长宁页岩气水平井柱塞工艺技术研究与应用

Horizontal-well plunger technology and its application to shale gas,Changning block,Sichuan Basin

长宁页岩气井初期压力高,产气量大,能够自喷带液生产,但递减较快,进入低压小产量阶段后,自身能量无法将井筒内液体带到地面,气井估算最终采出量的40%需要靠人工举升采出。柱塞工艺作为主要的排水采气技术措施,在页岩气水平井的应用中存在一些难点,如井下限位器的设计、工艺介入时机的选择、水平井钢丝的作业难度等。针对这些问题,通过建立一套可视化井筒气液两相流实验模拟装置,设置不同的液量、气量、井斜角度及流速,观察气液两相的井筒流动规律,同时综合考虑其他因素得出结论,从而指导工艺实施目标井段与工艺介入时机,并在此基础上进行钢丝作业工具的配套、柱塞工具的选型,形成了适用于长宁页岩气区块的一套柱塞工艺技术。实验结合现场的研究结果表明:①井斜60°~70°附近为柱塞工艺实施的最佳目标井段;②日产气量降到1.2倍临界携液流量之前,为柱塞工艺的最佳介入时机;③引入滚珠扶正器、井下飞轮以及研制滚轮柔性短节等低摩阻工具,解决了工具串在水平井大井斜角施工时的摩阻问题;④优选出柱状柱塞、旋转柱塞作为长宁区块主体柱塞。经现场应用,这一套柱塞工艺技术的施工及运行效果良好。2020年在长宁页岩气井中成功实施柱塞工艺87口井,工艺后平均单井日增产气量0.5×10^(4) m^(3),年增产气量1.02×10^(8) m^(3)。

Despite the natural flow,large gas production,and initially high pressure,some shale gas wells in Changning block,Sichuan Basin,show a quick production decline.In particular,producing energy in the period of low pressure and low yield is not sufficient to carry the liquid from wellbore to surface,and 40%of estimated ultimate recovery(EUR)will be lifted artificially.Plunger is a major technology for drainage gas recovery.But,its application to shale gas horizontal wells is confronted with some issues,e.g.downhole positioner design,intervention timing,and operational difficulty of horizontal-well wireline.So,a plunger technology was presented for shale gas production in this block.Specifically,a visualized experimental simulation facility was established to observe the gas-liquid two-phase flow at wellbore under different fluid volume,gas volume,borehole inclination,and flow velocity.Moreover,coupling with other factors,the conclusion was made to designate horizontal sections for operation and intervention timing.In addition,some supporting tools for wireline operation and appropriate plunger were selected.Results show that(1)the borehole section with inclination of 60–70°is optimal for plunger operation;(2)the time before daily gas production rate decreases to 1.2 times the critical liquid-carrying flow rate is also optimal for plunger operation;(3)ball centralizer,downhole flywheel,and such tools with low frictional resistance as flexible roller pup joint can help address the issue of frictional resistance against the tool string in a horizontal well with large inclination;and(4)both cylindrical and rotary plungers are the best candidates for shale gas production in Changning block.Its application has proved a good performance.In 2020,the application to 87 shale gas wells in this block demonstrates the gas production increase by 0.5×10^(4) m^(3)/d and 1.02×10^(8) m^(3)/a,individually.