The Research Of SP Flooding System Based On HAWP For Sub-Layers In Daqing Oilfield

Over the past years,most OOIP of the major reservoirs in Daqing Oilfield has been displaced after efficient exploitation of polymer flooding,so substaitial Enhanced Oil Recovery(EOR)after water flooding of the sub-layers with relatively larger remaining reserves has become the main objective to maintain stable production of oilfields in the future.Compared with the main reservoir,the sub-layers have lower permeability,smaller reservoir pore radius and median grain diameter,significant increase of clay and shale content,and severe flat and vertical heterogeneity,which bring a huge problem for cost-effectively implementing conventional alkali-surfactant-polymer(ASP)flooding which applies to Class 1 reservoir in sub-layers.Moreover,the use of mid-molecular weight polymer to solve the injectivity problem under low-permeability conditions also brings problems like excessive polymer consumption,serious reservoir damage,increasing adsorption loss of surfactant and the chromatography of chemical agents and so forth.The problems above are inevitable and difficult to resolve,therefore,it is highly urgent to carry out the investigation of alkali-free and effective surfactant-polymer(SP)combination flooding technique in the sub-layers of Daqing oilfield.This research is not only a major problem at home and abroad,but also a development direction and leading frontier topic of petroleum exploration technology.In view of reservoir characteristics of lower permeability and severe flat and vertical heterogeneity in Daqing sub-layers,this paper,according to the efficient tackifying,profile-controlling and flooding properties of associative polymers generated by the special molecular structure,studied the tackifying property,hydrodynamic sizes of aggregates,injectivity and conductivity as well as profile-controlling and flooding properties of associative polymers with different molecular structures and established a method to design the molecular structure of associative polymer for SP combination flooding based on reservoir characteristics.Thus the basic molecular structure parameters of the associative polymer whose application properties can meet the requirements of SP combination flooding in Daqing sub-layers was determined through this method,Then the pilot associative polymer(DP-1)was obtained by enlarging the polymerization system.Additionally,from the point of the technical requirements generated by alkali-free SP combination flooding for surfactant,the screening and development work of surfactant was carried out and HD series gemini surfactants were finally synthesized.Then the effects of polymer associative monomer content,surfactant type and the mixing conditions on the rheological and interfacial properties of SP system were clearly recognized by thoroughly investigating the solution properties of surfactants and the interaction law between associative polymer and surfactant.As a consequence,the combination surfactant(DMN)for SP system was obtained.On the basis of the above-mentioned investigations,an SP combination flooding system(DP-t/DMN)was established and the comprehensive properties of the system were studied.The results show that,DP-1 has a good compatibility with DMN and the interfacial tension of the system can reach 10-3 mN/m order of magnitude at the surfactant concentration range of 0.03%?0.3%;the SP system with a 40 mPa·s viscosity can reduce more than 30%consumption of polymer compared with HPAM whose molecular weight is 16000 KDa and the system has better stability,anti-adsorption property,emulsifying property and injectivity and conductivity.At last,the displacement efficiency of DP-1/DMN SP combination system was estimated by physical simulation method and the injection method was optimized,so that the EOR of the SP system was further enhanced more 21.74%than water flooding under laboratory conditions,which was higher than exsting flooding effects in multiples.The findings provide an efficient approach and technical reserve for the cost-efficient development of sub-layers in Daqing oilfield,and provide reference for substantial EOR after water flooding in high clay mineral content,low permeability and high heterogeneous reservoirs.