Effective evaluation of formation wettability plays a key role in determining reservoir fluid distribution and flow properties. Knowledge of formation wettability is very crucial for carrying out a better control of reservoir performance and enhancing field production prediction, especially in complex reservoirs.
The methods generally employed for determining rock wettability, both qualitative and quantitative, were revised. Detailed analyses of relative permeability curves from steady state core tests, generally used in the qualitative analyses, show that their resultant shapes, not only depend on rock wettability, but also on pore space geometry. Studies have shown that, for better results, alongside relative permeability curves, capillary curves and core samples pore geometry are needed to determine wettability.
Unlike qualitative evaluation, quantitative wettability techniques require direct laboratory measurements and provide adequate results with response to the solid surfaces and liquids used. In conventional laboratory tests on reservoir rocks the contacting liquids used are usually well defined, but the interacting solid surface (pore surface) remains partially unknown. It isn’t quite clear what core (pore) surface is suitable for the right results to be obtained – pure (clean) mineral surface or ‘stained’ (with oil of some thickness). Core ageing can only restore a certain (unknown) wettability, as the real in situ formation wettability before drilling and coring has always been undefined and, ageing periods can never meet up with the formation geological time. Hence alternative core preparation methods are needed.
This article focuses not only on the development of new drilling, coring and core handling methods, but also on more effective wettability measurement and calculation techniques, necessary to meet the present day challenges of complex reservoirs and hence optimize production.References
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