Modeling of BHA dynamic behaviors
Juliana Santos
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1
Viatcheslav Priimenko
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1
Junichi Sugiura
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1
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J. Sugiura Schlumberger Stonehouse Technology Center
, Stonehouse, Gloucestershire GL10 35X,
UK
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J. Santos (&) V. Priimenko Laboratory of Petroleum Engineering and Exploration, North Fluminense State University Darcy Ribeiro
, Rod. Amaral Peixoto, km163, av. Brennand, s/n, Imboacica, Macae, RJ 27925-535,
Brazil
Lateral and torsional vibrations of drill strings used in oil well operations are considered. This work presents finite-element-based bottom hole assembly model which addresses natural frequencies determination, and torsional and lateral oscillations on the near vertical well. In terms of the excitations of the developed finite-element model, forces are applied on the bit with time history generated using an Auto-Regressive Moving-Average digital filter. Due to the random pattern of the forces at the drill bit, a stochastic dynamic approach is adopted in investigating the problem. The method of Newmark-beta direct integration is used. It is hoped that this study will enhance the interest in using stochastic dynamic techniques in drilling system analysis and design, as they can capture quite appropriately the inherent uncertainty of the bit forces and, potentially, of other sources. The implementation of torsional degree of freedom during the development of MATLAB code has been considered new attribute regarding previous works based on the same research line. The results from the code developed attained a good agreement with the commercial SPA2000 Advanced 14.0.0 Structural Analysis Program software.
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In the type of deep drilling operations that are commonly
used for hydrocarbon exploration and recovery, there are a
few common designs. These drilling operations typically
make use of drill strings, which are pipes that transmit both
drilling fluid and torque necessary to rotate a drill bit. The
top end of a drilling string typically has the machinery
necessary to pump the drilling fluid, and either a top or kelly
drive to provide torque for the drill bit. Pipe typically
encases the string below, to contain the drilling fluid. The
lower end of the string, consisting of the drill bit, collars and
other components that are collectively known as the bottom
hole assembly (BHA), is the region of many failures
(Macdonald and Bjune 2007). Typical problems that are
encountered include severe stickslip, lateral vibration, hole
enlargement, which induce poor directional control.
Inevitably this problem causes costly drilling equipment failures.
Development of downhole measurement technique with
high frequency resolution has helped appreciating the
significance of these vibrations and their impact on equipment
failure. Providing consistent and reliable time histories, which
are used to study random vibration on drill string, is always of
great importance. These problems include random loading
force and acceleration at the bit and random formation contact
properties. A general vibration perspective of the oil and gas
drilling process can be found in Spanos et al. (2003).
One approach to reduce the cost associated with the
failures is to use BHA dynamic simulation software and
preemptively mitigate the anticipated problems. The ability
to pinpoint the source and effects of torsional, axial and
lateral oscillations enables users to qualify design changes
to the drill-string configuration and optimize parameters,
prior to drilling the well, thus minimizing the traditional
trial and error approach and operator risk.
More recently, nonlinear and time-domain modeling
solutions have become possible (Spanos et al. 2002). This
is critical to achieve the required level of accuracy to make
meaningful contributions to drilling system behavioral
prediction. While the finite-element method has been used
for a number of years in the oilfield, it has been limited to
sections of the drill string or discrete components.
Simulations for the entire drilling system are exceptionally time
consuming and complex both in setup and computational
time. These factors are considered when planning the
length of drilling intervals to be analyzed.
The paper pursues an analysis of the drill-string dynamic
nonlinear problem by resorting to finite-element modeling
of the string and using the Newmark-beta direct integration
and Monte Carlo simulations to capture the salient features
of the problem.
Dynamic modeling of the drill string
A drill string on a drilling rig is primarily composed of drill
pipe, drill collars and drill bit. Its function is to convey
drilling fluid (via the mud pumps) and torque (via the kelly
drive or top drive) to the drill bit. The drill string is hollow
so that drilling fluid can be pumped down through it and
circulated back up the annulus, creating clearance between
the drill string and the casing/open hole (ASME 2011). A
typical drill string can extend over several kilometers.
The BHA is made of a drill bit, which is used to
break up the rock (...truncated)