CHAPTER 3 RESERVOIR ROCK FLUID INTERACTIONS

Course Outline

Capillary Pressures & CP Curves

Surface and interfacial tension

Pressure & Temperature Gradients

Fluid distribution in reservoirs

Net pay thickness & Volumetrics

Drive mechanisms

Wettabilityo Measure of the attraction between rock surface and the fluids in the reservoir

o The wetting fluid the one most attracted to the rock surface

Water Wet

(most fields)Oil Wet (clay&carbonates)

o Different types exhibit different production performance

o Oil wet systems tend to exhibit early water breakthrough and lower initial

water saturation.

WettabilityThe definition is defined as tendency of one fluid to spread on or adhere to a

solid surface in the presence of other immiscible fluids

It is based on contact angle of water surrounded by oil

The wettability of reservoir rocks to the fluids is important in that the

distribution of the fluids in the porous media is a function of wettability.

Because of the attractive forces, the wetting phase tends to occupy the smaller

pores of the rock and the nonwetting phase occupies the more open channels

Oil

Water

Water

Water-wet Oil-wet

< 90o = water -wet> 90o = oil-wet

90o = intermediate wettability

A variation of up to 20 o is usually considered in defining intermediate wettability.

WATER-WET OIL-WET

Ayers, 2001

FREE WATER

GRAIN

SOLID (ROCK)

WATER

OIL

SOLID (ROCK)

WATER

OIL

GRAIN

BOUND WATER

FR

EE

WA

TE

R

OIL

OIL

RIM

< 90 > 90WATER

OilAir

WATE

R