Directional Drilling Applications

Directional drilling is the art of directing and deviating the wellbore along a predetermined trajectory to get to preplanned targets. At the first days in drilling industry, a deviated well was considered as a disadvantage for many reasons:

- Directed well was more time consuming to reach to the producing zone

- Failure of the drill string leading to fishing operations
- Difficulties to control the trajectory

Applications of Directional Drilling

Sidetracking

During drilling operations, the drill string can be stuck by differential or mechanical mechanisms or it can be lost due to string failure (Click Here). In the case where the fish cannot be pulled out the hole, the well has to be sidetracked. Sidetracking starts by placing a cement plug (Click Here) at the top of the fish which allows for a good foundation to kick off the wellbore. The deflecting can be performed by using a whipstock or positive displacement motor (PDM) with a measurement while drilling tools (MWD). Sidetracking the wellbore can be also performed from a cased hole, where a window is opened in the casing and the wellbore is directed across this window.

Fig 01- Sidetracking

Overcoming Geological Problems

There are some situations when drilling operations can be difficult. Many problems can be faced due to the type of formations such as drilling through salt dome or passing through a fault. For instance, drilling though salt dome can cause multiple problems like large washouts, corrosion and even loss of circulation; a directional well can be drilled to bypass this type of formation structure. Drilling through an inclined fault can lead to difficulties to control the bit behavior and causing the bit to deflect when passing across the fault plane. Directional drilling helps to drill through faulted formations without crossing the fault line.

Fig 02- Fault Drilling

Inaccessible Locations

It is not always possible to reach targets vertically even if it is the best option. For many reasons, the drilling rig cannot be placed above the producing zone. The hydrocarbons reservoirs can be beneath the man-made structures or naturel objects which are protected. Directional drilling can be the only option to get to the reservoirs without harming the nature or causing environmental problems. The same case can be faced for offshore drilling where the locations can be restricted due to shallow gas zones or environmental issues.

Fig 03- Inaccessible Locations

Multiple Wells from Offshore Location

It is impractical and uneconomical to drill large number of vertical wells to produce from reservoirs beneath the seabed. The option for this situation is fixing a platform on the seabed and drilling directional boreholes which are carefully planned to optimize the recovery. In some cases, a sub-sea template is used to drill multiple wells from a semi-submersible drilling structure and tie back these wells to a platform.

Fig 04- Multiple Wells

Horizontal Drilling

Deviated wells with more than 70° inclination angle are considered as horizontal wells. Multiple problems can be faced when drilling this type of wells which can increase their drilling cost. There are many advantages for drilling a horizontal well:

- Increasing the drainage area of an offshore structure

- Overcoming gas and water conning problems

- Increasing the contact area with the reservoir

- Increasing the productivity by intersecting vertical fractures

Fig 05- Horizontal Drilling

Relief Wells

When the well control equipment and procedures failed leading to an uncontrolled situation called a blowout (Click Here), a deviated well is drilled as a remedial solution. The technique is drilling from an adjacent surface location to the source formation of the uncontrolled flow as closely as possible or even to the uncontrolled well itself. When getting to the target, a kill mud is pumped to regain the control.

Fig 06- Relief Well

Controlling Vertical Wells

There are some geological structures force the bit to deviate leading to unplanned deviation and drilling problems. Using the directional techniques can help to control and correct the verticality of the wellbore.