准噶尔盆地东部地区侏罗系烃源岩及其低熟气形成条件

Source rock condition and the formation of Jurassic low-maturity gases in the eastern Junggar Basin

源岩条件是低熟气形成的重要因素,准噶尔盆地东部地区侏罗系烃源岩分布范围广,厚度大,有机质为腐殖型烃源岩,RO值绝大多数都小于1.0%,具备有利于低熟气形成的源岩基础。通过地球化学分析,发现侏罗系烃源岩埋深为2 200~4 500m,RO值变化幅度很小,基本都在0.5%~0.8%之间。同一口井和不同区域的侏罗系烃源岩,都表现出随着埋深增加RO值变化范围较小,还未达到常规意义上的生气高峰阶段,并且在此演化阶段保持了很长的地质历史时间。针对实际地质情况,开展温度和时间条件下低熟气形成的热解生烃模拟实验研究,实验结果表明,330℃和350℃时,烷烃气产量较低,随着时间增加（3~30d）产气量变化很小,加热温度370℃和390℃,随着时间增长,气体增加量在14~21d达到最高峰,之后到30d呈缓慢增加或基本保持不变,相对同一温度3d时产气量增加2~2.5倍,即RO值增高0.2%~0.3%时,烷烃气生成量有显著增加,说明时间效应对低熟气形成有重要作用,并且受温度条件的限制。

Source rock condition is an important factor in the formation of low-mature gas.The Jurassic source rocks are widely distributed with large thickness in the eastern Junggar Basin.The organic matter type isⅢ,and its maturity is less than 1.0%.Geochemical analysis showed that RO（%）changes slightly,basically between 0.5% and 0.8%from 2 200 mto 4 500 m.The RO（%）variation is small with the increase of the depth of source rocks,indicating that it has not reached the gas generation peak,and this evolutionary stage holds a long geological history of time.To obtain information about the influences of heating time and temperature during the evolution of sedimentary organic matter,with hydrous pyrolysis,twenty experiments were conducted at different temperatures and heating time.The results showed that alkane gas production is low and change little with increasing pyrolysis time（3-30days）at 330℃and 350℃.With the increase of simulation temperature（370℃ and 390℃）,the alkane gas production reaches the peak at 14-21 days,and after that to the day 30 it showed a slow increase or nearly unchanged,relative to the same temperature for 3days,the gas production increased 2-3times,i.e.,ROincreased by 0.2%-0.3%.The amount of hydrocarbons gas increased significantly.That means,the effect of time on the evolution of low-mature gas may be related to the maturity.