Craig H. Phelps

A New Biopolymer for High-Temperature Profile Control: Part 1-Laboratory Testing

This paper reports on an extracellular polysaccharide produced by Alcaligenes bacteria that has been crosslinked to form firm gels that are stable for long periods at elevated temperatures. The biopolymer can be gelled with multivalent ions such as Cr{sup +3}; it can also be gelled at the 2,000-to-4,000-ppm level without Cr{sup 3+} in high-salinity ({approximately}20% total dissolved solids (TDS)) brines. Gel samples have been stable for 2 years at 74 and 90{degrees} C. Gels could be formed over a wide pH range, but best long-term stability was achieved in the pH range of 7 to 8. A flow test of Alcaligenes biopolymer gel in Berea sandstone at 74{degrees} C showed that the gel gave a brine permeability reduction factor of 320.

Selective penetration of biopolymer profile-control gels: Experiment and model

Abstract Profile control treatments using polymer gels can improve waterflood performance by reducing fluid channeling through higher-permeability “thief” zones. The success of such treatments often depends on placing the gel preferentially in the thief interval. Laboratory coreflood data presented in this work clearly shows that certain xanthan-based profile control gels exhibit the property of “selective penetration”. Selective gels flow preferentially into higher-permeability media and resist penetration into tighter media. These gels could, therefore, eliminate the need for mechanical zone isolation and thus reduce the cost of profile control treatments significantly. Selective flow behavior is a function of the process variables such as permeability and injection rates, and is only exhibited over a fixed range of conditions. Selective, modified xanthan/chromium gels stable to at least 120°C have been formulated. A mathematical model is being developed to simulate selective flow behavior. This model will predict: (1) the rate and extent of gel penetration into various formation layers when polymer is injected without mechanical isolation, and (2) the resulting change in the injection flow profile.