葡北油田天然气重力混相驱注气井天然气水合物的形成及防治

Formation and prevention of gas hydrate in gas injectors for gravity miscible flooding in Pubei Oilfield

葡北油田天然气重力混相驱注气井井筒内发现有水合物形成,严重影响了注气井的注气效率。基于Pipesim建模对注气井水合物形成管段及影响因素进行了分析,研究了通过提高天然气初始温度和采用水套炉加热井口天然气以预防水合物形成的技术可行性。研究结果表明,目前注气条件下,在距压缩机出口300~2000 m的输气管线及井筒深度小于1025 m的范围内具备水合物形成的温压条件;随天然气初始温度和注气速度增加,当井口气体温度低于对应水合物形成最高温度时,输气管线形成水合物段缩短,井筒内形成水合物段先增长后缩短,当井口气体温度高于水合物形成最高温度时,输气管线不形成水合物,井筒内形成水合物段缩短;提高天然气初始温度和采用水套炉加热井口天然气能够使注气压力小于40 MPa、注气速度大于5×104 m^(3)/d的注气井不形成水合物,是有效的水合物预防方法。

Hydrate is formed in the wells of the gas injectors for natural-gas gravity miscible flooding in Pubei Oilfield,which seriously impacts the gas injection efficiency of the gas injectors.The pipe sections with hydrate and the influence factors were analyzed based on Pipesim modeling,and the technical feasibility of increasing the initial temperature of natural gas and heating the wellhead natural gas by using a water jacket heater to prevent the formation of hydrate was researched.It is indicated that under current gas injection conditions,there are suitable temperature and pressure conditions for the formation of hydrate in the gas pipeline 300-2000 m away from the compressor outlet and in the well above the depth of 1025 m.With the increase of initial natural gas temperature and gas injection rate,when the wellhead gas temperature is lower than the highest temperature for the formation of corresponding hydrate,the gas pipeline section with hydrate gets shorter and the hole section with hydrate gets longer first and then shorter;and when the wellhead gas temperature is higher than the highest temperature for the formation of corresponding hydrate,no hydrate is formed in the gas pipeline and the well section with hydrate gets shorter.What’s more,increasing the initial temperature of natural gas and heating the wellhead natural gas by using a water jacket heater can prevent the formation of hydrate in the gas injectors with gas injection pressure less than 40 MPa and gas injection rate more than 5×104 m^(3)/d,so it is an effective hydrate prevention method.