Page 398 - Petrophysics 2E

366 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

heptane to decrease the solvency of asphaltenes, exhibited larger contact
angles (-140") than surfaces equilibrated with the undiluted crude
oil (-75"). Thus, the contact angle increases (the system becomes
more oil-wet) when asphaltenes are deposited on the surfaces. This is
important to oil production because it indicates that some deposition of
asphaltenes on the rock surfaces around a producing well will cause the
zone to become more oil-wet. This oil-wet zone will reduce the capillary
end effects that cause a high water saturation and thus a high water/oil
producing ratio.

WlLHELMY PLATE MEASUREMENT CONTACT ANGLES
OF
The Wilhelmy plate method yields direct measurements of the
adhesion tension (Figure 6.4) acting on the perimeter of a plate, as well

n Microbalance and computer

Force, T mN

Moving down
~

Force, mN I

up t

Moving

(b)
Figure 6.4. Wtlbelmy plate method for measurement of advancing contact angle
(a) and receding contact angle e).