烃源岩对致密油分布的控制作用——以四川盆地大安寨为例

Controlling Effect of Source Rocks on the Occurrence of Tight Oil——Taking the Da'anzhai Reservoir of Sichuan Basin as an Example

为了研究烃源岩在致密油富集中的意义,本文以有机质含量相对较低、但油气产量较高的四川盆地大安寨为例,通过地球化学分析和理论计算等手段,探讨了烃源岩在致密油生成、排驱和运移等方面的作用。岩心系统热解分析表明,大安寨烃源岩主要集中在中部大一三亚段,有机质含量较高,而上下灰岩段中的泥岩夹层有机质含量则偏低。油岩对比证实,石油主要来自大一三亚段TOC>1%的暗色泥岩,说明石油生成后,经历了一定程度的运移和聚集过程,以垂向运移为主,运移方向既可以向上,也可以向下。大安寨工业油井均位于TOC>1.2%、生油强度大于10万t/km2范围内,主要油田则主要位于TOC>1.4%、生油强度大于20万t/km2范围内。生烃增压既是主要的排烃动力,也是油气充注的主要动力;要形成工业性油气聚集,烃源岩的局部富集非常关键,TOC>1%、连续厚度达到20m的烃源岩,可为大安寨致密油富集提供充足的油气来源。

In order to study the significance of source rocks on tight oil accumulation,the Da’anzhai interval was taken as an example,which is characterized by high oil production and low organic matters. By means of geochemical analysis and theory calculation,we discussed the effect of source rocks on oil generation,explosion and migration. Systemic Rock-Eval analysis showed that excellent source rocks occurred in the middle of the interval,i. e.,the Dayisan Subsection,and oil-rock correlation indicated that oil was mainly derived from the Dayisan dark shale with TOC value higher than 1. 0%,rather than the shale occurred in the Dayi Subsection or the Dasan Subsection. Thus,the oil had experienced a series of migration and accumulation processes,mainly in vertical,and the direction could be both upward and downward. Most of the industrial wells were located in the area where the source rock with TOC value was higher than 1. 2% and oil generation intensity higher than 10×104t/km2,and the discovered oilfields were distributed in the area where TOC value higher than 1. 4% and oil generation intensity higher than 20×104t/km2. The overpressure caused by hydrocarbon generation,is the major force that not only drove oil expulsing out of the source rocks,but also charged oil into the tight reservoirs. In order to form industrial oil accumulation,excellent source rocks enriched in local area is especially important. The continuous source rocks with TOC value higher than 1. 0% and thickness higher than 20 m can provide enough oil sources for the Da’anzhai tight oil reservoirs.