oa Preservation Index of Organic Matter From Illite / Smectite (R3) Relationship

There are factors that directly affect organic matter (OM) evolution; such as sedimentation, burial, organic productivity, oxygen saturation in water column and sediments, ocean circulation, sediment particle size and sedimentation rate. (Emerson & Hedges, 2003; Meyers, 1997).

However, there is another factor that has not been considered which is directly related to OM adsorption in clays (Illite/Smectite I/S). I/S is a determining factor for OM preservation (Heges & Keil, 1995).

We analyzed X-ray diffraction, SEM, Rock Eval and Biomarker data in two formations with clay content belonging to the Upper Cretaceous and Upper Jurassic. A correlation was observed between I/S vs TOC (%) and I/S (%) vs S2. Two mathematical models are proposed for each formation.

The results show that physicochemical water column conditions and OM depositional environment are not determinant factors to influence in OM preservation. OM responds to an adsorption process with I/S. Also I/S presence is altered by diagenetic processes which indirectly affect OM preservation.

The OM-IS analysis influences in volumetrics quantification, porosity and effective adsorption of methane gas ( S. Chen et al., 2016 ; Shangbin C. et al., 2016 ). The evaluation with this criterion pretends to be a tool for potential and volumetries estimation in unconventional resources.