Synthesis And Performance Evaluation Of Hyperbranched Pentaerythritol-based Filtrate Reducer

High-temperature and salt-resistant filter-loss-reducing agents have always been the core treatment agents for drilling fluids in deep wells and ultra-deep wells,and are also the focus of research in the field of oilfield chemistry.The existing anti-high temperature and anti-salt filter-loss agents often have the problem of high temperature viscosity reduction or high temperature thickening during the use in the oilfield,which leads to uncontrollable rheological performance of drilling fluids and a series of accidents.To address this problem,this paper hopes to synthesize an anti-high-temperature filter-loss-reducing agent with low impact on the rheological properties of drilling fluid based on polymer physics and chemistry.A pentaerythritol-based hyperbranched filter loss reducer PPAAN-1 was synthesized by a free radical reaction using pentaerythritol as the core structure of the polyalkenyl monomer tetraallyl ether(PPTE),acrylamide(AM),2-acrylamido-2-methylpropanesulfonic acid(AMPS),and N-vinylpyrrolidone(NVP)as raw materials.The effects of the amount of tetraallyl ether(PPTE),the ratio of monomer masses(AMPS,AM,NVP),the reaction temperature and the amount of initiator(AIBN)on the synthesized product were investigated using AV and the API filtration loss after aging at220℃as evaluation indexes.Based on the orthogonal experiments,the effect of the amount of tetraallyl ether(PPTE)on the apparent viscosity of the filter loss reducers was further considered,and the optimal synthesis conditions for the high temperature and low viscosity filter loss reducers PPAAN-1 were finally confirmed:the amount of PPTE added was 17%,AMPS:AM:NVP=2:6:1,the reaction temperature was 55°C,and the initiator(AIBN)was 0.2%.The molecular structure,chemical composition,and thermal stability of the filter loss reducer were confirmed by qualitative characterization analysis of the product based on the synthesis of filter loss reducers with optimal reaction conditions.The results show that the high temperature resistant and low viscosity filter loss reducer consists of acrylamide(AM),2-acrylamide-2-methylpropanesulfonic acid(AMPS)and N-vinylpyrrolidone(NVP),and its molecular structure meets the original design requirements,has good thermal stability,and can meet the requirements of resistance to220℃.The performance of the high-temperature and low-viscosity filter loss reducer PPAAN-1 was evaluated in freshwater-based slurry and brine-based slurry.The evaluation results show that the filter loss reducer PPAAN-1 not only has good filter loss reduction performance,can resist 30%sodium salt and 220℃,but also compared with other foreign filter loss reducers,it can still be in good drilling fluid rheology while maintaining the filter loss reduction effect under high temperature and pressure.The self-assembled structure,adsorption with clay particles,influence on mud cake morphology and particle size distribution of drilling fluid of PPAAN-1,and the mechanism of the filter loss reducing agent were also studied.The results show that PPAAN-1 has good adsorption performance and can effectively adsorb with clay particles through its own adsorption groups,which can fix the clay fine particles in the mesh structure of the filter loss reducing agent,thus blocking the large filter loss channels.In high temperature and high pressure conditions,it can still adsorb on the surface of clay particles,avoiding the agglomeration of clay particles in spherical shape due to high temperature dehydration and the influence of Na~+,improving the hydration and dispersion of clay particles in high temperature and high salt environment,reducing the solid phase content in mud,improving the mud cake quality of drilling fluid,thus further reducing the permeability of mud cake and realizing the anti-temperature and anti-salt filter loss reduction of the filter loss reducer.