琼东南盆地乐东、陵水凹陷中新统岩性地层圈闭成藏条件

Hydrocarbon accumulation condition of Miocene litho-stratigraphic trap in Ledong & Lingshui sags,Qiongdongnan basin

区域构造-沉积背景分析及大面积三维地震资料处理结果表明,渐新世早期受红河断裂走滑侧翼拉分作用,琼东南盆地乐东、陵水凹陷形成了大规模的崖城组海陆过渡—半封闭浅海相烃源岩。该区主要勘探目的层系为中新统深水沉积储层,其中,上中新统黄流组轴向水道分为海南隆起水系提供主要物源的早期水道和昆嵩隆起秋盆河提供主要物源的晚期水道,2期水道砂岩具有不同的空间展布规律和沉积形态;中中新统梅山组坡控海底扇受物源和古地形影响发育斜坡水道型、盆底扇型和底流改造型等3种沉积样式,不同沉积样式控制不同的储层沉积和物性特征。这2种类型深水储集体在沉积和差异沉降作用下形成4种类型岩性地层圈闭,其下伏深部地层由于水热和生烃增压作用而形成区域范围的裂隙网络,从而沟通了深部烃源岩地层,使天然气在超压和浮力作用下运移到中新统岩性地层圈闭富集成藏。

Regional tectonic-sedimentary background analysis and large-area 3D seismic interpretation results show that large scale marine-continental transitional facies and half closed marine facies source rocks of Yacheng Forma- tion develop in Ledong ＆ Lingshui sags due to the Red River flank strike-slip pull-apart fault in Early Oligocene. The main objective exploration strata in this area are deep water deposited reservoir during the Miocene. Upper Miocene Huangliu reservoir is axial channel sandstone, which is composed of the early channel whose source is provided by river system of Hainan uplift and the late channel whose source is mainly from ancient Qiupen River of Kunsong uplift, and both axial channels exhibit different spatial distribution patterns and deposit morphologies. Slope break-control submarine fan of Meishan Formation is influenced by provenance and palaeotopography in Mid- dle Miocene, which can be divided into such three types as slope channelled fan, basin floor fan and bottom current reworked fan, and different fan deposited styles have different sedimentary and physical properties. These two kinds of reservoirs can form four types of litho-stratigraphic traps under sedimentation and differential settlement. Regional fracture networks in the deep formation caused by over-pressure of hydrothermal processes and hydrocarbon generation can connect deep source rock, so gas is driven by overpressure and buoyancy force to migrate into the Miocene litho-stratigraphic trap to accumulate and form pool.