OS3B-7:USE OF SEISMIC DATA TO CHARACTERIZE POTENTIAL GAS HYDRATE BEARING SEDIMENTS OFF THE EAST COAST OF TRINIDAD

Uwaila IYARE

University of the West Indies, Trinidad Tobago

Trinidad and Tobago is endowed with abundant conventional hydrocarbons both onshore and offshore. A significant amount of the reserves have been found in the shallow water shelf area offshore eastern Trinidad.  In recent years,  the exploration work in the deep water blocks beyond the shelf (>1000m), has proved the existence of unconventional natural gas resources in the form of gas hydrates.

It is important to note however, that not much work have been done to identify and quantify gas hydrate reserves present in this deep water area.  This paper looked at the prospect of the occurrence of gas hydrate in the Block 25A area.  3-D post stack seismic reflection data were examined for the main seismic signature of gas hydrate i.e. a bottom-simulating reflector (BSR), and other geophysical features of hydrate accumulations. The paper also provides an indication of the in situ resources of the seismically inferred gas hydrate accumulations and estimates of the volume of gas trapped as gas hydrates in the study area. This possible resource was estimated using reservoir parameters observed in geological depositional environments similar to Trinidad.

The marine seismic data set covered approximately 219 km² in an area where the Orinoco delta overlaps the Barbados accretionary complex along the leading edge of the Caribbean plate. The post stack seismic reflections data showed that prominent seismic bottom-simulating reflectors (BSRs) are presented and indicate the existence of gas hydrate in the sediment. Enhanced seismic reflections’ showing high amplitude values was observed beneath the BSR, and indicates the presence of free gas. Also observed was a reduction in amplitude strength of seismic sections just above the BSR.

This was interpreted as blanking.The bottom simulating reflector (BSR) was mapped over an areal extent of 62.628 km² or approximately 29% of the study area. The volume of gas trapped as gas hydrates in the study area was estimated to range between 9.9 BCF/ km² and 43.3 BCF/ km², with a mean of about 23.5 BCF/ km²