Geological criteria and methods to increase condensate extraction at the late stage of gas condensate deposits' development

Formulation of the problem. Ukraine is one of the oldest oil and gas producing countries in the world. Maximum volumes of gas (68 billion m3 per year) were extracted in 1975-1978. After this period, production began to decline. About 18 billion m3 of gas was extracted in 2019 in Ukraine. The question arose of studying ways to increase the annual production of gas and condensate from old fields. The total residual reserves of deposits in late operation are estimated at more than 200 billion m3 and are classified as difficult to extract. Review of previous publications and studies. Scientific publications consider technologies and ways to increase hydrocarbon extraction. Bikman E. S showed the dynamics of the specific condensate content in gas formation depending on the formation pressure at the fields of Ukraine. Reducing pressure during the development of gas condensate deposits with a high initial content of condensate in the formation gas to the condensation start pressure leads to "avalanche" condensation of liquid hydrocarbons.This causes the loss of heavy hydrocarbons in the depletion process of this type of field. There are two ways to increase hydrocarbon recovery of gas condensate fields:to use methods to maintain reservoir pressure in the initial stages of their development, and to use secondary methods of condensate extraction that fell in the reservoir at the later stages. Object of research: gas-condensate fields with significant volumes of condensate that have fallen into them, and the possibility of its extraction at a later stage of development. Results. In this study, the authors identified systems of gas-condensate fields development to ensure the extraction of condensate in the formation. The article considers five theoretically possible options to improve the energy efficiency of gas condensate fields. For practical use, two methods are recommended: gas bypass from deposits with high pressure and low condensate content in deposits with lower formation pressure and high condensate content; continued depletion of deposits at low formation pressures less than the maximum condensation pressure. The organization of gas bypass in order to increase the extraction of condensate from depleted formations is possible under the condition of low condensate content and higher formation pressure in the deposit from which it is planned to carry out gas bypass. The transfer of gas from a deposit with higher values of the average condensation factor to a deposit with lower values is inefficient. The authors apply a mathematical device which can be used to forecast development of two deposits in the mode of gas bypass with definition of alignment time of formation pressures in their depletion. It is established that the use of the cycling process at the late stage of gas-condensate fields operation at formation pressures less than the maximum condensation pressure (P reservoir