Research And Application On Sealing Channeling And Remedying Casing Leakoff System For Pucheng Oilfield

After 30 years of development,the formation had been washed for a long time,there have been forming large pores;Duing to excessive development and injection,cementing quality,perforating,construction and oil wells mismanagement,the cement outside the casing has been damaged,which leaded to the formation of channeling,that seriously affected the normal production of oil wells in Pucheng Oilfield.Cement and resin sealing agent which are commonly used are easy to leak off before solidification,so they can not effectively reside in the blocking layers.What's more the resin sealing agent can't remain stable in high temperature environment.In addition,the conventional sealing channeling methods are difficult to determine the dosage,at the same time,because the slurry has good rheology,bad suspension property,bad consolidation property,short thickening time,long initial setting time,brittleness,after the sealing agent was injected into the sealing layer,it is easy to leak off and precipitate before solidification,which lead to the low success rate in the first time.Aiming at solving the problem of Pucheng Oilfield and the weakness of the current sealing agents,we developed a thixotropic sealing system.This sealing agent has good thixotropy and “right-angle thickening” feature that can be a good solution to the existing problems of current sealing agent.According to the high temperature and high salinity conditions in Pucheng Oilfield,we designed the dosage of the main agent and the additives.Through a series of experiments,we researched the effect of the main agent's and additives' dosage on the thickening time,compressive strength,thixotropic,rheological properties and so on and determined the best formula of the thixotropic sealing agent: W/C=1:4+suspending agent 10~15%+gallant 1~3%+thixotropic agent 0.3~0.5%+low temperature coagulant 2.5%~3.5%(when the temperature is between 40~60?)+FH high temperature retarder 2.0~3.0%(when the temperature is between 120 ~130?).In order to meet the requirements of the oilfield,we evaluated the salt resistance(compatibility with the formation),curing time and compressive strength at different temperatures,thixotropic,suspension,water loss under high pressure,“right-angle thickening” properties,sealing performance and testing the thickening time of simulated field injection process.After been used in the oilfield,it indicated that thixotropic sealing agent can effectively improve success rate and extend the period of validity,and the process is simple,the construct cycle is short,it can save more than 40~50% cost than the conventional overhaul technology,and the ultimately input-output ratio can be as large as 1:3.