川西侏罗系气藏气井井底污染类型分析与净化工艺应用

Downhole Pollution Types Analysis and Purification Process Application for Gas Wells of Jurassic Gas Reservoirs in Western Sichuan Basin

目前川西地区已开发的侏罗系气藏进入低压低产阶段,部分气井存在不同程度的井底污染。通过气井生产历史及动态特征,借助动态监测手段,可以间接反映气井是否存在污染;通过直接对气井返排物进行分析,可以确定污染物的类型。川西侏罗系气藏气井目前存在的污染类型主要有:残留压裂液/砂污染、泥浆漏失污染及泡排药剂乳化污染。由于气井普遍自身能量较低,仅依靠化学药剂开展井底净化效果不佳。因此,目前普遍采取"化学净化+物理助排"组合工艺,确保污染物在能稀释溶解的同时也能排出井筒。具体组合工艺主要有三种:"井底净化+放喷"适用于产量略低于临界携液流量的气井;当气井自身产量远低于临界携液流量时,依靠放喷无法有效返排出井底污染物,可采取"井底净化+车载气举";当污染气井需要配合开展气举作业但附近无气源时,可采取"井底净化+槽车气举"。

At present,the developed Jurassic gas reservoirs in Western Sichuan Basin have entered the stage of low pressure and low production,and downhole pollution at various degrees appeared in partial gas wells.Production history and performance of the gas wells and dynamic monitoring can indirectly reflect whether there is pollution in the gas wells.Analysis of flowback material in the gas wells can determine the type of pollutants.The major types of downhole pollution in the gas wells of Jurassic gas reservoirs in Western Sichuan Basin are residual fracturing fluid&sand,mud loss and emulsification of foam drainage agents.The effect of purification by chemical agent only is not good because of the low energy of gas wells.Technology combination of chemical purification and physical drainage is adopted to ensure the pollutants to be diluted and dissolved and flow away from the well.Specifically,there are three combinations:downhole purification with blowout may be applied to the gas well that its production is lower than the critical liquid carrying flow rate,bottomhole purification and gas lift on board may be applied when the pollutants can′t flow back effectively by blowout for much lower production of gas wells than the critical liquid carrying flow rate,and bottomhole purification and gas lift by tanker may be applied when the gas lift should be done for the polluted gas wells without gas source around.