Directional Drilling & Why it's required?

Directional Drilling is the science and an art of controlling the DIRECTION & DEVIATION of a well bore to a pre-determined underground target or location.

Why is Directional Drilling required?

Directional wells are required where we can't drill a vertical well or can't continue vertical drilling.

To name a few, below are given some of the reasons/applications of Directional Drilling.

1. Inaccessible locations-

Directional wells are preferred when the surface location directly above the reservoir is inaccessible due to man-made or natural reasons.

                                                                  

2. Multiple wells from an offshore structure-

Moving an offshore platform require huge amount of money and time. So to save this, multiple wells from single offshore structures are drilled. The directional wells are designed to intercept reservoir over a wide range. Many oil fields will not be economically feasible if not for this technique.

3. Relief wells-

Directional drilling techniques are used to drill relief wells in order to kill the blow outs. Relief well is drilled to intercept or pass within a few feet off the bottom of 'blow out' well. The 'blow out' well is then killed by circulating the calculated amount of high density fluid through the well, into and up the well.

(Blow out- Uncontrolled flow of formation fluids such as oil, gas, water or a mixture of these from a well up to the surface.)

4. Controlling vertical wells-

Directional drilling techniques are used to 'straighten crooked holes' when deviations occurs in a well which is supposed to be vertical.

5. Sidetracking-

Sidetracking out of an existing well bore is a directional drilling technique employed to by pass an obstruction (fish) in the original well bore, or to sidetrack a dry hole.

(Fish- Anything left in the hole such as junk metal, parts of drill string, hand tool etc.)

 

6. Salt Dome drilling-

Directional drilling programmes are used to overcome problems associated with drilling in the salt domes, by drilling at one side of the dome and then deviating around or underneath the overhanging cap.

(Salt domes - Dome-shaped structures in sedimentary rocks, formed where a large mass of salt has been forced upwards. Such structures often form traps for oil and gas.)

7. Fault Drilling-

It's difficult to drill a vertical well through a steeply inclined fault plane to reach the underlying hydrocarbons bearing formation; instead well bore is deflects perpendicular or parallel to the fault plane for better production.

In unstable areas well bore may be at risk due to the possibility of slippage or movement across the fault zone. Shearing of casing can also occur.

Formation pressures across the fault zone may also affect the hole-conditions.

 8. Onshore drilling to Offshore locations-

When a reservoir lies offshore but, quite close to the land then, in such cases drilling from onshore locations to offshore provides the most economical way of exploiting the reservoir.

 A Glimpse from the history-

Directional drilling were initially used as a remedial operation, either to sidetrack around stuck tools, or in bringing back well to the vertical, or to drill relief wells to kill blow outs.

In 1929, interest in directional drilling began on arrival of accurate means of measuring the well bore deviation. In 1930, the first directional well was drilled in Huntington Beach, California, USA. The well was drilled from onshore location into offshore oil sands.

Directional drilling received an unfavourable publicity until it was used to kill a wild well in 1934 near Con roe, Texas, USA. It was until then it subsequently gained a favourable recognition from both the companies and contractors as a favourable way of controlling blow outs.

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