Reservoir Zonation Based on Pore Network Characteristics: Demonstrated on Carbonates from the Middle East

Christie A. Callender, Cynthia M. Ross, John B. Turbeville

A new flow-unit/reservoir characterization method has been developed based upon pore network characteristics which control porosity, permeability, and capillary pressure behavior. The reservoir characterization method consists of identifying the number and characteristics of pore types associated with the reservoir intervals, predicting the volume of each pore type using neural network analysis of wireline logs, and identifying flow-units based on the dominance of a pore type or a distinct combination of pore types.

The size and shape of porosity as observed in backscattered images of thin sections are analyzed and objectively classified using an unmixing algorithm. In the study well, five pore types were identified ranging from micropores (5.08 µ) to large pores which were either isolated or well connected (197.98 µ). Each of the five pore types has an associated range of pore throat sizes as determined by capillary pressure tests.

The relative volume of each pore type is continuously determined for the entire reservoir interval within the well using neural network analysis of wireline log data. Reservoir zonation is based upon the dominance of a pore type or a distinct combination of pore types as determined by the researcher. In the study well, reservoir zonation based upon pore network character was able to identify a highly effective flow zone which corresponds to an interval where premature flood water break through has been identified. Porosity and permeability data were not sufficient to identify this interval.

This process can be automated and applied to other wells within the field provided that the study well data is representative of the reservoir interval. Identifying flow-units based upon pore type volumes and their associated pore throat size distributions have important implications to the prediction of water production, permeability contrasts, and sweep efficiency. This reservoir zonation method could provide the critical parameters to improve reservoir engineering simulations and the design of more effective completion strategies.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995