Reservoir Drive Mechanism

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Advanced Reservoir Engineering
Reservoir Drive Mechanism Material balance
equation
Instructor Dr. B. Rostami E-mail
Rostami.ipe_at_gmail.com Web page www.brostami.com
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Primary Recovery Mechanisms
The recovery of oil by any of the natural drive
mechanisms is called primary recovery.
There are basically six driving mechanisms that
provide the natural energy necessary for oil
recovery (1) rock and liquid expansion
drive (2) depletion drive (3) gas cap
drive (4) water drive (5) gravity drainage
drive (6) combination drive.
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Primary Recovery Mechanisms
Rock and liquid expansion drive
It happens in under saturated oil reservoir
As the expansion of the fluids and reduction in
the pore volume occur with decreasing reservoir
pressure, the crude oil and water will be forced
out of the pore space to the wellbore.
Because liquids and rocks are only slightly
compressible, the reservoir will experience a
rapid pressure decline.
Topic for term project Geomechanical rule in
reservoir simulation? Does it rock expansion or
compaction?
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Primary Recovery Mechanisms
Depletion drive mechanism
? solution gas drive ? dissolved gas drive ?
internal gas drive.
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Primary Recovery Mechanisms
Depletion Drive
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Primary Recovery Mechanisms
Gas Cap Drive
(1) expansion of the gas cap gas, and (2)
expansion of the solution gas as it is liberated.
Reservoir pressure
Water production
Gasoil ratio
Ultimate oil recovery
20 to 40
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Primary Recovery Mechanisms
Gas Cap Drive
Size of the original gas cap
Vertical permeability
Oil viscosity
Degree of conservation of the gas
Oil production rate
Dip angle
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Primary Recovery Mechanisms
Gas Cap Drive
Comparison Gas cap drive reservoirs tend to flow
longer than depletion drive reservoirs
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Primary Recovery Mechanisms
Water Drive Mechanism
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Primary Recovery Mechanisms
Water Drive Mechanism
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Primary Recovery Mechanisms
Water Drive Mechanism
If the reservoir has one or more lenses of very
high permeability, it may be economically
feasible to perform remedial operations to shut
off this permeable zone producing water.
As the reservoir heterogeneity increases, the
recovery will decrease, due to the uneven advance
of the displacing water.
In a very active water drive where the degree of
pressure maintenance is good, the role of
solution gas in the recovery process is reduced
to almost zero, In the case of water derive gas
reservoirs the recovery efficiencies reduced in
compare to depletion drive gas reservoirs,
because of the bypassed gas.
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Primary Recovery Mechanisms
Reservoir heterogeneity
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Primary Recovery Mechanisms
Gravity Drainage Drive
As a result of differences in densities of the
reservoir fluids
In order to take maximum advantage of the gravity
drainage producing mechanism, wells should be
located as low as structurally possible.
For the reservoir to be operating solely as a
result of gravity drainage, the reservoir would
show a rapid pressure decline.
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Primary Recovery Mechanisms
Gravity Drainage Drive

• Low gasoil ratios from structurally located low
  wells. This is caused by migration of the evolved
  gas up-structure due to gravitational segregation
  of the fluids.

• The gravity drainage mechanism does not become
  operative until the reservoir pressure has
  declined below the saturation pressure,

• If the liberated solution gas is allowed to flow
  upstructure instead of toward the wellbore, then
  high oil saturation in the vicinity of the
  wellbore can be maintained.

• Wells should be located as low as structurally
  possible.

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Primary Recovery Mechanisms
Gravity Drainage Drive
There are five factors that affect ultimate
recovery from gravity drainage reservoirs
(1) Permeability in the direction of dip
(2) Dip of the reservoir
(3) Reservoir producing rates
(4) Oil viscosity
(5) Relative permeability characteristics
Topic for term project When does the gravity
drainage happen and how it works? What are the
important affecting parameters?
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Primary Recovery Mechanisms
Combination drive mechanism
Two combinations of driving forces are usually
present in combination drive reservoirs (1)
depletion drive and a weak water drive, or (2)
depletion drive with a small gas cap and a weak
water drive.
Ultimate recovery from combination drive
reservoirs is usually greater than recovery from
depletion drive reservoirs but less than recovery
from water drive or gas cap drive reservoirs. Why?
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Primary Recovery Mechanisms
Combination drive mechanism
These types of reservoirs usually experience a
relatively rapid pressure decline.
The gas cap will shrink due to production of
excess free gas, in which case the structurally
high wells will exhibit a decreasing gasoil
ratio. Large volumes of oil can be lost as a
result of a shrinking gas cap.
In most combination drive reservoirs it will be
economically feasible to institute some type of
pressure maintenance operation, either gas
injection or water injection, or both gas and
water injection, depending upon the availability
of the fluids.
Topic for term project Gas injection or gas
re-cycling in a saturated oil reservoir to avoid
gas cap shrinkage
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Primary Recovery Mechanisms
Combination drive mechanism
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Primary Recovery Mechanisms
Example of simulation term project
Base case modeling Recovery mechanisms
quantification Sensitivity analysis Production
report
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Primary Recovery Mechanisms
Example of simulation term project
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Primary Recovery Mechanisms
Example of simulation term project
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Material balance Equations
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Material Balance Equations
The MBE, when properly applied, can be used
to ? estimate initial hydrocarbon volumes in
place ? predict reservoir pressure ? calculate
water influx ? predict future reservoir
performance ? predict ultimate hydrocarbon
recovery under various types of primary drive
mechanisms.
Initial volume volume remaining volume removed
Three different forms of the MBE are (1)
generalized MBE (2) MBE as an equation of a
straight line (3) Tracys form of the MBE.
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Material Balance Equations
Basic Assumptions in the MBE
Constant temperature
Reservoir characteristics
uniform porosity, permeability, and thickness
characteristics, the shifting in the gasoil
contact or oilwater contact is uniform
Fluid recovery
is independent of the rate, number of wells, or
location of the wells.
Pressure equilibrium
All parts of the reservoir have the same pressure
and fluid properties are therefore constant
throughout.
Constant reservoir volume
Assumed to be constant except for rock and water
expansion or water influx that are specifically
considered in the equation.
Reliable production data
All production data should be recorded at the
same time period.
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Material Balance Equations
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Material Balance Equations
The total initial volume of the hydrocarbon system
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Material Balance Equations
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Material Balance Equations
There is no water or gas injection
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Material Balance Equations
Increasing Primary Recovery
Improving oil recovery during primary production
as ? well control procedures, and ? reservoir
control procedures, e.g., pressure maintenance.
Well control
Acidizing, paraffin control, sand control,
clean-out, and other means actually increase
ultimate production from that well. If the
production of gas and water from an oil reservoir
can be minimized, a larger ultimate production
may be obtained.
Excessive drawdown in a solution gas drive
reservoir through excessive producing rates
often causes excessive deposition of paraffin in
the tubing and reservoir. Keeping gas in
solution in the oil by keeping the well pressure
as high as possible minimizes the paraffin
deposition.
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Material Balance Equations
Increasing Primary Recovery
Well control
Many unconsolidated formations tend to flow sand
through perforations and into the producing
system when flow rates are excessive. It maybe
possible to improve this situation with screens,
gravel packing, or consolidating materials.
The proper positioning of wells in a reservoir
also plays a big part in the control of gas and
water production.
The proper well spacing needs to use in a
particular reservoir. Recognition is given to
the pressure distribution that will prevail in
the drainage area of a well when the economic
limit is reached.
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Material Balance Equations
Increasing Primary Recovery
Total reservoir control
If produced water or produced gas can be injected
without adversely affecting the amount of water
or gas produced, the amount of oil produced at a
particular reservoir pressure can be increased.
It is well known that the most efficient natural
reservoir drive is water encroachment. The next
most efficient is gas cap expansion, and the
least efficient is solution gas drive.
When two or more drives operate in a reservoir,
it is not always clear how much production
results from each drive. One convenient method
of estimating the amount of production resulting
from each drive is to use material balance drive
indices.
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Material Balance Equations
Reservoir driving indices
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Material Balance Equations
Reservoir driving indices
Note that for a depletion drive reservoir under
pressure maintenance operations by gas injection
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Material Balance Equations
Reservoir driving indices
At point A some of the structurally low wells are
reworked to reduce water production
At point B work over operations are complete,
producing rates are relatively stable
At point C some of the wells producing relatively
large, volumes of water are shut in
At point D gas is being returned to the
reservoir, and the gas cap drive index increases