Study On The Preparation And Application Of Salt-tolerant Instant Drag Reducer For Slippery Water

Nowadays,with the change of energy situation,shale gas exploitation has been rapidly developed as a kind of clean energy.Currently,hydraulic fracturing is the main technology to explore shale gas,and slickwater has been widely used as the key operating fracturing fluid.In consideration of the "well-factory" method in shale gas exploitation,fluid preparation usually adopts continuous mixing technology and has higher requirements of dissolution rate of drag reducer in slickwater.At the same time,in order to save fresh water resources,the flowback which are injected into the formation are supposed to be simply disposed as reused operating fluid,higher requirements of salt resistance of drag reducer are been raised as well.So preparing an efficient salt-resistance drag reducer has an important significance on shale gas exploitation.In this paper,the main monomer is acrylamide(AM)which introduced with salt-resistance 2-acrylamido-2-methylpropanesulfonic acid(AMPS),ammonium sulfate solution as dispersion medium to prepare suspended particles of instant salt-resistance drag reducer by means of dispersion polymerization.This paper focuses on the influence of reaction conditions on the stability of the system,which is the basis of the preparation of stable friction reducer.It has been found that molecular weight of dispersion stabilizer,pH value and concentration of dispersion medium have great influences on the stability of the system.The molecular weight of the stabilizer can easily affect the steric hindrance force of the polymer particles and the concentration and pH value of the dispersion medium can easily affect the electrostatic repulsion of the polymer particles.When Mn is 600000 and Mw is 850000 of dispersion stabilizer,dispersing medium concentration is 35wt%,and pH value is 7.5,the coordinated action of various influencing factors can the polymer particles being stably existed in the dispersion system.Otherwise,in this paper,the influencing factors of dispersion polymerization were investigated on the viscosity average molecular weight and product morphology as the basis for evaluation,and the optimum preparation conditions for the stable drag reducer are:monomer concentration is 12wt%,the monomer ratio n(AM):n(AMPS)=7.5:1,the reaction temperature is 60?,35wt%dispersion medium,0.75wt%dispersion stabilizer,pH value is 7.5,initiator dosage is 0.05wt%,reaction time is 4 hours.The relative molecular of the polymer can reach 1.51×107 g/mol with the optimum condition,which meet the characteristics and requirements of drag reducer polymer.Dissolving the synthesized friction reducer into pure water to prepare slickwater,result shows that drag reducer can be completely dissolved within 98s,which shows a good solubility.The apparent viscosity is 2.04mPa·s when the effective dosage of drag reducer is 0.024wt%,the drag reduction rate can reach 81%at the volume flow rate of 40L/min and remains unchanged at 80? and under the shear rate of 10000s-1.Studies have found that monovalent ions can not change the drag-reduction performance absolutely,and multivalent ions can affect its drag reduction performance only in high ion concentration.The drag-reduction performance decreases obviously only when the calcium ion concentration reaches 75g/L,Fe3+concentration reaches 20g/L,SO42-concentration reaches 100g/L.When the calcium ion concentration exceeds 125g/L,Fe3+concentration exceeds 40g/L,SO42-concentration exceeds 250g/L,the drag reduction rate decrease separately to 41.2%,37.3%and 0,which could not play a good drag reduction effect.However,its tolerance of salinity is very good,indicating that the drag reducer has a good salt resistance.In addition,it was found that the changes in concentration of drag reducers and high-valent ions affect the apparent viscosity and drag reduction efficiency of the slickwater system.On the one hand,the increased non-structural viscosity of the drag reducer owing to hydration increases the drag reduction efficiency,while the high-valence anion polymer agglomerates via electrostatic compression,resulting in a decrease in the non-structural viscosity and drag reduction of the system.On the other hand,high anions bridge with drag reducer molecules,which increases the viscosity of the structure and decreases the drag reduction efficiency.Therefore,it should pay attention to the non-structural viscosity of the drag reduction while using slickwater systems.Prepare slickwater with the selected formula of 0.024wt%friction reducer+0.3wt%clay bulking agent+0.3wt%drainage aid in a 100g/L of high salinity water,results show that good compatibility between auxiliaries,the drag reduction efficiency of the slickwater system reaches 76.3%and drag reducer can be completely dissolved within 107s,showing good salt tolerance and instant.The overall performance is also excellent.The slickwater system prepared by the friction reducer in high salinity solution meet requirements of shale fracturing.