Dependency of Wettability Alteration on Hydrocarbon Composition and Interfacial Tension in Gas/Condensate Systems
- J. Fahimpour (Heriot-Watt University) | M. Jamiolahmady (Heriot-Watt University) | M. Sohrabi (Heriot-Watt University) | J. Mills (Heriot-Watt University)
- Document ID
- Society of Petroleum Engineers
- EAGE Annual Conference & Exhibition incorporating SPE Europec, 10-13 June, London, UK
- Publication Date
- Document Type
- Conference Paper
- Society of Petroleum Engineers
- 1.8 Formation Damage, 5.5 Reservoir Simulation, 5.8.8 Gas-condensate reservoirs, 5.2 Reservoir Fluid Dynamics, 5.2.2 Fluid Modeling, Equations of State, 5.2.1 Phase Behavior and PVT Measurements, 4.1.2 Separation and Treating, 5.8.7 Carbonate Reservoir, 4.1.5 Processing Equipment, 4.6 Natural Gas
- gas condensate, interfacial tension, contact angle, wettability alteration
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In gas-condensate reservoirs, soon after the pressure falls below the dew-point pressure, condensate liquid drops out of the gaseous phase. In such conditions, high surface energy minerals render spreading of the condensate film on the rock surface, wetting out the pores' surfaces. Condensate consequently starts to accumulate, restricting the open paths for the flowing gas, which could result in significant reduction in well productivity.
Modifying the surface energy of the reservoir minerals by chemicals, aiming at altering the rock wettability from strongly liquid-wetting to intermediate gas-wetting conditions, has been proposed as a solution to improve the oil mobility around the wellbore and mitigate the corresponding blockage issues.
Over the last decade, large numbers of experimental investigations have been dedicated to study the performance of different chemical groups on wettability alteration of reservoir rocks. However, in all these studies, conventional fluids, e.g. decane/air, have been used to measure the contact angles at oil/gas/rock boundary. In this paper, for the first time, gas/condensate fluids, with various compositions and at different interfacial tensions (IFTs) have been used to evaluate the performance of wettability modifiers under more realistic conditions. The observations revealed that at similar IFT values, as the number of carbon atoms increases, i.e. there are heavier hydrocarbons (e.g. C1/nC10), the condensate/gas/treated rock contact angle (?condensate/gas ) increases, whilst for the lighter hydrocarbons (C1/nC4), the condensate wets the rock surface quickly. IFT also showed a significant impact on the treatment performance. That is, at lower IFTs, smaller contact angles through the liquid phase were observed, e.g. for C1/nC10 mixture, when IFT decreased from 10 to 1.5 mN/m, ?condensate/gas reduced from 65° to 40° towards liquid-wet.
The results highlight the significance of the dependency of the wettability modifiers performance to the original fluid composition and thermodynamic conditions in a gas-condensate reservoir. This also underlines the careful considerations that are required in design and application of these treatments in such reservoirs.
In gas condensate reservoirs soon after pressure falls below the dew point, particularly in the vicinity of producing wells, retrograde condensate drops out of the gas phase (Danesh et al., 1991; Henderson et al., 1998). In such conditions surface forces between rock and fluid system significantly impact the fluids' distribution and their flow characteristics within the porous media (Al-Syabi et al., 1997). High energy surfaces of the reservoir rocks compared to the low interfacial tension (IFT) system between gas and condensate renders complete wetting of the rock surface by the condensate phase, hence condensate exists as a thin film while gas occupies the centre of the pores (Danesh et al., 1988; Haniff and Ali, 1990, Jamiolahmady et al. 2000). As pressure continue to decline and more condensation occurs, a condensate build-up region expands around the wellbore impeding the well productivity. There have been a number of significant productivity losses due to condensate banking reported, even for lean gas condensate reservoirs, (Afidic et al., 1994; Engineer, 1985).
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