INVESTIGATION ON THE EFFECT OF STRESS ON CEMENTATION FACTOR OF IRANIAN CARBONATE OIL RESERVOIR ROCKS

摘要

Electrical resistivity is one of the important petrophysical properties of oil reservoir rocks.Cementation Factor or Formation Resistivity Factor(FRF)is widely used in studies to estimate porosity and water saturation.Some researchers have studied the effect of many factors on the cementation factor”m”,mostly with sandstone rocks,and occasionally with carbonates rocks.Since the carbonate rocks contain nearly half of the world’s petroleum reserves and also most of Iranian oil and gas reserves,therefore it is very important to determine the petrophysical properties of carbonate rocks.This paper reports an experimental investigation on the influence of variations in confining pressure on cementation factor of some Iranian carbonate rocks with similar and substantial high porosity in two different oil fields.This work included the following sequences: cleaning and drying,porosity and Pore Size Distribution determination,and electrical resistivity measurements at different confining pressures.The Pore Size Distribution carried out with high pressure mercury intrusion techniques.Cementation Factor was calculated for both field’s rocks at each pressure.Effect of confining stress on electrical properties of rock samples were studied.This study indicates that the influence of the confining pressure variations depends on the nature and pore structure of rock sample.Even though pore volume and porosity changes were same for both reservoir samples,but rock samples with non-uniformly pores have higher change of cementation factor and resistivity,than rocks with uniformly pores due to confining pressure variations.The above conclusion empowered the idea that,electrical resistivity of rocks is function of Pore Size Distribution and therefore resistivity of rocks strongly depend on the way that fluids are distributed in the pore space.