川中古隆起震旦系-下寒武统温压演化及其对天然气成藏的影响

根据热史研究成果，结合川中古隆起沉积埋藏史，恢复了震旦系-下寒武统烃源岩成熟度演化历史，确定了原油裂解的时期。利用盆地模拟方法，恢复了一维单井和二维剖面的压力演化历史，分析了川中古隆起震旦系-下寒武统异常压力的成因机制。烃源岩成熟度演化历史表明，震旦系-下寒武统烃源岩经历了早期生油、二次生油、干酪根裂解生气及晚期原油裂解四个演化阶段；原油裂解的开始时间大致是中、晚三叠世。川中古隆起震旦系-下寒武统主要经历了常压-增压-卸压的压力演化过程，白垩纪中期寒武系达到最大压力系数约1.7；威远-资阳地区压力系数较低，高石梯-磨溪构造带压力系数相对较高。研究发现快速埋藏、生烃作用及原油裂解是该地区超压形成的主要因素；燕山-喜山期的构造抬升使剩余压力降低，现今寒武系在局部地区仍保持超压。温压演化对天然气生成、运移、成藏及后期保存具有重要影响。

Characteristics and Effects on Gas Accumulation of the Sinian-Lower Cambrian Temperature-pressure Field in the Central Paleo-Uplift,Sichuan Basin

The  evolution of  maturity of the Sinian-Lower Cambrian source rocks was reconstructed,  and the starting  time for oil cracking was also determined on the basis of  the tectono-thermal history of Central Paleo-uplift, Sichuan Basin. The pressure evolution of some typical wells and 2D profile was simulated and the genetic mechanism of abnormal pressure in the Sinian-Low Cambrian was analyzed. The  evolution  of maturity  indicated that the Sinian-Lower Cambrian source rocks experienced four stages, including first oil generation, second oil generation, kerogen cracking and late oil cracking. Oil cracking started at Middle-Late Triassic. The paleo-pressure evolution of the Sinian-Lower Cambrian consists of normal pressure, overpressure and pressure relief. The pressure coefficient of Cambrian maximized about 1.7 in Middle Cretaceous, and it was higher in Weiyuan-Ziyang area than Gaoshiti-Moxi structural belt. Rapid burial, hydrocarbon generation and late oil cracking are the primary factors for the overpressure. The excess pressure was relieved due to the tectonic uplift in Yanshan-Himalaya Periods, which resulted in the normal pressure in Sinian of the whole area and in Cambrian of Weiyuan-Ziyang area. However, the pressure coefficient of Cambrian maintains a high value about 1.5 in Gaoshiti-Moxi structural belt. The evolutions of temperature and pressure impacted gas generation, migration, accumulation and preservation significantly.