This paper describes experiments and simulation of gas injection processes with hysteresis. Two complete gas- and oil injection cycles have been performed at the reservoir conditions of 300 bar pressure and 100 °C temperature under X-ray Computer Tomography (CT) surveillance to obtain oil and gas in-situ saturation values at irreducible water saturation. The reservoir condition core flood experiments were performed on restored North Sea reservoir cores with use of live pre-equilibrated oil and gas phases at reservoir conditions by separator liquid samples and excess gas.

The core flood conditions were designed prior to the physical experimental program by using a reservoir simulator. The basis for the history matching was the CT in-situ saturation measurements of oil and gas in six cross sections along the length axis of the core versus pore volumes (PV) of equilibrium gas injected, oil and gas production volumes versus PV injected and the differential pressure recordings across the core during the injection experiments.

The experiments are history matched by use of the ECLIPSE reservoir simulation package. In this procedure the well completions are specified with an explicit transmissibility factor. Injection and production dummy grid blocks are connected to inlet and outlet end of the simulation grid. The production wells are controlled by either bottom hole pressure or the total reservoir fluid rate; the injection wells are rate controlled according to the physical rates. A systematic sensitivity study by isolating variables has been done in matching production history, in-situ saturation values of gas and oil, and differential pressure recorded in the displacement experiments. The analysis of the results has identified the most important dynamic reservoir parameters and characteristics that control the recovery mechanism during each displacement sequence of the gas and oil injection experiments. The hysteresis functions in the two-phase gas-oil injection sequences have been investigated.

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