Gas blockage

Hanssen, J.E. Dalland, M. Foam for Effective Gas Blockage in the Presence of Crude Oil in Proceedings, SPE/DOE 7th. EOR Symposium, Society of Petroleum Engineers Richardson, TX, 1990, paper SPE/DOE 20193. 

Temperature gradients exist in a reservoir that has been subjected to steam-flooding, and therefore, a knowledge of the dependence of surfactant adsorption on temperature is important in the evaluation of steam-foam processes. Low adsorption levels in high-temperature or swept zones are beneficial to process performance because gas mobility reduction or gas blockage in the swept zones is desired. 

Figure 8. Repeatability of gas-blockage data for 0.50% Hostapur SAS foams in 100-cm packs of 8-darcy beads at 26 °C and no oiL...

Figure 9. Gas-blockage performance of foams in 200-cm long 8-darcy bead packs at 0.50% foaming agent solution in distilled water except as indicated Conditions no oil 21 °Cf and initial outlet pressure VQut 6 bar.

Gas blockage by foam in a porous medium may be more strongly impaired by oil, even at low residual saturations, than is the bulk... 

Figure 13. Foam gas-blockage performance at indicated temperatures in the presence of a North Sea crude at S. using 200-cm packs of 8-darcy beads at 6 bar. (Reproduced with permission from reference 13. Copyright 1993.)...

Figure 15. Gas-blockage performance of 2-methyl-1-propanol foams in 8-darcy bead packs of indicated length at 21 °C with Poul 6 bar. Foam generated at a constant overall pressure gradient AP/L 2 bar/m. (Redrawn from data in reference 25.)...

Figure 16. Gas-blockage performance of 1.0% Fluowet OTN foams in bead packs of indicated length at screening conditions, and in Bentheimer sandstone at reservoir conditions. Permeability is 1.4—1.8 darcy, temperature is 70 °C, and residual crude oil is present (except, 24-cm pack 8 darcy and 21 °C).

Summary Conditions for Obtaining Gas Blockage. Thus, we arrive at the following set of critical parameters, in order of importance, for characterizing gas-blocking foams in the laboratory ... 

In sandstones, values for Sw closer to connate (0.18 to 0.21 in 1.3-darcy Bentheimer) were obtained with fluorosurfactant foams, although gas blockage was as strong as in bead packs of comparable permeability (21). Because most of the water in such cores is presumed to occur in the smallest pores, which hold no foam (33), it probably means that the actual gas-blocking foam is also of a similar dry nature in the rock. 

The theory predicts that, in related data sets, the gas-blockage performance of different foams (expressed as kg should fall on a common straight line when plotted as a function of (AP — APT) /AP. 

Figure 19 shows experimental gas-blockage data for some model foam systems (31). Foams were generated in pressure-driven displacements of surfactant solution by gas. A gas-blocking state was reached with only gas entering and exiting the pack. At this state, the pressure drop was increased in steps and the stabilized Qg and AP were measured at each successive gas-blocking state. In the present context, the data are... 

Loss of Gas Blockage. In steady-state flow of foam, the major mechanism of foam decay is dynamic capillary suction coalescence (41, 51). This process may occur in earlier stages of an experiment with gasblocking foam but is expected to be less frequent later in the experiment. 

Evaporation. Some observations on breakdown of gas blockage by evaporation, which has not previously been considered as a decay mechanism, are reported here. 

An experimental method that may include all parameters found critical for achieving gas blockage has been defined and has allowed evaluation of the gas-blockage efficiency of foams in porous media. Recommendations for product selection are given. 

In [260], preparation conditions of gas-blocking foams were studied. Experiments were performed on cores filled with 100-pm glass beads with a permeability of 8.5 D. In absence of surfactants, the gas passed easily as a jet through the core filled with water. With the surfactant sodium alkyl ethoxysulphate increased from 0.1 to 0,5 wt.%, a foam piston was formed which pushed the surfactant solution. To achieve a gas blockage, the porous medium must exceed a certain minimum length greater than the length of travel for the displacement front to... 

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