Search

The transformation of the liquid menisci at pore throats is of great importance for mitigating the liquid-blocking effect of condensate reservoirs. Here, we reported a super gas-wetting peanut-like nanoparticle which can facilitate the liquid menisci to transform from concave shape to convex shape by coating a super gas-wetting adsorption with high surface roughness. The morphology and surface chemistry of gas-wetting nanoparticles were investigated by SEM, AFM, and XPS analysis. The mechanism of surface modification was further explored by TEM; the adsorption layer coated on the nanoparticle surface can be recognized as monolayer absorption. The gas-wetting model is recommended as the combination of the Wenzel model and Cassie-Baxter model, which is in close agreement with the results of AFM and contact-angle measurements. Core flooding visualization was performed to identify the effect of gas-wetting alteration on the transformation of liquid menisci in porous media. Results showed that the addition of gas-wetting nanoparticles could decrease the liquid saturations by inducing the transformation of liquid menisci in the pore throat. Additionally, a unique "amoeba effect" and miscibility effect can synergistically improve the mobility of the oil phase, further enhancing the oil recovery.

It is well-known that shale gas production is affected by the wettability of the reservoir. In this work, two gas-wetting alteration agents were synthesized and characterized by 1H NMR and FTIR. To evaluate the effect of the gas-wetting alteration agents on the shale wettability, the contact angle for droplets on the shale surface was detected, and the results showed that the contact angles of water and n-hexadecane increased from 36° and 0° to 119° and 88° after treatment with sodium [N-propyl-N-(perfluorooctanoyl)amino]acetate (SCF-102), while the contact angles increased to 122° and 110°, respectively, after treatment with sodium [N-[[N-(perfluorooctanoyl)amino]ethyl]amino]propionate (SCF-113). The surface free energy rapidly decreased from the primeval 72 to 10.3 and 6.8 mN/m at equal concentration. These values agreed with the results of spontaneous imbibition, the capillary tube rise test, and the fluid flow test. Additionally, the analysis with energy dispersive spectroscopy and scanning electron m...

Wellbore instability caused by the hydration of shale formations during the drilling process is the main technical problem in drilling engineering. The existing shale inhibitors mainly inhibit shale hydration through charge neutralization, intercalation, activity reduction, and/or plugging. Few shale inhibitors focus on reverse the wettability of shale surface. In the paper, the shale inhibition performance of silicone quaternary ammonium salt (SQAS), a material that can reverse the wettability of shale surface, was evaluated and the shale inhibition mechanism of SQAS was studied via particle size, zeta potential, contact angle, scanning electron microscopy (SEM), and shale water absorption analyses. The experimental results show that the use of SQAS could result in a relatively lower linear swelling rate of clay, and its rolling recovery rate of easily hydrated shale was as high as 64.25%, which is better than those of polyamine inhibitors. The study on the inhibition mechanism revealed that SQAS can chemically react with the shale surfaces to form a seamless hydrophobic film. The water contact angle on the shale surface was increased from 28.7° to 110.7°, which greatly reduces water penetration into shale and the water absorption capacity of clay minerals. The results of this study provide new technical ideas for the development of high-performance shale inhibitors.

The effect of gas-wetting on the liquid-blocking effect near a wellbore region is significant. Here, we functionally modified nano-silica particles with a size of approximately 40 nm each by using a fluorosurfactant and obtained a super gas-wetting nano-silica particles, which could improve the contact angles of brine and hexadecane from 23° and 0° to 152° and 140°, respectively, and decrease the surface free energy of rock surface from 72 to 1.6 mN/m. The decrease in the gas displacement was approximately 30%. FT-IR, SEM and EDS were employed to determine the morphological change in the rock surface before and after gas-wetting alteration. Results indicate that when the fluorosurfactant molecules are joined to the nano-silica surface, and C F bond is recognized. The grape-like particles forming a multi-adsorption on the rock surface, which play an important role in super gas-wetting by decreasing surface free energy and increasing roughness on the rock surface. The data of EDS was consistent with the results of FT-IR and SEM. To further understand the influence of gas-wetting alteration on the flow and distribution of fluids in porous media, visualization flooding was conducted. The results show that the initial liquid saturation in the micromodel decreased sharply from 33.23% to 20.77% after the gas-wetting treatment, and the contact angle of isolated brine droplet on the treated pore-wall was approximately 125°, which also verifies that pore wettability can be altered to gas-wetting. The analytical data of the oil displacement experiment demonstrates that the substantial decrease in oil saturation may contributes to enhancing oil recovery. Furthermore, the mobility of oil trapped in micro channels can also be enhanced significantly after gas-wetting alteration due to the presence of methane.

Gas condensate reservoirs are generally recovered using a pressure depletion drive. Gas can condensate into the liquid phase near the wellbore region when the reservoir pressure falls below the dew point pressure, which can kill gas deliverability. Wettability alteration is an effective means of overcoming this problem; core wettability can be altered from liquid-wet to gas-wet to alleviate the effect of condensate accumulation near the wellbore region. To establish the effect of fluoropolymer on wettability alteration in a gas-condensate reservoir, a gas-wetting alteration agent was synthesized by emulsion polymerization using different molar ratios of fluorine-containing monomers and acrylic monomers. FTIR and SEM were performed to analyze the structure of the gas-wetting agent. Contact angle measurements were used to assess surface alteration by the Owens two-liquid method. The effects of alteration agent concentration, salt concentration, pH and temperature on gas-wetting alteration were also evaluated. Results showed that the best molar ratio of fluoropolymer monomer to acrylic monomers was 1:2. The egg-like structure of the fluoropolymer latex on the core surface mainly contributes to gas-wetting alteration. The contact angles of brine and oil can be altered from 23° and 0° to 137° and 67° by 1 wt% FP-2 treatment, respectively. The surface free energy of the core was reduced from 67.52 to 1.66 mN/m. Moreover, the treated cores remain gas-wetting up to 100 g L−1 of salt solution, 120 °C and within the pH range of 5–7. This novel gas-wetting alteration agent can be used to solve the problem of liquid blocking effects in gas condensate reservoirs and improve gas recovery significantly.

In gas condensate reservoir, liquid condensation near the wellbore region might kill gas well deliverability, research shows that gas-wetting alteration can be one of effective methods to alleviate liquid condensation in porous media. However, the wettability of cores can only be altered from liquid-wetting to intermediate gas-wetting, making the improvement for gas well deliverability very limited. To achieve super gas-wetting alteration, nano-silica was modified functionally by the fluorosurfactant FG40. To evaluate the influence of gas-wetting alteration on cores, the contact angle measurement, Owens two-liquid method, capillary rise, and imbibition spontaneous tests in the CH 4 -liquid-core system were conducted, respectively. The results showed that the wettability of the core can be altered to intermediate gas-wetting or super gas-wetting after treatment by the FG40, FP-2, and FG40 modified nano-silica. The contact angles of the brine and decane on the core surface increased from 23° and 0° to 152° and 127°, respectively, after the 0.5% FG40 modified nano-silica treatment; these angles are obviously higher than in those cores treated with FG40 and FP-2 solutions at an equivalent concentration. Meanwhile, the surface free energy of the cores sharply decreased from about 70 mN/m to approximately 0.61 mN/m after the FG40 modified nano-silica treatment. The results of the capillary rise and imbibition tests were also consist with that of the contact angle measurement; the liquid levels of brine and decane significantly decreased from 27 and 13.5 mm to −20 and −7 mm, respectively, after treatment by the FG40 modified nano-silica solution. The imbibition of brine and oil in the core also decreased sharply due to the super gas-wetting alteration. Results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) demonstrated that the botryoidal structure of gas-wetting particles plays a vital role in gas-wetting alteration, which can alter the wettability of the core from strong liquid-wetting to super gas-wetting.

Liquid condensation near the wellbore region may cause cessation of gas production in gas-condensate reservoirs when pressure drops lower than its dew point. It is believed that gas deliverability can be enhanced by altering the wettability of reservoirs to gas-wetting. In order to investigate the influence of wettability alteration on the displacement efficiency of gas-condensate, contact angle measurement and gas flood tests were conducted. Results show that core wettability can be altered from liquid-wetting to intermediate gas-wetting or preferential gas-wetting by the fluorosurfactants FG24 and FG90. The contact angles of brine and decane indicated that core wettability can be altered from liquid-wetting to preferential gas-wetting by FG24 at a concentration of 0.3%, and by FG90 at 0.5%. Surface free energy before and after core treatment was measured by Owen's two-liquid method, the results showing that core surface free energy sharply decreased from 70 to about 3 mN/m after FG24 treatment. Oil disp...

Gas condensate reservoirs often experience a sharp reduction in gas deliverability when the wellbore pressure drops under its dew point, this is known as liquid-blocking effect in gas condensate reservoir. Many solutions with limited effectiveness were proposed to figure out the problem, and wettablity alteration is proven to be one of effective measures for liquid-blocking effect. Recent investigations show that the wettability of core near wellbore region can be permanently altered from water-wet or oil-wet to intermediate gas-wetting with the fluorosurfactant treatment, and the mobility and distribution of fluids in porous media can also be significantly improved after gas-wetting alteration. The objective of this study was to find out the effect of gas-wetting alteration by fluorosurfactant modified nano-silica on the gas recovery in methane-liquid-rock system. The fluorochemicals are widely used to change the surface properties of solid to achieve a surface with a low surface free energy. In this study, gas-wetting alteration on solid surface is achieved with fluorosurfactant and fluoropolymer. In order to obtain a super gas-wetting, nano-silica particles with a size of 40 nm was functionally modified by fluorosurfactant. Contact angle measurement, Owens two-liquid method, and capillary rise in methane-liquid-core system were conducted to evaluate the effect of gas-wetting alternation on the cores wettability and gas recovery. Data of Contact angle measurement showed that the core wettability can be altered to gas-wetting or super gas-wetting after FG40, FP-2 and FG40 modified nano-silica solution treatment, the contact angles of brine and decane on core surface increased from 23° and 0° to 152° and 127° after treated by 0.5% FG40 modified nano-silica solution, respectively. The surface free energy of cores before and after treatment shows that the sueface free energy decreased from 70 mN/m to approximately 0.61 mN/m. The results of capillary rise and imbibition test verified that of the contact angle measurement and surface free energy, the liquid levels of brine and decane significantly decreased to -20 and 7 mm when the wettability of capillary atered to gas-wetting. Analysis of SEM and TEM indicated that the gas-wetting nano-silica can form a gas-wetting adsorption layer with coarse structures on core surface, which play a vital role in super gas-wetting. In summary, the cores wettability can be altered from liquid-wetting to super gas-wetting by the novel fluorosurfactant modified nano-silica, and gas deliverability can be significantly improved due to super gas-wetting alteration.

Liquid condensation in the reservoir near a wellbore may kill gas production in gas-condensate reservoirs when pressure drops lower than the dew point. It is clear from investigations reported in the literature that gas production could be improved by altering the rock wettability from liquid-wetness to gas-wetness. In this paper, three different fluorosurfactants FG1105, FC911, and FG40 were evaluated for altering the wettability of sandstone rocks from liquid-wetting to gas-wetting using contact angle measurement. The results showed that FG40 provided the best wettability alteration effect with a concentration of 0.3% and FC911 at the concentration of 0.3%.