RE: mmm17 Dec 2018 12:55
ddboy
ddboy
Based on news from Sound and previous drilling it looks like the Tagi age-equivalent, ‘non-reservoir ‘in TE-9 is actually a pretty good cap-rock! Very similar as to the Mercia Mudstone which is the top-seal to the Sherwood Sandstone at the Wytch Farm oil-field, except at TE-9 there was no good lower Tagi sandstone.
Furthermore, cementation of the pore spaces probably took place soon after the fine-grained sandstone was deposited or possibly just before the gas was migrating. The TE-9 results reported ‘gas readings in both the TAGI and Palaeozoic intervals showed a range of C1 to C5 hydrocarbons’. So, we’ll probably see same in TE-10. Either way, unless petroleum arrives to completely fill a trap before diagenesis clogs up the pores, reservoir effectiveness will be destroyed, but some gas bubbles remain.
Moroccan geologists see distinct lithologies in the Tagi with the best reservoir near the base. These comprise a first-order trend over the Tagi sequence. At the base are perennial braidplain to ephemeral sheetflood systems (good reservoirs) which grade upwards to ephemeral lacustrine/playa lake conditions (non-reservoirs). This trend culminated in deposition of the salt, and reflects a long-term waning of sand supply and increasing ‘flashiness’ of river water arriving in the fluvial system which was touched on at the DD.
Work by Onhym and Prism Seismic during Fastnet’s tenure improved the understanding of both the structural mapping and the reservoir presence in the area covered by 3D seismic. Simple RMS amplitude analysis enabled extraction of ‘geobodies’ where the best TAGI sand development may be present - although this approach has never been tested by the drill. Maybe something for TE-11 instead of a high risk Palaeozoic prospect.
3D seismic seems to be the key. As well as the TE-5 Horst, Fastnet mapped a number structural leads in the Contract Area, including SBK that tested gas in 2000. Fastnet realised that none of the structures - including SBK, the A1 structure and the TE-10 strat trap - warranted drilling on 2D seismic and 3D seismic would be required over the leads to develop prospects with a tolerable CoS. In contrast, Sound elected to drill rather than spend more money/time on 3D seismic, which seemed like a reasonable compromise at the time. Fastnet identified further leads within the 3D seismic grid over the TE-5 Horst which remain un-drilled and might become satellites to the TE-5 development.
I imagine similar discussions have taken place in `Sevenoaks and Rabat in recent weeks. BM and the team have a real challenge on their hands - one of the most difficult geo-puzzles to solve. Yes, the gas is there, but where is the best Lower Tagi reservoir?