Many conventional laboratory investigations have been performed on laboratory — synthesized samples. These allow the flexibility of creating samples that have desired characteristics. Few laboratory-synthesized samples have been examined for uniformity, and this characteristic is often (perhaps hastily and undeservedly) assumed. Several methods are in use for making HBS, and each has its advantages and disadvantages.

Hydrate from ice. In this method, powdered ice is slowly melted in the presence of methane at the appropriate pressure and temperature [187]. As the ice melts, methane hydrate is formed. Sequential freezing and melting events can result in very high conversions to hydrate. The hydrate can then be chilled in liquid nitrogen, powdered, mixed with a selected chilled mineral medium, and compacted into a hydrate-bearing medium. Nanoscale examination of HBS formed this way by scan­ning electron microscope compares favorably to natural HBS from the Mallik site [186]. HBS formed this way will typically fill pores as well as be part of the frame of the medium.

Hydrate from partially water saturated media—Excess Gas. In this method, a pre­scribed amount of water is uniformly added to a mineral medium, compacted into a sample vessel, and the hydrate stability conditions are exceeded [61, 87, 208] . Hydrate formed using this technique typically cements mineral grains together forming a stiff sample [208].

Hydrate from partially water saturated media—Excess Water. Using a somewhat different approach, Priest et al. [154] formed methane hydrate by placing the quan­tity of gas needed to form a specific amount of hydrate in a porous sample, pressur­izing the sample with water, and then chilling the sample to bring it into the hydrate stability field. Their work suggests that hydrate interaction with the sediment is strongly dependent on hydrate morphology, with results indicating that hydrate formed this way is frame supporting. Additionally, natural GH may exhibit a differ­ent seismic signature depending on the environment in which it formed.

Hydrate from dissolved guest phase. In this method, water containing dissolved methane is flowed through a chilled porous medium where hydrate is formed. Although there have been some successes using this technique, it is difficult to con­trol and time consuming [184, 185].

Micromodel studies of gas hydrates. Several studies have been performed allowing direct microscopic examination of hydrate formation, aging, and dissociation in transparent micromodels [76-78, 191, 192]. These studies show formation of hydrate with and without a gas phase, formation of dendritic hydrate crystals that age over time into particulate hydrate crystals, and faceted hydrate crystals formed at low subcooling. The presence of a water film between the hydrate and the micro­model cell walls has been observed in some tests, but not in others leading to the conclusion that hydrate may cement grains together when formed with a low degree of subcooling.