Daqing Oilfield Associating Polymer Oil Displacement Efficiency And Mechanism

It's very important for Daqing oilfield to invest and/or develop a favorable EOR because Daqing oil field is the biggest one in China, as well as 20ed in the world. Most investigations show that a Yumen oil field be developed if oil recovery of Daqing should be increased by 1% Original Oil In Place (OOIP). Actually, Polymer flooding is the most favorable one of EOR technologies in Daqing oil field resulted from successes in both technique and economy through pilot, industrial and business tests because of oil production of 120-150t of a ton of polymer or that of 10%-12%OOIP of oil recovery.The HPAM displacement mechanism is thought traditionally as to increase brine viscosity, to improve mobility control ratio, to decrease brine permeability so as to improve sweep efficiency but displacement efficiency. But in this decade, some of experts, investigators, researchers and professors suggest that HPAM flooding is not only improve sweep efficiency but also do displacement efficiency, somewhat same as surfactant. This results from the viscoelastic behavior of HPAM molecules due to the elongation, deformation and relaxation because of the molecule flexible as HPAM solution moves through out a converged throat or conversely. The viscoelastic behavior of HPAM molecules is of improving displacement efficiency. This opinion was proved by microscopic displacement technology while the quantification was not carried out.Unfortunately, the most favourite of polymer flooding is not appear in Daqing oil field because of shortage of rheology, especially viscosity of polymer solution although polymer flooding technology has been used in the level of business. Actually, HPAM is widely used as a viscosifying agent in polymer flooding in Daqing oil field. The HPAM solution viscosity is decreased seriously because of existing of cations, especially of ion Ca²⁺, Mg²⁺. For example, the apparent viscosity of 1000mg/l of HPAM is 40-50mPa.s using fresh water (salinity is 918mg/l) to solve and dilute, but 15 mPa.s using produced brine (salinity is 3600-4000mg/l, concentration of ion Ca²⁺, Mg²⁺ is 20-40mg/l) to solve and dilute at 45℃ of reservoir temperature. Secondly, the viscosity loss is 50-70% because of shear degradation at 4000^-1-6000s^-1 of high shear rate.So it's very important for us to develop new polymers which are of high viscosifying, salt-toleration, shear toleration, thermal and thermo toleration and long period stability. This is a good way to improve deeply technical and economic interests of polymer flooding.At the state of the art, Hydrophobic Associating Water-Soluble Polymer (HAWSP) is the favorable polymer for flooding, which is of high viscosifying, salt-toleration, shear toleration, thermal and thermo toleration and long period stability. It's essential for thepolymer is that some hydrophobic chemical groups be inserted in the long main chains of HPAM molecules so as to form 3D reversible super-molecular net structure. So the viscosity of HAWSP solution is higher than that of HPAM although molecular weight and concentration of HAWSP lower than that of HPAM. For the HPAM, the favorable way to viscosify is to improve the molecular weight.It's obvious that the HAWSP is of characteristics of thermo and thermal toleration, salt-toleration, shear toleration, and viscoelasticity, so it's of good promise for the future. It's very import to study or investigate the microscopic displacement mechanisms, rheologies, viscoelasticity and quantification of displacement efficiency of HAWSP because the structure of HAWSP is different from that of HPAM. You know some of them for HPAM are not understood throughout.The aims of the paper are: (1) to understand thoroughly the microscopic displacement mechanisms in porous media, and rheologies and viscoelasticities of HAWSP solution, (2) to quantify the displacement efficiency in order to optimize HAWSP injection process, and (3) to optimize the polymer simulator of which is included the characteristics of HAWSP and displacement efficiency.Results of this paper as follow show that the apparent viscosity, n ?, of HAWSP solution is sum of structural viscosity, n, and bulk viscosity, n b. HAWSP is of favorable salt toleration. The apparent viscosity decreases slightly as salinity increases in the range of 0-lOOOOmg/l. This implies Daqing produced brine could be used in HAWSP technology. HAWSP is of favorable shear toleration. The long period stability or aging test is favorable. And the Resistance Factor and Residual Resistance Factor are 14.51, 3.63, respectively, for the HAWSP brine on Daqing reservoir cores, but 10.51 and 1.71 for HPAM fresh water at same viscosity.Oil recovery of HAWSP brine is higher 3%-4%OOIP than that of HPAM fresh water at same chemical slug and viscosity. This results from the micro-sweep efficiency and displacement efficiency.The rheologies of HAWSP brine are very complex as HAWSP concentration lowers than Critic Association Concentration (CAC). The apparent viscosity decreases sharply as increase of shear rate in range of 0.02'1-0.07s'1. This maybe results from the disappearance or decrease of associating degree or level although the association exists a little. It is a constant in the range of 0.07"1-5.0s"1 of shear rate. In this situation, the apparent viscosity increases because the association existing inner molecules transferred to that existing inter-molecules, but it decreases because association disappears or associating degree or level decreases due to the shearing. The apparent viscosity depends on the difference. Therheology of HAWSP brine is of characteristic of pseudo-plastic solution. The rheologies of HAWSP brine are also very complex as HAWSP concentration is higher than CAC. The much higher HAWSP concentration is, the more obviously pseudo-plastic characteristic of HAWSP brine appears, and the more lower shear rate range is of which Newton fluid is. Based on laboratory experiment, all data in pseudo-plastic range is in line with Power-Law Model. The corrective coefficient is 0.97 as concentration of HAWSP is higher than CAC. Microscopic experiment results in laboratory show nine mechanisms of HAWSP may displace efficiency in porous media. Actually, one or more of them is/are of displacing efficiency. Microscopic experiment results in laboratory exhibit that main mechanisms which displace efficiency of HAWSP in porous media at the conditions of Daqing reservoir are: viscoelasticity, deformable piston flowing and emulsification flowing.RRFs of glycerol on Daqing reservoir cores are the constant of 1. This results from that the glycerol molecules could not be adsorbed or/and retentioned on rock because of its inorganic while produced brine or/and fresh water is injected as a buffer.Oil recovery of xanthan solution increases slightly as injection velocity increases in the permeability range of 317X103 u m2-1823X103 u m2. But final oil recovery increases obviously as a HAWSP chemical slug size is injected. The level of increase of oil recovery in 0.5m/d-1.5m/d of injection rate is higher than that of in 1.5m/d-5.0m/d. The displacement mechanisms and viscoelasticity could be used to explain the results.The concentration of HAWSP is a key or important factor affecting seriously on displacement efficiency. But both permeability and injection velocity affect slightly on it as the concentration of HAWSP is lower than CAC. This implies the difference between oil recovery of HAWSP and that of xanthan goes to zero.Displacement efficiencies on homogenous cores compacted conform favourably with those on Daqing reservoir cores and stratiform heterogeneous cores compacted. The function of displacement efficiency as permeability, injection rate, and concentration of HAWSP, has been obtained in the paper.