Carbon dioxide and nitrogen are necessary for an intensification of oil-and gas-extraction. They can be received from the flue gases formed after burning of natural gas. The analysis shows that is more favourable at the beginning in co-generation plant working on natural gas to make the electric power and heat, and then to allocate a carbon dioxide and nitrogen. Thus there are two complex problems: products of combustion after co-generation plant contains 8-10 % of oxygen; the potential of received heat appears low. Some variants for decision this problems are offered. It has allowed to create an independently and effectively working multi-purpose energotechnological complexes using only natural gas, with the purpose of manufacture the electric power, heat, liquid low-temperature carbon dioxide and pure gaseous or liquid nitrogen. Energotechnological complexes allow includes in the structure also an cryogenic air separation plants that promotes the expansion of nomenclature of made products, in particular, liquide oxygen. In these complexes the high energy potential of natural gas is completely realized.