Simulating the reservoir pressure maintenance strategy by injecting HC and non-HC gases into the Achimov reservoirs

   Prerequisites for the study are selection of the optimal agent to maintain reservoir pressure and setting the optimal conditions under which the maximum condensate recovery factor is achieved.   The aim of the article is to assess the technological efficiency of methods for increasing condensate recovery while maintaining reservoir pressure by injecting hydrocarbon (methane) and non-hydrocarbon (nitrogen, carbon dioxide) gases.   The subject of this study is the Ach3-4 reservoir within the Novo-Urengoyskoye license area of the Urengoy field. The most effective methodology for identifying the stated issue is the outcome of hydrodynamic calculations conducted on a composite hydrodynamic model implemented in ECLIPSE 300 format. In order to model one of the sections of the Ach3-4 reservoir, a development element was selected in which the average parameters corresponded to those of the full-scale model. The efficiency of the selected methods was evaluated by comparing them with the baseline scenario, which represents the conventional approach to the development of the Ach3-4 reservoir on depletion. The injection start was set in a dynamic model after removal of 30, 50 and 85 % of gas initially in-place and at a steady pressure of 18, 37 and 40 MPa, provided that gas recovery factor was achieved on depletion. The technological efficiency of the development options was evaluated by examining the dynamics of the condensate recovery factor in relation to the dynamics of the gas recovery factor. The optimal option was identified based on the maximum value of the condensate recovery factor. The results of the studies conducted to increase condensate recovery from reservoirs indicate the effectiveness of using carbon dioxide as an agent. The condensate recovery factor depends on the ratio of injection and production wells, the time of the start of reservoir pressure maintenance and the number of pore volumes pumped. The efficiency of carbon dioxide injection at late stages of development increases dramatically when the minimum mixing pressure is reached.