海陆过渡相三角洲沉积体系陆源有机质沉积特征及其影响因素的模拟实验研究

Experimental Simulation of Terrigenous Organic Matter Sedimentary Characteristics and Its Influencing Factors in Transitional Facies Delta Depositional System

【目的】海陆过渡相三角洲沉积体系由于油气成藏条件优越,广泛发育陆源海相烃源岩,陆源有机质是其主要的母质来源。为了探究海陆过渡相三角洲沉积体系中陆源有机质的沉积特征及其影响因素,开展了陆源有机质沉积模拟实验。【方法】通过碳硫分析仪检测总有机碳含量,结合3D激光扫描技术,实现了实验条件下陆源有机质搬运沉积过程的动态定量表征。【结果】(1)在三角洲平原,陆源有机质主要在河道漫溢处、废弃河道、砂坝背流面等部位局部富集,剖面上主要以透镜型、断续型、互层型分布;在三角洲前缘和前三角洲,有机质平面上呈席状展布,剖面上以厚度较大的条带型分布;(2)陆源有机质在缓坡三角洲体系搬运距离较远,随着三角洲沉积厚度逐渐增大,三角洲初始坡度对陆源有机质搬运距离的影响减小;(3)水动力强度和波浪是影响有机质搬运距离的重要因素,水动力越弱越有利于有机质的沉积,在三角洲平原低能环境中存在有机质局部富集区。波浪会阻止有机质向前搬运并在三角洲前缘形成多个砂坝,有机质沉积于坝间凹槽呈环带状;(4)在海陆过渡相三角洲沉积体系内,从三角洲平原到三角洲前缘—前三角洲区域的有机碳含量逐步升高,进入陆架区,随着搬运距离的继续增大,有机碳含量减少。【结论】通过深入研究陆源有机质的富集部位和影响因素,建立了水槽实验模式下陆源有机质沉积模式,这对海陆过渡相三角洲沉积体系的油气探勘开发提供了重要的依据。

[Objective]Owing to favorable hydrocarbon accumulation conditions,terrigenous marine source rocks are widely developed in the transitional facies delta sedimentary system,and terrigenous organic matter is the main source material.To investigate the sedimentary characteristics and influencing factors of terrigenous organic matter in the transitional deltaic sedimentary system,a simulation experiment of terrigenous organic matter deposition was con-ducted.[Methods]The dynamic quantitative characterization of terrigenous organic matter transport and deposition process under experimental conditions was realized using a carbon and sulfur analyzer to detect total organic carbon content with three-dimensional(3D)laser scanning technology[.Results](1)In the delta plain,terrigenous organic matter mainly accumulates locally in the overflow areas of river channels,abandoned river channels,and the flow surface behind sandbar.In the profile,the distribution of terrigenous organic matter is mainly lens,discontinuous,and interbedded type.In the delta front and fore delta,the organic matter is distributed in a sheet on the plane,and it is distributed in strips with large thickness in the profile.(2)The transport distance of terrigenous organic matter in the gentle slope delta system is relatively long.With the gradual increase of the sediment thickness of the delta,the influence of the initial slope of the delta on the transport distance of terrigenous organic matter has decreased.(3)Hydrodynamic strength and waves are important factors affecting the transport distance of organic matter.The weaker the hydrodynamic force,the more favorable the deposition of organic matter is.Waves prevent organic matter from moving forward and form multiple sand bars in the delta front.Organic matter is deposited in annular bands in the grooves between the bars.(4)In the transitional facies delta depositional system,the organic carbon content grad-ually increases from the delta plain to the delta front-pre-delta area and then decreases as the transport distance con-tinues to increase.[Conclusion]The enrichment sites and influencing factors of terrigenous organic matter has been deeply established,and the sedimentary model of terrigenous organic matter in the flume experiment model provides an important reference for oil and gas exploration and development in the transitional facies delta depositional system.