5th Conjugate Margins Conference, Porto de Galinhas, Pernambuco, Brasil, 22-25 August 2017
Article by Ian Davison, Earthmoves Ltd
The 5th Conjugate Margins Conference was held near Recife in Brasil this year after the conference was postponed last year due to the outbreak of the Zika virus and the state of the global petroleum industry. About sixty-five people attended the event with approximately half the participants being international delegates. The conference was held in the Enotel beach resort, appropriately situated overlooking the South Atlantic Ocean and the Pernambuco Basin, which was the subject of several talks. There was a healthy spread of ages at the conference with many good talks given by young researchers. Despite the reduced number of attendees the conference was a great success with high quality academic and petroleum industry talks and plenty of lively discussion. I believe we should have more of these specialised conferences with no parallel sessions. This permits exposure to topics and issues outside of one’s knowledge comfort zone, and importantly, one gets to know most of the participants by the end of the conference. I cannot mention every talk in the conference so I have picked out a few of the highlights below, so sorry to the other speakers if you do not see your names below.
The conference began with a stimulating keynote talk by Marina Abelha of the Brazilian National Petroleum Agency (ANP), where she outlined the huge opportunities which are on offer in the forthcoming 14th Brasil round and various future Production Sharing Contract rounds. Marina summarised the current activity in Brasil which highlighted the reduction in drilling activity with only seven exploration wells drilled in the last twelve months. There are only four pre-salt carbonate fields currently producing in Brasil, but these are responsible for 1.3 million bopd of production from just 77 wells. This indicates the huge future potential production which can be expected from these unusual reservoirs. She also mentioned the worrying occurrence of mantle-derived C02 which has been encountered in ten dry wells so far. It is a very difficult to predict which structures will be oil-filled and which may be filled with CO2.
Several talks followed on the structure of the Brazilian basins, the underlying and adjacent Precambrian basement structures and models for extension. Renata Schmitt presented a talk on the new IGCP project no.628 Gondwana continental fit map which is due to be released in 2018. The reconstruction will take into account internal deformation of the plates and she outlined the main shear zones boundaries which have been active during Gondwana break-up. Marta Perez-Gussinye gave a stimulating overview of the findings from numerical modelling which outlined the reasons for different modes of extension due to the variation in strength of the lower crust. Weak lower crust gives rise to a wider margin with small offset faults (e.g. Campos-Santos segment) whereas a strong lower crust leads to coupling between the mantle and the crust with narrow margin development larger faults and possible mantle exhumation (e.g. Camamu-Almada) occurring. Jose Ricardo Goncalves described the structure of the Pernambuco Basin where an unusual localised occurrence of synrift salt occurs. There are no wells in this basin but several oil slicks have been observed in the area where the thickest synrift fill occurs.
Ian Davison spent the last hour of the day reviewing the formation of Seaward Dipping Reflectors and showing their influence on hydrocarbon prospectivity in Gabon and Sergipe-Alagoas. The high quality seismic evidence from the South Atlantic indicates the down dip terminations of the reflectors are not faulted, and the diffuse termination may be the contact with irregular magma chambers. The Mozambique Lebombo onshore SDR sequence provides important clues to the importance of dyking and mass transfer of material from below the erupted lavas to above them. He suggests this is the main cause of the observed subsidence of the lava reflectors which can be up to 20 km thick in the Pelotas Basin, rather than magma loading or extensional faulting that has been suggested by previous authors. The following day Tim Reston described the 3D geometry of detachment faulting observed offshore northern Iberia where the detachment appears to coincide with the Moho and produces an extremely strong reflector which exhibits mega-grooves parallel to the slip direction. Several faults appear to be active at any one time which sole down onto the detachment and the low angle surface must have a very low angle of friction to allow sliding which is presumably serpentinised and tectonised mantle.
Katie Hernon described the geology of the Porcupine and Goban Spur Basins which are conjugate to the Orphan and Flemish Pass Basins. So far only several small sub-commercial fields have been discovered in Jurassic rotated fault blocks. However, Providence Resources are currently drilling an interesting well testing lower Tertiary and lower Cretaceous stratigraphic traps for the first time in the Porcupine basin. Hans BjØrnseth described the thick pre-salt rift and sag basins of the Congo and Gabon segment and showed the Melania source rock appears to have acted as an effective detachment surface with listric faults soling out at this level. The timing of faulting may have coincided with the onset of hydrocarbon generation form the source rock.
On the last day Leonardo Pichel gave a fascinating talk on ramp synclines developed in the Santos Basin due to downslope sliding of overburden sediment down and over a base salt ramp. This produces characteristic synclines with unconformities onlapped by sediment which was deposited during downslope sliding over the ramp. He showed how common these features are in the Brasilian basins, and how stacked unconformities can develop due to sliding over two closely-spaced ramps.
Conference co-chairs Joao Aduato de Souza Neto and Julio Cesar Horta de Almeida, Haydon Mort, and their team deserve special mention for organizing and running a successful conference under very challenging circumstances. All delegates appreciated their hard work and benefited from attending this important biennial gathering in such a beautiful setting.
Next year the conference will return to it place of origin – Halifax, Nova Scotia, Canada – on August 19-22, 2018. The conference will have three days of consecutive oral and poster sessions, two salt-related short courses, a core display and several field trips. More information is available on the conference website www.conjugatemargins.com. Note that this site also archives previous conference’s programs, extended abstracts, field trip guidebooks and the like for free downloading.