Multi-technique comparison to assess the effect of bioturbation on porosity: a study case for reservoir quality in contourites

In recent decades, contourites—as sediments deposited or reworked by bottom currents— have begun to be considered important targets for deep-sea petroleum exploration and exploitation. The incidence of bioturbation, a common feature in contourite deposits, on petrophysical properties has never been approached in detail, however. Here, detailed comparative analysis of the impact of ichnological features on contourite rock properties is initiated through the application of different techniques: (a) X-ray micro-computed tomography (Micro-CT), (b) mercury intrusion porosimetry, and (c) analysis of impregnated thin sections. These three techniques were employed to study two types of contourite deposits, namely clastic (Miocene Morocco) and calcareous ones (Eocene–Miocene Cyprus). The results evidence the suitability of a multi-technique approach. Particular strengths and weaknesses may be encountered for each method depending on the type of material, the ichnological features, and the particular objectives. Trace fossils analysed in calcareous contourites show a neutral effect. In contrast, the burrow lining of Macaronichnus in the clastic contourites has a positive incidence on porosity. The appearance of this ichnotaxa could invigorate the reservoir capacity of bioturbated contourite deposits. Thus, we suggest that detailed analyses must be conducted focusing on ichnological features other than the ones traditionally considered. Still, this is a preliminary effort, and more detailed studies are needed to support the obtained results, and eventually extrapolate them to further contourite deposits.