改造型盆地油气赋存-成藏理论体系纲要

中国沉积盆地的鲜明个性特征之一是后期改造强烈而普遍。此特征深刻地影响着油气的赋存条件和成藏效应,明显增加了地质研究和油气勘探的难度。改造型盆地和盆地复杂改造地区已成为中国油气勘探和资源接替的重要领域。盆地后期改造的主要形式可分为隆升-剥蚀、沉降-深埋、热力作用、流体活动和构造变形五种类型。在自然界,多种地质作用同时参与的复合式改造更为普遍。改造型盆地特征复杂多样,油气赋存和成藏过程集多类含油气盆地中诸多油气藏之众合。本文将改造型盆地油气赋存-成藏的核心理论纲要式归纳为:原盆控源、过程控储、改造控藏、多源成藏、动态聚散、晚期定位。原盆控源,即改造型盆地的烃源岩是在改造前原盆富烃凹陷中所形成,改造后留存的烃源岩规模及特征决定盆地油气的贫富和分布。各类储层的形成和保存总体受岩石原生物质沉积-埋藏成岩和次生改造重塑两大阶段全过程的控制,称之为过程控储。盆地或地区后期改造过程及结果的个性特征直接控制着该地区油气的赋存、成藏-定位和分布特点,即改造控藏。后期多种形式的改造可引发多源油气富集成藏,既含来自不同深度、不同成熟度烃源岩的油气同储成藏,又有源自不同类型、不同世代烃源岩的油气混聚成藏,还包括烃类与各种非烃类气体同储或同盆共存成藏。盆地经受多期次构造变动和改造必然导致油气发生多次动态聚散和晚期成藏-定位。将晚期成藏与定位连在一起就较全面地概括和体现了不同时代盆地大多油气藏形成的要点和勘探界关注的重点。

Hydrocarbon occurrence and accumulation processes in reformed basins—theories outline

One of the distinguishing features of sedimentary basins in China is widespread, strong late-stage reformation. Late-stage basin reformation has a profound impact on the hydrocarbon occurrence conditions and accumulation processes, and poses significant challenges to geological research and oil and gas exploration. Reformed basins and the affected areas have become important targets for petroleum exploration and resource replacement in China. The five main types of late-stage reformation are uplift-denudation, subsidence-deep burial, thermal action, fluid activity, and tectonic deformation. In nature, complex reformation involving concurrent geological processes is more common. Reformed basins are structurally diverse, where petroleum occurrence and accumulation involve a combination of many reservoirs types. In this paper, the core theories of hydrocarbon occurrence and accumulation in reformed basins are outlined, which can be summarized into the ideas of ‘source control by prototype basin, reservoir control by diagenetic process, accumulation control by reformation, multi-source accumulation, dynamic accumulation-dispersion, and late positioning’. ‘Source control by prototype basin’ means the source rock of a reformed basin is formed in the hydrocarbon-rich sag of the prototype basin prior to reformation, and its current scale and property determines the hydrocarbon richness and hydrocarbon distribution in the basin. Two major diagenetic processes—original material deposition-burial and secondary reformation-remodeling—control the formation and preservation of various types of reservoirs—so is called ‘reservoir control by diagenetic process’. And ‘accumulation control by reformation’ refers to the regional late-reformation features and outcomes have direct control on the hydrocarbon occurrence, accumulation-positioning and distribution in the region. Multiple late-reformations can lead to multi-source reservoir developments, such as co-reservation and accumulation of hydrocarbons from source rocks with variable depth and maturity, mixed hydrocarbons from source rocks of different types and generations, as well as co-storage/co-existence of hydrocarbon and various non-hydrocarbon gases in the same basin. The basin has undergone multi-stage tectonic evolution and reformation, which inevitably lead to hydrocarbons multi-stage dynamic accumulation-dispersion and late-stage accumulation-positioning. Understanding the late-stage accumulation and positioning can help to understand the formation mechanisms of most hydrocarbon reservoirs of different eras.