A database of archived drilling records of the drill cuttings pilesat the North West Hutton oil platform

Roy Marsh

School of Medicine, Health Policy and Practice, University of East Anglia, Norwich NR4 7TJ, UK

Abstract

Drill cuttings piles are found underneath several hundred oil platforms in the North Sea, and are contaminated with hydro-

carbons and chemical products. This study characterised the environmental risk posed by the cuttings pile at the North West Hutton

(NWH) oil platform. Data on the drilling fluids and chemical products used over the platform�s drilling history were transferred

from archived well reports into a custom database, to which were added toxicological and safety data. Although the database

contained many gaps, it established that only seven chemical products used at NWH were not in the lowest category of the Offshore

Chemicals Notification Scheme, and were used in only small quantities. The study therefore supports the view that the main en-

vironmental risk posed by cuttings piles comes from hydrocarbon contamination. The (dated) well records could help future core

sampling to be targeted at specific locations in the cuttings piles. Data from many platforms could also be pooled to determine

generic �discharge profiles.� Future study would benefit from the existence, in the public domain, of a standardised, �legacy� database

of chemical products.

� 2003 Elsevier Science Ltd. All rights reserved.

Keywords: North sea; Cuttings; Oil; Decommissioning; Risk

1. Introduction

Most of the 440 and gas platforms in the North Sea

will be decommissioned over the next 25 years. The

debate on the potential environmental impacts of de-

commissioning has focused on the fate of the platform

structures (DTI, 1995). However, there are also poten-

tial risks associated with the drill cuttings piles foundunderneath 250 platforms in the UK and Norwegian

sectors (CORDAH, 1998). These piles were created over

a period beginning in the early 1970s. Some piles have

reached a height of more than 5 m and can reach a di-

ameter of up to a 100 m (Shell, 1997; CORDAH, 1998).

The total volume of the piles is estimated to be 700,000

m3 in the central North Sea and 500,000 m3 in the

northern North Sea (UKOOA, 2001a,b). Cuttings pilesare not found in the southern North Sea, since the

currents there are strong enough to wash discharges

away before they can settle on the sea bed. A 1% limit to

oil-on-cuttings came into force in 2000 (OSPARCOM,

1992), obliging drilling operators to transport their drill

cuttings onshore, for treatment or disposal. New cut-

tings piles are therefore not being formed.

Cuttings piles are contaminated with mud, a viscous

fluid used to facilitate drilling. Three broad types of mud

have been used in the North Sea: water-based (WBM),

oil-based (OBM) and synthetic, esther-based (SM).

Diesel was used for OBMs until it was banned in 1984,being replaced by SMs, which have lower-toxicity to

humans. Mud also contains various chemical products,

whose uses include lubricating, cleaning and cementing.

All chemical products used on the UK continental shelf

must be listed in the Offshore Chemical Notification

Scheme (OCNS), classified into �Groups� based on their

potential biodegradation, bioavailability and toxicity.

The OCNS list is maintained by the UK�s Centre forthe Environment, Fisheries and Aquaculture Science

(CEFAS, Web––http://www.cefas.co.uk/ocns).

Cuttings piles are a potential environmental risk.

Greenpeace have called for �the oil and gas companies

[to] return the sea bed to the state it was prior to oil and

gas development� (Greenpeace, 2001). This would entail

the costly physical removal of the piles. Other optionsE-mail address: roy.marsh@uea.ac.uk (R. Marsh).

0025-326X/03/$ - see front matter � 2003 Elsevier Science Ltd. All rights reserved.

doi:10.1016/S0025-326X(03)00041-9

www.elsevier.com/locate/marpolbul

Marine Pollution Bulletin 46 (2003) 587–593

include leaving the piles in situ, treating or capping

them, or removing them for treatment onshore (COR-

DAH, 1998). In 2001, the United Kingdom Offshore

Operators Association (UKOOA) sponsored a £4.4million study of the cuttings piles at the Beryl and

Ekofisk 2/4-A platforms (UKOOA, 2002). This study

examined cuttings recovery technologies, sediment dis-

turbance modelling, natural degradation, and the envi-

ronmental impact of cuttings piles. Core samples taken

from the two piles were tested for ecotoxicity. The study

findings were inconclusive. The study could not �con-

clusively rule out the presence of [� � �] non-hydrocarboncomponents which could have contributed to the overall

acute toxicity of the samples� (UKOOA, 2002, p. 45).

Further, generic studies of the ecological impact of

cuttings piles have been carried out by the US Envi-

ronmental Protection Agency (EPA, 1999).

From March 1998 to May 1999, a study was under-

taken of the ecotoxicological risk posed by the cuttings

pile found under the North West Hutton (NWH) oilplatform. This study was funded by (then) Amoco, and

is reported in Gerrard et al. (1999). NWH is located

about 130 km north-east of the Shetland Isles, in block

211/227A of the UK sector. Drilling at NWH effectively

stopped in 1991. The cuttings pile lies at a depth of 140

m and has a volume of about 25,000 m3.

Here, we report on an accompanying study of the

platform�s archived drilling records. This study soughtto estimate the quantity of cuttings, mud, chemical

products and hydrocarbons discharged over the entire

platform drilling history. This would constitute an upper

bound on the quantities resident in the cuttings pile

today.

2. Methods

Data on NWH�s drilling activities and usage of

chemical products were obtained from the mud and well

reports, archived in Amoco�s London and Aberdeen li-

braries. These reports had originally been filed during

drilling by on-site engineers. Where necessary and fea-

sible, the data were reformatted, �cleaned� and standar-

dised into metric measures. Data were obtained in hardcopy or CD-ROM format, and were entered into a

custom relational database. This database was designed

to respect the principles of referential integrity (Con-

nolly and Begg, 1999), facilitating subsequent analysis.

The core entity in the database was the �well interval� (or

�section�). Interval diameters were generally 36, 26, 17.5,

12.25, and 8.5 in. All materials used at the 233 intervals

of the 53 wells were recorded, covering the entire historyof drilling operations at NWH.

Cuttings. The total mass of cuttings discharged was

calculated from the length and diameter of the the well

interval, using the standard formula (as given in nu-

merous well reports) ½3:6 � A2 � B=10000�, where A is

the borehole diameter in inches, and B is the hole depth

in feet. Interval lengths were calculated either as the

Total Depth (TD) to TD figures for each interval, orfrom SPUD depth to TD for the initial 36 in. hole.

Mud. The quantities of mud used were explicitly re-

corded in the well reports for only 35 of the 53 wells.

Mud usage was therefore calculated indirectly, based

on a simple �mass balance� formula: Mud Used ¼ Mud

Input)Mud Output. Other terms found in the reports

were treated as synonyms: �Lost� (for �Used�); �Recov-

ered,� �Salvaged� or �Backloaded� (for �Output�); and�Received� or �Built� (for �Input�).Chemical products. The quantities of chemical pro-

ducts used were given in the well reports. Other sources

provided information on the products� composition,

toxicity, regulatory human exposure limits, and the

standard UK risk and safety codes. For generic pro-

ducts, these sources were public domain, such as the

directory of the UK�s Committee on Substances Haz-ardous to Health (COSHH, 1988), and governmental or

laboratory Web sites (for example, the Physical & The-

oretical Chemistry Laboratory at Oxford University,

and the CEFAS list (CEFAS, 2002)). For proprietary

products, the main sources of information were the

Materials Safety Data Sheets (MSDS) obtained from the

principal mud suppliers for NWH. An Internet search

was also made, using the Google search engine (www.google.co.uk), with the search expression �<PRODUCT

NAME> AND MSDS.� The Yale and Cornell Univer-

sities� MSDS �gateway� sites were also used.

Hydrocarbons. The �oil on cuttings� figures given in the

well reports were not used, since these were based on a

�retort analysis� procedure which is understood to have

been unreliable in the 1980s. The hydrocarbon content

of the mud was instead determined to be the average ofthe figures given in the �Mud Property Recap� sections of

three randomly chosen well reports.

3. Results

Cuttings. Almost 52,000 tonnes of cuttings were dis-

charged at NWH.Mud. For the whole platform, 661,432 barrels of mud

is shown in the well records as �Input,� with 338,363

Table 1

Mud losses at North West Hutton

Total

inputs

Losses Losses/

inputs

All intervals 661,432 323,069 0.49

Only OBM intervals 593,119 267,095 0.45

Only OBM, no �poor data� 455,004 214,360 0.47

Only diesel OBM intervals

(A1–A15)

238,975 103,134 0.43

588 R. Marsh / Marine Pollution Bulletin 46 (2003) 587–593

Table 2

Generic and proprietary products used at North West Hutton

Substance MSDS OCNS ECO TOX

1 ABE 73 1,000.00 l

2 ANCO HI-LUBE Y Y 2,000.00 l

3 ANCOCIDE Y Y 2,450.00 l

4 ANCOQUAT 67,200.00 l

5 ANCOQUAT FC Y N 23,450.00 kg

6 Ancoquat �I� Y N 102,200.00 l

7 Baroid 2,238.00 m

8 BUT-IL 2,082.00 l

9 Butyl Oxitol Y 2,082.00 l

10 BW Eurogel E 2,600.00 kg

11 Carbogel 8,725.00 kg

12 Carbogel 1 39,025.00 kg

13 Carbomix 104,638.00 l

14 Carbomul 12,000.00 l

15 Carbomul H.T. 190,368.00 l

16 Carbotec HW 39,200.00 l

17 CARBOTROL A9 12,500.00 kg

18 Carbovis 11,250.00 kg

19 Ceraseal E 750.00 kg

20 CMC HEC 12,800.00 kg

21 CRONOX 1,457.00 l

22 CRONOX 666 C 1,249.00 l

23 Cronox 668 416.00 l

24 Cronox 669 416.00 l

25 CW 3/4 2,498.00 l

26 CW2 215,254.00 l

27 CW3 303,934.00 l

28 CW4 251,640.00 l

29 D DETERGENT 1,600.00 l

30 D21 Defoamer 208.00 l

31 DEFOAMER Y Y 325.00 l

32 Delta P E 21,478.00 kg

33 Drill Carb E 2,250.00 kg

34 Driltreat 12,951.00 kg

35 Driltreat E Y 1,376,150.00 l

36 Duratone 96,129.00 kg

37 EUROGEL (BW) 1,000.00 kg

38 Ez Mul 935.00 kg

39 Ez Mul 259,183.00 l

40 Ez Spot B Y 71,008.00 l

41 FCL 2,309.00 kg

42 G-100 3,375.00 kg

43 GEL 201.00 m

44 Geltone Y 218,816.00 kg

45 Geltone 4,542.00 l

46 H.E.C Y E N 12,350.00 kg

47 HPD Polymer 4,275.00 kg

48 Invermul 880.00 kg

49 Invermul 176,777.00 l

50 Invermul L 12,074.00 l

51 KCI POWDER 51,725.00 kg

52 KCL 14,650.00 kg

53 KCL/ANCOQUAT I 1,070,824.00 l

54 KENCAL-L 25.00 kg

55 KENCAL-L 51,627.00 l

56 KENGEL 128,793.00 kg

57 KENOL L 7,286.00 l

58 KENOL-ES 2,420.00 kg

59 KENOL-ES 300,607.00 l

60 KENOL-ESV2 16,654.00 l

61 Kenox 11,850.00 kg

62 KENSPERSE 11,033.00 l

(continued on next page)

R. Marsh / Marine Pollution Bulletin 46 (2003) 587–593 589

barrels as �Recovered,� leaving a balance of 323,069

barrels as �Used� (i.e. �Lost�). The Lost-to-Input ratio is

0.49. That is, almost half the mud used on the platform

was discharged overboard (or left in the boreholes).

Diesel-based mud was used on the first 15 intervals,

accounting for 36% of total inputs (Table 1).

Chemical products. The final database shows that 157

products were used at NWH, stored as 2000+ records. Iftrivial redundancy due to varying units (�kg,� �l,� �sx,� �m�)and concentrations (calcium chloride at 86%, 88%, etc.)

is discounted, then about 130 distinct products remain.

Some of the chemical products given as �Input� were

still in the mud recovered at the end of each interval�sdrilling run, and so were not lost to the environment. An

attempt was made to estimate quantities involved by

using the mud Output/Input ratio for each well intervalas a pro rata multiplier for that interval�s chemical

product usage. Unfortunately, such estimation was

sensitive to any gaps in the mud records, and was

therefore abandoned. The �Input� quantities were then

taken as an (admittedly worst-case) indicator of the

quantities of chemical products which could currently be

in the cuttings pile.

Table 2 shows the chemical products used at the

platform, and also indicates the availability of MSDSand OCNS information (on either the Revised list or an

old list). MSDSs for 19 products were found, nine of

which also gave ecotoxicological data. Ecotoxicological

data were found for four products for which other

MSDS data could not be found. Seventeen products

were found in the current, Revised OCNS list. Two

products were found on an old OCNS list. The table

does not show the products identified by the Oslo-ParisConvention (OSPAR) as �Plonor,� �Posing Little or No

Table 2 (continued)

Substance MSDS OCNS ECO TOX

63 Kentrol-L 5,413.00 l

64 KLEENZZ-120 27,271.00 l

65 Kwikseal Y E N 20,237.00 kg

66 LIQUID CASING E 5,114.00 kg

67 LUBRAGLIDE E 44,182.00 kg

68 MAGCOGEL Y Y 9,100.00 kg

69 Magnocol 1,850.00 kg

70 mcs-b 1,200.00 l

71 MCSA 1,800.00 l

72 MILGEL E 1,550.00 kg

73 Milplug Fine 750.00 kg

74 ML 1013 1,457.00 l

75 N-BUTYL OXITOL 2,082.00 l

76 Oil Faze 6,023.00 kg

77 Oil Mud 1,041.00 l

78 OMC Y 12,076.00 l

79 OMW (Oil Mud wash) Y N 32,682.00 l

80 Pre-mix 32,112.00 l

81 Rhodopol 12,935.00 kg

82 RX-02 Y 2 Y 4,371.00 l

83 RX-08 Y 1 Y 9,784.00 l

84 S491 416.00 l

85 SIX UP 4,380.00 l

86 Slik5 Y 247,711.00 l

87 SMX 8,750.00 kg

88 Soltex Y D N 1,136.00 kg

89 Super Seal 1,102.00 kg

90 SURFLO 3,123.00 l

91 Surflo CW4 29,561.00 l

92 Surflo S30 Y 100.00 kg

93 Surflo S30 97,409.00 l

94 Surflo S300 208.00 l

95 Venfyber Y 104,957.00 kg

96 VERSACOAT Y N 73,070.00 l

97 VERSAMUL Y Y 97,634.00 l

98 VG69 Y Y 81,801.00 kg

99 VR 28,501.00 kg

100 Walnut Y E N 7,150.00 kg

101 WO DEFOAM B 80.00 l

102 Wyoming Bentonite 7,050.00 kg

103 XC Polymer Y E Y 12,008.00 kg

104 XCD Polymer E 16,993.00 kg

590 R. Marsh / Marine Pollution Bulletin 46 (2003) 587–593

Risk to the environment� (OSPAR, 2002). Seven prod-

ucts were identified as not being in the lowest category

on either OCNS list (Table 3).

Safety and toxicity information was generally sparse,

even for the better-reported products. An example is

MI�s Versacoat, an emulsifier for drilling fluids. This was

used on eight wells in the second half of the 1980s. The

MSDS for Versacoat lists the active ingredients asmethanol, diethylenetriamine and fumaric acid, each of

which has is own risk phrase and Chemical Abstracts

Service number. Versacoat is described as �flammable�and �harmful,� but there is little information on the

product�s natural bio-degradation, and no information

on its ecotoxicity or anaerobic biodegradation (the

condition prevailing in the bulk of the cuttings pile).

Versacoat does not appear in the Revised OCNS list.Hydrocarbons. The estimated hydrocarbon content of

the mud was 62.5% by volume. That is, about 26 million

litres of hydrocarbons were lost from the platform in the

mud.

4. Discussion

Mud. Clearly, not all mud lost from NWH was taken

up in the cuttings pile. A certain proportion would

have been either recovered or carried away by water

currents. However, a reliable estimate of the latter

would require sophisticated hydrodynamic modelling.

Until this is done, there is no alternative to the worst-

case assumption that all the mud lost went into the

cuttings pile.Chemical products. In the Revised OCNS, �the ton-

nage limits triggering prior notification of use are set for

the cumulative quantity of all products (including muds)

within each hazard group used at individual sites per

year� (CEFAS, 2000, p. 35). That is, the more hazardous

the product, the lower the tonnage threshold at which

the company must notify the government. Bearing in

mind the quantities used, none of the products shown inTable 3 that carry a Revised OCNS rating would require

prior notification of use. This suggests that they are not

of current concern. However, the status of products that

are no longer in use, carrying a risk rating only under

the old OCNS scheme, remains unclear. The old OCNS

categories ceased to exist with the expiry of category 0

on 1st January 2000, being wholly replaced by OSPAR�sHarmonised Offshore Chemical Notification Format.

The old OCNS products can no longer be used off-

shore, and �the old numerical categories cannot . . . betranslated into Revised OCNS groups, since the latter

are derived from a more comprehensive set of tests�(CEFAS, 2000). However, the old OCNS categories

arguably still have some significance, in that the cuttings

piles are still on the seabed, and there is no other source

of comprehensive toxicity information.

Specifically concerning anaerobic bio-degradability,

the OCNS Guidelines remark: �If [an anaerobic biode-gradation test] is not conducted, the substance will be

assumed to be non-biodegradable in anaerobic condi-

tions� (CEFAS, 2000, p. 30). This makes no claim about

ecotoxicity. The tone of some MSDSs is less neutral. For

example, the MSDS for VG69 (a viscosifier, of which 81

tonnes was used at NWH) states: �Product is insoluble in

water and likely not to be harmful to aquatic environ-

ment� (Rockwood, 2001).Overall, the information found on the chemical

products used at NWH was clearly limited. There were

gaps in the well reports, including missing entries in the

Input, Outputs or Used sections, along with the in-

complete reporting of the mud transfers between wells

and between platforms. Some well reports did not in-

dicate at what stage in drilling the products had been

used Compositional and toxicity data were also incom-plete, and often only qualitative (�skin irritant�). The

composition of some proprietary products was com-

mercially confidential (for example, VG69, as supplied

by Rockwood Additives). Conversely, for some generic

products, such as diethylenetriamine, several MSDSs

were found from different sources, and it was not clear

which source was the most authoritative. Moreover,

safety data were sometimes associated with a propri-etary product (such as �Ancocide,� 2450 l of which was

used in the final wells A51 and A52) and sometimes with

Table 3

The seven products used at NWH which were not in the Lowest OCNS Group/Category

Additive Supplier Function OCNS Specific concerns �Worst-case� estimate

Roemex RX-02 Magcobar Imco Surfactant 2 Endocrine disruptor 4371 l

Roemex RX-08 Magcobar Imco(M-I Drilling

Fluids UK Ltd)

Surfactant 1 Endocrine disruptor 9784 l

Ez Spot Baroid Drilling Fluids (Halli-

burton Brown & Root Ltd)

Emulsifier and lubri-

cant

B (no details found) 71,008 l

Soltex Baroid Drilling Fluids (Halli-

burton Brown & Root Ltd)

Shale inhibitor D Metals 1136 kg

CRONOX 666 Baker Petrolite Corrosion inhibitor C (no details found) 1249 l

FCL Milpark Completion fluid 4 Chromium 2309 kg

WO Defoamer Milpark Cementing defoamer B (no details found) 80 l

R. Marsh / Marine Pollution Bulletin 46 (2003) 587–593 591

that product�s generic ingredients (such as Glutaralde-

hyde, which forms 25% of �Ancocide� by volume, and is

given a �C� category under OCNS). Finally, several

products (such as �Amido amide�) remained unidentifiedthroughout.

These gaps in information were in part due to the

limited time the researchers had to locate informa-

tion that in some cases was two decades old. It is

clear that the reporting regime of that time cannot now

be objectively audited (occasional anecdotal references

in the well reports to irregular procedures are insuffi-

cient in this respect). Consequently, the level of accu-racy of the well reports cannot be gauged. In addition,

the interpretation of the terms used in the well reports

is unclear––for example, whether �Lost to surface,��Lost/Dumped� and �Discharged overboard with cut-

tings� have precisely the same meaning. The expertise of

an �insider� (such as a drilling engineer) would have

helped in these cases, but this was not available during

the study.A more fundamental uncertainty lies in the indeter-

minacy of some of the data. For example, the molecular

weight of hydroxethyl cellulose ranged in one supplier�sspecification from 60,000 to 100,000. The concentration

of active ingredients in the medium also varied.

In the face of such gaps and uncertainties, it is clear

that the desk study of NWH records supports a quali-

tative risk characterisation, rather than a quantitativerisk assessment. The study has nevertheless identified all

the products used at NWH since drilling began. It has

also established that the seven products that do not

appear to be in the lowest (least harmful) OCNS cate-

gory were used in small quantities only. Concern has

been raised by Greenpeace over the metal content of

Soltex, one of these products (Greenpeace, 1995).

However, the composition of Soltex is a trade secret(CPC, 2000) and Greenpeace�s sources are unknown. It

is tentatively concluded that the presence of chemical

products in the NWH cuttings pile is of less concern

than the evident hydrocarbon contamination of the pile,

as reported in Gerrard et al. (1999).

Future research could take a number of directions.

The behaviour of discharged mud in the water column

could be hydrodynamically modelled. The feasibility ofthis would depend on the availability of sufficiently de-

tailed data on the weather, tidal conditions and the

drilling regime during NWH�s period of active opera-

tion. Alternatively, time-stamping of well records could

allow core sampling to be targeted at those locations

where specific contaminants were most likely to be

found in the cuttings pile. Lacking such clues, the field

study of the Beryl and Ecofisk piles, carried out byUKOOA, sampled only the surface 20–50 cm (UKOOA,

2001a,b, pp. 9–10). Finally, if the NWH cuttings pile

data could be pooled with data from other North Sea

platforms, then a range of generic platform �discharge

profiles� could perhaps be determined, enhancing the

interpretability of individual platform data.

In summary, study of archived data is a natural

complement to field studies, especially given its far lowercost. It is to be hoped that the data presented here will

be more fully exploited in future. The greatest obstacle

to such exploitation is the inaccesibility of the safety and

(eco-) toxicity data for drilling fluids and their consti-

tutents. The difficulty facing a journalist or a researcher

wishing obtain such data has been pointed out elsewhere

(Reddy et al., 1995). Thousands of MSDSs are distrib-

uted in an ad hoc fashion across numerous suppliers�Web sites, many of whom charge registration fees. In-

formation may also be commercially confidential, even

for products no longer in use. Future study would

therefore be greatly helped by the creation of a stan-

dardised international �legacy� database on all the

chemical products which are, or have been, used on oil

platforms. The database would include the information

found in MSDSs and in the OCNS lists––even the ob-solete lists––along with explanatory notes. This infor-

mation should arguably be in the public domain and

free.

Acknowledgements

The work was carried out while the author was Re-search Associate in School of Environmental Science, at

the University of East Anglia. The Project Manager was

Dr. Simon Gerrard. General correspondence should be

addressed to the author. Specific queries concerning

ecotoxicological aspects of the NWH cuttings pile

should be addressed to Dr. Alastair Grant, at the School

of Environmental Science.

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