柴达木盆地巨型油气富集区的确定及勘探成效——改造型盆地原盆控源、改造控藏之范例

柴达木盆地位处全球新生代构造活动最为强烈的青藏高原北部,盆地的演化和改造明显受高原形成动力学环境的控制,属于"强改造型"盆地。根据盆地属性及其所处动力环境的个性,揭示了盆地油气赋存条件和成藏主控因素的特点。柴达木盆地前期30年油气勘探无重要突破的主要原因之一,是对盆地属性缺乏深刻认识。改造型盆地油气资源的贫富及分布,直接受原盆富烃坳（凹）陷以及其中的烃源岩在改造后的留存状况所控制,即"原盆控源"。对古近纪原盆恢复等综合研究揭示,现今的柴达木盆地西南部处于古近纪盆地腹部的富烃坳陷区,其中的烃源岩主体保存尚好;确定该区环英雄岭逾3×10⁴km²的地区为巨型油气富集区和重点石油勘探区。强改造作用使得柴达木盆地西部从古近纪较简单的富烃坳陷结构演变为现今由隆起、凹陷、断阶和斜坡等构造单元构成的复杂格局。此改造过程和结果直接控制着油气藏（油气田）的特征、分布、成藏模式和资源规模,简言之,改造控藏。盆地发生强烈改造的时间晚、地下深部的围压强等鲜明的个性改造特征,对油气的成生、运移、聚集和耗散而言,利大于弊。目前,在创新理论的指导下,油气勘探的成效显著,相继发现了5个不同类型的亿吨级大油田。改造型盆地油气富集区的确定构建了区内已发现和待发现油气藏之间的内在联系和预测依据,开拓了持续发现多个油气田的广阔勘探领域。

Determination of giant hydrocarbon enrichment area in Q aidam Basin and its exploration results: an example for source-controlling of original basin and reform-controlling reservoir in a reformed basin

The Qaidam Basin is located in the northern part of Qinghai-Tibet Plateau where the Cenozoic tectonic activity is most intense in the whole world. The evolution and reformation of the basin is obviously controlled by the dynamic environment formed by the plateau, and it is a "strongly reformed" basin. Based on the special attributes and dynamic environment of the basin, this study reveals the hydrocarbon occurrence conditions and main controlling factors of the basin. It is one of the main reasons for no important breakthroughs in oil and gas exploration of the Qaidam Basin in the early 30 years that the researchers have not gained a deep understanding of the basin attributes. The abundance and distribution of oil and gas resources in the reformed basin are directly controlled by the hydrocarbon-rich depression (or sag) and the retained source rocks after reformation in the original basin, namely "source-controlling of original basin". A comprehensive study on the restoration of Paleogene original basin reveals that the current southwestern part of Qaidam Basin was once located in the hydrocarbon-rich depression area in the hinterland of the Paleogene basin, and the main source rocks are well preserved; there is a giant hydrocarbon enrichment area of more than 3×10⁴km² around Yingxiongling area, i.e., a key oil exploration area. Due to the strong reformation, the Qaidam Basin has been evolved from a relatively simple hydrocarbon-rich depression structure in the Paleogene to a complex structure including such tectonic units as uplift, sag, fault terrace, and slope. The process and results of the reformation directly control the characteristics, distribution, accumulation pattern and resource scale of oil and gas reservoirs or fields, i.e., reform-controlling reservoir for short. The strong reformation of the basin occurred late and the confining pressure in the deep underground was strong. These distinctive reformation characteristics have more advantages than disadvantages for the generation, migration, accumulation and dissipation of oil and gas. Currently, under the guidance of innovative theories, remarkable results have been achieved in oil and gas exploration, and five types of 100-million-ton-level great oil fields have been discovered successively. The determination of the hydrocarbon enrichment areas in the reformed basin has established the intrinsic connection and prediction basis between the discovered and undiscovered oil and gas reservoirs in the study area, and has opened up a broad exploration field for the continuous discovery of multiple oil and gas fields.