Online Journal for E&P Geoscientists

Planteblat, Caroline ^*2; Caline, Bruno ³; Pabian-Goyheneche, Cécile ⁴; Massonnat, Gérard ¹
(1) Geomodeling Expert, TOTAL, Pau, France. (2) Geomodeling and uncertainties, TOTAL, PAU, France. (3) Exploration in Carbonates, TOTAL, PAU, France. (4) Research and Development in Carbonates Reservoir, TOTAL, PAU, France.

Geological modeling of diagenetic processes in carbonates reservoir is still a challenge as thus far as neither stochastic nor physicochemical simulations can correctly reproduce complexity of features generated by processes. An alternative way to reach this objective deals with process-like methods that simplify the algorithms while preserving all geological concepts (from data interpretation and models) in modeling process. Based on geological concepts and knowledge, the aim of the methodology is to conceive a 3D consistent and realistic model of diagenetic overprints on initial facies resulting in petrophysical properties at reservoir scale.

The principle of the method is related to a lattice gas simulator combined with a random walk. This enables the numerical solution of the stochastic differential equation, which characterizes the main mechanisms leading to the formation of diagenetic overprints (i.e karstic networks, dissolution affected zones, cementation zones, dolomitizing zones). This spatio-temporal probabilistic model is conditional, and also constrained by the dataset (wells core and logs and dynamic field data).

This method developed in a research group is well adapted to handle dolomite reservoirs through the propagation of dolomitizing fluids. Based on sedimentological and stratigraphical analyses a facies model of the Venetian platform (Lias, NE Italy) has been first of all constructed at outcrop scale by using a numerical simulation which allows the combination of depositional history complexities of carbonates systems in a 3D view. Multistage of diagenetic processes, including different stages of dolomitization are then simulated and superposed. Another outcrop application is used to test the ability of the method, focused on dissolution features in particular on karst development and its evolution. These stochastic simulations lead to multi-realizations of petrophysical distribution, including uncertainties and the creation of alternative and equiprobable models realizations.

Calibration of the model parameters used for matching the observed data of the field case proves the robustness and the accuracy of the diagenetic concepts and diagenetic calendar. Multi-realizations mostly follow the patterns identified on the outcrop, and validate both the field results and the modeling methodology.