福建漳州低温断裂带地热系统数学模拟研究

RESERVOIR MODELLING OF ZHANGZHOU LOW TEMPERATURE FRACTURE ZONE SYSTEM, FUJI-AN, CHINA

本文依据地质、地球化学研究和地热到量资料,建立了漳州地热系统的数值模型.该模型解释了自然状态下漳州地热系统可能的热量和质量传递.模型覆盖面积约60×40km^2,囊括了与盆地中央地热异常有关的各水文地质单元;模型深度≥8km,模拟了大气降水的受迫对流及其在地壳深部花岗岩中引起的热量和质量迁移.用浅部井温、深部热储温度以及地表自然热损失作为拟合参数,进行的数值模拟给出了漳州地热系统的渗透率结构,并且表明,漳州地热系统由一个受迫对流腔组成,热量由深循环的大气降水从热源基底层中汲取,并汇集于一个由断裂交汇产生的高渗透率菱形管道中上升,在浅部沿断裂再分配而形成带状的漳州地热异常区.驱动漳州地热系统的背景热流≤80mW/m^2,但地下水的补给和排泄严重地干扰了区域地表热流分布,使得大面积补给区出现低热流( ≤40mW/m^2),而在排泄区内,由于浅层冷水的直接补给而出现高、低热流并存的格局.

This paper presents a conceptual model which explains the likely heat and mass transfer of the Zhangzhou system in its natural state. The model is extended to an area of 60 × 40km and 8km in depth to simulate the forced con-vecting of meteoric waters and transferring of heat and mass in a granitic crust. The permability structure is obtained by numerical modelling using observed well temperature, deep heat reservoir temperature and calculated natural heat loss as matching parameters. Modelling has shown that the Zhangzhou system constitutes a terrain-forced convection cell which sweeps the heat from the resource basal layers into the segments of the deepreaching prismatic, vertical fracture conduits of limited lateral extent. The system is driven by the crustal heat ( ≤80mW/m2) and the forced convection induced by high terrain. The secular fluid movements at and above the resource base ( about 4 km in depth) reduce significantly the heatflow in the upper crust over a large area.