The Effect of Fluoropolymer on Wettability Alteration of Sandstone at Elevated Temperatures

Abstract

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.

Morphology and Surface Chemistry of Gas-Wetting Nanoparticles and Their Effect on the Liquid Menisci in Porous Media

“…The accumulation of condensate easily causes an annular blocking area near the wellbore region during the isothermal depletion production, resulting in a sharp reduction in the flow efficiency, further curtailing the gas deliverability. , Gas-wetting alteration derives from the classical theory based on the wettability alteration, , which has proved to be a feasible and cost-effective stimulation to alleviate the liquid blockage of the condensate reservoir. The performance of gas-wetting alteration mainly depends on the agents, condensate, the geometry of pore throat, and the liquid menisci, among which both gas-wetting agents and the flow of liquid menisci play vital roles in mitigating the liquid-blocking effect.…”

Synthesis and Evaluation of Two Gas-Wetting Alteration Agents for a Shale Reservoir

“…At low concentration, a few molecules adsorbed onto the surface of the shale through van der Waals forces, and the adsorbed molecules are easily desorbed or replaced by molecules in other solutions . At higher concentrations, the adsorption capacity is greater than that of desorption, and as a result, more gas-wetting alteration agents are adsorbed on the shale and form a gas-wetting molecular layer on its surface , so that the wettability of the shale is altered from strong liquid-wetting to gas-wetting. With a further increase of the concentration, the adsorption capacity of the shale surface tends to be saturated and the wettability becomes stable …”

Study on Wettability Variation for Removing Liquid Block in Condensate Gas Reservoir

“…The prepared silica sol was put into a stainless steel bottle, then the natural sandstone core was soaked in the sol. After closing the bottle, it was maintained at 120°C for 40 min [10,11], allowing for the porous medium of the core to sufficiently absorb the sol. The cores were then taken out and dried in an oven at 105°C for 1 h. Later, the core was soaked in FC3721 solution at 120°C for 48 h, and then the core was removed and dried at 105°C for 48 h.…”