Analysis Of Temperature And Pressure Of Well ZK212on Yangyi Geothermal Field In Tibet

It is important to analyze and control the temperature and pressure during drilling toensure high safty and high efficiency. Compared to petroleum drilling, geothermaldrilling has more possibility of leaking off. To get high production, well site is alwayslocted on a place with high geothermal gradient, which is tending to lead a highwellbore temperature and boiling of fluid in borehole which could cause blowingout.Meanwhile, prediction of temperature and pressure of reservoir can provide basicdata for production.Yangyi geothermal field is one of the geothermal fields in Tibet, locating in YangyiVillage, Dangxiong, west of Lhasa and southwest of Yangbajing. The field is amongDangxiong-Yangbajing-Duoqingcuo active belt, distributed to the west of the N-Strending Yangyi faulted basin, and connected with Getaguo basin to the north.This paper analyzed the temperature, formation pressure, leakoff pressure andfracturing pressure of ZK212based on the measurement and observation onsite,including the leakoff observation, inlet temperature and outlet temperature of drillingfluid, borehole temperature, and borehole water level. Besides, a leakoff test was alsoconducted on field. Furthermore, the pressures mentioned above were calculated andan isoline map of zero-pressure of part of Yangyi geothermal field was drawn with theintegration of the data obtained in1990.The reservoir temperature is220℃and reservoir penetration coefficient is0.053cm/s,by analyzing bubble point pressure with the method developed. Besides, the boilingpoint of ZK212is at depth of490m. Equivalent density of formation pressure gradientis0.906g/cm3and zero point elevation is4688.13m. Equivalent density of losspressure gradient and equivalent density of fracturing pressure gradient are growing as depth increases, and less than0.97g/cm3and1.4g/cm3. H-W equation is suitable tothe prediction of fracturing pressure gradient but not to loss pressure gradient.Considering all well data of ZK212and wells around, it tends to leak off whenwellhead elevation is lower than zero point elevation, otherwise, it tends to blow out.Consequently, it is necessary to locate the well site in order to avoid leaking off orblowing out.