前陆盆地的类型及油气远景

CLASSIFICATION OF FORELAND BASINS AND ASPECTS OF HYDROCARBON RESOURCES

根据前陆盆地形成的大地构造背景，前陆盆地可分为5类，即周缘前陆盆地。弧后前陆盆地。破裂前陆盆地。陆内前陆盆地和走滑前陆盆地。前陆盆地形成于挤压构造环境，具有一些相似的成因特征，如沉降中心与沉积中心不一致；沉降曲线呈陡、缓、陡3段；沉积物遭受挤压变形．根据变形强度的差异．可分出3到5个变形带等。形成于不同大地构造背景中的前陆盆地具有不同的充填特点和盆地结构，也具有不同的油气远景。周缘前陆盆地是由于陆-陆碰撞，在俯冲板块上产生的挠曲盆地，常由被动大陆边缘裂谷盆地转化而成。盆地充填具有双层结构，早期发有复理石前陆盆地，堆积厚度巨大，发育厚度较大的生油岩系；后期发育磨拉石前陆盆地，为向上变粗的序列，发育有较厚的储集岩系。这类前陆盆地具有极好的油气远景。孤后前陆盆地与A型俯冲作用有关，可以由弧后裂谷盆地转化而成。盆地充填可具双层结构或仅有单后结构，早期发育火山复理石前陆盆地，堆积厚度大，发育有较厚的生油岩，后期为火山磨拉石盆地。这类前陆盆地具有较好的油气远景。破裂前陆盆地的形成是因基底卷入前陆变形作用，造成了块状隆起和基底褶皱所分隔的孤立盆地。这类盆地中沉积岩层厚度不大，油气远景欠佳。陆内前陆盆地形成于板内，远离碰撞造山带?

Foreland basins can be classified into 5 types in accordance with their tectonic settings: periland foreland basin, retroarc foreland basin, broken foreland basin, hinterland foreland basin and strike slip foreland basin. Foreland basins are formed in compressional tectonic environment and show some similar characteristics offormation. Such as discordance of depocentre and subsidence centre; 3 Segment of subsidence curve showingsteep,gentle and steep; and 3 to 5 deformation zones as a result of compression in sediments of foreland basins,are the common characters.The filling patterns and basinal structures are different in foreland basins formed in different tectonic settings and showed different hydrocarbon potential.Periland foreland basin is flextural basin formed in subducting plate resulted from continental - continentalcolision. It is generally transformed from rifting basin of passive continental margin. The basin showed duallaye structure of filling. The flysch foreland basin with great thickness was developed in the early stage andthick anrce eds were deposited; and molasse foreland basin with coarsing-upward sequence was developed inthe late stage and thick reserviors was formed. This kind of foreland basin is the most favorable petroliferousbasins.Retroarc foreland basin was related to A-type subduction and could be transformed from retroarc rif-tingbasin. Basin filling can be in dual-layer or single layer patterns. Volcanic-flysch forelang basin with thick sediments was developed in the early and source rocks were relatively thick; and volcanic-molasse foreland basin was developed in the late. This kind of foreland basin showed favorable hydrocarbon potential.The formation of broken foreland basin is due to basement involved foreland deformation, which resulted inidsed basins seParated by block uplift and basement fold- The sediments is thin and hydrocarbon poential ispoor in the basin. Hinterland foreland basin was formed in the interior of a plate and was far away from collisiona1 orogenicbelt. It may be related to long distance effect of collisional orogenic zone. The basin was filled in dual- or singlelayer patterns and dominated by molasse foreland basin with little development of eaxly flysch. This kind of foreland basin showed certain hydrocarbon potential.Strike-slip foreland basin was developed on both sides of main continental strike-slip system, accompanying with pull-apart basin. The basin filling pattern was single layer structured and molasse foreland basin was developed.The depocentre were obviously arranged in en echelon. Hydrocarbon potential in the basin was limited.The structures of foreland basin was asymmetric.Piedmont thrust, foreland depression, front slope and fron uplift were successively develoPed from orogenic ane to basin, in which distributi0n of hydIDCarbo accu-mulation was different: a) hydrOCaIfor was rnainly distributed in fods of hanging wall of piedInont thrust; b)hy~ was entrapped in stratigraphic and diagenetic traPs in foreland depression; c) sedimentary wedgethenned or pinch out towards the front slope, so accurnulation in sand driies sealed by upPer-dip pinch out orStraopaPhic onlaP can be formed; and d) large scale of anticline can be develoPed in front uplift, such as triangeare, draPe anticline, and faulted fold structures and so on are habitat of hydrocarbon.