浅水湖泊河口坝型三角洲前缘沉积特征与模式——以文安斜坡西5井区沙河街组三段为例

Sedimentary characteristics and pattern of mouth-bar delta front in the shallow lacustrine:A case of the 3rd member of Shahejie formation in well X5 area in Wen'an slope of Baxian

受控于不同的水流特征、物源供给和地形坡度,浅水三角洲河口坝发育程度和特征具有较大争议。以河北霸县凹陷文安斜坡西5井区沙河街组三段为例,采用井震心综合研究方法,以岩心相、测井相、地震相为标志,识别研究区浅水三角洲沉积微相类型;结合相对海平面升降变化,沉积微相、亚相的展布特征和演化规律,以及对古地貌和古水流分析其沉积控制因素和沉积模式,解释浅水河口坝型三角洲发育规律。结果表明:西5井区位于三角洲前缘末端,水动力较弱,砂泥比较低,河道相对稳定,属于缓坡河口坝型浅水三角洲,且地形坡度较缓、物源供给适中或不充分、水动力条件较弱、湖平面上升等因素控制浅水三角洲河口坝的发育程度。该结果对于厘清浅水三角洲河口坝形成的因素,指导该类型三角洲油气勘探开发具有重要的意义。

Shallow water delta is a hot research subject in domestic sedimentology.However,the development and characteristics of the shallow water delta estuary are still controversial due to the differences in water flow characteristics,which include material supply and terrain slope.In this paper,taking the3rd member of Shahejie formation in the well X5area of Wen'an slope in Hebei province as an example,the sedimentary microfacies of the shallowwater delta were identified and the deposition skeletons were established and compared by means of comprehensive research on core,seismic and logging and taking the core facies,logging facies and seismic facies as marks.According to the distribution and evolution of the relative sea level change,sedimentary microfacies,facies and the analysis of the sedimentary control factors and sedimentary patterns of the paleogeomorphology and paleocurrent,the regularity of the mouth-bar delta development was explained.The study indicates that the well X5area is located at the end of the delta front,with weak hydrodynamic force,low sandmud ratio and relatively stable channel.This area,which belongs to gentle slope delta shallow water delta,mainly develops underwater distributary channel,mouth-bar,underwater diversion bay and other sedimentary microfaciesand the mouth-bar develops especially sufficiently.Besides it is superimposed with the underwater distributary channel sandstone.It is concluded that the Wen'an slope is characterized by gentle terrain and the stable supply of the provenance.In addition,as the result of the lakelevel rise and the accommodation space increasing during the Oligocene Es3,and the tributary buoyancy is the main mechanism of the river mouth process of the delta,the mouth-bar develops well.At last,the pattern of the shallow water delta was analyzed and established,which indicates that the development degree of the mouth-bar of the shallow water delta is controlled by the factors such as gentle terrain slope,moderate or insufficient supply of material,weak hydrodynamic condition and rising lake level.