The oil and gas-condensate field being drilled by large length horizontal wells has been studied in this article. Major problems which occurred during its putting into development and in the course of the development have been stated. Based on the field development monitoring that includes mathematic modelling and actual operation results and logging surveys, the main reasons for gas breakthrough from the gas cap have been identified. The article presents the main ways of solving the problems concerned with gas breakthrough production decrease.
Key words: offshore oil and gas-condensate field, vast under-gas-cap zone, horizontal wells, GOR increase, ways of preventing gas breakthrough from the gas cap
