| China's heavy oil resources are rich,so far proven geological reserves is 16 tons of heavy oil.Thermal oil recovery(mainly steam flooding and steam huff and puff)is the main method of oil reservoir exploitations in china.Daqing heavy oil thermal recovery,due to the factors of reservoir heterogeneity,oil mobility ratio difference,resulting in steam channeling phenomenon,and difficulty is brought to the effective development of Daqing heavy oil.In this paper,the problem of steam channeling is in steam flooding and steam huff and puff of heavy oil block in Daqing,comprehensive analysis of previous chemical plugging technology of steam channeling.According to the technical characteristics of field thermal recovery of heavy oil,and put forward the PVA modified urea formaldehyde resin as steam channeling sealing agent,to the heated reversible gel as a technical scheme steam channeling sealing agent.First of all,through orthogonal experiments,the influence of various factors on the synthesis of urea formaldehyde resin was obtained.Then the best synthesis para meters were obtained by single factor experiment.The molar ratio of formaldehyde t o urea was 1:1.5,the addition of PVA is 0.5%,The joined proportion of urea was 70:25:5.The synthesis of modified urea formaldehyde resin was characterized by IR and injection.The study of PVA modified urea formaldehyde resin content,type an d concentration of curing agent,curing agent concentration on the effect of delayed solidification time and strength,and ultimately determine the best steam flooding cha nneling sealing agent formula system: 50%PVA modified urea formaldehyde resin cu ring agent +500mg/L ammonium chloride + 1000mg/L~10000mg/L delayed curing ag ent of ammonium sulfate.Secondly,the performance evaluation of above formula system,including: temperature resistance,salt resistance,aging resistance,shear resistance,plugging performance,etc..The evaluation results show that the formula system aging 60 d compressive strength at 300? can still reach 30Mpa;gelling again in the 3200r/min for 1min,the compressive strength can reach 35Mpa;In the 10000mg/L mineralized water,the state of the gel is still white uniform solid,the solid core plugging rate was more than 96%.Thirdly,the sealing agent for steam huff and puff was studied.From thermally reversible gel plugging mechanism and gelling mechanism,the MC20,MC450,HPMC50 three kinds of cellulose ethers with thermal reversible property and good gelling condition were screened,and the effects of main agent dosage on viscosity,gelation temperature and water content were studied.By adjusting the amount of water and the gelling temperature of the gel,the formula of the steam huff and puff agent system was determined as follows: 6.5%MC20+(1%~5%NaCl,1%~10% urea,1%~10%NH4SCN).Finally,the performance evaluation of the steam huff and puff agent system was carried out.The evaluation includes: salt resistance,thermal stability,sealing performance,etc.The results showed that the viscosity of cellulose ether gel with the same mass fraction changed a little with the increase of salinity at 80;After 86 hours of 200? temperature,the thermally reversible gel is still able to gel;The core plugging rate can reach 95% and the plugging strength can reach 3.08 MPa.According to the results of laboratory studies,it can be concluded that the above two kinds of sealing agent can be used to achieve the sealing effect of steam channeling in Daqing,which is of great significance to enhance the recovery of heavy oil in Daqing. |
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