Horizontal Drilling | What is a horizontal drilling?

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Horizontal Drilling, Horizontal Wells, Horizontal Well, Directional and Horizontal Drilling

Well Configurations

Horizontal drilling begins with a more-or-less vertical surface section (the one exception being slant drilling rigs, where this section is pre-inclined), followed by a bend section, which progresses from approximately 0° to 90° inclination with depth, and finally by a horizontal or lateral section. The transfer of weight to the drill bit during the horizontal drilling phase involves different concepts, which translate into different well configurations. We may generally distinguish these configurations, based on radius of curvature, as long turn radius, medium turn radius, short turn radius and ultra-short turn radius (Figure 1, Horizontal drilling methods):

Horizontal drilling methods, applications of horizontal well technology, horizontal well, applications of horizontal well, Horizontal Wells, Directional and Horizontal Drilling — **FIGURE 1**

The considerations that enter into selecting one of these well configurations include

cost
well spacing and lease restrictions
conditions of re-entry wells
reservoir rock characteristics
production methods
well objectives
problem-causing lithologies above the pay zone
amount of total horizontal departure
completion methods
availability of specialized downhole tools
kick-off depth constraints
horizontal displacement constraints

Table 1 and Table 2, below, compare the basic characteristics of long, medium and short radius wells.

Table 1: Comparative Characteristics of Horizontal Drilling Methods (Mitchell, 2006)
	Long Radius	Medium Radius	Short Radius
Build rate	$2^{\circ}$ to $6^{\circ}$ per $100\ ft$	$6^{\circ} - 35^{\circ}$ per $100\ ft$	$5^{\circ} - 10^{\circ}$ per three feet
Build radius (ft)	1000 – 3000	160 – 1000	20 – 40
Hole size (in)	No limits	$4\tfrac{3}{4},\ 6\tfrac{1}{8},\ 6\tfrac{1}{2},\ 8\tfrac{1}{2},\ 9\tfrac{7}{8}$	$4\tfrac{3}{4},\ 6\tfrac{1}{2}$
Drilling Method	Rotary or steerable motor systems for curve and horizontal sections	Specially designed motors for angle build section; rotary or steerable motor systems for horizontal sections.	Specially designed deflection tools or articulated motors for angle build section; rotary tools and special drill pipe for horizontal sections.
Tubulars used	Conventional tubulars.	Heavy wall drill pipe for build rates of up to 15° per 100 ft; special service drill pipe for higher build rates.	Special articulated tubulars; special drill pipe with short articulated motors.
Drill bit	No limits	No limits	Rotary: No limits Motor: Diamond or PDC
Drilling fluids	No limits	>No limits	No limits
Surveying	No limits	MWD capabilities limited for hole sizes smaller than $6\tfrac{1}{8}$ – inches	Special
Coring	Conventional coring, no limits	Conventional coring, no limits	3-foot core barrel, 1-inch diameter core

Table 2: Comparative Characteristics of Horizontal Wells (IADC/SPE)
	Long Radius	Medium Radius	Short Radius
Selective completion capabilities	Yes	Yes	No
Multiple pay zones	No	Yes	Yes
Artificial lift capabilities	All types	All types	Rod pumps in vertical portion
Workover capabilities	Yes	Yes	Yes
Typical productivity index increases in non-fractured zones	3.5	2.5	2.5
Typical productivity index increases in fractured zones	$> 10$	$> 10$	Depends on fracture distribution
Production enhancement ratio (horizontal/vertical well)	6	7	Varies widely; can be from 1 to 100
Cost ratio (horizontal/vertical well)	$> 2$	$> 2$	1.5