摘要
为了阐明四川盆地川西—川中地区侏罗系中统沙溪庙组一段(以下简称沙一段)浅水三角洲沉积特征及其油气勘探意义,以岩心、测井及连片三维地震资料为基础,系统分析了该区沙一段浅水三角洲的沉积背景、沉积微相类型、砂体展布规律及地球物理响应特征,并建立了沉积模式。研究结果表明:①沙一段沉积期古地形平缓,水体浅且频繁升降,干湿交替气候条件下发育大型浅水三角洲,水下分流河道砂体累计厚度介于15~40 m,宽度介于300~8000 m,延伸距离最远达200 km;②水下分流河道砂体呈网状分布,包裹于分流间湾泥岩中,可形成大型岩性圈闭,占前缘沉积面积的50%以上,而逆粒序河口坝则仅零星发育且规模小(单层厚度不超过6 m);③地震响应表现为中—强振幅“顶谷底峰”亮点特征,顺河道为强振幅连续反射,横切河道向两侧振幅减弱,高分辨率三维地震资料对砂体精细刻画至关重要;④沙一段浅水三角洲前缘砂体物性较好(孔隙度介于7%~13%,渗透率介于0.01~1.00 mD),与下伏三叠系上统须家河组烃源岩构成高效源储组合,支撑了川中天府气田(天然气探明储量达1500×10^(8)m^(3))等规模气藏的发现。结论认为,浅水三角洲不仅是当前四川盆地陆相致密气增储主体,其“宽河道、厚砂体、优配置”的沉积模式,更为该盆地内须家河组、侏罗系中统凉高山组等同类储层的油气勘探提供了可复用的地质模型与技术范式。
To clarify the sedimentary characteristics and hydrocarbon exploration significance of shallow-water delta in the first member of Middle Jurassic Shaximiao Formation(hereinafter referred to as Sha-1 Member)in the western-central Sichuan Basin,the sedimentary setting,sedimentary microfacies types,sand-body distribution patterns,and geophysical response features of Sha-1 Member were analyzed systematically,and a sedimentary model was established,using the core,logging and contiguous 3D seismic data.Research results are shown as follows:(i)During the sedimentation period of Sha-1 Member,the paleotopography was gentle,with shallow water body that rose and fell frequently,a large shallow-water delta was developed under the alternating humid-arid climates,contributing the subaqueous distributary channel sand bodies with the cumulative thicknesses ranging 15-40 m,the widths of 300-8000 m,and the maximum extension up to 200 km.(ii)The subaqueous distributary channel sand bodies are distributed in a reticulate pattern,enclosed within interdistributary bay mudstones,possibly forming large-scale lithologic traps,and accounting for more than 50%of the front sedimentary area.In contrast,the reverse-graded river mouth bars are sporadically developed and small in scale(with individual layer thickness not exceeding 6 m).(iii)The seismic responses reveal the bright spot of“trough at the top and peak at the bottom”with medium to strong amplitude.Strong amplitude continuous reflection is observed along the channel,while the amplitude weakens to both sides of the channel in the transverse direction.High-resolution 3D seismic data are crucial for the fine characterization of sand bodies.(iv)The shallow-water delta front sand bodies of Sha-1 Membershow good physical properties(with the porosity of 7%-13%,and the permeability of 0.01-1.00 mD),and form an efficient source-reservoir assemblage with the underlying source rocks of the Upper Triassic Xujiahe Formation,supporting the discovery of large-scale gas reservoirs such as the Tianfu Gasfield in the central Sichuan Basin(with proven reserves of 1500×10^(8)m^(3)).In conclusion,the shallow-water delta is the main contributor to the current increase in continental tight gas reserves in the Sichuan Basin;besides,its sedimentary model featuring wide channel,thick sand body and optimal configuration provides a reusable geological model and technical paradigm for hydrocarbon exploration of similar reservoirs in the Xujiahe Formation and the Middle Jurassic Lianggaoshan Formation within the basin.
作者
吴长江
张晓丽
贾敏
杨棵
王自剑
李兰
WU Changjiang;ZHANG Xiaoli;JIA Min;YANG Ke;WANG Zijian;LI Lan(Exploration and Development Research Institute,PetroChina Southwest Oil&Gasfield Company,Chengdu,Sichuan 610041,China)
出处
《天然气勘探与开发》
2025年第4期15-26,共12页
Natural Gas Exploration and Development
基金
中国石油西南油气田公司科学研究与技术开发项目“四川盆地中生界陆相含油气系统及气藏分布规律研究”(编号:20230301-08)。
关键词
四川盆地
侏罗系中统沙溪庙组
浅水三角洲
水下分流河道
沉积模式
地震响应
岩性圈闭
致密气
Sichuan Basin
Middle Jurassic Shaximiao Formation
Shallow-water delta
Subaqueous distributary channel
Sedimentary model
Seismic response
Lithologic trap
Tight gas
