Zwitterionic Polymer Inhibitors And Inhibitory Water-based Drilling Fluids

One of the most important methods of preventing collapse is to enhance the inhibition of water-based drilling fluid.As long as the shale formation contains montmorillonite or imam mixed clay minerals,water-based drilling fluids need to consider the use of anti-collapse technology.In this paper,the zwitterionic polymer inhibitor with relatively low molecular weight was developed under the guidance of the idea that the inhibitor molecule entered the montmorillonite mineral layer.The inhibition mechanism was evaluated and its inhibition mechanism was studied.On this basis,a new type of inhibitive water-based drilling fluid was developed with the synthesized inhibitor as the core treatment agent.In this paper,the molecular structure of the inhibitors was designed based on the inhibition mechanism and performance requirements.On this basis,three polymerization monomers such as N,N-Dimethyl-N-2-propenyl-2-propen-l-aminium chloride(DMDAAC),2-Methyl-2-propen-l-ol(MP)and 2-acrylamido-2methylpropane-sulfonic acid(AMPS)were being selected to synthesize zwitterionic polymer inhibitor DAM by aqueous solution polymerization.Through optimizing initiator dosage,monomer concentration,monomer ratio,reaction temperature and reaction time on reaction conditions by the reaction system,the optimum reaction conditions of DAM:dosage of initiator is 4%,the total monomer concentration is 30%,the monomer ratio of AMPS:DMDAAC:MP = 4:3:4,the reaction temperature is 65 C,the reaction time is 7h.DAM was characterized by infrared spectroscopy,molecular weight distribution and thermogravimetric analysis.The results show that the molecular structure and the molecular weight of the synthesized product are in good agreement with the expected design.It is low molecular weight copolymer,and has good thermal stability,before 288℃,no significant degradation occurres.A series of properties of DAM,such as inhibition,resistance to temperature,salt and calcium tolerance and viscosity reduction were evaluated in laboratory.The results show that DAM has excellent inhibitory performance.When the amount of DAM is 2%,the linear expansion rate of bentonite can be reduced from 50.4%to 17.6%.In addition,DAM temperature resistance up to 140 ℃,salt resistance up to 15%,anti-calcium up to 1%,the apparent viscosity of the polymer slurry from 32.5 mPa·s reduced to 19 mPa·sThe inhibitory mechanism of DAM was analyzed by using environmental scanning electron microscopy,laser particle size distribution analyzer,Zeta potentiometer,X-ray diffractometer and water activity meter.It is found that the inhibitory effect is mainly achieved by two effects:(1)it adsorbs on the surface of clay particles to neutralize the negative charge and compression the diffusion double layer,reducing the Zeta potential;(2)it enters the clay crystal layer and pulls the crystal layer,weakening crystal layer expanding trend.On the basis of DAM,the treatment agents such as coating agent,fluid loss reducing agent,tackifier,lubricant and weighting agent for drilling fluid were selected to develop different kinds of inhibitory water-based drilling fluid,and their performance were evaluated.The results show that the rheological properties of the three drilling fluids are excellent;the normal pressure loss is lower than 5mL;the loss at 120℃ 3.5MPa is lower than 20mL,salt and calcium pollution and anti-soil pollution performance are more excellent;the recoveries of the red soils under the three drilling fluids are higher than 95%.They can be used for drilling operations in mudstone formations.