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?