Research And Application Of Plugging Technology Of Old Well In Depleted Negative Pressure Gas Storage

Aiming at the problems of serious leakage,heterogeneity and high reservoir temperature in Wen23 old well of depleted negative pressure gas storage,this paper developed a high gas tightness based on the old well plugging system of Wen96 gas storage.The temperature-resistant and slow-swelling plugging system realizes the efficient residence of the system in the missing section and effective plugging of the entire well section.The type of components of the system was optimized through systematic experimental evaluation in the room.The concentration of components was optimized through curing time and curing strength experiments of the system under different concentration combinations.The formula of the system was as follows:Superfine cement(water-cement ratio 1:1.2)+1～3%cementitious curing agent+0.3～0.5%thixotope regulator+1.4～1.8%high temperature compound retarder+6～10%grid structure forming agent+2～5%compound bridge blocking particles+0.15～0.2%high temperature suspension agent.The curing strength of the system at120℃is more than 20MPa,which can meet the standard of plugging.The application performance of the developed high-airtight,temperature-resistant and slow-swelling plugging system has been systematically evaluated.The research results show that the particle size of the ultrafine cement system is smaller than that of ordinary plugging agents and can match various types of penetration.The formation with low rate has good thixotropy and"right angle thickening"effect.The initial consistency is less than 28BC,and the temperature resistance of the system is more than 145℃,the suspension stability is good,the thickening time is adjustable from 4 to 9h,and the compressive strength exceeds 25MPa.The indoor leakage resistance simulation experiment shows that the penetration depth of the system is 45.5%lower than that of the cement plugging system in the simulated sand filling pipe core with a permeability of 12μm~2,which indicates that the system can effectively reside in the high permeability zone to reduce the leakage and improve the plugging ability.Based on the development status of the target well area,analyze the causes of gas leakage caused by the plugging of old wells in the gas storage,and choose cement retainer plugging as the most important plugging method,and propose"stratum+outside pipe+wellbore"with different gas formation conditions.The technology of plugging and squeezing,focusing on stratum squeezing,establishing old well treatment methods,squeezing radius design methods,and putting forward the plugging concept of"one segment,one adjustment",The stepwise composite injection method of pre-injection slug,anti-loss main slug and multi-layer plugging slug was established,and the evaluation method of different slug construction on site was developed to further ensure the efficient plugging of different old wells.The on-site implementation of the plugging of old wells of gas storage is mainly based on the further optimization of trial concentration and construction technology in the laboratory,according to different well conditions.The field application shows that the new system has strong plugging ability and excellent anti-leakage ability,and the standard rate of engineering acceptance after plugging is 100%.According to the situation of the leakage section,the DPW23well with serious leakage actually injected 126m~3 of multi-slugs.According to the on-site construction pressure data,the injection pressure increased normally during the injection process,up to 28.0MPa.The new system realized the injection based on the excellent anti-leakage performance.Under the condition of constant volume,the plugging performance is improved significantly.After construction,the pressure test is 15MPa,and the pressure drop within 30min is≤0.5MPa,and the pressure test is qualified,which meets the engineering pressure requirements for squeezing construction.