Fluid-Phase Behaviour for a Miscible-Gas-Injection EOR Project in a Giant Offshore Oil Field With Large Compositional Variations

Abstract

Abstract Gas injection as an EOR method is being considered for the giant Al Shaheen field, located offshore Qatar. The field is characterized by large lateral variations in fluid properties across the field. The oil gravity ranges from 16 to 38 °API and significant variations in initial GOR and saturation pressure are observed. The field is developed with horizontal wells with up to 35,000 ft long reservoir sections. The oil gravity may vary considerably along a horizontal well, which needs to be considered when evaluating further field development options involving miscible as well as immiscible gas injection. An extensive experimental program aimed at establishing a model for the miscibility behavior for this complex fluid system is described. The work resulted in the development of an equation of state (EOS) model capturing the miscibility behavior across the range of API gravities, as well as a set of black oil correlations consistent with the EOS. A method for initializing compositional reservoir simulations with the developed EOS based on API, GOR and saturation pressure maps of the field was developed. This methodology allowed a finely discretized compositional variation to be represented in the compositional simulation models giving an accurate and detailed fluid phase behavior description.