再论陆相三级层序内四分方案及其在油气勘探中的应用

结合在陆相盆地中的实例研究，将一个发育完整的陆相三级层序细分为4个体系域：低水位体系域（LST）、水进体系域（TST）、高水位体系域（HST）和水退体系域（RST），称为I型层序。或者一个层序可以不发育低水位体系域，而由水进体系域、高水位体系域和水退体系域组成，称为II型层序。低水位体系域发生在湖平面（基准面）快速下降时期;水进体系域出现在首次湖泛面到最大湖泛面之间;高水位体系域形成在高水位时期的湖平面相对静止期;水退体系域形成在湖平面缓慢下降期，在沉积物供给速率大于可容空间增加速率时形成。一般低水位体系域发育小型进积式准层序组，纵向沉积环境变浅，在盆地边缘形成河流下切作用；水进体系域发育退积式准层序组，沉积环境自下而上明显变深；高水位体系域发育加积型准层序组，纵向沉积环境变化不大，且多为静水沉积；水退体系域发育大型进积式准层序组，沉积环境自下而上明显变浅，沉积体系向盆地中心推进。结合对松辽盆地的实例研究，分别阐述了断陷盆地和坳陷盆地中各不同体系域的油气藏分布规律：低水位体系域主要在断陷盆地的陡坡侧和坳陷盆地的深水区发育透镜状岩性油气藏；水进体系域主要在断陷盆地的陡坡带发育上倾尖灭型岩性油气藏，在缓坡带和坳陷盆地的斜坡带发育地层超覆油气藏；高水位体系域主要以深水区的透镜状岩性油气藏为主；水退体系域在断陷盆地中主要发育地层不整合遮挡油气藏，在坳陷盆地中主要发育断块油气藏以及断层遮挡油气藏。从而,以理论与实践相结合的方式，阐明了陆相层序四分体系域的实用性。

Re-Discussion on the Four Division Scheme About Continental Sequence Stratigraphy and Its Application on Oil and Gas Exploration

Utilizing the practical study on the continental basins,the authors divide the whole third-order sequence into four systems tracts, which are lowstand systems tract (LST), transgressive systems tract (TST), highstand systems tract (HST) and regressive systems tract (RST),named sequence type I. If LST is undeveloped in a third order sequence, it forms the assemblages of TST, HST and RST，named sequence type II. LST occurred in the rapid declining period of lake level (base level). TST appeared with first lake flooding surface and maximum lake flooding surface. HST formed in the relative static high lake level period. RST formed in the gradual lake-level fall stage, and the supplying rate of sediments was more than the increasing rate of accommodation space at that time. Generally, LST consists of small scale progradational parasequence sets, vertically, the sedimentary environment is shallower, and river downcutting forms in the basin margin. TST consists of retrogradational parasequence sets, and the sedimentary environment becomes deeper from bottom to up. HST consists of aggradational parasequence sets, and the sedimentary environment changes little or is in standing water. RST consists of large scale progradational parasequence sets, and the sedimentary environment becomes shallower from bottom to up. Finally, the practical study on Songliao basin has been introduced to respectively expound the distribution regularities of oil and gas reservoirs in different system tracts in depression basin and fault basin. LST develops mainly lens-shaped lithologic reservoirs in the steep slope side of fault basin and deep-water area of depression basin. TST forms mainly updip thin away type lithologic oil & gas reservoirs in steep slope belt of fault basin, and forms stratigraphic overlap lithologic oil & gas reservoirs in the gentle slope belt of fault basin and slope zone of depression basin. HST mainly consists of lens-shaped lithologic reservoirs in deep-water area. RST develops mainly stratigraphic unconformity screened oil and gas reservoirs in fault basin, and developes fault block reservoirs and fault screened oil & gas reservoirs in depression basin.Thus, in the combination of theory and the practice, the practicality of the four division about continental sequence stratigraphy has been illustrated.