Xanthan and succinoglycan

Comparison of Xanthan and Succinoglycan. The physical properties of succinoglycan and its solutions are similar to those of xanthan. 

Entanglement and weak gel formation are characteristic of some oilfield polysaccharides such as guar and starch, but are present only weakly, if at all, in both xanthan and succinoglycan solutions. Solutions of xanthan and succinoglycan are thus able to pass through porous media such as rock, while guar and starch cannot because of their gel-like nature. Hence the different uses of these polymers in the oilfield. 

Degradation. There is, however, a second, more important, feature. Above the transition temperature we have shown that both xanthan and succinoglycan are more susceptible to degradation (5). This may be because the polymer side chains become dissociated from the main chain, in a similar manner to the unfolding of proteins. Viscosity changes, however, indicate that main chain linkages have become more... 

Transition temperature and stability are, therefore, closely linked. The rate of viscosity loss of both xanthan and succinoglycan solutions increases about 100 fold as the molecules become disordered above T. This may be a problem, as some users of xanthan in heavy brines have discovered, but it can be used to advantage. 

Plant biomass, including algae, is a very important source of renewable polysaccharides, some of which have original properties compared with those of synthetic polymers, as shown in Table 24.1 [ 1-3]. Cellulose and starch are discussed respectively in Chapters 16 and 15. The corresponding animal-derived chitin [4] is covered in Chapter 25. The microbial water soluble polysaccharides like hyaluronan, xanthan and succinoglycan [1, 2, 5] are dealt with in Chapter 13. This chapter focuses on the polyelectrolytes based on polysaccharides from plant and algae. 

Succinoelvcan. Initially identified advantages of this polymer, succinoglycan, were that aqueous solutions of it were more viscous than solutions containing an equal concentrations of xanthan, and that the polymer tolerated higher concentrations of salt, in the sense that solutions passed more readily through microporous filters. These properties made the polymer of potential interest for EOR. 

The relative stabilities of xanthan and Shellflo-S can be reversed. We have made measurements in a number of brines, including calcium bromide (5), and found that xanthan solutions were less stable than those of succinoglycan above about 400g/l (c. 2M). 

Shellflo-S. In one area at least, biotechnology has something to offer the oil industry. Many of the polymers used in drilling fluids are based on natural products. They can be cheap like starch or guar or offer performance no synthetic can match, such as xanthan or succinoglycan. Shellflo-S is for use now in such areas as well completion, but more widespread use could follow if its particular range of properties are seen to be useful, and the cost of production is reduced. 

Both polysaccharide molecules are relatively stiff, stiffer even than simple cellulosics such as HEC, and have a molecular masses in excess of two million. Recent work by Rinaudo and coworkers (Personal communication) and Crecenzi and colleagues (Int. J. Biol. Macromol., submitted) has shown that succinoglycan molecules are also stiffer than those of xanthan. 

Shellflo-S, succinoglycan is an interesting new polymer for use in the oilfield, in many ways complementary to xanthan. It is particularly appropriate for use in well completion fluids at moderate temperatures, where a more pseudoplastic rheology than that provided by HEC, and a more rapidly breaking polymer than xanthan is required. 

Pig. 31. Examples of some bacterial polysaccharide structures (A) succinoglycan (B) xanthan (C) gellan in the native form and after deacylation. 

Fungi and bacteria Bacterial cellulose, dextran, pullulan, schizophylan, lentinan, xanthan, curdlan, gellan, succinoglycan... 

---