Optimising the under-reamer string design for wells at Hai Thach field, Nam Con Son basin

PETROVIETNAM

PETROVIETNAM JOURNAL

Volume 6/2020, pp. 37 - 44

ISSN 2615-9902

OPTIMISING THE UNDER-REAMER STRING DESIGN FOR WELLS

AT HAI THACH FIELD, NAM CON SON BASIN

Hoang Thanh Tung¹, Nguyen Pham Huy Cuong², Tran Hong Nam³, Le Quang Duyen⁴, Dao Thi Uyen⁴

¹Petrovietnam Drilling and Well Services Corporation (PV Drilling)

²Bien Dong Petroleum Operating Company (Bien Dong POC)

³Petrovietnam Exploration Production Corporation (PVEP)

⁴Hanoi University of Mining and Geology (HUMG)

Email: tunght@pvdrilling.com.vn

Summary

According to the drilling program approved for Hai Thach ﬁeld, the drilling section below the 16” casing liner (14.85” internal

diameter) will be carried out by two separate BHAs: ﬁrst drilling the 12.25”section by PDC bit to the section target, then under-reaming

the wellbore to 14.5”and 16.5”diameter in order to run 13.625”casing string. Using two separate BHAs for reaming the wellbore certainly

leads to a time increase in the run in hole (RIH) and pull out of the hole (POOH) of the drill-string and hence the associated costs such as

rig and other related third party services. Therefore, it is necessary to study and calculate the optimal drill-string design to ensure the

wellbore under-reaming as well as to minimise the drill-string running time, thereby improving the Drillex and Capex. The application

of the optimised reamer string design in the wells of Hai Thach ﬁeld has brought a feasible concept that can be applied for other wells

having similar proﬁles and geological stratigraphy in Vietnam in the future.

Key words: Under-reamer string optimisation, wellbore reaming, drill-string simulation, reamer string design, Hai Thach ﬁeld.

1. General

Well HT-xx is designed with a well proﬁle completed

by a 30” conductor pipe and 22” surface casing × 16” cas-

ing liner × 13.625”intermediate casing × 10”intermediate

casing and 5.5”production tubing (Table 1).

Because the 14.5” PDC bit was not available in the

market at the time of drilling operation, it required more

time as well as higher cost to order due to the customised

design and manufacture. Therefore, the solution in this

situation was to use a pilot drill-string with the 12.25”PDC

bit for reaming the borehole below 16”casing shoe to the

two diameters of 14.5” and 16.5” to reach the target men-

tioned above.

According to the well design, the 16.5” hole section

is used for 13.625” casing running, the wellbore diameter

must reach 16.5” to ensure suﬃcient annular for cement-

ing to achieve the highest quality and eﬃciency.

2. Optimal solution design

2.1. Primarily approved design

But the fact is that the 16” casing liner has internal di-

ameter of only 14.85”. It is, therefore, merely possible to

drill inside casing with a bit of 14.5” when going through

cement below the 16” casing shoe and then reaming the

hole up to 16.5”; however, the 14.5” PDC bit cannot bring

up the borehole diameter up to 16.5” for 13.625” casing

running and cementing. So, the under-reaming equip-

ment is needed to achieve the required wellbore diam-

eter of 16.5” for running the 13.625” intermediate casing

(Figure 1).

With the approved drilling program as described

above, for reaming the wellbore to 16.5” for the 13.625”

casing section, it is necessary to have two BHAs with de-

tails as follows (Tables 2 and 3).

- 12.25”pilot BHA, and

- 12.25”× 14.5”× 16.5”under-reaming BHA.

With pilot under-reaming BHAs, the drilling operation

needs to run the process at least twice. It includes mak-

ing up 12.25” pilot BHA then drilling to section target and

POOH for 12.25” × 14.5” × 16.5” under-reaming BHA and

Date of receipt: 14/6/2018. Date of review and editing: 14 - 28/6/2018.

Date of approval: 5/6/2020.

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PETROLEUM EXPLORATION & PRODUCTION

Table 1. Casing speciﬁcation for well HT-xx [1]

Inner

ꢂreꢁꢁure

ꢆꢂꢁiꢉ

4,900

6,360

ꢊuter

ꢂreꢁꢁure

ꢆꢂꢁiꢉ

4,090

3,870

ꢋield

ꢁtrenꢅth

ꢆꢌ1ꢍꢍꢍ lꢇꢁꢉ

7,521

ꢄeiꢅht

ꢆlꢇꢈftꢉ

ꢊꢀ

ꢆinꢉ

Iꢀ

ꢆinꢉ

ꢀeꢁcriꢂtion

ꢃrade

30” Conductor

22” Surface casing

16” Intermediate casing

13.625” Intermediate casing

X56

X80

P110

456

224

96

88.2

73.2

68.7

39.0

29.7

23.0

30

22

16

13.625

10.75

10

7.625

5.5

27

20

5,278

3,065

3,191

2,660

2,516

1,231

959

729

14.85

12.375

9.394

8.672

6.625

4.376

4.67

6,920

2,340

4,800

Q125

10,030

13,670

15,050

12,620

19,670

14,530

SM125S

P110

10,810

13,370

11,080

20,180

14,540

10.75” × 10” Production casing

7.625” Contingency liner

5.5” Production liner

5.5” Production tubing

SM13CRS-110

5.5

- Calculate, run the simulation to

ensure that the drilling-string tools work

stable for the formation to be drilled,

30” Conductor pipe

Hammering

- Review hole cleaning eﬃciency

and hydraulic model, simulate drilling

parameters to select the BHA design for

the highest ROP,

30” Conductor @320 m TVD

26” Hole section

#1: 26" BHA (Motor /MWD) drill vertical to Section

TD 1347.0mTVD /1348.0 mMD; WBM, KCL /PHPA

9.2~9.5 ppg MW

- Review the inﬂuence of directional

drilling equipment in the process with the

proposed BHA,

20” Surface casing @ +/- 1,341.5 m TVD

18.125” Hole section

Kick - oꢀ & Build & turn right section

#1. 18.125" Hole BHA (RSS/MWD/LWD/DH

Dynamic), KOP 1,458 mMD, 1.8º/30m BUR,

Complete build/turn to Max. 32.0º

Inclination/5.5º

Azimuth to section TD SBM 10.5 - 12.5 ppg MW

[Normal Barite]

13.625” x 16”

Swell Packer

- Check the change of well trajectory

during drilling and reaming operation.

16” Intermediate Casing @ +/- 1,341.5 m TVD

12.25” x 16.5” Hole Section

Hold & Tangent Section [32.0º Inclination / 5.5º

Azimuth]

It is a must to consider all key ele-

ments and factors of well design, drilling

equipment, drill bit, geological features,

well trajectory, drilling ﬂuids, drilling hy-

draulics, drilling parameters as well as oth-

er related factors. The results of the engi-

neering study shown that during drilling

and reaming, the proposal for BHA drilling

and reaming from 12.25” to 14.5” diame-

ter by SHO - Staged Smiths Hole Opener

(Figure 2) and 16.5”Rhino Reamer with an

integrated BHA (with 3 diﬀerent cutting

inserts including drill, ream the borehole

by Rhino Reamer up to 16.5"). "The Rhino

Reamer XC gets around the limitations of

the existing reaming equipment from an-

other manufacturer and oﬀers some out-

standing features such as full activation

with hydraulic mechanism or acceptance

of multiple open/close times during op-

eration (Figure 3).

10.75” x 10”

#1. 12.25" Pilot BHA (RSS/MWD/LWD/DH

Dynamic) to section TD.

#2. 12.25" x 14.1/2" x 16.1/2" Under Reamer BHA

to section TD; SBM 14.5 - 15.9 ppg MW [Normal

Barite]

Casing Tie Back

13.625” Intermediate Casing @ +/-2,870 m TVD

12.25” Hole Section

Hold & Tangent Section [32.0º Inclination / 5.5º

Azimuth]

#1. 12.25" BHA (RSS/MWD/LWD/DH Dynamic) to

section TD; SBM 17.3 ppg MW [Fine Grind Barite]

10” Intermediate casing @ +/-3,356 m TVD

8.5” Hole Section

Hold & Tangent Section [32.0º Inclination / 5.5º

Azimuth]

7.625” Contingency liner @ +/-3,500 m TVD

5.5” Production Tubing @ +/-3,816 m TVD

#1. 8.5”BHA (RSS/MWD/LWD/DH Dynamic)

to well TD; SBM 17.2 - 17.3 ppg MW [Fine Grind

Barite]

Figure 1. Well HT-xx proﬁle.

reaming the borehole up to 16.5” as required for 13.625” casing running

and cementing. Undoubtedly, this process takes more time for POOH and

RIH, which obviously pumps up the costs related to rig waiting and third

parties services. Therefore, having an integrated solution to reduce the

cost but ensure the quality and eﬃciency of well construction is crucial.

2.2. Optimal solution proposal

To propose an optimal solution for BHA drilling and reaming, it is req-

uisite to consider the following:

Rhino reamer XC has been put into op-

eration worldwide since September 2012

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Table 2. 12.25” pilot BHA conﬁguration [2]

ꢄuter

diameter

ꢅinꢆ

ꢊccu.

lenꢉth

ꢅmꢆ

ꢄꢁ

ꢅinꢆ

Iꢁ

ꢅinꢆ

ꢇenꢉth

ꢅmꢆ

ꢇower

connection connection

ꢈꢃꢃer

ꢀo.

ꢁeꢂcriꢃtion

1

2

3

4

5

6

7

8

9

Bit - PDC - ꢀxed cutter

AutoTrak steering unit

Lower flex stabiliser

OnTrak II - MWD sensor sub

BCPM - MWD power and pulser sub

CoPilot

12.25

Nozzle 5x20

2.480 6.625 Reg

6.625 Reg

9.5 T2

0.400

2.530

3.630

7.010

3.600

2.300

1.100

1.700

1.000

56.40

9.500

28.20

9.500

9.400

1.000

152.00

2774.03

0.40

2.93

11.860

9.500

8.000

8.125

8.000

8.250

8.000

8.250

8.000

5.500

12.125

11.75

2.813

2.875

2.880

2.813

9.5 T2

6.56

9.5 T2

13.57

17.17

19.47

20.57

22.27

23.97

25.67

26.67

83.07

92.57

120.77

130.27

139.67

140.67

292.67

3066.7

9.5 T2

Top stop sub NM

7.625 Reg

6.625 Reg

VX54

Sub - filter

2.813 7.625 Reg

2.813 6.625 Reg

Float sub (non-ported plunger)

10 String Stabiliser

11 Sub - X/O

11.375

12 Drill collar x 6

13 Jar

14 Drill collar x 3

15 Accelerator

16 Drill collar x 1

17 Sub - X/O

18 5.5” HWDP ×16

19 5.5” DP

4.000

4.778

VX54

Table 3. 12.25”x14.5”x16.5” under-reaming BHA [2]

ꢄuter

diameter

ꢊccu.

lenꢉth

ꢅmꢆ

ꢄꢁ

ꢅinꢆ

Iꢁ

ꢅinꢆ

ꢇenꢉth

ꢅmꢆ

ꢇower

connection connection

ꢈꢃꢃer

ꢀo.

ꢁeꢂcriꢃtion

ꢅinꢆ

1

2

3

4

5

6

7

8

9

Bullnose

8.000

6.625 Reg

0.40

2.10

String stabiliser

12.250

8.000

9.500

8.000

8.125

8.000

8.250

8.000

8.250

8.000

5.500

2.813

3.000

2.700

2.813

4.000

4.778

6.625 Reg

7.625 Reg

6.625 Reg

VX54

6.625 Reg

7.625 Reg

6.625 Reg

VX54

1.70

Float sub (non-ported plunger type)

Bit-hole opener (SHO)

Under reamer

3.80

14.500

16.500

4.00

7.80

4.50

12.30

21.70

23.40

25.40

26.40

82.80

92.30

120.50

130.00

139.40

140.40

292.40

Drill collar

9.40

Float sub (non-ported plunger type)

String stabiliser

1.70

12.250

2.00

Sub - X/O

1.00

10 Drill collar x 6

11 Jar

56.40

9.50

12 Drill collar x 3

13 Accelerator

14 Drill collar x 1

15 Sub - X/O

16 5.5” HWDP x16

17 5.5” DP

28.20

9.50

9.40

1.00

VX54

152.00

VX54

2772.60 3065.00

and some oil operators have successfully combined well

drilling and reaming but no one has applied the method

with 3 integrated cutting stages. Especially, this BHA pro-

posal has never been applied for HPHT wells not only in

Vietnam but also all over the world so far. Some limita-

tions of the optimised design are the equipment capabil-

ity to ream up borehole and hole cleaning, and monitor

the well trajectory, namely:

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PETROLEUM EXPLORATION & PRODUCTION

- Existing wellbore diameter

expansion

combination

equipment

of

uses

mechanical

a

mechanisms (ball-drop) to activate

the cutter block and retains only

one hydraulic mechanism during

operation. Since this combination

can be used only for a single opening

and closing cycle of cutting blades,

it reduces the equipment ﬂexibility

during the reaming. This also makes it

diﬃcult to drill a well through complex

geologic formations and the design

will greatly lower the hole cleaning

eﬃciency during and after drilling.

Figure 2. Staged hole opener - SHO of Smiths Bit [3].

- Normally being activated by a

ball-drop mechanism, reamer is only

located above the MWD tools and

cannot be placed close to the drill

bit. This fact leads to the bare hole

increase below the borehole reaming

section. The length of borehole to be

expanded leads to an extreme risk for

the casing seat point in the abnormal

or high pressure as we need to place

the casing seat on the strongest and

most stable foundation possible to

guarantee the drilling to the next well

section.

- The incompatibility between

the cutting mechanisms of the

equipment leads to decrease ROP and

extend the drilling time.

2.3. Engineering study result

Simulation is run for proposed op-

timal BHA options and engineering/

design study as speciﬁed in Table 4.

The proposed drilling tool speci-

ﬁcations are brought into calculation/

simulation and check for stability

through diﬀerent types of formation.

The output is indicated in Table 4.

The bending stress for BHA is

checked with drilling parameter input

relevant to the types of drilled forma-

tion (Figure 5).

Figure 3. Rhino reamer XC [4].

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Table 4. The proposed BHA options

ꢀꢁtion ꢂ 1

ꢀꢁtion ꢂ 2

ꢀꢁtion ꢂ ꢃ

ꢀꢁtion ꢂ ꢄ

ꢈaꢉ.

ꢀꢊ

ꢇccum.

ꢋenꢌth

(ft)

ꢈaꢉ.

ꢀꢊ

ꢇccum.

ꢋenꢌth

(ft)

ꢈaꢉ.

ꢀꢊ

ꢇccum.

ꢋenꢌth

(ft)

ꢈaꢉ.

ꢀꢊ

ꢇccum.

ꢋenꢌth

(ft)

ꢅꢆꢇ 2

ꢅꢆꢇ 2a

ꢅꢆꢇ 2ꢍ

ꢅꢆꢇ 2c

(in)

6.7500

7.0000

8.2500

8.0000

8.2500

8.0625

8.1250

9.5000

9050.00

974.714

476.026

472.746

441.746

410.578

318.058

284.571

99.531

96.251

6.7500

7.0000

8.2500

8.0000

8.2500

8.0625

8.1250

9.5000

9050.00

979.927

481.239

477.959

446.959

415.791

323.271

289.784

104.744

101.464

6.7500

7.0000

8.2500

8.0000

8.2500

8.0625

8.1250

9.5000

9050.00

986.487

487.799

484.519

453.519

422.351

329.831

296.344

111.304

108.024

6.7500

7.0000

8.2500

8.0000

8.2500

8.0625

8.1250

9.5000

9050.00

989.767

491.079

487.799

456.799

425.631

333.111

299.624

114.584

111.304

ꢎꢏꢎꢐ ꢊꢑ

ꢎꢏꢎꢐ ꢆꢓꢊꢑ ꢉ1ꢔ

ꢕuꢍ ꢖ ꢗꢒꢀ

ꢊrill collar ꢉ 1

ꢇccelerator

ꢊrill collar ꢉ ꢃ

ꢘar

ꢊrill collar ꢉ ꢔ

ꢕuꢍ ꢖ ꢗꢒꢀ

ꢙloat ꢚuꢍ ꢛnon ꢁorted

ꢁlunꢌer tꢜꢁeꢝ

ꢕuꢍ filter

ꢕtrinꢌ ꢚtaꢍiliꢞer

Toꢁ ꢚtoꢁ ꢚuꢍ ꢟꢈ

ꢠoꢖꢁilot

ꢅꢠꢑꢈꢖꢈꢓꢊ ꢁower

and ꢁulꢚe ꢚuꢍ

ꢀntrack II ꢡ ꢈꢓꢊ

ꢚenꢚor ꢚuꢍ

ꢢhino reamer

ꢕꢆꢀ

ꢎꢏꢎꢐ ꢊꢑ

ꢎꢏꢎꢐ ꢆꢓ ꢊꢑ ꢉ1ꢔ

ꢕuꢍ ꢖ ꢗꢒꢀ

ꢊrill collar ꢉ 1

ꢇccelerator

ꢊrill collar ꢉ ꢃ

ꢘar

ꢊrill collar ꢉ ꢔ

ꢕuꢍ ꢖ ꢗꢒꢀ

ꢙloat ꢚuꢍ ꢛnon ꢁorted

ꢁlunꢌer tꢜꢁeꢝ

ꢕuꢍ filter

ꢕtrinꢌ ꢚtaꢍiliꢞer

Toꢁ ꢚtoꢁ ꢚuꢍ ꢟꢈ

ꢠoꢖꢁilot

ꢅꢠꢑꢈꢖꢈꢓꢊ ꢁower

and ꢁulꢚe ꢚuꢍ

ꢀntrack II ꢡ ꢈꢓꢊ

ꢚenꢚor ꢚuꢍ

ꢕuꢍ ꢗꢒꢀ

ꢢhino reamer

ꢕꢆꢀ

ꢎꢏꢎꢐ ꢊꢑ

ꢎꢏꢎꢐ ꢆꢓꢊꢑ ꢉ1ꢔ

ꢕuꢍ ꢖ ꢗꢒꢀ

ꢊrill collar ꢉ 1

ꢇccelerator

ꢊrill collar ꢉ ꢃ

ꢘar

ꢊrill collar ꢉ ꢔ

ꢕuꢍ ꢖ ꢗꢒꢀ

ꢙloat ꢚuꢍ ꢛnon ꢁorted

ꢁlunꢌer tꢜꢁeꢝ

ꢕuꢍ ꢙilter

ꢕtrinꢌ ꢚtaꢍiliꢞer

Toꢁ ꢚtoꢁ ꢚuꢍ ꢟꢈ

ꢠoꢖꢁilot

ꢅꢠꢑꢈꢖꢈꢓꢊ ꢁower

and ꢁulꢚe ꢚuꢍ

ꢀntrack II ꢡ ꢈꢓꢊ

ꢚenꢚor ꢚuꢍ

ꢕuꢍ ꢗꢒꢀ

ꢢhino reamer

ꢕtrinꢌ ꢚtaꢍiliꢞer

ꢕuꢍ ꢗꢒꢀ

ꢎ 1ꢒ2ꢐ ꢊꢑ

ꢎ 1ꢒ2ꢐ ꢆꢓꢊꢑ ꢉ1ꢔ

ꢕuꢍ ꢖ ꢗꢒꢀ

ꢊrill collar ꢉ 1

ꢇccelerator

ꢊrill collar ꢉ ꢃ

ꢘar

ꢊrill collar ꢉ ꢔ

ꢕuꢍ ꢖ ꢗꢒꢀ

ꢙloat ꢚuꢍ ꢛnon ꢁorted

ꢁlunꢌer tꢜꢁeꢝ

ꢕuꢍ filter

ꢕtrinꢌ ꢚtaꢍiliꢞer

Toꢁ ꢚtoꢁ ꢚuꢍ ꢟꢈ

ꢠoꢖꢁilot

ꢅꢠꢑꢈꢖꢈꢓꢊ ꢁower

and ꢁulꢚe ꢚuꢍ

ꢀntrack II ꢡ ꢈꢓꢊ

ꢚenꢚor ꢚuꢍ

ꢕuꢍ ꢗꢒꢀ

ꢢhino reamer

ꢕuꢍ ꢗꢒꢀ

9.5000

12.250

9.5000

90.674

85.097

79.003

75.395

67.850

9.5000

12.250

9.5000

95.887

90.310

87.030

83.422

75.877

9.5000

12.250

9.5000

102.447

96.870

93.590

89.982

82.437

9.5000

12.250

9.5000

105.727

100.150

96.870

93.262

85.717

11.750

56.039

11.750

64.394

11.750

70.954

11.750

74.234

16.500

14.500

12.250

33.039

13.529

0.8990

9.500

16.500

14.500

8.0000

12.250

41.404

38.124

18.614

5.4910

0.8990

9.500

16.500

14.250

8.0000

14.500

8.0000

12.250

47.964

44.684

25.174

21.894

18.614

5.4910

0.8990

9.500

16.500

9.5000

14.250

8.0000

14.500

8.0000

12.250

51.244

47.694

28.454

25.174

21.894

18.614

5.4910

0.8990

ꢅit

ꢅit ꢚuꢍ

ꢅit

ꢕtrinꢌ ꢚtaꢍiliꢞer

ꢕuꢍ ꢗꢒꢀ

ꢕꢆꢀ

ꢅit ꢚuꢍ

ꢅit

ꢕꢆꢀ

ꢅit ꢚuꢍ

ꢅit

Figure 4. Results of stability calculation of the integrated BHA when drilling and reaming through sandstone and shale formations.

Figure 5. Simulation results with parameter input corresponding to the integrated drilling and reaming BHA through sandstone.

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Figure 6. The simulation results show the inﬂuence of directional drilling equipment to the proposed integrated BHA.

The simulation shows the inﬂuence

of directional drilling equipment to the

proposed integrated BHA.

Simulation of well geometry/trajec-

tory changes and hydraulic model per

integrated BHA option and selection of

cutting blades shape for 3 cutting stage

mechanisms is shown in Figure 7.

The results of the well trajectory

change simulation during drilling and

reaming are shown in Figure 8.

Figure 7. Simulation of the well geometry change during drilling and reaming.

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Figure 8. Simulation of the well trajectory change during drilling and reaming.

Figure 9. Cutting shape/blades of drill bit, Stage Hole Opener and Rhino Reamer.

After engineering study in turn with the BHA pro-

posed options (Figure 10), the selection of suitable in-

tegrated BHA for the drilling and reaming and with

the optimum cutter shapes of the reaming and drilling

equipment to the all-purpose 13.625” casing running

and cementing as well as the requirements for the sta-

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The goal of borehole reaming is

achieved by a single BHA instead of two as

originally designed.

Drill pipe

Drill Collar

Drill pipe

Drill collar

Centraliser

The borehole reaming equipment is

completely controlled by hydraulics in-

stead of both mechanically activated (ball-

drop) and hydraulic operation.

MWD sensor

sub

MWD sensor

sub

Centraliser

Drill collar

MWD

The proposed BHA can be used for

multiple opening/closing cycles.

Rhino

Reamer

MWD

It is important to note that the bare

hole (pilot hole) distance under the cas-

ing seat should be the shortest to ensure

a good foundation for the casing seat. The

proposed BHA minimises bare hole below

the reaming section, thereby reducing the

risk for casing seat.

Ball drop

reamer

Centraliser

Drill collar

Centraliser

Bull nose

Auto track

Staged hole

opener (SHO)

The proposed integrated BHA with

three cutting mechanisms for HPHT wells

was carried out in well HT-xx at Hai Thach

ﬁeld by PV Drilling V Rig with very high

economic eﬃciency. It has been proven to

save more than USD 1 million for the Bien

Dong 1 ﬁeld development project.

Drill-bit

Drill bit

(a)

(b)

(c)

Figure 10. Pilot BHA (a); Under-reaming BHA (b); Proposed integrated BHA with 3 cutting mechanisms (c).

bility of the BHA proposed, the hole cleaning eﬃciency, the compat-

ibility of diﬀerent cutting mechanisms of per equipment, the ability to

control the well trajectory.

Reference

[1] Bien Dong POC, “05-02-HT-4P

drilling program”, 19/8/2015.

Thus, in addition to serial advantages such as increasing the well-

bore stability by reducing the back-reaming time, mitigating the dura-

tion of the drilling ﬂuids impacting the formation, lessening the risk of

diﬀerential sticking mechanisms due to the diﬀerence between pore and

hydrostatic pressures, the application of integrated BHA combined with

the borehole reaming has saved the drilling time thereby saving rig cost

and contributing to improving the economic eﬃciency for Capex/Drillex.

[2] Baker Hughes, BHA design.

[3] Smith Bits, “10.5/8-14.1/2 in staged

hole opener speciﬁcation”.

[4] Schlumberger, “14250/Rhino

Reamer, tool dimension drawing”.

1

3. Conclusion

[5] Bien Dong POC, “Internal technical

report of 12.1/4” bit run; 12.1/4”x14.1/2”

hole opener run; 14.1/2”x16.1/2” under

reamer run”.

To select the appropriate design of drilling BHA combined with

reamers, the following points need to be assessed: the stability of the

proposed BHA for the formation to be drilled; hole cleaning eﬃciency

and hydraulic model according to drilling parameters input for the

highest ROP; the inﬂuence of drilling equipment on well trajectory.

[6] PV Drilling, “IADC equipment list of

PV Drilling V (TAD) rig”.

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