Skin Factor and Damage
Near Wellbore condition/Skin factor
Skin:
- damage skin (+)
- stimulation (-)
- completion skin:
- structure skin:
- partial completion (+)
- slanted (-)
- completion:
- perforation (+) or (-)
- slotted liner (+)
- gravel pack
- screens
Total skin effect: 𝑠𝑠𝑡𝑡 = ∑ 𝑠𝑠𝑖𝑖  (𝑠𝑠𝑖𝑖 = 𝑠𝑠𝑠𝑠𝑠𝑠 , 𝑠𝑠𝑝𝑝𝑝𝑝 , 𝑠𝑠𝑑𝑑 ….)
Near Wellbore condition/Skin factor
Formation Damage Skin :
1.
2. Vertical Well
 Completion Skin :
S (+)
S (-)
Near Wellbore condition/Skin factor
* Muskat Model:
𝑞𝑞𝑀𝑀 =
2𝜋𝜋𝜋𝜋ℎ𝑤𝑤 ∆𝑃𝑃 1 + 7 ∗
𝑞𝑞𝑐𝑐 =
𝑠𝑠𝑐𝑐 = 𝑙𝑙𝑙𝑙
𝑟𝑟𝑒𝑒
𝑟𝑟𝑤𝑤
𝑟𝑟
𝜇𝜇𝜇𝜇𝜇𝜇 𝑟𝑟𝑒𝑒
𝑤𝑤
𝑟𝑟𝑤𝑤 log
𝜋𝜋ℎ𝑤𝑤
2ℎ
2ℎ𝑤𝑤
2𝜋𝜋𝜋𝜋𝜋∆𝑃𝑃
𝑟𝑟
𝜇𝜇 𝑙𝑙𝑙𝑙 𝑟𝑟𝑒𝑒 + 𝑠𝑠𝑐𝑐
𝑤𝑤
1+7 ∗
ℎ
ℎ𝑤𝑤
𝑟𝑟𝑤𝑤 log
𝜋𝜋ℎ𝑤𝑤
2ℎ
2ℎ𝑤𝑤
Near Wellbore condition/Skin factor
* Papatzacos Model (Anisotropy, Iani =
ℎ
ℎ𝐼𝐼
ℎ𝑤𝑤
𝑠𝑠𝑐𝑐 =
𝒌𝒌𝑯𝑯
𝒌𝒌𝑽𝑽
):
1
𝜋𝜋
1
ℎ𝑤𝑤𝑤𝑤
𝐴𝐴 − 1
− 1 𝑙𝑙𝑙𝑙
+
𝑙𝑙𝑙𝑙
2 + ℎ𝑤𝑤𝑤𝑤 𝐵𝐵 − 1
ℎ𝑤𝑤𝑤𝑤
2𝑟𝑟𝐷𝐷
ℎ𝑤𝑤𝑤𝑤
Where:
𝐴𝐴 =
ℎ𝑤𝑤𝑤𝑤
ℎ𝑤𝑤
=
ℎ
1
1
𝐵𝐵 =
ℎ𝐼𝐼𝐼𝐼 + 3�4 ℎ𝑤𝑤𝑤𝑤
ℎ
ℎ𝐼𝐼𝐼𝐼 + 𝑤𝑤𝑤𝑤
4
ℎ𝐼𝐼𝐼𝐼
ℎ𝐼𝐼
=
ℎ
𝑟𝑟𝐷𝐷 =
𝑟𝑟𝑤𝑤
𝐼𝐼
ℎ 𝑎𝑎𝑎𝑎𝑎𝑎
Near Wellbore condition/Skin factor
2.2 Inclined (or Slanted ) Well Skin Factor:
ℎ
𝜭𝜭
Where:
𝛾𝛾 =
EXAMPLE!
1
𝐼𝐼𝑎𝑎𝑎𝑎𝑎𝑎
+
𝑐𝑐𝑐𝑐𝑐𝑐 2 𝜃𝜃
1−
1
2
𝐼𝐼𝑎𝑎𝑎𝑎𝑎𝑎
Near Wellbore condition/Skin factor
3. Completion Skin for perforation:
TOP VIEW
0°, 360°
180°
LATERAL VIEW
Before perforation
𝑠𝑠𝑣𝑣
120°
TOP VIEW
𝑠𝑠𝑤𝑤𝑤𝑤
𝑠𝑠𝐻𝐻
After perforation
3.1 Perforation skin effect:
𝜃𝜃: phasing
𝑙𝑙perf ∶ length of perforation
𝑟𝑟𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 : perforation radius
EXAMPLE!
𝑎𝑎θ from table 6.1
4. Combined skin factor of damage and perforation
Case 1: 𝑟𝑟𝑠𝑠 > 𝑙𝑙𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 + 𝑟𝑟𝑤𝑤
(𝑠𝑠𝑑𝑑 )𝑝𝑝
𝑟𝑟𝑠𝑠
Case 2: 𝑟𝑟𝑠𝑠 < 𝑙𝑙𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 + 𝑟𝑟𝑤𝑤
𝑟𝑟𝑠𝑠
𝑘𝑘
= (𝑠𝑠𝑑𝑑 )𝑜𝑜 +
𝑠𝑠
𝑘𝑘𝑠𝑠 𝑝𝑝
𝑘𝑘
𝑠𝑠 = 𝑠𝑠𝑐𝑐 + 𝑠𝑠𝜃𝜃 + (𝑠𝑠𝑑𝑑 )𝑜𝑜 +
𝑠𝑠
𝑘𝑘𝑠𝑠 𝑝𝑝
𝑠𝑠 = 𝑠𝑠𝑐𝑐 + 𝑠𝑠𝜃𝜃 + 𝑠𝑠𝑝𝑝 ’
𝑠𝑠𝐻𝐻 ′ = 𝑙𝑙𝑙𝑙
𝑟𝑟𝑤𝑤
𝑟𝑟𝑤𝑤 ′′(𝜃𝜃)
𝑠𝑠𝑝𝑝 ′ = 𝑠𝑠𝑉𝑉 ′ +𝑠𝑠𝐻𝐻 ′ +𝑠𝑠𝑤𝑤𝑤𝑤 ′
𝑟𝑟𝑤𝑤 ′′(𝜃𝜃)
𝑙𝑙𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝
4
for 𝜃𝜃 = 0
𝑎𝑎𝜃𝜃 𝑟𝑟𝑤𝑤 + 𝑙𝑙 ′ 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 for 𝜃𝜃 ≠ 0
1
1
𝑟𝑟𝑒𝑒
2
𝑟𝑟𝑠𝑠
∆𝑃𝑃 = ∆𝑃𝑃1 + ∆𝑃𝑃2
𝑞𝑞𝑞𝑞
𝑟𝑟𝑒𝑒
∆𝑃𝑃 =
𝑙𝑙𝑙𝑙 + (𝑠𝑠𝑑𝑑 )𝑝𝑝
𝑟𝑟𝑤𝑤
2𝜋𝜋𝜋𝜋𝜋
(𝑠𝑠𝑑𝑑 )𝑝𝑝 = ln
𝑟𝑟𝑠𝑠
𝑟𝑟𝑤𝑤
𝑞𝑞𝑞𝑞
𝑟𝑟𝑒𝑒
∆𝑃𝑃1 =
𝑙𝑙𝑙𝑙
2𝜋𝜋𝜋𝜋𝜋 𝑟𝑟𝑠𝑠
𝑘𝑘
𝑘𝑘
−1 +
𝑠𝑠
𝑘𝑘𝑠𝑠
𝑘𝑘𝑠𝑠 𝑝𝑝
𝑞𝑞𝑞𝑞
𝑟𝑟𝑠𝑠
∆𝑃𝑃2 =
𝑙𝑙𝑙𝑙 + 𝑠𝑠𝑝𝑝 + 𝑠𝑠𝑑𝑑
𝑟𝑟𝑤𝑤
2𝜋𝜋𝑘𝑘𝑑𝑑 ℎ