辽河盆地东部凹陷北段复式断陷层序地层与油气

辽河盆地为中国东部大陆裂谷渤海湾裂谷系的北延部分，是中、新生代发育起来的断陷盆地。 东部凹陷北段是辽河盆地的一部分，也有人将其称为裂谷段，具典型的裂谷盆地的发育特征。经过多条横切构造走向的剖面研究，证实了东部凹陷北段为复式断陷，断陷的走向与盆地走向基本平行。所谓的复式断陷为两个或两个以上的半地堑以某种方式组合而成，在一定时期内，相邻的次一级半地堑各有独立的沉积物供给系统，但当各个次级半地堑充填满以后，相邻的次级地堑具有统一的物源供给系统和水系联通特征，以较大的整体断陷形式继续发育。在控盆断裂一侧的断陷内层序发育较全，而斜坡及边缘地带层序发育不完全，通常缺失低水位体系域或水退体系域。复式断陷不同断陷内的层序，主要受旋回内不同级别幕式构造运动和气候周期性变化的控制，两者的共同作用影响着湖平面的升降和可容空间的变化。由于相邻断陷对物源侵入的阻挡作用，在一定的时期内，各断陷发育独立沉积体系和构造部位的差异，导致了层序地层格架内生储盖层及其组合的发育差异。厚度最大的密集段发育在TST与HST之间，是区域性的生油岩； LST，TST底部，HST顶部、RST通常构成有利储层；密集段也通常成为较好的盖层。在上述因素的作用下，东部凹陷北段复式断陷湖盆中的油气，主要富集在有利构造岩相带的水退体系域、水进体系域和低水位体系域中。层序地层格架内油气藏类型及发育规模存在一定的规律：在缓坡一侧的断陷内，易形成地层超覆型油气藏、地层不整合遮挡油气藏；在陡坡一侧的断陷内，易形成透镜状油气藏、背斜油气藏，起决定作用的是生储盖层的发育状况及其与有利的构造圈闭条件的配置关系。

SEQUENCE STRATIGRAPHY AND OIL AND GAS IN THE COMPLEX FAULT DEPRESSION OF THE NORTHERN SECTION OF EAST DEPRESSION IN THE LIAOHE BASIN

 The Liaohe basin is situated at the northern section of the Baohai Bay rift system. It is a fault depression developed in the Mesozoic and Cenozoic. The northern sect of the east sag in the Basin, also called rift section, was developed with typical characteristics of rift basins. It is a complex fault depression basin parallel to the strike of the Liaohe basin, which can be demonstrated by the research of the interpretation section of traverse in the northern sect of the east sag, The complex fault depression is a combination of two or more half grabens, with each of these grabens having its own independent sediment-supplying systems. Once these half-grabens were filled, there would have a uniform sediment-supplying system and drainage system and would continue to develop as a larger entity of the faulting depression. The fault side of the half-graben is usually developed with complete depositional sequences while the slope side of the half graben is usually developed with incomplete sequences with absence of lowstand systems tract or regressive systems tract. Depositional sequences in different depressions of the complex faulting lacustrine basin were mainly controlled by both the episodic tectonic movements with different orders and the periodical palaeoclimatic variations. Both of these parameters controlled fluctuation of lake level and also variations in accommodation spaces. Because the adjacent faulting depressions have different sedimentary sources, in a certain period, each of these depressions has its own independent sedimentary systems, which resulted in differences in the development of the combination of source-reservoir-capping rocks. The condensed section with maximal thickness were developed at a place between TST and HST, constituting regional source rocks whereas the favorable reservoirs were developed at the bottom of LST and TST and the top of HST and RST. The condensed section can also serve as cap beds of the reservoirs in the TST and LST. In consideration of above analyses, in the complex fault lacustrine basin at the northern sect of east sag, oil and gas were mainly enriched in RST, TST and LST, where favorable tectonic lithofacies associations were developed. It is suggested that there are some regularities for types and scales of the reservoirs in the sequence stratigraphic framework. The slope side of the half-graben is usually developed with onlap and unconformity shade oil reservoir types, while the fault side of the half-graben is usually developed with lenticular and anticline oil reservoir types; The most important controlling factors are the development of source-reservoir-cap combinations and its relationship with favorable tectonic traps.