26-02-2013, 10:34 AM
Underbalanced Drilling
Underbalanced.PDF (Size: 989.43 KB / Downloads: 87)
Introduction
• Why drill Underbalanced - theory and results
• Techniques for achieving Underbalance
• Surface considerations
• Downhole technology
• Lessons learned
Why Drill Underbalanced
• Production
– Minimize formation damage
– Improve initial and long term production rates
• Improve ROP
• Reduce payback time by initiating production
earlier
• Eliminate or reduce expensive stimulation and
clean up procedures
• Cost – Short term pain for long term gain
Well Selection Criteria
• Formation Pressure - How depleted, depth?
• Reservoir Properties - Permeability/porosity, structure...
• Expected Production Rate - Must handle produced fluids
on surface while drilling
• Rock Strength - Will hole collapse?
• Produced fluids
- Gas vs. Oil
- Chemistry - CO2/H2S
Pros and Cons of Each Technique
• Two phase flow
– Interferes with conventional MWD
– Suitable for re-entries
• Parasite string
– Provides additional injection volume with
two phase flow
– Limited to installation at less than 50°
– Can be damaged when installing
– Provides external conduit to surface-safety risk
Software
• Allows planning and modelling of potential scenarios
• Inputs: geometries, reservoir pressure, fluid
descriptions, temperature
• Models effects of:
– Reservoir influx
– Surface injection rate
– Surface pressure
– Compressive/non-compressive fluids
• Calibrated with Pressure-While-Drilling sub to actual
conditions
Surface Monitoring System
Advanced, Proven Sensors
• Pressure/temperature: casing annulus, standpipe,
N2 injection line, and separator
•Venturi flow meters (N2 injection rate and flare line)
and Mass flow meters (fluid flow rate and density)
•H2S sensors (if required)
• Infrared Continuous Gas analyzer (total hydrocarbon %)
• Ultrasonic Tank Level sensors
Conclusions
• SSDS have drilled over 300 underbalanced wells
in Canada
• Three different techniques have been developed
• ROP improvements of up to 10x, average
of 2-4x realized
• Production rate improvements of 10x, average
of 3x realized
• SSDS is continuing development of techniques
and equipment