Yawanarajah, S.¹, A. Benbakir², F. Guehria¹, M.  Touami² 
(1) Schlumberger, Algiers, Algeria 
(2) Sonatrach, 

ABSTRACT: Reservoir Characteristion of Fractured Cambrian Reservoirs in Zones 1a and 1c of the Hassi Messaoud Field, Algeria

It has long been recognised that the faults in the Hassi Messaoud field are necessary for the successful production from the Cambrian sandstone reservoirs. What is less understood is the dual nature of these faults: they can both control transmissibility through permeability enhancing fractures, and control trapping (sealing) through permeability reducing diagenesis. The key to optimally exploiting this or any fractured reservoir is the ability to predict the existence and properties of both. An integrated reservoir characterization study was conducted in Zones 1a and 1c to confirm the above premise. 
To aid in production, fractures must both be open and connected to a reasonable hydrocarbon-bearing reservoir with sufficient volume for exploitation. Fault-zone diagenesis on the other hand will divide the reservoir into small compartments bound by partial fault (diagenetic) seals, the sealing properties of which depend on the clay content of the sands and the amount of cataclasis. The rapid reservoir thickness and petrophysical changes seen in Zones 1a and 1c, as well as the variable well production history, indicate the effects of compartmentalization and reservoir heterogeneity. The well production history from the intensely faulted Zone 1C show high initial production rates followed by a sharp decline, characteristic of production from a fractured reservoir with minimal matrix contribution. The less faulted Zone 1A however has wells that have maintained their production rates, suggesting matrix contribution. Transient analysis of some wells confirms the geological features as described, in addition to the production profile, which was successfully rendered by reservoir modeling.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.