Mud Diapirs and Mud Volcanoes Associated with Gas Hydrates System in the Sinu Fold Belt of Colombia, South Western Caribbean and its Significant in the Petroleum System.

Abstract

Summary The accretionary Sinu fold belt of Colombia presents numerous gas and oil seeps often associated with mud volcanoes. Truncation and folding of reservoir rocks against mud diapirs have been erroneously considered as potential structures for hydrocarbon traps ignoring the significance of the thick Gas Hydrate Zones (GHZ) present in large offshore areas of the South Western Caribbean Sea. Seismic images of the Sinu fold belt clearly indicate that mud diapirs and volcanoes are associated with GHZ that are present at shallow depths as indicated by the Bottom Sea Reflector (BSR) as it is observed in large and numerous offshore areas in the South Western Caribbean Sea. Hydrocarbon generation and migration in the Sinu Fold belt, Colombia, started in the Paleocene, following gas migration through fault planes took place reaching the sea floor, these thermogenic gases including oil and condensate, were progressively trapped as gas hydrates forming seals as the GHZ became thicker and larger in area. Then in a continuous basin subsidence, and a high sedimentation rate, gas hydrates layers were buried and preserved due to a low geothermal gradient. As gas hydrates layers were buried to deeper depth, temperature increased and the Gas Hydrate Stable Zone became unstable and melted down liberating great volumes of gas and oil that migrates upward forming mud diapirs and mud volcanoes as they reached the sea floor and the coastal surface. These sequence of events indicates that mud diapirs and volcanoes are the results of destruction of Gas Hydrate Stable Zones that were previously formed by migration and trapping of thermogenic gases originated in deep hydrocarbon kitchen beneath the strata were mud diapirs were derived from. This new interpretation considers that mud diapirs and volcanoes constitute the seal formation rock of the petroleum system, also this new interpretation explains the lack of hydrocarbon discoveries in the Sinu Fold belt of Colombia and propose to explore beneath the mud diapirs and gas hydrates zones in the Sinu fold-belt and other similar location in the South western Caribbean Sea. Carbon isotopic analysis (13C/12C) on methane samples obtained from mud volcanoes in the Sinu fold belt indicate a mixture of thermogenic and biogenic gases. This situation is explained by the presence of a bacteria consortium that generate methane during microbial degradation of oil. However, the petroleum system explained above indicate that thermogenic gases and associated oils are the main hydrocarbon resource in the south western Caribbean Sea.