桑托斯盆地地层生热率及热结构研究

Estimation of heat generation in the Santos basin with natural gamma logging data

岩石生热率是研究地球内热的一个重要的参数。根据自然伽马与岩石生热率的关系,利用盆地4口钻井的自然伽马测井曲线,计算出桑托斯盆地主要岩石或矿物及地层的生热率。统计了2964个自然伽马测井数据值,主要岩石或矿物的生热率从大到小依次为:泥岩、砂岩、页岩、玄武岩、石灰岩、硬石膏和盐岩;盆地地层的生热率随深度增加显著降低,生热率体现出受控于岩性变化的特征。以S1井为例,根据岩石生热率和热流的关系,计算出盆地中各个组的生热率,Marambaia组、Itajai-Acu组、Itanhaem组、Ariri组、Guaratiba群、Camboriu组生热率分别是(1.36±0.16)μW/m^(3)、(1.52±0.15)μW/m^(3)、(1.30±0.3)μW/m^(3)、(0.46±0.18)μW/m^(3)、(0.64±0.23)μW/m^(3)、(0.37±0.07)μW/m^(3),盆地沉积地层产生的热量占表层大地热流的13.62%,因此沉积地层具有一定的产热潜力,对区域有机质的成熟度有一定的影响。建立了岩石圈分层生热模型,其中地壳热流贡献为15.38 mW/m2,占表层大地热流的30.76%,地幔热流贡献值为34.62 mW/m2,地壳和地幔的热流比例为0.44,具有“冷壳热幔”的特征。

Rock heat generation is an important parameter for the study of heat in the Earth.According to the rela-tionship between the natural gamma and heat generation of rocks,the heat generation of the main lithology or min-erals and strata in the Santos basin is calculated using the natural gamma logging curves of the four wells in the basin.In this paper,2964 natural gamma logging data values are collected.The main heat-generating lithology or minerals are clay,mudstone,sandstone,shale,basalt,limestone,anhydrite,and salt rock.With the increase in depth,the heat generation of the strata in the basin decreases significantly,which is controlled by the change of lithology.Taking S1 as an example,the heat generated by the sedimentary strata in the basin is calculated according to the relationship between the heat generation and heat flow of the rocks.The heat generation of the Marambaia Forma-tion,Itajai-Acu Formation,Itanhaem Formation,Ariri Formation,Guaratiba Group,and Camboriu Formation is 1.36±0.16μW/m^(3),1.52±0.15μW/m^(3),1.30±0.3μW/m^(3),0.46±0.18μW/m^(3),0.64±0.23μW/m^(3),and 0.37±0.07μW/m^(3),respectively,accounting for 13.62%of the surficial heat flow.Therefore,the sedimentary strata in the study area have a certain heat generation potential,which exhibits an impact on the maturity of the regional organic matter.A layered model of the lithospheric heat generation rate is established,in which the contribution of crust heat flow is 15.38 mW/m2,which accounts for 30.76%of the surface Earth heat flow,and the contribution of mantle heat flow is 34.62 mW/m2.The ratio of crust and mantle heat flow is 0.44,which is characterized by the cold crust and hot mantle.