Abstract: Water based gels, comprising Xanthan gum(XC) cross linked with cross linking agent, such as trivalent chromic ions(Cr(Ⅲ)), are now finding widespread use for near well-bore water and gas shut-off in the oil industry. The study on the rheology of gel is very important to understand and to improve the in-situ application of the gels technology. 　　In this paper the viscoelasticity of the systems of XC cross-linked with Cr(Ⅲ) in the presence of dodecyl-oxypropyl-β-hydroxyl-trimethyl-ammonium bromide(C12NBr) has been investigated. The viscoelasticity measurements were performed on a RS 75 controlled stress rheometer(Haake Co.)operating in an oscillating mode. Determination of the G′ and G″ vs shear stress was performed at a fixed frequency of 1.0 Hz and the moduli vs frequency relationsbip were determined at a fixed shear stress of 1 Pa. For the XC aqueous solution, the storage (i.e., elastic) modulus G′ could not be measured under the experimental condition. For the cross linking system G′ value increased it was and always larger than the G″ value at shear stress less than 0.5 Pa, i.e., the gelling system has more solid or elastic properties. The elasticity of gel is weakened and its viscosity is enhanced in the presence of C12NBr. 　　The main effect of the addition of C12NBr to XC gel is to destroy the network structure of the gel. It is resulted from the binding between C12NBr and XC, i.e., cross linking agent Cr(Ⅲ)was replaced by C12N＋. This is testified by binding isotherom of C12NBr on XC.

Key words: Xanthan Gum(XC), Gel, Dodecyl-oxypropyl-β-hydroxyl-trimethyl-ammonium bromide(C₁₂NBr), Storage moduli(G′), Loss moduli(G″)