Researchers have recently determined that capillary pressure plays a dominant role in controlling the texture, and hence the rheology, of foam flowing through a porous matrix. Of particular interest, the capillary pressure was found to reach a characteristic value, the limiting capillary pressure, at a relatively high fractional flow of gas, fg. If fg was increased further, the capillary pressure was reported to remain at the limiting value, the foam texture was coarsened, the liquid saturation remained constant, and the steady state foam pressure gradients were proportional to liquid velocity and independent of gas velocity.

The experiments in these recent reports were all performed at low temperatures. We report the results of foam flow experiments conducted at 150°C. The experiments were designed to characterize steady-state nitrogen foam flow by measuring pressure gradients in a 6.2 μm2 sandpack over a wide range of gas and liquid velocities and fractional flows.

We found that steady-state pressure-gradient responses, and hence foam rheology, could be divided into two distinct environments that were characterized by the value of fg. Interestingly, the pressure gradient response to gas and liquid velocity in one environment was exactly reversed in the other. In one environment, where fg was less than 0.94, the pressure gradient was dependent on gas velocity and was reasonably independent on liquid velocity. The pressure gradients were proportional to gas velocity to about the 0.31 power. In the other environment, where fg was greater than 0.94, the pressure gradients were dependent on liquid velocity and were reasonably independent on gas velocity. The pressure gradients were proportional to liquid velocity to about the 0.33 power. The transitions that occurred at fg of 0.94 likely correspond to the point at which the limiting capillary pressure was reached. The liquid saturation was low and nearly constant, about 0.06, in both flow environments.

At very high gas velocities, when fg was greater than about 0.998, steady-state flow was replaced by a chaotic-like flow in which the pressure gradient fluctuated and fell to very low levels in downstream sections of the sandpack.

You can access this article if you purchase or spend a download.