Chemical Treatment Enhances Xanflood Polymer
Authors: Patton John T. 
Published: December 2007

This paper was prepared for the 48th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Las Vegas, Nev., Sept. 30-Oct. 3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Field and laboratory tests indicate that dissolving xanthan in water is the most troublesome problem associated with the Xanflood process. Poor dissolution produces xanthan particles which plug filters and injection wells. Caustic treatment alters the xanthan structure to produce clarified, more filterable solutions. Treatment cost is minimal and is more than offset by improved performance and lower royalties on the performance and lower royalties on the modified form of xanthan.

Introduction

During the past ten years, the concept of using polymeric additives in water flooding for mobility control to improve oil recovery has been vigorously explored. The results of numerous lab and field tests are available in the literature. In recent years, the use of surfactants to produce tertiary oil has provided increased incentive to develop an acceptable polymer for mobility control. Experience from surfactant field tests confirms the necessity of including a mobility control additive as previously determined in laboratory previously determined in laboratory studies.

Fluid mobility is defined as a ratio of the fluid's permeability to viscosity, as shown in equation 1. For years, it was generally accepted that if one desired to lower the mobility of water, either the viscosity

(1) k=-----

could be increased or the permeability decreased. This reasoning is still valid; however, the advent of surfactant flooding adds a new restraint, causing a shift in the thinking concerning mobility control. Additives which lower mobility by reducing permeability do so by adsorbing on the reservoir permeability do so by adsorbing on the reservoir rock surfaces, thus reducing the size of the capillary pores through which the water must pass. The adsorption process necessarily pass. The adsorption process necessarily removes the additive from the water and hence a denuded water bank will always precede water containing the mobility control additive. This water, stripped of polymer, cannot effectively propel the surfactant bank through the reservoir. For this reason, it is desirable to use a non-adsorbing polymer to maintain mobility control at the polymer to maintain mobility control at the trailing edge of the surfactant bank where it can be effective.