Interwell connectivity in a karstic geothermal reservoir through tracer tests
Pang Jumei1,2, Pang Zhonghe1, Kong Yanlong1, Luo Lu1,2, Wang Yingchun1,2, Wang Shufang3
1. Key Laboratory of Engineering Geomechanics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029;
2. University of Chinese Academy of Sciences, Beijing 100049;
3. Beijing Institute of Geological Environment Monitoring, Beijing 100195
The inhomogeneity of karstic geothermal reservoirs makes it difficult to determine the inter-well connectivity between injection and exploitation wells. Tracer technology can quantify the flow parameters,depict the characteristics of karstic reservoirs effectively,reveal the extent of hydraulic connections,detect flow channel and flow velocity between an injection and a production well,and predict possible cooling of production wells due to long term waste water reinjection. Therefore,it is very effective to study inter-well connectivity of karstic geothermal reservoirs. This paper presents a tracer test in Xiongxian karstic geothermal reservoir of the Niutuozhen geothermal field in North China as an example. The targeted geothermal reservoir of the tracer test is Wumishan Formation of Jixian System. In the multi-well tracer test,sodium fluorescein was chosen as tracer and was injected into a well called WQ2. 10 other wells around it were used as monitoring wells. The test data were interpreted by solving mass transport model in fractured medium. The geothermal reservoir's properties of preponderant channel's length,flow velocity,longitudinal dispersivity and recovery rate were obtained through interpretation of tracer test data. The inter-well connectivity information are gained correspondingly and suggestions are made to adjust the layout of reinjection and production wells in the studied geothermal field.