Author(s): S. Smith & V. Rasouli
Drilling deviated and horizontal wells is commonly used in the oil and gas
industry for different purposes.
Particularly in unconventional reservoirs such as
gas shales or tight formations, horizontal wellbores provide a larger exposure to
the formation, which enhances the production from such tight formations.
increase in torque and drag forces downhole in deviated borehole trajectories is
one of the technical challenges that needs to be carefully studied during the
There have been a number of different approaches to the way that
torque and drag has been modelled in the industry.
These include the soft string
and stiff string approach and accounting for the effects of viscous fluid flow.
soft string model treats the drill string as a cable and assumes that it lies against
the low side of the wellbore, meaning that the stiffness of the drill string is not
On the other hand, stiff string models take into account the
stiffness and bending moment in the drill string and the radial clearance in the
Fluid flow during drilling results in the loss of the normal component
of fluid pressure on the drill string as the flowing condition becomes dynamic.
There is also an additional tangential component caused by viscous drag on the
drill string due to the fluid flow.
In this paper we will present the findings of a study aimed at determining the
most appropriate type of torque and drag modelling approach that should be
applied for Norwest Energy’s Redhill South-1 well and future wells of similar
Redhill South-1 was directionally drilled to test the gas potential of the
Permian sands in a fault dependent structural closure.
Both soft and stiff string
approaches will be studied.
The necessity to account for viscous drag effects will
also be analysed.
torque and drag, soft string, stiff string, viscous fluid flow.
Size: 538 kb
Paper DOI: 10.2495/PMR120091
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