Petrophysical interpretation of 2 exploration wells in offshore Angola

Abstract

Logging data from gamma ray, neutron-porosity, density, resistivity etc, are helpful to perform the qualitative and quantitative evaluation of the drilled wells. Parameters like water resistivity, porosity, water saturation etc, can be estimated by using the logging data.

The Archie equation based method was a suitable method for all zones, due to the fact that no zone of interesting showed volume of shale bigger that 50%.

In order to determine the water saturation in the formation, formula expressing the relationship between the true resistivity (Rt) and the formation parameters affecting the resistivity was used. The picket plot was a suitable method to estimate the water resistivity.

Could be concluded that when no pressure data is available, as in the case of JOIA well, the logging curves, neutron and density, by plotting them in the neutron –density crossplot (qualitative evaluation), can be used to estimate the type of fluid in the formation. Although the results were not as accurate as from the pressure or core data. The neutron-density crossplot is indicating existence of oil in JOIA well reservoir.To have good permeability estimation, it’s necessary to have enough core data so that the regression line can be drawn.

This paper presented applications of the petrophysical theories for qualitative and quantitative evaluation of two explorations wells of offshore Angola that will be called EKS and JOIA well respectively, with help of a petrophysical software called Techlog.