The Numerical Modeling And Recharge Technique Analysis Of The Wumishan Formation At Cangxian Uplift

Jixian system Wumishan formation, of which the geothermal water head falls continuously for the large-scale concentrated exploitation, is one of the main exploiting reservoirs in Tianjin. For the sake of the sustainable development of geothermal resource, Tianjin introduces, with good results, the "pumping while recharging" exploitation pattern. The aim of this study is to discover the change of hydrodynamic force field during exploitation, estimate its exploitation potential and educe an appropriate arrangement of reinjection wells.Based on the geology and hydrological geology investigation data of Wumishan formation, the hydrogeology conceptual model is founded. It can be generalized that:1) The permeability of heat-storage reservoir is controlled by geological structure and fault; 2) The disclosed heat-storage reservoir temperature is influenced by circulation depth of geothermal fluid; 3) In Tianjin the pressure field of Wumishan formation is high on both south and north while low in the middle area. In downtown and its suburb it is a pressure minima, a water cone.The mathematical model is built based on AQUA3D. It has passed through model verification and parameter estimation, so can be thought to be credible and a reflection of actual hydrogeology condition. In use of this model, the exploitation potential of Wumishan formation is estimated and "pumping while recharging" exploitation model is analysesed. It is shown that: 1) If the production life is 100 years and maximal tolerated depth of water level is 200 meters,the maximal yield in study region is 9.14×106m3/a. The groundwater exploitation potential that is estimated with "groundwater resource potential modulus" method lays in "less potential level". 2) Periphery reinjection has more advantage for the long-term control of regional heat-storage reservoir pressure compared with local reinjection. 3) The temperature of heat-storage reservoir changes little in reinjection condition. 4) Reinjection well should be set at heavy layer and avoid the marginal area of aquifer. Also there should be a distance between 800m to 1000m to exploitation well so as to prolong the break time. Keyword: Wumishan formation numerical modeling exploitation potential...