Downhole throttling designed for ultra-high pressure gas wells in western Sichuan Basin and technologies of putting into production
Recent years have witnessed the growing emergence of ultra-high pressure gas reservoirs with the advancement of natural-gas exploration and development.In central Sichuan Basin,some gas wells with ultra-high pressure reveal the initial formation pressure up to 130 MPa and the shut-in wellhead pressure achieving 110 MPa,respectively.Traditional techniques and processes to control gas hydrate are inadequate to secure the safe production in such wells.In contrast,the technology of downhole throttling,as an efficient control means,can not only improve the safety of gas production,gathering and transmission system but reduce surface-construction costs.And it has been widely applied to Southwest Oil&Gasfield,and Changqing and Tarim Oilfields.It is also urgent to make a feasibility study on its applica-tion to ultra-high pressure gas wells in central basin.Thus,taken some methods to calculate key parameters into account and combined with in-situ parameters,both design and application of downhole throttling process were discussed for those wells with ultra-high pressure.More-over,deviation factors calculated from DAK,LXF and modified LXF methods were compared with the measured one,which indicates that the LXF method is more suitable for this sort of gas reservoirs;(ii)two parameters of both throttle depth and orifice diameter are involved in throttling design.The depth can be attained from repetitive calculation by putting relevant parameters into corresponding formula,so as to enable the temperature after throttling to be higher than the hydrate-generating temperature at the parallel depth.The diameter is selected with all consideration to pressure,temperature,and expected production;(iii)for these gas wells,during the period from well opening to sta-ble operation of the downhole throttle,wellhead is confronted with high-pressure throttling.As a result,preventing wellhead pin valve from ice blockage at the moment of well opening is critical for the safe production in a certain well where downhole throttles are landed;and(iv)for ultra-high pressure gas wells in different blocks,all variations in wellhead pressure,temperature,gas production and undercooling degree of gas hydrate with time under different well-opening systems were simulated by using transient software,so that an optimal system is select-ed to ensure these wells in smooth production.These research results lay a foundation and provide a technical option for in-situ application of downhole throttling to ultra-high pressure gas wells in western Sichuan Basin.
Ultra-high pressureDownhole throttlingDeviation factorChart methodDAK methodLXF methodPutting into pro-ductionWell opening
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