陆相含油气盆地沉积体系再思考:来自分支河流体系的启示

Rethinking on the sedimentary system of terrestrial petroliferous basins: insights from distributive fluvial system

通过分析分支河流体系的基本特征,对分支河流体系在陆相含油气沉积盆地沉积体系研究和油气勘探中的意义进行分析和讨论。分支河流体系是指河流从某一顶点开始进入盆地并呈放射状展布的沉积体系,包括最大规模的巨型扇、中等规模的河流扇以及小规模的冲积扇。分支河流体系广泛发育在拉张、挤压、走滑和克拉通盆地中,占据了沉积盆地大部分地区;河道呈分支状分布,但不一定同时都在活动;河道规模向下游逐渐减小,泛滥平原和河道所占面积之比不断增加,沉积物粒度逐渐变细。分支河流体系的沉积模式与冲积扇模式外形相似,但内容相差很大。河流流域盆地梯度和流域面积与分支河流体系的表面坡降和面积具有正相关性。分支河流体系是随着现代地球信息技术发展而提出的,也是冲积扇沉积学、河流沉积学和陆相沉积体系研究不断深入的结果,是陆相盆地沉积学与现代计算机和地理信息技术融合发展的结果。分支河流体系的研究促进了扇状沉积体系分类描述的系统化,促进了沉积微相和沉积模式的多样化,促进了沉积过程响应解释的精细化,促进了源汇体系分析的定量化。分支河流体系启发了对陆相盆地沉积体系展布模式、陆相沉积体系中河流沉积作用、陆相盆地岩相古地理格局以及陆相盆地油气勘探潜力的再思考。研究分支河流体系对完善中国陆相沉积储层地质理论体系具有重要意义。

In this paper, the fundamental characteristics of the distributive fluvial system(DFS) are briefly described, and the significance of DFS research in the sedimentology and oil and gas exploration within terrestrial petroliferous basins is analyzed and discussed. Rivers in the DFS enter the basin from a vertex and radiate into the sedimentary system. DFS includes the largest mega-fan, medium-sized fluvial fan and the smallest alluvial fan. DFSs occupy most of the sedimentary basins including the rift basins, the compressional basins, the strike-slip basins and the craton basins. The rivers on DFS are distributive, but not always active simultaneously. Downstream in the DFS, the scale of channels decreases and the grain size becomes finer, whereas the ratio of flood plains to channel deposits increases. The sedimentary model of the DFS share the similar shape with the alluvial fan, but their nature is signigicantly different. The slope and area of DFS is positively related to the slope and area of the draining basin. The concept of DFS is the product of the integration of terrestrial basin sedimentology(e.g., research in alluvial fan sedimentology, fluvial sedimentology, and terrigenous sedimentary systems) with modern computer and geo-information technology. DFS research can promote systematization of classification description of fan-shaped sedimentary systems, diversification of sedimentary microfacies, development of sedimentary model, refinement of interpretation of sedimentary process response, and quantification of source-sink system analysis. China’s oil and gas resources are mainly terrigenous in origin. It is therefore of great significance to study DFS for perfecting the theoretical framework of terrigenous sedimentology and reservoir geology in China. The study of DFS enlightens us to rethink the distribution pattern of sedimentary systems, the fluvial depositional system, the lithofacies paleo-geographic pattern, and the potential of oil and gas exploration in terrestrial basins.