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岩盐热导率是砂泥岩的2~3倍,高热导率使盐下地层热量快速向上传递而降温、盐上地层热量快速增加而升温。库车前陆盆地三叠系—侏罗系烃源岩主要发育区被厚度超过1 500m的古近系—新近系膏盐岩覆盖,中间相隔白垩系砂、泥岩。地层温度实测数据统计表明,紧邻古近系膏盐岩的地层温度出现明显跳跃,膏盐岩及盐上构造层的地温梯度大于盐下构造层白垩系的地温梯度。膏盐岩不发育的地区具有单一的地温梯度。深部烃源岩热演化史数值模拟表明,随膏盐岩厚度增大,盐下深层侏罗系烃源岩地层温度和热演化程度均降低,1 500m膏盐岩可使侏罗系烃源岩地层温度和RO值分别降低15℃、0.35%;受岩盐的影响,深部三叠系—侏罗系烃源岩生气高峰期延迟至库车中晚期—第四纪,生气中心位于克拉苏构造带,与晚期盐下大规模构造圈闭的有效期相匹配,有利于盐下大气田的形成。烃源岩热演化史模拟结果与现今发现的天然气成熟度分布也十分吻合。
The thermal conductivity of rock salt is 2 to 3 times that of sandstone and mudstone. The high thermal conductivity makes the heat in the salt layer rapidly transfer upward and cool down, and the heat in salt strata rapidly increases while warming. The main development area of Triassic-Jurassic source rocks in the Kuqa foreland basin is covered by Paleogene-Neogene gypsum salt rock with a thickness of more than 1 500 m, separated by Cretaceous sand and mudstone. The measured data of formation temperature show that the temperature of the formation immediately adjacent to the Paleogene gypsum rock salt has a clear jump, and the geothermal gradient of the gypsum salt rock and the salt structural layer is greater than the geothermal gradient of the Cretaceous in the salt structural layer. Gypsum rocks are not developed areas with a single geothermal gradient. The numerical simulation of the thermal evolution history of deep source rocks shows that with the increase of the thickness of gypsum salt rock, the temperature and thermal evolution of the deep Jurassic hydrocarbon source rocks in the salt field decrease. The 1 500 m gypsum salt rock can make the Jurassic source rocks The formation temperature and the RO value decreased by 15 ℃ and 0.35% respectively. Due to the influence of rock salt, the peak period of the deep Triassic-Jurassic hydrocarbon source rocks delayed to the middle and late Quaternary, and the gas center was located in the Kelasu tectonic belt , Which matches with the validity of the large-scale structural traps under late salt, is favorable to the formation of giant gas fields under salt water. The simulation results of thermal evolution history of source rocks are in good agreement with the distribution of gas maturity discovered so far.