IMPACT OF GAS LIBERATION EFFECTS ON THE PERFORMANCE OF LOW PERMEABILITY RESERVOIRS: TRD-1 WORK PACKAGE H “RESERVOIR DRIVE FROM SECONDARY GAS CAP DEVELOPMENT IN LOW PERMEABILITY RESERVOIRS”.

Production from the North Sea reservoirs often results in pressure decrease below the bubble point. The
gas is liberated from oil, in the form of bubbles or a continuous flowing phase. In such cases, the two
phases, gas and oil, flow in the reservoir simultaneously, and the flow is governed by the values of relative
permeabilities. One of the challenges in forecasting and history matching the performance of low
permeability reservoirs is related to uncertainties in relative permeabilities. In this work, we use a novel
experimental approach to determine the oil relative permeabilities below the critical gas saturation. A
mathematical model has been created to reconstruct both the gas and the oil relative permeabilities for the
whole saturation range. We apply the obtained relative permeabilities for the case of a low permeability
chalk reservoir in the North Sea, where differences in well productivities may be the results of liberated gas
as single bubbles or a continuous flowing phase. We demonstrate a reasonably good match can be
obtained to the historical well production data. Few cases where the match was not satisfactory are also
analyzed, and the difference may be attributed to an imprecise fluid model. The developed experimental
and modeling methodology may be applied to other reservoirs developed by the solution gas drive
mechanism.