l6 rock properties; wettability

8/9/2019 L6 Rock Properties; Wettability

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Holditch - Reservoir Technologies July 1999

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In oil-wet rocks, contact angle, !, is greater than 90oand lessthan 180o.


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Example:


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Example:

Waterflooding an oil reservoir in which the reservoir rock ispreferentially oil-wet

Gas injection in an oil- or water-wet oil reservoir

Pressure maintenance or gas cycling by gas injection in a

retrograde condensate reservoir


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Artifical cores were created with increasing concentrations of

organo-silanes to make the cores progressively more oil wet.

The USBM wettability number ranged from 0.649 (strongly

water wet) to -1.333 (strongly oil wet).

Lab work4 shows that a strongly water-wet system will have

breakthrough of water after most of the production of oil has

taken place, and very little production of oil will occur after

water breakthrough.

For oil-wet systems, water breakthrough occurs earlier in the

flood and production continues for a long period after water

breakthrough at a fairly constant water/oil production ratio.


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The above figure4 shows that the core can change its

wettability characteristics from water-wet to oil-wet after

immersion in oil for long times.

Under waterflooding, oil-wet rock will generally have lower

recovery than water-wet rock.


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Note that wettability measurements using core samples yield

an indication of wetting preference of the rock in the lab!

. Notnecessarily in the reservoir.

Knowing the wettability does not allow us to predict multi-

phase flow properties. We still need to know capillary pressure

and relative permeability in order to predict the multi-phase

properties. However, knowing the wettability helps us

understand the reservoir and anticipate or explain its behavior.


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1. Amyx, J.W., Bass, D.M., and Whiting, R.L.: PetroleumReservoir Engineering, McGrow-Hill Book Company New

York, 1960.

2. Tiab, D. and Donaldson, E.C.: Petrophysics, Gulf Publishing

Company, Houston, TX. 1996.

3. Core Laboratories, Inc. A course in the fundamentals ofCore analysis, 1982.

4. Donaldson, E.C., Thomas, R.D., and Lorenz, P.B.:

Wettability Determination and Its Effect on Recovery

Efficiency, SPEJ(March 1969) 13-20.

l6 rock properties; wettability

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