致密油源储特征与聚集机理——以准噶尔盆地吉木萨尔凹陷二叠系芦草沟组为例

Geological characteristics of source rock and reservoir of tight oil and its accumulation mechanism: A case study of Permian Lucaogou Formation in Jimusar sag, Junggar Basin

基于岩心观察、岩石样品薄片鉴定和X射线衍射矿物分析、烃源岩样品有机碳含量测定、岩石热解等方面的研究及储集岩高压压汞和核磁共振等分析,结合其埋藏及生烃史,分析准噶尔盆地吉木萨尔凹陷中二叠统芦草沟组烃源岩特征及储集岩特征,探究其源储组合及致密油聚集机理。芦草沟组烃源岩有机质类型总体上为Ⅰ型和Ⅱ型,TOC值平均为4.6%,整体上为优质烃源岩,处于低成熟—成熟阶段。烃源岩可划分为页岩、泥岩和粉砂质泥岩3类。芦草沟组储集岩整体上具有低孔低渗特征,高压压汞与核磁共振实验表明：纳米级孔喉（孔喉半径主体为50-500 nm）是储集空间的主体。储集岩可划分为泥质粉（细）砂岩、白云质粉（细）砂岩和砂屑白云岩3类。芦草沟组具有纵向上＂源储共生＂、横向上连续分布的源储组合关系,且烃源岩持续生烃。综合分析认为：自晚侏罗世至今,芦草沟组烃源岩大规模持续生烃增压为致密油聚集提供持续动力和物质供应,保障了石油在致密储集层中持续有效地充注聚集,形成大规模致密油资源。

The source rocks and reservoirs in the Middle Permian Lucaogou Formation of Jimusar sag, Junggar Basin, NW China and its source-reservoir assemblages were studied to reveal accumulation mechanism of the tight oil, on the basis of core observation, thin slice identification, X-ray diffraction analysis, TOC test and rock pyrolysis test of source rock samples, and mercury injection and nuclear magnetic resonance of reservoir samples, combined with burial history and hydrocarbon-generating history of source rocks. It is concluded that the Lucaogou Formation source rocks mainly have typeⅠandⅡorganic matter, with an average TOC of 4.6%, indicating they are high-quality source rocks in low mature-mature stage; and they can be divided into three types, shale, mudstone and silty mudstone. The reservoir rock in Lucaogou Formation features low porosity and low permeability; mercury injection and NMR（nuclear magnetic resonance） tests show that nano-scale pores and throats（with radius of 50-500 nm） constitute the main reservoir space, and the reservoirs can be classified into three types, muddy siltstone, dolomitic siltstone, and dolarenite according to lithology. The source rocks and reservoirs alternate with each other in vertical direction and are distributed continuously in lateral direction, and the source rocks have been generating oil and gas constantly. It is concluded through comprehensive analysis that since the Late Jurassic, the source rocks in Lucaogou Formation have been generating oil continuously and massively, causing high pressurization, and providing constant driving force and oil supply, as a result, the oil has been charged into the tight reservoirs effectively and continuously, forming abundant tight oil resources.