Gas hydrates: importance and applications in petroleum exploration

A recent hydrate resources assessment (Kvenvolden, Workshop Panel Discussion Proceedings (1998a) 1; Geological Society of London Special Publication, 137 (1998b) 9) concluded that gas hydrates might represent the most important gas resource for the next century estimated at 10(13) and 20 X 10(15) m(3) (standard conditions) of methane gas in onshore and deep offshore areas, respectively. Even though it is probable that these figures are overestimated, especially in offshore areas, and even though gas hydrates cannot be economically produced at present, they remain, however. an important gas resource and also need to be carefully considered in deep offshore petroleum exploration for different reasons. Gas hydrates fir st of all act as an efficient seal: significant amounts of gas can be trapped in some circumstances beneath the base or hydrate stability zone (HSC), or the bottom simulating reflector (BSR). Furthermore, as the stability of hydrates is effectively constrained thermodynamically, the BSR, if present, can he used as a direct thermal indicator. Predicting heat how is of great importance for modelling purposes in poorly explored offshore areas whenever there are no well data available. In addition, gas hydrates are a good direct hydrocarbon indicator: the presence of a strong BSR at the base of a gas HSZ and of foe gas indicates that the petroleum system has been active since a recent period. As exploration moves more and more towards deeper offshore areas, an accurate assessment of drilling and production hazards is of prime importance as they directly impact the exploration cost. (C) 2001 Elsevier Science Ltd. All rights reserved.