This document discusses capillary pressure concepts including: 1) Capillary pressure is the pressure difference between two immiscible fluids separated by an interface, usually calculated as the pressure difference between the non-wetting and wetting phases. 2) Capillary pressure curves show the relationship between fluid saturation and height above the free water level, with the drainage curve always higher than the imbibition curve. 3) Displacement or entry pressure is the pressure required to force the non-wetting fluid through an initially wetting-phase saturated sample.

1. Displacement capillary presseur
Of preparation :
Ben Omar Amor
Ahmima Elhadi
Seddiki Abdelhah
Under supervision of :
Haffsi

2. Content
 Introduction
 Capillary Pressure Concept and Definition
 Drainage and imbibitions Capillary Pressure Curves
 Displacement capillary pressure
 Uses of Capillary Pressure Data

3. wettability
The tendency of one fluid to spread on or adhere to a solid surface in the presence of other
immiscible fluids
 Water wet : is that the small spaces and all the surfaces of our core matrieal and the and the grains are
coated with water and oil may present but it will be in the middle of the pore spaces or in the large
pore spaces , the opposite in oil wet
 Fractional wet : some portions strongly oil wet , rest water wet
 Mixed wet :
Large pores oil wet
Small pores water wet
 Intermidiate wet : equal oil or water wet
 Neutral wet

4. • Water exists at all levels below 2 , and both water and
oil exist at all levels above 2 .
• Oil and water pressure gradients are different because
their density is different .
• At level 2 , pressure in both the water and oil phases is
the same .
• At any level above 2 , such as level 3 , water and oil
pressures are different .
• This difference in pressure is called the capillary
pressure .
Capillary Pressure Concept

5. Capillary Pressure Definition :
The pressure difference existing across the interface separating two immiscible fluids . It is usually
calculated as :
Pc = Pnwt - Pwt
One fluid wets the surfaces of the formation rock ( wetting phase ) in preference to the other ( non -
wetting phase ) .
Gas is always the non - wetting phase in both oil - gas and water - gas systems .
Oil is often the non - wetting phase in water - oil systems .
 Water - gas system . Pc = Pg - Pw
 Water - wet water - oil system . Pc = Po - Pw
 Oil - gas system . Pc = Pg - Po
Capillary Pressure Concept

6. Relation between Capillary Pressure and Fluid Saturation :
For uniform sands , reservoir fluid saturation
is related to the height above the free water
level by the following relation :

7. Fluid Distribution in Petroleum Reservoirs
Free water level ( surface )
is the level at which water - oil capillary pressure zero ,
i.e. the pressures in both water and oil phases are equal .
• Above the free water level , oil and water can coexist .
Above this level , there usually exists another level ( or surface )
called the water - oil contact WOC.
Fluid Distribution in Petroleum Reservoirs

8. Water Oil Contact
Below the WOC , only water can be produced
Above the WOC , both oil and water can be produced .
At some point above the WOC , water will reach an irreducible
value and will no longer be movable Likewise , a free oil level and
an oil - gas contact ( OGC ) may exist as shown in the figure .

10. Transition zone
The oil transition zone is the zone occurring between the zone of 100 % water saturation ) and
the zone of 100 % hydrocarbon saturation ( S₁ ) which
consists of mobile water above the irreducible
water saturation .

12. Transition zone
Transition zone height is partially a function of the density
difference between the two fluids .
For a given rock quality , the transition zone will be smaller
for larger density differences ( e.g. gas and oil ) and larger
for smaller density differences ( e.g. heavy oil and water ) .
This relationship is evident from the relation between
capillary pressure and the height above the free - water level .

13. Capillary Tube Model - Air - Water System :
Capillary Tube Model - Air - Water System :
Water rise in capillary tube depends on the density
difference of fluids.

14. From a similar derivation , the equation for capillary pressure for an oil / water system is :

15. Drainage and Imbibition Capillary Pressure Curves
Drainage and Imbibition Capillary Pressure Curves :
The drainage curve is always higher than the imbibition curve .
 Si = Initial or irreducible wetting phase saturation .
 Sm = critical non - wetting phase saturation .
 Pd = entry pressure or displacement pressure .

16. Drainage Process :
Fluid flow process in which the saturation of the non - wetting increases .
Mobility of non - wetting fluid phase increases as non - wetting
phase saturation increases .
Imbibition Process :
Fluid flow process in which the saturation of the wetting
phase increases and the non - wetting phase saturation decreases .
Mobility of wetting phase increases as wetting phase
saturation increases .

17. The entry ( displacement ) pressure
is defined as the pressure required to force the
non - wetting fluid through an initially
wetting - phase - saturated sample .
Is the amount of extra presseur required to force the
non wetting phase to displace the wetting phase

19.  So from the last equation we can determine the wettability of the core or the system :
 we known that Pc = Pnw – Pw
 if Pc is positive we have a drainage process , that represent displacement of the wet phase
by the non-wet phase
 if Pc is positive we have a spontaneous imbibition process , that represent displacement
of the non-wet phase by the wet phase
 if Pc is negative we have a forced imbibition process , that represent displacement of the
wet phase by the non-wet phase

20. How to differentiate between D/SI
 We known :
Pc

21. Uses of Capillary Pressure Data
 Determine initial water saturation ( Swi ) in the reservoir .
 Determine fluid distribution in the reservoir .
 Determine residual oil saturation ( Sor ) for water flooding applications .
 Determine pore size distribution index .
 May help in identifying zones or rock types .
 Input for reservoir simulation calculations .