The Research Of Mechanism And Technique On Polymer Flooding Decreasing Pressure And Enhancing Injection Ability

According to the investigation actuality of the basic theory study on polymer flooding,surfactant solution decrease pressure of injection and increase ability of injection, this paper study systemically on viscoelasticity of polymer, permeability mechanics and enhance oli recovery, surfactant solution decrease pressure of injection and increase ability of injection. Base on result studied, high-concentration polymer flooding and surfactant solution decrease pressure of injection and increase ability of injection was studied at the same time. The results of the study are significant to enrich the basic theory study of relative fields and accelerate development of these subjects.The research results of the paper can be divided into four special topic, which will be briefly introduced separately as follows:1. The viscoelasticity of polymer solutionThe viscoelasticity of HPAM and xanthan gum(XA) was study by experimental testing in this part, the factors affect on viscoelasticity was analyzed too.Through steady shear flow experiments and dynamic mechanics experiment, the purpose are disclosing difference of viscoelasticity between HPAM and xanthan gum, effect of viscoelasticity rule on various factors.It is shown that first normal force difference and apparent viscosity of HPAM solution increase with the increase of shear rate or molecular weight or concentration or the decrease of salinities, and that the viscoelasticities of XA solutions also increase with the increase of concentrations as HPAM solutions. No obvious difference exists between the energy-storage moduli and the loss moduli of both types of polymer solutions. There was a good linear relation between elastic viscosity/shear viscosity and shear rate. Under seepage flow of oil reservoirs, It can occur a elongation flow of HPAM solutions.2. The pilot test and laboratory test of high-concentration polymer floodingThe results on artificial cores with a Dykstra-Parson Coefficient of 0.72 show that an incremental recovery over water flooding of more than 20% OOIP can be obtained by early time injection of the high molecular weight, high concentration polymer solution, the earlier the better. The incremental recovery is comparable to alkali/surfactant/polymer flooding but at a lower cost.In Daqing Oil Field, a pilot test of high concentration polymer injectivity was conducted on 6 injection wells in August 2002. Three wells are injecting in high permeable pay zones and the other 3 wells in low permeable pay zones. The range of effective permeability (Keff) of the pay zones is 0.354 ~1.06 um2. The results show that high permeable formations (Keff>0.890 um2) are suitable for continuous injection of high concentration polymer solutions (concentration 2,000 ppm ~ 2,500 ppm, molecular weight 17 million Daltons, viscosity 200 ~ 250 mPa.S). In September 2003, the average fluid production of each well was 94.2 tons per day, the average daily oil production of each well was 23.7 tons and average water cut was 74.9%. Compared to low concentration (1,000 ppm) solution flooding, the average fluid production per day of each well remained steady, the daily oil production of each well increased 6.2 tons (an increase of 35.4%) and the average water cut decreased by 6.6%. The results show that the injection of high concentration polymer fluid is very effective and the pilot area will be further expanded.3. The experiments and mechanism of surfactant solution decrease pressure of injection and increase ability of injectionIt is shown that: high-concentration polymer's inject pressure decrease 47.86%~67.01% after NOS inject into core 1.0 PV; the inject pressure was not up after inject into core 90 PV polymer solution; the lower of NOS interfacial tension(IFT), the lower high-concentration inject pressure.The mechanism of surfactant solution decrease pressure of injection and increase ability of injection are: (1) Get rid of polymer film on the wall of sandstone by inject one of oxidant solution. (2) Surfactant washes out part of residual oil and largen permeability. It is shown that, the amount of moving oil increased, the amount of residual oil decreased, the oil and water's equal permeability move to right; the area which water and oil are both exist is wider. (3) There is an adsorptive film formed by injecting surfactant on the wall of sandstone, the film is thiner than that of polymer, so it affect little on permeability. Otherwise, the surfactant film can prevent polymer thick film rebuilding, so permeability is not down more.4. The pilot test of decrease high-concentration injecting pressureThe data that six well pilot test shown that: it did decrease high-concentration injecting pressure after the surfactant decreased pressure technic or resin sand fracture technic were employed. The result after using technic above accord with demand that pressure is lower than cracking pressure. It is much better that surfactant decreased pressure if permeability is higher. The period of increasing injection which use surfactant is 2 times more than common fracture. If interlayer is better, and it is necessary that monolayer increase injection, resin sand fracture is predominant, otherwise, the surfactant is better.It is shown that polymer with high-concentration and high- molecular weight solution flooding recovery is 18~24%, and it break through the limit that polymer flooding recovery is 12%. The higher concentration, the higher recovery enhanced. So high-concentration polymer solution can enhance oil recovery further more.