Directional drilling

For the first time began to be applied in the middle of the XX century. The founders of this method are American oil workers John Eastman, Roman Heins and George Feiling, who first used it in 1934 to extract oil from Conro, Texas ^[2] . In the USSR, a similar method with the support of the Baku scientist M.P. Guluzade was first used by the Azerbaijani oil worker Aga Neymatullah to extract oil from hard-to-reach fields: on land, in 1941 (Baku’s Bibi-Heybat region), and in the Caspian Sea, in 1946-47 ^[3] .

The technology of controlled oblique drilling developed gradually. To deviate the layout of the bottom of the drill string (BHA, Eng. BHA ) from the vertical, wedge deflectors were installed in the well (whipstock, whipstock ); drilling was done using traditional rotary assemblies. However, directional wells created by this technology often did not reach the target formations, with significant deviations from the target azimuths ^[4] .

In non-vertical sections of wells with an inclination of more than 12 degrees, if necessary, further changes in the zenith angle can be applied downhole rotor layout with stabilizers and weighted drill pipes, which creates a deflecting load on the bit. The build assembly is used for cornering, the pendulum assembly for reducing. To preserve the accumulated angle, a stabilized layout is used (tangent, packed assembly) ^{[4] [5]} .

Beginning in the 1960s, layouts with a curved adapter and a downhole motor (for example, using a screw drive downhole motor or a turbo-drill ), were used for directional drilling. Initially, the adapter curves had a fixed angle of inclination from 0.5 to 1 degree ^[4] . The direction in such arrangements was set by turning the drill string, however, to change the angle of inclination, it was necessary to rise to the surface and replace the adapter.

Later, adapters with controlled bending (from 0 to 4 degrees), set from the surface without lifting the layout from the well, were invented and introduced. They were also used in conjunction with downhole engines, forming a steerable motor ^[4] . Such an engine can be used in two modes: rotary (rotary) drilling, in which the force is created by a rotary table or top drive, and a sliding mode in which the drill string does not rotate and the bit is driven by a downhole motor. In the sliding mode, the azimuth angle of deflection is set by turning the column, and the zenith angle is set by the bend of the controlled adapter ^[4] .

Since the 1990s, rotary steerable systems (ENG, the Rotary steerable system ) have been developed , allowing to control the inclination of the well during rotary drilling without sliding periods ^[6] . Initially, they were used for drilling wells with large deviations from the vertical, but then they became widely used for drilling wells of any profiles ^[4] .

The development in the 2000s of directional drilling with horizontal sections up to 3-4 kilometers long, together with a multi-stage hydraulic fracturing allowed starting economically viable gas production in North America, and then light oil from dense reservoirs from shale formations (see Shale Revolution ) ^{[7] [8]} .

• When the final section is tilted and coincides with the formation slope, most of the well passes through the productive formation.
• Perhaps drilling in deposits, vertical access to which is difficult or impossible (deposits under cities, lakes, drilling offshore deposits from the shore)
• The possibility of cluster drilling, when the wellheads are grouped in a small area and they can be drilled by a single drilling site with little movement. For example, the offshore drilling platform can prepare about 40 wells from one site.
• Oblique drilling allows you to create silencing wells (relief well) while preventing accidents, for example, to stop a gusher. The silencing well begins to be drilled from a safe distance, then directing it precisely to the emergency well for injection of a jamming solution.

Early attempts at directional and horizontal drilling were significantly slower than vertical projects due to the need for frequent stops and well profile surveys, as well as slower drilling of the rock. Then, with the development of downhole motors and measurement tools, the drilling speed increased and the measurement was simplified.

For inclined wells, the zenith angle in which does not exceed 40 degrees, it is possible to use traditional measuring means lowered into the well on the cable. With large angles and the presence of horizontal sections, it is required to apply more complex means.

For wells with large angles, the prevention of sand entering the well is also complicated.

• DIRECTIONAL DRILLING TECHNOLOGY // EPA (Eng.)
• Development of Directional-Drilling Technology // Oilfield Review Interactive, Number 2. Schlumberger (Eng.)
• Steve Devereux, Drilling Technology in Nontechnical Language // PennWell Books, 2012, ISBN 9781593702649 , Chapter 8 "Directional and Horizontal Drilling" pp. 173-196 (Eng.)

• A. Messer, A. Povalikhin, Exploration and Development. Advanced drilling technologies , October 03, 2006
• Aberdeen, The unsung masters of the oil industry. // Economist, Jul 21st 2012 (eng.)