深层海相凝析油气藏成因机制与富集主控因素——以塔里木盆地顺北4号断裂带为例

Genetic mechanism and main controlling factors of deep marine condensate reservoirs: A case study of the Shunbei No.4 fault zone in Tarim Basin, NW China

塔里木盆地顺北地区4号断裂带发育典型凝析油气藏,凝析油气成因机制与富集主控因素不明制约了勘探向外围的拓展。基于有机地球化学特征与区域地质背景综合分析,明确了顺北4号断裂带凝析油气成因机制与富集主控因素,主要取得以下3点认识:(1)顺北4号断裂带发育原生的凝析油气藏,凝析油气藏的形成主要受到有机质差异演化,多期成藏以及次生作用影响。(2)顺北4号断裂带凝析油气藏整体次生作用较弱,但是中段和南段所经历的次生作用相对强于北段;次生作用包括原油裂解作用、气侵作用以及TSR作用。(3)顺北4号断裂带北段凝析油气藏富集程度明显高于中段和南段;凝析油气富集高产主要受到输导条件以及储层规模控制,断裂活动强度越大,输导条件越好,储层规模越大,膏盐岩越薄也越有利于油气沿走滑断裂向上运移,从而导致油气高产富集。

Typical condensate reservoirs are developed in the No.4 fault zone in Shunbei area of the Tarim Basin.The exploration expansion is restricted by the unclear genetic mechanism and main controlling factors of condensate accumulation.Based on the comprehensive analysis of organic geochemical characteristics and regional geological background,the genetic mechanism and main controlling factors of condensate accumulation of the No.4 fault zone in Shunbei area are identified,and the following understandings are mainly obtained:(1)the condensate oil and gas reservoirs in the No.4 fault zone in Shunbei area are mainly primary condensate reservoirs,and the formation of condensate reservoirs is mainly affected by the differential maturation of organic matter,multi-phase accumulation and secondary alteration;(2)the overall secondary effect of condensate oil and gas reservoirs in the Shunbei No.4 fault zone is relatively weak,but the secondary effect experienced by the middle and southern sections is relatively stronger than that of the northern section;secondary processes include oil cracking,gas invasion,and TSR;and(3)the enrichment degree of condensate oil and gas reservoirs in the northern section of the Shunbei No.4 fault zone is significantly higher than that in the middle and southern sections;the enrichment and high production of condensate oil and gas are mainly controlled by transport conditions and reservoir size.The stronger the fault activity,the better the transport conditions,the larger the reservoir size,and the thinner the gypsum salt rock,which is more conducive to the upward migration of oil and gas along strike slip faults,resulting in high production and enrichment of condensate.