摘要:
中国东部箕状断陷湖盆短轴方向,常常发育扇三角洲和辫状河三角洲,二者均可形成良好的油气储集体,但在岩芯以及地球物理资料的识别上常常容易混淆。通过对它们沉积特征、地球物理资料特征、含油气性和控制因素的对比研究和分析认为:扇三角洲是陡坡带冲积扇直接入湖形成,地震反射特征为楔形前积,沉积物成分成熟度和结构成熟度均低于辫状河三角洲,沉积特征反映重力流和牵引流双重作用;辫状河三角洲是缓坡带辫状河入湖形成的三角洲,向湖盆方向推进较远,地震反射特征为叠瓦前积,沉积特征反映牵引流作用。扇三角洲易形成构造-岩性油气藏和岩性油气藏,有利相带为扇三角洲前缘水下分流河道、席状砂以及前扇三角洲容易发育的滑塌浊积扇;辫状河三角洲易形成地层-岩性油气藏和岩性油气藏,有利相带为辫状河三角洲平原辫状分流河道,辫状河三角洲前缘水下分流河道、河口坝、席状砂以及半深湖中的浊积岩体。古气候变化、构造-古地貌以及湖平面变化速率三者共同作用于扇三角洲和辫状河三角洲的沉积特征,其中构造-古地貌是主控因素。结合二者沉积特征差异,建立了中国东部箕状断陷湖盆扇三角洲和辫状河三角洲沉积模式图,以期能对相似构造背景下扇三角洲和辫状河三角洲的分析与研究提供一定的指导作用。
Abstract:
Fan deltas and braided river deltas are widely developed along the direction of minor axis in half-graben rift lake basin of East China. Both of them can form good oil and gas reservoir, but the identifications of them in well core and geophysical data are easy to confuse. Through the comparison and analysis of sedimentary features, geophysical data, oil-gas-bearing and controlling factors, we conclude that fan deltas are formed by alluvial fans running into lake along steep-slope zone and its seismic reflection characters is wedge foreset. The sediment composition maturity and structural maturity of fan deltas are lower than that of braided river deltas. The sedimentary features of fan deltas reflect the gravity current and tractive current sediments combined effection. Braided river deltas are formed by braided river flow into lake far away along gentle slope zone and its seismic reflection characters is imbricate foreset. The sedimentary characters of braided river deltas reflect the tractive current sediments effection. Fan deltas can form fault-lithologic reservoir and lithologic reservoir. Its favorable reservoir zone includes underwater distributary channel, sheet-like sand of fan delta front and slump turbid fan formed in pre-fan delta. Braided river deltas can form strata-lithologic reservoir and lithologic reservoir of which favorable reservoir includes braid-river channel of braid river delta plain and underwater distributary channel, mouth bar, sheet-like sand of braid river delta front. Besides above, turbidity sandstone is also favorable reservoir in fairly deep lake. The sedimentary features of fan deltas and braid river deltas are controlled by palaeoclimate, tectonic-palaeogeomorphology and lake level fluctuations; Tectonic-palaeogeomorphology is the critical factor among them. The depositional model of fan deltas and braided river deltas in half-graben rift lake basin of East China is established by combining the sedimentary features difference between them so as to provide guidance to analysis and research for them in similar geological background.
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