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Author: David Alejandro Contreras Díaz, Business Development Manager at TGS
TGS' 2D seismic example (NWAAM 2012 reprocessed in 2018)
This is the first of a series of articles that I will be co-authoring with my counterpart and colleague in The Republic of Guinea’s Office National des Pétroles (ONAP), Cherif Diallo -Upstream Director, and TGS’ senior geoscientist, Felicia Winter.
TGS was one of the early movers in the MSGBC basin. Quick in recognising the full potential of the offshore area, the company in 2012 planned and acquired the first of two regional and complementary 2D campaigns – the so-called NorthWest Africa Atlantic Margin (NWAAM Phase 1 and in 2017 Phase 2 (link) – that served as the regional tool for hydrocarbon explorationists to screen and mature their prospect ideas from Mauritania to the Republic of Guinea. To bring these programs to market, TGS effectively positioned itself (and continue to do so) to become the partner of choice with each of the governments that comprise this emerging region: Mauritania, Senegal, The Gambia, the AGC (Agence de Gestion et de Coopération entre le Sénégal et la Guinée-Bissau), Guinea-Bissau and the Republic of Guinea.
2014 and 2015 became the pivotal years for the basin due to the exploration success and discoveries of SNE (now Sangomar) in Senegal (made by Conoco, Cairn and FAR) and Tortue on the Senegalese-Mauritanian border made by Kosmos.
Fast-tracking to 2018, TGS embarked in a multi-acquisition and reprocessing opportunity to move to the next stage of investment, and bring to the market an ultra-regional 3D dataset of almost 30,000 sq.km. The Jaan 3DMC survey was born (link), comprised of six new acquisitions that were merged, harmonized and homogenized via the reprocessing of nine vintage 3D surveys. The resulting PSDM and PSTM products are now the go-to-dataset to understand the complexities of the central and southern portions of the MSGBC basin.
Jaan (orange polygon on the left) was conceived to chase the succesful palaeo-shelf edge trend (PSET) prospectivity -proven in SNE- towards the south, all the way to almost the limit of Guinea-Bissau with the Republic of Guinea, where similar plays can be found as well as differing opportunities. Deep-water and ultra deep-water clastic reservoirs (structural and structural/stratigraphic nature plays) are bountiful and so are salt-related structures in both the shelf and in the basin. Even carbonate plays, historically under-explored in this region, are now well identified with expected reefal facies and with both 4WD and 3WD trappings.
The overall results and in particular, the geochemistry of several of the cores analysed is quite exciting ... they will help NV teams revise, re-calibrate and in some cases reassess the prospectivity seen, studied and perceived in more frontier regions of the MSGBC basin
This great program was complemented with the acquisition of 114,670 sq.km Multibeam (light blue polygon above) and SeaSeep coring program or the MB&SS campaign in the MSGBC (link). The overall results and in particular, the geochemistry of several of the cores analysed is quite exciting (please get in touch to know more), and we believe that they will help NV teams revise, re-calibrate and in some cases reassess the prospectivity seen, studied and perceived in more frontier regions of the MSGBC basin, like Southern Guinea-Bissau or the AGC area.
Having the luxury of using the sheer scale of these complementary datasets, our geoscientists are now able to draw some very valuable insights and conclusions of what the MSGBC future looks like. One of them is the natural extension of the Cretaceous clastic fairway towards the south of the basin, into a very structurally complex region, but highly prospective: the Guinea Plateau.
So let’s dive in!
From previous regional interpretation, we gain a framework of the main structures and sequence changes across the margin. The high pass filtered Bouguer Anomaly (left figure above) showcases the main structures with the interpretation of play domains superimposed (central figure). The basin imprints on the shelf are easily distinguished from the deepwater domain. Seismic interpretation superimposed in form of domain polygons (central figure highlighting the presence of the carbonate platform, salt bodies, presence of volcanics) enable the identification of the southern edge of the Guinea Plateau, the Guinea Transform Fault System (GTFS) and seen also on the right side in context with TGS’ 2D library, with E-W movement and also appreciated in the figure below.
Zooming in on Guinea’s margin, it’s easy to appreciate how exciting this whole area is from a tectonic point of view. For example, a westwards extensional regime related to the rift of the margin is appreciated in the offshore portions of the AGC and Guinea-Bissau area. This westward movement meets the transform fault regime of the GTFS in the south which, being a dextral strike slip system, poses an eastward movement for Guinea’s shelf. Those opposing directions cause a tectonic strain that is released by NE-SW fault trends dissecting the shelf area perpendicular to the coast and margin edge. These driving forces provide an intriguing background for trap mechanisms in the fairways.
In order to correctly interpret the different play fairways, the depositional framework has to be well understood, which you can appreciate on the composite seismic line (figure above), which runs from the NW offshore Senegal to the south and then SE along the Guinea shelf.
The transect is running from the complicated and quite rugose slope environment offshore AGC and Guinea-Bissau onto the Guinea Plateau following the margin up-dip onto the shelf offshore the Republic of Guinea. The primary sequences are interpreted on this 2D seismic line, setting the context for the play fairway interpretation.
The post rift sediments are getting thinner in certain areas closer to the shore as expected, but that does not rule out the very interesting prospectivity of Cretaceous sequences in the deep-water. It’s also noticeable the rift basin structure buried below, which has been under-explored and that should contain a Jurassic petroleum system that has intrinsic source rocks and fluvial-clastic-reservoir potential, with easy access to charge (via the main extensional faults).
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