Preparation And Performance Optimization Of Composite Water-absorbing Resin Workover Fluid System

At present,the leakage problem in workover operation is more and more frequent,especially for those oil and gas wells whose reservoir pressure coefficient is complex and changeable due to long-term unbalanced injection and production.The lost circulation causes the leakage of solid and liquid phases in the workover fluid to the depth of the formation,which not only causes the waste of workover fluid,but also causes the decline of production after workover and the long recovery cycle of productivity.More seriously,it will damage the physical and chemical balance of the reservoir and cause damage to the reservoir that is difficult to repair.Therefore,it is of great significance to develop a reservoir protective workover fluid system that can be both blocked and unblocked.An organic/inorganic composite water absorbing resin temporary plugging agent（P-AAMT）was synthesized using 2-acrylamide 2-methylpropane sulfonic acid（AMPS）,acrylamide（AM）,and modified montmorillonite（O-MMT）as raw material,N N’-methylene bisacrylamide（MBA）as crosslinking agent,and ammonium persulfate（APS）-sodium bisulfite（OS）as initiator.The research results indicate that the delamination of O-MMT under the action of intercalation agents and polymerization reaction heat is distributed in the polymer matrix,which enhances the cross-linking strength of the polymer and makes P-AAMT exhibit stronger compressive and thermal stability performance.The controlled released encapsuled breaker（CREB）with a double-layer coating structure was prepared using cellulose as the coating material by an extrusion spheronization-Wurster fluidized bed coating method.The research results indicate that only adjusting the viscosity or thickness of the coating solution cannot achieve sustained release.Only by extending the migration channel of stearic acid in the inner layer through a double-layer coating structure can the sustained release effect be achieved.Based on the reservoir and water quality characteristics of the oil production S plant,a high efficient and low damage workover fluid system（LDHE）has been developed through formula optimization.The formula is:standard brine+3%P-AAMT+2%Ca CO₃+4%CREB+0.3%XG+1.5%TDC-15+1.0%CI-109+0.3%OB-2+0.002%THPS.The research results indicate that LDHE workover fluid has good thermal stability,rheological properties,salt resistance,and good compatibility with formation water.The indoor experimental results show that the workover fluid has good sealing and reservoir protection capabilities at 100℃,with a leakage rate of only 5.8%and a core permeability recovery value of 92.13%.