Petroleum Engineering 406
Lesson 4
Well Control
Read
• Well Control Manual
– Chapter 9
• Homework 2 Due Feb. 3, 1999
Content
• Development of Abnormal Pressure
• Properties of Normally Pressured
Formations
• Properties of Abnormally Pressured
Formations
• Casing Seat Selection
Knowledge of Pore and Fracture Pressures Leads to:
• More effective well planning
• Maximize penetration rates with balanced
drilling
• Safer and more economical selection of
casing points
• Minimize trouble due to lost circulation and
kicks
Knowledge of Pore and Fracture Pressures Leads to:
• Better engineered production and test
equipment
• Better understanding of local geology and
drilling hazards
• More accurate analysis of drilling data and
electric logs
Normally Pressured Formation
Fluids Squeezed out
with compaction
Abnormal Formation Pressures
• Due to:
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Incomplete compaction
Diagenesis
Differential Density in Dipping Formations
Fluid Migration
Tectonic Movement
Aquifers
Thermal Effects
Incomplete compaction
Fluids trapped in
place
Fluids begin to
support overburden
Diagenesis
• At 200oF to 300oF Clays undergo chemical
alteration. Montmorillonite clays dehydrate
and release some of the bound water into
the space already occupied by free water,
increasing pressure
Differential Density in Dipping Formations
Fluid Migration
Tectonic Movement - Uplifting
Tectonic Movement - Faulting
Aquifers
Thermal Effects
• Theories
– Increased temperature with depth and chemical
reactions cause increased pressures
– Increased pressures caused increased
temperatures
Salt Formations
Pressure Gradient
D
e
p
t
h
Pore press. gradient
Overburden gradient
Salt formation
Shale Properties used to Predict
Pore Pressures
• Shales are used because:
– Most pressure transition zones occur in
relatively thick shales
– Properties of clean shales are fairly
homogeneous at any depth, and can be
predicted with some degree of accuracy.
Shale Properties used to Predict
Pore Pressures
• Shales are used because:
– A deviation from the expected can be
interpreted as a change in pressure gradient
– Detecting these deviations in low permeability
shales gives an early warning prior to drilling
into pressured permeable formations, thus
avoiding kicks.
Normally Pressured Shales
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Porosity Density Conductivity Resistivity Sonic travel time Temp. gradient -
Decreases with depth
Increases with depth
Decreases with depth
Increases with depth
Decreases with depth
Relatively constant
Abnormally Pressured Shales
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Porosity Density Conductivity Resistivity Sonic travel time Temp gradient -
Higher than expected
Lower than expected
Higher than expected
Lower than expected
Higher than expected
Increases
Porosity Density
Shale Density
Conductivity Sonic
Temperature gradient - Increases
D
e
p
t
h
Normal Trend
Top of Geo-pressure
Temperature
Pore Pressure Prediction Occurs:
• Prior to drilling
• During drilling
• After drilling
Before Drilling
• Offset mud records, drilling reports, bit
records, well tests
• Geological Correlation
Before Drilling
• Open Hole Logs from
offset wells
Before Drilling
• Seismic data
During Drilling
• Kick - SIDPP and HSP in DP can give
accurate measurement of formation pore
pressure
• LOT - gives accurate measurement of
fracture pressure
During Drilling
• Correlation of penetration rate
to offset logs
• Changes in shale penetration
rate
During Drilling
• Shale density Change
– Mercury pump
– Mud balance
• Fill mud balance with clean shale until it balances at
8.33 ppg
• Fill the balance cup with water and determine total
weight
• Calculate shale bulk density:
– SBD=8.33/(16.66-Total Weight)
During Drilling
• Shale density Change - Density column
During Drilling
• Mud gas content
change
During drilling
• Shale cutting change
During Drilling
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Mud chloride change
Increase in fill on bottom
Increase in drag or torque
Contaminated mud
Temperature change
During Drilling
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Abnormal trip fill-up behavior
Periodic logging runs
Drill-stem tests
MWD or LWD tools
Paleontology
During Drilling
• dc-exponent
– P=K*(W/D)d*Ne
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P=penetration rate of shale
K=formation drillability
W=weight on bit
D=bit diameter
N=rotary speed
d=bit weight exponent
e=rotary speed exponent
During Drilling
d-exponent and dc-exponent
During Drilling
After Drilling
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Log evaluation
Flow tests
BHP surveys
Shut-in pressure tests
Analysis of mud reports, drilling reports,
and bit records