渤南低凸起西端浅水三角洲沉积特征——以B地区新近系明化镇组下段为例

Sedimentary characteristics of shallow water deltas of western part of Bonan low uplift:a case study of Neogene lower Minghuazhen Formation in B area

根据钻井、测井、地震及薄片等分析化验数据,文中开展了渤南低凸起西端B地区新近系明化镇组下段浅水三角洲沉积特征研究。B地区砂体以浅水三角洲水上及水下分流河道为主,决口扇及天然堤仅局部发育,未发育河口坝。浅水三角洲的沉积类型为浅水曲流河三角洲,发育具有一定弯度的分流河道,砂体厚度在4~9 m,宽度在100~1000 m,向湖盆方向连续性好,延伸可达数十千米,分流河道不同部位可见直条、微弯曲、弯曲形态,局部分流河道分叉形成分支,数量多小于3支。明下段主力油组浅水三角洲沉积特征受基准面下降旋回控制,较缓的古地形、较浅的古水体环境以及中等偏弱的河控强度是该区具有一定弯度分流河道形成的基础。研究成果深化了该区浅水三角洲沉积特征认识,有助于指导油田的开发,也可为类似区块提供借鉴。

Based on drilling, logging, seismic dates and thin sections, this paper carried out a study on the sedimentary characteristics of the shallow water delta in the lower Minghuazhen Formation of the B area in the western part of Bonan loweruplift.The sand bodies in the B area are mainly composed of upperriver and subaqueous distributary channels, the sediment of crevasse fan and natural levee are only locally developed, and no debouch bar is developed. The sedimentary type of the shallow water delta belongs to meandering-river shallow water delta. The low-curvature winding distributary channel sand body is 4-9 m in thickness and 100-1000 m in width, and it has good continuity in the direction of the lake basin and can extend for tens of kilometers. It can be seen that the straight, slightly curved and curved river forms are developed at different parts of the channel, part of the winding distributary channel bifurcates to form branches,and the number of branches is less than 3 branches. As a whole, the main oil group in the lower Minghuazhen Formation is controlled by the base level descending cycle, the gentle paleo-topography, shallow paleowater environment and moderate to weak river control strength are the basis for the formation of low-curvature winding distributary channel in this area. The research results have deepened the understanding of the shallow water delta deposition in this area, which is helpful to guide the development of the oil field, and can also provide reference for similar areas.