Product  Descriptions :J55|N80 Slotted Liner

Slotted liners are used in gravel packed completions to prevent the production of gravel pack sand or can be used in stand-alone service when the formation grain size is large. Slot widths are often referred to in terms of "gage" or "gauge". Slot or screen gage is simply the width of the opening in inches multiplied by a 1,000. For instance, a 12 gage screen has openings of 0.012 inches. Slotted liners are manufactured by machining slot openings through oil-field tubulars with small rotary saws. Slotted liners are fabricated in a variety of patterns as illustrated in Figure.

The minimum slot widths that can be achieved is about 0.012 inches; however, slots widths cut below 0.030 inches in thickness involve higher costs because of excessive machine down time to replace broken saw blades that become overheated, warped and break. While the slotted liners are usually less costly than wire-wrapped screens, they have a smaller inflow area and experience higher pressure drops during production.

Slotted liners also plug more readily than screens and are used where well productivity is low and economics cannot support the use of screens. The single slot staggered pattern is generally preferred because a greater portion of the original strength of the pipe is preserved. The staggered pattern also gives a more uniform distribution of slots over the surface area of the pipe. The single slot staggered pattern is slotted with an even number of rows around the pipe with a typical 6 inch longitudinal spacing of slot rows.

SLOTTED LINER GEOMETRIES

The slots can be straight or keystone shaped as illustrated in Figure. The keystone slot is narrower on the outside surface of the pipe than on the inside. Slots formed in this way have an inverted "V" cross-sectional area and are less prone to plugging since any particle passing through the slot at the OD of the pipe will continue to flow through rather than lodging within the slot.

STRAIGHT AND KEYSTONE SHAPED SLOTS

The length of the individual slots is gauged on the ID of the pipe. Usual practice dictates 1½ inch long slots for slot widths 0.030" and under, 2 inch long slots for slot widths between 0.030 to 0.060 inches and 2½ inch long slots for slot widths 0.060 inches and larger (see Figure 6.4). Slot width tolerance is generally 0.003 inches for widths 0.040 inches and wider and 0.002 inches for widths less than 0.040 inches.

STANDARD SLOT LENGTHS

Slotted liners are generally designed to have a 3 percent open area relative to the OD surface area of the pipe although open areas up to 6 percent are feasible in some cases. The number of slots per foot required to achieve a given open area is calculated with the equation below.

where: N = required slots/foot (if N < 32, round up to the nearest multiple of four, if N > 32, round up to the nearest multiple of 8) Pie = constant (3.1416) D = outer diameter of pipe (inches) C = required open area (percent) W = slot width (inches) L = length of slot measured on ID of pipe (inches)

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