GAS HYDRATE AND FREE GAS VOLUMES IN MARINE-SEDIMENTS - EXAMPLE FROM THE NIGER DELTA FRONT

Bottom simulating reflectors (BSRs) detected on reflection seismic rec ords from various deepwater locations world-wide, are known to occur a s a response to the formation of gas hydrates above the reflector, and accumulation of small amounts of free gas below the reflector. Althou gh estimates of enormous potential energy resources, and dramatic clim ate change scenarios have been discussed on account of the BSRs, our c onclusions with respect to the commercially recoverable amounts of ene rgy from gas hydrates and free gas associated with BSRs on the Niger D elta front, are disappointingly negative. We base our estimates on rec ent results from BSR-penetrating scientific drilling, a review of natu ral gas hydrate observations, and on theoretical considerations of gas hydrate formation and host sediment conditions. The main conclusions are as follows: 1. Natural gas hydrates and BSRs most probably occur a s a direct consequence of focused and diffusive vertical fluid escape. 2. The mean maximum amount of gas hydrates residing in sediments abov e the BSR is most probably only 3% by volume. 3. The mean maximum amou nt of free gas charge in the sediments below even well developed (stro ng) BSRs is only 5% by volume. 4. Currently there is no commercial pot ential for recovering and exploiting 'trapped' energy sources in the f orm of BSR-associated gas hydrates and free gas on the Niger Delta fro nt, mainly because they occur as dispersed, rather than concentrated d eposits. (C) 1997 Elsevier Science Ltd.