深层页岩气井压窜特征与产能维护对策——以四川盆地泸203井区北部为例

Frac-hit characteristics and productivity maintenance strategies of deep shale gas wells:A case study of northern Lu 203 well block in the Sichuan Basin

中国页岩气勘探开发已经进入产业化、规模化的新阶段,随着页岩气钻井平台井部署数量的逐步增多,页岩气水平井压裂施工规模的逐步增大,压裂施工过程中普遍存在新井压裂时压裂液窜入老井的问题。四川盆地泸州地区下志留统龙马溪组页岩储层天然裂缝发育程度高,压窜频率显著高于一般页岩气区块,严重制约了该地区深层页岩气规模效益开发。为实现该地区页岩气压窜井的有效治理,总结了泸203井区页岩气井压窜特征,建立了考虑压窜的页岩气藏物质平衡方程及压裂液侵入量计算方法,并在此基础上开展了一系列压窜井排液复产与产能维护现场试验。研究结果表明:①泸203井区具有压窜距离复杂、压窜路径复杂、压力变化复杂三大特征;②压裂液侵入量可反映压窜严重程度,侵入量越大,页岩气井复产越困难;③提出了“包围歼灭,近排远采”的区域整体排液复产对策,现场应用效果显著,复产后区域产气量总体恢复至压窜前水平。结论认为,建立的压裂液侵入量计算方法和整体排液复产对策可为深层页岩气压窜井有效治理提供指导,并为同类型页岩气藏的产能维护提供参考和借鉴。

Exploration and development of shale gas reservoirs in China has stepped into a new stage of industrialization and largescale production.With the increasing number of shale gas platform wells and the increasing scale of fracturing operation by shale-gas horizontal well,it is a common problem that fracturing fluid flows into old wells during the fracturing of new wells.The highly developed natural fractures in the Longmaxi Formation shale reservoir make the frequency of frac-hit in the Luzhou Block of the Sichuan Basin significantly higher than that in the common shale gas blocks.The frac-hit problem of shale-gas horizontal well has a serious restriction to the large-scale benefit development of deep shale gas in this block.In order to effectively treat the frac-hit of shale-gas wells in the Luzhou block,this paper summarizes the frac-hit characteristics of shale gas wells in Lu 203 well block,and establishes material balance equation and fracturing fluid encroachment calculating method considering frac-hit.Based on this,a series of field experiments of fluid drainage and productivity maintenance of frac-hit wells are carried out.And the following research results are obtained.First,Lu 203 well block exhibits three major characteristics,i.e.,complex frac-hit distance,complex frac-hit path,and complex pressure change.Second,the fracturing fluid encroachment can reflect the severity of the frac-hit.The greater the fracturing fluid encroachment is,the more difficult it is to restore the production of a shale gas well.Third,the regional overall fluid drainage and production restoration strategy called"encircle and eliminate;fluid drainage near fracturing wells,and gas production far away from fracturing wells"is put forward,and its field application effect is remarkable,with the regional gas production after the production restoration increasing to the level before the frac-hit.In conclusion,the established fracturing fluid encroachment calculating method and the overall fluid drainage and production restoration countermeasures can provide a guidance for the effective treatment of frac-hit in deep shale gas wells,as well as a reference for the productivity maintenance of the similar shale gas reservoirs.