3. Productivity and injectivity both depend primarily on near wellbore pressure
drop called SKIN. A positive skin decreases productivity while a negative skin
increases productivity. Skin is a function of formation damage and perforation
parameters which are
-perforation spacing (inverse of shot density)
-diameter or radius of perforation
-length or depth of perforation
-shot phasing or angular distribution of shots
4. Research has shown that these parameters are controllable
parameters and if optimized properly can lead to a very low value of
skin and optimum productivity.
5. CASE STUDY
Given a well with the following parameters
• hp=perforation spacing 0.25ft
• h=vertical length of perforation interval 60.0ft
• Ht=formation thickness 100.0ft
• Ѳd=well deviation 90.0ft
• Ѳp=shot phasing 90.0˚
• Kdd=formation drilling damaged zone permeability 40.0md
• Kh=formation horizontal permeability 100.0md
• Kpd=perforation damage zone permeability 20.0md
• Ldd=length of drilling damage zone permeability 0.5ft
• rw= well radius 0.3646 ft
• lp= Length of perforation 1.0ft
• rp=perforation radius 0.0208ft
6. Rpd=perforation damage zone radius 0.0625ft
Y=distance between top of sand and open interval 20ft
Pe=reservoir pressure 5800 psia
Bottomhole flowing pressure 4500 psia
Oil viscosity 1.2cp
Oil formation volume factor 1.2RB/STB
Reservoir radius 600 ft
Vertical permeability 20md
8. Using the different calculations and formulas the results were
SKIN = 2.69
FLOW RATE = 6333.517 bbl/day
At this parameters of perforation, the well produced a POSITIVE SKIN.
But if these parameters are optimized we are sure to get a skin value of 0 or
negative which will in turn increase productivity.
9. OPTIMIZATION
The general aim of optimization is to get the best controllable parameters that
will give the optimum production from the reservoir. Our optimization process
will be based on this quotation from Brooks. J. E et al (1996)
“Increased shot densities reduces perforation skins. If formations are
laminated or have high anisotropy (significantly different vertical and
horizontal permeability) shot density needs to be high. Also high shot
density is effective if deep penetration is not possible.”
11. OPTIMIZATION FOR LENGTH
Length was increased from original so as to increase depth of perforation beyond
damaged zone and it was varied at different shot phasing angles
Table 1: Table of values for skin against length for different angles
skin 2.689 1.189 0.444 -0.033 -0.377 -0.645 -0.862
lp 900 1 1.5 2 2.5 3 3.5 4
skin 2.85 1.29 0.51 0.01 -0.36 -0.64 -0.87
lp450 1 1.5 2 2.5 3 3.5 4
skin 4.17 2.48 1.67 1.16 0.08 0.52 0.3
lp00 1 1.5 2 2.5 3 3.5 4
skin 2.79 1.25 0.48 -0.01 -0.37 -0.64 -0.87
lp600 1 1.5 2 2.5 3 3.5 4
skin 2.8 1.25 0.5 0.02 -0.32 -0.59 -0.8
lp1200 1 1.5 2 2.5 3 3.5 4
skin 2.9 1.34 0.61 0.15 -0.18 -0.43 -0.63
lp1800 1 1.5 2 2.5 3 3.5 4
12. Figure 1: Graph of skin against length for different angles
-2 -1 0 1 2 3 4 5
1
1.5
2
2.5
3
3.5
4
Skin (Sp)
lengthofperforation(Lp)(ft)
skin vs length 180 skin vs length 120 skin vs length 60 skin vs length 0 skin vs length 45 skin vs length 90
13. OPTIMIZATION FOR RADIUS
Radius was increased from original so as to increase hole size so as to get
adequate flow area and it was varied at different shot phasing angles
Table 2 : Table of values for skin against radius for different angles
skin 2.69 1.39 0.62 0.09 -0.31 -1.42 -1.92 -2.1 -1.94
rp900 0.0208 0.04 0.06 0.08 0.1 0.2 0.3 0.4 0.5
skin 2.85 1.57 0.79 0.26 -0.15 -1.27 -1.75 -1.9 -1.7
rp450 0.0208 0.04 0.06 0.08 0.1 0.2 0.3 0.4 0.5
skin 4.17 2.92 2.21 1.74 1.39 0.37 -0.13 -0.17 1.42
rp00 0.0208 0.04 0.06 0.08 0.1 0.2 0.3 0.4 0.5
skin 2.79 1.42 0.62 0.07 -0.33 -1.48 -2.01 -2.22 -2.14
rp600 0.0208 0.04 0.06 0.08 0.1 0.2 0.3 0.4 0.5
skin 2.8 1.49 0.71 0.18 -0.2 -1.32 -1.84 -2.03 -1.92
rp1200 0.0208 0.04 0.06 0.08 0.1 0.2 0.3 0.4 0.5
skin 2.9 1.56 0.8 0.29 -0.09 -1.15 -1.63 -1.68 -0.95
rp1800 0.0208 0.04 0.06 0.08 0.1 0.2 0.3 0.4 0.5
14. Figure 2: Graph of skin against Radius for different angles
-3
-2
-1
0
1
2
3
4
5
0 0.1 0.2 0.3 0.4 0.5 0.6
Skin(Sp)
Radius of Perforation (rperf) (ft)
skin vs rp 90 skin vs rp 45 skin vs rp 0 skin vs rp 60 skin vs rp 120 skin vs rp 180
15. OPTIMIZATION FOR PERFORATION SPACING
Perforation spacing was decreased from original so as to increase shot density
because shot density is the inverse of perforation spacing so as to produce wells at
lower pressure differentials and it was varied at different shot phasing angles.
Table 3: Table of values for skin against perforation spacing for different angles
skin 1.43 1.5 1.56 1.63 1.98 2.33 2.69
hp90 0.07 0.08 0.09 0.1 0.15 0.2 0.25
skin 1.39 1.48 1.57 1.65 2.07 2.47 2.85
hp45 0.07 0.08 0.09 0.1 0.15 0.2 0.25
skin 3.51 3.52 3.54 3.56 3.7 3.91 4.17
hp0 0.07 0.08 0.09 0.1 0.15 0.2 0.25
skin 1.36 1.43 1.51 1.59 1.99 2.39 2.79
hp60 0.07 0.08 0.09 0.1 0.15 0.2 0.25
skin 1.56 1.61 1.67 1.73 2.01 2.43 2.8
hp120 0.07 0.08 0.09 0.1 0.15 0.2 0.25
skin 1.85 1.89 1.92 1.97 2.23 2.53 2.9
hp180 0.07 0.08 0.09 0.1 0.15 0.2 0.25
16. Figure 3: Graph of skin against perforation spacing for different angles
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
0.07
0.08
0.09
0.1
0.15
0.2
0.25
Skin (Sp)
heightofPerforation(hp)
skin vs hp 180 skin vs hp 120 skin vs hp 60 skin vs hp 0 skin vs hp 45 skin vs hp 90
17. • Looking at all the graphs it is clear that a shot phasing of
600 is the best angle for the lowest possible skin for all
parameters , as noted an increase in length will keep
reducing the skin so making reference to statement “*” we
decided to keep length of perforation at 4ft.
• Also radius was kept at a reasonable hole size of 0.15ft
due the the angular distribution of the shots.
• Also making reference to the statement by BROOKS and
the 600 angular distribution, the perforation spacing will be
kept at 0.0837ft (which gives a shot density of 12spf)
18. Therefore optimized parameters are
-Shot phasing 600
-Length of perforation 4ft
-Perforation spacing 0.083ft
-Radius of perforation 0.15ft
With these parameters skin is reduced to -1.91 (negative skin) and flowrate is
increased to 11632.25bbl/day
19. REFERENCES
1. Brooks. J. E, Behrman .L, Smith. P et al. “Perforating Practices that optimize productivity”.
Rosharon, Texas. BP Amoco, Houston, Texas. 1996.
