Uncertainty Approach for OIIP Estimate of a Fractured Basement Reservoir of Middle East

By

Sylvie Odile Delisle¹, Vivien de Feraudy¹

(1) TotalFinaElf, Pau, France

 Basement fractured reservoirs are probably the most uncertain type of reservoir to be characterise and model: difficulties in structural definition, in prediction of facies evolution, in evaluation of a poly-tectonised material.

Our approach enables to define a ranking of the different fracture types (from the micro-fracture to the fault) then to model each of them with proper characteristics through a geostatistical approach with JACTA(TM) software. Stochastic generation of as many parameters as wished using geostatistical methods gives multiple equiprobable images of the field to evaluate.

The building of the 3D model from seismic interpretation is a key point to elaborate a consistent structural pattern of main faults. This is our first scale of fracturing which will be modelled.

Well data (imagery and core) give us crucial information on the two other fracture scales: small scale fracturing and sub-seismic objects.

Small scale fracturing may be sometime considered as a second order player (mineralisation or poor connectivity) whereas sub-seismic objects can play a major role in OOIP amount as well as in productivity. They can be stochastically simulated from parameters calibrated on geological data. Typical parameters simulated are: frequency, strike, dip, length, width, and petrophysical properties.

Influence on OOIP of the uncertainty in each parameter can be evaluated separately giving a good idea of the relative impact of each of them then a ranking of parameters to be refined.