藏北地区钻孔大地热流值测量

本文利用藏北地区三口天然气水合物钻孔测温数据，在分析样品热导率测试结果基础上，计算了藏北地区的热流值.对于样品热导率值，首先根据样品孔隙度对实验室测试结果进行了饱水校正，计算热流时采用的是对应井段的岩石热导率饱水校正值的厚度加权平均值.地温梯度以三口钻孔48 h的测温数据为基础，回归三口井的地温梯度，计算时去除了浅部受地表温度和冻土带对温度影响的数值.A钻孔地温梯度分为200~438 m和438~882 m两段回归，分段热流的加权平均值作为钻孔热流值，计算结果为42.7 mW·m^-2； B钻孔和C钻孔回归地温梯度时未分段，热流计算结果分别为58.3 mW·m^-2、70 mW·m^-2.综合分析认为，岩石圈断裂、地幔上涌、碰撞造山过程中的剪切生热等因素可能造成了班公湖—怒江缝合带以南热流值较高，而北部羌塘地块热流值相对较低.

Measurements of borehole heat flow in northern Tibet

The heat flow values of northern Tibet were calculated based on three gas hydrate wells' temperature logs and core thermal conductivity analysis. Laboratory thermal conductivity test results were first calibrated by using associated core porosity and a 100% water-saturated model, then the arithmetic average thermal conductivity was determined from the corrected values, which were weighted by a factor proportional to the interval thickness. Geothermal gradients were from the linear regression analysis of the borehole temperature data, which was logged within 48 hours after TD. The shallow interval temperature data was filtered out to avoid the impact of ground temperature and permafrost. Two different geothermal gradients were derived from well A. A weighted average of the two zones for well A resulted in a heat flow value of 42.7 mW·m^-2. Well B and well C only had one geothermal gradient. Heat flow values of 58.3 mW·m^-2 and 70 mW·m^-2 were calculated for well B and well C, respectively. Some factors, such as crustal faults, mantle upwelling and shear heat from overthrust terrains, may lead to higher heat flow values in the south of Bangong Co-Nujiang suture zone. Conversely, the heat flow value is relatively low in the north of the suture zone.