| With continuous developing of low and ultra-low permeability reservoirs, hydraulic fracturing technology had become one of the most direct and effective methods for increasing production and injection. The performance of the fracturing fluid was a key factor which decided the success or failure of fracturing operation. At present, guanidine gum and its derivatives were generally recognized as the commonly thickener used for water-based fracturing fluid, but some of damage to the reservoir and the volatile supply of goods and price had limit their widespread use in oil and gas development. Therefore, the research of synthetic polymer thickener got more and more attention.Through a great deal of comprehensive investigation and analysis of the research status for fracturing fluid at home and abroad, This thesis had synthesized a kind of much-branched polymer served as low-damage fracturing fluid thickener which would have the advantages of high viscosity, strong carrying capacity and no residue and provide a better choice for low permeability reservoirs. The main contents of this thesis completed were as follows:Firstly, PAMAM functional skeleton monomer, which acted as the most important synthetic source for much-branched polymer, was synthesized via Michael addition and amidation condensation reaction using ethylenediamine and methyl acrylate as initial raw materials and modified by3-dimethylamino propylamine and maleic anhydride. Secondly, a kind of functional skeleton monomer core based much-branched polymers(MBPAM-8) were synthesized with AM, AA and hydrophobic monomers as arms. And then, some reaction conditions, including concentration of the functional skeleton monomer, hydrophobic monomer, total monomers, initiator and temperature of reaction,were optimized. In addition, PAMAM functional skeleton monomer and much-branched polymer were characterized by fourier transform infrared spectrometry(IR), nuclear magnetic resonance(NMR) and elemental analysis(EA) to prove that the product was the same as expected. Meanwhile, thickening properties, rheological parameter and anti-shear ability of MBPAM-8were also studied. Finally, the surfactant type and concentration were optimized before the formulation of much-branched low-damage fracturing fluid was determined as:0.4%～0.5%MBPAM-8+0.03%～0.05%SDBS. Refering to petroleum industry standard of china, the fracturing fluid performance was evaluated systematically by water-based fracturing fluid evaluation methods.Experimental results showed that the viscosity of branched low-damage fracturing fluid system, under90℃and the shear rate of170s－1, still remained more than90mPa·s after been shearing for2h and its limited temperature could be up to115.8℃which reflected its good ability of heat and shear resistance. Since the value of flow index "n" and consistency coefficient "K" were0.307～0.371and3.72～4.91Pa·sn, it presented excellent thickening power. The break time was approximate6～7h at25℃,60℃and90℃when0.15%of (NH4)2S2O8was used as breaker. Then, the viscosity of gel breaking liquid was between2.7to3.9mPa·s. Moreover, its surface and interfacial tension were23.7～25.9mN/m and0.56～0.6mN/m. The damage rate of permeability was only10.5%～14.1%owing to no residue from the gel breaking liquid which had good compatibility with formation water. All the results indicated that much-branched low-damage fracturing fluid system had strong thickening ability, good breaking performance, low surface tension, no residue and low damage etc.The low damage fracturing fluid viscosifier synthesized in this thesis further perfected the water-based fracturing fluid system and had great guiding significance for promoting the fracturing technique development of conventional and unconventional low permeability reservoirs. |
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