Effective geological factors (facies, diagensis and tectonic) for reservoir characterization of Ilam Reservoir zone C1 (Ahwaz oilfield)

Geological studies is essential for running a water flooding project. So, understanding the geological factors is important such as sedimentary environment, diagenetic processes, and reservoir fault behavior to obtain a proper understanding of rock / water / oil properties. In this study, due to the early breakthrough of some wells in west of Ahwaz field as well as the reduction of reservoir pressure in this area, it was decided to perform a water flooding operation, which so far have not been practiced in Iran.

Therefore, geological study have done in Ilam reservoir of AZ-116 in view of diagenesis, facies and tectonic. In this study were used polarizing microscope, electron microscope, core data, petrophysical evaluation and reservoir model.

From a sedimentological point of view, the C1 zone of the Ilam reservoir of Ahwaz is composed of components of frequently oligostegina hemiplegic microscopic organisms in the sedimentary environment of the open seas. Such a facies, which is composed of calcareous micritic mud, should not inherently have porosity. But the process of meteoric diagenesis before lithification has increased its reservoir quality. Chalky reservoir with porosity of 5% to 27% (in the western part of the reservoir from 15% to 27% porosity) and Klinkenberg permeability of 1 to 10 milli-darcy and sometimes 100 milli-darcy. It also provides conditions for the porethroats from 20 to often several tenths of microns. But the reason for the development of different meteoric diagenesis across the reservoir has to be follwed to the Zagros tectonic events of the Cretaceous period. During the Cretaceous, extensional basement crust of the Mesozoic period reactivated and affected the paleogeography of the basin. So that along these north-south faults in zone C1 of Ilam reservoir of Ahwaz, we see different diagenetic processes in west area incontrast to other part of reservoir, just before litification.

Appropriate impact of geological factors (facies, diagensis and tectonics) has provided ideal conditions for water flooding operation.