SAGA injection: a new combination IOR process for stratified reservoirs

Abstract

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.

Simulating CO2 EOR Process: Numerical Investigation Based on the Experimental Results

“…The empirical model calculates foam mobility reduction factor and accounts for effects of various parameters, like, for example, critical surfactant concentration, capillary shear thinning, drying of foam, oil sensitivity and temperature on foam generation, stability and propagation in the reservoir (Cheng, et al 2000). Field experience showed successful FAWAG (Foam Assisted Water-Alternate-Gas) injection and successful application of simulation tools to predict foam behaviour (Cheng, et al 2000, Hanssen and Surguchev 1994, Hanssen, et al 1995, Skauge, et al 2002, Surguchev and Hanssen 1996.…”

Foam Application in North Sea Reservoirs, I: Design and Technical Support of Field Trials

“…Extensive reservoir evaluations showed that early gas breakthrough may be a potential problem. Application of foam for gas mobility control, fluid diversion, and blocking to reduce GOR in production wells was identified as attractive method to improve WAG performance [7][8]. Based on the promising results from the foam treatment studies it has been decided to evaluate a field pilot project.…”

“…Production well foam treatment against gas cusp at the UK North Sea field was analyzed and pilot results discussed [6]. For injectant diversion, foam application by alternate injection of foamer and gas was found to offer a significant potential of improving WAG process efficiency in the other North Sea field (planned Norwegian North Sea pilot) [7,8,10]. Evaluation of these different foam processes allowed to identify the following critical foam parameters for field applications: gas mobility reduction factor, foam persistence, volume of foamer injected, foamer adsorption.…”

Foam Pilot Evaluations for the Snorre Field, Part 2: Numerical Simulations and Economical Evaluations

“…4 Placement of a, surfactant slug and subsequent foam generation in the swept high permeable top layer was successfully demonstrated and gave efficient injectant diversion info the love permeable layers, resulting in complete sweep of the reservoir model by continued WAG . The proces, termed SAGA (Surfactant Alternating Gas Ameliorated) Injection, indicated significant potential of improved oil recovery by a suite of simplified reservoir simulations using a cross section from the Staffjord Formation .…”

“…The proces, termed SAGA (Surfactant Alternating Gas Ameliorated) Injection, indicated significant potential of improved oil recovery by a suite of simplified reservoir simulations using a cross section from the Staffjord Formation . 4 However, a large scale field test of SAG injection in the Snorre WAG pilot area witti interwell distances of 700-1500 meters has been considered to involve too high economic risk and be too time consuming witti respect to the necessary data recordmg, for a first step pilot. Therefore, to reduce the risk (cost and time) a production well test has been recommended (small amounts of surfactants are required compared to an injector treatment).…”