Optimization And Evaluation Of High Strength Chemical Gel Plugging System

Hang jin qi block is a key development area of Dong sheng gas field in Ordos Basin.The Liu jia gou stratum in this mining area is broken and micro crack are developed,and crack leakage is easy to occur.Conventional plugging technology is difficult to solve the problem of leakage in this area,but the plugging system of Chemical Gel can effectively block the lost circulation.At present,the research of the plugging system is still in the primary stage,and further improvement is needed.In view of the existing shortcomings,the basic characteristics,formulation optimization and modification tests of the Chemical Gel plugging system were carried out in this paper.The compressive strength,rheology,safe construction time and plugging ability are improved.The specific conclusions are as follows:(1)CJ-1 and JL-1 are mixed with water to form the Chemical Gel slurry.Under certain conditions,it can be consolidated into the Chemical Gel solid.The research shows that the density of Chemical Gel is between 1.42g/cm~3～1.56g/cm~3,with low density and small disturbance to stratum.The AV is not higher than 52 m Pa·s,the PV is not higher than 35 m Pa·s,and the YP is not higher than 20 Pa,so it has good pumpability.The higher the temperature and pressure,the shorter the thickening time.The higher the temperature,the higher the compressive strength.The optimum formula CG-1 has the highest compressive strength at 120℃,the compressive strength at 8h of high pressure curing is 24.1MPa,and the compressive strength at8h of high pressure curing at 160℃is 17.0MPa.Under low temperature,prolonging curing time can improve the compressive strength of Chemical Gel.(2)The dispersant can improve the rheology of the plugging system of the Chemical Gel,reduce the viscosity and improve the pumping ability of the system.USZ was selected as the dispersant for the plugging system of Chemical Gel.The compressive strength of CG-2(CG-1+0.3%usz)cured at 120℃for 8h under high pressure is up to 25.1MPa,which still keeps high strength.(3)The retarder GH-9S and the retarder GH-8 can extend the thickening time of Chemical Gel plugging system under high temperature and high pressure conditions and improve safe construction time.GH-9S is easy to reduce the viscosity of the system and the stability of the system.Using sodium bentonite to improve the stability of the system,the content of GH-9S in the Chemical Gel can be increased,so as to prolong the thickening time effectively.7%sodium bentonite+2.4%GH-9S can prolong the thickening time of CG-1 at 140℃/90MPa to 242.3min.GH-8 has little effect on the rheology of the plugging system and has good temperature resistance.Under 160℃/100MPa,1.6%GH-8 can prolong the thickening time of CG-1 to204.2min.(4)Calcium carbonate,ultra-fine and polysilicon fiber can be used as plugging agent for plugging system of Chemical Gel,so as to improve plugging ability.Calcium carbonate ultra-fine has a weak procoagulation effect on Chemical Gel,which can improve the compressive strength of Chemical Gel in a small range.Polysilicon fiber has good retardation effect on Chemical Gel,which makes plugging operation safer,but has a slight effect on reducing strength.(5)The plugging system of Chemical Gel has good antifouling ability for saturated saline solution and drilling fluid.