As oil and gas production
moves into deep water, the formation
of gas hydrate has been a primary flow assurance challenge in the
deep water pipelines. Because of the complex composition of crude
oil and various additives, the objective of this work is to study
the effect of additive hydrophilic–hydrophobic property on
hydrate formation in the emulsion, which usually occurs in pipelines.
The formation experiments of methane hydrate in emulsion with the
same water cut but surfactants of different hydrophilic lipophilic
balance (HLB) values were conducted. The emulsion was prepared with
mineral oil, deionized water, and two types of non-ionic surfactants
(Span 80 and Tween 80). The experimental results indicate that with
the HLB value increasing, the emulsion was divided into relatively
stable water-in-oil, the phase transition region, and stable oil-in-water;
meanwhile, the effect of the hydrophobic surfactant on hydrate formation
also changed from inhibition to promotion to inhibition. In addition,
hydrate formation is closely related to pressure, temperature, and
stirring speed. The higher the pressure and the lower the temperature,
the easier the methane hydrate formation. The increase of stirring
speed within a certain range (less than 300 rpm) could significantly
shorten the induction time of methane hydrate formation and accelerate
the formation rate. As the stirring speed continued to rise to 500
rpm, the induction time of methane hydrate formation became longer,
but the formation rate had a significant acceleration.
Solid fluidization is a current promising
method to explore hydrate
resources. The rheological properties of hydrate slurry are significant
to solid fluidization and prevent hydrate blockage during pipeline
transportation. To determine the impact of hydrate on the rheological
properties of mudflow, a rheological experiment was conducted on methane
hydrate slurry formed from a mudflow, which was prepared with marine
sediment sampled from South China Sea. It was found that both mudflow
and hydrate slurry exhibited viscoelastic fluid properties. The existence
of hydrate substantially increased the apparent viscosity of the mudflow,
and when the hydrate formed at a rapid rate, the apparent viscosity
rose rapidly. With different initial pressures, the amount of hydrate
formed in mudflow was different. A larger water conversion rate would
increase the viscosity of the hydrate slurry significantly. Meanwhile,
a yield stress measurement was conducted by stress sweep after hydrate
formation. When the water conversion fractions were 17.8%, 20.3%,
and 21.2%, the yield stresses of the hydrate slurry were 57.8, 465.2,
and over 10,000 Pa, respectively. In addition, a frequency test sweep
was conducted, and the results showed that the existence of hydrate
would significantly increase the elasticity of the slurry.
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