| Gas wells in Qiaokou Gas Field, which is a deep gas-condensate reservoir with lowpermeability and low porosity, are encountering problems of short stably productionperiod, quick reduction in both gas production rate and tubing pressure, severe wellboreloading, etc.. These problems directly impact the stable or normal gas production of thegas field. Therefore, wellbore unloading techniques may become the critical bottleneck ofdeveloping Qiaokou gas-condensate field. This paper aims at studying the status and lawsof wellbore loading, screening out suitable unloading technologies for Qiaokou field, anddetermining specific unloading technique according to the geologic characteristics of thefield and gas well conditions in various development stages, in purpose of improvingunloading effectiveness and extending the stable production period of gas wells inQiaokou gas field.Major studies and achievements(1)Study of status and law of well loadingWell loading status is studied using kinetic energy factor. A kinetic energy factor of 8is selected, with reference to the statistical data of gas wells in Zhongyuan Oilfield, to bethe lower limit for identifying annular flow. By analyzing the factors impacting liquidcarrying capacity and using modified liquid droplet model, a relationship of tubingpressure and tubing size vs minimum gas rate capable of carrying liquid in Qiaokou fieldhas been developed. And the law of liquid loading in gas wells of Qiaokou is concludedby using the data of flowing pressure gradients, and differential pressure between tubingand casing.(2)Suitability study and development research of well unloading technologiesSuitability of current well unloading technologies is analyzed in this paper andunloading technologies of slim tubing, plunger gas-lift, gas-lift by skid-mounted N2 unitand complex unloading technology are determined for applying in Qiaokou field,simultaneously supported by pumping unit and ESP. All these suitable unloadingtechnologies are researched.(3)Well selection criteria and well unloading plan for performing unloadingtechnologies of slim tubing, plunger gas lift, gas lift by skid-mounted N2 unit andcomplex unloading technology are determined, in accordance with the geologiccharacteristics of Qiaokou gas field and the well conditions in different developmentstages. The results of unloading technique of gas-lift by skid-mounted N2 unit performedon wells Qiao 74 and Qiao 81 demonstrate that it is the most suitable unloading techniquefor deep gas-condensate field of low permeability and high formation pressure.Results of studies show that slim tubing unloading technique is suitable for applyingin initial development phase so that gas wells with low productivity can be put intoproduction by using slim tubing unloading technique;in the middle phase and tail phaseof development, so long as the formation pressure is OK, wells incapable of flowing canreturn to flow by unloading the wellbore using plunger gas-lift;the technique of gas-liftby skid-mounted N2 unit can be used as a temporary unloading method for maintainingnormal gas production and daily wellbore unloading;for establishing sustained productionin gas wells with liquid loading, other more suitable unloading techniques must beconsidered. When a specific unloading technique can not work effectively, complexunloading technology can be attempted.Results of the studies achieved in this paper can be made use of for performingwellbore unloading in other gas-condensate fields similar to Qiaokou. |
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