Effects of Different Factors on Methane Hydrate Formation Using a Visual Wellbore Simulator.

During hydrate exploitation, the formation and decomposition of hydrate in the wellbore are affected by many factors such as salinity, temperature, pressure, gas-liquid ratio, and so on. In the drilling process, inhibitors will be added into the drilling fluid, to prevent the formation of hydrates in the wellbore to form blockages. In order to explore the influence of these factors on the formation and decomposition of hydrates, a visual wellbore simulator was used to study the formation, inhibition, and decomposition of hydrates in the wellbore, which affected these factors. First, the accuracy of device was verified, and then the effects of water type, pressure, inhibitor, and gas-liquid ratios (GLR) on methane hydrate (MH) formation were studied. The results show that (1) In fresh water, after the formation of methane hydrate, the pressure of methane gas in the container drops by 6.73 MPa, while in 10% NaCl brine, the pressure of methane gas in the container only drops by 1.24 MPa, since the NaCl is a thermodynamic inhibitor, which inhibits the formation of MH, the amount of dissolved gas in the brine is less, resulting in less pressure drop within the container. (2) Compared with fresh water, the kinetic inhibitor GID3 can better inhibit the generation of MH, but when the dosage of GID3 is 1.0 and 2.0 wt %, the pressure drop of MH in the container is 0.71 and 2.18 MPa, respectively. Therefore, excess inhibitor will reduce its inhibitory effect. (3) When the pressure and GLR increase, the hydrate can absorb more methane after it is formed. However, when there are inhibitors in the fluid, the law of dissolved methane becomes complicated. (4) Appropriate decomposition solution helps to accelerate the decomposition of MH and reduce hydrate blockage in the wellbore during drilling. This article provides a reference for the formation of hydrate in the wellbore during hydrate exploitation.