多旋回盆地叠合-复合控藏在常规非常规天然气勘探中的实践

四川盆地是我国典型的多旋回盆地,更是最重要的天然气基地,发现了大量的常规、致密砂岩、页岩气田。具有海相、海陆过渡相、陆相垂向叠加与平面分区明显、纵向多期构造运动叠加改造的特点,形成了全盆地、全层系含气。本文以普光气田、涪陵页岩气田和中江致密砂岩气为实例,阐述了叠合-复合控藏的概念,即叠合盆地油气成藏和富集的各种要素均受相互关联的多种因素的控制,不同要素间既有时间上的累加和空间上的叠置,也有横向上地质体因某种原因而结合在一起,比如构造与岩性体、构造与地层等。叠合控制油气的形成与演化,复合控制油气的富集与定位,进一步论述明确多旋回盆地叠合-复合控藏研究内容对油气勘探研究与实践具有重要的指导意义。通过对四川盆地典型大型气田实例剖析,表明四川盆地大型气田均是受多旋回盆地叠合-复合控藏的结果,即叠合控制油气的形成与演化,复合控制油气的富集与定位。本文系统分析总结四川盆地大型气田油气形成、成藏与富集规律,结合四川盆地勘探开发现状,针对四川盆地多旋特征提出油气勘探三个方面的重点研究内容:(1)构造古地理研究,厘清构造格局、储层、烃源和圈闭空间的叠合、复合关系以及对油气形成的控制作用;(2)区域地质构造演化研究,明确不同期次构造叠合关系以及对成油、成气、油气富集的控制作用;(3)构造分级与控藏研究,精细构造分级明确不同级次构造对气水关系、富集、储层改造控制作用。

Superimposition and composition control on hydrocarbon reservoirs in multi-cycle basins: Concept and practice in conventional and unconventional natural gas explorations

The Sichuan basin is a typical multi-cycle sedimentary basin in China and an important natural gas base with a large number of conventional, tight-sandstone and shale gas fields. The whole-basin, trans-stratum gas-bearing reservoirs are formed by predominantly vertical superimposition of marine, marine to non-marine transitional and continental strata with horizontal tectonic subdivision, and multi-cycle tectonic superimposition and modification in the vertical direction. In this study, the Puguang gas field, Fuling shale gas field, and Zhongjiang tight-sandstone gas filed are taken as examples to demonstrate the concept of superimposition and composition control on oil/gas pool formation—i.e., in superimposed basins every controlling factor affecting oil and gas accumulation and enrichment is controlled by many interrelated elements. Such factors not only increase in number with time but also are superimposed in space; and by unknown mechanism geological unites can combine together, such as structural and lithological bodies, and structural and stratigraphic traps. In general, superimposition controls oil and gas formation and evolution while composition controls oil and gas accumulation and position, and this rule applies to all large gas fields in the Sichuan basin. Therefore, further understanding of the superimposition and composition control in multi-cycle basins is of great significance for guiding oil and gas exploration research and practice in the Sichuan basin. This article systematically analyzes and summarizes the rule of hydrocarbon formation, accumulation and enrichment in large gas fields in the Sichuan basin. And, based on the exploration and development status of the Sichuan basin and multi-cycle characteristics three key research areas are proposed: (1)Tectono-paleogeography research aiming to clarify the superimposition and composition relationships between tectonic pattern, reservoir, hydrocarbon-source and trap-space, and their control over pool formation; (2)Regional tectonic evolution research towards better understanding the multi-cycle tectonic superposition process and its control on oil and gas generation and enrichment; (3)Structural classification and reservoir controlling research towards fine structural classification and better understanding the multi-stage structural control on gas-water relationship, hydrocarbon enrichment and reservoir transformation.