Effect Of Drilling Fluid Circulation On Well-bore Temperature Distribution And Stress

In the process of ultra-deep drilling and geothermal drilling,the temperature near the bottom hole is very high,and the formation stress near the borehole wall will change because of the thermal stress caused by the variation of well-bore temperature during drilling.In the drilling process,the cuttings can be removed by drilling fluid circulation,the bit part can be cooled and the bottom wall rock can be cooled.Due to the change of rock temperature around the well,certain thermal stress will be produced,which may lead to the instability of the well wall.This paper mainly studies the influence of drilling fluid on well-bore temperature distribution and the influence of temperature change on well-bore stress state.There are three main aspects of the work accomplished:The variation of thermal expansion coefficient of granite,slate and shale at high temperature is analyzed by studying the thermal expansion characteristics of rock.It is concluded that the change of thermal expansion coefficient of three kinds of rocks from room temperature to about 300 degrees is relatively smooth.The growth rate is about 30%,among which the coefficient of thermal expansion of granite is the smallest.The equation of well-bore temperature distribution considering the temperature difference between inside and outside of shaft wall is established,and the discrete form of well-bore temperature distribution under unsteady condition is given,and the well-bore temperature distribution under steady condition is solved.The influence of heat transfer effect on the temperature distribution is considered.The stress field around the well is studied by using the characteristics of rock thermal expansion and well-bore temperature distribution.The results show that considering the temperature difference inside and outside the shaft wall,the stress distribution results are significantly affected.Summary: this paper first studies the thermal expansion characteristics of rock,then analyzes the influence of temperature difference on well-bore temperature distribution equation,and analyzes the influence of rock thermal expansion characteristic and temperature distribution equation on well-bore stress field.The rule of stress redistribution in well-bore is obtained.