The Stress Analysis And Thermal Loss Research For An Intubation Closed Injection-production Integration String Used In Thermal Recovery Wells

In order to solve problems in the steam huff and puff, an intubation closed injection-production integration string has been designed, but there is no study of heat loss and stress analysis about this new type of string. This paper builds the wellbore heat loss calculation model based on the physical model of the integrative string and made sensitive analysis on factors like string type, wellhead steam dryness and formation parameters. Also, the force analysis is studied during the process of lowering, pulling the string and working and the calculation model is built. The models are amended by using proper mathematic methord and a software is made. Calculation results show the error is smaller than 3% and the software has good precision. In the matter of wellbore heat loss, study shows that using this type of string can increase the downhole steam dryness by 12% and decrease the wellbore heat loss by 26.64% compared with ordernary tubes. When other parameters are stable, it is helpful to decrease the drop of steam dryness and improve the effct of steam injection by enhancing the value of the wellhead steam dryness. When the value of formation(cement sheath) thermal conductivity is greater, the downhole steam dryness is lower and wellbore heat loss is greater. But the downward gravity will decrease as the themal conductivity arises. In the process of production, it can also make the wellhead oil temperature arise and decrease the wellbore heat loss by about 40%. If electrical heating is used, there will be the optimal heating power and it’s 40 kW in the calculation case. In the matter of the force analysis, the string can be devided by the packer into two parts. The wellhead tension will arise at first and then fall along with the depth of lowering the string the bottom half string and there will be a maximum. While lowring the top half one, the wellhead tension will increase all the time. When pulling the string out, the wellhead tension is greatest at the beginning. The maximum of wellhead tension during lowering/pulling the bottom and top half string is 162.14MPa(379.10MPa), 127.28MPa(608.73MPa). The bottom half string will be broken at the process of being pulling out because of the great oil viscosity so it is wisable to choose segmental salvage. In the process of injection and production, the string will extend because of the change of pressure and temperature in the wellbore, so it’s necessary to use compensating tube and it should be under the neutral point. In the case, the position of the neutral point is 1348.83 m and the compensating tube is at the position of 1350 m so it meets the requirement. The extention of the string which is 1400 m long is 4.5m/1m at the process of injection/production, so it’s appropriate to design the compensating length by 4.5m/km. The calculation thesis and the software have been applied well in the Hekou oil recovery enterprise and can be used in other similar oil field.