Fluid Prediction in Near-Field Prospects Using PVT Modeling
Caillet, Gerard, Lucy Burns, Francois Montel, Total, Pau, France
This paper presents a methodology for a better prediction of the fluids in near-fields prospects, to reduce the uncertainties linked to the nature of the fluids. A well developed understanding of the distribution of the fluids in a basin can be approached with a reasonable confidence by PVT modelling.
The methodology consists first in a review of the different fluid types to get a synthetic description of the fluid distribution, including composition and property gradients (Saturation pressure, Rs, density). The mechanisms responsible for compositional grading give valuable information about the conditions of trapping.
Then, a reference fluid is selected, corresponding to a typical “source” fluid. A unique equation of state, calibrated to this reference fluid, is used to represent and compare all the fluids of a same area.
When the fluid types are not directly explained by the pressure and temperature conditions in the reservoirs, they can be derived of mixtures, either fluids from different sourcerocks, or fluids from same source-rocks at different maturity levels.
In a case study the fluids were classified into three groups: 1) under-saturated light oils, the “source” type fluid; 2) gas condensate, a mixture of the “source” fluid and dry gas; 3) gas and oil at equilibrium, a mixture of the “source” fluid and wet gas. The dry gas comes from source-rocks at a high level of maturity. The wet gas is thermodynamically interpreted as the result of stripping.
With integration of the PVT and geological approaches, it becomes possible to accurately predict the fluid types in the prospects of the studied area.