OTC 19800
Medium Radius Horizontal Sidetracks Reduce Time, Cost and Risks in
HT Ghawar Field Wells
Michael A. Simpson, Abdul Al-Hamid, Yusri Faraj, Mohamed Khalil, Roberto Duran, Clayton L. Miller, and
Shaker Al-Khamees, Saudi Aramco, and Jeff Stewart, Halliburton
Copyright 2009, Offshore Technology Conference
This paper was prepared for presentation at the 2009 Offshore Technology Conference held in Houston, Texas, USA, 4–7 May 2009.
This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been
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Abstract
Saudi Aramco’s first medium radius horizontal sidetrack
gas well, Haradh-AX1, was drilled and completed in June,
2008 in a record time of 48.7 days with 4,989 ft of
reservoir contact and a 33% reduction in overall cost.
The previous, Khuff-C Horizontal sidetracks which
included the same operations; de-completion, sidetracking
and re-completion, averaged 83 days with 3,441 ft of
sidetracked lateral across the Khuff-C.
Directional drilling in the medium radius lateral after
building at 12°/100 ft to a sail inclination of 88° was
characterized by better bit performance, lower torque and
drag, improved wellbore stability and steerability.
In the previously employed long radius horizontal
sidetrack design, extensive milling operations were
required to gain access to the 8-3/8” open hole to
sidetrack. The 8-3/8“long radius build section would then
be drilled from the Base Jilh Dolomite, across the
troublesome and sometimes abnormally pressured Lower
Jilh and Sudair Shale formations to the top of the Khuff-C
where a new 7” liner would be run and cemented. The 57/8” lateral would then be drilled across the Khuff-C and
an open-hole completion run.
In the medium radius design, the sidetrack (ST) could be
made deeper, in the same pressure regime, by cutting a ST
window in the existing 7” liner 450 ft true vertical depth
(tvd) above the Khuff-C target reservoir, kicking off and
drilling 5-7/8” hole across the Khuff-C to total depth (TD).
This paper further details the time and cost savings
possible from the application of proven medium radius
drilling technology from Saudi Aramco’s Arab-D
Horizontal Oil wells produced from 6,500 ft tvd to the
deep gas wells produced from the Khuff formation at
12,000 ft tvd, a new drilling environment.
More medium radius horizontal sidetracks are planned and
a similar medium radius Khuff-B Horizontal ST, ANDRAX1, which built at 32°/100 ft, was just successfully
completed at 14,819 ft with a 2,400 ft horizontal section.
Introduction
Previously, a total of nine horizontal re-entry/sidetracks
were performed on existing poor to non-producing gas
wells in the Ghawar field of Saudi Arabia owned and
operated by Saudi Aramco. The general procedure was to
mill out the 7” liner overlap (500 ft -1100 ft) to around
150 ft below the 9-5/8” shoe.
The milling was extremely tedious and time consuming
because of milling related problems such as the formation
of “bird’s nests” (packing off of swarf in the milling
annulus), stuck pipe, inconsistent mill performance and
difficulty maintaining milling fluid low-end rheology.
A cement sidetrack plug would then be set in the 8-3/8”
open hole, after which the sidetrack would be kicked-off
with a long radius build trajectory (typically 3 to 7°/100 ft)
to the top of the Khuff-C formation and a new 7” liner was
run and cemented in place.
Once the usually higher pressured by as much as 2,400
psi, Khuff-A & Khuff-B formations are cased off, the 57/8 in. section of the long radius trajectory would continue
building inclination to about 90° across the target
producing zone; the Khuff-C; using the minimum required
mud weight to drill to TD.
An alternate approach was to set a whipstock in the 9-5/8”.
casing above the 7” liner top, cut an 8-3/8” window in the
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OTC 19800
9-5/8” casing and continue drilling with a long radius
build trajectory in the same manner as cited above to the
7” liner point in the top of the Khuff-C. It was not always
possible to apply this approach in all horizontal sidetrack
candidate wellbore configurations.
To minimize torque and drag, a lubricant was added to the
drilling fluid after making a cost-benefit comparison
between using a lubricant with a (Positive Displacement
Motor) PDM vs. a Rotary Steerable system for drilling the
horizontal section.
By applying a medium radius horizontal drilling
trajectory, considerable improvements could be achieved;
mainly because it makes it possible to drill the entire
horizontal sidetrack through one pressure regime and hole
section, and thereby considerably reduce drilling time, cost
and risk.
A 73 pounds per cubic foot (pcf) low solids-non dispersed
drilling fluid system was selected to minimize reservoir
damage using the minimum required overbalance to
maintain control of formation pressures during drilling
operations. The hydraulics program and the wellbore
cleaning techniques were designed to avoid cuttings build
up in the horizontal section.
Well Objective, Trajectory Selection
For the candidate well, HRDH-AX1 the requirement from
the Gas Reservoir Management Department was to decomplete the vertical well, clean-out the 7” liner, drill a
5,000 ft lateral into the Khuff-C Reservoir and run a new
completion.
Initially, two options were considered, the first consisted
of milling out 870 ft of 7 in. liner, setting a 9-5/8”.
whipstock, cutting a sidetrack window in the 9-5/8 in.
casing, drilling 2,985 ft of 8-3/8” open hole and
setting/cementing a new 7” liner. The 5,000 ft 5-7/8”
lateral would then have to be drilled to TD. The total
estimated time for this option was 80 days.
The second option was to mill out 1,070 ft of 7” liner, set a
cement sidetrack plug in the open hole and perform the
sidetrack operation in 8-3/8” hole to the top of the KhuffC; then run and cement a new 7” liner. The 5,000 ft of 57/8” lateral would then have to be drilled to TD. The total
estimated time for this option was 85 days.
Applying medium radius horizontal drilling, the whipstock
could simply be set in the 7” liner, a 5-7/8” window cut,
and the 5-7/8” lateral drilled with a 12°/100 ft build rate
from below the Khuff-B reservoir into the Khuff-C
formation and reservoir. The total estimated time for the
medium radius option was only 50 days along with
significant cost and risk reductions and was therefore
selected. Wellbore schematics and the directional plan are
shown in Figures 1, 2 and 3.
Well design considerations.
For cutting the sidetrack window, a single trip mechanical
whipstock was selected with a conventional
(lead/follow/dress) tri-mill assembly to cut the window. It
was deemed advantageous to minimize dog-leg severity
across the window section and rat hole and to re-dress the
window if any of the mills came out more than 1/8” undergauge.
Torque and drag analysis were performed prior to the start
of operations to select the optimum drill string
configuration and to avoid drill string failures which may
have led to time and cost consuming fishing operations.
Drilling Results
De-completion / Whipstock / Window
The well was de-completed in a total of seven days. A
GR/CCL log was run prior to running the whipstock for
correlation purposes and to assure the whipstock was not
set across a casing collar.
It was critically important that the whipstock was set at the
correct depth, i.e., below the higher pressured Khuff-B
reservoir to avoid differential sticking problems while
drilling the lateral across the Khuff-C formation later on.
The proper whipstock setting point was selected at 11,104
ft. The cutting of the window from 11,104 ft to 11,116 ft
and drilling out of 5 ft of rat hole was accomplished in
four days; two BHA’s (bottom hole assembly’s) were used
for this purpose, the second trip was used to dress out the
window in order to avoid problems later on while tripping
through it. High viscosity hole cleaning pills were also run
to assure adequate borehole cleaning.
Directional Drilling
The build section was drilled with a build-up rate of
12.1°/100 ft with an average rate of penetration (ROP) of
10.3 ft per hour (fph). For the first build assembly, an
International Association of Drilling Contractor’s (IADC)
code 6-2-7 tungsten carbide insert (TCI) bit was run on a
7/8 lobe low speed/high torque PDM with (adjustable bent
housing (AKO) set a 1.5°. The TCI bit was run because of
its superior tool face control as compared to PDC’s across
the build section. The build section was successfully
drilled in 15 days very close to the plan line as shown in
Figure 4.
PDC bits were used to drill the rest of the trajectory with a
“soft landing” into the lateral section of this carbonate
reservoir, with ROP’s up to 26.1 fph and 495 ft progress
per day at the end of the 4,989 ft lateral.
The lateral section was drilled in 28 days with an average
ROP of 18 fph to a TD of 16,810 ft MD/11,904 ft TVD. A
total of five BHA's were used to control inclination and
azimuth in the well; two for the build-up section, two for
drilling the lateral section and one for lateral section
geosteering to TD.
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entry sidetracks for Saudi Aramco in the Ghawar
Field.
Detailed BHA's, Motor performance and bit runs are
shown in Tables 1, 2 and 3.
Drilling Optimization
The bulk of the overall time savings were achieved in the
open hole drilling section, whereas the de-completion,
whipstock setting and window cutting operation times
were basically the same as in previous wells as shown in
Figure 12. A great portion of the time and cost savings in
the drilling phase are attributed to the fact that on bottom
drilling time constituted 51% of the total time, while trip
time was only 19%. Good hydraulics and drilling fluid
properties resulted in only 8% circulating time to sweep
and clean the hole. A detailed operational summary is
given in Figure 5.
The regular additions of the commercial lubricant
achieved torque reductions ranging from 2,000 to 2,500 ftlb. The open hole friction factor was reduced from 0.38 to
0.22 as shown in Figures 6 and 7.
•
Planning and careful performance tracking are
essential tools to achieve optimum performance
from each bit and BHA run.
•
The use of a commercial lubricant in the drilling
fluid system and good hydraulics were very
effective in reducing torque, drag and hole
problems.
•
The theoretical advantage of reducing build
section length to reduce overall torque across the
trajectory was fully realized in HRDH-AX1.
•
It is apparent that the Khuff-A, B and C
reservoirs all have sufficient thickness and
spacing such that they can be selectively sidetracked into and drilled in the same pressure
regime and hole size, using medium and short
radius trajectories.
By carefully selecting, monitoring and re-analyzing BHA
and bit performance, several impressive bit runs were
achieved in this well, the last two bit runs were both in
excess of 2000 ft. Detailed performance data is provided
in Figures 8, 9 and 10.
Figure 11 depicts the drilling days vs. depth curve; the
total operation time employed was 48.7 days compared to
56 days planned.
Completion
The well was completed with a 7” production packer and
4-1/2” carbon steel tubing string in 10 days.
Acknowledgements
The authors wish to thank the management of Saudi
Aramco and Halliburton for permission to publish this
paper. Special thanks to Saudi Aramco Drilling Foreman
Ghazi Ali, Nick Copely and Kenton Paul; without whose
hard work and expertise, this project may not have been
successful.
Conclusions
• The Medium Radius horizontal drilling technique
was successfully applied on the Haradh-AX1 well
with a build rate of 12.1°/100’.
References
1. Schuh, F. J.: “Horizontal Well Planning – Build
Curve Design,” SPE Reprint Series No. 33
“Horizontal Drilling,” 1991.
•
A reduction of 34 operating days and 33% in
operating cost was achieved using the Medium
Radius Horizontal Drilling Technique with
conventional BHA’s, Drill Pipe and Directional
Tools compared to the last nine Long Radius Re-
2.
Joshi, S.D.: Horizontal Well
Pennwell Books, Tulsa (1991).
Technology,
3.
Azar, J. J. and Robello S, G.: Drilling
Engineering, Pennwell Books, Tulsa (2008).
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30”
108 ft
24”
440 ft
18 5/8”
1843 ft
13 3/8”
6308 ft
9 5/8”
8446 ft
7”
11983 ft
Fig. 1. HRDH-AX1 Pre Re-entry/Workover Wellbore Schematic
30”
108 ft
24”
440 ft
18 5/8”
1843 ft
13 3/8”
6308 ft
7” Packer
9 5/8”
10,949 ft
8446 ft
TOW 11,104 ft
EZSV 11,122 ft
BOW 11,116 ft
16,810 ft MD/11,904 ft TVD
7”
11983 ft
5313 ft
Fig. 2. HRDH-AX1 Post Re-entry/Workover Wellbore Schematic
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Fig. 3. HRDH-AX1 Directional Plan.
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SECTION DETAILS
PLAN VIEW
Fig. 4. HRDH-AX1 Actual Directional trajectory
BHA #
MOTOR
RUN #
1
2
3
4
5
6
7
1
2
3
4
5
HOLE
SIZE (IN)
5.7
5.875
5.85
5.875
5.875
5.875
5.875
INC. IN
(DEG)
1.3
1.6
2.1
19.4
79.8
86.2
89.3
INC. OUT
(DEG)
1.6
2.1
19.4
79.8
86.2
89.3
75
DRLG
(HRS)
10
2
19
73
28
119
130
OBJECTIVE
ORIENT WHIPSTOCK
DRESS WINDOW
BUILD UP
BUILD UP
LAND INTO RESERVOIR
GEOSTEERING DRILLING
LATERAL GEOSTEERING
Table 1. BHA Summary
MOTOR
RUN #
LOBE
OD
(IN)
BEND
(DEG)
DLS
(°/100 FT)
1
2
3
4
5
7/8
4/5
4/5
4/5
4/5
4.75
4.75
4.75
4.75
4.75
1.5
1.5
1.5
1.5
1.5
16
15
12
12
8
Table 2. Motor Summary
ROP
(ORI)
(FT/HR)
10
7
3
10
6
ROP
(ROT)
(FT/HR)
6
11
18
20
18
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BIT #
STYLE
1
2
3
3RR
4
SL51
DSX411X
SCD320
SCD320
HCM407Z
OD
(IN)
5.875
5.875
5.875
5.875
5.875
TFA
2
(IN )
0.389
0.442
0.435
0.435
0.383
FOOTAGE
HRS
ROP
DULL GRADE
174
582
367
2281
2273
19
73.25
27.5
119.08
129.5
9
8
13
19
18
1-1-WT-A-E-I-ER-PR
3-3-BT-G-X-I-LN-BHA
1-1-CT-G-X-I-WT-BHA
1-4-CT-G-X-I-NO-BHA
1-2-CT-A-X-I-NO-TD
Table 3. Bit Summary
Fig. 5. Operation Summary/Time Breakdown
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Fig. 6. Torque Reduction with lubricant in mud system.
Fig. 7. Friction factor reduction with commercial lubricant in drilling fluid
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Fig. 8 -BHA Breakdown
Fig. 9. BHA Performance
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Fig. 10. – BHA Footage
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Fig. 11. – HRDH-AX1 Days vs. Depth Drilling Curve after Setting Whipstock @ 11,104 ft
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35
PROGRAM
ACTUAL
33
30
28
25
20
DAYS
15
10
10
10
7
7
4
5
2
2
2
0
DE-COMPLETION
WHIPSTOCK
WINDOW
OPERATION
DRILLING
Fig. 12. Actual/Planned Distribution Time
COMPLETION