1

Logging-while-coring — New Technology Advances Scientific Drilling

D. Goldberg*, G. Myers*, K. Grigar**, T. Pettigrew**, S. Mrozewski^, C. Arceneaux^, T. Collins^, & Shipboard Scientific Party, ODP Leg 204

* Lamont Doherty Earth Observatory,

** Texas A&M University, ^ Schlumberger Drilling and Measurements

ABSTRACT A jointly developed logging-while-coring system was deployed and tested during Ocean Drilling Program Leg 204 on Hydrate Ridge off the coast of Oregon. The system consists of two existing devices modified to be used together — a Schlumberger Resistivity-at-Bit™ tool and a Texas A&M University wireline-retrieved core barrel and latching tool. This combined approach will allow for precise core-log depth calibration and core orientation within a single borehole, and without at pipe trip, providing both time saving and unique scientific advantages. This successful test during Leg 204 marks the first simultaneous use of coring and logging-while-drilling technologies. The test was conducted in 788.5 m water depth at the crest of southern Hydrate Ridge (Site 1249) in July 2002. Eight cores were recovered from Hole 1249B with 32.9% recovery, on average, through a 45 m interval and as high as 67.8% in one core. All eight cores were processed and archived normally on board the D/V JOIDES Resolution. High quality logs and image data were recorded in the downhole tool memory over the entire 74.9 m drilled interval. The log data were processed post-cruise and correlated to recordings of conventional logs in nearby Hole 1249A. The logging while coring system will be deployed in harder formations with higher resistivities at future Ocean Drilling Program sites in 2003. It is expected that the logging-while-coring systems will be utilized more routinely at such locations, where rig time constraints may otherwise preclude coring in difficult drilling environments. INTRODUCTION Merging state-of-the-art wireline coring and logging while drilling technologies provides two vital data

sets without sacrificing time or adding risk associated with longer open hole times. Until now it has not been possible to continuously collect large diameter core and in situ logging data simultaneously. Logging-while-drilling (LWD) and wireline logging measurements are typically made following coring in all Ocean Drilling program (ODP) holes. Continuous wireline-retrievable coring is routine in nearly all ODP drill holes, whereas industry coring programs are often limited in key intervals due to time and cost constraints. The ODP routinely drills holes up to 2000 m deep without a riser in water depths ranging from 300 m to 6000 m. Sea water is utilized at high pressure to clear the hole of cuttings. Following the coring operations, the hole is logged with conventional wireline tools. In cases where drilling is expected to be difficult and wireline log quality poor, LWD technologies are employed. A dedicated LWD hole is often the only alternative to collect in situ log data in such difficult drilling environments. We pursue this joint development of a new logging-while-coring technology in order to achieve two primary objectives:

1) reduce the time required to log after drilling and coring has been completed in a hole; and,

2) make in situ measurements using LWD over the same cored interval in a particular hole.

The system development, testing and deployment was conducted jointly by the Ocean Drilling Program groups at the Lamont-Doherty Earth Observatory and Texas A&M University and Schlumberger Drilling and Measurements.

2

SYSTEM DESIGN AND TESTING A schematic layout of the logging-while-coring system is depicted in Figure 1. To make this concept a reality, a core barrel was selected that fit through the throat of a modified Schlumberger Resistivity-at-BitTM (RAB-8TM) Tool. Only the Motor Driven Core Barrel (MDCB) among the ODP’s coring systems is sufficiently narrow to fit within the 3.45-inch annulus of the RAB-8. Minor modifications of the MDCB were required to accommodate the tool length and latching mechanism. A typical RAB-8 battery ordinarily occupies the annular space in the tool. The RAB-8 battery was redesigned to retain the annular space, allowing the MDCD to pass through. In addition, the standard ODP bit size is 9 7/8-inches, considerably smaller than conventional bits used with the RAB-8 collar. A new resistivity button sleeve and slick stabilizer were fabricated to accommodate the ODP bit. The tool standoff from the borehole wall for the modified RAB tool is nominally 0.185-inches for this ODP configuration. Using the GVR-6 in the ODP environment, the standoff is 0.375-inches. Following the fabrication of all required MDCB and RAB-8 parts, the logging-while coring system was assembled and test fit at the Schlumberger Drilling and Measurements facility in Sugar Land, TX (Fig 2a). This ensured that the components mated properly and assembly could be accomplished in the field. A coring test through low-grade cement was also conducted using the Genesis rig at this location and successfully recovered core through the RAB-8 (Fig 2b). Both tests were conducted prior to deployment of the system at sea during Ocean Drilling Program Leg 204 on Hydrate Ridge off the coast of Oregon. OCEAN DRILLING PROGRAM TESTS The logging-while-coring system was deployed on the D/V JOIDES Resolution for use on ODP Leg 204, offshore Oregon, in July 2002. The test was conducted in 788.5 m water depth at the crest of southern Hydrate Ridge at ODP Site 1249 (Figure 3A & 3B). Drilling proceeded ahead to 30 m below sea floor where coring operations began with sequential 4.5-m, then 9-m-long cores recovered through gas hydrate-bearing clay sediments to 74.9 m depth. A standard ODP 9 7/8-inch-diameter four-cone bit was used and the rotation rate increased from 15 to 45

RPM with depth. Average penetration rate was ~8 m/hr. Eight cores were recovered from Hole 1249B with 32.9% recovery, on average, through a 45 m interval. Cores recovered using plastic liners have a slightly narrower diameter (2.35”) than standard ODP cores, yet recovery as high as 67.8% was reached (Table 1). Two 9-m (2.56” diameter) cores were taken without liners and achieved up to 42.3% recovery after being extruded from the barrel. Without liners, however, handling and further core processing and archiving is limited. All eight cores were processed and archived normally on board the D/V JOIDES Resolution. Figure 4 illustrates the first core recovered from Hole 1249B prior to measurement and processing. Core measurements including density and magnetic susceptibility were made onboard the JOIDES Resolution using a multisensor track. Bulk density, porosity and grain density core measurements were made on discrete samples. The occurrence of gas hydrates in the core material and their rapid dissociation precluded the measurement of natural gamma activity in the cores. These measurements require an extended length of time to complete the measurement process. High quality logs and image data were recorded in the downhole memory of the RAB-8 tool over the entire 74.9 m drilled interval in Hole 1249B. The RAB-8 tool was also calibrated post-deployment in salt water calibration tanks at Sugar Land, TX. The tool functioned properly during this test and the calibration showed the field data are reliable. RESULTS Figure 5 shows a summary of the primary core and drilling data acquired in Hole 1249B including resistivity images, and the resistivity and gamma ray logs from the RAB-8. Core measurements of discrete samples from Hole 1249B are presented at discrete depths from 29.9-75.0 m below seafloor (mbsf) as well as multisensor track core measurements. Core measurements have a depth accuracy of ±0.5 meters. Since core recovery averages only 32.9% in this hole, depth matching between core and log measurements may be somewhat imprecise at specific depths. Ties are made using density, magnetic susceptibility and gamma ray data, and for example, all three

3

measurements increase near 60 mbsf, indicating a change in lithologic content. Downhole drilling parameters recording during coring in Hole 1249B are also indicated in Figure 5. Hole 1249B was drilled to maintain a rate of penetration of 20 m/hr over each cored interval. Weight-on-bit ranged widely, however, as it was difficult to control precisely in these shallow and soft sediments. The time after bit (of the RAB-8 measurements) varies due to the time required to drill and recover each core, and substantially more time than standard drilling or LWD operations is required. The difference between drilling ahead and coring time may introduce some uncertainly in the core to log depth correlation. Core photographs of core 5-A (43 mbsf) indicates a gas hydrate rich core that largely dissociated creating a “mousse”-like fabric. The reflective areas are an indication of where the gas hydrate existed. Core 6-A (49 mbsf) indicates a change in the composition of the cored material. The mixed recovery in these materials is reasonable given that the MDCB core barrel is designed to be used in harder rocks. The MDCB system cuts core by rotation, filling of the barrel slowly as the bit advances. A piston-type core barrel is more conducive to high recovery of low-strength materials. The MDCB core barrel will be modified in the future to shorten the core length and reduce friction as the core enters the barrel. These are important changes aimed at improving core recovery with this system. A comprehensive suite of LWD data was acquired in nearby Hole 1249A using GVR-6TM and VDNTM tools (Fig. 6). The lateral offset between Hole 1249A and 1249B is 40 m. A difference of approximately 0.5 meters in water depth exists between the two sites. The logs from Hole 1249A show the rate of penetration and time after bit curves are lower than in Hole 1249B and remain relatively constant for the drilled interval (Fig. 6). The RAB-8 data collected in Hole 1249B are compared with GVR-6 data from nearby Hole 1249A in Figure 7 which shows important similarities and differences. The large increase in resistivity in the upper interval in both holes corresponds to the presence of gas and gas hydrate. Some variation in the image quality between the holes may be associated with the greater time after bit for the RAB-8 measurement (e.g. coring versus drilling operations). The gamma ray shows a linear trend with

an offset that may be attributed to the difference in standoff between the RAB-8 and GVR-6 tools. In general, the image data in Hole 1249A and 1249B correlate well, with differences due to environmental conditions and lateral variations in geologic heterogeneity between the two sites. CONCLUSIONS The deployment of a new logging-while-coring system for ODP drilling on Hydrate Ridge successfully acquired resistivity and gamma ray logs, and resistivity image simultaneously with core in Hole 1249B. This system offers the significant advantages of providing core and log data over the same drilled interval, and saving rig time. Time requirements for the logging while coring system are the same as for coring operations alone. Core recovery during this test reached 68.9% and averaged 32.8% over a 45 m drilled interval in shallow, soft marine sediments. Future deployments of the logging-while-coring system in harder rock environments offer the potential for improved core recovery using the motor driven core barrel. Core recovery in soft sediments may be increased by modifying other ODP core barrels to fit within the 3.45 inch annulus of the RAB-8 collar. Measurements on recovered core may be correlated directly with log data over the same drilled interval. LWD data from both conventional and while-coring operations at a nearby site agree well, and indicate the presence of gas and gas hydrate in clay rich sediments at this location. ACKNOWLEDGEMENTS Aleksandra Janik synthesized all the log and core data. We thank the Leg 204 shipboard party. Transocean Sedco Forex and crew, Sugar Land Engineering and Technical staff for their efforts to develop and deploy this new technology. This project was supported and funded by the National Science Foundation and the Department of Energy/National Energy Technology Laboratory. REFERENCES Lovell, J.R., R. A. Young, R. A. Rosthal, L. Buffington, and C. L. Arceneaux Jr., Structural Interpretation of resistivity-at-the-bit images, Trans.

4

SPWLA Annu. Logging Symp., 36th, pap. TT, 12pp. 1995 Leg 204 Logging Summary http://www.ldeo.columbia.edu/BRG/ODP/ODP/LEG_SUMM/204/leg204.html Leg 204 Shipboard Science Party, 2002, Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 204: College Station, TX. http://www-odp.tamu.edu/publications/ prelim/204_prel/204toc.html ABOUT THE AUTHORS Dave Goldberg is a Senior Research Scientist at the Lamont- Doherty Earth Observatory and Director of its Borehole Research Group, which manages logging services for the Ocean Drilling Program. He received B.S. and M.S. degrees in marine geophysics from MIT in 1981 and a Ph.D. degree in borehole geophysics from Columbia University in 1985. He is an active member of the Society of Professional Well Log Analysts, the Society of Exploration Geophysicists, and the American Geophysical Union. Greg Myers is presently serving as the Manager of Technical Services for the Borehole Research Group at the Lamont-Doherty Earth Observatory of Columbia University. Greg graduated from Rutgers University and has been involved with the field of borehole geophysics, field service, data analysis, tool research and development, new technology integration and operations management. He has participated in four Ocean Drilling Program Legs and is an active member of the Society of Professional Well Log Analysts. Kevin Grigar – Engineer – Texas A&M University Tom Pettigrew – Operations Manager - Texas A&M University

Stefan Mrozewski – Drilling Services Engineer – Schlumberger Drilling and Measurements Chuck Arceneaux – NGC Data Quality Manager - Schlumberger Drilling and Measurements Tony Collins – Principal Engineer Sustaining Schlumberger Drilling and Measurements Ocean Drilling Program Leg 204 Participants Gerhard Bohrmann, GEOMAR Kiel, Germany; Anne M. Tréhu, Oregon State University; Frank R. Rack, Joint Oceanographic Institutions Inc.; Nathan L. Bangs, University of Texas at Austin; Samantha R. Barr, University of Leicester; Walter S. Borowski, Department of Earth Sciences; George E. Claypool, Consultant; Timothy S. Collett, U.S. Geological Survey; Mark E. Delwiche, Idaho National Engineering and Environmental Lab; Gerald R. Dickens, Rice University; David S. Goldberg, Lamont-Doherty Earth Observatory; Eulàlia Gràcia, Unitat de Tecnologia Marina; Gilles Guèrin, Lamont-Doherty Earth Observatory; Melanie Holland, Arizona State University; Joel E. Johnson, Oregon State University; Young-Joo Lee, Korea Institute of Geoscience and Mineral Resources (KIGAM); Char-Shine Liu, National Taiwan University; Philip E. Long, Pacific Northwest National Laboratory; Alexei V. Milkov, Woods Hole Oceanographic Institution; Michael Riedel, Geological Survey of Canada; Peter Schultheiss, GEOTEK Ltd.; Xin Su, China University of Geosciences; Barbara Teichert, GEOMAR Kiel, Germany; Hitoshi Tomaru, University of Tokyo; Marta E. Torres, Oregon State University; Maarten Vanneste, Universitetet i Tromsø Norway; Mahito Watanabe, Geological Survey of Japan, AIST; Jill L. Weinberger, University of California, San Diego

5

Table 1: Coring Summary in ODP Hole 1249B. Core # Advance Recovery % rec. 1W 29.9 m - - 2A 4.5 3.05 67.78 3A 4.5 1.92 42.67 4A 4.5 1.15 25.55 5A 4.5 0.93 20.67 6A 4.5 2.06 45.78 7A 4.5 0.57 12.67 8A 9.0 3.81 42.33 9A 9.0 0.52 05.78 total 45m average 32.9%

Figure 1. The logging while coring system developed by ODP and Schlumberger. The motor driven core barrel depicted in yellow passes through a modified Schlumberger RAB-8 collar to allow the acquisition of resistivity and gamma ray data while collecting a full core.

Figure 2A. Testing the logging while coring system at the Schlumberger Genesis rig.

Figure 2B. Successful Genesis rig test yielding first core through a RAB-8 tool.

6

Drilling Sites

CA

SC

AD

EA

RC

W120û124û128û50û

46û

42û

-1200

-1100

-100

0

-900

-800

1249

125¡09' W 125¡ 06' W 125¡ 03' W

44¡36'

N

44¡ 33'

N

A

Hyd

rate

Rid

ge

B

Figure 3A and 3B. Location map and bathymetry of Hydrate Ridge test site off the coast of Oregon.

Figure 4. Core recovered using the logging while coring system aboard the Ocean Drilling Program drillship, JOIDES Resolution.

7

Depth (mbsf)

RA

B-8

Sta

tic I

ma

ge

De

ep

Re

sis

tivity

Orie

nta

tio

nN

ES

WN

Lo

wH

igh

(oh

m-m

)

RA

B-8

Re

sis

tivity

BD

AV

(o

hm

-m)

02

04

00 10

20

30

40

50

60

70

40

60

80

RA

B-8

Ga

mm

a R

ay

GR

(g

AP

I)

0.5

11

.5

RA

B-8

Co

re

MS

T D

en

sity

(g

/cm

3)

1.5

51

.65

1.7

5

(g/c

m3

)

RA

B-8

Co

re

Bu

lk D

en

sity

54

58

62

66

RA

B-8

Co

re

Po

rosity

(%)

2.6

82

.72

2.7

6

RA

B-8

Co

re

Gra

in D

en

sity

(g/c

m3

)

0 10

20

30

40

50

60

70

02

04

0

(r

ela

tive

un

its)

RA

B-8

Co

re

MS

T M

ag

. S

usc.

10

20

30

40

03

00

06

00

0

RA

B-8

Tim

e a

fte

r B

it

RT

IM (

s)

Pe

ne

tra

tio

n R

ate

RO

P5

(m

/hr)

204-1

249B

-5A

-1, 15-3

0 c

m

Mousse-lik

e a

nd s

oupy

textu

re c

aused b

y d

issocia

tion

of hydra

te

204-1

249B

-6A

-2, 57.5

-77.5

cm

Cla

y w

ith d

ark

gre

enis

h p

atc

h

and d

ispers

ed s

ponge s

pic

ule

s

1249B Core

Recovery

2A

3A

4A

5A

6A

7A

8A

9A

20 cm15 cm

Core

Photo

s

Figure 5. Data acquired from Site 1249B including resistivity images, resistivity and gamma curves and data from core collected through the logging while coring system.

8

RAB Static Image

Medium Resistivity

Orientation

Low High(ohm-m)

Depth

(m

bsf)

0

10

20

30

40

50

60

70

80

Density Correction

(DRRT)

GammaRay

Differential Caliper Density

Photoelectric Effect

Porosity

RPM Averagedover 5ft

Shallow Resistivity Average

Medium Resistivity Average

Deep Resistivity Average

Density Correction(DRHO)

Resistivity Time after Bit

Rate of Penetration

0

10

20

30

40

50

60

70

80

0.2 250ohmm

0.2 650ohmm

0.2 250ohmm

0 70API 0 2in 1 2g/cm3

2 4b/e

-0.1 0.1g/cm3

0.0 0.3g/cm3

50 90% 10 50m/hr

400 1500hr

10 60rpm

Leg 204 Hole 1249A LWD (GVR-6 and VDN)

Figure 6. Data acquired using the GVR-6 and VDN tools from Hole 1249A, adjacent to Hole 1249B.

9

1249b RAB-8 Static Image

Deep Resistivity

OrientationN E S W N

Low High(ohm-m)

1249A GVR-6 Static Image

Deep Resistivity

OrientationN E S W N

Low High(ohm-m)

00 1010 2020 3030 4040 5050

00 5050 100100 150150 200200

0

10

20

30

40

50

60

70

80

90

RAB-8 (1249B) and GVR-6 (1249A)

Resistivity

BDAV (ohm-m)

0 20 40 60 80 100

0

10

20

30

40

50

60

70

80

90

RAB-8 (1249B) and GVR-6 (1249A)

Gamma Ray

GR (gAPI)

Figure 7. A comparison of responses between the RAB-8 to the GVR-6 tools in adjacent holes.

10