大型斜坡区冲积-河流体系沉积特征与岩性油气藏形成条件——以准噶尔盆地春光区块沙湾组为例

准噶尔盆地春光区块新近系沙湾组有大型缓斜坡沉积背景，具有良好勘探前景。以岩心、钻井、测井及地震资料为基础，开展沉积层序及油气藏分析，明确了沙湾组一段沉积特征：基准面上升早期，辫状河砂体连片发育，其侧翼方向与冲积扇切割接触；上升晚期泛滥平原分隔冲积扇及曲流河体系；下降旋回冲积扇与辫状河重新大面积发育，垂向上表现出退积、洪泛泥岩及进积的旋回特征。进一步总结得到大型斜坡区冲积-河流体系相关的岩性油气藏发育条件：①基准面旋回变化造成沉积分异是岩性圈闭发育的物质基础：上升早期形成规模型冲积扇辫流砂坝岩性圈闭，上升晚期形成曲流砂坝岩性圈闭；②基准面上升晚期洪泛 泥岩层是岩性油气藏发育的顶板条件；③不整合面及其相关渗透层是辫流砂坝岩性油气藏形成的疏导条件，断裂与渗透性辫状河砂体合理配置是曲流砂坝岩性油气藏形成的疏导条件。在基准面上升旋回中，冲积扇辫流砂坝及曲流砂坝岩性圈闭与顶板和疏导条件合理匹配，具有较大的勘探前景。

Sedimentary characteristics of alluvial-fluvial systems and forming conditions of lithologic reservoirs in the large slope area: a case study of Neogene Shawan Formation in Chunguang block,Junggar Basin

A large scale of gentle slope sedimentary background indicating a good exploration prospect is developed in Neogene Shawan Formation, Chunguang block Junggar Basin. On the basis of core, drilling, well-logging and seismic data, sedimentary sequence and hydrocarbon reservoir are analyzed in this study. The sedimentary characteristics in the 1st Member of Shawan Formation are defined as follows: in the early stage of base level rise, the sand body in the braided river is developed contiguously with its flank cutting the alluvial fan; in the late stage of rise, the flood plain separates the alluvial fans and meandering stream systems. A large area of alluvial fans and braided rivers start to develop again in the falling cycle, presenting a vertical cycle characteristic of retrogradation, flooding mudstone and proradation. This paper summarizes the requirements for the development of lithologic hydrocarbon reservoirs related to alluvial fan-river sedimentary system in large slope area: (1) The sedimentary differentiation caused by base level cycle provides a material base for the development of lithologic trap: large-scale alluvial fan-braided river sandbank lithologic traps are developed in the early stage of base level rise, and meander sandbank traps are developed in the later stage; (2) Flooding mudstone in the later stage of base level rise is the roof condition for the development of lithologic reservoirs; (3) Unconformity surface and its related permeable zone provide the drainage conditions for braided sandbank lithologic reservoirs, and the reasonable disposition of faults and permeable sand body of braided rivers provide the drainage conditions for the formation of meander sandbank lithologic reservoirs. In the ascending cycle of base level, alluvial fan-braided river sandbank and meander sandbank are reasonably matched with the roof condition and channel condition, indicating a favorable exploration prospect.