Research On High-temperature Resistance And Salt-tolerance Thinner For Drilling Fluid And Mechanism Of Action

With the longitudinal development of petroleum exploration，the number of deep well，ultra deep well temperature over200℃is also more and more，downhole drilling condition iscomplicated in the formation.In the drilling process，with the increase of drilling depth，asignificant rise in temperature in wellbore，drilling fluid gelled problem become more andmore serious，and the viscosity agent plays an very important role in adjusting drilling fluidrheological property.Copolymer adhesive is a very important type，its structure could bedesigned and adjusted，we can through the selection of monomer，the synthesis process ofoptimization compound viscosity agent satisfy the temperature resistance and environmentalsafety.This paper mainly discussed a method of producing high-temperature viscosity polymer.The terpolymer called MAA has been prepared from maleic anhydride acid(MA)，sodiumallylsulfonate(SAS)and AMPS in water pHase by using the ammonium persulfate as theinitiator，H2O as the solvent. The experiment surveyed the influence of reaction conditions toproduct yield rate and performance and determined the optimal synthetic scheme. Thestructure of the copolymer were also investigated by IR analysis.Through the experiment wehave stuided its Salt and Calcium resistance and the best suitable pH range，we also havestuided its interaction mechanism with the clay particle.By UV－visible spectropHotometer，LS-POP laser particle size analyzer and X-pert PRO MRD-type X-ray diffraction，we havestudied the thinner MAA adsorption mechanism on the clay，the particle size and the claylayer spacing of crystal，Through the above experiments to explore its mechanism of reducingwater-based drilling fluid viscosity.The results show that the optimum conditions of the copolymerization temperature thesynthesis of MA/SAS/AMPS terpolymer:the copolymerization temperature is85℃， thereaction time is4h，the mass ratio of initiator and total monomer is3.0%，n(MA)：n(SAS)：n(AMPS)=1.0∶0.8∶0.8，monomer concentration is45%.The experimental results indicatedthat when the addition of the thinner was0.5%in fresh water-based slurry，its apparentviscosity decreased from45mPa·s to30mPa·s， the thinning rate was70.2%at roomtemperature，and apparent viscosity decreased from50mPa·s to34mPa·s，the thinning ratewas42.8%when the water-based slurry adding0.5%thinner was aged at220℃for16h.Studied the thinning mechanism and influence of high temperature on the effects of viscosity reduction，the conclusion as follows:①The adsorption quantity of viscosity reduceron clay particles was analyzed，when reducing agent dosage is5000mg·L-1，after220℃agingfor16h adsorption amount decreased from43.9mg·g-1to32.9mg·g-1，and the degradationrate decreased from70.2%to42.8%， high temperature causes desorption of viscosityreducer，which is the main reason for reducing viscosity reduction.②After high temperatureaging，particle diameter increased and the size distribution turned wider with increase of thecontent of viscosity reducer，adding0.3%viscosity reducer makes the particle size increasenearly four times，particle size becomes bigger which is one of the reasons which resulted indecrease of viscosity of the drilling fluid.③Montmorillonite layer spacing of drilling fluidwhich was treated by different concent of viscosity reducer after high temperature aging.Thecrystal layer spacing of dry montmorillonite remains unchanged，it indicates that the viscosityreducer is not into the crystal layers， but act on the surface of the clay particles.