Solution Properties Of Mobility Control Polymers
Authors: Unsal Esref , Duda John Larry , Klaus E. Erwin , Liu Han Tai 
Published: December 2007

The solution properties of xanthan gum are presented for application in Pennsylvania oil sands of low presented for application in Pennsylvania oil sands of low permeability. A precise low-shear capillary viscometer permeability. A precise low-shear capillary viscometer has been designed to evaluate the solutions prepared by orifice and propeller blending. Relative molecular weights as a result of mechanical degradation have been obtained from intrinsic viscosity measurements. The effects of salt content, polymer concentration, temperature, mechanical degradation, and shear rate on viscosity are discussed.

Introduction

The technical and the economic feasibilities of chemical flooding as an enhanced oil recovery technique have been the subject of many controversies in the petroleum world in recent years. Now most people believe petroleum world in recent years. Now most people believe that the economics will enable this method of recovery to be commercialized in the coming years.

Bradford, Pennsylvania No. 3 oil sands are of low permeability (an average of 8.5 millidarcies) and permeability (an average of 8.5 millidarcies) and moderate temperatures (68 deg. F). They have already been water flooded and the residual oil saturation is around 30%. The oil in the formations is of low viscosity (3–5 cp). These features make the Bradford field an attractive possibility for chemical flooding. The flood consists of two solutions: a surfactant slug that mobilizes the oil and a polymer buffer which pushes the slug toward the production wells. This paper will address itself to the preparation and the evaluation of polymer solutions made from xanthan gum for use in the Bradford, Pa. field.

Knowing the solution properties of a polymer buffer is the first step in predicting its mobility in the reservoir. Viscosity under different environmental conditions and injectivity are the most important properties. The measurements must be made under conditions properties. The measurements must be made under conditions which match the flood. The other two steps in studying the flow of polymer solutions through porous media are core or porous media tests and field experiments. The findings from these investigations must be coupled with models of the porous media to be flooded to design solutions and develop the injection procedure.

Here the focus will be on the solution properties measured in the laboratory. Viscosity at low shear will be the prime evaluation criterion.

One of the challenges in measuring the solution properties of a mobility control polymer is to properties of a mobility control polymer is to characterize and simulate the flow conditions in the oil sand. A precision low-shear capillary viscometer has been designed for this purpose. The importance of mixing these solutions well has been overlooked in many investigations. How well the polymer is dispersed determines the injectability of the solutions.

Mechanical degradation takes place when excess pressure drops are imposed on the polymer in turbulent pressure drops are imposed on the polymer in turbulent flow. A way of measuring the extent of this degradation is to obtain the effective molecular size of the polymer in solution by the intrinsic viscosity polymer in solution by the intrinsic viscosity technique.

Typically, the narrow openings to the micropores in the oil sand might be 1 to 5 pm or more. The task then is flowing these macromolecules through holes of similar size. Permeability reduction is not desired in controlling the mobility in tight sands such as the Bradford No. 3. Also, since the polymer concentrations used are very low, losses due to adsorption and mechanical entrapment should be minimized.

There has been limited research conducted on xanthan gum. Healy and Reed used this gum in their core tests to investigate immiscible microemulsion flooding. Trushenski, Dauben, and Parrish studied the viscosity of xanthan gum at different shear rates. MacWilliams, Rogers, and West investigated this also as well as looking at the short-term stability. Gogarty presented some field test results. Injection of xanthan gum solutions is discussed by Burnett and Lipton.

Low Shear Capillary Viscometer:

Shear rates between 1 and 100 sec-1 are typical for tight formations such as Bradford No. 3 sand.