷成6井二叠系烃源岩热演化史与生烃史

Thermal Evolution History and Hydrocarbon Generation History of Permian Source Rocks in Well Cheng6,Dongdaohaizi Sag

东道海子凹陷是准噶尔盆地重要的生油生烃凹陷之一,二叠系岩层是东道海子凹陷的主要烃源岩层位和主要油气产层。以成6井为研究对象,通过对该区的油气地质、地球化学分析,运用盆地模拟技术对该井在6490m左右的二叠系下乌尔禾组和风城组的烃源岩进行埋藏史、热演化史模拟分析。分析结果显示,东道海子凹陷从294Ma开始就以100m/Ma的沉降速率开始沉降,从晚二叠系开始沉降速率明显变小,到了早侏罗世(198Ma),东道海子凹陷在5Ma的时间段内快速沉降,到195Ma沉降速率有所下降,在150Ma时经历了一次抬升剥蚀,137Ma以后又进入短时间的快速沉降阶段,最后在110Ma时沉降速率开始缓慢下降,随后保持均匀沉降速率。风城组烃源岩早在中二叠世(265Ma)前就进入了生油门限,对应的古地温为120.4℃;下乌尔禾组的烃源岩在中三叠世左右(约240Ma前后)进入生油门限,对应的古地温为96.39℃。现今两套烃源岩都处于过成熟阶段。早三叠世至中侏罗世(250~166Ma)是两套烃源岩热演化的关键时期,中侏罗世(174Ma)和晚白垩世(96Ma)为两套烃源岩生烃的关键时期。

Dongdaohaizi Sag is one of the important oil-generating and hydrocarbon-generating sags in the Junggar Basin,and the Permian strata are the main source rock layers and the main oil-gas pay zones in the Dongdaohaizi Sag.Based on the oil and gas geology and geochemistry analysis in Well Cheng6,the burial history and thermal evolution history of the source rocks in the Lower W uerhe Formation and Fengcheng For-mation of Permian at about 6490m are simulated by basin simulation technology.The analysis results show that the Dongdaohaizi Sag began to subside at a subsidence rate of 100m/Ma since 294Ma,and the subsi-dence rate became significantly lower since the Late Permian.By the Early Jurassic(198Ma),the Dongdaohaizi Sag began to subside rapidly within 5Ma,and the sedimentation rate decreased by 195Ma.At 150Ma,it expe-rienced an uplift and denudation and then entered a short period of rapid subsidence after 137Ma.Finally,the subsidence rate began to decline at 110Ma slowly,and then a uniform subsidence rate was maintained.The source rocks of Fengcheng Formation entered the oil generation threshold as early as the Middle Permian(265Ma),and the corresponding paleo-temperature was 120.49C.The Lower Wuerhe Formation source rocks en-tered the oil generation threshold around the Middle Triassic(around 240Ma),and the corresponding paleo-temperature was 96.399C.Nowadays,both sets of source rocks are in the over-mature stage.The Early Triassic to Middle Jurassic(250-166Ma)is the key period for the thermal evolution of the two sets of source rocks,and the Middle Jurassic(174Ma)and Late Cretaceous(96Ma)are the key periods for the hydrocarbon gener-ation of the two sets of source rocks.