Numerical Modeling Of The Bedrock Geothermal Reservoir In The Xiaotangshan Area Of Beijing, China

Xiaotangshan, Beijing, is one of regions with the earliest reconnaissance and thehighest level of development. By2005, there were nearly100geothermal wells in theXiaotangshan region and annual exploiting quantity exceeded350×104m3.Over-exploitation of geothermal groundwater which leaded to continuous declining ofgeothermal groundwater is a problem in the Xiaotangshan geothermal filed. Oneeffort of controlling the declining of geothermal groundwater and relief pressure ofgeothermal resource in Xiaotangshan is to add reinjection wells.Type of the Xiaotangshan geothermal field is conduction geothermal field.Cambrian System strata (∈), Jixian System Tieling Group strata (Jxt) and JixianSystem Wumishan Group strata (Jxw) are the main bedrock reservoirs. The upperstrata, including Quaternary System (Q), Jurassic System (J) and Qingbakou System(Qb), form cap rocks for these bedrock reservoirs.Fully developed fractures in the Xiaotangshan area play a very important role inoccurrence, migration and storage of geothermal water. The cold water coming fromnorthern mountain area is heated and transferred into geothermal water by the deepand heat conductive Huangzhuang-Gaoliying fault. Other associated faults such as theDaliushu-Huluhe fault connect hydraulic connection between source of deep heat andgeothermal reservoirs, which forms space and channels for migration and storage ofheat. This makes deep high temperature geothermal water concentrates in relativelyshallow places. All these contribute the Xiaotangshan geothermal anomalous area.FEFLOW software was adopted to generalize study area. In plane, the model isa fan-shap region ring-fenced by faults, its area is nearly115km2. Vertically, themodel is about3310m and is divided into20layers. The sea level is set as thedatum plane for the model. Simulation of coupled water and heat was used in studyarea. The differential equations of groundwater flow and the equation of heat transportwere applied in model. Because obtained parameters of study area are rare, method of debugging experience value for final value was adopted in the model.Measured data of observation wells were used for adjusting groundwater flow inthe model. Temperature field in the model was adjusted by measured initialtemperature, because geothermal reservoirs’ temperature remained constant indecades according to data collected. The results of both adjusting were acceptable.In the predicting calculation, two plans were designed, and simulation periods ofboth plan were5years. In plan one, the model parameters remained constant; Inplan two, a reinjection well was added which recharged the model at a rate of920m3/d during the heating period of a year. Results of the two plans reveal thatgeothermal water level will continue to decline with current condition, but properaddition of quantity of reinjection water will relief the pressure of geothermalresources and the geothermal water level will stop declining. Temperature of modelchanged little in both of the plans.