Summary
Drilling on top of the mesa in the Piceance basin presents a significant
lost-circulation and stuck-pipe challenge to operators wanting to exploit the
gas reserves in the area. Operators have experienced losses that exceed 4,000
bbl of mud when the intermediate section is drilled using conventional
techniques. This is because of a combination of natural fractures and weak
rock. Various strategies have been deployed to tackle the problems, including
underbalanced-drilling (UBD) operations and directional casing while drilling.
A new technique implemented by an operator in the Piceance basin is described
in this paper; it involves acquiring real-time equivalent-circulating-density
(ECD) data and control of mud weight in the annulus by use of direct air
injection through a parasite aerating string (PAS).
During the development stages of this new process, a real-time
annular-pressure sensor was run in the bottomhole assembly (BHA) to gather
diagnostic data. Analysis of the data shows conventional drilling practices
often yield up to 3 lbm/gal variation in ECD exposed to the formation. The
analysis also suggests that there is a fracture-reopening gradient of
approximately 8.3 lbm/gal and that there are significant ECD variations during
connections. The new strategy shows that these wells can be drilled with an ECD
in the range of 5-7 lbm/gal using conventional water-based-mud systems. This
strategy allows wells with a narrow mud-weight window to be drilled without
significant mud loss to the formation. This approach avoids the use of complex
multiphase models, and the downhole ECD can be displayed on the driller's
console in real time from the data measured by the annular-pressure sensor and
sent through the mud-pulse-telemetry measurement-while-drilling (MWD) tool.
Alternatively, if an annular-pressure sensor is not included in the BHA, the
downhole ECD can still be estimated accurately by use of a simple spreadsheet
calculation (Scott 2009). This gives a measure of flexibility in deploying the
technique to the wellsite. Expert personnel were used in the initial diagnostic
stages to establish the procedures and validate the effectiveness of the
technique. After that, they will not normally be required at the wellsite to
manage the process in subsequent wells because the ECD data from the
annular-pressure sensor can be understood by the driller, and the alternative
spreadsheet solution, if used, can also be managed by the wellsite supervisor
to calculate a reliable downhole ECD measurement. The ECD data enable the
driller to control and keep the annular pressure within recommended limits,
ensuring that lost circulation risk is reduced and wellbore stability is
maintained.
The alternative approach of using conventional well-design techniques would
result in multiple casing strings and in cost overruns, while more-advanced
techniques such as directional casing while drilling and UBD would require
specialized equipment and crews. This new technique uses existing and common
drilling technologies along with new software tools for geomechanics analysis
and drilling surveillance to achieve a fit-for-purpose solution. This paper
presents a risk-management technique using today's conventional technologies to
successfully mitigate lost circulation risk in the Piceance basin.
© 2010. Society of Petroleum Engineers
View full textPDF
(
8,483 KB
)
History
- Original manuscript received:
8 December 2008
- Meeting paper published:
17 March 2009
- Revised manuscript received:
20 May 2010
- Manuscript approved:
30 May 2010
- Published online:
18 November 2010
- Version of record:
16 December 2010
View Cart
