龙凤山气田大通径免钻桥塞分段压裂先导试验

Pilot tests of staged fracturing involving large-diameter drill-free bridge plugs in the Longfengshan gas field

龙凤山气田是以特低孔、特低渗储层为主的构造—岩性气藏,水平井分段压裂改造中采用的可钻桥塞通径小,压裂结束后需将桥塞钻掉,既延长投产周期,又增加施工风险。大通径免钻桥塞配套可溶球的分段压裂技术中,大通径桥塞拥有足够大的流通通道,可溶球在压裂阶段具有可靠的密封性,压裂完较短时间内可形成流道,允许桥塞留在井筒内,不干扰后期放喷或生产。室内开展了可溶性球在不同温度清水、原胶液和返排液中的溶蚀实验,发现可溶球在清水中几乎不溶解,在原胶液或返排液中均可溶解,在95℃返排液中完全溶解需要约90h,完全满足分段压裂时间的需要。在龙凤山气田3口井进行了大通径免钻桥塞射孔联作分段压裂先导试验,压裂注入总液量15 078m^3,最高泵注压力66.9MPa,停泵压力15~34MPa,平均注入排量7.8m^3/min,压后日产气14.16×10~4m^3,日产油22t,与易钻桥塞工艺相比节约施工时间6d,节省费用43万元。该技术施工后可直接进行放喷投产,充分发挥了压裂投产一体化优势,在致密低渗气藏开采中具有一定的推广价值。

Longfengshan Gas Field is featured by structural-lithologic gas reservoirs,mainly with ultra-low porosity and ultra-low permeability.The diameter of the drill-able bridge plug that is used in horizontal well staged fracturing is so small that the bridge plug must be drilled after the fracturing.This not only lengthens the period before production but also increases the risk during operation.However,the large-diameter drill-free bridge plug used with dissolvable ball can provide an enough flow path while the dissolvable ball can keep the excellent sealing performance during the fracturing and leave a flow path in a short time after fracturing.Then,the bridge plug is left in the wellbore and does not influence the open flow or the production.The dissolution experiment of the dissolvable ball was conducted in fresh water,gel liquid and the fracturing flow-back fluid.It was found that the ball cannot dissolve in fresh water but can do in gel liquid and the fracturing flow-back fluid.The time for the ball entirely to dissolve in fracturing flow-back fluid should cost 90 hours,which can effectively satisfy demands for fracturing operations in horizontal wells during effective acting time.Pilot tests were conducted in three wells in the Longfengshan Gas Field,with total volume of fracturing fluids of 15 078 m 3,the maximum pumping pressure of 66.9 MPa,pump-off pressure of 15–34 MPa and average fluid pumping rate of 7.8 m 3/min.Productivity was enhanced significantly with the total gas production rate of 14.16×10 4m 3/d and the total oil production rate of 22t/d.Compared with the drill-able bridge plug,this technique can save operational time of 6d and cost of 430 000 RMB.The research results show that the staged fracturing involving large-diameter drill-free bridge plugs can provide suitable solutions for the deeply-buried reservoirs in the Longfengshan Gas Field,where the plug drilling via coiled tubing in long horizontal section is difficult and low in time efficiency.With the advantage of integral fracturing and production,this technique can be promoted more extensively in development of tight low-permeability gas reservoirs.