基于自然伽马测井的徐家围子断陷沉积层生热率研究

Heat Production Rate Calculation Using Gamma-ray Logging of the Sedimentary Formation in the Xujiaweizi Fault Depression

以徐家围子断陷为研究对象,研究生热率特点及其对地温场的影响。利用18口重点钻井内3062个自然伽马值,依据自然伽马与生热率(GR-A)之间的关系,计算其生热率的数值,建立岩性-生热率的对比图,估算研究区放射性物质生热对大地热流的贡献以及对深部地层的增温效应。结果显示,徐家围子的平均生热率为(1.229±0.394)μW/m^(3),岩性是生热率的主要影响因素,流纹岩的生热率最高,平均值为2.30μW/m^(3),凝灰岩、安山岩、火山角砾岩的生热率平均值也较高,分别为2.19μW/m^(3)、1.75μW/m^(3)、1.69μW/m^(3),而砾岩的生热率最低,为1.00μW/m^(3),砂岩的生热率平均值为1.07μW/m^(3),泥岩的生热率平均值为1.72μW/m^(3),煤的生热率平均值为1.32μW/m^(3)。根据地层生热率,估算徐家围子沉积层生热贡献的热流为4.92 mW/m^(2),约占地表总热流70.5 mW/m^(2)的7%,沉积层生热对地温梯度的贡献约为2.8℃/km,放射性生热对属于“热盆”的松辽盆地的地温场具有不容忽视的影响。

Xujiaweizi fault depression was taken as research object to study the characteristics of heat generation rate and its influence on geothermal field.On the basic of the 3062 natural gamma logging values in 18 boreholes,the average values of heat generation rate were calculated,GR-A profile of representative boreholes was presented,and the contribution of radioactive heat generation of sedimentary layers to the surface heat flow was estimated.The results shows that the heat generation rate of sedimentary layers in the Xujiaweizi fault depression is(1.229±0.394)μW/m^(3).Lithology is the factor controlling the heat generation.The heat generation rate of rhyolite is the biggest,its average is 2.30μW/m^(3).The average heat generation rate of tuff,andesite and volcanic breccia is also higher,the average are 2.19μW/m^(3),1.75μW/m^(3),1.69μW/m^(3).The lowest heat generation rate of conglomerate is 1.00μW/m^(3).The average value of sandstone is 1.07μW/m^(3),the average value of mudstone is 1.72μW/m^(3),and the average heat generation rate of coal is 1.32μW/m^(3).It is estimated that the sedimentary layers contribution 4.92μW/m^(3)about 7%to the surface heat flow,and approximately 2.8℃/km to the geothermal field.It was significant to the hydrocarbon resource evaluation and exploration target optimization.