To 3D or not to 3D?5 Jun 2025 03:06
part 1.
@jimmy23:
in your first of many posts yesterday, you stated that new 3d is needed since “previous seismic interpretations have encountered unexpected results when actually drilled”, with subsequent arguments based around that. let's look at those actual drills, and see what difference 3d would have made.
mou-1. successfully penetrated the bright spot seen on 2d seismic, found 12m net of gas-charged tgb2 sands as expected, plus unexpected 10m net of thin beds. post-drill realisation that tgb2 extended over far greater area. ultradrill mud interacted with expanding clays. 3d would have added nothing to these results, other than possible pre-drill identification of more extensive tgb2, which drilling identified anyway. it would not have identified expanding clays, nor probably the thin beds.
mou-2. to avoid the expanding clay issue seen in mou-1, purebore silicate drilling mud was used. the slump would have been visualised on 3d, but 3d would not indicate that it was potassium silicate rich volcaniclastics that were going to interact with the drilling mud.
mou-3. this well successfully passed through the slump due to change of drilling mud. 3d seismic would have shown the shallow a-sands gas, but would not have indicated that it was under such high pressure, so the problem would have been the same. formation damage lower down would still be the same, because 2d or 3d, precautionary overbalanced drilling would still have been necessary.
mou-4. despite only having 2d, the well successfully penetrated both neogene & jurassic as planned. lack of flow testing has nothing to do with lack of 3d seismic.
mou-5. 2d seismic failed to differentiate between salt and carbonates. this is likely to be because salt, being crystalline and ****genous, has the same s-wave conduction velocity as carbonate/dolomite with 15-20% porosity. if the carbonate porosity was less, as you have suggested previously on multiple occasions, the boundary would have shown up clearly. 3d would help the visualisation, but i firmly believe that ftg (gravity survey) would be necessary to complement the 3d – this would help identify both mobilised salt and the profile of the basement rise that the jurassic reef is built upon. i agree with you that carbonate reefs can be discontinuous both horizontally and vertically, and i have always said i have no intention of selling my prd holding until at least 4 holes have been stuck into titanosaurus.
so should prd have used 3d? the area covered by mou-1 to mou-5 is around 200km². at a very conservative $50k per km² we get to $10m. although some of this is scrubland, there are also built-up areas, extensive olive groves with irrigation systems, a motorway, major roads, two large rivers and a gas pipeline for the poor vibroseis trucks to negotiate. this will complicate matters and push up the price – even a modest $12m is the same price as an additional 4 wells.