不同构造背景下礁滩的发育特征和差异性

生物礁、颗粒滩或礁滩复合体是碳酸盐岩储层发育的重要物质基础,了解其演化过程和时空分布规律,对预测礁滩型储层具有重要意义。为此,通过对塔里木盆地、四川盆地的实例解剖,分析了稳定和活动构造背景下台缘礁滩与台内滩在发育位置、规模、形态以及时空分布等方面的异同。结论认为:在稳定构造背景下,台缘礁滩体生长主要受控于沉积作用和海平面变化,具有生命周期长、多期稳定发育,纵向厚度大、横向迁移明显的特点;而在构造活动期,板块内部隆坳格局的改变造成台缘带多次迁移,虽然台缘礁滩也是多期发育,但是继承性差且规模较小;此外,板内断裂活动通常会导致沿断层走向方向形成新的台地边缘建造,这类台缘礁滩与断裂活动密切相关,通常生命周期较短,以加积生长为主,厚度可以较大,但横向迁移特征不明显。而颗粒滩的形成,在构造稳定期主要与局部原始古地形高有关,具有单层厚度薄、横向相变快、数量多、分布面积广的特点;但在构造活动背景下,受区域构造古隆起的控制,在斜坡部位形成环状分布的高能滩,单层厚度大,横向连续性好,分布面积广。

Development characteristics and differences of reef shoal complexes under different tectonic settings

Bioherms, granular beaches and reef shoal complexes are the important material foundation for carbonate reservoir development. To understand their evolution and distribution is of great significance to carbonate reservoir prediction. Based on the case studies of Tarim and Sichuan basins, the similarities and differences were discussed between reef shoal complexes on platform margins and intraplatform beaches under both stable and active tectonic settings in respects of location, scale and morphology as well as temporal and spatial distributions. Under stable tectonic settings, the growth of reef shoal complexes is mainly controlled by sedimentation and sea level change and they are characterized by a long life cycle, stable development at multiple stages, a large vertical thickness, and apparent lateral migration. In contrast, under active tectonic settings, the changes of ancient uplift and depression framework result in the frequent migration of platform margins. Although shoal complexes are also developed at multiple stages, they are poor in inheritance and small in scale. In addition, intraplate fault activities may result in the formation of new platform margin complexes along the strike of faults. These reef shoal complexes are closely related with fault activities and featured by a short life cycle, predominance of aggradation, a relatively large thickness but insignificant lateral migration. Under stable tectonic settings, the formation of granular beaches is mainly related with regional palaeotopographic highs and they are characterized by small single layer thickness, rapid lateral change of facies, a large amount and a large distribution area. While under active tectonic settings, ring shaped high energy shoals are developed on slopes under the control of regional paleohighs and featured by a large single layer thickness, good lateral continuity and a large distribution area.