stogit advanced monitoring approach

Stogit Tecnomare Snamprogetti

IGU Working Committee 2 Workshop on “Safety on UGS”

Rome, 2-4 October 2007

Stogit Advanced Monitoring Approach

Vanni Damiani, Daniele Marzorati (Stogit) Francesco Gasparoni (Tecnomare) Gianluca Patrignani (Snamprogetti)


•Stogit manages 8 of the 10 Italian gas storage facilities

•Location: 7 in the Po alluvial Plain (Northern Italy), 1 in the Apennines (Central Italy)

•All are located in depleted gas production reservoirs at average depths of between 1000 to 1500 m

Introduction


Background

•Stogit activities are based on experience acquired within the Eni Group in 40 years of operations

• first gas storage activities: 1964 (Cortemaggiore) • storage pressure initially maintained <=Pi

• in August 2002, with the authorisation of the Ministry of Trade and Industry, Stogit for the first time in Italy experiments storage in a reservoir (Settala) at pressures above the original reservoir pressure (P>Pi)

•as integral part of a plan aimed at increasing storage capability, Stogit has defined a new monitoring strategy (“Advanced Monitoring Approach”) to support correct and safe operation at high overpressure conditions


Geodesy Geophysics Geochemistry Process

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AIR -

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SURFACE -

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SOIL -

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SAR topography

monitoring

Basic monitoring

RST logs

Wellhead

pressure

Bottom pressure


Geodesy Geophysics Geochemistry

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AIR -

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SURFACE -

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GasFinder

remote sensing

Mobile geochemical

surveys

Advanced monitoring

4D microgravity &

gravity gradient

Deep borehole

geodesy

Geochemical

stations network Microseismic

stations network

Deep borehole

microseismics

Annular pressure


Geodesy Geophysics Geochemistry

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AIR -

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SURFACE -

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Experimental activities (R&D)

Geomechanical monitoring

Fingerprint

techniques

Pore pressure Compactation Leak-off pressure


Advanced Monitoring Approach: why?

• to ensure continuous, real-time, permanent monitoring of the stability and integrity of reservoirs with geological and structural conditions operated in overpressure

• to safeguard the surrounding environment

• to give early warning of potentially hazardous situations (such as leakages, fracturation etc.)

• to give demonstration to the stakeholders of the correct and safe management of the reservoir

• to increase the knowledge base so that behaviour of the site can be understood and simulated

• to collect data useful for the study and evaluation of future development scenarios


Surface microseismic network

Purpose: detection of micro-earthquakes around the field area

Working principle: a network of automatic seismological stations recording H24 ground motions and transmitting data to a remote data management centre

Results:

• catalogue of seismic events

•3D seismicity pattern

• characterisation of seismogenic geological structures


Surface microseismic network - technical details

• includes 10 to 20 seismometric stations spaced approx. 5 km and equipped with:

– 3D, 1-80 Hz seismometers

– 24 bit digitiser

– GPS time reference

• continuous 100 Hz data acquisition (1-40 Hz useful band) and real-time wireless data transmission

• allows high-precision detection of local earthquakes with magnitude 1 to 4 at depth range 1 to 5 km


Purpose: detection of fracture occurrence and fault formation/reactivation Working principle: borehole observatory installed in a dedicated well (1200-1500 m), connected via umbilical cable to a Surface Station managing data acquisition, processing and networking Results: maps of seismic events

Deep borehole microseismic observatory


Deep borehole microseismics - technical details

• instrumented string including 5 modules spaced approx. 50 m

• based on

– 3C borehole geophones (10-500 Hz)

– 1000 Hz sampling rate

– 24 bit digitisers

– GPS time reference

– continuous acquisition

– real-time event detection (LTA/STA algorithm) and transmission

– local storage of all data

• allows detection of micro earthquakes with magnitude -3 to 2 within 500 m from borehole


Purpose: monitoring of formation

movements/settlement, determine fracture orientation, understand fracturing process Working principle: precision tiltmeters integrated in the borehole observatory

Deep borehole geodesy

Technical data •Self levelling sensors (within +/- 10°)

•Range +/- 300 µrad •Resolution <5 nanorad •1 measure/minute


Geochemical Monitoring Network

Purpose Continuous, “real-time" detection of anomalous CH4 contents pattern in free air, surface soil, shallow water tables Working principle • a network of stations placed

in selected points over the gas storage field

• automatic sampling and chemical analyses of CH4 contents in air, soils ad water tables

• Infrared and Flame Ionization techniques


Geochemical Monitoring Network – technical details

Results • time trend anomalies detection for CH4 contents

• location of zones with anomalous CH4 content trend

Technical data •Coverage: 1 station/5-10 km2 •Precision: ≥ 1 ppm CH4 in air, soil and water

•Sampling rate: 12 meas./day


Annular pressure monitoring

Purpose: continuous, real-time monitoring of gas leakages through defective wells Working principle: Pressure gauges applied to well casing valves Results: Pressure time series analysis in correlation with reservoir charge / discharge activities. Search for anomalous responses of gas pressure over the field Technical data

• Coverage: 1 well each 5-10 km2 • Precision: <1 bar


Purpose: determine the variations of fluids subject to storage / injection / production cycles inside a reservoir Working principle Time-lapse (4D) methods, based on microgravity measurements and relevant gradient (innovative technology developed by Eni method; submitted for international patent)

Time-Lapse Micro-Gravity & Micro-Gravity Gradient


A typical survey includes up to 1000 stations. Duration 10 working days (6 persons organised in 3 shifts) Main advantages of the method

• capability to detect possible reservoir compartmentalisations

• applicable both in onshore & offshore scenarios

• easy integration with seismic • cost effective technology • no environmental impact

Time-Lapse Micro-Gravity & Micro-Gravity Gradient


Gas leakage remote sensing

Purpose: Detection of CH4 pattern in free air over the entire area of a gas storage field Working principle: airborne methane laser sensor (GasFinder) mounted on an helicopter flying 10-50 m over the area Results: Location of zones with anomalous CH4 content trend Technical data

• Coverage: 1-5 measures / 1000 m2 over a XY grid

• Precision: ≥ 10 ppm CH4 • Timing: 100 km2/day


Geochemical Surveys

Purpose: Detection of anomalous CH4 content in free air, surface soil, shallow water tables Working principle: Field surveys using gas samplers and portable high-sensitivity FID CH4 detectors; laboratory analysis of samples collected Results: Maps, pattern recognition, time trend anomalies detection for CH4 contents Technical data: • Coverage: 1-3 samples / km2 • Precision: ≥ 1 ppm CH4 (in air, soil,

water) • Timing: 10 km2 / day


SAR topography

Purpose: Monitoring of the surface elevations micro-change during time (subsidence / uplift phenomena) Working principle: Satellite radar images processed with Differential Interferometry (DInSAR) methods to obtain micro-displacement trends of a series of "scatter points" mapped over the area of interest Results: Maps of topography elevations change Technical data

• Coverage: 10-1000 km2 • Precision: 1 mm elevation • Timing: 1 map/year


Data management infrastructure

• All data are collected in an integrated geographical database management system

• The system supports GIS applications and dedicated analysis, studies and modelling

• A multidisciplinary pool of experts read and analyse data to watch the status of reservoirs during storage activities


Experimental (R&D) activities

• advanced geochemical techniques (like isotopic techniques and fingerprint analysis) to recognise the origin and source of CH4 detected in air, soils and water

• downhole permanent monitoring of geomechanics parameters of the reservoir (like pore pressure, compactation, and horizontal stress)

• an integrated geomechanical model of the reservoir capable to analyse integrity of the sealing and predict possible occurrence of fracturation phenomena

• advanced leak detection technologies (infrared hyperspectral imaging systems), to enable quick and cost effective detection and quantification of fugitive methane leaks


Conclusions

• Stogit has launched a monitoring program aimed at supporting a safe and efficient management of gas storage reservoirs operated at P>Pi

• Stogit approach

– combines traditional and innovative techniques

– combines periodic surveys with continuous, in-situ observation

– is multidisciplinary (combines geophysics, geochemistry, geodesy, environmental monitoring tasks)

– focus on a permanent infrastructure, ensuring operativity 24/7/365

• This approach is tailored to the specific conditions and risks at each storage site

– dimensions and time scale of the application

– storage pressure

– reservoir characteristics

– sensitivity of the area


Program status

• First objectives (4 year project started 2006), are

– to set-up a network of 5 gas storage reservoirs fully instrumented, including relevant communication infrastructures

– to develop the data management infrastructure (SismoGIS)

• Within mid 2008 the start-up of the first fully instrumented node of the network (Fiume Treste) is scheduled

• Completed and ongoing activities

– 4D microgravity & gravity gradient surveys in one field

– Detailed design and development of surface and deep borehole microseismic and geodetic network

– Detailed design of the geochemical stations networks

– First (blank test) mobile geochemical survey

stogit advanced monitoring approach

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