1. Coal Bed Methane Cementing Best Practices
10/2/2002

2. The Basics
Best Practices for “conventional well” cementing still apply
Optimize Flow Rates
Condition Drilling/Wellbore Fluids
Use Spacers and Flushes
Centralize the Pipe
Pipe Movement
Plan to Control Gas Flow

3. Optimize Flow Rates
As with all wells, the key to successful cementing is removal of wellbore fluids and subsequent replacement with cement
Pump Rates can greatly enhance our ability to remove mud, drilling fluids, coal fines and LCM material.
In many parts of the world CBM wells are drilled w/ clear fluids so “mobilization” of the fluids is not a major problem.
In general, faster rates clean the hole better.

4. Conditioning Drilling/Wellbore Fluids
Clear Drilling/Wellbore Fluids – In general these materials do not build gel strength and are therefore easily removed, the exception is when they are carrying large amounts of fines and LCM. In these scenarios it is best to reduce as much as possible the LCM.

5. Conditioning Drilling/Wellbore Fluids (con’t)
Drilling Muds – These materials will usually build gel strength. The reduction of gel viscosity is highly recommended to enhance removal.
Break Circulation frequently while running pipe
Reduce Pv, Yp as low as possible while still controlling settling
Maintain Gel Strength as low as possible w/ a flat Gel Strength profile
Reduce Mud filtrate loss – thins the filtercake across permeable zones
Horizontal Well applications will require more viscosity to control settling

6. Spacers and Flushes
Must be matched to the specific Drilling Fluid system to insure compatibility
Highly recommended to separate cement slurries from drilling fluids, preventing contamination
Used to enhance drilling fluid removal efficiency
May incorporate Lost Circulation Materials LCM Materials should be removable –
i.e.. acid soluble to reduce permanent formation damage

7. Centralization
Pipe should be centralized to provide for zonal isolation
Well conditions and Geometry govern the type centralizers used

8. Pipe Movement during Cementing Operations
Pipe should be either rotated or reciprocated to enhance the cementing performance
In general either movement will be acceptable. However care must be taken when reciprocating if Lost Circulation or gas or water flows have been observed or if the drill string has shown tendencies toward sticking

9. Gas Control Considerations
Many CBM Projects are drilled under balanced w/ Water, Air, Foam or Mist. Gas Flow Potential can be difficult to measure, but should be accounted for
Short Transition time and Thixotropic cementing systems are recommended
Use of “Gas Generator” additives can also alleviate gas migration

10. CBM Zonal Isolation Challenges
Formation damage
Isolation within producing zones
Cement fallback
Displacement of washouts across coal
High fracture initiation pressures
Loss of cement returns

11. Current Wellbore Configurations
CBM Pay behind Pipe – Conventional
May require Multistage cementing
Inflatable packer technology
Foam Cementing Processes***
Puddle Technique
Top Set
Pay penetrated
All of the above techniques
Pay un-penetrated
Standard cementing techniques

12. Case History Powder River Basin Rocky Mountain USA
Conditions
’ TD, Vertical, 100OF BHST 8 3/4” hole X 7” Casing – Water, Mist or Air drilling fluid, Lost Circulation and cement fallback are common problems, cement to surface req’d
Spacers – Fresh water or reactive
Cement – ppg Thixotropic, accelerated High Early blends, w/ LCM Foamed Cement systems ppg
Pump Rates – 1-2 BPM
Other - reciprocation

13. Case History Raton Basin Rocky Mountain USA
Conditions
’ TD, Vertical, 120OF BHST 7 7/8” hole X 5 1/2” Casing – Water, Mist or Air drilling fluid, Lost Circulation and cement fallback are common problems, cement to surface req’d
Spacers – Fresh water w/ Acid soluble LCM
Cement – ppg Thixotropic, accelerated High Early blends w/ LCM, Gas Migration control Foamed Cement systems ppg
Pump Rates – 3-4 BPM
Other – Centralized, reciprocated

14. Case History Price, Utah Basin Rocky Mountain USA
Conditions
’ TD, Vertical, 110OF BHST 7 7/8” hole X 5 1/2” Casing – Mist or Air drilling fluid, Then loaded w/ mud to log, Lost Circulation and cement fallback are common problems, cement to surface not req’d. Generally raise cement 500 ft above top coal or back to surface if no loss.
Spacers – Fresh water
Cement – ppg Thixotropic, accelerated High Early blends w/ LCM
Pump Rates – 3-5 BPM
Other – Centralized, Generally not reciprocated

15. Case History Black Warrior Basin Southeast USA
Conditions
’ TD, Vertical, 130OF BHST 7 7/8” hole X 5 1/2” Casing – Water, Mist or Air drilling fluid, Lost Circulation and cement fallback are common problems, cement to surface req’d
Spacers – Gelled Fresh water w/ LCM and Poz/cement Scavenger slurries
Cement – ppg Thixotropic, accelerated Poz/Cement blends w/ LCM, extenders Foamed Cement systems
Pump Rates – 3-4 BPM
Other – Centralized, reciprocated

16. Case History Cotton Plant Basin Southeast USA
Conditions
’ TD, Vertical, 135F BHST 7 7/8” hole X 5 1/2” Casing – Water, Mist or Air drilling fluid, Lost Circulation and cement fallback are common problems, cement to surface req’d
Spacers – Reactive and gelled water
Cement – ppg Thixotropic, accelerated Poz/Cement blends w/ LCM, extenders
Pump Rates – 3-4 BPM
Other – Centralized, reciprocated

17. Case History Moomba Basin Australia
Conditions
4000’ TD, Vertical, 140F BHST 7 7/8” hole X 5 1/2” Casing – Water-base mud drilling fluid, cement to 2000’, Gas migration is common problem
Spacers – Treated KCL water
Cement – Foamed Premium Cement 15.8 ppg foamed to 10.5 ppg for a lead and 13.5 ppg across the coal zone ppg – Some Multi Stage processes w/extended, thixotropic Poz/cement blends
Pump Rates – 3-4 BPM (Fluid)
Other – Centralized

18. Cementing Process Conclusions
Well Conditions Drive Cementing Processes
Use Good Cementing Practices for best Results
Foam Cementing Process are Optimum where available
Thixotropic Slurries are also Preferable
Use care to prevent loss of Materials into potentially productive intervals
Use “removable” products where losses are inevitable