长岭凹陷断陷期生烃阶段性与成藏圈闭的选择性

松辽盆地长岭凹陷断陷期烃源岩主要发育在火石岭组、沙河子组和营城组,由于受断拗转换期构造运动和嫩江运动的影响,烃源岩演化具有明显的阶段性。依据长岭油气田现今埋深与烃源岩成熟度的关系,分别建立了断陷期和拗陷期烃源岩埋深与烃源岩成熟度的关系式,进行了剥蚀量恢复和古地温梯度求取,系统研究了断陷期烃源岩的生烃演化过程,认为烃源岩具有早期生烃和二次生烃的特点;结合圈闭形成时间的分析,认为不同阶段生成的油气具有成藏选择性:生烃早期只有地层和岩性圈闭能够成藏;进入高–过成熟阶段,构造圈闭可以成藏,而当烃源岩进入拗陷期的二次生烃阶段,各种圈闭均可再次进行天然气的充注。

The Stages of Hydrocarbon Generation and the Selectivity of Reservoir-Forming Trap in Changling Sag in Songliao Basin

The source rocks of downfaulted period in Changling sag in Songliao basin are mainly found in Huoshiling formation, Shahezi formation and Yingcheng formation. Because of the effects of tectonic movement in fault-depressed conversion period and the Nenjiang movement, the evolution of the source rocks is of obvious stages in nature. By study on the relationship of present buried depth and source rock maturity of source rocks in Changling oil-gas field, the correlation equations of them in downfaulted and depression periods are established, respectively, conducting the recovery of denudation amount and the calculation of paleogeothermal gradient. The systematic study of the process of hydrocarbon-generation and evolution of source rocks in downfaulted period, it is considered that the source rocks are characterized by both early hydrocarbon generation and secondary hydrocarbon generation. Combined with the analysis of the trapforming time, it is believed that the oil and gas formed in different stages has the reservoir-forming selectivity. In early stage, the stratigraphic trap and lithologic trap may form reservoirs; when entering into high mature-overmature stage, the structural trap may form reservoir, while the source rocks entered into depression period and the secondary hydrocarbon generation stage, all traps in this basin could form reservoirs by the recharging of oil and gas.