Development And Application Of Rheology Modifier For Deepwater Water-Based Constant-Rheology Drilling Fluid

During deepwater drilling,even in tropical waters,sea floor temperatures are relatively low,typically around 5℃and in some areas as low as-3°C.The low temperature characteristics of seawater have a serious impact on the performance of drilling fluid,mainly reflected in the obvious thickening of drilling fluid at low temperature,the increase of circulating equivalent density and the easy leakage of casing shoes,which seriously affect the safety,economy and efficiency of drilling engineering.In order to solve the above problems,this study carried out the development and application research of constant rheological water-based drilling fluid flow pattern regulator in deep water based on CNOOC’s"13th Five-Year Plan"major project"Research on Evaluation Method and Technology of Drilling and Completion Fluid System in Deepwater Development Wells"（CCL2017ZJFN2296）.In this paper,on the basis of investigating the domestic and foreign research present situation,based on the win min polymer in response to the temperature in the process of volume of fluid mechanics and the molecular conformation changes obviously,using acrylamide（AM）and N-isopropyl acrylamide（NIPAM）as monomers,using free radical aqueous solution copolymerization,developed for deep water constant rheological fluid flow pattern regulator.Through the optimization of reaction conditions such as the molar ratio of monomer,reaction temperature,reaction time,the amount of initiator and the quality of solvent and orthogonal test analysis,the best synthesis process was determined,and the constant rheological flow type regulator PNAAM was prepared.The product was characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis.It was proved that the molecular structure of the synthesized product was consistent with the designed target product.The experimental results show that PNAAM can resist the high temperature of 120℃,and it still has a certain viscosity increasing and cutting effect in the bentonite base slurry with30%Na Cl and 1.0%Ca Cl₂,and it has a better flow pattern regulation effect than XC.The changes of turbidity and particle size of PNAAM in aqueous solution with different temperature were studied by turbidimeter,nanometer laser particle size analyzer and scanning electron microscopy.The microstructure of bentonite slurry with PNAAM was observed at different temperatures and conditions.The influencing factors of LCST and its flow pattern regulation mechanism were analyzed.The results showed that the LCST of PNAAM increased with the increase of salt concentration and addition.Moreover,PNAAM after LCST can effectively improve the density of bentonite cake.Studies have shown that salt and other factors affect the LCST of the polymer by affecting the strength of hydrogen bonding force between the amide group and water on the temperature-sensitive side chain.PNAAM changes the hydrophobic association strength of polymer molecular chain through the action strength of hydrophobic groups in the temperate-sensitive side chain before and after LCST,and then affects the viscosity of drilling fluid,and plays the effect of increasing viscosity and cutting.Taking PNAAM as the core,the constant rheology water-based drilling fluid system was formed through the optimization of treatment agent:4.0%bentonite+0.3%Na₂CO₃+0.2%PNAAM+1.0%PAC-LV+0.15%FA-367+1%AP-1+2%NP-1+2%methyl oleate+20%Na Cl+barite(we-ighted to 1.5g·cm^-3).The temperature resistance of the system can be up to 120℃,with good anti-leakage,inhibition,plugging,lubrication and constant rheological properties.Ratio of rheological parameters at different temperatures were:AV_4℃:AV_25℃<1.30、AV4℃:AV65℃<1.80、PV4℃:PV25℃<1.20、PV4℃:PV65℃<1.70。...