--> Modeling Early Marine CaCO3 Cementation in a Giant Carbonate Reservoir, Saudi Arabia

AAPG ACE 2018

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Modeling Early Marine CaCO3 Cementation in a Giant Carbonate Reservoir, Saudi Arabia

Abstract

Pseudo-coupled forward depositional and diagenetic models have been conducted to simulate the early marine cementation processes in a giant carbonate reservoir, eastern Saudi Arabia, using the reactive transport modeling code Toughreact. The models are constructed in a sequence stratigraphic framework, based on the depositional model of a single shoaling upward cycle of a shelf-interior homoclinal carbonate ramp related to this reservoir. Time-series cement profile and reservoir porosity distribution have been predicted from the models. The results indicate that the intensity of submarine cementation is related to carbonate depositional environment, platform architecture, facies, and textures; it is a function of the supply of solutes from seawater, which in turn depends on sedimentation rates and the effectiveness of chemically active water transport from the surface into the sediments. The modeling results compare well with the results from the petrographic point counting of the thin sections in this reservoir interval.

Incorporating depositional processes into the diagenetic model significantly improves reservoir quality predictions compared to those exclusively diagenetic models. The former generates an “onion ring” type cement profile, with the largest amount of cementation being shifted toward the interior, while the latter creates an “eggshell-shaped” profile where most cementation occurs at the seawater-sediment boundary. Considering the fact that the timescale of diagenetic process in carbonate reservoirs is comparable with depositional process, depositional and diagenetic modeling should be approached in an integrated way.