大角度波浪控制下的浪成砂坝新模式

A novel sedimentary pattern of wave-induced sandbars under high-angle wave incidence

浪成砂坝为波浪改造后二次沉积产物,传统沉积模式认为其主要呈平行岸线条带状展布,但忽视了波浪入射角与岸线夹角的差异会导致沉积模式的巨大差异。结合珠江口盆地惠州凹陷以及青海湖现代浪成砂坝沉积特征,研究总结了大角度波浪控制下的浪成砂坝差异沉积模式。结果表明:①受限于东沙隆起,惠州凹陷南缘局部区域存在显著的“峡谷效应”,波浪呈大角度入射,且由于沉积期发育位置不同导致的水动力环境不同,2个邻近油田砂体在沉积过程中受波浪改造后,形态和规模存在巨大差异。②引入海岸动力学沿岸输沙机理,结合野外地质考察成果,将浪成砂坝分为全封闭斜交岸线型、平行岸线型和半开放斜交岸线型3类,并提出了一种大角度波浪控制下的浪成砂坝新模式。③实钻结果证实,该模式下迎风翼和背风翼的砂坝形态、规模及叠置样式差异巨大,且砂体之间易形成“连而不畅”的岩性油气藏。新模式对指导浪成砂坝型储层的勘探与开发具有重要的理论与现实意义。

Wave-induced sandbars,wave-reworked deposits,are considered to resemble bands parallel to shorelines as reflected by the traditional depositional model,which,however,ignore the fact that varying angles between wave incidence direction and shoreline orientation can lead to significant differences in sedimentary patterns.In combination with the sedimentary characteristics of modern wave-induced sandbars in both the Huizhou Sag,Pearl River Mouth Basin(PRMB),and Qinghai Lake,we investigate and summarize differential sedimentary patterns of wave-induced sandbars under high-angle wave incidence.Key findings are as follows:(1)Constrained by the Dongsha Uplift,local areas on the southern margin of the Huizhou Sag manifest significant“canyon effect”,leading to high-angle wave incidence.Moreover,due to the different hydrodynamic environments at varying occurrence positions during deposition,the sand bodies of two neighboring oilfields in the Huizhou Sag exhibit significantly distinct morphologies and scales post-wave reworking;(2)Based on the dynamic sediment transport mechanism for shorelines,along with field geological survey results,wave-induced sandbars are categorized into three types:the totally closed shore-oblique type,the shore-parallel type,and the semi-open shore-oblique type.Moreover,a novel sedimentary pattern of wave-induced sandbars under high-angle wave incidence is developed;(3)Drilling results corroborate that under the novel sedimentary pattern,wave-induced sandbars on windward and leeward flanks differ enormously in morphology,scale,and superimposed style.Furthermore,lithologic hydrocarbon reservoirs with poor connectivity are prone to form between the sand bodies.The novel sedimentary pattern holds critical theoretical and practical significance for guiding the exploration and exploitation of reservoirs of wave-induced sandbars.