Geological and Petrophysical Modeling of a Heterogeneous Mid-Cretaceous Carbonate Reservoir from SW Iran

Taghavi, Ali Asghar¹, Atle Mørk² (1) Reslab Integration AS, Stiklestadveien 1, Trondheim, Norway (2) SINTEF Petroleum Research, Trondheim, Norway

The reservoir characterization and modelling of the mid-Cenomanian to early Turonian upper Sarvak Formation has been improved through the integration of geological and petrophysical data.

The main heterogeneity of the reservoir is in the vertical direction due to facies and locally diagenesis, whilst in the horizontal direction it is due primarily to diagenesis since there are no significant lateral facies variations. The sequence stratigraphic analysis has resulted in defining eight medium scale sub-sequences which have been used as the basis for constructing geological framework. In order to capture the reservoir heterogeneity, rock types were defined by integrating depositional facies, diagenesis, and porosity-permeability relationships, as well as capillary pressure data. Such rock types are an indication of the flow units in this reservoir. The flow units are thus controlled by sequence stratigraphic framework. The geological framework and rock type information as well as porosity-permeability distribution have been used to construct the vertical layers to achieve the heterogeneity. The horizontal cells have been defined relatively small to be able to capture small scale heterogeneities.

The rock types were deterministically and stochastically modeled in the sequence stratigraphic framework by their volume fraction in each zone. A pixel-based stochastic method has resulted in more reliable models after understanding the geology of the reservoir. Testing alternative geological scenarios, as well as different horizontal correlation ranges have shown petrophysical modelling using stochastic method and relatively large horizontal correlation range results in more probable adequate petrophysical models.

Various realizations of reservoir models have been created. These have been chosen after being ranked and have been used as input to predict the reservoir performance and to define the development plan for the field.