Directional Drilling(2)

Directional Drilling

Elaborated by:BOUBAKRI Mohamed Amine

REMILI Mohamed Anouar

BOUAZIZ Houda

DHOUIBI Amir

Plan:

1) Introduction

2) Applications of directional wells

3) Types of directional wells

4) Kickoff Methods

5) Survey Methods

Definition of Directional Drilling

Directional drilling can generally be

defined as the science of directing a

wellbore along a predetermined trajectory to

intersect a designated subsurface

target.

History

While the use of directional (or horizontal) drilling technology has increased dramatically since the mid-1980's, the technology itself dates back to 1891, when the first patent was granted for equipment to place a horizontal hole from a vertical well.

In 1929, the first truly horizontal wells were drilled at Texon, Texas and many horizontal wells were drilled in the USSR and China during the 1950's and 1960's, with limited success.

Weakening of oil prices, coupled with the need to reduce finding costs and the development of new downhole devices, resurrected horizontal drilling technology in the late 1970's and early 1980's.

Applications of directional wells:

The most common application of directional drilling techniques is in offshore drilling. Many oil and gas deposits are situated well beyond the reach of land based rigs. Drilling a large number of vertical wells from individual platforms is both impractical and uneconomical.

Source: Drilling Engineering Baker Hughes Workbook

Directional wells are often drilled because the surface location directly above the reservoir is inaccessible, either because of natural or man-made obstacles.


Sidetracking out of an existing wellbore is another application of

directional drilling. This is done to bypass an obstruction (“fish”) in the original wellbore, to explore the extent of a producing zone in a certain sector of a field, or to sidetrack a dry hole to a more promising target.


Directional techniques are used to drill relief wells in order to “kill” blowouts.


Directional wells are also drilled to avoid drilling a vertical well through a steeply inclined fault plane which could slip and shear the casing.


Directional drilling programs are sometimes used to overcome the problems of drilling near salt domes. Instead of drilling through the salt, the well is drilled at one side of the dome and is then deviated around and underneath the overhanging cap.



In the case where a reservoir lies offshore but quite close to land, the most economical way to exploit the reservoir may be to drill directional wells from a land rig on the coast.

Types of directional wells

Applications:

-Deep wells with large horizontal displacements

- Moderately deep wells with moderate horizontal displacement, where intermediate casingis not required

Applications:

- Multiple pay zones - Reduces final angle in reservoir - Lease or target limitations - Well spacing requirements- Deep wells with small horizontal displacements

Disadvantages:

- Logging problems due to inclination- Risk of keyseating- Increased torque & drag

Applications:

- Appraisal wells to assess the extent of a newly discovered reservoir- Repositioning of the bottom part of the hole or re-drilling- Salt dome drilling

Disadvantages:

- Formations are harder so the initial deflection may be more difficult to achieve- Harder to achieve desired tool face orientation with downhole motor deflection assemblies(more reactive torque)- Longer trip time for any BHA changes required

Kickoff Methods

• Whipstock

• Downhole motor and bent sub assembly

• jetting

Whipstock

Advantages :

this operation usually takes less time.

Disadvantages

- a sharp dogleg (The degree of curvature) - the casing whipstock assembly is not recommended if there is a considerable distance to drill below the sidetrack. This is because problems can occur when trying to pull stabilizers back into the casing through the window.

In recent years, improvements in the design of the system have eliminatedthe need for so many trips in and out of the hole

Downhole motor and Bent Sub assembly

Advantages:

- A downhole motor and bent sub combination will drill a smooth,continuous curve, which makes dogleg severity more predictable than with other deflection tools. -They can be used in most formations. In addition, since there is no rotation from the surface. - It is possible to use a wireline “steering tool” for surveying and orientation while drilling. - Alternatively, a MWD system can be utilized.

Disadvantages:

- that reactive torque changes the tool face when drilling commences, which may also make it difficult to keep a steady tool face. - Also the motors are expensive and require maintenance.

Jetting (or badgering) is a technique used to deviate wellbores in softformations. The technique was developed in the mid 1950s and supersededthe use of whipstocks as the primary deflection technique.

Advantages of Jetting• It is a simple and cheap method of deflecting well bores in softformations. No special equipment is needed.• Dogleg severity can be partly controlled from surface by varying the number of feet “jetted” each time.• The survey tool is not far behind the bit, so survey depths are notmuch less than the corresponding bit depths.• Orientation of tool face is fairly easy.• The same assembly can be used for normal rotary drilling.

Disadvantages of JettingThe technique only works in soft formation and therefore at shallowdepths. For this reason, jetting is mainly used to kick wells off at shallow depths.In jetting, high dogleg severities are often produced. Deviation is produced in a series of sudden changes, rather than a smooth continuous change. For this reason, it is normal practice to jet an undergauge hole and then open it out to full gauge, which smooths off the worst of the doglegs.

The purpose of directional survey is to:

- Determine the exact bottomhole location in either azimuth (0 to 360°) or quadrant (NE, SE, SW, NW) form.- Monitor the actual well path to ensure the target will be reached- Orient deflection tools for navigating well paths- Ensure that the well does not intersect nearby wells- Calculate the TVD of the various formations to allow geological mapping- Evaluate the Dog Leg Severity (DLS), which is the total angular inclination and azimuth in the wellbore, calculated over a standard length (100 ft or 30 m)

Survey Methods:

Survey Methods

• Steering Tools

Survey Methods

• MWD

Comparison of Vertical and Horizontal Well

Source: by Advanced Resources International under Contract 68-W-00-094.

Source: by Advanced Resources International under Contract 68-W-00-094.

Conclusion

The technology of directional drilling has solidly moved into the arsenal of the oil industry over the past 10 to 12 years. A particular synergism of developments among equipment, techniques, and economically driven efficiency requirements has caused widespread consideration and testing of this technology. In many basins and reservoirs, properly applied horizontal drilling technology has demonstrated an incremental advantage over vertical wells.

Thanks for your attention

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Directional Drilling(2)