莺歌海盆地沉积层生热率及其热流贡献

Sedimentary layer heat production rate and its heat flow contribution in Yinggehai Basin

沉积层热流作为大地热流的一部分,可以有效促进沉积盆地深层—超深层烃源岩有机质热演化过程。岩石放射性生热率作为重要的热物性参数,是研究沉积层热流的基础数据之一。文中利用莺歌海盆地35口重点井的自然伽马值,根据前人提出的自然伽马和生热率关系的经验公式,计算出12051个生热率,获得了莺歌海盆地各个地层的生热率,并据此估算了莺歌海盆地沉积层热流贡献及其对深部地层的增温效应。结果表明:莺歌海盆地沉积层平均生热率为1.14μW/m^(3),岩性对生热率影响较大,泥岩平均生热率最大,为1.81μW/m^(3),其次是粉砂岩,平均生热率为1.49μW/m^(3),最小的是白云岩,仅为0.73μW/m^(3)。根据各个地层的平均生热率,计算出莺歌海盆地沉层平均热流值为8.0 mW/m^(2),占地表总热流值的10.1%,沉积层热流值分布与沉积层厚度特征保持一致,在中央凹陷带最大,2个斜坡带较小,沉积层生热率对深部地层地温梯度贡献为5.3℃/km。因此,沉积层的放射性生热对莺歌海盆地地温场有较大影响,在进行相关研究时不容忽视。

Sedimentary layer heat flow,as a part of the terrestrial heat flow,can effectively promote the thermal evolution process of organic matter in deep and ultra-deep hydrocarbon source rocks in sedimentary basins.The radioactive heat generation rate of rocks,as an important thermophysical parameter,is part of the basic data for the study of sedimentary layer heat flow.Using the natural gamma values of 35 key wells in Yinggehai Basin,12051 values of heat production rate were calculated and the heat production rate of each formation in Yinggehai Basin were obtained according to the empirical formula of the relationship between natural gamma and heat generation rate proposed by previous authors,and the contribution of heat flow in the sedimentary layers of Yinggehai Basin and its warming effect on deep stratums were estimated based on the results.The results show that the average heat generation rate of the sedimentary layers in Yinggehai Basin is 1.14μW/m^(3),lithology has great influence on the heat generation rate,and mudstone has the largest average heat generation rate among all rocks,which is 1.81μW/m^(3),followed by siltstone,with an average heat generation rate of 1.49μW/m^(3),and dolomite has the smallest heat generation rate,which is only 0.73μW/m^(3).Based on the average heat generation rate of each stratum,the average heat flow value in the sedimentary layers of Yinggehai Basin was calculated to be 8.0 mW/m^(2),which accounted for 10.1%of the total heat flow on the ground surface,and the distribution of the heat flow value in the sedimentary layers was consistent with the thickness characteristics of the sedimentary layers,which was the largest in the central depression zone,smaller in two slopes,and the contribution of the heat generation of the sedimentary layers to the temperature gradient of the deeper strata was 5.3℃/km.Therefore,the radiative heating of the sedimentary layers has a large impact on the ground temperature field of Yinggehai Basin,which should not be neglected in related researches.