Capillary - adsorption effects in gas condensate systems in tight rocks - vertical variation of hydrocarbon composition

Author: S. Nagy 

This paper describes the complex phenomena related to mixing and segregation processes occurring during secondary migration and post-filling time of oil and gas-condensate system.

The model of segregation of composition using diffusion and convection inside reservoir is analyscd entirely: lithology, heterogencity, and compartmentalized structure.

The impact of adsorption, ca-pillarity, thermal, and barodiffusion effects is discussed.

The paleo-history of filIing and mixing proccsses is considered as a important factor for present status of reservoir fluid.

The paper discusses the non-equilibrium phenomena in the porous medium in presence of thermal gradient. The main goveming factor driven composition is gravity, especially in the high asphaltenes content oils and for near-critical oils/gas condensate system.

The new term (related to the capillary pressurc) in thc composition grading equation in the saturated transition region of adsorption-condensation area (for liquid phase) is presented and a new algorithm to find saturated Gas-Oil Contact (GOC) in the adsorption-capillary condensation area is given.

The algorithm is based on the Modified Tangent PIane Criterion for Capillary Condensation (MTPCCC) (Nagy 2002). The present paper shows difference driven by capillarity phenomena in the transition region on hypothetical example.

The paper discusses the difference between traditional (average) and grade composition of reservoir fluid in estimation OIIP/GIIP.