STUDY ON THE SEISMIC CHARACTERISTICS OF THE GAS HYDRATE SYSTEM IN THE NIGER DELTA

Abstract

Gas hydrate system is generally indicated by seismic indicators like bottom simulating reflection (BSR) and underlying high amplitudes (often caused by free gas zones: FGZs), but not all BSRs and underlying high amplitudes are caused by hydrates or free gas. In this study, we choose apparent polarity attribute to help identify hydrate-related BSR and FGZs, both of which are characterized by negative apparent polarity and high amplitude. In the study area, the gas hydrate system is mainly distributed in areas with gravitational structures including growth faults and related rollover anticlines. Faults, chimneys, unconformity and permeable sandstone beds can act as fluid migration conduits, supplying gas to the shallower gas hydrate system. When gas hydrates dissociate or the FGZs are critically overpressured, these conduits can also play a role in gas recycling between the FGZs and hydrate-bearing strata with some of the free gas escaping to the seabed and even to the atmosphere. Generally, apparent polarity is an effective attribute to identify hydrate-related BSR and FGZs, and fluid migration pathways are of great importance for the formation of gas hydrate system in this study area.