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Geological Society, London, Special Publications; 1995; v. 84; p. 111-123;
DOI: 10.1144/GSL.SP.1995.084.01.12
© 1995 Geological Society of London

Water and Gas Injection Methods

SAGA injection: a new combination IOR process for stratified reservoirs

Jan Erik Hanssen1, Leonid M. Surguchev1, Idar Svorstøl2 & Tore Blaker2

1 RF — Rogaland Research, P.O. Box 2503 Ullandhaug, N-4004 Stavanger, Norway
2 Saga Petroleum a.s., P.O. Box 490, N-1301 Sandvika, Norway

Specific features of North Sea sandstone reservoirs and reservoir fluids determine quite special conditions for water-alternating-gas (WAG) injection which must be taken into account when tuning WAG parameters for the particular stratification and anisotropy of a heterogeneous reservoir. Combining advantages of waterflooding and gas injection, WAG can be very effective in stratified reservoirs. Even so, gravity segregation and early breakthrough may cause poor sweep, especially in reservoirs with low restriction to the cross-flow within the layers and with low permeable layers underlying high permeable layers. The first part of this paper presents results of WAG prediction and process tuning for a reservoir of this class. The second part introduces a new process for selectively controlling injectant flow, surfactant-alternating-gas-ameliorated (or SAGA) injection, which may yield further improvement. In this process, a foaming surfactant added to part of a water half-cycle preferentially enters the swept region. Foam that is generated by gas/surfactant displacement in a subsequent gas half-cycle will block or reduce further entry of gas and water into the high permeable layer, diverting injectant to unswept layers as the reservoir is maintained on WAG flood. Analytical estimates and numerical simulations indicate positive effects of SAGA injection on oil recovery and GOR over WAG injection. Simulation results quantifying the effect of foam plugging, injection parameters and time factor on WAG performance are discussed. Experiments in a physical stratified reservoir model demonstrate the selective placement of foamer, foam-plug generation, and effectiveness of the combined action of WAG and foam. The visualization of physical model experiments is essential for demonstrating foam process mechanisms and is useful in illustrating segregation and viscous/gravity effects in SAGA injection.