GEOLOGI MINYAK & GAS BUMI

Saturation

Wettability &

Capillary Pressure EBS 2014

UNDIP e-Library Procedures

References stored at the Geo Computing Lab (Ground Floor) in the PC-6 Hard Disk – as shared files

Log-in to PC-6 and get to: Libraries/My Document/for undip use only

If PC-6 occupied then Log-in to other PC and look at Network/komputer6/for undip use only

Further Readings

Glover, P.W.J., “Introduction to Petrophysics and

Formation Evaluation”, Département de Géologie et de

Géologique Université Laval – CANADA; an MSc Course

Notes. Chapter 4

Doddy Abdasah, “Basic Reservoir Enginering”, ITB,

Chapter 2

Adams, S.J. and R.J. van den Oord, 1993, “Capillary

Pressure and Saturation – Height Functions”, Shell Internal

Document, Chapter 2

Mayer-Gürr, A., 1976, “Petroleum Engineering” , pp 33 - 46

Satter, A . et al, 2008, “Practical Enhanced Reservoir

Engineering” pp 47 - 62

Important Quote to Remember

HC Trapping

Basic concepts of accumulation / trapping

Pore space initially filled 100% with water

Hydrocarbon migrate up dip into traps

Hydrocarbons distributed by capillary pressure

and gravity different (buoyancy force)

Connate water saturation remains in the

hydrocarbon zones (Irreducible Water Saturation

- Swi)

Video – Migrating and Trapping

Oil n Gas Traps

Petroleum Reservoir

HC migrated into reservoir until an impermeable rock (“seal”) stopped the migration

Fluid Saturations

Basic concepts of accumulation

Pore space initially filled 100% with water

Hydrocarbon migrate up dip into traps

Hydrocarbons distributed by capillary pressure and gravity

Connate water saturation remains in the hydrocarbon zones (Irreducible Water Saturation - Swi)

Oil and gas migrates into reservoir – Water Saturation (Sw) decreasing

Oil Saturation (So) increasing

Gas Saturation (Sg) increasing

Sw + So + Sg = 100%

Fluid Saturations

Amount of oil per unit volume = ø (1 – Sw) = ø So

Note: Matrix = solids

Wettability

Relative adhesion of two fluids to a solid surface

In porous medium containing two or more immiscible fluids, wettability is a measure of the preferential tendency of one of the fluids to wet, spread or adhere to the surface

In a water-wet brine-oil-rock system, water will occupy the smaller pores and wet the major portion of the surfaces in the larger pores

In areas of high oil saturation, the oil rests on a film of water spread over the grain surface

Contact Angle; small angle = wet

• Fluid A attracted to the solid molecules more than Fluid B =

Fluid A is wetting

• Fluid A displaces most of Fluid B from the surface

• Not all of Fluid B removed from the surface

Wettability in Reservoir

Water / Oil System – Water is often the

wetting fluid

Water / Gas System – Water is always the

wetting fluid

Oil / Gas System – Oil is the wetting fluid

Contact Angle and Capillary Pressure

h

• Water / Gas system – Water is the wetting fluid

• Water inside the tube raised due to capillary pressure

• h is a function of R (size of the tube)

Gas

Water

Smaller tube – higher Pcap

Cap Pressure spontaneously draws fluid into the tube

Gas / Water System

• Tube filled with gas

• Water (wetting) is introduced at other end of the tube

• Capillary pressure will spontaneously draw the water

Capillary Pressure Implications in Nature

In the source rock – when oil and gas are formed

from kerogen, water will push the oil and gas

mixtures out of the micropores to migrate out of the

source rock (Primary Migration)

Gas reservoir with water drive – water easily

encroach to the well bore (water coning)

Oil migrated into reservoir – forced by buoyancy

Buoyancy generates pressure (displacement pressure)

against the capillary pressure

Macropores – more oil

Micropores – less oil

When HC migrating into

reservoir:

• HC can easily enter

larger pore size

(macropores)

• HC can not enter

smaller pore size due to

capillary pressure

restriction

Cap Pressure Data from Lab

• Applying small pressure

– Sw remains 100%

• Sw starts to decrease at

a certain entry pressure

(displacement pressure)

• Sw continue to

decrease progressively

at higher cap pressure

• At a certain point with

increasing pressure –

Sw reach a plateau

(Swi – Irreducible Water

Saturation)

Displacement pressure

Swi

Reservoir Heterogenity

Capillary Pressure Effect Seen from Logs

Water

Zone

Transition

Zone

Swirr

Zone

Drainage and Imbibition

•“Drainage” is the

displacement of the wetting

fluid (water) by a non-

wetting fluid (oil)

• Notice that water

saturation never goes to

zero

• “Imbibition” is the

displacement of non-

wetting fluid by a wetting

fluid

•Notice that oil saturation

never goes to zero

Implication of Drainage and Imbibition

HC Trapping:

There is always small percentages of water in

the pore spaces regardless of displacement

pressure (HC Column Height)

HC Production:

After production there is always oil/gas remaining

in the pore spaces regardless of production

methods applied

The Role of Rock Texture

Swi

Low

High

Rock heterogeneity makes OWC does

not seem to be flat

Video – Summary of this Lesson

Any Questions or Comments?