Page 88 - Principles of Applied Reservoir Simulation 2E

Part I: Reservoir Engineering Primer 73

or completely block the flow of fluids through pipeline networks. Heating the
gas or treating the gas-water system with chemical inhibitors can prevent the
formation of hydrates, but increases operating costs,
Gas hydrates are generally considered a problem for oil and gas field
operations, but their potential commercial value as a clean energy resource is
changing the industry perception. The potential as a gas resource is due to the
relatively large volume of gas contained in the gas hydrate complex. In
particular, Makogon, et al. [1997] have reported that one cubic meter of gas
3
hydrate contains 164.6 m of methane. This is equivalent to one barrel of gas
3
hydrate containing 924 ft of methane, and is approximately six times as much
gas as the gas contained in an unimpeded gas-filled pore system [Selley, 1998,
pg, 25]. The gas in gas hydrates occupies approximately 20% of the volume of
the gas hydrate complex. The remaining 80% of gas hydrate complex volume
is occupied by water.
Gas hydrates can be found throughout the world [Selley, 1998; Makogon,
et al., 1997]. They exist on land in sub-Arctic sediments and on seabeds where
the water is near freezing at depths of at least 600 to 1500 feet. For instance,
favorable conditions for gas hydrate formation exist at sea floor temperatures
as low as 39°F in the Gulf of Mexico and as low as 30°F in some sections of the
3
North Sea. According to Makogon, et al. [ 1997], over 700 trillion m in explored
reserves of methane in the hydrate state exist. Difficulties in cost-effective
production have hampered development of the resource.

Exercises

Exercise 8.1 Use the definitions in Table 8-1 and Eq. (8-1) to derive Eq. (8-2)
fromEq. (2.3).

Exercise 8.2 (A) Which drive index in Table 8-1 will be largest in a field
containing a dead oil that is subjected to pressure depletion? (B) Suppose a dead
oil reservoir is subjected to a peripheral waterflood. Identify the two drive
indices in Table 8-1 that will have the greatest influence on oil recovery.