Horizontal Drilling

Horizontal Drilling

Horizontal drilling is a directional drilling process aimed to target oil or gas reservoir intersecting it at the “entry point” with a near-horizontal inclination, and remaining within the reservoir until the desired bottom hole location is reached.

While the construction of a directional well often costs much more than a conventional well, initial production is greater of a conventional well.

Horizontal drilling provides more contact to a reservoir formation than a vertical well and allows more hydrocarbons to be produced from a given wellbore.

For example, six to eight horizontal wells drilled from one location, or well pad, can access the same reservoir volume as 16 vertical wells.

Using multi-well pads can significantly reduce the overall number of well pads, access roads, pipeline routes and production facilities, minimizing habitat disturbance, impacts to the public and the overall environmental footprint.

Horizontal wells are usually drilled to enhance oil production and in some situations the improvement may be dramatic – enabling development of a reservoir which would otherwise have been considered uneconomic.

There are many kinds of reservoir where the potential benefits of horizontal drilling are evident:

• in conventional reservoirs
  • Thin reservoirs; Reservoirs with natural vertical fractures;  Reservoirs where water (and gas) coning will develop; thin layered reservoirs; heterogeneous reservoirs;
• in unconventional reservoirs
  • shale gas/oil, tight gas/oil, CBM, heavy oil, oil sands, etc

The initial vertical portion of a horizontal well is typically drilled using the same rotary drilling technique that is used to drill most vertical wells, wherein the entire drill string is rotated at the surface (the drilling of vertical sections is also possible by the use of downhole motor just above the bit, like the VertiTrak or TruTrak, where only the bit rotate while the drilling string remains firm).

From the kickoff point to the entry point the curved section of a horizontal well is drilled using a hydraulic motor mounted directly above the bit and powered by the drilling fluid.

Steering of the hole is accomplished through the employment of a slightly bent or “steerable” downhole motor (today the technology of directional drilling has improved by the use of the “RSS: Rotary Steerable System” that permit to steer an hole continuing the rotation of the drilling string. The RSS increase the safety and the drilling efficiency).

Downhole instrument packages that transmit various sensor readings to operators at the surface are included in the drill string near the bit.

Sensors provide the azimuth (direction versus north) and inclination (angle relative to vertical) of the drilling assembly and the position (x, y, and z coordinates) of the drill bit at all times.

Additional downhole sensors can be, and often are, included in the drill string, providing information on the downhole environment (bottom hole temperature and pressure, weight on the bit, bit rotation speed, and rotational torque).

They may also provide any of several measures of physical characteristics of the surrounding rock such as natural radioactivity and electrical resistance, similar to those obtained by conventional wire line well logging methods, but in this case obtained in real time while drilling ahead.

The information is transmitted to the surface via small fluctuations in the pressure of the drilling fluid inside the drill pipe.