STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

604 Drilling and Well Completions
Analysis of the cycle of operation shows that for any one hole the sum of
operations 1 and 2 is equal to one round trip; the sum of operations 5 is equal
to one-half a round trip; and the sum of operations 3, 4, and 6 may, and in
this case does, equal another one-half round trip, thereby making the work of
drilling the hole equivalent to two round trips to bottom, and the relationship
can be expressed as
Tc 2(T, - T,) (4-29)
where Tc = ton-mile coring
T, = ton-miles for one round trip at depth D, (depth where coring started
after going in hole, in feet)
T, = ton-miles for one round trip at depth D, (depth where coring
stopped before coming out of hole, in feet)
Setting Casing Operations. The calculation of the ton-miles for the operation
of setting casing should be determined as in round-trip operations as for drill
pipe, but with the effective weight of the casing being used, and with the result
being multiplied by one-half, since setting casing is a one-way (one-half roundtrip)
operation. Ton-miles for setting casing can be determined from
T, = D(L, + DXW, 1 +
10,560,000
(4-30)
Since no excess weight for drill collars need be considered, Equation 430 becomes
D(L, + D)(W, ) +
DM
T, = (4-31)
10,560,000 2,640,000 (i)
where TI = ton-miles setting casing
L,, = length of joint of casing in ft
Wcm = effective weight per foot of casing in lb/ft
The effective weight per foot of casing Wm may be estimated from data given
on Figure 4-78 for drill pipe (using the approximate Ib/ft), or calculated as
Wcm = Wca (1 - 0.015B) (4-32)
where Wc. is weight per foot of casing in air in Ib/ft
B is weight of drilling fluid from Figure 4-79 or Figure 4-80 in lb/gal
Short Trip Operations. The ton-miles of work performed in short trip operations,
as for drilling and coring operations, is also expressed in terms of round
trips. Analysis shows that the ton-miles of work done in making a short trip is
equal to the difference in round trip ton-miles for the two depths in question.
This can be expressed as
T, = T, - T5
where TsT = ton-miles for short trip
T, = ton-miles for one round trip at depth D, (shallower depth)
T, = ton-miles for one round trip at depth D, (deeper depth)
(4-33)