古地貌对重力流沉积控制作用及与天然气成藏的关系——以莺歌海盆地中新统为例

PALAEOGEOMORPHOLOGIC CONTROL ON GRAVITY FLOW DEPOSITS AND GAS RESERVOIR FORMATION:A CASE STUDY FROM THE MIOCENE IN YINGGEHAI BASIN

针对莺歌海盆地中央底辟带下步有利勘探方向不明的问题,以储层与成藏研究为重点,研究了古坡折、古沟槽、古沉降中心等古地貌单元及组合样式对重力流沉积的控制作用及与天然气成藏的关系。结果表明:古挠曲坡折带是诱发重力流的地带,限制性的古沟槽决定了沉积物的注入位置、推进方向,盆内不均衡沉降形成的古沉降中心控制了大型重力流海底扇沉积卸载区域。宏观上,重力流沉积体常在挠曲坡折下低位体系域发育,横向上易与挠曲坡折上的三角洲沉积断开,纵向上易与上覆海侵-高位体系域浅海富泥沉积构成良好的储盖组合,有利于岩性圈闭的形成。由于古沉积中心的由北往南迁移,导致北部东方区烃源早熟,早期成藏,而南部乐东区为烃源晚期快速生烃成藏的特征。综上研究,指出了中央底辟带中新统重力流储集体分布,为该区下步勘探方向提供了理论支撑。

For the purpose to identify the next exploration target which has remained unclear so far in the central depression of the Yinggehai Basin,and based on the principles of reservoir formation and gas accumulation,this paper studies the palaeogeomorphologic patterns and their control over gravity flow deposition and gas reservoir formation.Results show that the increases in slope and water depth near the flexure slope break is the key condition for submarine fan to form,and the limited grooves and valleys determine the injection mouth and the direction of sediment movement,and the subsiding centers formed by the uneven subsidence controls the unloading area for submarine fan deposits.Gravity flow sediments are always deposited under the slope break in the LST,and,therefore,disconnected to the deltaic deposits near the slope break.It is easy to form a good reservoir-cap association with overlying shallow sea mud deposit formed in the TST-HST as covers.It is favorable for the formation of effective trap.Since the paleo-depocenter migrated from north to south,the northern Dongfang region is precocious and matured.However,the organic matter in the Ledong region is matured late but rapid.Based on the above research,this paper points out that the central depression of the Yinggehai Basin is a favorable area for next cycle of exploration.