Research On Water Based Low Friction Anti Sloughing Drilling Fluid For Extended Reach Wells In Eastern South China Sea

In view of the problems of the existing offshore water-based drilling fluid system PLUS/KCl system,such as insufficient inhibition performance,anti-wear and drag reduction ability,this study determines the optimization technical path of water-based drilling fluid system for extended reach wells by analyzing the existing formation data in the South China Sea and combining with the domestic research status of extended reach drilling fluid development.In addition,two kinds of key additives,modified vegetable oil acyl polyether amine called SLIP-W and cationic polymer inhibitor called HIB-3,which are suitable for extended reach water-based drilling fluid system,have been developed and optimized through corresponding functional structure design.Based on these two agents,the performance of the original offshore PLUS/KCl drilling fluid system was optimized and improved to meet the drilling needs of extended reach wells in the eastern South China Sea.Finally,a set of low friction and strong inhibition soilless seawater drilling fluid system BIOFLUID was formed.The basic formula of the system is as follows:Seawater+0.2%Na OH+0.2%Na₂CO₃+0.3%PAC-LV+0.6%PF-PLUS+0.2%BIOVIS+0.5%PF-PLH+2%SLIP-W+3%HIB-3+2.0%PF-FLOTROL+1%PF-Green Seal+3%LSF+5%Na Cl+3%KCl+Barite.After a series of systematic evaluation experiments,it is found that the high temperature and high pressure filtration of BIOFLUID drilling fluid system is only about9m L?10m L at 100?.In general,the filtration rate of the system is low,and the drilling fluid can effectively form thin and pliable mud cake in the filtration process,so as to reduce the pollution caused by mud invasion to the reservoir,,reduce the pollution caused by mud invasion to the reservoir,and improve the wellbore stability.Indirectly,it can also reduce the friction torque in the drilling process by reducing the thickness of mud cake.In terms of the rheological property of the system,the dynamic shear force of BIOFLUID drilling fluid system is controlled at about 13Pa,and the dynamic plastic ratio is around0.52,It has excellent rheological properties,which is conducive to the formation of flat laminar flow propulsion of drilling fluid in the annulus of horizontal section and high angle section.It can effectively carry rock and improve the cleaning efficiency of the wellbore at low annulus return speed.In terms of lubrication performance,only 2%SLIP-W can reduce the lubrication coefficient of the system to about 0.074,which has excellent anti-wear and drag reduction function and can ensure large displacement at sea In general,the system has good resistance to drilling cuttings,seawater invasion,salt invasion,calcium invasion and other pollution,and has a certain shielding and plugging effect on the formation,which can effectively protect the reservoir.In addition,on the premise of ensuring that the basic performance can meet the requirements,the density of BIOFLUID system can be adjusted in the range from 1.1g/cm³ to 1.5g/cm³.A series of research results show that the improved BIOFLUID drilling fluid system can meet the needs of extended reach drilling in the eastern South China Sea.