Rheology of Foam and Its Implications in Drilling and Cleanout Operations

Experimental analysis was carried out to study the rheological properties of foam. Foam was generated by simultaneously injecting air and an aqueous solution of the foaming agent through a coiled tubing foam generator. Foam was injected at the bottom of an annulus with 4.0-in. (i.d.) casing diameter and 1.5-in. (o.d.) tubing diameter. Qualities ranged from 0.65 to 0.95. Shear rates ranged from 150 to 1000 sec⁻¹. Effective viscosities were calculated and were found to range from 60 to 500 cps. Results showed that flowing foam behaved as a pseudo-plastic fluid with no yield value; effective foam viscosity decreased with an increase in shear rate for a fixed quality. For shear rates in the range 500 sec⁻¹ to 1000 sec⁻¹, the effective foam viscosity was independent of foam quality. This is useful since most field applications fall in this range.