Study On Modification Of Supercritical/Liquid CO₂ Fracturing Proppant

With the further development of mature oil fields,unconventional oil reservoirs have become the focus of attention in the industry.However,tight reservoirs have the characteristics of low yield,low permeability and low porosity,which are difficult to exploit and develop.The liquid/supercritical CO2 fracturing technology can effectively extract dense reservoirs.The surface of proppant commonly used for fracturing is hydrophilic and cann't be dispersed in liquid/supercritical CO2 fracturing fluid.The surface of the proppant needs to be modified.In this paper,hexamethylenedisilazane(HMDS)and erucic acid chloride(EAC)synthesized from erucic acid and thionyl chloride were used to modify the surface of proppant by small molecule self-assembly method.The surface of the modified proppant was characterized by Fourier transform infrared spectroscopy,which proved that the modifier was successfully grafted onto the surface of the proppant.The contact angle and surface energy of the modified proppant were tested by contact angle measuring instrument.The contact angle was 135°,and the surface energy SE was 30.2 dyn?cm^-1.The surface morphology of the modified proppant was observed by scanning electron microscopy and atomic force microscopy,which proved that the modification was successful.The modified proppant was tested by liquid percolation experiment.The seepage rate under water and kerosene was compared.The seepage rate of water in the proppant after modification was 0.0093 m L·s^-1,which the permeation rate of kerosene was 0.0925 m L·s^-1.The results show that the hydrophobicity of the modified proppant is significantly improved compared to conventional proppants.In this paper,hydrophobically modified nano-silica particles were used as modifiers,the proppant was hydrophobically modified by physical methods of epoxy resin mixed coating and chemical methods combined with urea-formaldehyde resin.The contact angle of the modified proppant was more than 122°and the surface energy SE was less than 36.1 dyn?cm^-1.The thermogravimetric results showed that the thermal stability of the modified proppant wasimproved greatly and nano-silica particles was successfully observed by scanning electron microscopy.The percolation experiment showed that the water percolation rate was0.0124m L·s^-1,which the kerosene permeation rate was 0.145 m L·s^-1.The hydrophobicity of the modified proppant has improved significantly.Finally,the basic properties of the modified proppant,which is related to CO2 fracturing were studied,including the proppant breaking rate,acid solubility,activation index,water repellency rating,fluid resistance ratio and dispersion in supercritical/liquid CO2.The fracture rate of the modified proppant reduced about 30%.The acid solubility reduced about 50%.The surface activation index of the proppant was above 50%,and the water repellent level was the highest of the four grades.The proppant fluid resistance ratio after modification was more than1.The modified proppant can be relatively uniform with non-polar CO2 dispersion without agglomeration.It proved that the method of non-polar modification of the proppant surface is feasible and should be useful in CO2 fracturing mining.