New Strategies for Designing the Horizontal Well Profiles

There are three

sections, namely:

1.   Vertical section: It is drilled from sea bed (mud  line) until KOP (the point  where deviating or sidetracking begins).  

2-Turned (Curved or angle-build) section: It is drilled from KOP to the end-of-curve (EOC). This section includes the first-build arc, the straight tangent, the second-build arc.

3. Horizontal section: It is drilled from the end of second-build arc or the end-of-curve (EOC) to the end of the proposed distance to be drilled horizontally in the pay zone, in accordance with the type of the horizontal well to be drilled.

The design of horizontal well based on three method:-

1-The simple tangent build curve method:-

The three major sections that form a horizontal well may be designed as follows:-

1-The build-radius of the first-build arc:

R=5730/B

2-Height of the first-build arc:

  D1=R(sin I2-sin I1)

3-Height of the straight-tangent:

       D2 = L2 Cos I2

4-Height of the second-build arc:

D3=R( Sin I3 - Sin I2).

5-The length of the first section of horizontal well = KOP

KOP = TVD – D1 - D2 - D3

6-The displacement of the first-build arc:

H1 = R ( Cos I1 - Cos I2)

7-The displacement of the straight-tangent:

H2 = L2 - Sin I2

8-The displacement of the second -build arc:

H3= R( Cos I2 - Cos I3)

9-The length of the first-build arc:

L1 =100(I2 - I1 )/B

10-The length of the second-build arc:

L3=100(I3 – I2)/B

11-The measured depth at the end of the first-build arc:

MD1 = KOP + L1

  12-The measured depth at the end of the straight tangent:

MD2 = MD 1+ L2

  13-The measured depth at the end of the second build arc:

MD3 =MD2 + L3

*The length of the second section =

L1 + L2 + L3 = MD3 - KOP

 

2-circular arc method:-

  It is a special design is based where,

R=H=TVDTEP-TVDKOP

   Thus. BUR may be determined as   follows:

BUR=5730/R

  =5730/(TVDTEP-TVDKOP )

Circular arcs are usually drilled only in areas where target entry point (TEP) and directional performance are well known

EX:-the Austin Chalk-amorphous limestone

3-Compound build curve method:-

This method have more than one planned build up rate and one or more tangent sections  where, different build up rates will be designed for the upper and lower sections.

EX:-a 4°/100 ft build rate may be used in the
upper section followed by a 8°/100 ft build up rate below the tangent section.

 

Accordingly, the recent advance for selection of the appropriate well profile is a function of the following,

1-Vertical depth of KOP and target selection. This KOP is selected based on hole problems, casing set depths, BHA performance, ROP, . . . etc.

2-Horizontal displacement to target entry point (TEP).

3-Completion design.

4-Formation evaluation program.

5-Hole size in the reservoir.

Thus, the optimum KOP should be selected based upon the following:

1-Minimizing hole problems.

2-Minimizing the amount of hole open during directional drilling operations.

3-The planned casing set depths.

4-The performance  of directional  drilling  assemblies  within  various formations.

5-The expected drilling rate within the various formations.

—

After selecting the optimum KOP, the vertical depth to the target can be determined as mentioned before. This will determine the build radius options available. These options should be refined by considering horizontal displacement to the target entry point (TEP). If the planned profile is compatible with the completion, evaluation program, and desired hole size, the profile selection is complete. If a parameter is not compatible, a design parameter must be altered or compromised, as shown in Table

 

read more "New Strategies for Designing the Horizontal Well Profiles"

Horizontal Drilling Problems

WOB (Weight On Bit)

Conventional bit weight for efficient drilling is about 2000-5000 lbf per inch of bit diameter.

Motor assemblies are more efficient with bit weight less than rotary assemblies.

Bit weight may be increased by reducing drag and torque and by using the split assembly .

 

  

 

Torque and Drag

 

• Drag is a force restricting the movement of the drill tools
  in directions parallel to the well path.
• Torque is the force resisting rotation movement.
• Excess drag and torque cause directional-drilling problems especially in turning and horizontal sections in horizontal well.
• Reducing drill string weight reduces drag and torque at high quality of mud with good chemical and physical properties that are essential.
• Oil base mud should be considered for more demanding situation because its good lubricating qualities.

Hole Cleaning

• A particular problem that arises in drilling horizontal wells is the difficulty of the removing the rock cuttings from the horizontal section of the well.
• The source of the problem is that cuttings tend to settle in the bottom of the hole and allow mud to pass above without transporting them.
• High fluid velocities and polymer muds are commonly used for efficient hole cleaning and minimizing formation damage.
• Also, these can be good reason to use oil-based muds to control shale swelling.

Water Sensitive Shale

• • Shale layers frequently tend to collapse in contact with fresh water This can be prevented by using oil-based drilling fluids.
  • These fluids usually consist of an advent emulsions of water in diesel oil together with other additives.
  • Fluids of this type have been used in the North Sea.
  • Water-based muds can be inhibited to reduce the attack in water-sensitive shales by the addition of NaCl or CaCl2.
  • These additives reduce the chemical activity of the water and its tendency to penetrate into the water-sensitive shale.
  • Inhibited water-based muds are not as effective as oil-based muds for the protection of shales, but they are cheaper and less damaging environmentally.

Directional Control

• Overcoming the force of gravity is a fundamental problem in directional and horizontal drilling.

• BHA includes bits,motor,non-magnetic drill collar and MWD tool

• BHA section controls the hole trajectory but does not contribute to WOB.

• This section should be  kept as lightweight as possible to minimize torque and drag. 

read more "Horizontal Drilling Problems"

Horizontal well completion

the completion that can be run through a given radius of curvature will depend on

1.the radial clearance between the completion item and hole(liner size),

2. the length and flexibility of the completion,

3.the rating of the connection

 

Horizontal well Completion Options

 

1.Open hole 25%

2.Slotted Liner 55%

3.Liner with Partial Isolations  15%

4.Cemented and Perforated Liners 5%

 

 Open hole 25%

1.This type of completion is the simplest and cheapest typed used in consolidated & competent reservoir Rock with almost no sand production.

2.It is represented 25% from total or all completions worldwide

 

  Slotted Liner 55%

1.It is used with or without a screen

2.It is used when the reservoir is unconsolidated or loosely consolidated sands.

3.It is formed 55% from all completions worldwide and it is considered as a prevailing well completion type.

4.its main purpose

—to guard against hole collapse

—to provides a convenient path to insert various tools such as coiled tubing in a horizontal well

●

  Liner with Partial Isolations  15%

—Slotted liner in open hole with blank sections and External Casing Packer (ECP).

—This is 15% of total completions worldwide.

—

  Cemented and Perforated Liners 5%

—It is expensive and used in long-radius horizontal sections or for medium-radius horizontal sections. It is formed only 5% of all completions worldwide.

—Problems like difficulty of cement job or leakage of cement sheath may arise in this type

 

read more "Horizontal well completion"

Horizontal Wells (why and advantages)

 

read more "Horizontal Wells (why and advantages)"

Horizontal drilling methods(Reason and methods )

The choice of drilling method depends upon:

— Cost,

—Well spacing and

—Mechanical conditions of a vertical well bore

—In addition, reservoir consideration.

—

 BUILD RATES

—Ultra-short Radius

—Short Radius

—Medium Radius

—Long Radius

 ULTRA-SHORT RADIUS

—45 to 90 degrees per foot

—Special equipment

—Horizontal lengths of 100’ to 200’

—Used in unconsolidated, heavy oil sands and soft formation.

—Impossible to log the open hole section.

 

—An ultra-short radius drain hole is drilled using endless 1¼ inch tubing.

—Uses a jet under high pressure to cut the formation and advance the endless tubing.

— twenty-four laterals can be drilled at the same horizon.  

SHORT RADIUS

—1.5 to 3 degrees per foot.

—Needs special equipment

—Mechanical and motor systems are available.

—Typically used in sidetracking existing wells to bypass water producing or troublesome.

—Bending stress and fatigue can be a problem

—200’ to 1000’ horizontal section

—The horizontal section can be cased with a slotted liner or left open hole. 

—Open hole logging capabilities are limited for the horizontal section.

 

MEDIUM RADIUS

— The first medium radius wells were drilled in 1985

—6 to 35 degrees per 100’ build rates

—Uses conventional equipment

—Horizontal section lengths have been drilled over 7000’ but typically 2000’ to 4000’

LONG RADIUS

—2 to 6 degrees per 100’ build rates

—Uses conventional equipment

—Horizontal section lengths have been drilled over 10,000’ but typically 3000’ to 5000’

—No problem with bending stress, fatigue or completion equipment

—Build section is steerable, which means the motor can be rotated in the build section

—Offshore uses long radius almost exclusively since longer departures are required before the well gets to be horizontal

—Wells are more easily logged.

    

read more "Horizontal drilling methods(Reason and methods )"