B41oa oil and Gas Processing Section a flow Assurance Heriot-Watt University

1.2.1 Interesting Properties of Gas Hydrates 
Gas hydrates have very interesting properties. The important ones can be 
summarised as: 
Hydrate Capture Volume 
Gas hydrates can capture large amounts of gas – they can hold up to 15 
mole% gas. Thus one volume of hydrate can hold up to 175 volumes of gas at 
standard conditions. 
Many of the gases that form gas hydrates are generally considered to be 
insoluble in water (e.g. methane) yet, in the case of a hydrate, the gas may be 
up to 15 mole% of the total. Some researchers are considering the storage 
and transportation of oil and gas in the form of solid gas hydrates. 
Hydrate Guest Selectivity 
Hydrates remove light components from oil and gas. Gas hydrates are formed 
from relatively small molecules (e.g., C
1
-C
4
, CO
2
and N2). Therefore, their 
formation removes light components from oil and gas. 
This property could be bad news if gas hydrates are formed inadvertently, as 
their formation will increase the viscosity of the remaining oil. However, some 
researchers consider this as an opportunity for separating oil and gas under 
controlled conditions and reducing the load and size of conventional 
separators. 
Hydrate Formation Temperature 
Gas hydrates can form at temperatures well above 0
o
C (see figure 4 for 
methane hydrate). The presence of gas molecules in the cavities stabilises the 
crystal lattice. In general, near spherical molecules with sizes near to that of 
the cavity are the best for gas hydrate formation, such species have strong 
van der Waals forces with the oxygen atoms in the surrounding water 
molecules. The potential formation of gas hydrates at temperatures well above 
ice point has both positive and negative impacts, which will be discussed later. 
Hydrate Density 
Gas hydrates are generally lighter than water, with the exception of gas 
hydrates of high molecular weight compounds, such as CO
2
, Xe, etc. Gas 
hydrates formed in almost all reservoir fluids are lighter than water, facilitating 
their separation and/or transportation. 
The fact that gas hydrates of CO
2
are heavier than water could be used as a 
useful technique for the disposal of this greenhouse gas in deep ocean waters. 

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TOPIC 1: Gas Hydrates 
 
 
 
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ERIOT
-W
ATT
U
NIVERSITY B41OA December 2018 v3