Establishment And Applications Of Wellbore Flow Model In Deep Geothermal Well Drilling With DTH Air Hammer

Compared with the traditional mud positive circulation drilling technology,DTH air hammer drilling technology not only has the advantages of resisting well deviation,high mechanical drilling speed,protecting reservoir and large water volume after well completion,but also has been widely used in geothermal well drilling.The biggest cost of DTH air hammer drilling is the rental and oil consumption of air compressor and booster,which is closely related to gas injection and air pressure.Under the condition of large formation water yield,DTH air hammer can not work due to its working characteristics,which requires higher gas injection and air pressure.Based on this,the corresponding wellbore flow model of the DTH air hammer drilling is established to calculate the minimum gas injection and air pressure.The main research work of this paper is as follows:(1)The working principle,technical characteristics and application of DTH air drilling technology are analyzed.The experience of drilling parameters control is summarized.(2)The cycle flow model of the DTH air hammer drilling in geothermal well is established by combining the positive circulation flow model and the annular flow model of the annulus in the DTH air hammer drilling,and the method of calculating the minimum gas injection is deduced.The model is verified after being programmed with MATLAB.The results show that the annular flow model is closer to the actual value than the normal circulation model of DTH air hammer drilling for the calculation of flow parameters;The calculation results of the minimum gas injection are closer to the actual value of geothermal wells than other models,but there are still some deviations.(3)Combined with the practical example of Huaihua geothermal well,the flow parameters under different formation water yields are calculated and the influencing factors are analyzed by using the flow model of DTH air hammer drilling.The variation curves of wellbore pressure,liquid film thickness and droplet size under different formation water yield,annulus cross-sectional area,annulus hydraulic diameter and surface tension of gas and water are obtained.(4)The flow model of DTH air hammer is used to calculate the minimum gas injection rate and air pressure corresponding to different well depths and formation water yields,and the corresponding configuration requirements for air compressor and booster are given.The influence of drill pipe size on the minimum gas injection rate and air pressure is studied.In view of the problem of cuttings removal with air injection,the calculation method of the late time of cuttings is given and an example is calculated.It is concluded that while removing cuttings with air injection,the late time of cuttings is inversely correlated with the drill pipe size and gas injection volume,and positively correlated with the release pressure and formation water yield.