Further experimental investigation was undertaken to elucidate the mechanism involved in a new in situ gelation process. In this process a newly discovered bio-polymer produced by Cellulomonas Flavigena strain KU is used. The process is different from the more commonly known in situ gelation based on crosslinking of polymer molecules with heavy metal ions. The difference lies in the inherent physical property of the polymer that its physical state of solution changes to the state of gel by reducing the pH of its alkaline solution. More importantly, the gelation process is reversible. That is, transition from the gel state to the solution state and vice versa can be repeated by increasing or decreasing the pH of the solution.

The experimental investigation aimed at answering two fundamental questions:

  1. How selective and how uniform permeability reduction can be achieved within the core?

  2. How reversible is the permeability reduction induced within the core?

Experiments were performed in sand packs composed of two and three 10 cm long cells separated from the inlet face by an additional 2 cm long segment. Various injection schemes were tested while the pressure drop across each cell was monitored.

High degree of permeability reduction in the order of 100 to 6000 was achieved along the entire length of the sand pack. It was also possible to restore the initial permeability of the sand pack by injecting sodium hydroxide solution.

Creation of a layer of gel at the interface which is redissolved and re-gelled and which possibly moves in the direction of the flow path was considered a possible mechanism behind the uniform permeability reduction along the sand pack

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