Drop-off Section
For the drop-off portion of the hole, the forces acting on the unit section of the pipe are presented in Figs. 4.6 and 4.7. At equilibrium, the differential equation is:
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Fig. 4.6 : Direction of the normal force. Fn. in a dropoff section. (After Maidla. 1987). |
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Fig. 4. 7: Forces acting on a small casing element within the dropoff section. |
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Fig. 4.8 : Vertical and plan view of a typical deviated well. |
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VERTICAL DEPTH |
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TRIHEDRON i?: Tangent Unit Vector j?: Principal Normal Unit Vector [?: Binomial Unit Vector |
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Fig. 4.9 : Force acting on a small element within the buildup section. (After Maidla. 1987.) |
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EAST DEPARTURE |
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SOUTH DEPARTURE |
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VERTICAL DEPTH |
dF
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(4.37; |
—= fb(WRsma + Fa) + WR cos a da
When Eq. 4.37 is solved for the pulling out operation, the tensional load is given by:
Fa7 = I<D Fai — Y-~p ^ ~~ 1 ^S’n K° S’n 01 ‘
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(4.38) |
+ 2 fb (cos a2 — I’d cos Qj )] and similarly for the running in operation:
, WR r.
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F — A do |
I<D Fai — T—J—>2 [(fb — 1 )(sin q2 — Ad sin «j) ‘ J b
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(4.39) |
■ 2 fb (cos a2 — KD cos Qi)]
where:
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(4.40) |
KD = eh(°2-a l)