河套盆地临河坳陷咸湖烃源岩生烃机理

Hydrocarbon generation mechanism of saline lake source rocks in Linhe Depression,Hetao Basin

近年来,河套盆地油气勘探陆续取得突破,但有关该地区咸湖相烃源岩的生烃机理尚未开展系统研究,制约了该区块下一步勘探开发。以临河坳陷固阳组和临河组烃源岩样品为研究对象,开展岩石热解、氯仿沥青“A”、饱和烃气相色谱—质谱、古生物孢粉鉴定、干酪根显微组分、干酪根有机元素、XRD全岩和黏土矿物分析等地球化学分析实验。研究结果表明:①咸湖相烃源岩具有丰富的物质基础,浮游生物、藻类、细菌和高等植物等均可提供母源;②矿物和特殊元素具有加速生烃的作用,含膏泥岩加速上层烃源岩的热演化,伊/蒙混层之间的转化、碳酸盐矿物和黄铁矿组合一定程度上能促进生烃,富S干酪根中S元素的存在降低活化能,加速生烃;③咸化湖盆中环境对烃源岩生烃影响较大,发育于强还原和伽马蜡烷指数低于1.5沉积环境中的烃源岩,有机质丰度和生烃潜力随着还原性和水体盐度的增强而升高,高地层水矿化度和pH值为7~9的环境也有利于加速生烃;④研究区烃源岩具有2期生烃特征,生烃高峰对应的R O值分别为0.6%和0.9%。通过生烃机理研究,明确临河坳陷咸湖相烃源岩具有生成低成熟油和成熟油的特征,油气资源丰富,勘探潜力较大。

In recent years,breakthroughs have been made in oil and gas exploration in the Hetao Basin.However,the hydrocarbon generation mechanism of the saline lake source rock has not been studied,which limits further exploration and development in the study area.Taking the source rock samples of Guyang and Linhe formations in Linhe Depression as the research object,geochemical analysis experiments were carried out such as Rock-Eval,chloroform bitumen“A”,saturated hydrocarbon gas chromatography-mass spectrometry,paleontological sporopollen identification,kerogen macerals,kerogen organic elements,XRD whole rock and clay mineral analysis.The results show that:(1)The source rocks of saline lacustrine facies are rich in material basis.Plankton,algae,bacteria and higher plants can provide sources.(2)Minerals and special elements have the effect of accelerating hydrocarbon generation.The gypsum-bearing mudstone accelerates the thermal evolution of the upper source rocks.The transformation between the illite-smectite mixed layers and the combination of carbonate minerals and pyrite can promote hydrocarbon generation to a certain extent.The existence of S element in S-rich kerogen reduces the activation energy and accelerates hydrocarbon generation.(3)The environment in the saline lake basin has a great influence on hydrocarbon generation.The organic matter abundance and hydrocarbon generation potential increase with the increase of reducibility and water salinity(gammacerane index less than 1.5).The high formation water salinity and pH 7-9 environment are also conducive to accelerate hydrocarbon generation.(4)The source rocks in the study area have two stages of hydrocarbon generation characteristics,and the RO corresponding to the hydrocarbon generation peak is 0.6%and 0.9%,respectively.Through the study of hydrocarbon generation mechanism,it is clear that the source rocks of saline lake facies in Linhe Depression have the characteristics of generating low mature oil and mature oil,which are rich in oil and gas resources and have great exploration potential.