BAKER HUGHES - Drilling Fluids Reference Manual

TABLE OF CONTENTS
Dodecahedron
Gas hydrates are crystalline structures consisting of hydrogen
bonded water lattices providing a cage like structure that host
molecules of natural gas. These gas molecules are trapped in
the middle of the cage with their repulsive energy stabilizing
the strong hydrogen bonds of the water lattice. Common
hydrate structures may contain eight to twenty-four cavities,
with each cavity having a single molecule of gas. The final
composition of the gas hydrates being approximately 15 %
gas and 85 % water. Gas Hydrates are described as gas
concentrators with the breakdown of a unit volume of
methane hydrate at a pressure of one atmosphere producing about 160 unit volumes of gas.
HYDRATE FORMATION & OCCURRENCE
Hydrates are found naturally in the sediments in deep cold marine environments. They may also be
incorporated into the formation.
Gas hydrates are formed by anaerobic bacteria digesting organic matter (detritus) under the ocean
floor. During the digestion process mainly
Gas Hydrates Offshore Sakhalin Island methane is produced along with small
amounts of carbon dioxide, hydrogen
sulfide, propane, and ethane. The produced
gases rise, dissolving in the water between
the ocean sediments.
When the temperature, and pressure
conditions at the ocean bottom are
appropriate (high pressure and low
temperature) hydrates are formed. In
addition to the formation of hydrates, vast
reservoirs of methane gas often form
beneath hydrate layers. Methane hydrate is
stable in ocean floor sediments at water
depths greater than 1000 ft (300 m), and
where it occurs, it is known to cement
loose sediments in a surface layer several
hundred meters thick.
When hydrates are incorporated into the
formation they have to be maintained during the drilling operation to avoid the collapse of the
surrounding seabed.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 13-12