New Insight into Microporous Carbonates and Impact on Recovery Factor: Example From Mishrif Reservoir in Irak

Laurent Lambert¹, Benjamin Sallier², Bruno Caline¹, Gerald Hamon¹, Eric Davaud³, and Christophe Durlet^4
1Total, Pau, France
²Addax Petroleum Ltd, Geneva, Switzerland
³Geneva University, Geneva, Switzerland
⁴Universite de Bourgogne (FRANCE), Dijon, France

Microporous carbonate reservoirs in the Middle East are characterised by heterogeneous reservoir quality which remains poorly understood. Updating of static and dynamic models is needed to better forecast oil production and optimise field development plan of these difficult reservoirs. This implies an improved understanding of the key-parameters that control transition zone development, occurrence of water breakthrough in highly permeable beds and large volume of remaining oil trapped in low permeable beds.
Technical approach is based on an integrated study of texture, pore network geometry and petrophysical measurements of Mishrif Fm and outcropping analogues for Kharaib and Shuaiba Fm. Methods including SEM, geochemical analyses, and 3D X-ray microtomography, have been applied in order to properly describe and interpret both the fined-grained matrix and the resulting microporous network.
A late phase of dissolution locally took place prior to or associated with hydrocarbon migration, leading to a decrease in crystal diameter and resulting in a significant increase in permeability. This suggests that distribution of the more permeable intervals is controlled by the timing of oil migration. Conversely, cementation due to chemical compaction seems to selectively affect clay-enriched carbonate facies. Field-scale distribution of these low permeable facies will then rely on the depositional and sequence stratigraphic models.
Interpretation of the drainage capillary pressure curves together with pore network geometry is required to define reservoir rock types in order to asses the distribution of water saturation in oil reservoirs. Pore study reveals the composite nature of pore network due to imbrications of variable amount of coarse pores in microporous network. This integrated approach allows evaluating the impact of pore network architecture on water saturation and recovery factor in microporous carbonates.

AAPG Search and Discovery Article #90072 © 2007 AAPG and AAPG European Region Conference, Athens, Greece