Drilling and Excavation Technologies for the Future (1994) / Chapter Skim
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7. Directional Drilling and Tunneling
7. Directional Drilling and Tunneling
Pages 101-134
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From page 101... ...
Such holes are almost always of circular cross section, because the excavation method consists of rotating some form of cutter head against the rock face. The drive mechanism for Be cutter head is normally quite bulky and is rigidly attached to a cutter head because of the need to transmit the required power.
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From page 102... ...
Conversely, straight holes are drilled by rigid drilling assemblies provided with cutter heads or drill bits that have no sideways cutting teeth and that fit snugly in the hole. Directional Tunneling Tunnel boring machines excavate a constant cross section of tunnel (usually circular)
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From page 103... ...
for sewer work. The machines consist of a powered cutter head and steering assembly dlat is pushed forward by a jacking system from a launching pit.
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From page 104... ...
r Forward Guide \ Rear Gnpper FIGURE 7.2 Plan view of a TBM turning in a "crabbing" mode (after Robbins Co., 1993~. Large TBMs obtain steering information by observing the position of a laser beam spot cast on a target mounted on the machine, the laser source being mounted on a fixed support some way to the rear of the tunnel.
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From page 105... ...
In addition to He control of direction, other important issues include surveying methods; borehole stability and cuttings removal in inclined boreholes; the reservoir engineering aspects of horizontal wells; and the various special problems associated
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From page 106... ...
In extended reach drilling, maximum reach depends on the target depth, as well as maintenance of good borehole conditions and a sufflciently steep angle to allow the drilling assembly to slide forward so as to apply weight to the bit. The technology is advancing rapidly.
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From page 107... ...
, a I,000-ft-Iong horizontal well has about twice the productivity of a vertical well if the reservoir thickness is 400 ft. and this figure increases about five times if the reservoir height decreases to 100 ft.
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From page 108... ...
In an extended reach hole, this requirement becomes one of making the contact between the drilling assembly and the hole wall as friction free as possible, allowing for tile flattest "sail angle." (For Me record-breaking hole recently drilled in the North Sea, this was 82 degrees from the vertical; Anon., 1993b.) For hole angles flatter than this and for horizontal holes, We drilling assembly has to be pushed forward by the action of a thrusting section of heavy pipe or collars located furler up the hole in a more steeply inclined interval (Figure 7.4~.
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From page 109... ...
Several considerations govern the choice of curve radius and therefore the drilling method. For extended reach wells, the maximum reach is attained wig large tubulars and gentle curvature.
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From page 110... ...
For the above reasons, holes are often drilled with two curved sections joined by an inclined straight interval (Schuh, 1989; Figure 7.5~. This allows the turning tendency of He BHA to be assessed during He drilling of the first curve and the straight section to be shortened or lengthened to allow the second curve to hit He target exactly.
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From page 111... ...
This is known as "building angle." Conversely, a first stabilizer located a distance behind He bit will allow the bit to hang down and drill ~ Some bits, particularly polycrystalline diamond cutter (PDC) drag bits' do tend to change azimuth by "waLlcing" to the left or right.
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From page 112... ...
The degree of curvature that may be achieved is quite low, typically ~ to 5 degrees per hundred feet, and He use of pendulum assemblies is generally restricted to fi~-s~ze (greater Han 6 inches) drilling assemblies.
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From page 113... ...
Curvatures of 2 to 5 degrees per hundred feet are typical, resulting in turning radii of 300 to 1,000 ft or so. Pendulum angle building or dropping l VERtlCAL WELL: .....
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From page 114... ...
If it is desired to drill straight ahead, this may be achieved without removing the directional drilling assembly, by applying a slow rotation (some tens of revolutions per minute) to Me drill stem from the surface.
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From page 115... ...
An interesting feature ofthe Hughes Christensen "Navigation Drilling System" is that whereas most of He bent sub/motor combinations have He motor axis displaced from the main axis of the drilling assembly, and therefore push He bit sideways as well as tilting it, the Navigation Drilling System uses a double bend to tilt the bit from below the motor, thus causing the deviation of the hole to occur mostly by the tilt of the bit. This is claimed to give more consistent steering.
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From page 116... ...
116 Drilling and Excavation Technologies for the Future Build Motor String Stablizer ~D~ Valve ~~Bent Sub Low-Speed, \\ HighTorque Motors \: Kickoff Sub/— Upper Bearing Housing With Stabi izer Hold Motor Low-Speed, High-Torque Motor LULL 'I ~ t String Stabilizer DO - exulted Woint Housing 1 a~ Bearing Housing Wig Stabilizer FIGURE 7.8 Equipment for drilling medium-radius curves (Sheikholeslami and others, 19891. Short-Radius Methods A short-radius drilling memos described by Parsons and Fincher (1986)
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From page 117... ...
This guide is sufficiently flexible to be forced straight to enter the vertical hole, but in this state it exerts about 1,000 Ib of sideways force, so that upon leaving He whipstock, the assembly drills ahead along a curve. In front of Be guide is a conventional bit, while to the rear of the guide are lengths of flexible drive pipe, composed of interlocking steel elements that allow torque to be transmitted even though the pipe can flex.
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From page 118... ...
At Me forward end of the tubing, a jet nozzle allows high-pressure water to be directed at the rock to be drilled, while the pressure of the water inside the tubing feeds it forward into the hole created by the water jet. A horizontal drainhole I.5 to 2.5 inches in diameter is thus created, which, under favorable circumstances, extends a hundred or more feet from We vertical well (Dickinson and others, 1992; Figure 7.
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From page 119... ...
119 ed by the exit of high-pressure water from the ports force the drilling head up or down (Figure 7.111. This steering method is of interest because it does not generate Me steering force by pressing some part of the drilling assembly against the hole wall.
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From page 120... ...
Methods Using Coiled Tubing Recent work has involved the drilling of directional and horizontal holes in which the drilling assembly is attached to a coiled tubing unit rather than to conventional drill pipe. This technique is particularly interesting in reservoirs where there are open fractures that have different reservoir pressures.
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From page 121... ...
The requirements are characterized by a need for good directional control and for penetration in relatively soft terrain. A subsidiary requirement is that since much of He work is done near inhabited areas, the drilling equipment and methods are preferably nonintrusive.
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From page 122... ...
In soft ground, drilling may be carried out by using a drill pipe rotating inside a "washover pipe" that is periodically advanced to catch up with Me drilling assembly. The washover pipe carries the return mud and cuttings back to the surface so that erosion of the borehole is minimized and Me hole is prevented from collapsing.
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From page 123... ...
For this application, "gyropigs" are being developed that will record directional data as they are pumped down the pipeline (Spiekhout, 1991~. Generally, "in-hole" devices are used in the longer, deeper holes, either because the holes are too deep for the surface sensors to detect the drilling assembly accurately or because the surface locations are inaccessible.
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From page 124... ...
—either an impact penetrator with oblique face similar to that described above, or a down hole air motor and bent sub developed by Maurer Engineering Co. (Houston)
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From page 125... ...
: ~ // ,.,~ c: ~~~essed air ~ 'God _ _~'~_' .' //,, i// / ~ ~.~//~/// 125 . ~ ~Y////~//////~ LEGEND 1 Drill frame 2 Percussive downhole tool system A Carriage assembly 8 On-off valve C Air swivel D Drill pipe E Downhole valve F Shock absorber G Flex sub H Percussive mole with connector sub I Slanted nose steering device and electronics housing J Bent sub steering device and electronics housing K Circulating sub L Air motor M Drill bit N Tracking electronics P Surface launch adaptor R Anchor posts FIGURE 7.13 "True Trac" guided drilling equipment QIair, 1989b)
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From page 126... ...
· Drill bits: Since transmission of weight to the drill bit is critical in much directional drilling, particularly extended reach drilling, Here is a need for research to develop drill bits that have high cueing ability at low weight on He bit. Such very aggressive bits may have to be
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From page 127... ...
· Smart directional drilling: The committee endorses research efforts Hat combine geologic inputs with directional information to allow smart drilling, for example, to follow a particular oil-bearing formation at depth, or to seek or avoid stable or unstable, polluted or clean strata for directional services or environmental projects. Research should be undertaken to develop sensor/guidance systems Hat avoid service lines or over buried structures in the near surface.
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From page 128... ...
I., 198S, Simultaneous multiple entry hydraulic fracture treatments of horizontally drilled wells: SPE 18263, SPE Annual Technical Conference and Exhibition, Houston, Tex., Oct. 2-5, Richardson, Tex., SPE, p.
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From page 129... ...
62 66. Eddison, A., and Symons, I., 1990, Downhole adjustable gauge stabilizer improves drilling efficiency in directional wells: SPE 20454, 65 Annual Technical Conference and Exhibition, New OrIeans, La., September 23-26, Richarson, Tex., SPE, p.
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From page 130... ...
D., and Pittard, F I., 1990, Open hole drilling using coiled tubing and a positive displacement mud motor: SPE 20459, 65th Annual Technical Conference and Exhibition, New Orieans, La., Sep.
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From page 131... ...
L., 1983, Horizontal drainhole drilling techniques used for coal seam resource exploitation, SPE 18524, SPE 63rd Annual Technical Conference and Exhibition, Houston, Tex., 2-5 October, Richardson, Tex., SPE, p.
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From page 132... ...
H., 1992, Horizontal slim-hole drilling wig coiled tubing: an operator's experience: lADCISPE 23875, SPE/lADC Drilling Conference, New OrIeans, La., Feb. IS-2l, Richardson, Tex., SPE, p.
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From page 133... ...
A., and Button, D M., 1989, Drilling and production aspects of horizontal wells in the Austin chalk: SPE 19825, SPE Annual Technical Conference and Exhibition, San Antonio, Tex., Oct.
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From page 134... ...
C., and Willis, D N., 1986, Successful high angle drilling in the Stati~ord field: SPE 15465, 6Ist SPE Annual Technical Conference and Exhibition, New OrIeans, La., Oct.
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