Subsurface Enablement : Brent Well Abandonments · Shell Exploration and Production Company UK May 2011 1 Subsurface Enablement : Brent Well Abandonments DEVEX – The Production

Shell Exploration and Production Company UK 1May 2011

Subsurface Enablement : Brent Well Abandonments

DEVEX – The Production &

Development Conference

11th -12th May 2011

Gerry Moorhouse

Production Technologist

Shell Aberdeen

Many thanks to: Reservoir Engineering, Geology and

Petrophysics colleagues: Claire Woods, Dave Sharpe, Chris

Bugg, Eduardo Delgado and the many people who have

contributed.

Shell U.K. Ltd

CAUTIONARY STATEMENT

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The United States Securities and Exchange Commission (SEC) permits oil and gas companies, in their filings with the SEC, to disclose only proved reserves that a company has demonstrated by actual production or conclusive formation tests to be economically and legally producible under existing economic and operating conditions. We use certain terms in this presentation that SEC's guidelines strictly prohibit us from including in filings with the SEC. U.S. Investors are urged to consider closely the disclosure in our Form 20-F, File No 1-32575, available on the SEC website www.sec.gov. You can also obtain these forms from the SEC by calling 1-800-SEC-0330.

2March 2011

Well Abandonment

“That’s Just for Well Engineering”

Outline of Presentation

4

Well Abandonments: UK Governance & Geological

Interpretation

Reservoir Pressurisation: Dealing with Previous Sidetracks

and Well Abandonment Legacy

Cement Logging and Petrophysics: Beyond CBLs

Summary of Subsurface Contribution: Framework for

Abandonments

UK Legislation is Goal Setting, does not prescribe

methodology

UK Oil & Gas Publish “Guidelines for the Suspension and

Abandonment of Wells” . These include “rules” but in general

are based on a rational approach to abandonments including

implementation of “rock to rock” barriers and restoration of

“caprocks”.

UK W. A. Governance

1

5

Copyright of Shell UK Exploration and Production 6May 2011

Isolations required

between distinct

permeable zones and

surface

Distinction between

hydrocarbon bearing,

pressure regime,

water bearing

Geology &

Petrophysics provide

interpretation. Each

field will be different

UK Oil and Gas Guidelines - Distinct Permeable Zones


Understand origin and migration

path of any hydrocarbons

sampled

Wellbore investigations e.g.

cased hole logging to identify

hydrocarbons in permeable

formations

Permeable Zones Hydrocarbon Bearing?

δδδδD (0/00) Methaneversus

δδδδC13(0/00) Methane

What can be assumed? Is a simple approach necessarily

conservative? What are the benefits of a rational approach

that honours field and basin data, geology?

Reservoir Repressurisation

2


Objectives

� Have an understanding both of the likely range of eventual

recharge pressures and timescales over which this will occur

�Understand the ability of shallower shales to act as barriers to

flow - strength versus depth and time

�Use better annular cement (or squeezing shale) further away

from perforations – prove by cement logging

Risks

�Current reservoir state provides no guarantee that observations

today (eg no leaks or pressure build up) provide a reliable future

prediction

�Uncertainties in Material Balance

Objectives of Reservoir Recharging Study


Geology

�Estimate size of Brent regional aquifer

�Identify potential recharge paths

Reservoir Engineering

�Build dynamic model for range of aquifer geometries, sizes

and properties

�History match model and discard scenarios that were

inconsistent with production and pressure data for Brent

and surrounding fields

�Assess range of recharge rates and pressures with

remaining models

Workflow


Low aquifer:

�No indication of

communication between Brent

and Statfjord fields

�Fault throws along western

and eastern boundaries

greater than Brent reservoir

thickness

High aquifer:

�All fields with similar

overpressure (approx 25 bar)

share common aquifer

Brent Regional aquifer size range


High volume aquifer attached to entire western side of model (poor history match)

Infinite aquifer attached to western side of model excluding Dunlin field

High volume attached to western side of model excluding Dunlin field, reduced compressibility

Recharging rates and uncertainty range

High volume

aquifer attached to

entire western side

of model failed to

honour Dunlin field

pressure data,

therefore set upper

limit to aquifer

connectivity


Well Abandonment

today includes the

full legacy of

development

drilling and

previous

abandonments for

slot recovery

Reduce Risks from Previous Sidetrack Activity


Some of the previous

slot recovery isolations

are higher risk than what

we would currently aim

to achieve

It is almost impossible to

re-enter wellbores after

sidetracks have been

completed

A mitigation is to

complete a barrier at a

shallower depth

How to Reduce Risks from Previous Sidetrack Activity

Utsira Shale

layers

Frigg -Skade permeable formations

Horda Shales

Balder sands

Shetland Shales

Reservoir

Brent

Rock to rock barriers require that the integrity of the seal

between casing and formation (usually assumed to be

primary annular cement) be known and that its ability to

provide hydraulic isolation be assured. Cement logs can

provide basis to assess annular isolation.

Cement Logging and Petrophysics

3

Shell U.K. Ltd

DETECTING GAS IN OVER-BURDEN FORMATIONS

Logging Conditions:•Challenging!•Expected Low Gas Saturation.•Large casings•Dual Casing strings (or pull casing)•Pulsed Neutron Log

Logging Conditions:•Challenging!•Expected Low Gas Saturation.•Large casings•Dual Casing strings (or pull casing)•Pulsed Neutron Log

• Pulsed Neutron Logs identified Gas at Low Saturations – complemented wellbore observations

Min ID Formation AHDBDFTVDBDF

(in) Top (ft) (ft)

DFE

WHD-Susp flange with 2 x 4" valves. Tested to 500psi

MR220 - mid element (TOF = 104ft) (P/T 500psi)

MSL

Sea

Top of solids behind 13 ⅜" casing (CBL 30/01/2010)

Seabed

643 643

Possible high 20" TTOC

20" TTOC

30" Shoe

HUTTON

9 ⅝" suspension string Formation

13 ⅜" High TTOC , rathole ignored, hole in gauge

20" Shoe

Utsira sst 4 2,017 1,996

Utsira shale 4 2,184 2,157

Utsira sst 3 2,285 2,253


Utsira sst 2 2,621 2,566


13 3/8" TTOC

Utsira sst 1 3,018 2,913


Skade sst 3,564 3,319

13 ⅜" casing x/o 72# to 68#

Frigg sst 4,661 4,025

5,897 4,780

TTOC

TOC - tagged / 10klbs & tested / 2200psi) HORDA

Shale

13⅜" HMN plug at 7066ft (tagged / 5k)

9 ⅝" casing cut at 7,090 ft

BALDER 7,215 5,558

LISTA Fm 7,648 5,813

13 ⅜" top of window Maureen Fm 8,178 6,135

Top 7" PBR

8,582 6,387

9 ⅝" top of window

SHETLAND

GROUP

TTOC 7" Liner

TOC - tagged with 10klbs on 16.0ppg cement

plug 7" HMN bridge plug 14004ft (P/T 500psi)

X-Unconf.

3.920 Top of PBR / Anchor (PBR sheared) Kimmeridge 14,231 9,195

3.920 Halliburton MHR Production Packer 14,277 9,227

BRENT

GROUP

HX4 PES plug (c/w prong/catcher top14293ft )

WEG DUNLIN GROUP14,299 9,242

14,588 9,435

4 1/2" Top of Liner Hanger

Hanger slips 4 1/2"

7" Shoe

STATFJORD

Possible TOC at loss zone FORMATION

4 1/2" Liner Shoe

C C

DESCRIPTIONCURRENT WELL STATUS

918 ft

combined

Shell U.K. Ltd

CBL Feb 2010CBL Feb 2010USIT Feb 2010USIT Feb 2010

CBL Nov 1981CBL Nov 1981

13 3/8’ casing Shoe @ X960 ft AHBDF

IDENTIFY SQUEEZING SHALES

Summary of Subsurface Contribution

to Successful Well Abandonments

5


Provide the framework for well

abandonments:

� Identify reservoir recharging Use as a basis to evaluate the vertical

extent of the “caprock” that provides a

viable seal with sufficient strength

Address legacy abandonment issues

� Identify permeable zones

that represent a risk of lateral

communication between wells –

investigate for presence of

hydrocarbons

Subsurface Contribution Summary


Identify nature and sealing

capacity of Shale

Formations as natural

vertical barriers to flow

� Predict whether shales will

squeeze and hence provide

self healing well annular

barriers

Subsurface Contribution Summary (continued)


Improve current well designs wrt eventual

abandonments

�Explicitly consider and incorporate into well planning

documents the basis of the future abandonment

�Do not overly simplify the nature of the over-burden

Impact of operations and well activities, in particular

sidetracking on eventual abandonments

�Slot recovery should be considered the same as

permanent well abandonment as opportunity to rectify

is very limited

Integrated Approach - Not Just for Well Engineering

Lessons Learnt

Q & A

Fault between Brent and

Statfjord fields is proven

to be sealing against

differential pressures of

4000 psi

Most likely ingress routes

are along the western

edge, south of the Dunlin

field and between the

Hutton and Ninian fields,

where the throw on the

major bounding fault is

smallest

Notes 1 Brent aquifer potential recharge paths

DEVEX - The Production and Development Conference 11th -12th May 2011

Subsurface Enablement : Brent Well Abandonments

G Moorhouse E Delgado C Woods C Bugg

Shell Exploration and Production UK

Abstract

Complications identified in early well abandonments forced a re-think away from individual well by well abandonment

design to a system wide view dictated by the geology of the over-burden. Oil and Gas Guidelines for Well

Abandonments specify that distinct permeable zones are to be isolated from each other and from the surface. For

Brent, the over-burden geology has been assessed and lumped into major distinct permeable zones, including those

that provide the possibility of cross-flow between wellbores and sealing shales. Restoring the integrity of upper

“caprocks” across multiple wellbores is challenging but provides better assurance on a systematic basis that well

abandonments will be successful. A critical tool deployed as part of the well abandonments and which has been

instrumental in providing data to shape the evolution of the abandonment philosophy has been cement bond logging.

As well as the historic role of providing data as to the integrity of the annular cement, the use of Ultrasonic bond

logging tools and Gamma provides valuable formation data. For Brent, this has improved the understanding of the

nature and location of sealing shales as caprocks. An upside is that squeezing shales have been identified and

verified and which provide robust annular isolations. A significant part of the Brent Well Abandonment Philosophy has

been the comprehensive assessment of reservoir recharging. This has resulted in better appreciation of the value of

multiple caprocks in the overall well abandonment philosophy. Improved value of well abandonments can follow from

the Philosophy.

Presentation Abstract

Documents

Subsurface Enablement : Brent Well Abandonments · Shell Exploration and Production Company UK May 2011 1 Subsurface Enablement : Brent Well Abandonments DEVEX – The Production