Essential Principles of Petroleum Well Drilling

Abnormally Pressured Shallow Formations

Abnormally pressured shallow formations can result from upward fluid migration due to:

• Leaky fault
• Leaky cement or casing
• Improperly abandoned underground blowout

Steps Not Included in Well Drilling

Steps in well drilling do not include: building drilling equipment.

Drilling Rig Power System Selection

To select the power system of a drilling rig, one needs to consider the weight of the drill string.

Formation Fracture vs. Pore Pressure

Is formation fracture pressure always higher than formation pore pressure? Yes.

Causes Excluded from Abnormal Pore Pressure

Causes of abnormal pore pressure do not include: drilling.

When Not to Use Oil-Based Drilling Fluids

We would not use oil-based drilling fluids to increase safety, as they can pose additional risks.

Typical Drilling Mud Type

A typical drilling mud is a Bingham plastic fluid.

Mud Viscosity During Drilling Start

When we start drilling, the viscosity of mud would decrease.

Mud Viscosity When Drilling Stops

When we stop drilling and circulating, the viscosity of mud would increase.

Fracture Pressure Gradient and Production

Fracture pressure gradient would increase with oil and gas production.

Casing String Failure Modes Excluded

Failure modes of casing string do not include: chemical corrosion.

Action for a Dry Hole

When a dry hole is drilled, one should plug and abandon the well.

Cuttings Transport in Enlarged Boreholes

In an enlarged borehole interval, cuttings transport efficiency will be lower than in normal borehole intervals.

Purpose Excluded from Directional Drilling

The purpose of directional drilling does not include: to avoid wellbore breaks and lost circulation.

Highest Collapse Requirement for Casing

The highest collapse requirement for a casing string is at the bottom of the casing.

Highest Tension Requirement for Casing

The highest tension requirement for a casing string is at the top of the casing, close to the wellhead.

Casing Collapse Strength and Tension

The collapse strength of a casing string will decrease with increasing tension.

Drag Bit Cutter Material

Cutters of drag bits can be made from diamond.

Main Types of Rotary Drilling Bits

Two main types of rotary drilling bits are drag bits and rolling cutter bits.

IADC Drill Bit Classification (647H)

A drill bit with IADC code 647H is classified as: tungsten carbide, hard, sealed friction bearing, horizontal applications.

IADC Code Breakdown

• Series: 1-3 (milled tooth), 4-8 (tungsten carbide)
• Type: 1 (softest), 4 (hardest)
• Bearing/Gage: 6 (selected friction bearing)
• Features: H (horizontal applications)

Avoiding Drill String Buckling

To avoid buckling of drill strings, an engineer should design the string and make the neutral point fall inside drill collars.

Main Types of Cementing Processes

The three main types of cementing processes are:

• Primary: Full string, liners, large pipe, stage cementing
• Squeeze: Shoe, casing (up-hole), open-hole (lost circulation)
• Plugging: Open-hole plug back, casing

Drilling Fluid for Shortest Bit Life

Which of the following drilling fluids provides the shortest bit life for the same bit? Salt mud.

Functions of Drilling Fluids

Functions of drilling fluids include:

• Cool and lubricate the bit
• Remove cuttings
• Prevent caving of formation

Types of Drilling Fluids

Types of drilling fluids include:

• Water-based
• Oil-based (used to minimize damage, enhance borehole stability)
• Air mists and foams (used for damage control, stability, ROP, contamination)

Drilling Weight and Weight on Bit

Drilling weight will usually increase with increasing weight on bit.

When a Kick Occurs

A kick occurs when pore pressure (P_pore) > mud pressure (P_mud).

Drilling Rate and Rotary Speed

Drilling rate will usually increase with increasing rotary speed if borehole cleaning is satisfactory.

When Lost Circulation Occurs

Lost circulation occurs when pore pressure (P_pore) < fracture pressure (P_frac).

Drilling Rate and Depth

Drilling rate will usually decrease with increased depth.

Mud Viscosity When Drilling Stops (Bingham Plastic)

When we stop drilling and circulating, the viscosity of a typical drilling mud (Bingham plastic fluid) would increase.

Causes of Lost Circulation

Causes of lost circulation include:

• High mud weight
• Formation fracture/fault
• Higher permeability formation

Purpose of Surface Casing

One of the purposes of running a surface casing is to protect the aquifer.

Pressure During Drill String Tripping

When tripping the drill string, does pressure decrease?

Porosity in Normally Pressured Formations

In normally pressured formations, porosity would decrease with depth.

Drilling in Mature Fields

In drilling a mature field, one should use low density drilling fluid to avoid formation fracturing.

Fracture Pressure vs. Pore Pressure

Is fracture pressure greater than pore pressure? Yes.

Functions of Casing

Functions of casing include:

• Stabilize the borehole
• Protect the aquifer
• Control production
• Install production equipment
• Enable further drilling