Preparation And Properties Of Modified Polystyrene Microspheres Used As Ultra-low Density Proppant

Low permeability and shale gas reservoirs account for a large proportion of the world's energy, while the exploration efficiency is not ideal due to the restriction of oil and gas development technology. So the petroleum and shale industry has been a screen with poor utilization, serious environmental pollution and high cost. The entire industry urgently tend to large-scale and resource-oriented. Recent years, the water carrying fracturing was successfully used in reservoirs. Compared with traditinal hydraulic fracturing, results shown that the water carrying fracturing has higher yield, lower production costs and less environmental pollution. This procedure needs proppant with low density as water, while the density of traditional proppants are very high (above 2.5 g/cm3), leading to a poor carrying capacity of fracturing fluid. Till now, commercial ultra low density (ULW) proppants are poor in heat resistance and strength. As mentioned above, the research of ULW proppant with low density, high strength and high heat resistance is imminent. Doped and coated polystyrene microspheres were provided as a new ULW proppant material in this study.Firstly, graphite/PS microspheres and SiO2/PS microspheres used as ULW proppant were prepared via in situ suspension polymerization, and its mechanism was descripted briefly. The product was confirmed by FTIR, SEM, DSC and TGA, and the effect of graphite and nano-silica amount on the performance of proppant were investigated. The results shown that the density of proppant was slightly increased, as the increase of filler content. The sphericity of all prepared proppantare above 0.9, the heat resistance was increased with the increase of filler content. The optimal dosage of graphite and nano-silica were 2.5% and 1.0%, respectively. When the dosage of graphite was 2.5%, the ture density and bulk density were 1.048 and 0.598 g/cm3, respectively. The sphericity value was 0.94, and the percentage of damage as low as 2.2% at 52 MPa and 3.5% at 68MPa, the 5% weight loss temperature as high as 325 ?.When the dosage of nano-silica was 1.0%, the ture density and bulk density were 1.0604 and 0.6137 g/cm3, respectively. The sphericity value was 0.94, and the percentage of damage as low as 1.2% at 52 MPa and 3.0% at 68MPa, the 5% weight loss temperature as high as 372?.To further improve the performance of ULW proppant, epoxy/phenolic resin coated CB/PS microspheres were prepared by impregnation and heat curing, and its mechanism was also descripted briefly. The product was confirmed by FTIR, SEM and TGA, and the effect impregnation liquid concentration on the performance of proppant was investigated. The results shown that with the increase of the concentration the compressive strength and heat resistance were improved. When the impregnating solution concentration was 20%, the ture density and bulk density were 1.0637 and 0.6124 g/cm3, respectively. The sphericity value was above 0.9, and the percentage of damage as low as 1.25% at 52 MPa and 2.22% at 68 MPa, the 5% weight loss temperature as high as 373? and the acid solubility as low as 0.11%.Finally, the properties and price of ULW proppants prepared in this study and commercial proppants (ceramic, coated sand ULW-1.75, ULW-1.25 and ULW-1.05) were compared. The results shown that the prepared ULW proppants were lower density and acid etching rate, better sphericity and conductivity, higher heat resistance and compressive strength. Among them, epoxy/phenolic resin coated CB/PS microspheres offers a more effective candidate for petroleum and shale gas fracturing.