Petroleum Engineering 406

1
Petroleum Engineering 406

• Lesson 4
• Well Control

2
Read

• Well Control Manual
• Chapter 9
• Homework 2 Due Feb. 3, 1999

3
Content

• Development of Abnormal Pressure
• Properties of Normally Pressured Formations
• Properties of Abnormally Pressured Formations
• Casing Seat Selection

4
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

5
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

6
Normally Pressured Formation
Fluids Squeezed out with compaction
7
Abnormal Formation Pressures

• Due to
• Incomplete compaction
• Diagenesis
• Differential Density in Dipping Formations
• Fluid Migration
• Tectonic Movement
• Aquifers
• Thermal Effects

8
Incomplete compaction
Fluids trapped in place
Fluids begin to support overburden
9
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

10
Differential Density in Dipping Formations
11
Fluid Migration
12
Tectonic Movement - Uplifting
13
Tectonic Movement - Faulting
14
Aquifers
15
Thermal Effects

• Theories
• Increased temperature with depth and chemical
  reactions cause increased pressures
• Increased pressures caused increased temperatures

16
Salt Formations
Pressure Gradient
Depth
Pore press. gradient Overburden gradient
Salt formation
17
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.

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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.

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Normally Pressured Shales

• Porosity - Decreases with depth
• Density - Increases with depth
• Conductivity - Decreases with depth
• Resistivity - Increases with depth
• Sonic travel time - Decreases with depth
• Temp. gradient - Relatively constant

20
Abnormally Pressured Shales

• Porosity - Higher than expected
• Density - Lower than expected
• Conductivity - Higher than expected
• Resistivity - Lower than expected
• Sonic travel time - Higher than expected
• Temp gradient - Increases

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Porosity Density Conductivity Sonic
Shale Density
22
Temperature gradient - Increases
Depth
Normal Trend
Top of Geo-pressure
Temperature
23
Pore Pressure Prediction Occurs

• Prior to drilling
• During drilling
• After drilling

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Before Drilling

• Offset mud records, drilling reports, bit
  records, well tests
• Geological Correlation

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Before Drilling

• Open Hole Logs from offset wells

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Before Drilling

• Seismic data

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During Drilling

• Kick - SIDPP and HSP in DP can give accurate
  measurement of formation pore pressure
• LOT - gives accurate measurement of fracture
  pressure

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During Drilling

• Correlation of penetration rate to offset logs

• Changes in shale penetration rate

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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
• SBD8.33/(16.66-Total Weight)

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During Drilling

• Shale density Change - Density column

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During Drilling

• Mud gas content change

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During drilling

• Shale cutting change

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During Drilling

• Mud chloride change
• Increase in fill on bottom
• Increase in drag or torque
• Contaminated mud
• Temperature change

34
During Drilling

• Abnormal trip fill-up behavior
• Periodic logging runs
• Drill-stem tests
• MWD or LWD tools
• Paleontology

35
During Drilling

• dc-exponent
• PK(W/D)dNe
• Ppenetration rate of shale
• Kformation drillability
• Wweight on bit
• Dbit diameter
• Nrotary speed
• dbit weight exponent
• erotary speed exponent

36
During Drilling
d-exponent and dc-exponent
37
During Drilling
38
After Drilling

• Log evaluation
• Flow tests
• BHP surveys
• Shut-in pressure tests
• Analysis of mud reports, drilling reports, and
  bit records