Elapsed drilling time (seconds)

Site 808

0

50

100

0

10

20

30

SWOB (Klbs)

DWOB (Klbs)

Cross Wavelet

DWOB/SWOB

Period (sec)

DWOB/SWOB

Ratio (filtered)

1248

163264

128256

-3.0

-1.5

0.0

1.5

3.0

Heave (m)

-0.50.00.51.01.52.0

20000 25000 30000 35000 40000 45000 50000 55000 60000 65000 70000 75000 80000 85000 90000 95000 100000 105000 110000 115000

50

100

150

Top Drive

Torque

AHC OFF AHC OFF AHC OFF AHC OFF AHC OFF

Seafloor

Simplified Depiction of a Heave Motion Compensator

Mounted on a Drillship

Cy

lin

de

r

Top

Drive

Cy

lin

de

r

Controller

Accelerometerle Drawworks

1. The heaving motion of the

ship is recorded by the

accelerometer and the data

sent to the controller.

2. The controller anticipates

the needed compensation and

issues the command to the

cylinders.

3. The variations in weight on

bit and torque are measured

near the bit and reviewed

during drilling and following

the drilling operation.

The long drill pipe can act like

a spring and lessen some of

the variability of downhole

drilling parameters.

Sensors mounted on the ship

measure a wide range of

drilling parameters that give the

driller good indication of what is

happening at the bit.

Heave motion compensators use

sensors, electronics, software,

large hydraulic cylinders and

pumps to decouple the motion of

the ship from the motion of the bit

while drilling. This is done to

maintain a near constant weight on

the bit while drilling. Ideally the

weight on bit should remain

constant for best coring results,

however this is extremely difficult, if

not impossible due the complex

nature of this task.

Weight on bit and torque

increase and decrease with

the heaving motion of the

ship

Sensors installed in the drill pipe

near the bit provide critical feed

back on the variation of downhole

weight on bit. These data are

transmitted up the drill string in

real time.

Heave

0.0 0.1 0.2 0.3 0.4 0.5

Frequency (Hz)

0

0.5

1

1.5

2

Pow

er

1173 Top Drive AmpsSpectrum for AHC ON and OFF

AHC OFF

AHC ON

AHC suppresses heave

effects in torque by factor

of 2.5

500

500

-0.6

0.0

0.6

0 100 200 300 400

0 100 200 300 400

Wavelet depicting Frequency change248

163264

128256

Period

Fourier transform depicting

frequency change

Wavelet depicting amplitude change

frequency

amplitude change

-1.8-1.2

-0.60.0

0.61.2

1.8

0 100 200 300 400 500

0 100 200

248

163264

128256

248

163264

128256

Pe

rio

d

frequency

Amplitude change

Time (seconds) Time (seconds)300 400 500

60

SWOB (Klbf)

0

10

20

30

40

DWOB (Klbf)

Site 808 SWOB - DWOBAHC On

4859-4916 mbrf4947-5012 mbrf5033-5117 mbrf5138-5213 mbrf 5234-5319 mbrf

5040

RAW DATARAW DATA

3020100

RAW DATARAW DATA

RAW DATARAW DATA

18000 18500 19000 19500 20000 20500 21000 21500 22000

Elapsed drilling time (seconds)

50

55

60

65

To

p D

rive

Am

ps

1173 Top Drive Amps (Torque)AHC ON and OFF

AHC ON AHC OFF

Characterization of the dynamics of ship heave and its effect on

downhole drilling and coring has been long sought after in the

Ocean Drilling Program. Operating in the Nankai trough region, the

JOIDES Resolution acquired new data of downhole parameters

using commercially-available Measurement-While-Drilling (MWD)

tools at two drilling sites. Our objective during ODP Leg 196 was to

record weight-on-bit, rate of penetration, torque, and pump

pressure near the bit as drilling proceeded. Digital instruments

installed on the rig floor simultaneously acquired vital surface

information of the drilling parameters. Although the sampling rate

afforded by the downhole tools is insufficient to resolve wave

periods of 8-10 seconds, longer wavelength changes are clearly

observed. Wavelet transform analysis was used to eliminate

window length restrictions with conventional Fourier analysis and

to retain the time-specific information recorded in the raw signal.

The integration of the uphole and downhole data sets and

subsequent wavelet analysis show less variation with heave than

in previous experiments near Antarctica where sea states reached

4 meters. The ratio of surface to downhole weight-on-bit for the

two data sets in the >30 second spectral window varies

systematically with changes in sea state, water depth, pipe depth

and driller input. We are thus able to study the effects and drilling

dynamics in changing sea states and in water depths up to 5500

meters and to evaluate the operation of the shipboard heave

compensation systems. As a result of these analyses, ODP is

deriving an empirical approach for operational use to describe

downhole and uphole drilling parameters under a variety of

conditions and in different geological environments.

Ship Heave Effects on ODP Drilling Dynamics: analysis of MWD data in the Nankai TroughGreg Myers1, Philippe Gaillot2, Dave Goldberg1 and the Leg 196 Scientific Party1 Lamont-Doherty Earth Observatory, Borehole Research Group, Palisades, New York

2 Université de Montpellier 2, Place Eugène Bataillon, Montpellier, France

1. ABSTRACT

2. OVERVIEW

6. CONCLUSIONS

Drilling

Pipe Change

Drilling

Pipe Change

3. ACQUIRED DATA

73000 74000 75000 76000 77000 78000 790000

1

2

3

Downhole Torque

(K ftlbs)

73000 74000 75000 76000 77000 78000 790000

10

20

30

DWOB

(Klbls)

Site 808Downhole Weight on Bit and Torque

Elapsed drilling time (seconds)

AHC ON

AHC ON

AHC OFF

AHC OFF

Site 1173

40

60

80

100

Top Drive

Amps

Surface WOB

30 sec (Klbs)

0

10

20

30

40

50

-3-2-1

012

3

Heave (m)

Elapsed drilling time (seconds)

0 10000 20000 30000 40000 50000 60000 70000

2.0

1.0

-0.5

0

Downhole WOB/

Surface WOB ratio

5

5

15

25

Downhole WOB

(Klbs)

Environmental Conditions

Site 1173Water Depth 5500m Sea State

<2M

Data Transmission Rate 12Hz (3.0 bps)

Sample Interval 4.9 sec

Site 808Water Depth 5500m

Sea State ~1m

Data Transmission Rate 16Hz (6.4 bps)

Sample Interval 2.5 sec

AHC OFF AHC OFFAHC OFF AHC OFF

Torque is

sampled lower

than once every 10

seconds. Downhole

weight on bit is sampled

once every 2 seconds which

allows higher frequencies,

such as heave to be

observed.

At low

frequency,

dowhhole torque

responds to heave

effects. The AHC

suppresses torque

by a factor of 2.5

Wavelets

offer some

advantages over the

Fourier transform in that

the time domain is perserved

so changes in signal

frequency and ampliitude

can be graphically

depicted at the time of

their change

Correlation

between DWOB and

SWOB is strong in all sea

states, with or without the

AHC. SWOB values are

roughly 2 times higher

than DWOB, over all

frequencies.

T41A-0852

Downhole WOB

is suppressed by the

AHC at heave periods of

10 seconds and higher.

DWOB/SWOB ratio is

approximately 0.4-0.5 at

these periods.

4. Results - Downhole Weight on Bit

Wavelet Transform Overview

DWOB(Klbs)

DWOB (Klbs)

43500 43600 43700 43800 43900 440005

10

15

20

Site 808 DWOBComparison of AHC On and Off

45500 45600 45700 45800 45900 46000Elapsed drilling time (seconds)

5

10

15

20

AHC OFF

AHC ON

Approx 10 sec period measured near the bit

10 sec period is suppressed

Downhole measurements made in real-time while drilling have been

demonstrated to be vital for determing the performance of heave

compensation equipment. Data was transmitted from 6000m depth

through the drill pipe at up to 6 bps and recorded at the surface using

MWD technology.

The Active Heave System installed on the JOIDES Resolution appears

to reduce downhole weight on bit and torque variations resulting from

ship motion by a factor of up to 2.6 under these test conditions.

Wavelet Analysis shows little reduction by the Active Heave

Compensation System of downhole weight on bit at long periods(0.5 to 2

min.)

A downhole measurement system with a higher sampling rate (<2 sec

for each measured parameter) is needed to further the investigation of

downhole drilling dynamics at higher frequencies.

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Frequency (Hz)

0

0.1

0.2

0.3

0.4

0.5

Pow

er

Site 808 DWOB Spectra

AHC ON

AHC OFF

Ship HeavePeriods

AHC ON and OFF

AHC reduces avg.

DWOB variations in

the heave frequency

by a factor of 2.6

RAW DATARAW DATA

RAW DATARAW DATA