海相浪控砂质临滨坝沉积构型差异性及沉积动力学机制研究

There are many types of nearshore sandbar in wave-dominated sandy shoreface, and the sedimentary architecture and formation process is controlled by many sedimentary factors, it is of great significance to study the difference of sedimentary architecture and the mechanism of sedimentary dynamics in nearshore sandbar, which can direct the fine characterization of such reservoirs in the middle and late stages of development and develop sedimentary theory. This project takes the modern sediments of Rongcheng Bay and Laizhou Bay in Shandong Peninsula as prototype model, sediment numerical simulation technology based on sediment hydrodynamics is used. Firstly, using satellite maps, experimental analysis and modern observation, the sedimentary architecture model of typical modern nearshore sandbar is established, deposition numerical simulation is carried out under the condition of modern sediment boundary parameters, and the result is compared with modern sedimentary models to verify the reliability of simulation; then a series of single factor simulation experiments are designed to simulate the sedimentation process of nearshore sandbar under different main controlling factors, the quantitative knowledge base of it is established under different sedimentary conditions, the formation mechanism of sedimentary architecture difference of nearshore sandbar is analyzed; finally, based on the characteristics of sedimentary simulated hydrodynamic distribution, the critical conditions for initial development, evolution and preservation of different types of wave-controlled sandbar are determined, the characteristics of sedimentary hydrodynamic variation under different main controlling factors is discussed, and the quantitative control of hydrodynamic variation on sedimentary architecture of nearshore sandbar is also studied, the sedimentary dynamic mechanism of wave-controlled nearshore sandbar is summarized.

海相浪控砂质滨岸体系中临滨坝类型多样，其沉积构型及形成过程受多种沉积因素控制，研究临滨坝沉积构型差异性及沉积动力学成因机制，对指导此类储层在开发中后期精细解剖、深化沉积学理论具有重要意义。本项目以山东半岛荣城湾、莱州湾现代临滨坝沉积为原型，采用基于泥沙水动力的沉积数值模拟技术，首先利用卫星地图、实验分析及现代观测，建立现代沉积区典型临滨坝沉积构型模型，以现代沉积边界参数为条件进行沉积数值模拟，并与现代沉积模型对比，检验模拟可靠性；然后设计多组单因素模拟实验，模拟不同主控因素下临滨坝沉积过程，建立不同沉积条件下浪控砂质临滨坝沉积定量知识库，分析临滨坝沉积构型差异性形成机理；最后，综合沉积模拟水动力分布特征，确定不同类型浪控砂质临滨坝的初始发育、演化及保存临界条件，探讨不同主控因素下沉积水动力变特征化及水动力变化对临滨坝沉积构型的定量控制，总结海相浪控砂质临滨坝沉积动力学成因机制。

针对海相浪控砂质临滨坝沉积构型特征分布复杂、形成与演化受多种因素控制等问题，本项目开展了临滨坝沉积构型差异性及沉积动力学成因机制研究。通过现代沉积与沉积数值模拟分析，进行了多因素对比模拟实验，取得了如下认识：典型临滨坝的形成及演化过程可分为锥形坝、弯月坝、单一复合坝、单一复合坝扩大生长、单一复合坝停止发育等5个时期，不同类型的坝体是不同演化阶段的产物；不同类型的坝体表现出不同的沉积构型叠置关系，锥形坝以小型锥状沙坝为特征，垂直于海岸方向呈正锥形分布，弯月坝是靠近锥尖部位的沉积物受冲刷形成，锥顶不断的向岸迁移，水体携带后期沉积物不断发生沉积，形成弯月状平滑顶部，复合坝由多个单期次弯月坝沉积改造形成，在平面上形成窄条带状的坝体，在复合坝形成之后继续发生沉积，复合坝的厚度及宽度增大，平面形态也由初期的窄条带状发育为宽条带状，当复合坝发育到一定规模，复合坝顶部出露水面，坝体与海岸线间围合形成典型的泻湖环境；临滨坝的形成受海岸线形态、海岸坡度、物源供给、波浪大小及方向等影响，不同坝体形态与上述因素存在较强关系；建立了临滨坝定量特征大数据库，分析了不同条件下形成的临滨坝定量关系，临滨坝厚度、宽度、列数受海岸坡度、波浪大小控制，临滨坝宽厚比总体呈正相关性，但相关性受多种因素控制；总结了典型临滨坝形成的水动力特征及沉积动力学成因机制，锥形坝形成于较平坦的海岸底形之上，形成受控于上冲流、裂流及局部平行岸线方向的小规模沿岸流，弯月坝形成于上冲流对坝体的侵蚀与沉积，复合坝主要受上冲流、底流活动的控制与改造，坝体附近水动力场大小及方向变化较快，临滨坝的形成受近岸上冲流、底流、沿岸流及裂流等复杂的水动力场的控制。