Foam mobilization

Laboratory studies of foam flow in porous media suggest that the relative foam mobility is approximately inversely proportional to the permeability. This means that foam has potential as a flow-diverting agent, in principle sweeping low-permeability regions as effectively as high-permeability regions [716]. 

High pressure equipment has been designed to measure foam mobilities in porous rocks. Simultaneous flow of dense C02 and surfactant solution was established in core samples. The experimental condition of dense CO2 was above critical pressure but below critical temperature. Steady-state CC -foam mobility measurements were carried out with three core samples. Rock Creek sandstone was initially used to measure CO2-foam mobility. Thereafter, extensive further studies have been made with Baker dolomite and Berea sandstone to study the effect of rock permeability. 

Also, other dependent variables associated with CO2-foam mobility measurements, such as surfactant concentrations and C02 foam fractions have been investigated as well. The surfactants incorporated in this experiment were carefully chosen from the information obtained during the surfactant screening test which was developed in the laboratory. In addition to the mobility measurements, the dynamic adsorption experiment was performed with Baker dolomite. The amount of surfactant adsorbed per gram of rock and the chromatographic time delay factor were studied as a function of surfactant concentration at different flow rates. 

In this section the laboratory measurements of CC -foam mobility are presented along with the description of the experimental procedure, the apparatus, and the evaluation of the mobility. The mobility results are shown in the order of the effects of surfactant concentration, CC -foam fraction, and rock permeability. The preparation of the surfactant solution is briefly mentioned in the Effect of Surfactant Concentrations section. A zwitteronic surfactant Varion CAS (ZS) from Sherex (23) and an anionic surfactant Enordet X2001 (AEGS) from Shell were used for this experimental study. 

The Effect of Surfactant Concentrations, The effect of surfactant concentrations on CC -foam mobility is plotted on a log-log scale in Figure 3. The presented data points are the average mobility values obtained from a superficial velocity range of 2-10 ft/day, with the CC -foam fraction was kept constant around 80%. With Berea sandstone, ZS and AEGS surfactants were used. The measured average permeability of the Berea sandstone with 1% brine was 305 md. With Baker dolomite, AEGS was used to make comparison with Berea sandstone. The permeability of the Baker dolomite was 6.09 md measured with 1% brine solution. 

Foam mobility has been proven to be strongly dependent also on bubble size and bubble distribution by size (foam texture) [162,163]. The latter is affected by the dispersion technique used, solution concentration, etc. (see Chapter 1). 

The pre-generated foam introduced in a porous medium (rock) evolves a major part of its liquid that fills the narrow pores and moves through them. The gas and a certain number of films occupy the larger pores. Through part of larger pores the gas can advance. Thus, foam mobility means the separate mobilities of the gas and liquid in the presence of a foam. 

Final laboratory testing of CO2 foam was performed in Shell s CT facility (11-12L Tertiary miscible and immiscible CO2 corefloods, with and without foam mobility control, were scanned during flow at reservoir conditions. The cores were horizontally mounted continuous cylinders of Berea sandstone. Table I lists pertinent core and fluid data. 

Carbon Dioxide—Foam Mobility Measurements at High Pressure... 

Figure 1. Schematic of the C02 foam mobility measurement apparatus.

Effect of Surfactant Concentrations. The effect of the surfactant concentration on foam mobility has been studied extensively. The surfactant under investigation for this effect was Varion CAS, a zwitterionic surfactant from Sherex. The rock under study was Berea sandstone which has a permeability of 308 9 md measured by using 1% brine solution. The permeability using N2 gas at atmospheric pressure was 1000 6.2 md. 

Whenever the concentration was increased, sufficient pore volumes were used to wash the core thoroughly. Some of the data were repeated in order to assess the reliability of the apparatus. The order of magnitude of the mobility was the same for all measurements at each particular concentration, independent of total flow rate. This indeed demonstrates the sensitivity and viability of this foam mobility measuring apparatus. 

Figure 3. Effect of surfactant concentration on foam mobility.

Although not pointed out in the test, it may be observed from the data that there is some effect on mobility of velocity or total flow rate. Some shear thinning or pseudoplastic behavior has been observed under certain conditions. This is, of course, the more favorable of possible non-Newtonian behaviors for foam mobility control, since it would mean that less thickening occurred in the vicinity of the injection well, than further out in the formation. 

Hirasaki, G.J., Miller, C.A., Pope, G.A., 2006. Surfactant based enhanced oil recovery and foam mobility control. 3 Annual Final Technical Report for DOE project (DE-FC26-03NT15406, July. 

Two notable approaches have been used to include the role of pore constrictions in the pressure gradient required to drive lamellae through porous media. Falls et al. (48) added a viscous resistance that accounted for pore constrictions and that acted in series with the straight-tube flow resistance of Hirasaki and Lawson (18). Prieditis (41) and Rossen (42—44, 46) computed the static curvature resistance to the movement of a single bubble and also trains of bubbles through a variety of constricted geometries. Rossen considered the role of bubble compressibility (43), asymmetric lamella shapes (44), and stationary lamellae (46) on foam mobilization. 

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