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:– 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

Depth

Pressure Gradient

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

• 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

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

Porosity Density Conductivity Sonic

Shale Density

Temperature gradient - Increases

Depth

Temperature

Normal Trend

Top of Geo-pressure

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

• Mud chloride change

• Increase in fill on bottom

• Increase in drag or torque

• Contaminated mud

• Temperature change

During Drilling

• 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

• 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 Drillingd-exponent and dc-exponent

During Drilling

After Drilling

• Log evaluation

• Flow tests

• BHP surveys

• Shut-in pressure tests

• Analysis of mud reports, drilling reports, and bit records