2. Schlumberger / Client Confidential
2015 International Perforating Symposium Europe
IPSE-15-28
Laboratory Assessment of Perforation Tunnel Stability and Sanding Propensity, Using Reservoir Wellcore
Schlumberger / Client Confidential
Graham Fraser, Tullow Oil
Chris Chow, ProDuce Consulting
Brenden Grove, Duncan Sanford, Schlumberger

3. Schlumberger / Client Confidential
Agenda
Field development objectives
Technical challenges & risks
Laboratory program
Program design
Results
Conclusions
Implications to field development
Schlumberger / Client Confidential
IPSE-15-28

4. Field Development Objectives
Deepwater asset, offshore West Africa
Completion strategy = cased & perforated
~Vertical wells
Large HSD guns, DP charges
No mechanical sand control (region where SC is common)
Goals = Maximize productivity & ultimate recovery
Critical to ensure wells will produce:
Sand-free
With low skin
Reliably (including depletion, water encroachment, etc.)
Also consider water injectors (shut-in, stimulation, etc.)
Schlumberger / Client Confidential

5. Technical Challenges & Risks
Tunnel stability and sand production
During perforating:
Mechanical shock loading during jet penetration
Wellbore dynamics & large drag forces in first ~second
During production:
At expected field rates
At depletion stresses
With watercut
Address both single-perf behavior and system effects
Schlumberger / Client Confidential

6. Schlumberger / Client Confidential
Laboratory Program
Launched to address & quantify risks
Perforate & flow, using actual reservoir wellcore
Downhole stress, dynamics, and flow conditions
2 phase program:
Phase I: 3 tests (tunnel stability, sand production, injector shut-in)
Phase II: 3 tests (quantify long-term sand production, to ensure within facilities constraints)
Schlumberger / Client Confidential

7. Perforating Laboratory – Brief Introduction
Field
Wellbore
In-situ stress
Reservoir
Rock type, strength,
Porosity, permeability
Etc.
Pore fluid type & pressure
Perforating gun system
Casing(s)
Cement
Schlumberger / Client Confidential
Laboratory
Reservoir
Pore fluid pressure
Wellbore
Confining Stress
Perforating Objective: establish a highly productive flowpath between reservoir and wellbore

8. Test Program Design (1/2)
Use reservoir wellcore
Trim/square ends
Stack similar strength pieces to assemble each target
Encapsulate for load transmission
Stress & perforate at downhole conditions
Schlumberger / Client Confidential

9. Test Program Design (2/2)
Production flow at > field rates
Simulate depletion
Increase stress
Introduce water cut
Monitor tunnel stability and sand production real-time
Rate
Stress
Flow & Diagnostics Schematic
Schlumberger / Client Confidential
Water Cut

10. Test Program Execution & Results – Phase I
3 tests
Tests 1 & 2 – 39g charge (12SPF)
Test 3 – 20g charge (27SPF)
Formation properties:
Turonian sandstone
UCS ~ 2, ,400psi
Permeability ~ 200mD
Porosity ~ 18%
All tests shot on static balanced conditions
Dynamic underbalance ranging from 2,000-2,400psi
Static effective stress = 3,200psi
Dynamic effective stress (DES) ~ 5,200 – 5,600psi
Test #3 (as example) summarized on following slides
Schlumberger / Client Confidential

11. Phase I: Test #3 Build up core assembly Displace crude with OMS
Perforate
Production flow (multiple rates) – establish stable PI
Q, dP vs. time
Q vs dP

12. Water hammer transient
Phase I: Test #3
5. Lifecycle sanding risk
Stage 3: water cut
Stage 2: stress
Stage 1: rate
6. Water hammer (injector shut-in)
3 cycles conducted
(1 shown)
Flow: Q,dP vs time
Flow: Q vs dP
Water hammer transient
7. Injector stimulation treatment
Acid Injected at T~145F
OMS post-flush
Solvent pre-flush

13. Phase I: Test #3 – Sand Detection & Collection
Equipment & Set-up
Results
Real-time Sand Indicator
Density spike in downstream flowmeter: early time sanding event
Physical Sand Capture
Blue dots: sand mass collected (grams)

14. Phase I: Test #3 – Tunnel Integrity
Screenshot of video during high rate flow
Casing hole viewed from wellbore
View from ~10-15” inside tunnel
Stable Intact Tunnel Confirmed

15. Test Program Execution & Results – Phase II
3 tests
Test 1 – 39g charge (12SPF)
Test 2 – 20g charge (27SPF)
Test 3 – drilled hole
Reservoir wellcore
Extended field rates, to establish sanding concentrations (pptb – lb sand / thousand bbl oil)
Depletion stress
Watercut (10%, 20%, 30%)
Test #1 (as example) summarized on following slides
Schlumberger / Client Confidential

16. Phase II: Test #1 Build up core assembly Displace crude with OMS
Perforate
Sanding flow (extended duration) – rate, dP, watercut, density
2.8 lpm
Oil flow
Cleanup flow
(2-3 lpm)
1.4lpm
oil flow
1.4 lpm
Oil+watercut

17. Phase II: Test #1
10% watercut; sand production equivalent to < 5 pptb & decreasing
4. Sanding flow (extended duration) – rate, sand collection
1x-2x field rates: sand production equivalent to < 2 pptb
Cleanup flow
(2-3 lpm)
1.4lpm
oil flow
2.8 lpm
Oil flow
1.4 lpm
Oil+watercut

18. Phase II: Test #1 – Tunnel Integrity
Stable Intact Tunnel Confirmed

19. Schlumberger / Client Confidential
Summary & Conclusions
Laboratory program conducted
to assess sanding risk during and after perforating
Realistic downhole environment
reservoir cores, field charges, stress, flow
Life-of-well scenarios replicated
Scaled rates, depletion stress, water cut
Findings:
Minimal risk of tunnel collapse and catastrophic sanding
Minimal sand produced over extended flow durations
<1-2 pptb at twice nominal field rate
<5 pptb at field rates with watercut
Conclusion: Cased & Perforated is a viable option
Schlumberger / Client Confidential