Reconstructing the Early Depositional History of a Failed Ocean Basin From a Large 3-D Dataset Acquired in the Colombia Basin, Western Caribbean Sea, Offshore Colombia

Abstract

Between the summers of 2015 and July 2016 Anadarko Petroleum Corporation acquired over 100 TB of 3D seismic data in the Western Caribbean Sea. The Esmeralda survey covers an area of almost 30,000 km² in water depths ranging from 1,700 to 4,000m.

The data were acquired in an ultra-deepwater play fairway in the heart of one of the world’s last unexplored Tertiary deepwater fan systems that was deposited by the Magdalena river. The Magdalena fan is a huge accumulation of Tertiary clastics over 10 kms thick. It sits above an unknown anomalously high amplitude, low frequency seismic facies deposited on what appears to be oceanic crust.

The 3D dataset shows aerially extensive and thick potential DHI anomalies in the fan sediments connected by normal faults to a deeper anomalous seismic facies speculated to be the source rock. The age of the reservoirs and source rock are unknown because there are no direct conventional well ties to the 3D data and only long-distance 2D seismic line ties to sparse DSDP/ODP well control. Regional geology suggests the reservoirs are Mio-Pliocene in age and the source rock is Cretaceous, implying good source rock sitting on oceanic crust.

In order to investigate how source rock could be sitting on oceanic crust, the 3D dataset was datumed on a seismic horizon near the top Cretaceous to remove the post depositional regional dip caused by differential crustal loading from the Magdalena Fan. The resulting time slices from the 3D cube show the basement fabric of the failed ocean basin including the extinct spreading ridge and fracture flow lines. Since the anomalous seismic reflectors filling the basement topography are roughly parallel to the datum horizon, time slices through them effectively represent moments in time during the early depositional filling of the Colombia basin and the seismic morphology represents the depositional facies.

Slicing upward though the cube the thick high amplitude low frequency facies abruptly changes to a widespread thin polygonally faulted interval after which the facies are low amplitude and seismically transparent. The seismic morphology change represents the moment in time when the subsiding basin switched from restricted circulation and anoxia (lacustrine?) to open marine and oxic conditions. Time slices above the datumed horizon record the post-thermal subsidence transition to the Tertiary filling of the basin from the Magdalena River and show the morphologic features of the Magdalena Fan.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018