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ACG Field Geohazards Management: Unwinding the Past, Securing theFutureAndrew W. Hill

1, Kevin M. Hampson

2, Andy Hill

2, Christopher Golightly

3, Gareth A. Wood

1, Mike Sweeney

4and

Martyn M. Smith5

1BP America,

2BP International Ltd.,

3Go-Els Ltd.,

4Retired (Formerly BP International Ltd.),

5BP Azerbaijan

Copyright 2015, Offshore Technology Conference

This paper was prepared for presentation at the Offshore Technology Conference held in Houston, Texas, USA, 47 May 2015.

This paper was selected for presentation by an OTC program committee following review of information contained in an abstract submitted by the author(s). Contentsof the paper have not been reviewed by the Offshore Technology Conference and are subject to correction by the author(s). The material does not necessarily reflectany position of the Offshore Technology Conference, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without thewritten consent of the Offshore Technology Conference is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words;illustrations may not be copied. The abstract must contain conspicuous acknowledgment of OTC copyright.

AbstractThe super-giant ACG field lies in the Azerbaijani sector of the south Caspian Sea. The significant complexity of the

geohazards setting over the field was realized in 1993 when negotiations for the PSA to develop the field were still ongoing.

This resulted in the need to understand geohazard risks being recognized in the Minimum Obligatory Work Program terms

set out in the Contract of the Century in October 1994.

Over the last twenty years work to define and refine understanding of the multiple geohazard issues has been ongoing. Work

started in early 1995 with the completion of two deep geotechnical boreholes and a PSA-wide geophysical and geological

geohazards campaign that delivered an early, first pass geohazards stop-light map and supported delivery of the Early Oil

Project (1997).

The results of these two initial pieces of work formed the basis of the first PSA-wide integrated geohazard study that

addressed the threats of individual sources of geohazard to Full-Field Development planning. These included, amongst other

issues: slope instability, mud volcano stand-offs and fault risks, all being included in the first integrated geohazards risk map

of the PSA in 1999.

Since this time, direct experience, in drilling and facilities installation, has driven the need for an ongoing update of data and

improvement in geohazard understanding. New sources of hazard, such as the implications to riser-less drilling from super-

saline soils, have had to be assessed and new data acquired to assist in mitigation of the risks identified.

Most recently HR3D data has been acquired across the entire PSA which, tandemed with AUV seabed and shallow profiler

imagery has been used to guide a further series of geotechnical campaigns. These results have been used to drive an update to

geohazards zonation addressing, in particular, slope instability in field areas previously considered too sensitive fordevelopment.

This paper provides a timeline of geohazards activity on the ACG PSA over the past twenty years as a background to other

papers being offered in the technical session that discuss how specific geohazard data acquisition and analysis issues have

been addressed.

IntroductionThe super-giant Azeri-Chirag-Guneshli (ACG) field complex, with estimated reserves of 5.4billion barrels oil equivalent, lies

in the Azerbaijani sector of the south Caspian Sea, 130km to the east of Baku in water depths of 95 to 425m (Figure 1).

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Figure 1: Location of the Super Giant Azeri-Chirag-Guneshli field structure offshoreAzerbaijan, Caspian Sea in the AIOC PSA. Note: the Guneshli field to the north-west of thePSA boundary developed prior to the 1994 PSA and operated by SOCAR.

The field complex, which is made up of three individual structural culminations Azeri, Chirag and Guneshli, with a shared

oil-water-contact, was discovered during the Soviet Union era - prior to Azerbaijan gaining independence in 1991. The north-

western, shallow water, area of the Guneshli field was placed into production prior to independence and continues to the

current day.

Following independence, a number of foreign operating companies were invited to bid for the rights to develop individual

parts of the field complex. As studies continued by the Operators it became clear that the three fields all shared a common oil

reservoir, and that separate development of the structures would be counterproductive to the efficient development of the

total resource. As a result, in early 1993, the State Oil Company of the Azerbaijan Republic (SOCAR) initiated consolidation

of negotiations into a single production sharing contract (Williams and Hession, 1997). This culminated in the signing of a 30

year Production Sharing Agreement (PSA) contract, The Contract of the Century, with ten different joint-partner operating

companies in October 1994. Signing of the PSA agreement led to the formation of the joint operating company Azerbaijan

International Operating Company (AIOC).

Since 1995 the ACG complex has undergone phased development by AIOC through: the upgrading of an existing platform,

installation of seven new fixed platforms, three subsea well manifolds, laying of approximately 1200km of subsea in-field

and export pipelines to shore (Figure 2) and the drilling of over 160 wells (Appraisal and Production). Peak production per

day from the field has reached up to 835,000 barrels-a-day.

Figure 2: Current development status of the ACG Complex. West to East: onshore terminal at Sangachal, oil andgas export and produced water re-injection pipelines, three Deep-Water Guneshli (DWG) subsea water injectionmanifolds, DWG Platform Complex (Phase III), Chirag Oil Project (COP) Platform, Chirag Platform (EOP), WestAzeri Platform (Phase II), Central Azeri Platform Complex (Phase I) and East Azeri Platform (Phase II).

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All this has been delivered in the face of an extreme level of marine geohazard complexity that was identified ahead of the

signing of the PSA, recognized in the Minimum Obligatory Work Program (MOWP) in the PSA agreement, and has had

impact upon all drilling and development activity over the past 20 years of ACG activity. Geohazard understanding continues

to be refined to the current day through the acquisition of improved quality data (geophysical surveys and geotechnical

boreholes) and ongoing integrated studies.

Initial Geohazard EvaluationsThe ACG field comprises a tightly folded, north-west to south-east trending anticline. The anticline lies along a structural

trend that represents the offshore extension of the Caucasus fold belt.

Fold development is inferred to be controlled by deep thrust faults whose expression propagate upwards and splay to intersect

the main reservoir intervals. The thrusts themselves are the result of the juxtaposition of the Apsheron ridge to the presence

of the subduction of the South Caspian Basin beneath the Mid-Caspian Basin. As a result, seismicity is high, with local

seismogenic sources located beneath the continued uplift of the ACG fold.

The review of potential geohazard complexity across the Chirag and Azeri culminations was started by BP in late 1992 in the

review of the sparse 2D exploration seismic data that was then available for evaluation. The data showed a level of

geohazards complexity at the seabed that, at the time, was unknown outside of the deep-water Gulf of Mexico (Campbell and

Hooper, 1993). There was clear evidence from the data of the presence of: extensional faulting along the anticlinal crest

reaching to, and offsetting, the seabed, and recent slumping and mass transport deposits on a massive scale. There were also

multiple direct hydrocarbon indicators in the shallow section, indirect evidence of seepage, and large, extant, and other

possibly buried mud volcano features. The area also was also known to be characterized by significant earthquake activity.

In early 1993 visits were started to Baku to visit with SOCAR, their technical departments and with academic institutions

with relevant experience and understanding of the geohazard setting across the fields. As a result of the first of these visits,

over a week in January 1993, a cartoon was developed (Sweeney, 1993, Figure 2) to portray to management the complexity

of the setting and the superimposition of differing geohazard issues that had been identified as being of potential impact to

operations across the structure. A summary report of understanding written in February 1993 concluded that: it should be

realized that the level of risk to operations from geohazards faced in the Chirag. areas is of an order of magnitude higher

than anywhere else in the world that BP operate (Hill, 1993).

Figure 3: Cartoon showing understanding of potential ACG field Geohazard complexitydeveloped after a first visit to Baku, January 1993.

At the time a total of thirteen exploration and appraisal wells had been spudded across the length of the structure that was the

subject of ongoing negotiations: five on Azeri, seven on Chirag and one on the deep-water segment of Guneshli. Of these,

some had experienced problems in the shallow overburden. These problems included direct shallow gas and shallow water

flow issues in drilling, or in annular isolation due to issues with cementation. A single, two-piece, platform had been installed

on the Chirag segment of the field but had yet to be brought into production. A further platform installation had started on the

deep-water part of the Guneshli field but had been abandoned due to problems in installation.

In support of drilling and development activities across the field complex SOCARs Engineering Geology Institute

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(KMNGRU) had undertaken a total of 243 geotechnical/geological boreholes. This, quite remarkable, level of borehole

effort, and allied testing and analysis, compared to a relatively sparse amount of shallow geophysical profiling that had been

acquired to tie the borehole results. At the time this approach was in contrast to the western approach of high geophysical

effort calibrated by relatively sparse, targeted, or site specific, geotechnical borehole effort. Regardless of the philosophical

approach to site investigation, this borehole resource was immediately recognized as being of tremendous value to the

support of future studies. Additionally it was found that the State Geodesy Committee had published a series of good quality

bathymetric charts across the entire PSA. While these were on the basis of single-beam echo sounder data, the detail shown

indicated a relatively high level of acquisition effort. These again were recognized as a valuable potential resource.

From all these efforts it underlined that conditions across the area were equally as complicated as had been considered at first

sight. The remnants of the seafloor ridge, that suggested the presence of the deeper anticlinal structure, which defined the

fields, was heavily disturbed at the seabed. The three culminations of the fields themselves were separated (Guneshli to

Chirag and Chirag to Azeri) by the presence of major extant seafloor mud volcanos. In addition to these two major mud

volcanos, at least one other major mud volcano was recognized to exist on the Azeri structure.

The ridge area of the Chirag field was seen to be heavily effected by extensional faulting that reached to seabed.

On the southern limb, and running the entire length, of the structure was a major scarp defining the edge of major seafloor

slumping of unknown, yet clearly recent, age. On the Azeri structure this scarp was found to be well to the north of the

structural axis of the field.

Other geohazard features were suggested on the limited geophysical or sonar profiles available, while geotechnical analyses

and descriptions suggested a variety of soil conditions, of which the interaction of the presence of the major mud volcanos on

soil behavior was an immediate cause for concern.

At the time, however, the main industry codes were almost non-existent on the topic of marine geohazards management for

field developments with potentially relevant documents having 1% or less content on this topic (Sweeney, 2014). At the

start of the ACG studies, for example, it would be another 14 years before the IOGP published any industry guidance on

marine slope stability analysis (IOGP, 2009). So, at the time, for those working geohazardous seafloor terrains there was

almost no guidance, and appropriate practice had to be created from ongoing experiences.

As negotiations continued towards the signing of the Contract of the Century , in October 1994, background work

continued to put in place an outline program of work to be undertaken to better understand the geohazards complexity

immediately upon entry; to support first appraisal drilling and early field development. As a result of this, delivery of site, or

geohazard, survey requirements were identified directly within MOWP of the PSA contract (Azerbaijan, 1994).

Initial Detailed Studies: 1995-96The newly formed Azerbaijan International Operating Company (AIOC), a joint-venture into which member companies

contributed staff and expertise, was expected to deliver a number of activities and reviews within a set timeframe. Of these

relevant to site investigation understanding were to:

Undertake a field-wide environmental and geohazards survey of the entire PSA (c450sqKm).

Evaluate the existing Chirag Platform for its potential use in an Early Oil Project (EOP).

Deliver well site specific surveys to support an immediate three well appraisal drilling program.

Separate study strands were led by different participant AIOC partner companies, from the onset BP, initially with Statoil

support, took the lead for site investigation support, while Exxon took the lead on earthquake design criteria - particularly

how this applied to the potential use of the existing Chirag platform.

While it had already been realized, the signing of the PSA brought into stark relief the difficulties of delivering world class

site investigation activities in the Caspian Sea. The unique enclosed nature of the Caspian (Guliyev, 2007), the limited

breadth of entry canals to the Caspian and the seasonal nature of their availability (open May to November only) meant that

simply bringing vessels to deliver the work, as would be the case anywhere else in the world, was not feasible. These issues,

which remain to the current day, are described in detail in allied papers: Dingler et al (2015) on geophysical site investigation

delivery and Hill et al. (2015) on geotechnical site investigation delivery.

Given the requirements of MOWP, the very first offshore operations performed by AIOC was the installation of a cantilever

borehole rig over the side of the existing Chirag Platform to drill a pair of geotechnical boreholes to evaluate the shallow soil

profile. These were performed in late January 1995 only three months after the signing of the PSA. Drilled in 121m of water,

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the paired boreholes, one drill and sample and one drill and CPT, were completed to a depth below mudline (BML) of 150m.

Regardless of the volume of known pre-existing geotechnincal engineering information that existed across the PSA, given a

relative degree of uncertainty on comparability of testing rationales, soil samples from these boreholes were subjected to an

exhaustive, for 1995, set of analyses - to derive both geotechnical engineering parameters and understand the geological

depositional environment and age of the soils encountered (e.g. Figure 4, Simmons, Henton and Lowe 1995). It is notable

that the rigor applied to soils classification in these two boreholes resulted in the definition of eight Soil Units, I through VIII,

for soils present across the ridge of the PSA. This categorization, despite much ongoing study and learnings gained since1995, has remained solid and largely unchanged to the present day.

Figure 4: Chirag Borehole 1 Analyses - showing properties of the geotechnically defined Soil UnitsI to VII, and relative biostratigraphic biofacies, Palyno Zones, Paleo Climate Variation, DepositionalEnvironments and the

14C age date for sediment just below the current day seabed.

In parallel to the delivery of the Chirag boreholes, the mobilization of a vessel was started to undertake a field-widegeohazards study. Building on recent experiences from West of Shetlands, UK in 1993-94 (Hamilton, 1996) and recognizing

the complexity of the setting, a Blanket approach was selected to deliver PSA -wide understanding, to support ongoing

studies of processes and general complexity, and to then high-grade the regional approach with site specific geophysical

studies for well and platform locations as these were identified.

The immediate impact of this was the mobilization of a vessel in April of 1995 to undertake the work: starting with detailed

evaluation around the Chirag Platform, verification of individual SOCAR well locations, delivery of regional coverage of the

PSA, initial study of potential export pipeline routes to various landfall locations, and clearance surveys of harbor

approaches. Four months of geophysical field-work followed (Dingler et al. 2015).

The geophysical survey of the PSA, despite the limitation of some of the systems available for use (Orren and Hamilton,

1998) verified the absolute nature of the geohazards complexity across the PSA at the seabed, within the foundation zone and

across the top-hole drilling interval (Figures 5 and 6).

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Figure 6: 1995 Regional 2D HR dip profile across the Azeri field showing main structural elements. Comparequality to more recent 2013 HR3D Pre-Stack Depth Migration data in Figure 14 (Dingler et al., 2015)

Efforts also continued to benefit further from existing in-country knowledge and understanding. A major effort was

undertaken to review the geotechnical borehole inventory and translate the records to western equivalents for comparison to

the results at Chirag. Similarly onshore fieldtrips and sponsored studies continued with Azerbaijani academic geoscience

specialists, such as the Geology Institute of Azerbaijan (GIA). A key focus was developing understanding in onshore mud

volcano form and habitat (Hovland et al., 1997), to be used as analogs in analysis of the offshore setting (Figure 7).

Figure 7: June 1996, Right: two of the authors and translator with mud volcano experts from the Geology Institute ofAzerbaijan (GIA) undertaking field mapping at the Bahar mud volcano. Left: ground effects from a recent eruption andscale of boulder inclusions in the mud volcano breccia at Bahar.

Discussions with the Department of Navigation and Mapping, of the Azerbaijan Navy and the State geodesy Committee

emphasized the importance of monitoring long-term and seasonal sea-level variations within the Caspian Sea (Dingler et al.,

2015). At the time sea levels were at close to a 15 year high - almost 3m above the late 1970s, but still 25.3m belowoceanic

levels. This has been a subject of careful observation by AIOC ever since due to multiple implications to operations and

development.

From the results of the 1995 regional geophysical campaign a qualitative overview of understanding resulted in delivery of a

simple Stop Light map that summarized potential limitations on the PSA developability from the geohazards standpoint

(Figure 8). This made use of the Common Risk Segment approach (Grant et al., 1996) but took into account solely:

Seabed Slope Angle

Seabed Faulting presence

Mud Volcanos at current day seabed

Shallow Gas in the Top-Hole Section

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The proportion of Red,or Stop, immediately evident reinforced the potential complexity and limitations to layout of any

potential Full-Field Development (FFD) solution.

Figure 8: 1996, Stop-Light Geohazard Zonation map produced from a qualitative assessment of the results of the 1995PSA wide geohazards survey. Green: no perceived obstacle to development to Red: significant impediment todevelopment or no-go area. The dark blue line is the field oil-water-contact, light blue lines bathymetric contours. Grid

squares are 5x5km.

Appraisal DrillingThe start of appraisal drilling, as required under MOWP, started in 1996 with the spudding of the GCA-1 appraisal well on

the south flank of the Chirag structure, 1km to the west of Chirag Platform.

Top-hole drilling confirmed the presence of thin shallow water flow sands in the Surakhani formation sealed below thin

anhydrite markers. The possibility of shallow water flow risk had been flagged pre-drill on the basis of: pre-existing SOCAR

well issues described within the PSA, and the presence of consistently anomalous high deposition rates from the Miocene to

recent times. However, at the time, as shallow water flow was only just emerging as an issue in the deep-water Gulf of

Mexico (Alberty et al. 1997) and considered, by some, to be special to the Gulf, the problem was initially a surprise in

operational delivery of the well, but did not cause a problem to its safe delivery. The criticality of the correct positioning of

casing shoes to mitigate shallow water flow zones was brought home in 1997 with the requirement to re-spud the GCA-3

appraisal well due to an ongoing shallow water flow from the upper Surakhani. From this point onwards the importance todrilling of a full understanding of the geohazard setting of each individual well and well center was recognized. It has driven

the adoption of an integrated approach that includes careful geophysical analysis of the setting and the incorporation of

geotechnical engineering properties with pore pressure profiles into top-hole well design and delivery (Al-Khafaji et al.

2015a and 2015b).

All these efforts combined, reviewed in detail by AIOC partner subject matter experts through 1996, provided confidence in

moving forward with EOP and delivery of first oil in 1997. However all the experiences and information gained in the first

two full years of PSA operations, emphasized the need to undertake an in-depth study of individual geohazard subject strands

and to then combine these outputs in a fully integrated study to deliver detailed guidance for FFD.

First Integrated Full-field Geohazard Assessment: 1997-99Following a detailed review by partners in London in July 1997 it was agreed that an integrated study of geohazard issues

should go forward. This two year study delivered an integrated understanding of shallow geohazards and their implications

for facility and wells layout across the entire field.

It should be emphasized that due to the unique nature of the Caspian, and the facilities available for construction (Luberski et

al., 2008 and Kearney et al, 2008) and installation (Wilson and Munro-Kidd, 2008) of offshore facilities there were, and

remain, certain limitations purely from fabrication and installation to a layout that could be chosen for a development. This

meant that there was a preference to position major, fixed, production facilities in shallower waters, north of the Main

Headwall Scarp, or MHS (Figure 5) in water depths less than c175m (c575 feet) in depth. However, to minimize total drilling

distances from any one platform location it was required, particularly on the Azeri culmination, to position facilities as close

to the MHS as possible from the safety standpoint. This, therefore, emphasized the need for a detailed consideration of the

geohazards implications to the safe positioning of facilities relative to the MHS and the associated safe delivery of drilling

operations.

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The first integrated full-field geohazard assessment, therefore, sought to develop the simplistic entry point common risk

segment approach (Figure 8) to a semi-quantitative assessment of separate contributory geohazard risk elements and to then

combine them into a single spatial understanding for use in guidance of FFD planning.

Key elements of this study included, but were not limited to:

Building a PSA-wide ground model by Fugro,

Geochronology of sediment samples to support the dating of geological features, Regional Probabilistic Seismic Hazard Assessment by URS,

Slope Stability Evaluation: modelling of a series of cross PSA transects by NGI,

Fault Displacement Hazard Assessment by Geomatrix Consultants, and

Mud Volcano Hazard assessment by Professor B. Voight of Penn State University.

The result of the studies was a series of contributory reports summarized into a single technical summary report (Golightly

and Hampson, 1999). The findings were also summarized in a Facilities Geohazard Study Planning and Development Map

(Figure 9). In comparing this to the output of the 1995 work, the level of detail layered into the chart emphasizes the

development of understanding, and the continued impact of the superimposition of different geohazard challenges to FFD

planning.

Figure 9: 1999, Facilities Geohazard Study Planning and Development Map, produced from the first Integrated GeohazardsStudy 1997-1999. Note the increased level of complexity included, multiple sources of risk factors identified andsuperimposed atop each other relative to Figure 8. Deeper blue colors, for example, relate to mud volcano stand-off zones.

One conclusion that remained consistent, however, was that the only area that appeared devoid of geohazard complexity was

a slim band of the PSA along its northern flank. On the Azeri field this lay well off the crest of the field structure. As a result

of this, one of the most important deliverables from the integrated study was definition of the safe stand-off distance for

facility locations from the top of the MHS for the Azeri field segment. This work was relied upon to define facilities

locations (four platforms and associated pipelines) for FFD planning. However the results also continued to place low

confidence on the safe placement of facilities below the escarpment and, for this reason, those areas were avoided for initial

development concepts.

The integrated approach towards geohazards assessment on ACG for AIOC development screening was a first within BP.

The approach was exported to the Gulf of Mexico where the approach of acquisition of early blanket geophysical data

coverage followed by targeted geotechnical calibration to develop an integrated geological model was adopted, and further

developed, on the Mad Dog, Atlantis (Jeanjean et al., 2003), Holstein (Liedtke et al., 2002) and Thunder Horse fields

(Horkowitz et al., 2002) before being re-imported for application in the Caspian on the first phase of the Shah Deniz field.

The approach was also applied and improved upon on for the integrated geohazard assessments of Ormen Lange, Norway

(Bryn et al., 2004), West Nile Delta, Egypt (Evans et al., 2005) and Deep Water Angola (Hill et al., 2010).

Full-Field Development 2003-07FFD was delivered in three separate phases (Luberski et al. 2008). Phase I entailed the siting of the Central Azeri platform

complex and allied export pipelines to shore, Phase II West Azeri and East Azeri platforms and related infield and export

pipelines, and finally Phase III with the installation of the Deep Water Guneshli (DWG) platform complex and three subsea

water injection manifolds.

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Each platform location was initially chosen on the basis of the results of the 1999 Integration Study, but then underwent full

geophysical and geotechnical site investigation to refine the final location addressing foundation integrity and top-hole safety.

The drilling platforms were each designed with 48 well slots. To help facilitate rapid ramp up of production at each platform

a 12 slot drilling template was pre-set at each location and wells pre-drilled through the template using a semi-submersible

drill-rig.

It was in the pre-development wells at the West Chirag template that a unique geohazard issue was identified in drilling soils

in Soil Unit VIII when drilling the top-hole section with seawater. Segments of some casings were found to have moved

laterally by more than 1m at a depth only 150m below mudline (BML) creating significant dog-legs (Figure 10).

Figure 10: Exaggerated perspective representation of the pre-drill 20 wellcasing profiles at West Azeri Template after discovery of the problem drillingthrough hyper-saline soils with low salinity Caspian sea-water. The mauvewellbore was the most recent of the pre-drills.

The cause was identified as the presence of high pore-pressure, hyper-saline, structured and reactive clays. The salinity of

Caspian seawater is brackish. Fluid of high salinity in the super-saline soils encouraged fresh [drilling] water to flow into thesoil due to an osmotic effect. Such a flow lead to softening of the formation, hole collapse and compromised wellbore

stability. In the West Azeri setting, where Soil Unit VIII turned out to be at its most saline within the PSA, this resulted in the

template having to be abandoned, a new template installed, and practices identified to minimize the possibility of repetition.

Procedures adopted included driving closed end conductors from platforms as deep as possible and use of premium inhibitive

water based mud on drilling out (Al-Khafaji et al. 2015).

For the future delivery of safe and efficient top-hole drilling at existing and new drill centers, it re-emphasized the need for

obtaining a precise understanding of site specific soil and pore-pressure profiles for each platform location. It also confirmed

the necessity of drilling a deep geotechnical borehole to sample the soils and undertaking direct pore-pressure measurements

using a piezoprobe, supported, where possible, with downhole in-situ Hydraulic Fracture Tests (HFT). These, all required

tying back to HR multi-channel seismic data on a well by well basis.

DWG Subsea Manifolds 2004-08The addition of subsea water injection manifolds to supplement water injection from wells from the DWG platform complex

(Richmond and Barralet, 2008) marked the first time in the PSA that development activities were considered down dip of the

MHS in the deeper waters of the PSA. Two of the manifolds, the South and East manifolds would be placed in relatively

deep-water compared to previous PSA facilities.

In 2004 the geophysical site investigation for these locations adopted a new approach with the acquisition of blanket HR3D,

rather than HR2D, data that included MBES and deep-tow combined sonar and profiler data in a single pass. This resulted in

the first real step change in the quality of shallow geophysical data. The data allowed analysis of full well bore geohazards

analysis of deviated well paths and total flexibility in adjustment of pipeline alignments, and still provide early assessment of

conditions to engineers ahead of detailed geotechnical evaluations.

Chirag Oil Project (COP) 2007-2010

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The AUV data gathered in 2007 delivered a step change in the quality of imagery of both seabed and shallow soils

morphology, allowing immediate improved understanding of recent geological processes. These data prompted the

acquisition of further phases of AUV data acquisition over the remainder of deep-water Azeri area (2011) and Chirag and

Guneshli (2014) that further improved upon the data of 2007.

Figure 13: AUV Bathymetric Model developed from successive surveys. The increased morphological detail defined across theentire model, irrespective of water depth, should be compared to the 1995 image (Figure 5). Coverage was extended in 2014 to infillthe deep-water area of Chirag and Guneshli (see Figure 17).

To provide further understanding of the deeper foundation and the top-hole drilling intervals, two phases of HR3D

acquisition were undertaken in 2013 and 2014 to complete a full suite of modern, high quality, multi-spectral, hydrographic

and geophysical imagery across the PSA. This included undershooting each of the platforms to re-confirm top-hole drillingconditions.

Figure 14: HR3D Pre-stack Depth Migration Image. The quality of image should be compared against the HR2D image (Figure 6) froma similar location across the Azeri field, which now supports the level and quality of structural and stratigraphic mapping shown.

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Combined, these data have allowed development of a refined study of geohazard processes across the PSA. Detailed

integration of these results started in 2012 and enabled delivery of an initial update of the Full-Field Geohazards Assessment

in 2013 (Figure 15).

Figure 15: 2013, Ranked Facilities Geohazard Guidance Map, using a more standardized Common Risk Segment (CRS)approach to visualization of complexity and impact with existing pipeline and cable development infrastructure overlain.Note: the area below the MHS continued to largely remain a cautionary color at this time.

With the availability in 2013 and 2014 of new HR3D and AUV data, integration studies have continued to the current day to

refine understanding in the deeper waters initially of the Azeri field before moving onto the deep-water flanks of Chirag and

Guneshli culminations.

Specifically work has been undertaken to model the failures that created the embayments below the MHS in the Azeri sector

of the field. This has, for the first time, made use of the Shear Band Propagation approach to modelling of slope instability

(Gray, Puzrin and Hill, 2015) and to extend this spatially beyond the previous modelling of 2D sections using the Limit

Equilibrium approach, by making use of GIS functionality (Rushton, et al. 2015). For the first time, modelling results have

been able to accurately model the failure styles, the original drivers for the failures, and the sensitivities around the driving

forces that might result in recurrence of failure. All this has contributed to a significant increase in prediction confidence.

Integration of the geoscience data, carefully calibrated by geophysically targeted geotechnical boreholes in 2014, has allowed

the deep-water segment of the Azeri field to be subdivided into areas of similar landslide risk sensitivity due to a combinationof contributory geohazard risk factors (Figure 16) and each risked quantitatively for acceptability.

Figure 16: 2014, Azeri Field Facilities Landslide Risk and Geohazard Planning GuidanceMap. Colours relate directly to severity of Landslide Risk, overlain cross hatching relates tomud volcano flow risk. Note the existing infrastructure above the MHS: West Azeri, CentralAzeri and East Azeri Platforms and infield and export pipelines.

The GIS approach has been taken further to allow spatial sensitivity analysis of different slope instability events and their

direct implication to different types of development facilities (trees, manifolds, flowlines etc.). GIS functionality now allows

engineers undertaking concept screening to consider these risks spatially. Once coded within the GIS, parametric studies can

be carried out readily to test the sensitivity of the slope stability to uncertainties in the input data. This is extremely

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informative in determining those parameters worthy of being constrained further through additional data gathering effort.

In short, for the first time, integrated geohazards study has been able to wind the geological clock back to understand the past

development of the ACG seabed morphology seen today, and to then quantitatively predict the future risks to the installation

and operation of different facility types over the lifetime of production - regardless of concept layout being considered

(Figure 17).

Figure 17: Possible future ACG Development concepts (pink) under concept screening consideration on thebasis of the guidance coming from quantitative spatial Geohazard risk analyses. With the exception of thepossible addition of a fixed platform, concept focus is on additional subsea production or injection concepts.

While geohazards concerns continue to exist and require ongoing study; be they the possible effects of seabed current scour

in the DWG segment (Figure 18) or the ongoing attention to detail, on a well-by-well basis in drilling, understanding has now

been brought to a new level of reliability to support planning.

Figure 17: 2014, sun shaded AUV MBES bathymetric model: Uninterpreted left, interpretation summary right. Middle top: the maincone of the Guneshli mud volcano. Recent mud volcano flows and subsidiary mud volcano cones (yellow), seabed current relatedscour flutes or comet marks (cyan) and carbonate seepage concretions (magenta).

ConclusionsThe development of geohazard understanding within the AIOC PSA has been a continuously improving process for the past

twenty-two years to develop, refine and advance models to reduce operational risk to ongoing drilling and developments.

This has supported multiple phases of development and has allowed the production, to date, of **billion barrels of resources

from this super-giant field in a complex geohazard setting.

Delivery has been based upon:

Pre-entry realization of complexity and early communication to management for inclusion in early workprograms.

Utilization of an on-entry blanketapproach to geophysical assessment of baseline conditions.

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Early geotechnical investigation and calibration by borehole or core to directly assess soil conditions andprovide age dating.

Use of a diverse set of geohazard specialists to deliver an integrated geohazards model.

Recognition of the need to update, or improve on, the geophysical or geotechnical data inventory to supportrefinement of geohazard models.

Uptake of cutting edge geophysical or geotechnical technologies in data acquisition or analysis.

A commitment to continually improve understanding to support engineering in its broadest sense.

Over the past twenty years ACG has been used as a laboratory to develop cutting edge approaches to geohazards assessment

that have been exported, refined, re-imported and further developed. The work described here has been a major support to the

development of the general philosophy of industry geohazards study in complex settings (Jeanjean et al., 2005) and its

consideration over the full license life cycle (Hill and Wood, 2015).

Geohazards specialists, involved in study of the ACG area, continue to look to the future to see what the next significant step

forward in geohazard technique may be that will provide further insight and understanding.

Seismic techniques, making use of, for example, ocean bottom receiver cables, or nodes, are already being looked at in terms

of different types of imagery (comparative VP and Vs sections etc.) that they may allow (Hill, Hill and Hill, 2014). Full

Waveform Inversion velocity models have already been developed both to better define mud volcano throat patterns in the

subsurface and also to feedback to assist in improved migration of 3D Data volumes (Tough et al., 2010). With the

availability of field wide HR3D seismic volumes, seismic attributes, such as AVO, are being pursued to test what they mayprovide by way of further improvements in the characterization of the overburden for well planning (Gherasim et al., 2015).

Similarly there is focus on continuing improvement of geotechnical tools (downhole piezoprobes or in-situ piezometers).

There remains, currently, another nine years of PSA duration as defined in 1994 by the Contract of the Century. The

platforms that have been installed to date have a total of over 260 slots available for drilling, yet, to date, only about half that

total has been utilized. The approach to the analysis of geohazards in the top-hole section will be needed to support drilling

for the remaining life of the PSA. Life of field economics for each platform requires drilling to be equally successful in

drilling the 1stwell from a platform as it is in the 48 thwell.

The success in addition of extra development facilities will require ongoing accurate description of surface installation

acceptability and drilling safety.

Data therefore will continue to be acquired to improve understanding, or to verify that drilling or foundation conditions

remain unchanged. This will support continued improvements in integrated study and breakthroughs in understanding and

achieve operational integrity to the end of the production life cycle of this super-giant resource.

Acknowledgements

The authors would like to thank: BP, SOCAR (the State Oil & Gas Company of Azerbaijan) and the AIOC partnership

(Chevron, Inpex, Statoil, Exxon-Mobil, TPAO, Itochu and ONGC Videsh Ltd.) for permission to publish this paper.

The cooperation and support over the past twenty years of the Department of Navigation and Mapping, Naval Force of the

Azerbaijan Republic, the Engineering Geology Institute of SOCAR (KMNGRU), the Geophysical Trust of SOCAR, the

Geology Institute of Azerbaijan (GIA) and the State Geodesy Committee of Azerbaijan is recognized for their significant

contribution to understanding - especially in the early days of the PSA.

The authors also wish to recognize all those that have contributed to the development of geohazard understanding of the

ACG field over the past 20 years in the work that has been summarized here.

Nomenclature14C - Carbon 14 [age dating technique]

ACG - Azeri-Chirag-Guneshli

AIOC - Azerbaijan International Operating Company

AUV - Autonomous Underwater Vehicle

AVO - Amplitude vs. Offset

BML - Below Mud Line

BSL - Below [Caspian] Sea Level

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COP - Chirag Oil Project

CRS - Common Risk Segment

DWG - Deep-Water Guneshli

EOP - Early Oil Project

FFD - Full Field Development

FWI - Full Waveform Inversion

GCA - Guneshli-Chirag-Azeri

GIA - Geology Institute of AzerbaijanGIS - Geographic Information System

HFT - Hydraulic Fracture Test

HR - High Resolution (Seismic with Dominant Frequency in 100-200Hz range)

KMNGRU - Engineering Geology Institute of SOCAR

MBES - Multi-Beam Echo-Sounder

MHS - Main Headwall Scarp

MOWP - Minimum Obligatory Work Program

PSA - Production Sharing Agreement [Area]

SOCAR - State Oil Company of the Azerbaijan Republic

VHR - Very High Resolution (Seismic with Dominant Frequency >>1000Hz)

VP - P Wave Velocity

VS - S Wave Velocity

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