Hybrid polymers and the use as additives in deep wells

The invention relates to water-soluble or water-swellable hybrid polymers comprising: a) 5 wt .-% to 95 wt .-% of a water soluble and / or water-swellable polysaccharide polymer selected from the group consisting of carrageenan, xanthan gum, karaya gum, tragacanth gum, chitosan, guar gum, locust bean gum, Sclerotium Gum , gellan gum, agar, fenugreek gum, konjac gum, more preferably xanthan gum, carrageenan, guar gum, chitosan, fenugreek gum, konjac gum, tragacanth gum, or a chemically modified form of said polysaccharide polymer, and b) 5 wt .-% to 95 wt .-% of a synthetic polymer containing one or more recurring structural units of the formula (1) contains or consists of wherein R Y is a chemical bond, O, CH A represents mean DS (O) POH, PO POR3oder Q