TWIN OIL-WELL DRILLING IN THE USSR

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP80-00809A000700230097-8
• Release Decision: RIPPUB
• Original Classification: U
• Document Page Count: 7
• Document Creation Date: December 22, 2016
• Document Release Date: July 13, 2011
• Sequence Number: 97
• Publication Date: April 18, 1955
• Content Type: REPORT

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STAT
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Some 300,000 meters have been drilled and 170 wells finished by the twin-
well. method since it was first initiated in 1950. The method has been mainly
employed in the Azneft'. Dagoeft', and Kuybyshevneft' associations. In the
latter association, the volume of twin-well drilling has been increasing con-
siderably each year.
Initiated in 1950 with the use of a centering apparatus, the method was
discontinued in Azneft' after the rigs began to break down, but was resumed in
1952 with new equipment (special rig, rotors, and transferable crown block, the
latte" replacing the centering device). The volume or such drilling in Azneft'
has increased considerably in 1953, and the indexes for all completed wells
have been satisfactory-. However, the volume in Dagneft' has been declining
lately.
The yrincipal advantages of twin-well drilling over single-well, or sin.- -
bore, are that two holes are hored at the same time, drillisG; time is reduced,
and less equipment is needed.
In twin-well drilling, the running-in and lifting operations are performed
simultaneously, the lifting of tools from one hole being tied in with the running-
in of tools into the other hole. The preparatory and ancillary work for one
bore is almost completely tied in with other work for the second bore. Waiting
for the cement to harden in one bore is tied in with other work in the second
bore. The rig erecting and assembly work is reduced considerably, and the work
involved in moving the rig is cut in half. The investment of capital and the
use of metal in twin-well drillir are reduced considerably.
In late March 1953, the economic section of the Technical Council of the
Ministry of Petroleum Industry USSR considered the effectiveness of twin-well
drilling and, based upon its study of the method in the Kuybyshevneft' and
Dagneft' associations up to September 1952, decided that twin-well drilling
would thereafter replace single-shaft directional drilling. In addition, the
economic section found that, by employing twin-well instead of vertical drilling
in settled contour conditions, it would be possible to increase the technical
and economic indexes for commercial speeds of drilling 10-15 percent and that
well construction costs could be cut by 6-8 percent.
The estimates which have been proven for conditions in Tatneft' Association
show that if the speed of drilling is stepped up 15 percent in the first 2 years
after twin-well drilling is initiated, and then increased in subsequent years to
20 percent, as compared with single well drilling, the well-month exploitation
should increase between 14 and 18 percent, inasmuch as 25 percent more wells
would be finished with one machine. (See Table 1, below.)
Considering the balance of time involved during 1. 1/2 years in drilling
exploitational, single-bore directional wells, the conversion to twin-well
drilling with a single unit of drilling equipment has made possible the attain-
ment of a considerable increase in commercial and continuous [tsiklovykh]
speeds of the depth driven.
Table 2 (below) provides information on the experience of twin-well drilling
in Stavropol'neft' Trust of Azneft' Association. In this region it was theoret-
ically possible to calculate the average saving of time shown in the table for
a 1,300-meter operating well driven through rock-bearing strata.
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The actual technical and economic indexes obtained in twin-well drilling
in Stavropol'neft' Trust and other rayons indicate some definite achievement.
However, it must be concluded that the existing potential of twin-well drilling
is not being used satisfactorily. There are enormous reserves in twin-well
drilling which, if realized, could considerably increase the commercial and
ccrtinuous (mechanical?] drilling speeds and thereby cut well construction
ccsts.
Table 3 compares the actual and potential technical-economic indexes
(under comparable conditions) for wells drilled in Stavropol'neft' Trust
under the existing organization and technological conditions for drilling
directional wells.
When the commercial speeds of the better-drilled wells in Stavropol'neft'
Trust (tinder comparable conditions) are compared, the actual speed ratio weighs
heavily in favor of twin-well drilling. This can be seen in Table 4.
To show the further effect of twin-well drilling, the principal indexes
of the single-bore and twin-bore methods are compared on the basis of 3 years'
experience in Dagestan. This can be seen in Tables 5 and 6. The comparison
was made for commercial and mechanical speeds and for the time balance in
drilling.
The wells drilled are divided into three groups, depending on the depth.
The "A" group includes wells 890-950 meters deep; the "B" group, wells 1,100-
1,250 meters deep; and the "C" group, wells 1,500 and more meters deep.
Neither exploitational, single-bore, double-col um: structure [dvvkhkol.onykh
konstruktsiy] wells, nor explorator^ wells are included in the comparison, inas-
much as the speed of drilling is low in both cases. Nor does the comparison in-
clude wells which have been rebored and involve a large percentage of unproduc-
tivity, or those wells which are not at least as deep as other single-bore wells.
Table 5 shows that the commercial and mechanical speeds are higher in i:ne
case of twin wells than in single-bore wells, but the drive for depth is some-
what less.
All the wells hove been drilled under the same conditions. The pressure
on the bit varied between 5 and 7 tons in the upper part and between 8 and 10
tons in the lower po't. The pumps o4erated at 32-36 liters per second. In
the cane of cone wells, both single and twin, the pressure on the bit was in-
creased to 12-15 tons, while the water feed was increased to 40-42 liters per
second. The mud solution was the same for all wells drilled, inasmuch as they
were drilled under the same geological conditions. The specific weight of the
mud solution varied between 1.25 and 1.32 grams per cubic centimeter. Viscosity
varied between 40 and 50 seconds, while the amount of sand in the solution
varied between zero and 2 percent.
As can be seen from Table 6, it takes less time to drill one meter of
twin well than one meter of single-bore well. For instance, 1.56 hours are
required to drill one meter of single-bore well of the B group, as compared
with 1.15 hours in the case of a twin well. To drill one meter of the C group,
an average of 2.02 hours are required for single bore wells as compared to 1.74
hours for twin wells.
T`,e nroductive time per meter drilled varies in the case of both single
and twin "ohs, depending on the depth. For instance, if no emergencies, idle-
ness, _ repairs are involved, one meter of twin well in the B group can be
drilled in .86 hour, compared with 1.09 hours required for the same distance
of single-bore well. In the C group, one meter of twin well can be drilled in
1.3 hours, whereas the same distance of single bore well required 1.39 hours.
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The technological process of running-in and pulling the tools is different
in twin-well drilling from that of single-bore drilling. In the latter, the
string of pipe must be pulled to replace the bit or turbo-drill pipe, whereas
in twin-well drilling the pipe is pulled in one bore at the same time it is
lowered into the adjacent bore.
In analyzing the unproductive time, the instruction of the Ministry of
Petroleum Industry USSR relating to idleness has been taken into consideration.
This time includes all idle periods, such as repair time, complications, and
elimination of emergencies. The loss of time is considerably higher in single-
bore than in twin-well drilling. It has been found from the experience of
drillers in Dagestan that, under normal twin-well drilling operations, wells
up to 1,700-1,800 meters deep can be drilled without any additional repair
work being required. It follows, from the technological process of twin-well
drilling itself, that the idle time charged to the well declines when compared
to single-bore drilling.
In Izberbash, for instance, the idleness averaged .16 hour per driven
meter in twin-wells of the B group (1,100-1,250 meters deep). In the case of
single-bore wells of this group, the idleness has risen to .18 hour for the
same depth. In the C group (1,500 or more meters deep), the idleness per meter
amounted to .19 hour in twin wells and .29 hour in single-bore wells.
There is also a difference in time required to eliminate emergencies in
the two types of wells. An average .17 hour is required per driven meter of
single-bore wells of the B group. This time compares with .328 (less than
13/100) hour for the same distance in the case of twin-wells. In the C group,
.233 (over 23/100) hour is required in single-bore wells, as compared with .15
hour in twin wells. These comparisons can be seen in Table 6.
Table 1. Well-Months of Exploitation During Drilling
of Twin and Single Wells (Average per Machine)
1st 2nd 3rd 4th
year year year year
Single-Bore 3 4 4 5
Twin 11 4 6 6
Well-days of exploitation,
including wells converted
Single-bore
Twin
Increase in well-months
of exploitation in
estimating for one
machine per year of
drilling
495 1,848 3,3214 4,960
464 2,120 3,834 5,862
Single-bore
Twin
Percent increase
6oo 660 726 798
690 760 870 958
15 15 20 20
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STAT
Type of Work
Involved
;d:c',?nr.ical drilling
Ric.r.i. g-in, pul.li-
Jo .ink tools
.rc -1honing well
Ccmcn'. hardenirs
Road?inr? other
ntal work
Ream Ira
Eliminate emer-
encies, etc.
Idleness due to
organization
Time Balance for Possible Time
Single Bore In Twin-Well
Drilling Drilling
Hours Percent Hours Percent
1,650 66.1 7,800 65.4
':I.> 1,000 36.4
375 35.0 375 13.6
50 2.0 100 3.6
125 5.0 125 4.6
75 3.' 75 2.4
boo 24.0 200 7.2
7.0 175 6.4
12.0 400 14.5
15.0 375 13.7
Table 3. Actual and Potential Technical-Economic
Indexes in Stavropol'neft' Tract in Devonian
and Rock-Hearin.;; Formations
Dcv:-Ian Furration (,=vera:-e depth 1,800 rne'.err)
Actual Average Potential Average
Index Index
Singe ".'win Twin
Bore Well Well
Commercial drilling
speed, in meters
per machine month
'''echrolorical idleness,
percent of drilli,i:
t ;.me
Changes in well coats
(coefficient)
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B. Rock-Bearing Formation (Average depth 1,300 meters)
Actual Average Index Potential Average Index
Commercial drilling
speed, in meters
per machine month
Technological idle-
ness, percent of
drilling time
Table 4. Commercial Speeds for a Group of
Wells in Stavropol'neft' Trust
(Meters per Machine-Month)
Single Bore Twin Wells
Devonian 'ormation
Rock-bearing
formation
Single Bore, Single Twin
Directional Vertical Well
Twin Well
680
Directional Vertical
330-350 420-450
Type Group Wells
Single-
Bore
Commercial and Mechanical Speeds in Dagestan
Average
Depth of
Grou m
890
1,160
1,712
915
1,175
1,686
Commercial
Speed
m mach-mo
Mechanical
Speed
m hr
Bits Used
per Well
Rod
Meters
Drilled
per Bit
926.0
500.4
3.21
32.5
35.7
370.8
2.87
85.7
20.0
977.0
9.19
34
2
o
688
6
4
.
37.8
.
.2
34.4
34.1
403.0
3.56
91.6
18.11
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Table 6. Time Balance (in flours) per Meter Drilled
(Based on 33 Wells in Izberbash)
Group A (890-950 meters deep)
Meters drilled per hour,
including:
Productive time
Mechanical drilling
Running-in, pulling
Unproductive time
Repairs
Idleness
Emergencies
Group B (1,100-1,250 meters deep)
Meters drilled per hour,
including:
Productive time
Mechanical drilling
Running-in, pulling
Unproductive time
Repairs
Idleness
Emergencies
Group C (1,500 and more meters deep)
Meters drilled per hour,
including:
Productive time
Mechanical drilling
Running-in, pulling
Unproductive time
Repairs
Idleness
Emergencies
.69
.128
.122
.086
.030
.032
.024
1.09
.326
.246
.470
.120
.180
.170
1.39
.363
.27
.63
.105
.292
.233
.66
.120
.120
.190
.027
.112
.051
.86
.25
.19
.30
.07
.165
.128
1.30
.290
.33
.44
.100
.190
.150
N.
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