Slotted Liner Basic Knowledge

Slotted liners are extensively used in SAGD wells and other thermal applications for its superior structural capabilities to withstand installation loads and operation loads in contrast to other sand control devices. For better comprehension, basic knowledge of slotted liner is partly presented below. If you have any other problem, please contact us for suggestion or other related information.

Slotted liner patterns

Three slot patterns are designed for different characteristics (shown below). Compared to staggered and straight slot patterns, gang slot pattern has superiorities over installation torque-loading capacity and substantially improves the liner’s resistance to lateral bucking and collapse pressures.

Staggered slotted liner with slots evenly spaced around circumference
Staggered Slotted Line

Staggered slots features alternate slot evenly spaced around the circumference with offset.

Gang slotted liner with multiple slots evenly spaced around circumference
Gang Slotted Liner

Gang slots feature multiple slots evenly spaced around circumference in a staggered pattern.

Straight slotted liner with slots evenly spaced around circumference without offset
Straight slotted liner

Straight slotted liner features slot columns spaced evenly around the circumference without offset.

Slot profiles

Slot profile poses great importance on sand control and plugging performance. According to its different geometry, there are two slots – straight cut slot and seamed keystone slot. In almost horizontal completions in SAGD, seamed keystone slot performs much better than typical straight cut slot, and cost a little more.

Straight cut slot, both internal and external width shares the same size
Straight Cut Slot

Straight cut slots are designed for the same width through ID to OD. Straight slots feature more wear-resistant than seamed keystone slot.

Seamed keystone slot better for anti-plugging
Seamed Keystone Slot

Seamed keystone slot – width at the liner surface is narrower than width on the pipe interior. It features anti-plugging and self-cleaning.

Slot density

Slot density refers to the number of slots per foot of pipe. It is determined by the open area of the pipe's outer surface. Open area is an important factor of reducing the sand control capacity of a slotted liner. Generally speaking, open area ranges from 2% to 4%.

When the open area, the slot width and the diameter of the liner are determined, the slot density per foot can be calculated by the following formula:

N = 12πD C
100 W L

N stands for slot density or the number of slots per foot
D stands for outside diameter of the liner in inch
C stands for open area, percentage
W stands for slot width in inch
L stand for the length of slot in inch

Example: For a 4.5" slotted liner, its open area is 3%, the slot width is 0.02 inch, the slot length is 1.5', so what is the number of slot per foot?

According to the formula above, the required Number of slots is shown below:

N = 12×π×4.5×3 = 172

Note: This formula is just a conventional calculation for either straight slot or seamed keystone slot.

Adverse factors on plugging of slotted liner.

Anti-plugging is a vital element for the evaluation of slotted liners. Four factors which are probably cause plugging are found.

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