Experimental study on the in-situ foam performance stabilized by microbial polysaccharide and its diverting characteristics at high temperature

Abstract

Foam fluid shows good performance as diverting agent for reservoir stimulation, but complex generation procedure and high flow friction restrict its further application especially in offshore fields. To overcome these limitations, the objective of this study is to create stable in-situ foam system and investigate its potential in diverting fluid in heterogeneous reservoirs at high temperature. To prepare in-situ foam system, self-generated gas system was analyzed in terms of gas production volume and production efficiency. Foaming agents and foam stabilizers were optimized at the temperatures ranging from 70 ℃ to 90 ℃. Then in-situ foaming performance of the system combining self-generated gas reactants (sodium nitrite and ammonium chloride), the foaming agent (alpha olefin sulfonate), and the foam stabilizer (diutan gum) without blender was investigated based on foaming volume and bulk stability. Single core and parallel core flooding experiments were applied to investigate the plugging ability and diverting characteristics of in-situ foam. The results showed that the large pore volume was blocked by in-situ foam even at 150 ℃ as shown by the increase of residual resistance factor during subsequent water flooding. Parallel core flooding experiments also proved the diverting ability of in-situ foams as the diversion ratio of low-permeability core was higher than that of high-permeability core during subsequent water flooding. Moreover, the diversion performance of in-situ foam strongly depended on the permeability contrast, environment temperature, permeability of low-permeability core, and injection rate. Although diversion failed when permeability contrast was more than 10, in-situ foam also had good thermal stability and diverting ability at 150 ℃ in the permeability contrast range of 3 to 8. Such stable in-situ foam shows promising potential as diverting agent in heterogeneous formation for reservoir stimulation at high temperature.