Synthesis Of High-temperature Resistance And Salt Tolerance Polymer As Fluid Loss Reducer And Interaction Of Polymer With Montmorillonite

With the development of oil industry at home and abroad and the ever-increasing demand for oil, the exploitation and development of oilfield was shifted from shallow strata to deep strata and from shallow sea to deep sea, which has made a claim for higher temperature and higher salt concentrations in drilling fluid. Polymer with improved high temperature resistance and salt tolerance was collected as additive to enhance the high temperature stability of water-base drilling fluid. According to the theories of molecular structure design, four different monomers were optimized as follows:2-acrylamido-2-methyl-propane sulfonic acid (AMPS), acrylamide(AM), N,N-dimethyl acrylamide (DMAM) and N-vinylpyrrolidone (NVP). Quadripolymer as high temperature fluid loss reducer was synthesized by adopting free radical water solution polymerization method, which effectively improved the performance of water-base drilling fluid with high temperature resistance and salt tolerance.1. Preparation and characterization of P(AMPS-AM-DMAM-NVP) quadripolymerThe optimum conditions of synthesis were determined through orthogonally designed experiments and altering monomer concentration methods as follows:the initiator potassium persulfate (KPS) dosage 0.3 wt% (of monomer concentration), the monomer molar ratio AMPS:AM:DMAM:NVP=3:4:2:1, the chelator ethylene diamine tetraacetic acid (EDTA) dosage 0.15 wt% (of monomer concentration), the reaction temperature 75℃, the monomer concentration 30 wt% and the reaction time 6h. The Fourier transform infrared (FTIR) spectroanalysis revealed the presence of four monomers and confirmed the effectiveness of the reaction. The Element analysis showed the composition of synthetic polymer was in accord with designed polymer. The average viscosimetric molecular weight of quadripolymer was obtained by the intrinsic viscosity method, which was 72.23x 104. Both thermogravimetric-differential scanning calorimetry (TG-DSC) method and the retainable ratio of intrinsic viscosity showed the synthetic polymer had good high temperature resistance property.2. Evaluation of filtration control properties about P(AMPS-AM-DMAM-NVP) quadripolymer at different mud The results of rheological and filtration experiments showed quadripolymer concentrarions, temperature, NaCl concentrations and aging time had an important effect on the rheological and filtration properties of mud. Fresh water mud, salt water mud, compound salt water mud and saturated saline-water mud didn't increase viscosity and had good filtration properties after high temperature aging with the addition of quadripolymer. For fresh water mud and compound salt mud, the quadripolymer had same performance in controlling the filtration compared with the Driscal D. For salt water mud and saturated saline-water mud, it had better performance in controlling the filtration compared with the Driscal D. This shows that quadripolymer can be expected to be applied in deep drilling.3. Research on the interaction of P(AMPS-AM-DMAM-NVP) quadripolymer with montmorilloniteIn order to explain better the high temperature resistance and salt tolerance of quadripolymer in clay dispersion, the total organic carbon analysis experiments(TOC) and rheological experiments were used to research the interaction of quadripolymer with montmorillonite. The results showed the adsorbance increased with increasing quadripolymer concentration until a plateau region presented, which confirmed Langmuir adsorption isotherms. The addition of electrolytes made the adsorbance of quadripolymer in the surface of particles increase. At lower concentrations, the effect of CaCl2 were more significant than NaCl. Saturated adsorption platform appeared with the increase of CaCl2 concentration, while the adsorbance continued to increase with the increasing NaCl concentration without the tendency of saturated adsorption.The results of rheological experiments revealed that the flow curves of quadripolymer solution could be well described by the power law model. The flow curves raised with increasing quadripolymer concentration. The viscosity decreased with increasing shear rate, which exhibited the shear shinning properties. For montmorillonite dispersion and quadripolymer-montmorillonite dispersions, flow curves could be discribed by the Herschel-Bulkely model. With the increase of quadripolymer concentrations, yield value and consistency coefficient increased and flow indices decreased, which was confirmed with the oscillatory frequency scan measurements. With the addition of NaCl, yield value and consistency coefficient increased firstly and then decreased, while flow indices had the opposite tendency.4. Research on mechanisms of P(AMPS-AM-DMAM-NVP) quadripolymer in controlling filtrationAccording to theory of Colloid and Interface Chemistry, some mechanisms of quadripolymer in controlling filtration were initially proposed. It can be summarized as follows:(1) Electrostatic repulsive force, hydrophobic interaction and hydration repulsion force between particles were enhanced by using the adsorption of polymer in the particle surface, which stabilized the clay particles; (2) The viscosity of mud increased with the addition of polymer, which reduced the liquidity of filtrate and increased the resistance of percolation; (3) The network structure of clay system was formed with the addition of polymer, which improved coagulation stability of clay system. (4) The molecular size of polymer was within the scope of the colloidal particles. Hence, the addition of polymer was equivalent to increasing the content of colloid particles, which had an effect on plugging the pores of the filter cake.