Study Of Downhole Temperature Distribution Of Electrical Heating Wells Of High Pour-point Heavy Oil

The thickened oil has gradually become a vital energy source in the futuredevelopment of the world economy because of its great reserves. However, thesteam stimulation in many heavy oilfield of our country has developed into themiddle and later periods, and the production of oil is declining. As a newtechnology of secondary thermal recovery, the electrical heating of super-heavy oilhas been highly valued and used by major oil fields. It mainly includes three kindsof methods, which are the hollow pumping rod electrical heating, the tube electricalheating and the electromagnetic heating. But their energy consumption is very great.In order to optimize electrical heating efficiency and achieve the best heating effectwith the minimal energy consumption, the wellbore temperature field’s theorymodel of electric heating well needs to be analyzed and created. To verify andamend the theory model, the downhole temperature distribution needs to bemonitored. Then the electrical heating process can be optimized with the theorymodel.This article built the theory model of skin effect in tubular conductor based onelectromagnetic theory. ANSYS simulation models of skin effect in the hollowpumping rod electrical heating and the tubing electrical heating was built, to obtaindistribution of current in the conductor cross-section and electrical heating power.Besides, the numerical models of temperature of the section from the well bottomzone to the position of starting heating, the section from the position of startingheating to the position of working fluid level and the section from the position ofworking fluid level to the wellhead were built during the hollow pumping rodelectrical heating recovery. And the theoretical temperature model of the whole wellwas based on the heat transfer theory and energy conservation law, consideringthe coupling effect by geo-temperature field. By the iterative formulas, the curve ofwell’s temperature distribution was gotten after setting the initial parametersreasonably. Based on the theoretical temperature model of the hollow pumping rodelectrical heating well, the models of the tube electrical heating well and theelectromagnetic heating well was built.For the special working condition of the downhole temperature monitoring inthe electrical heating well, the downhole temperature monitoring system solutionbased on the all distributed Raman fiber optic sensor was adopted, after theanalysis of the principle of real-time temperature measurement with Raman fiberand its advantages. And the bare fiber was packaged by the GFRP-TPEE packaging structure, because of the bad conditions for downhole monitoring, theoptical fiber being easy to wreck and corrode, and requirements of long-distancemeasurement. Then the temperature sensitivity of the packaged fiber optic sensorwas calculated with the steady-state heat transfer principle. Meanwhile, the staticcharacteristic of sensor was obtained by the performance experiment.This paper got the complete wellbore temperature distribution curve withMATLAB, which is based on the hollow rod electrical heating theory model. Andthe downhole distributed temperature monitoring system of the electrical heatingwell was built, with which the tube’s temperature distribution curve was gained bymonitoring after three-hour hollow rod electrical heating. After comparing thetheory curve with the experimental curve, the theoretical calculation error waswithin a reasonable range and the theoretical model was proved feasible. Theelectrical heating parameters’s influences on wellbore temperature distribution wereanalyzed, with the established temperature theoretical model and ANSYSsimulation model of the hollow rod electrical heating well. Then electrical heatingparameters of the test well was optimized with the goal of improving the heatingefficiency and reducing energy consumption, considering the safety of theequipment. At the same time, taking a certain well in YiTong area for example, theeffect of the number of the segments with different heating power was studied,which is on the wellbore temperature curve. At last, the optimal segmented heatingprocess was chosen, considering the energy saving and the convenience of hollowrod’s manufacture and installation.