| In resent years,geothermal energy,as the clean energy with the feature of stable,widely distributed and low unit cost has vigorously promoted.There are still many key problems to be solved in the process of development and utilization of geothermal energy.This paper analysed some key issues of geothermal exploitation,utilization and recharge,provided affective theory for exploitation and utilization of geothermal.1.Study on wellbore temperature distribution during drillingA drilling fluid circulation temperature model for high-temperature geothermal well coupled with formation temperature,thermal and physical properties of the formation,and drilling fluid performance changing with temperature was established on the basis of the existing drilling fluid circulation temperature model with the characteristics of high temperature,geothermal gradient variation and formation lithology diversification in high temperature well.The results of the new model were compared with those of the existing model to verify its rationality.The effects of circulation time,mass flow rate of drilling fluid and inlet temperature of drilling fluid were analyzed.2.Study on wellbore pressure distribution during drillingDrilling fluid pressure in the well at different stages of the drilling process was analyzed.A model suitable for predicting the circulating pressure in high temperature geothermal wells coupled drilling fluid temperature,drilling fluid performance changing with temperature and cuttings was established and expressed in equivalent circulation density.The factors affecting the equivalent circulation density of drilling fluid(such as temperature,cuttings,drilling fluid flow rate and inlet temperature,etc.)were analyzed.The analysis results were used to adjust the drilling fluid parameters to ensure the equivalent circulation density inside safety density window;The influence of the drilling speed and the drilling depth on the fluctuation pressure in the well during the drilling was analyzed.3.Study on wellbore temperature and pressure distribution during productionThe temperature and pressure distribution models of single-phase fluid and gasliquid two-phase flow in production wells coupled with the physical properties of geothermal fluid changing with temperature were established based on the theory of mass,momentum,energy conservation and heat transfer.The fluid temperature,pressure and dryness are regarded as variables,and the pressure drop was calculated according to the two-phase flow theory.The equations in the model were described in segmented form and solved by iterative method.The effects of fluid mass flow on fluid temperature and pressure and flow pattern in the well was discussed,which provided a reference for optimizing production parameters.4.Study on wellbore temperature and pressure distribution during rechargeThe fluid temperature and pressure distribution model in the recharge well was obtained by modified the fluid temperature and pressure model in production well.The effects of recharge temperature,recharge amount and wellbore diameter on fluid temperature and pressure in recharge wells were analyzed,which provided basic parameters for temperature field changes of high temperature thermal reservoirs under pumping conditions.5.Study on temperature field distribution in geothermal reservoirThe boundary condition of bottom hole temperature simulated by the recharging well temperature model can describe the temperature field distribution of reservoir under high temperature to well system accurately.Well spacing and well flow have great influence on reservoir temperature field.Hydrogeological parameters have little influence on reservoir temperature change.Recharge wells should be located downstream from production well.Excessive exploitation of geothermal Wells will lead to changes in the hadrochemical environment of the reservoir,scale formation in the reservoir,and affect the porosity of the reservoir. |
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