Study on Formulation with Lower Initial Viscosity Gel/Alkali/Surfactant/Polymer After Polymer Flooding and Scenario Design of Field Test

Abstract

The blocks of polymer flooding have gradually entered into the stage of chase water flooding after polymer flooding in Daqing Oilfield and the comprehensive water cut is close to the exploitation limit of 98%. So it is urgent to develop some new technologies to further enhance oil recovery after polymer flooding. On the basis of laboratory research, a field test of alkali/surfactant/polymer flooding was carried out after polymer flooding in Daqing Oilfield in 2015, which achieved good development effect, but the polymer concentration was relatively large. Based on the field test of alkali/surfactant/polymer flooding, a new technology of the lower initial viscosity gel/alkali/surfactant/polymer flooding has further been studied according to the technical route combining plugging, adjusting and displacing, which can reduce the polymer dosage greatly under the premise of ensuring good oil displacing effect. In this paper, some laboratory studies are carried out, which realize significant technology breakthrough. Firstly, the adjusting and plugging agent of lower initial viscosity gel is screened out, which can be injected into the high permeability layers of low flow resistance like the water and migrate to the deep location of the high permeability layers and then gelatinize on spot. Therefore it can plug high permeability layers effectively and does not pollute the middle and low permeability layers at the same time. Secondly, the injection parameters of lower initial viscosity gel/alkali/surfactant/polymer system are optimized. The results of laboratory experiments show that the lower initial viscosity gel/alkali/surfactant/polymer system can enhance oil recovery by 13.5% OOIP under the optimal injection parameters, which is 1.2% OOIP more than that of the alkali/surfactant/polymer flooding and can save polymer dosage by 17.8%. In view of the good results obtained in laboratory experiments, the scenario design of field test is carried out and the incremental oil recovery is 10.1% OOIP predicted by numerical simulation. The field test is expected to start chemical flooding in 2021.