Preparation And Evaluation Of Gas-wetting Nanoparticles

When the reservoir pressure decreases to the dew point,gas will condensate into liquid near the wellbore region,leading to an increase in liquid saturation and decrease in flow efficiency of fluids.Consequently,gas-deliverability will be killed instead of having gas evolution.Gas-wetting alteration method has proved to be one of the most effective methods to address this problem,but the current gas-wetting alteration methods are limited in further improving gas-deliverability.To overcome these above limitations,this paper combined gas-wetting with nanoparticles to prepare gas-wetting nanoparticles.The effect of temperature,inorganic cation,pH on gas-wetting alteration,and the mechanism of gas-wetting nanoparticle were investigated.Additionally,visualization flooding experiments were performed to figure out the effect of gas-wetting alteration on the flow and distribution of fluids in porous media.Fluorosurfactants and fluoropolymers were used to alter the rock wettability from liquid-wetting to gas-wetting.Results showed that both FG40 and FP-2 can alter the rock wettability from liquid-wetting to gas-wetting or intermediate gas-wetting,the contact angles of brine and hexadecane can increase from 23° and 0° to 125° and 93° after treated by 0.3 wt% FG40 solution,respectively.Fluorosurfactant FG40 has more advantages in increasing contact angle and in decreasing the surface free energy compared with fluoropolymer.Moreover,the cores treated by FG40 remain gas-wetting up to 10000 mg/L of salt solution,140℃ and within the pH range of 1-10.The results of SEM show that FG40 molecules can alter rock wettability to gas-wetting by forming an adsorption layer with a compact and coarse structure,however,FP-2 molecules can form a cave-like adsorption layer on core surface.Therefore,rock wettability can be altered from liquid-wetting to gas-wetting by the adsorption of fluorine organic chemicals.Nanoparticles were functionally modified by fluorosurfactant and fluoropolymer to prepare gas-wetting nano-silica particles,results showed that the wettability of the core can be altered to intermediate gas-wetting or super gas-wetting after treatment by the FG40 and FG40 modified nano-silica.The contact angles of brine and hexadecane on the core surface increased from 23°and 0°to 152°and 127°,respectively,after the 0.3% FG40 modified nano-silica treatment;these angles are obviously higher than those cores treated with FG40 and FP-2 solutions at an equivalent concentration.Results of Imbibition test indicate that liquid saturation and imbibition rate can be decreased by gas-wetting alteration,water saturation and oil in core can decrease significantly.Results of FTIR indicate that when the fluorosurfactant molecules are jointed onto nano-silica surface,C-F bond and newly formed bond can be recognized.The results of SEM show that the grape-like particles can form a multi-adsorption layers on rock surface,which plays a vital role in super gas-wetting by decreasing surface free energy and increasing roughness.Grape-like adsorption layer and low surface free energy are two principles to achieve a strong gas-wetting surface.The results of visualization flooding show that water saturation and oil saturation in the micromodel decreased sharply from 33.23% and 55.02% to 20.77% and 29.12%,respectively,after gas-wetting nanoparticles treatment.The contact angle of isolated liquid droplet on the treated pore-wall was approximately 125°,which also verifies that pore wettability is altered from liquid-wetting to gas-wetting.The reason for this is that gas-wetting nano-silica particles can form gas-wetting adsorption layer on pore wall,which can facilitate the flow efficiency of fluid in porous media.