Research On Weak Gel Drilling Fluid Of Extended Reach Well

With the continuous development of drilling technology,the development proportion of extended reach wells is increasing year by year.The horizontal displacement of extended reach wells is long,and cuttings are easy to deposit to form cuttings bed,which leads to sand jamming and other accidents.Therefore,in addition to guaranteeing drilling speed,drilling fluid for extended reach wells should also have good rock carrying capacity.Conventional drilling fluid has poor thixotropy,is difficult to maintain when its viscosity is too high,and is prone to pump choking,drilling speed slowing down,or even sticking to the drill.If its viscosity is too low,debris suspension will be difficult,sand sinking will be serious,and even serious accidents of burying drilling tools will occur.Weak gel drilling fluid is a new drilling fluid,in which polymers can be cross-linked to form a three-dimensional network structure,forming a weakly crosslinked system which is mainly intermolecular crosslinking and intramolecular crosslinking.Weak gel drilling fluid has both the structural strength of the gel and the shear thinning property of the polymer solution.It has higher viscosity under low shear rate,can effectively suspend the cuttings,lower the viscosity at high shear rate,and improve the drilling speed.Therefore,it is necessary to carry out the experimental study of weak gel drilling fluid optimization,which is expected to solve the problem of rock debris suspension and easy to occur cuttings bed in extended reach wells.A new type of weak gel flow regulator RHC was prepared by free radical polymerization,xanthan gum and acrylic acid,acrylamide and other monomers under graft copolymerization with initiator,and then crosslinking polymerization with organic boron crosslinker.Its molecular structure was characterized by thermogravimetric analysis,infrared spectroscopy and permeation gel chromatography,and its effects on temperature,salt resistance and acid and alkali resistance were evaluated.The mechanism of improving rheological properties was also discussed.The experimental results show that the experimental slurry with a new weak gel flow regulator has high viscosity and good shear thinning rate,and the rheological property of RHC solution is stable after 120 degree rolling.A new weak gel flow regulator RHC was used as the key treatment agent to optimize the formulation of weak gel drilling fluid suitable for extended reach wells: clear water+0.2% carbonate sodium +20% organic salt +0.8% weak gel flow regulator(RHC)+0.3%inhibitor(BBJ)+2.5% filtration reducer(Redu I)+ 3.5% anti sloughing plugging agent(YFT)lubricant.The system still has a certain low shear rate viscosity and good thixotropy after hot rolling at 150 ?/16 h.API and HTHP filtrate loss are small,and the system has good temperature resistance,inhibition,pollution resistance and environmental protection.Weak gel water based drilling fluid system has been tested in Dagang Oilfield during extended reach well drilling.After using this drilling fluid system,the problems of low viscosity and difficult debris suspension at low shear rate of field drilling fluid are solved,the drilling rate is increased and the drilling cost is reduced.Compared with the adjacent wells,the completion time of the three test wells has been reduced,the average drilling time has been reduced by about 15%,and the average drilling cost has been reduced by about 10%.