Study Of Weak Gel System In North Buzachi Oilfield

Petroleum is a non-renewable resource, as the continuous development of recoverytechnology, which is getting more and more difficult to be recovered. At present, most ofoilfield in China have entered high water cut stage even extra high water cut stage and thereservoir heterogeneity is more serious, which cause many regular mining technology cannotenhance oil recovery further. Tertiary recovery technology is the main method in our countryin recent times, of which polymer flooding and ternary combination flooding can eachimprove over10%and20%on the basis of water flooding. But as to North Buzachi oilfield,since water flooding, production have some enhancement, but water injection group has shorteffective time and composite water cut has improved from48.6%in2007to66.1%in2009.The water cut raise quickly, and the recoverable degree is low and only is7.8%. Regularwater plugging is not so effective and cannot maintain the production and water easily, soonly polymer flooding is not so good; At the same time, the reservoir has strong heterogeneity,shallow buried depth, high viscosity and high salinity formation water. Finally, this articleproposes weak gel system to control and displace, select its formula, discuss its influencefactor, elaborate its crosslinking kinetics and analyze the result of weak gel system in NorthBuzachi oilfield.On the condition that sodium hydrate as catalyst we compound aluminum citrate,analyze it through infrared spectrum, reveal the structure of compounding material and provethe microstructure of aluminum citrate through the microscopic structure. Finally we selectthat key polymer is SD6800, optimal polymer crosslinking proportion is40:1, theconcentration of antiprecipitant KL-502is10mg/L, the concentration of oxygen scavenger is10mg/L, the result of SEM prove the crosslinking net system on this condition of NorthBuzachi oilfield.This article probe the gelation properties and influence factor to viscosity by viscositymethod, the result show that the higher the concentration of polymer, the shorter the time ofgelation. The result of atomic force microscope prove that the size of initial period of gelationis smaller than seven days after gelation, which accord with variation of the viscosity of weakgel system with the different time. Meanwhile, at the condition of different polymer crosslinking proportion, the larger the concentration of SD6800, the more notable theinfluence of crosslinking, and the gelation time connects with the viscosity of weak gelsystem. As to optimal weak gel system, a divalent metal cation have salt thickening ability infixed concentration range, but the divalent metal cation cannot tackify and weak gel cansustain higher concentration of divalent metal cation when several salt coexist. The disciplinethat pH value influence weak gelation time is that gelation time first increase and then reduceas pH value increase. That is to say, when the system is in or close to neutral condition, thecrosslinking between polymer and crosslinking agent is slowest, and alkali and acid havecatalytic action and viscosity of system is largest this moment. Weak gel system will haveshear degradation after shear, and the broken molecule chain still exist as glue group or gluemass, which can control and block off the large pore of formation.This article identify the rheology and dynamic viscoelasticity of weak gel systemthrough Anton Paar rheometer, reveal that weak gel system has shear thinning property, andthe higher the temperature is, the less the viscosity and dynamic viscoelasticity is, and G’ isabout1Pa. The gelation reaction dynamic curve of weak gel system is η=η₀+Kt_0.9,gelation reaction is close to zero order reaction from30℃～55℃. When temperature is higher,the rate constant of gleation reaction increase and the speed up time reduce correspondingly.Finally the viscosity of gel returns to85%of initial viscosity after shearing the weak gelsystem. Weak gel belongs to intermolecular cross-linking, certain number of moleculesconnects together and the diameter of equivalent ball is larger than initial polymer. Colloidaldispersion gel belongs to inner molecular cross-linking, and molecule curl so the diameter ofequivalent ball is smaller than initial polymer.The result of weak gel physical experiment show that the slope of pressure difference todisplacement velocity curve first reduce and then maintain unchanged, that is to say, thesystem show the property of shear thinning as the displacement velocity increase and thedisplacement velocity, the displacement velocity increase as the gelation time increase.Double column in parallel show that on the one hand, weak gel can improve fluid entryprofile, increase entry fluid and recovery of low permeable zone, on the other hand, it canfurtherly enlarge microscopic swept area and recovery, which can enhance oil recoverysignificantly as to non-crosslinking of the same concentration polymer.The test parameters were optimized through numerical simulation. The test injectionvolume should more than0.15PV and the injection should last3years. The injection rateshould be125m3/d. During the weak gel test in North Buzachi oilfield, the injection pressure of well NB6103increases and then keeps stable. The injection of weak gel imposes theresistance in reservoir and controls the breakthrough of water in high permeable zone. Up toOctober2010, the increased oil has reached16736t and the enhanced oil recovery hasreached0.34%.