Agbada sandstone water saturation: a function of capillary pressure

Abstract

Analysis of representative reservoir rock specimen such as cores yields fundamental information for effective exploration, description and exploitation. Deliverability of particular reservoir sand can be estimated from measured permeability and residual fluid, oil, gas or water. Porosity and permeability values vary considerably within the Agbada formation, with generally high values. Studies of some basic reservoir parameters yield an insight into reservoir performance and establishment of a sound basis for estimation and exploitation. Results obtained from petrophysical analysis shows that the sandstones from the formation are unconsolidated. Core plugs used in this analysis were oven dried and saturated with a brine of synthetic concentration 44000ppm and resistance of 0.143Ωm to serve as the in-situ water saturation at 100%. Results show that the amount of water dropout from the core plugs is dependent on the capillary pressure as value increases from 1.00-60.00 psi. Saturation exponent values calculated using log RI/log Sw is also a function of the water saturation and capillary pressure. Resistivity Index values increases with increase in capillary pressure and decrease in water saturation. This is an indication that if oil is injected into these samples (formation), an ever increasing pressure will be required to push out the net bit of water which is the wetting phase. For a system under capillary/gravity equilibrium, water saturation will decrease with increase in capillary pressure. The amount of saturation water in a particular formation such as the Agbada formation reflects the resistivity response obtained under test and it is a function of capillary pressure. These parameters can be affected by increased burial, compaction and therefore indurations.

Keywords: Agbada formation, capillary pressure, reservoir, sandstone, water saturation