Petroleum geology

Hydrocarbon Evidences

The Tumaco Basin fulfills the necessary conditions to be considered an important target for hydrocarbon exploration. The presence of oil and gas shows at the Remolino Grande-1, Majagua-1 and Chagüi -1 wells, indicates that the potential source rocks have locally reached the thermal maturity needed to produce oil and gas. In detail, the evidences found in three mentioned wells are:

For correlation purposes, four chronostratigraphic units of Late Oligocene to early Pliocene age, limited by unconformities, have been defined: (1) Late Miocene to Early Pliocene, (2) middle upper Miocene to late Miocene, (3) middle Miocene and (4) late Oligocene to basal middle Miocene. The depositional environmental succession indicates: (a) an Oligocene to middle upper Miocene deep sequence (slope), (b) a younger upper middle Miocene to upper Miocene (slope to platform) sequences.

Source Rock

The presence of source rocks in Tumaco Basin is supported by the results of geochemical analysis performed on dark siltstones and fine grained sandstones derived from Oligocene units.


The interpretation of 1D paleotemperatures models (Tumaco pseudowell), suggest that the intervals that reached depths below 20 000 ft, have entered the oil generation window. Taking as reference the gravimetric basement map, it is possible to identify two areas of hydrocarbon generation within the basin.

The 1D paleo-temperatures model suggests an expulsion peak that occurred during the last 3 to 7 million years. The presence of structural traps (if formed prior to the expulsion time) generated by fault-propagation folds, strike-slip faults systems, mud diapirs and flower structures, among others, along with the presence of late Miocene seal rocks (mudstones), may have induced the necessary conditions for the configuration of commercial prospects.

Reservoir Rock

The main potential reservoirs are limestones, sandstones and conglomerates deposited during the Miocene.

Seal Rock

The considered potential seal rocks are muddy strata interbedded in late Miocene sandstones and siltstones. Traps The generated hydrocarbons may have migrated and are possibly trapped in mud diapirs associated anticlines, roll-over folds associated to normal listric faults, wide closures associated with fault propagation folds, thrust related anticlines and numerous stratigraphic traps.

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