The Property Characteristics And Its Application Effect Study Of Cr³⁺ Polymer Gel

In recent years, the polymer flooding has been industrially applied in some oilfields, such as Daqing, Shengli and Henan, and has already got some effects on controlling water cut and increasing oil production. However, because the long-term development has resulted in the heterogeneity of reservoir and the contradiction between intrabed and interbed more severely in the practical application, and resulted in the inefficient circling of injected fluid in the high permeable layers. Moreover, with the production increasing of heavy oil reservoir and offshore reservoir with high temperature and high salinity year by year, the polymer flooding can not meet the practical require of oilfield. In addition, as polymer flooding transiting to non-essential reservoir, available polymer with large size which is designed and produced for main layer is difficult to match the pore size of non-essential layer, so at present, in many oilfield, mechanical shearing method was adopted to change polymer molecular structure and get polymer of small molecular size, which not only increase difficulty of polymer injection technology but also cause resource waste of high quality polymer.There have been abundant researches in home and abroad on viscosity property, influential factor, molecular hydromechanics diameter, molecular microcosmic structure, and the evaluation method of flow property of polymer solution and Al³⁺ polymer gel, and some important recognition have been acquired. However, exiting work that is related with rock pore structure character is little, so is research on gel condition and flow property of intra-molecular polymer gel composed of Cr³⁺ and polymer. The main reason for the phenomenon above is short of intensive comprehension of molecular configuration of polymer and polymer gel and their flow property mechanism. So carrying out base theory study on molecular configuration and flow property of Cr³⁺ polymer gel can remedy the wrong way of evaluating gel effect only depending on viscosity index and the recognition misunderstanding that is the higher the viscosity of polymer gel the better, guide development of new high-property polymer gel product, having a very important theoretical significance and application value. On the basis of existing study outcome, making use of apparatus monitoring, core flowing experiment and theory analysis method, from the macro and microeconomic point of view, the author studied molecular hydromechanics diameter, conformation structure and property character of polymer gel formed by partially hydrolyzed polyacrylamide and Cr³⁺, influence of porous media on gel effect of Cr³⁺ polymer gel, chemical component and gel condition forming Cr³⁺ intra-molecular polymer gel, physical simulating experiment of Cr³⁺ polymer gel profile modifying, and carried out field experiment and effect analysis of Cr³⁺ polymer gel profile modifying aiming at offshore oilfield.The results show that polymer gel which have different molecular configuration can be formed through changing the gelling conditions such as electrolyte concentration of solvent water, polymer and Cr³⁺ concentration and temperature. Under the condition of high temperature, high electrolyte concentration and low Cr³⁺ concentration, cross-linking reactions of polymer molecule and Cr³⁺ mainly occur among different branched chains of the same molecule, forming polymer gel with the molecular configuration of intra-molecular cross-linking which has the localized network molecular structure, and its molecular hydromechanics diameter is slightly higher than that of polymer molecule of same concentration. Compared with polymer solution of same concentration, apparent viscosity of intra-molecular cross-linking polymer gel remains almost unchanged, but the resistance factor and residual resistance factor of it are much higher, and residual resistance factor is higher than resistance factor, showing unique flow property.Under the condition of low electrolyte concentration and high Cr³⁺ concentration, cross-linking reactions of polymer molecule and Cr³⁺ mainly occur among different molecule chains, forming polymer gel with the molecular configuration of inter-molecular cross-linking which has the regional network molecular structure, and its molecular hydromechanics diameter is evident higher than that of polymer molecule of same concentration.Moreover. The pilot test results show that Cr³⁺ polymer gel profile modifying has good effect of increasing oil and decreasing water.