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Our solution required:


The confirmation of equilibrium between the two phases gives important reservoir information. It suggests that in producing from the oil leg there will be pressure support from the overlying gas cap, it provides a contact depth from which the reservoir in place volumes can be determined and it gives valuable indications about the reservoir connectivity and filling history.


The contaminated MDT gas and oil samples were compared with the OBM filtrate composition. The OBM composition was mathematically removed from the contaminated compositions.

EOS Modeling

The mathematically uncontaminated MDT gas and Oil compositions were then compared together in an Equilibrium plot at reservoir conditions. The good agreement with theory confirms the compositions of the uncontaminated oil and gas samples and is consistent with them being in equilibrium.

North Sea Oil/Gas Cap System

The Problem

The RFT pressure gradients from a North Sea field suggested a gas cap above an oil leg. However DST tests experienced gas coning or commingled flow from both zones while MDT samples proved to be contaminated with OBM. The problem was to derive representative fluid compositions for each phase and to determine if the fluids were in equilibrium, indicating vertical connectivity.