Assessing the Impact of Initial Carbonate Diagenetic Reactivity on Reservoir Properties
Ruhr-University Bochum, Institute for Geology, Mineralogy and Geophysics, Bochum, Germany
I here critically evaluate the question if the spatial and temporal distribution of carbonate mineralogies, characterized by their different diagenetic reactivity at the time of deposition, is a fundamental factor controlling the subsequent evolution of carbonate reservoir properties. If this were the case, then a wide range of “depositional facies architectures” could be grouped into a smaller number of “diagenetic facies architectures”. The concepts presented here represent a progress report.
I propose that these general considerations are significant. This is because most reservoir models are built on case-by-case basis and as a result, the more general patterns and similarities in diagenetic facies evolution between reservoirs with different depositional architectures will not be obvious. The hypothesis tested here relies on the substantially different thermodynamic properties (solubility) of the four dominant marine carbonate mineralogies at deposition: calcite and low-Mg calcite (<4 mole%) being the more stable/less reactive phases and aragonite and magnesian calcite (4 to >20mol% Mg) being the more reactive/less stable carbonate ones. Differences in stability depend on crystallographic properties with Mg²+; having a smaller ionic radius compared to Ca²+;. Substitution of Ca²+; with Mg²+; has a significant impact on the crystal lattice (Zhang et al., 2010), and the shift in the (104) d-spacing, i.e., the unit cell parameter, is roughly proportional to the amount of the Mg in the crystal structure. Dolomite, in contrast, is built by an ordered structure of alternating Ca-rich and Mg-rich layers and is thus stable (Warren, 2000).
AAPG Search and Discovery Article #120034©2012 AAPG Hedberg Conference Fundamental Controls on Flow in Carbonates, Saint-Cyr Sur Mer, Provence, France, July 8-13, 2012