Directional drilling


Directional drilling is the art and science involving the intentional deflection of a wellbore in a specific direction in order to reach a predetermined objective below the surface of the earth
  • At one time it was thought that all wells were vertical
  • Methods to measure deviation were developed in the 1920’s (initially acid bottle)
  • Directional drilling developed after 1929 when new survey instruments were available (inclination and direction)
  • The first controlled directionally drilled well was drilled in the Huntington Beach Field in 1930 to tap offshore reserves from land locations
  • Directional drilling became more widely accepted after a relief well was drilled near Conroe, Texas in 1934

  • Today, directional drilling is an integral part of the petroleum industry
  • It enables oil companies to produce reserves that would not be possible without directional drilling
  • One of the primary uses of directional drilling was to sidetrack a well even if it was to go around a stuck BHA

 
  • Sometimes multiple sidetracks are used to better understand geology or to place the wellbore in a more favorable portion of the reservoir
  • Straight hole drilling is a special application of directional drilling

  1. To keep from crossing lease lines
  2. To stay within the specifications of a drilling contract
  3. To stay within the well spacing requirements of a developed field
 
  • Drilling multiple wells from a single structure or pad
  • Most offshore development would not be possible without directional drilling
  • Inaccessible surface location
  • Drilling in towns, from land to offshore and under production facilities



  • Drilling around salt domes
  • Salt can cause significant drilling problems and directional drilling can be used to drill under the overhanging cap
  • Steeply dipping sands can be drilled with a single wellbore
  • Fault drilling
  • In hard rock, deviation can be a problem
  • Sometimes the bit can track a fault
  • Drilling at a higher incident angle minimizes the potential for deflection of the bit
  •  Relief well drilling
  • Directional drilling into the blowout when the surface location is no longer accessible
  • Very small target and takes specialized equipment
  •  Horizontal drilling
  • Increasing exposure of the reservoir to increase productivity
  •  Multilateral drilling
  • Drilling more than one wellbore from a single parent wellbore

  •        Extended reach drilling wells are characterized by high inclinations and large departures in the horizontal plane







  • Extended reach wells are wellbores where the horizontal departure is significantly higher than the true vertical depth of the well, which is the horizontal departure – TVD ratio (HD/TVD)
  • Extended reach wells have been drilled with HD/TVD ratios greater the 6/1.
    BP drilled a well at Wytch Farm with a measured depth of 34,967’ (10,658 m), a TVD of 5,266’ (1,605 m) and horizontal departure of 33,181’ (10,114 m) 
    •    There are four basic hole patterns
    •      Not all wells conform to the basic hole patterns and may be a combination of patterns
    •     For simplicity, the basic hole patterns are defined as:

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