湖盆萎缩期河湖交替沉积记录特点及沉积过程响应机制

Dynamic conditions of the shrinking period of the lacustrine basin dynamic has great differences with other basin evolution stages. Sedimentary deposits reflects the characteristics of rivers and lakes alternately. The fluvial deposition alternately is neither purely on the traditional understanding of the oxidizing environment of flooding plain on the water,nor the lacustrine basin environment with a stable water bodies.It reflects the unique characteristics of the lake is a part of the river and the river is a part of the lake. Dynamic conditions of the shrinking period of the lacustrine basin dynamic has great differences with other basin evolution stage , Sedimentary deposits reflects the characteristics of rivers and lakes alternate . In this study,we take Bodong depression lower Minghuazhen Formation deposition as an example. In order to find out the characteristics of rocks, sedimentary facies, sequence, ecology and facies evolution about this kind of deposit and confirm identification standard and evolution of style about the fluviolacustrine alternative deposition, we have combined core、logging and seismic and based on some methods of sedimentology, sedimentary geochemistry and seismic sedimentology. Based on lacustrine basin geodynamic characteristics in the shrinking period, we have identified the stage the main basin dynamic characteristic parameters.In addition, we have found out how different deposition control factors control the sedimentary response, identified dynamic geological environment and main control factors about the different sequence and facies structure and understood typical filling patterns in structural Lake shrinking period under different dynamic conditions by numerical sedimentary simulation experiment. So, We can deepen the understanding of continental lacustrine basin sedimentology and service mineral products exploration and development in the lacustrine basin shrinking period.

湖盆萎缩期盆地动力条件与其它演化阶段差异巨大，沉积体现出河湖交替的沉积特征。这种河湖沉积交替，既不是传统认识上纯粹的水上河泛氧化环境，也不是具有稳定水体的湖泊环境，而是体现出湖中有河、河中有湖的独特特点。本研究以渤东凹陷明下段沉积为例，岩心、测井和地震相结合，利用沉积学、沉积地球化学和地震沉积学方法，查明此类沉积的岩石、沉积相、层序、生态和相演化等特征，确定河湖交替沉积的识别标准和演化样式。基于湖盆萎缩期盆地球动力学特点，查清该阶段主要的盆地动力参数特征，通过数值沉积模拟实验，厘清不同沉积控制因素对其沉积响应的控制，查明不同层序和相结构的动力地质环境和主控因素，构造湖盆萎缩期不同动力条件下的典型充填样式，深化陆相湖盆沉积学认识，服务湖盆萎缩期矿产勘探开发。

河湖交互背是湖盆萎缩期或其它阶段河流水量周期性变化造成河缘周期性聚水的一种沉积背景。不同于滨浅湖湖水位周性变化形成岸线迁移的湖面扩大和收缩，而是由于河水涨落形成湖泊的形成、发展和衰亡。由于湖泊的存在进一步影响了河流的发育特征和整个沉积体系的沉积响应特征。总体上看河湖交互发育在潮湿沉积背景下，主要有两种类型，一种是湿地扇背景下DFS不同沉积段，特别是中下段具有较高地下水位的区域，另一种则是盆地中部的洪漫平原区。受河湖周期性变化影响，河湖交互沉积具有氧化和还原环交互，以还原环境为主的特点，总体上具有物源近成熟度低、以小型河道沉积为主砂层薄、河道交互少砂体连续性差等特征。基于现代沉积调查、沉积模拟实验和地下地质解剖，表明其发育有7种背景和模式，即扇(三角洲)湖共生、扇面末端扇模式、轴向河流与横向扇模式、河湖决口扇模式、伴湖档道和分支河道模式、网状分支河道模式和下切河道模式，这些模式代表了河湖交互的不同阶段，也可能在同一时期平面相互组合，主要取决于沉积水动力背景特征。基于河湖交互的发育特征和模式，形成了河湖交互砂体的地震刻画技术，即基于地震属性相的地震砂体识别和预测技术。该技术以地震属性模式的识别为基础，通过识别不同的地震属性并对其进行强化处理，奖其归为不同的成因过程，进而进行地质解释和砂体分布的预测。在渤东地区识别出3大类6种地震属性相模式，分别代表了富砂和贫砂的河湖交互背景，为砂体刻画提供了新的思路。基于砂体的展布，探讨了在河湖交互背景下岩性油气藏勘探主要基于模式选取刻砂体、断砂耦合画圈闭、深层连通找油源、多层叠覆评风险的评价思路。基于精细的地质解剖，识别了在河湖交互下的砂体内部结构样式，主要发育有7种储层内部结构样式，包括以大型河流为主到小型河流占优，从连片的叠覆砂体为特征到孤立的末稍河道砂体为特点，不同的储层结构形成不同的内部差异流动特征，从而形成了不同的剩余油分布格局。