川西坳陷孝泉—新场—合兴场地区须二段天然气气源判定及成藏分析

摘要

The analysis of natural gas composition and carbon isotope of the second member of Upper Triassic Xujiahe Formation in Xiaoquan-Xinchang-Hexingchang area of West Sichuan depression indicates that the natural gas is hybrid origin consisting of coaliferous gas and oil-cracked gas.It has three sources：①source rock of Maantang and Xiaotangzi Formation,humic-sapropelic organic material generated oil and gas and then the oil cracked into gas under high temperature;②source rock within the second member of Xujiahe Formation,gas-generated mainly,self-generating and self-reserving;③source rock within the third member of Xujiahe Formation,which did few contributions to the gas accumulation of the second member of Xujiahe Formation.By analyzing the dynamic relationship between gas charging history and the rock-tightening evolution,the gas reservoir of the second member of Xujiahe Formation is judged as a typical ＂subsequent tight sand gas＂ reservoir,whose accumulation process conformed to the specific mode of ＂early accumulation-seal up-late activation＂.%对川西坳陷孝泉—新场—合兴场地区须二段天然气组成及碳同位素的分析表明,须二段天然气为煤型气和油裂解气的混合成因气,其气源有3种：①马鞍塘组—小塘子组烃源岩,腐殖-腐泥混合型有机质生油生气,而后油在高温下裂解成气;②须二段内部烃源岩,以生气为主,自生自储;③须三段烃源岩对须二段天然气聚集也有贡献,但贡献极小。在对须二段气藏烃源岩生排烃高峰期天然气充注史与岩石致密演化之间的动态关系进行分析判定,认为须二段气藏属于典型的＂后成型＂致密气藏,其成藏过程符合＂早聚、中封、晚活化＂的成藏模式。