In the present work we investigate the questions raised in making effective algorithms for the gas flow characteristics calculated in the offshore gas pipelines, and account for possible pipeline glaciations in northen seas. Effective solution algorithms to the adjoint problem of heat exchange and an ice layer thickness calculation were selected. The effective algorithm of numerical solution of the general model of a gas mix transportation was compiled. Conducted research allowed the development of computational models of gas mix transportation through a long-length offshore gas pipeline in the northen seas. Based on numerical modelling, this research led to a number of practical suggestions to selecting the transportation regime, together with the gas pipeline construction and selection of the gas pipeline route relief. Calculation examples of the flow characteristics and of the ice grow dynamic are presented.