Evaluation of conditions for efficient nitrogen injection to maintain reservoir pressure during low-permeability reservoir development

Conducted research and development experience showed that flooding efficiency depends significantly on the size and structure of pores and pore channels. The decline in flooding efficiency in low-permeability reservoirs led to an active search for alternative working agents. The majority of projects involve the injection of carbon dioxide and hydrocarbon gases. The key parameters influencing the efficiency of gas-based methods are miscibility pressure and displacement efficiency. By these criteria, nitrogen is the least attractive working fluid, but for reservoir pressure maintenance purposes, this gas offers a number of advantages. There are no criteria for the applicability of gas injection, including nitrogen, for reservoir pressure maintenance. This article presents the results of nitrogen injection modeling using a composite 3D hydrodynamic model to assess the effectiveness of its use for reservoir pressure maintenance in low-permeability reservoir conditions in the range of permeability values from 1·10-3 µm2 до 12·10-3 µm2. A range of absolute permeability coefficient values was obtained for which a greater volume of injected nitrogen (74 %) was effective in maintaining reservoir pressure. The distribution of injected gas by action mechanisms was assessed depending on absolute permeability values. When adapting nitrogen injection technology to specific geological and physical conditions for reservoir pressure maintenance, one of the main tasks is to determine the permissible range of reservoir permeability values.

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