Summary
North Dakota Bakken oil recovery has increased nearly 100-fold over the last
5 years, driven by technological advancements in hydraulic fracturing and
completion design. For one North Dakota operator with 150 Bakken producing
wells, 22 of the wells have experienced at least one event of severe calcium
carbonate scaling in the pump and production tubing, leading to well failure.
Bakken wells are completed to a vertical depth of approximately 10,000 ft, with
horizontal laterals up to 10,000 ft, and are produced by means of multizone
hydraulic fracturing.
The operator initially conducted a typical scale-prediction study to reduce
well failures and maintain oil production. However, the scale-prediction study
was challenging to perform for these Bakken wells because of the variability of
the composition of the produced water. Attention then turned to the tracking
and analysis of historical field conditions. A "post-mortem" of data collected
from all failed wells because of scale was conducted, considering the failure
type, date, type of hydraulic-fracturing procedure, pump-intake pressure,
scale-inhibitor residual, calcium carbonate scaling index, geographic failure
concentration, production time to failure, and cumulative water production to
failure.
Results showed that 82% of the wells failed during early production (defined
as less than 20,000 bbls of water produced and 2 years' production since first
oil), after which failures became increasingly rare. This correlated with
transient alkalinity spikes in the water analyses attributed to
fracturing-fluid flowback during this critical period. Simulated blending of
fracturing and formation waters demonstrated that this was the most important
period to maintain high scale-inhibitor residuals because of high deposition
potentials.
This paper discusses the various field and laboratory studies conducted in
an effort to understand the problem, the results obtained, and the
implications. Also discussed is the evaluation of two scale inhibitors before
and after laboratory aging in simulated fracturing fluids.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
25 May 2011
- Meeting paper published:
12 April 2011
- Revised manuscript received:
10 January 2012
- Manuscript approved:
24 April 2012
- Published online:
10 October 2012
- Version of record:
26 February 2013
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