物源—地貌双控背景下海底扇沉积储层特征及勘探意义：以琼东南盆地梅山组为例

琼东南盆地中新统梅山组海底扇是南海北部天然气勘探的重要目标, 对其沉积机理、储层主控因素等进行深入研究对该区天然气增储上产有重要意义。根据海平面变化、海底地形地貌、同生断裂组合等因素, 本文将琼东南盆地海底扇分为陆棚扇、斜坡扇和盆底扇3大类。根据大量的钻井岩心及分析测试资料, 对该区海底扇储层进行了系统分析。研究表明, 不同物源以及不同地貌单元海底扇储层物性差异较大, 其中来自西部越东物源和西北部宁远河物源的盆底扇储层明显好于北部陵水河和万泉河物源的陆棚扇和斜坡扇。单一海底扇储层受到物源、海平面变化、扇体类型及内部构成以及底流改造等因素控制, 其中海底扇类型及其内部组成、底流改造等是影响和控制深水沉积体储层品质的主要因素。相比而言, 低位时期的缓坡断阶盆底扇、开阔洼地盆底扇和峡谷切割盆底扇是好-优质储层较为发育的深水沉积体, 是重要勘探目标; 而陡坡根部盆底扇和缓坡末级断阶盆底扇由于储层物性较差或储层不发育, 勘探风险较大。因此, 基于物源体系及地貌单元的海底扇储层研究成果可广泛应用于深水海底扇储层预测。

Sedimentary reservoir characteristics and exploration significance of submarine fan under the dual control of provenance and geomorphology: Taking the Meishan Formation in Qiongdongnan Basin as an example

The submarine fan of the Miocene Meishan Formation in the Qiongdongnan Basin is an important target for natural gas exploration in the northern South China Sea. Its sedimentary mechanism and main reservoir controlling factors directly influence the natural gas exploration and production in this area. According to sea level change, seabed topography and geomorphology, syngenetic fault combination etc., the submarine fan of Qiongdongnan Basin has been divided into three categories: shelf fan, slope fan and basin floor fan. Based on a large amount of measured data such as core and sidewall coring, this paper systematically analyzes the submarine fan reservoir revealed by drilling in this area. The study shows that the physical properties of the Meishan Formation submarine fan reservoir in Qiongdongnan Basin are not only affected by the buried depth, but also affected by the provenance and geomorphic units. Specifically, the basin floor fan reservoir from the western East Vietnam provenance and the northwestern Ningyuan River provenance are significantly better than the shelf fan and slope fan reservoir from the northern Lingshui River and Wanquan River provenance. The single submarine fan reservoir is controlled by such factors as provenance, sea level change, the type of fan body and internal composition as well as underflow modification. Among them, the type of submarine fan and its internal composition as well as underflow modification are main factors that affect and control the quality of turbidite reservoir. The gentle slope fault-terrace basin floor fan at the lowstand stage, basin floor fan in the open depression and canyon-cut basin floor fan are important exploration targets for their good-to-high quality reservoir. By contrast, the basin floor fan of steep slope root and gentle slope last-stage fault-terrace basin floor fan possess high exploration risks due to poor reservoir physical properties or undeveloped reservoir. Consequently, the research results of submarine fan reservoir based on provenance system and geomorphic units can be widely applied to the prediction of deep-water submarine fan reservoir.