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Oilfield Technology
May 2016
lw d/mwd Q&A
gyroMWD is designed to eliminate the need to use wireline
to acquire additional directional data while drilling, removing
the hazards and additional personnel associated with wireline
runs. Furthermore, gyroMWD surveys are obtained in under five
minutes, reducing the amount of non-circulating time compared
to the conventional solution. This lends itself to better wellbore
stability and lessening the likelihood of becoming stuck.
Continuous gyro tool face allows the directional driller
to drill a smoother wellbore, in the correct direction, almost
immediately. Managed dogleg severity in shallow hole results
in less torque and drag when drilling deeper and aids the
smooth running of completions.
Formationevaluation
The definitive wellbore survey is an item that has an impact
on every stage of well construction and operation. While
often accepted as absolute, the reality is that this survey
is merely the most likely location determined by a process
with inherent uncertainty. This uncertainty is accounted for
during the drilling process, however all too often it is not
properly communicated to the departments who inherit the
well once drilled. Failure to account for this uncertainty can
lead to inefficiencies in completions and production, as well
as adding challenges to accurate reservoir modelling. The
cost of reducing positional uncertainty is not great, however
surveying operations typically occur in parallel with the
drilling process and exceeding the needs of the drilling group
is viewed as an unnecessary luxury. There can be significant
value in this reduction of uncertainty for completions and
reservoir, however given that the survey programme is
defined without input from these other groups, this value is
often not realised.
As an example, two-section long lateral wells have become
standard for shale operators over the last several years. These
wells provide the maximum amount of contact area with the
formation pay while minimising well construction costs. As wells
continue to extend farther, their true location is less well known.
Wellbore positional uncertainty is quantified using ellipsoids
of uncertainty (EOU). This uncertainty can lead to wells being
located closer together or farther apart than they appear on
paper.
The EOU associated with a Standard MWD survey at total
depth of an extended reach horizontal well can reach over 400 ft
laterally in each direction. There is a real possibility that the well
Figure 2.
Slidingwith amotor can create rapid changes in curvature that will not be identifiedusing 95 ft surveys (left). Doubleshot better identifies
this hidden tortuosity resulting inamore accuratewellbore survey.
