The detachment and migration of colloidal particles is an important cause of permeability decline in the near wellbore region. It is shown that polymerizable ultra thin film can be utilized to immobilize fines on pore surfaces. The Surface Adsorption Polymerization (SAP) process developed here is a three step process requiring a sequential injection of a specific concentration of the surfactant, monomer, and initiator. An ionic surfactant is first adsorbed on the solid substrate or the porous medium. In the second step, a monomer is injected that preferentially resides in the surfactant layer. In the final step, an initiator is used to polymerize the monomer on the surface to form a solid ultra thin film which is very stable and effectively holds the colloids on the surface.
There are three major advantages of such a treatment. Firstly, there is a great deal of flexibility in the choice of monomers and surfactants used so that the mechanical and chemical properties of the film, can be tailored to meet the needs of a particular application. Secondly, when applied to porous media or microporous membranes the ultra thin film does not cause pore closure. The film is extremely thin and the thickness of the film can he controlled by using appropriate concentrations of the monomer and surfactant. Lastly, the polymerization does not occur in the bulk solution, resulting in minimal waste or damage caused by polymer formation in the bulk solution. The SAP process can be potentially applied to stabilizing fines in high rate producers, as a post flush after acidizing and in specialized applications such as steam huff and puff wells.
Colloidal 'fines' are ubiquitously present in oil and gas bearing rocks. These 'fines' are mineralogically diverse and are known to migrate with the flowing fluids and choke off pore throats. High fluid velocities, low salinities, high pH values and high temperatures are known to cause fines entrainment (1,2).
Various techniques and chemicals have been used to minimize fines migration and thereby increase well productivity. The most common chemicals in use today are polymers containing quarternary ammonium salts, hydrolyzable metal ions such as zirconium oxychloride and hydroxy aluminium. These chemicals adsorb on the mineral surfaces and prevent fines migration by shielding the negative electrostatic charge on the colloidal surfaces. There are three potential disadvantages with the treatments in use today (1) Charge neutralization does not prevent mechanical particle dislodgment at high fluid flow rates (2) The treatment is usually temporary since the polyvalent ions tend to desorb over time as large volumes of fluid are produced and (3) Some chemicals used are relatively expensive.
These disadvantages point toward the need for further research into fines stabilizing techniques. The hydrodynamic entrainment of particles can only be prevented by coating the particles with a solid thin film that is stable at high shear rates. This stable ultra thin film can either be formed in situ by polymerization or by crosslinking of surface adsorbed molecules. The present research is focused on developing a methodology for building such thin films in porous media and testing their effectiveness in immobilizing colloids.