SLOTTED LINER
At first Pipe is slotted by mill cutting; now with the development of new material and new processing technic, we use ceramic cutters and laser to cut the slots for high quality and efficiency. The two processing technic can get both straight slots and keystone slots.
Slotted liner has high mechanical strength and high flexibility to allow adequate bending, which makes it applicable in complicated well conditions, and can be used in open-hole horizontal well completion for sand control especially for wells with medium or coarse sands.
Laser cutting machine Laser cutting slotted liner
Ceramic cutter cutting machine Ceramic cutter cutting slotted liner
STRAIGHT SLOTTING
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It has straight sides, equal width throughout the wall of the casing, and is more easily clogged by sand grains from the formation, than the Keystone slot.
As more and more slots became plugged with sand, a decreasing quantity of oil is obtained until finally a fraction of the oil available is produced. The most successful down hole slot cleaning method to date is hydro-washing. |
KEYSTONE SLOTTING
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It is essential that the slots be made so that the sand grains will bridge across the outside of the openings, but will not lodge within the openings themselves. The opening is narrower on the outside surface of the casing than on the inside, so that any grain of sand that enters the slot will immediately find enough clearance to pass completely through without clogging.
Slots formed in this way have a "V" cross section, up to and including 15 degrees included angle. Experience has indicated, however, that a 6 degrees included angle is adequate. The angle of undercut starts at the extreme outer edge of the casing. Thus the outer edge is amply backed up by a thick body of metal to resist erosion.
Since this undercut slot offers less resistance to clogging or plugging, it also offers less resistance to formation fluid flow, thus reducing the amount of pressure drop. This, of course, will consume less formation energy and result in higher ultimate recovery.
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CHOOSING A PERFORATING PATTERN
Pipe is slotted with an even number of rows unless otherwise specified. This makes it possible to stagger the rows in order to preserve a greater portion of the original strength of the pipe and to secure an even distribution of slots over the surface of the pipe for more efficient drainage.
Usual practices for mill cutting or ceramic cutter cutting are:
- 1 1/2" length slots (or I.D.) for slot widths 0.030"
- 2" length slots (or I.D.) for slot width greater than 0.030"
- All slots are spaced on 6" longitudinal centers
Typical Slot Cross-Section (Longitudinal)
Typical Vertical Slot Configuration (Longitudinal)
DETERMINATION OF NUMBER OF SLOTS
PER FOOT OF PIPE
The number of slots per foot is determined by calculating the number required to achieve about 3% open area of the outer surface of the pipe to be perforated.
The following formulas and examples illustrate how to determine the number of slots per foot.
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Formula: |
No. slots / ft =  |
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Where: |
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Data from Table A |
A=O.D. surface area per foot of pipe (Sq. In./Ft.) |
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Data from customer |
C=Desired percent open area |
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Data from Tyler Sand Analysis |
W=Slot width in thousands of an inch |
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Standard practice |
L=Slot length measured on I.D. in inches |
Example:
A=207.3 sq. in. / ft. (5 1/2" O.D.)
C=2.78 percent open area
W=.060" slot width
L=2" slot length on I.D.
No. slots/ft. = 
= 48
Important Note: On 6" longitudinal centers, the number of slots per foot is always twice the number of rows of slots around the circumference. Thus, the 48 slots per foot, in the example, result in 24 rows as a specification.
Tubing and casing