Study Based On Modified Graphene Oxide As Nano-Drag Reduction In Low Permeability Reservoir Water Flooding

High injection pressure and poor ability of injection were universal problems in the low permeability reservoir water flooding. So decompression and augmented injection were important working contents in water flooding. Research and development of efficient chemical agent for decompression and augmented injection was one of the emphasis research in the field of oilfield chemistry. In our study, a nano drag reducing agent (nano-DRA) basing on hydrophobic modified graphene oxide was synthesized to realize drag reduction, depressurization and injection stimulation in the low permeability reservoir water flooding. The main results were listed as follows:(1) The modified Hummers method was utilized to synthesize graphene oxide:after mid-temperature reaction period, high-temperature stage at 98℃ was canceled and the reaction was continued at 35℃, in order to assure the reaction was in the low temperature, secure and stable condition. The graphene oxide was single layer or few layers which was synthesized by the modified Hummers method, and its thickness was around 1.1nm.(2) As the pH changed, the lateral size changed regularity of graphene oxide was clear, so it was feasible to synthesis graphene oxide sheets with controlled lateral size and achieved lateral size of graphene oxide sheets controllable optional operation by controlling pH of graphene oxide water solution.(3) Through modeling calculation, alkylamine was the best hydrophobic graphene oxide modifier, which had mild reaction conditions and product structure was stability. While alkylamine with different alky length reacted with graphene oxide, the longer alky was, the reaction reacted more easily, and more stable of the synthetic modified graphene oxide structure was. Although the amine groups of the alkylamine could react with the carboxyl groups along the edge of the graphene oxide sheets preferentially.(4) On the basis of simulation, a series of nano-DRAs M-GO were prepared by alkylamine with different alky length (C8～C18) to realize graphene oxide hydrophobic modification. The long-chain alkylamine was successfully grafted on the surface and edge of the graphene oxide sheets, along with reduction of oxygen-containing functional group on graphene oxide surface during the reaction. Five kinds of nano DRAs all could change the cores from superhydrophilic to superhydrophobic, and the hydrophobicity increased with alkylamine length.(5) GO-HDA and GO-ODA were able to reduce water injection pressure of low permeability core efficiently. After these two nano-DRAs were injected into the core, the subsequent water flooding pressure decreased 15.31% and 45.55% respectively, and the permeability ratio of cores were 1.18 and 1.84 times before injection, respectively. The optimum using parameters of GO-ODA was:20 mg/L-50 mg/L,1 PV-2 PV and 48 h adsorption time. The influence of temperature on the GO-ODA was small, and the scouring properties of GO-ODA was strong, when the accumulated injection reached into 200 PV, the permeability decreasing range was no more than 10%.(6) The water molecules adsorbing on the surface of low permeability sandstone reservoirs were chemical adsorption. It was a weak chemical adsorption that water molecules adsorbing nearby amide group’s N atoms of the nano-DRA GO-ODA-1, while its absorption to long-chain alky on the carbon surface of the GO-ODA-1 was a weak physical adsorption. The nano-DRA GO-ODA-1 adsorbing on the surface of low permeability sandstone reservoirs, was easily conducted spontaneously, also it was strong chemical adsorption, which usually adsorbed in parallel direction. Adsorption between GO-ODA-1 and GO-ODA-1 was not stable, and it was not easy to occur spontaneously, nano-DRA was not easy to gather each between pile blocking formation, which tended to form a single layer or few layers adsorption, less as far as possible to reduce the negative effect of formation plugging.(7) Based on the experimental research and conclusion of calculate, the mechanism of drag reduction/depressurization and injection stimulation was verified:1) the nano-DRA M-GO occurred adsorption competition with the hydrated layer on the surface of the sandstone reservoirs, formed M-GO strong adsorption sheets; 2) because of the adsorption of nano-DRA M-GO on the low permeability reservoirs’micro-channel and it’s superhydrophobic, superhydrophobic surface was formed on the walls of the pores, thus nano slipping effect to the water flow was produced; 3) water-proof and anti-swelling effect of the nano hydrophobic layer.