海拉尔盆地贝尔凹陷热演化史与油气关系研究

Study on the Relations between Geothermal History and Oil-Gas Generation in Beier Depression of Hailaer Basin

贝尔凹陷是是海拉尔盆地内勘探程度较高的一个南部凹陷,该凹陷沉积厚度大,地层发育全,生油条件十分优越,是海拉尔盆地主要产油气凹陷。主要烃源岩层是南屯组,其次是大磨拐河组和铜钵庙组。根据镜质组反射率、包裹体测温和磷灰石裂变径迹法恢复的贝尔凹陷古地温演化史表明贝尔凹陷早白垩世古地温梯度可达3.7～5.8℃/100m,高于现今地温梯度3.35℃/100m,古地温高于今地温。古地温恢复及热史模拟表明最高古地温是在早白垩世晚期达到的,下白垩统烃源岩热演化程度主要受古地温场控制。热演化史与油气关系研究结合烃源岩排烃史和伊利石测年结果表明贝尔凹陷油气成藏期主要有两期,分别为早白垩世晚期及古近纪以来,且以早白垩世晚期为主要成藏期。古近纪以来为第二成藏阶段,由于抬升剥蚀作用,目的层温度开始降低,生烃强度减弱,主要为早期形成油气藏的二次调整和二次生成的油气继续注入成藏。第二次成藏时期对贝尔凹陷油气藏的形成起着重要作用,是制约油气富集的重要因素。

Beier depression is the highly explored depression in Hailaer basin with complete and thick sedimentary sequence.The producing oil condition is very excellent,and it is the main oil-gas depression in Hailaer basin.The main hydrocarbon source rocks is from the Nantun group,next is Damoguaihe group and Tongbomiao group.The average paleogeothermal gradient recovered by the vitrinite reflectance and homogenization temperatures of fluid inclusion and fission track method is about 3.7~5.8℃ /100m,it is obvious higher than present geothermal gradient 3.35℃/100m,the paleotemperature is higher than present geothermal,the paleotemperature research and thermal history simulation show the max paleogeothermal value were reached in late Cretaceous,paleogeothermal field controlled maturity of hydrocarbon source rocks of Lower Cretaceous.Results of the geothermal history on the basis of illite dating results and hydrocarbon generated and hydrocarbon expulsed process show that the forming time of oil-gas reservoirs have two stages in Beier depression： late Cretaceous and early Tertiary.Late Creatceous is the main stage for Beier depression.The second stage is early Tertiary,it happened Lifting disintegration function in the stage,the goal stratum temperature started to reduce,the intensity of hydrocarbon production began to weaken,on the one hand,the oil-gas reservoirs formed in the first stage was adjusted;one the other hand,it was the second formation process of oil-gas reservoirs.The second forming stage of oil-gas reservoirs is important for the formation of oil and gas reservoirs in Beier depression and also the important factor for oil-gas accumulation in Beier depression.