Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Boundary Control and Estimation for Under-Balanced Drilling with
  Uncertain Reservoir Parameters   In under-balanced drilling, the bottom-hole pressure is kept below pore
pressure, causing pressure dependent influx of reservoir gas into the wellbore
that makes the system unstable at low drawdowns. In this paper we propose a
feedback controller which stabilizes the system around an arbitrary pressure
setpoint, using only topside measurement, and assuming unknown reservoir
parameters. A particular challenge with this problem is the distributed and
highly nonlinear nature of the system dynamics. As the control model we use the
``reduced Drift Flux Model'' which models gas-liquid flow as a nonlinear
transport equation with a non-local integral source term. The observer
estimates the distributed gas concentration, downhole pressure and reservoir
parameters by solving the system dynamics backwards relative to how the gas
rises in the well. The control inputs are then constructed by designing target
states over the next sampling period and again solving reversed dynamics to
obtain the required topside pressures. The resulting controller is implemented
with a 2 minute zero-order hold to accommodate the actuation limitation
situation on an actual drilling rig. The results are illustrated in simulations
with a industry standard Drift Flux formulation as the plant model.

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The categories of this paper are: atom-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: funct-an
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The categories of this paper are: adap-org
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The categories of this paper are: q-alg
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The categories of this paper are: chao-dyn
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ph
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The categories of this paper are: eess
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
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The categories of this paper are: econ
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The categories of this paper are: hep-th
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The categories of this paper are: q-fin
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The categories of this paper are: chem-ph
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The categories of this paper are: supr-con