Interpretation of the Fluid Distribution and GOR Behavior in the Yufutsu Fractured Gas-Condensate Field

Abstract

The Yufutsu field is a new naturally-fractured reservoir in Japan with negligible matrix porosity and permeability. This large reservoir contains near-critical gas condensate fluids with unusual fluid distribution and production. The GOR shows a decreasing trend. This is perhaps the first report of such an observation in the literature. Another interesting and perhaps related observation is that measured data in some wells show the gas richness decrease with depth; methane increases while heptaneplus decreases with depth. Steady-state data from 5-km long wells at shut-in conditions show liquid in the middle, and gas in the top and bottom.We used the expression of total diffusion flux (molecular, pressure, and thermal diffusion) to analyze and interpret the data in the Yufutsu field. One-dimensional and two-dimensional computations were performed using the Newton method and a new robust algorithm. Predictions were made in the entire reservoir using one single PVT sample in good agreement with data. Based on this work, it is concluded that thermal diffusion significantly affects the fluid distribution in the reservoir with consequence of decreasing the GOR produced.

Theoretical model of thermal diffusion factors in multicomponent mixtures

“…The model presented in this article, combined with the formalism of diffusion flux in multicomponent mixtures presented in our earlier article Ž . Ghorayeb and Firoozabadi, 2000 , provide a comprehensive theoretical framework for future experimental investigations of thermal diffusion factors in multicomponent mixtures. We believe the model also enjoys simplicity for practical applications.…”

“…Thermal diffusion or the Soret effect is important for the study of compositional variation in hydrocarbon reservoirs ŽWhitson and Belery, 1994;Ghorayeb and Firoozabadi, 2000b;. Ghorayeb et al, 2000 and for separating isotopic mixtures Ž .…”

Impact of fluid characterization on compositional gradient in a volatile oil reservoir

“…While reservoir temperature and pressure gradients are mentioned as the main causes of compositional grading, but this phenomenon is not limited to these factors (Hoier and Whitson 2000). In addition to the gravity segregation (Montel and Gouel 1985), thermal diffusion (Danesh 1998) and thermal convection (Saidi 1987;Ghorayeb and Firoozabadi 2000) which are affected by variations of temperature and pressure, other factors such as incomplete equilibrium distribution and immigration of hydrocarbons, presence of a dynamic aquifer in contact with a part of reservoir, asphaltene precipitation (Hirschberg 1988), heterogeneity of reservoir structure due to faults, variety of hydrocarbon distribution (such as paraffin and aromatic) in plus fraction (Danesh 1998;Schulte 1980) and biological degradation were cited in several publications (Ross and Farrimond 2010;Huang et al 2004;Larter and Wilhelmsb 2003). From a thermodynamic point of view, compositional grading models could be classified into two categories of equilibrium and non-equilibrium thermodynamics.…”

“…Onsager was the first who proposed a linear relationship between driving forces and fluxes of different phenomena in a process (Lebon and Jou 2008;Le Bellac and Mortessagne 2004). Based on the Onsager's theory, Ghorayeb and Firoozabadi developed a model to predict compositional grading in non-isothermal condition (Ghorayeb and Firoozabadi 2000). The main complexity of irreversible modeling is to evaluate the thermal diffusion factor.…”

“…The difference is in estimating properties of pure components and solubility parameters (Shukla and Firoozabadi 1998). Validation of this model was evaluated by applying to the Yufutsu Fractured Gas Condensate Field in Japan (Ghorayeb et al 2000). In another study, Shukla and Firoozabadi's model was performed to continuous thermodynamic with molecular weight as independent characterizing variable (Bakhtiari Nia and Movagharnejad 2007).…”