Accounting for a capillary pressure jump in a saturated porous medium for a more correct calculation of hydrocarbon reserves

Abstract

Relevance. The correct calculation of hydrocarbon reserves in various fields (oil, gas, gas condensate) is an important state task, because it allows you to properly organize field development in the future and ensure the rational use of natural resources of the state. In particular, the values of geological and recoverable reserves are assigned to a specific subsurface user and are recorded in departmental documents. Aim. To describe the effect associated with the calculations of the thermodynamic equilibrium of the mixture of hydrocarbons of the Karachaganak oil and gas condensate field at various formation depths with the capillary pressure jump taken into account. This makes it possible to clarify the value of the potential condensate-gas factor of reservoir gas and, as a result, to give a more accurate assessment of the geological reserves of hydrocarbon raw materials. Object. Analysis of the thermodynamic equilibrium of the hydrocarbon mixture of Karachaganak oil and gas condensate field, taking into account the capillary pressure jump, which takes place in a porous medium under reservoir conditions. Methods. Numerical modeling, analytical research. Results. Based on the previously developed methodology for calculating the phase equilibrium with the capillary pressure jump the correction of the potential condensate-gas factor of the formation gas of the Karachaganak oil and gas condensate field was carried out at various formation depths. The range of values of the condensate-gas factor difference for calculations both with and without capillary pressure jump was from 7,04 g/m3, with a condensate-gas factor value equal to 393 g/m3 for formation depth of 4000 m, to 64,47 g/m3, with a condensate-gas factor value equal to 547 g/m3 for formation depth of 4600 m. Based on the updated condensate-gas factor estimate, it is possible to clarify the condensate recovery coefficient during the development of a field without maintaining reservoir pressure or with partial maintaining reservoir pressure.

Keywords

• gas-condensate mixture
• phase equilibrium
• capillary pressure jump
• phase saturation
• condensate to gas ratio