Laboratory study of the reformability of xanthan/chromium (III) gels used in conformance treatments

One application of xanthan/chromium(III) gels in vertical conformance treatments is to allow the gel to form on the surface, to be degraded by shear during injection through the tubing and perforations, and to reform in the selected high permeability layers to reduce the horizontal permeability contrast between layers. The success of such an application depends on the ability of the gels to reform after having been degraded by high shearing conditions during placement.;A study of the behavior of the regelation of xanthan gels that have been degraded by shear was carried out in the laboratory. The shearing mechanism was accomplished by various shearing devices in which the shear intensity and shear duration were adjustable. The initial gelation of gels and regelation of degraded gels were identified by continuously monitoring the change of dynamic viscosities using dynamic oscillatory rheological measurements. The reformability of a gel was determined by the ratio of the recovered dynamic viscosity to the dynamic viscosity prior to the shear degradation.;The correlation of reformability of a gel and shearing conditions was made based on the regelation results derived from blender shearing and rheometer shearing. The reformability of a weak gel was found to depend on the shear intensity whereas the reformability of a strong gel was independent of the shear intensity. The effect of shear duration was found insignificant to the reformabilities of both types of gels. Consideration of gel holding time in field application shows that a prolonged gel holding time can lead to the loss of reformability for a strong gel but not for a weak gel.