Introduction to Petroleum Engineering

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Introduction to Petroleum Engineering

• Technishe Universiteit Eindhoven
• from 3nd April to 5th May
• College 4W100
• room MA-1.50
• Lectures tue/wen/thu 1330-1515

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Week 15
3 - The oil and gas reservoirs structures and
origin This lecture will introduce few basic
elements of petroleum geology as formation of oil
gas accumulations and their structures.
5 - Petroleum engineering economics This lecture
will highlight the economics of petroleum
projects. Overviews of drilling, production and
exploration costs will be given.
6 - Properties and PVT behaviour of hydrocarbon
mixtures The most important point in describing
the flow of oil and gas is the volumetric
behaviour and the more complex aspect of
vapour-liquid equilibrium.
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Week 17
7 - Driving mechanisms and production
forecasting One of the most important basic point
in correct understanding of the reservoir or well
production capability is the identification of
driving mechanisms.
8 - The production system surface facilities,
wells and reservoir This lectures aims to
introduce the structure of the oil gas upstream
industry with the peculiar objective to describe
the production system and its elements as well as
their complex interaction.
9 - The reservoir engineering and the connection
to the production engineering The high level of
complexity characterising the oil gas
reservoirs requires a specialised figure, the
reservoir engineer, that is called to manage the
reservoir in terms of flow and produced volumes
of oil gas.
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The production system surface facilities, wells
and reservoir- Driving mechanisms and
production forecasting
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Production system
Surface equipment
Well
Reservoir
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Petroleum recovery
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Recovery factor

• The recovery factor is defined as
• is formed by two components

Volumetric efficiency
Pore scale efficiency
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Volumetric efficiency

• The volumetric efficiency could be expressed as,
• where
• Ei is the vertical efficiency, it depends on
  vertical heterogeneities of the reservoir and
  from the mobility ratio
• Ea is the areal efficiency, it depends on
  geometric distribution of wells and from the
  mobility ratio

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Volumetric efficency
Ea
Chierici p. 139
Oil water
Oil water
water
Ei
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Pore scale efficiency

• The pore scale efficiency depends on the
  displacement process in the porous medium,
• knowing fw dependencies, the Ed dipends mainly on
  the mobility ratio

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Primary process

• Different producing process could act in a
  reservoir
• fluid expansion
• gas expansion
• liquid expansion
• free gas expansion
• gascap expansion
• porous volume changes
• connate water expansion
• reduction of porous volume
• water influx

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Production mechanisms

• The following production mechanisms could be
  identified
• solution gas drive
• gascap drive
• natural water drive
• compaction drive

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Solution gas drive
Recovery 2-10
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Gascap drive
Recovery 5-15
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Water drive
Recovery 5-35
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Comparison between production drives
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Production forecasting

• The production forecasting is a powerful tool in
  making decisions that must be linked to economics
• to forecast the production from a reservoir two
  ways could be followed
• material balance, an overall approach
• flow simulation, a detailed description
• more detailed simulations need more information
• in early stages material balance is used, is easy
  and fast
• when the needed information is available flow
  simulation is prefered to have also a confirm of
  acting phenomena

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Material balance equation

• The equation allows to evaluate the material
  balance after a reduction in pressure Dp in a
  reservoir with an initial volume of hydrocarbons
  N in SC
• the material balance could be expressed as,

Oil production
Oil expansion
Solution gas expansion
Gascap expansion
Reduction of porous volume
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Oil and dissolved gas expansion

• The volume change due to liquid expansion is,
• The dissolved gas expansion is,
• Summing the two terms we obtain the expansion of
  the oil initially in place

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Gascap expansion

• The total volume of gascap in standard condition
  is
• at the pressure p the volume in reservoir will be
• the expansion will be

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Change in pore volume

• The reduction of pore volume for hydrocarbon is,
• it can be expressed versus the pressure reduction
  ?p,

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Change in pore volume

• The final expression is,
• this balance term is usually neglected due to the
  low compressibility of water and rocks,
• Co 15x10-6 psi-1
• Cw 3x10-6 psi-1
• Co500x10-6 psi-1

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Reservoir Production

• The volume of produced oil in reservoir is equal
  to the sum of the produced oil at SC, Np, and the
  associated gas
• The production into the reservoir can be written
  as,
• where Rp is the production Gas-Oil Ratio

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General balance equation
Oil expansion
Solution gas expansion
Oil production
Reduction of porous volume
Gascap expansion
Water influx
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Istantaneous GOR equation

• As istantaneous Gas-Oil Ratio is defined,
• the gas production can be the results of free gas
  as well as of solution gas production. The two
  components can be written as,

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Istantaneous GOR equation

• From those definitions the following expression
  for GOR can be obtained,
• The gas and oil flowrate can be expressed by
  Darcy equation in radial flow form

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Istantaneous GOR equation

• Substituing the following equation for the
  istantaneous GOR is obtained,

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(No Transcript)
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Saturation equation
Gas cap expansion
Water influx
Gas cap expansion
Water influx
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How to use volumetric balance equations ?
Material balance eq.
Solution gas reservoir
Saturation eq.
Istantaneous GOR eq.
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Tarner Method (1944)
Produced Gas - from material balance eq.
Produced Gas - from istantaneous GOR eq.
Attention!
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Tarner Method
Choose a value for recovery factor
Calculate the produced gas from material balance
eq.
New value of recovery factor
Gp(MB) Gp(GOR)
Calculate the istantaneous GOR
Calculate the produced gas from istantaneous GOR
eq.
yes
End
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Solution from Tarner method
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Depletion drive reservoir
Fonte Cole, Reservoir Engineering Manual, 1969

• Depth 6500 ft
• Initial Pressure 2925 psia
• Bubble Pressure 2100 psia
• Reservoir Temperature 175 F
• Swi 15
• STOIIP 100,000,000 STB

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Oil Properties
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Summary of calculation results
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Recovery Factor,Reservoir Pressure and GOR
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Reservoir Performance time

• To link reservoir performance with the time a
  well defined production policy is needed,
• The link could be realized via the Productivity
  Index (PI o J) defined as,
• the Productivity Index can be related to
  reservoir characteristics by means of Darcy
  equation

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Production policy

• maximum daily flowrate 15,000 STB/d
• producing wells 60
• single well productivity index 0.75 Bbl/d/psi
• minimum bottomhole pressure 1500 psia
• reservoir productivity index
• 60 x 0.75 45 Bbl/d/psi

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Production flowrate procedure
Calculate maximum possible flowrate from PI
Reduce BHP
qmax gt qall.
BHP lt Pres
yes
Flowrate equal to qall.
yes
Flowrate equal to qmax
Next step
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Pressure production vs. time
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Secondary processes and pressure maintenance

• It consists in giving energy to the reservoir
  injecting non miscible fluids
• this process is also known as reservoir pressure
  maintenance
• objective is attain a better recovery increasing
  the volumetic displacement efficiency
• those processes are commonly known as

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Petroleum recovery II
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Factors influencing the secondary recovery

• Mobility ratio
• inclination of reservoir
• heterogeneities in the reservoir
• geometry continuity of reservoir
• production flowrates
• position configuration of wells

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Reservoir pressure vs. recovery factor
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Production pressure vs. time
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EOR and Improved recovery processes

• Objective of improved revoery is to increase the
  recovery factor over natural limits
• the processes act improving the volumetric
  displacement efficency as well as the pore scale
  displacement efficiency
• they are classified on the basis of their
  chemical physical interaction mechanisms among
  injected fluids, hydrocarbons and reservoir rocks

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Petroleum recovery III
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Vapour injection
Archer p. 205
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Huffpuff - alternate vapour injection
Archer p. 205
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In-situ combustion
Archer p.206
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Miscible gas displacement
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Polimers displacement