AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Consistencies in Vertical-to-Lateral Carbonate Facies Juxtapositions; A Direct Comparison Between Modern and Miocene is Possible
(1) National Coral Reef Institute, Nova Southeastern University, Dania Beach, FL.
(2) Carbonate Team, Shell International E&P, Rijswijk, Netherlands.
The search and extraction of hydrocarbons in carbonates demands an understanding of subsurface depositional anatomy and is greatly aided by facies juxtaposition statistics. The complexity of carbonate systems however makes detailed direct-characterisation of their 3D heterogeneity difficult. This problem is exacerbated in both outcrop and the subsurface where lateral constraint on facies architecture is typically poor to non-existent, though information on vertical stacking maybe rich. A tantalizing strategy to mitigate this disjoint lies in the use of Walther’s Law, which offers the possibility of using vertical transitions to elucidate lateral juxtaposition motifs. The implication being that a reservoir model, competent at least in terms of transition statistics, could be built against information harvested down-core. This approach is of course over simplistic as the architectural elements of a landscape, such as the size, shape, and complexity of geobodies, are as important in reservoir characterisation as are facies transitions. For this reason, interest has been paid to the use of modern depositional environments, with their laterally exposed facies belts, as analogues to the ancient. Markov models are one solution by which rules of facies transition can be blended with size, shape, and complexity distributions. Truth in the application of Walther’s Law is fundamental to this approach however, and few studies have investigated the degree to which WL can be applied in this manner. This work tackles this deficit by investigating two separate systems for transitions similarities; the first being the Late Miocene Llucmajor Platform (Mallorca), which offers good vertical control on facies stacking of a prograding coralgal reef system, and the second in the Modern for which lateral lithotope patterns have been mapped at fine resolution from satellite and aircraft (Tanapag Lagoon, Saipan). Using Monte Carlo simulation and Markov tests we show the vertical and lateral juxtaposition of lithologies in the two environments to be statistically inseparable (p=.05). We confirm that the rimmed shelf carbonate setting of Saipan is an appropriate depositional analogue for the Miocene reefs of the Tethys and strengthen the assumption that facies stacking in the Modern is broadly equivalent to that of the Miocene. The work is a precursor to incorporating juxtaposition tendencies harvested from depo-maps of modern environments into Markov-driven reservoir models.