The paper presents a methodology of hydrocarbon fuid composition calculation on the basis of gas and condensate profiles calculated in a black oil simulator. The methodology is based on the straight dependency of the condensate-gas factor (CGR) and the reservoir pressure (Pres). In order to determine a fluid composition a dependence function between a fraction of a hydrocarbon component and CGR is created using a PVT-simulator. Having a relationship between CGR and a hydrocarbon fraction a fluid composition can be calculated using the average CGR from black oil simulation results. This methodology gives a fraction of every individual component in comparison to composition modelling, where real components should be groupped in pseudocomponents. Proposed methodology assumes several constraints -the methodology should be applied just for gas condensate reservoirs without oil rims and the reservoir should be developed on depletion. In the work black oil and composition simulation results were compared. The paper can be useful for reservoir engineers working with gas condensates because it allows reducing simulation time without losing information about fluid composition.
The near-critical initial state of the formation fluid with a unique content of C5+ components in a tight reservoir with high temperature and abnormally high reservoir pressure (AHRP) causes significant difficulties in collecting samples of the formation fluid and assessing their adequacy to the actual reservoir mixture both in composition and identified phase state (gas condensate or oil) and phase behavior. The paper presents the result of the work of the project multidisciplinary team, which includes specialists from the PJSC «NOVATEK» group of companies and the leading Russian Institute of Oil and Gas Problems (OGRI RAS), of studying the near-critical gas condensate system in a HPHT tightreservoir. The effect of well completion and sampling conditions on the composition, phase state and phase behavior of fluid samples is shown. The influence of formation water and residual liquid hydrocarbons (HC), capillary effects, adsorption, and the specifics of the PVT-model tuning on the dew point pressure, the condensate lossdynamics, and the variation of composition and phase state of the fluid with depth is assessed. The results made it possible to clarify the understanding of the reservoir system,develop a program for further research, and improve the history matching of the flow model. The performed modeling of various factors in a porous medium for the conditions of the studied reservoir showed that the presence of formation water and capillary effects do not noticeably affect the phase behavior of the fluid, but the possible presence of scattered hydrocarbons and the adsorption / desorption of hydrocarbon components can lead to considerable changes in the dew point pressure and the condensate loss dynamics. The significant influence of the PVT model tuning on the calculated distribution of the initial fluid composition over the reservoir volume is demonstrated, including the position of the gas-oil contact and its type (classical gas-liquid contact or supercritical transition to the liquid state).
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