The Life Cycle of Brent Field

BRENT FIELD LIFE CYCLE 1

Running head: The Life Cycle of Brent Field

The Life Cycle of Brent Field, Block 211/29, United Kingdom, North Sea

From The Beginning of History to Present

Nazur Riza bin Norkaman

University of Malaya

Word Count: 1422 words


Abstract

The largest oilfield in UK jointly owned by Shell and Esso was discovered via seismic

reconnaissance, exploration and appraisal drilling since 1971. The monoclinal structure field as

interpreted a buried Jurassic tilted fault block contained two main payzones which were

eventually developed and produced for oil and gas. The field produced 1.99 MMSTB oil and 6.8

TCF of gas to date from its four production areas. The field is now undergoing decommissioning

efforts due to the decline in production.


CONTENTS

Title page..

Abstract....

Contents

Introduction .

Field Life Cycle

Contract and Lease......

Exploration and Appraisal ..

Field Development.......

Field Production

Field Decommisioning .

Reference.

Figures Caption...

1

2

3

4

6

6

6

10

11

15

16

19


The Life Cycle of Brent Field, Block 211/29, United Kingdom, North Sea: From The

Beginning of History to Present

Introduction

This paper will attempt to describe the illustrious history of one of the significant oil and

gas fields in North Sea. Readers can expect to learn the life cycle of Brent Field in the following

chapters starting from its early days of exploration to its present productions and

decommissioning efforts.

Oil and gas history in the North Sea began since 1859 and have been strongly motivated by

many geopolitical events, legislation and territorial disputes, change in economic climate and

long process of technological improvements that led to significant oil and gas discoveries in the

region (Brennand et. al, 1998). Despite the long history, the Brent field only came into picture

after a successful exploration program in the East Shetland Basin by Shell and Esso during the

third and Post-Ekofisk fourth licensing round in UK between 1970 to 1971. The Brent field is

located 186 km offshore, North-East Lewick, Scotland at water depth of 140 m (figure 1). The

flagship field on the UK Continental Shelf is operated by Shell UK Limited and is jointly owned

by Royal Dutch Shell (50%) and ExxonMobil (50%). It was the first giant discovery made in

UKs northern North Sea sector with largest accumulation in UK in barrels of oil equivalent term

(boe).


Figure 1: Location of Brent Field in the Northeastern international boundary of UK portion of North Sea.


Field Life Cycle

Contract and Lease

Brent field is located within block 211/29 of United Kingdom licensing area in Northern

sector of North Sea. The field was developed by Shell UK Exploration and Production on behalf

of Shell and Esso joint venture under production license P.117 awarded in the 3rd license round

in 1970. The current production license will expire in 2018 (Taylor et. Al, 2003).

Exploration and Appraisal

Brent field was first delineated through aeromagnetic reconnaissance and 1970 sparse 2

km x 2km 2D seismic grid which was also augmented by 1966 seismic vintage (figure 2). On

those seismic, the field resembles a buried monoclinally dipping high beneath a ubiquitous

unconformity. In July 1971, Shell decided to drill its first wildcat exploration well in the East

Shetland Basin to explore the potential of onlapping sand above the regional unconformity and

explore the unproven Pre-Cretaceous hydrocarbon play. Well 211/29-1 was drilled downdip from

the structure and found no significant sand development in the Tertiary section. However,

approximately five meters from the prognosed objective the well kicked causing oil and sand to

sprung to surface. Subsequent logging operations confirmed 43 m of undersaturated oil bearing

sand and 142 m of net reservoir sand were present in the vicinity (Taylor et al, 2011;IHS, 2014).


Figure 2: Complexity in the reservoir architecture and structural domain of Brent field was

studied in depth through well logs, core and seismic data. The field was first identified in 1970

on 2 km x 2 km 2D seismic but soon after, more infill lines were acquired in 1972, 1973, 1974

and 1979 to allow further exploration works on the field. A close 200 m spaced regular 2D grid

were acquired in 1980 to allow reservoir horizons to be mapped from Pseudo-3D data generated.

In 1986, the first 3D Brent seismic Survey was recorded and reprocessed for image

enhancements in 1989 and 1993. The last seismic acquisition program in the field took place in

1995 and it proved to realized the full potential of the field with superior data quality to map the

Brent and Statfjord eastern margins and slumps (IHS, 2014; Taylor et al, 2003).

The discovery reshaped pre-1971 sceptic notions which associated major structures mapped at

the base of Cretaceous level to be the top of basement (Knag, South & Spencer, 1995). It spurred

subsequent appraisal wells drilling from 1972 to 1974 to identify the limit of the structure,

establish the hydrocarbon column accumulated and ultimately perform well test on the payzones

appraised. From these appraisal wells and further seismic and stratigraphic framework studies

(figure 3 & 4), it was soon established that the Brent Field was actually located at the footwall of

N-S oriented, westerly dipping late Jurassic fault block consisting of two Mid Jurassic

hydrocarbon bearing reservoir formations; the Brent group and Statfjord formation (Livera and

Gdula, 1990). The entire discovery field is approximately 16 km in length and 5 km in width and

formed a combination structural and stratigraphic hydrocarbon trap sealed by Late Jurassic and

Cretaceous Syn-rift and Post-rift sediments (McLeod and Underhill, 1999). In a separate

exploration program, Brent South was discovered in 1973 in block 3/4A. Oil and gas within


similar petroleum system were discovered in Brent and Statfjord formation. The field was sold to

Shell and Esso in 1991 to be brought onstream through the Brent Field production facilities.

Figure 3: Brent field appears to be a monoclinally dipping structure beneath a regional

unconformity layer. The field is located within the east Shetland basin and lies within a major

fault terrace bounded to the west by Hutton Dunlin-Muchison fault zone and to the east by

Eastern Boundary faults. Five appraisal wells (211/29-2 to 211/29-5) were drill in succession

from 1972 to 1974 to evaluate the true hydrocarbon column within the structures and to delineate

the boundaries of the fields, besides to conduct production test in the Brent Group and Statfjord

reservoirs


Figure 4: Lithostratigraphic column of Brent field and the simplified cross-section

demonstrating the working petroleum system for the field.

The successful exploration and appraisal program conducted since 1971 have unlocked a

total resource estimate of 3.8 MMMSTB oil/condensate-in-place and estimated 7.5 TSCF of wet-

gas-in-place (figure 5). The total recovery from all reservoirs were expected to be 1988 MMSTB

oil and condensate and 6000 BSCF gas (Taylor et al, 2011).


Figure 5: Discovery of the giant Brent Field recorded a swift jump in creaming curve for

exploration discoveries in the North Sea. It opened up new opportunities for hydrocarbon

exploration in new Middle Jurassic Plays (Glennie, 1998).

Field Development

Based formation evaluation and well test results from well 211/29-1 and 211/29-2, the first

development plan for the field was planned in 1972 involving the placement of three concrete

legged platform. However, this planned was later revised to include a fourth fixed leg producing

platform following new discoveries and successful delineation of the field limits in the oil

province from four additional appraisal well drilling. Development drilling commenced in

February in 1972 from Platform B. All development wells were drilled as deviated wells to

provide drainage and down-dip production pressure support injection point for Brent and

Statfjord reservoirs. Since the Brent reservoir host two-third of the resource, the initial

development of the Brent Field exclusively focused in draining the mid-oil column reservoir for

production. The Statfjord reservoir and crestal slump features were developed much later

between 1994 to 1997 after better assessment were conducted based on improved data (figure 4).

Over the span of 38 years, a total of 349 wells were drilled for development and production


purposes (i.e producers, water and gas injectors, auxillary well) and was responsible for the

cumulative production of 1.99 MMSTB oil and 6.8 TCF of gas to date.

Figure 6: Brent Crestal Slump Model were able to be produced with improved 3D seismic data.

The advent of this model allow new development drilling to start in the crestal slump areas since

mid 1990s (Taylor et al, 2003).

Field Production

Brent field production came from four production areas, the Main, Horst, Graben block and

crestal slump which were essentially separated by E-W trending faults (figure 7). The first oil

came onstream from Platform B in 1976 and production from Platform D, A and C followed in

1977, 1978 and 1981 respectively (Figure 8). The first oil production was exported through Brent

Spar, a storage and tanker facility. In 1978, the Brent pipeline system was commission and

produced oil was exported to oil terminal in Sullom Voe in Shetland Islands through this system.

Production of gas through FLAGS line to St Fergus in Scotland started since 1982. The Brent

Field have went through significant increase in production since its early development days with

highest production peaked for oil in 1984 at 410 MBBL/D whilst the highest gas production

peaked in 1999 at 860 MMSCF/D (figure 9).


Figure 7: Location map of development and production well on the Brent structure (Taylor

et al, 2003; Livera & Gdula, 1990) .


Figure 8: Position of Brent Alpha, Bravo, Charlie, and Delta Platforms as well as

surrounding facilities (pipeline, flare, spar) within Block 211/29, UK (Taylor et al.,2003;

Shell, 2007).

Improvement of hydrocarbon recovery during Brent field production involved many efforts

and utilization of new technologies over time. Gas and water pressure support through injector

wells had begun since the early stages of production itself. As wells were watered out during

production, down dip completed wells underwent recompletion works or sidetracked to updip

positions within oil rim column. At Brent and Statfjord crestal slumps targets, detailed 3D

geological model were constructed and horizontal wells were drilled to understand the complex

nature of the reservoir and maximize production from this highly compartmentalized structure.


The field had also evolved from oil producer to gas producer through 1992 depressurization re-

development plan which had extended the fields lifespan between five to ten years. Shell had

also commissioned topside refurbishment projects and utilized various technologies such as coil

tubing drilling, high rate submersible pumps (ESP) and additional compressor train (ACT) and

new completion technologies to reach hydrocarbon pockets and boost its production.

Brent oil crude had become one of the major benchmark for the oil prices in the world

today thanks to the production that came from Brent oilfield which was characterized as sweet

crudes with 38 API (figure 10). The field had also contributed 8-10% of UKs domestic gas

demands since 2001 over a short spell before declining to only 1-2% in recent years.

Figure 9: The full production profile since 1971 to present. The field have witness two

plateaus of production due to renewed approach in development and application of advance


engineering solutions. Despite this reported values, Brent field production were seeing a

decline in production of 12% p.a-23% p.a.

Figure 10: Brent Crude Benchmark Price (ENI, 2013)

Decommisioning

In 2006, Shell initiated a long term Cessation of Operation plan for Brent Field as oil and

gas flow for the field were exhausted by natural depletion. The plan involves abandonment of

redundant oil and gas wells and decommissioning of offshore facilities which includes: four

topside facilities, Brent Alpha Steel jacket, 36 pipelines, reconfiguration off FLAG lines, and

removal of subsea facilities installed. The complex project would last for more than ten years

possibly beyond 2020. At present, production at Brent Delta have been halted while plans have

been tabled out to terminate production from Alpha, Bravo and Charlie platform beginning end

of 2013.


References

Casey, P. (2014). Embattled Brent: Analyzing threats to the benchmark's viability. retrieved

September 18, 2014, from Oil Price.com Web Site: http://oilprice.com/Finance/investing-

and-trading-reports/Embattled-Brent-Analyzing-Threats-to-the-Benchmarks-Viability.html

EDIN. (2014). Brent Field. IHS Inc.

Frazer, F. (1997). New drilling, completion technology critical to Brent redevelopment. retrieved

September 13, 2014, from Offshore Magazine Web Site: http://www.offshore-

mag.com/articles/print/volume-57/issue-8/news/production/new-drilling-completion-

technology-critical-to-brent-redevelopment.html

Gray, J. (2013). Petroleum prospectivity of the principal sedimentary basins on the United

Kingdom Continental Shelf. Retrieved from Department of Energy and Climate website:

https://itportal.decc.gov.uk/web_files/.../UKCS_offshore_2013.pdf

Glennie, K.W. (1998). Petroleum Geology of the North Sea: Basic Concepts and Recent

Advances.The Blackwell Science, Fourth Edition.

Hampson, G.J. Sixsmith, P.J, & Johnson, H.D. (2004). A sedimentological approach to refining

reservoir architecture in a mature hydrocarbon province: the Brent Province, UK North

Sea. Marine and Petroleum Geology, 21(4). retrieved September 17, 2014, from

http://www.sciencedirect.com/science/article/pii/S0264817203000941

Jolley S.J. (2007). Faulting and fault sealing in production simulation models: Brent Province,

northern North Sea. Petroleum Geoscience. Geological Society of London. Vol. 13, 321

340.


Knag, G. ., South, D., & Spencer, A. M. (1995). Exploration trends in the northern North Sea

(6062N). Norwegian Petroleum Society Special Publications. doi:10.1016/S0928-

8937(06)80040-8

Livera S.E., Gdula J.E. (1990). Brent Oil Field. TR: Structural Traps II: Traps Associated with

Tectonic Faulting. Treatise, 21-63, AAPG.

McLeod A.E. (1999). Process and products of footwall degradation, Northern Brent Field,

Northern North Sea. Petroleum Geology of Northwest Europe: Proceedings of 5th

Conference. , 91-106.

Miller, R., Sorrel, S., & Spiers, J. (2009). UKERC Review of Evidence for Global Oil

Depletion (4). UK Energy Research Centre.

N.A, (N.D). Brent Field, North Sea, United Kingdom. retrieved September 13, 2014, from

Offshore Technology.com Web Site: http://www.offshore-

technology.com/projects/brentfieldnorthseaun

Perkins, R. (2011). Shell shuts Brent oil, gas field after platform hitch. retrieved September 18,

2014, from Platts, McGraw Hill Financial Web Site: http://www.platts.com/latest-

news/oil/london/shell-shuts-brent-oil-gas-field-after-platform-8421877

Taylor, S.R., Almond, J., Arnott, S., Kemshell, D., & Taylor, D. (2003). The Brent Field, Block

211/29, UK North Sea. United Kingdom Oil and Gas Fields, Commemorative Millennium

Volume. Geological Society, 20. retrieved September 22, 2014, from

http://mem.lyellcollection.org/

Trewin, N.H. (2003). The Geology of Scotland, Chapter 19 Hydrocarbon .461-473 Bath, UK:

The Geological Society Publishing House


Yokogawa Electric Corporation. (2003). Yokogawa and Shell Revive North Sea Platform With

Fieldbus Technology. Retrieved from http://www.yokogawa.com/us/technical-

library/references/yokogawa-and-shell-revive-north-sea-platform-with-fieldbus-

technology-shell-uk.htm


Figure Captions

Figure 1. Location of Brent Field in the Northeastern international boundary of UK portion of

North Sea.

Figure 2. Complexity in the reservoir architecture and structural domain of Brent field was

studied in depth through well logs, core and seismic data. The field was first identified in 1970

on 2 km x 2 km 2D seismic but soon after, more infill lines were acquired in 1972, 1973, 1974

and 1979 to allow further exploration works on the field. A close 200 m spaced regular 2D grid

were acquired in 1980 to allow reservoir horizons to be mapped from Pseudo-3D data generated.

In 1986, the first 3D Brent seismic Survey was recorded and reprocessed for image

enhancements in 1989 and 1993. The last seismic acquisition program in the field took place in

1995 and it proved to realized the full potential of the field with superior data quality to map the

Brent and Statfjord eastern margins and slumps (IHS, 2014; Taylor et al, 2003).

Figure 3. Brent field appears to be a monoclinally dipping structure beneath a regional

unconformity layer. The field is located within the east Shetland basin and lies within a major

fault terrace bounded to the west by Hutton Dunlin-Muchison fault zone and to the east by

Eastern Boundary faults. Five appraisal wells (211/29-2 to 211/29-5) were drill in succession

from 1972 to 1974 to evaluate the true hydrocarbon column within the structures and to delineate

the boundaries of the fields, besides to conduct production test in the Brent Group and Statfjord

reservoirs

Figure 4. Lithostratigraphic column of Brent field and the simplified cross-section demonstrating

the working petroleum system for the field.


Figure 5. Discovery of the giant Brent Field recorded a swift jump in creaming curve for

exploration discoveries in the North Sea. It opened up new opportunities for hydrocarbon

exploration in new Middle Jurassic Plays (Glennie, 1998).

Figure 6. Brent Crestal Slump Model were able to be produced with improved 3D seismic data.

The advent of this model allow new development drilling to start in the crestal slump areas since

mid 1990s (Taylor et al, 2003).

Figure 7. Location map of development and production well on the Brent structure (Taylor et al,

2003; Livera & Gdula, 1990) .

Figure 8. Position of Brent Alpha, Bravo, Charlie, and Delta Platforms as well as surrounding

facilities (pipeline, flare, spar) within Block 211/29, UK (Taylor et al.,2003; Shell, 2007).

Figure 9. The full production profile since 1971 to present. The field have witness two plateaus

of production due to renewed approach in development and application of advance engineering

solutions. Despite this reported values, Brent field production were seeing a decline in

production of 12% p.a-23% p.a.

Figure 10. Brent Crude Benchmark Price (ENI, 2013)

The Life Cycle of Brent Field

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