The Research On The Water-based Drilling Fluid System With Viscoelastic Polymers

During the process of drilling the complex wells including the extended reach well and shale gas horizontal well,complicated conditions,such as diameter shrinkage,sticking,often occurred due to the difficulty of carrying cuttings or the shale hydration.To resolve the difficulty of carrying cuttings,bentonite or conventional polymer as the tackifiers were added in the traditional water-based drilling fluids(WBDFs).However,this could not meet the need,and will reduce drilling efficiency to a certain extent.Meanwhile,in order to inhibit the shale hydration,and keep the wellbore stable,the coating agents or shale inhibitors were added in WBDFs.However,these agents could not meet the need completely.In order to solve the above problems,two viscoelastic polymers were synthesized,and respectively used as the tackifier and the wallbore stabilizer.Then,the WBDFs with viscoelastic polymers were developed.To resolve the difficulty of carrying cuttings,a kind of hydrophobic association zwitterionic polyacrylamide derivative(ADBA)as the tackifier was studied.Through the hydrophobic association,electrostatic interactions and hydrogen bonding association,the agent can form a three-dimensional network structure.The agent possessed good rheological properties including increasing the viscosity,shear thinning and viscoelasticity.Meanwhile,the network structure and the sulfonic acid groups could improve the temperature resistance of ADBA.The clay-free WBDFs with a low density or high density using ADBA as the tackifier,possessed better rheology properties and controlling filtration than that with Polyacrylamide potassium(KPAM)as the tackifier.Aiming at the wellbore instability caused by the shale hydration,the polyving akohol(PVA)grafted polyacrylamide derivatives as the wellbore stabilizers(JWD)were studied.Due to hydrophilic groups,JWD could adsorb the shale,and it was conducive that JWD adsorbs on the surface of the shale or enters into layers.Meanwhile,the hydrophobic membrane was formed due to the hydrophobic groups,and it prevented the water molecules from contacting with the shale.In addition,via the adsorption,JWD could increase the binding force between the shale particles.This prevented the shale from spalling.Based on the synergistic effect,JWD could effectively inhibit the hydration swelling and dispersion of the shale,and achieve the goal of stabilizing borehole.The viscoelastic polymer high-performance WBDFs were formed with ADBA and JWD as the core agents,and association with other agents.The performances of environmentally friendly and low-density drilling fluid with the viscoelastic polymers were better than that of the potassium calcium polysulfide drilling fluid.Meanwhile,the WBDF possessed good anti-pollution abilities,such as anti-shale powder pollution up to 15%,and anti-NaCl pollution up to 30%.At last,the WBDF met the national requirements of the environmental protection.The properties including rheology,controlling filtration,and the inhibitory of the high-performance WBDF with high density,were similar to that of the oil-based drilling fluids.With the wellbore stabilizer(JWD)into the potassium calcium polysulfide drilling fluid,and wellbore stability type drilling fluid was formed.This possessed good rheological property and stabilizing wellbore performance.The drilling fluid was successful applied in H160 well and H1652 well in Hongshanzui blocks,and this drilling fluid can effectively reduce well diameter expansion rate and solve the wellbore instability problem.