HOLE TEMPERATURE VARIATION AND ITS EFFECTS ON GAS INJECTION RATE DURING GAS DRILLING

The currently used methods for calculating gas injection rate during gas drilling all take the temperature of natural formation at the same depth as the temperature of the annulus fluid,without considering the heat exchange occurred between the wellbore fluid and the formation.So the errors are inevitable.What's the worse,the error will become greater by the increase of the well depth.Based on Conservation of Energy Principle,this paper set up a mathematical model taking into consideration the effects on well fluid temperature by heat exchange between the wellbore fluid and the formation,etc.With the solution of annulus fluid temperature obtained from the model,the required gas rate was calculated.By comparing this calculated rate with the rate obtained using formation temperature,this paper found out that the gas injection rate obtained by assuming formation temperature was smaller,and would be much smaller by the increasing depth.Therefore to determine appropriate gas injection rate for gas drilling,this paper suggests the effects of heat exchange between the formation and the wellbore fluid should be taken into consideration when calculating the wellbore fluid temperature.