Reveal the Cause of Downhole Restrictions by Means of Knowledge Engineering
Stuck pipe is an example of an unwanted problem that causes high NPT and seems
to occur again and again. As 50 % of all stuck pipe incidents occur during tripping,
increased knowledge about how to recognize progressing downhole problems are
needed. Early warnings of stuck pipe are HKL restrictions, and early warnings of
HKL restrictions are symptoms. If the symptoms seen at surface can be related
to a HKL restriction type, preventing actions can be initiated at an early stage,
and stuck pipe can be avoided.
Four main causes of HKL restrictions have been analysed and related to symptoms
that can be recognized at the surface. The main causes are accumulating cuttings,
mechanically unstable wellbore, chemically unstable wellbore and local dogleg. By
means of the Knowledge Model, relationships between the symptoms and the main
causes were determined. The strength of the relation between each symptom and
the restriction cause was found and proved diversity among the main symptoms
of each restriction cause.
21 cases of HKL restrictions were found from drilling reports and RTDD obtained
from Statoil. Symptoms interpreted from the drilling reports were used as input
for the Knowledge Model which revealed the main cause of the restriction. The
model proved that 14 of the 21 restriction cases were caused by the error Reactive
The HKL signature of the 21 cases was interpreted and related to the restriction
causes. The interpretation showed that the signature of cuttings accumulating can
be separated from the signatures of mechanically instability.
Five restriction events were analysed using the Knowledge Model. The main cause
of the restriction events were found proving the Knowledge Models ability to de-
termine the restriction cause of downhole problems. The analysis proved that
Reactive Formation was the most frequent error to cause HKL restrictions, with
explanatory strength of 48 % as the highest in average.
Place, publisher, year, edition, pages
Institutt for petroleumsteknologi og anvendt geofysikk , 2013. , 126 p.
IdentifiersURN: urn:nbn:no:ntnu:diva-22907Local ID: ntnudaim:9082OAI: oai:DiVA.org:ntnu-22907DiVA: diva2:655057
Skalle, Pål, Førsteamanuensis