沉积事件对深水沉积过程的影响——以鄂尔多斯盆地华庆地区长6油层组为例

Influence of sedimentary events on deep water sedimentation process:a case of Chang 6 reservoir in Huaqing area,Ordos Basin

鄂尔多斯盆地华庆地区长6油层组的厚层砂岩为深水沉积。为研究该地区深水沉积过程和岩石成因机理,基于岩心观察、测井和录井资料以及岩石样品的分析测试资料,对华庆地区长6油层组深水沉积物在沉积期所遭受的重力流事件、火山事件、地震事件和缺氧事件进行了系统研究。结果表明:(1)重力流沉积事件在整个沉积过程中频繁发生,是造成砂体在深湖区大面积多层堆积的直接原因;(2)火山活动的强度和影响范围相对于长7油层组沉积期较小,凝灰质泥岩平均厚度仅为1.74 m,且主要分布在长62～63砂层组中,形成凝灰质泥岩的火山灰主要以河流搬运方式进入湖盆沉积;(3)岩心上的沉积构造特征反映了地震事件频繁发生,推测震级约为4.5～5.5级;(4)上述地质事件的共同作用导致了沉积期湖盆的缺氧事件的发生,致使深湖区沉积了富含有机质的烃源岩,与储集砂体在纵向上构成了良好的生储盖组合。

The thick sandstone of Chang 6 reservoir in Huaqing area,Ordos Basin,is considered as the result of deep-water deposition. The data of core photographs,wire-logging,mud-logging and rock samples analysis were used to analyze sedimentary process in deep-water area and petrogenesis mechanism,including four main sedimentary events(gravity flow event,volcanic event,seismic event,and hypoxic event)happened in deep-water deposition process in Chang 6 reservoir. The results show that:(1)Gravity flow deposition events occurred frequently during the whole deposition process,which is the direct cause of large-area multi-layer accumulation of sand bodies in the deep-water area.(2)The intensity and influence range of volcanic activity in Chang 6 deposition period is much smaller than that in Chang 7,only with 1.74 m of average thickness of tuffaceous mudstones which are mainly distributed in Chang 62 and Chang 63 sandstone. Based on locations and sizes of tuffaceous mudstone developed,volcanic ash was considered add into the basin by river carrying.(3)The sedimentary tectonic features of core reflect the frequent occurrence of seismic events,and the magnitude of the earthquake is estimated to be about 4.5-5.5.(4)The combination of the above sedimentary events led to the occurrence of hypoxic events during the depositional period,and as a result,the source rocks rich in organic matter were deposited in the deep-water area,which formed a good source-reservoir-cap assemblage with reservoir sand bodies vertically.