祁连山冻土区含天然气水合物层段岩心热模拟实验研究

以热模拟实验为手段,对祁连山冻土区DK-2和DK-3孔含天然气水合物层段岩心(泥岩、油页岩和煤)热模拟烃类气体的组分、碳同位素组成与天然气水合物进行对比,以探寻这些气源岩与天然气水合物气源之间的可能联系。实验结果显示:低温(300℃以下)条件下,产生的气体以非烃CO2为主,烃类气体含量少,且泥岩产生烃类气体量<油页岩产生烃类气体量<煤产生烃类气体量,表现出不同岩石吸附气体的差异性特征;随着热模拟温度增加,产生的烃类气体量明显增加,至500℃时达到最高,相反CO2产气量变化不大;随热模拟温度增加,泥岩、油页岩、煤所产生烃类气体的碳同位素值呈现先变轻后变重的演化趋势和δ13C1<δ13C2<δ13C3的正碳同位素序列特征;泥岩在350～400℃条件下或油页岩在380～400℃条件下所产生的烃类气体在组成和同位素特征上与天然气水合物中烃类气体较为相似,推测天然气水合物气源与深部泥岩或油页岩具有地球化学成生联系,相反煤产生的烃类气体虽然在组成上与天然气水合物中烃类气体较为相近,但两者同位素值相差较远,推测煤与天然气水合物气源关系不大。

Study of Thermal Simulation on Cores at Gas Hydrate-bearing Intervals in the Qilian Mountain Permafrost

Gas composition and carbon isotopes of hydrocarbon gases thermally simulated from cores(mudstone,oil shale and coal) were compared with gases from gas hydrate at gas hydrate-bearing intervals in the drilling of DK-2 and DK-3 in Qilian Mountain permafrost.The purpose is to explore possible links between these gas source rocks and gas sources of gas hydrates.The results indicate that thermally simulated gases are mainly composed of CO2 with a small amount of hydrocarbon gases on the low temperature conditions(<300 ℃);the yields of hydrocarbon gases from the mudstone,oil shale and coal gradually increase,displaying differences between adsorbing gas with different rock.With increasing of thermal simulation temperatures,yields of hydrocarbon gases from the mudstone,oil shale and coal obviously increase and reach maximum values at 500 ℃;conversely,yields of CO2 vary a little.With increasing of thermal simulation temperatures,carbon isotope values of hydrocarbon gas firstly become lighter and then heavier and are characteristics of normal carbon isotopic series of δ13C1 <δ13C2<δ13C3.The consequence suggests that hydrocarbon gases from mudstone in the range of 350 ℃ to 400 ℃ or from oil shale in the range of 380 ℃ to 400 ℃ have similar features of gas composition and carbon isotope with gas hydrate,indicating that the gas source of gas hydrate has geochemically genetic relation with deep mudstone or oil shale.In contrast,the gas composition of hydrocarbon gases from coal and gas hydrate are similar,but their carbon isotope values are incomparable,suggesting that the relationship between coal and gas source of gas hydrate is not closely associated.