东海盆地X凹陷Y气田的天然气成因、成藏模式及勘探意义

本文旨在厘清东海盆地X凹陷Y气田天然气成因，建立成藏模式，以指导下步勘探部署。本文从天然气组分、烷烃气碳同位素、轻烃、凝析油生物标志化合物等分析入手，系统研究了油气成因类型及来源，并结合构造演化史、生烃史分析，建立了Y气田成藏模式，提出了大中型气田的勘探方向。主要认识如下:（1）天然气组分碳同位素、轻烃和埋藏史分析表明，Y气田天然气为凹中始新统平湖组烃源岩在龙井运动期（距今13 Ma）生成的高成熟煤型气；（2）凝析油姥鲛烷/植烷、规则甾烷等特征，反映了凹中区平湖组烃源岩发育于弱氧化?弱还原潮坪、潟湖沉积环境，生烃母质中存在一定数量的低等水生生物；（3）Y气田具有“凹中区平湖组烃源岩、花港组大型水道砂储集体、挤压构造作用”时空耦合的成藏模式，明确了凹中挤压背斜带是X凹陷大中型气田勘探的主攻方向。

The genesis,accumulation model and exploration significance of Y gas field in X Sag,East China Sea Basin

The purpose of this paper is to clarify the genesis of natural gas of Y gas field, and establish accumulation model to guide the next exploration deployment in X Sag, East China Sea Basin. Based on the analyses of natural gas composition, carbon isotope of alkane gas, light hydrocarbon and biomarker compound of condensate oil, this paper systematically studies the genetic types and sources of oil and gas, establishes the reservoir accumulation model of Y large and medium-sized gas field, and puts forward the exploration direction of large and medium-sized gas field. The analyses of carbon isotope, light hydrocarbon and burial history show that the natural gas in Y gas field is highly mature coal type gas generated by the source rocks of middle Eocene Pinghu formation in the sag during the Longjing movement period (13 Ma BP). The characteristics of pristane/phytane and regular sterane of condensate oil reflect that the source rocks of middle Eocene Pinghu formation in the central sag are developed in tidal flat and lagoon sedimentary environment with weak oxidation weak reduction, and there are a certain number of lower aquatic organisms in the hydrocarbon generating parent material. Y gas field has a spatiotemporal coupling reservoir accumulation model of “Pinghu formation source rock, Huagang formation large channel sand reservoir and Mid-Miocene compressional tectonism” in the central sag. It is clear that the compressional anticline belt in the central sag is the main exploration direction of large and medium-sized gas fields in X Sag.