Diapositiva 1

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DMMMSA Department of Mathematical Methods and
Models for Scientific Applications
Monitoring and modelling 3-D ground movements
induced by seasonal gas storage in deep
reservoirs P. Teatini, G. Gambolati, N.
Castelletto, M. Ferronato, C. Janna Uni.
Padova, Italy E. Cairo, D. Marzorati Stogit
S.p.A., Crema, Italy D. Colombo, A. Ferretti, F.
Rocca T.R.E. S.r.l., Milan, Italy A. Bagliani,
F. Bottazzi Eni EP, Milan, Italy
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Outline

• Introduction
• The Lombardia field history, location, and
  geology
• Analysis and management tools fluid-dynamic and
  geomechanical modelling, PSInSAR monitoring
• UGS activity in the Lombardia field
  geomechanical response
• Future UGS scenarios land displacement
  prediction
• Summary and conclusions

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Introduction

• Underground Gas Storage projects are increasingly
  popular worldwide about 600 UGS plants currently
  active with an overall working gas volume of
  about 350 billions of Sm3
• Hazards safety related to public perception,
  economic risk and environmental impact
• Geomechanical issues
• Need for a comprehensive modelling and monitoring
  effort

• subsurface sealing caprock integrity
• surface land displacements

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The Lombardia field Location and geological
setting
Northern Italy, Po River plain normally
consolidated and pressurized basin
Three gas-bearing pools between 1050 and 1350 m
below m.s.l.
The reservoir is of stratigraphic type and
consists of Pliocene sandy sediments
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The Lombardia field Production life and UGS
program

• Primary production started from pool C in 1981
  with 2.7 GSm3 withdrawn until 1986 and 35 bar of
  pore pressure decline
• UGS started soon after superposing to the natural
  pressure recovery

• From 2002, UGS program has pushed the maximum
  pressure up to 103 pi with 30-35 bar cycles and
  1.2 GSm3 of working gas
• Objective pushing the maximum pressure up to
  107 and 120 pi

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Analysis and management tools PSInSAR data over
the Lombardia field
PSInSAR is a methodology for monitoring the land
displacements through the analysis of Synthetic
Aperture Radar (SAR) scenes acquired from
satellites over a number of benchmark points
known as Permanent Scatterers (PS)
Seasonal behavior of two PS compared to the
stored gas volume phase accordance The ground
surface breathes as the gas is pumped in and out
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Analysis and management tools PSInSAR data over
the Lombardia field
PSInSAR analysis of data acquired from

• November 2005 to April 2006 (left)
• April 2006 to November 2007 (right)

Seasonal movements of 8-10 mm (vertically) and
6-8 mm (horizontally)
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Analysis and management tools Fluid-dynamic and
geomechanical computational models
Gas/water dynamics in the reservoir is predicted
by the multi-phase flow simulator Eclipse
calibrated over the 1981-2007 period
Water dynamics in the connected aquifer is
predicted by coupling a 3D FE groundwater flow
simulator calibrated over the primary production
period 1981-1986
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Analysis and management tools Fluid-dynamic and
geomechanical computational models

• Geomechanics is predicted with the aid of the FE
  code GEPS3D developed by UniPD
• Non-linear hysteretic hypo-plastic law for the
  soil compressibility

• Anisotropic constitutive model calibrated using
  both vertical and horizontal PSInSAR
  displacements
• Five independent parameters bEh/Ev, gGh/Gv,
  nh, nv and scM,I/cM,II

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UGS activity in the Lombardia field Geomechanical
response
Calibration of the anisotropic model using the
2003-2007 PSInSAR measurements

• Selected parameters
• Very good match between measures and computation
• The parameters are consistent with literature
  data in the same basin

• b 3.0 and g 1.0
• nh 0.15 and nv 0.25
• s 4.0

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UGS activity in the Lombardia field Geomechanical
response
Measured (from PSInSAR) and simulated vertical
and horizontal displacements from April 2006 to
November 2006
Maximum vertical displacement simulated over the
reservoir
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Future UGS scenarios Pore pressure prediction
Two future UGS scenarios 107 pi and 120 pi
Increase of the stored gas volume by 65 and
180 relative to the current maximum storage

• Pore pressure variation in a cycle and its
  propagation in the connected aquifer 50 bar and
  70 bar
• No problems are expected for the caprock integrity

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Future UGS scenarios Land displacement prediction
Absolute value of the expected vertical
displacement (mm) during a seasonal
injection/extraction cycle

• From the current 10 mm at 103 pi to 17 mm at
  107 pi and 27 mm to 120 pi
• No problems are expected for the stability and
  integrity of surface structures because of the
  small differential displacements (lt 10-5 m/m)

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Summary and conclusions
Major points

• UGS at the Lombardia field is responsible for a
  10-mm excursion over the last five years which
  can increase to about 15 mm and 25 mm at 107 and
  120 pi with no expected consequences on surface
  structures
• The model calibration provides geomechanical
  parameters consistent with available studies on
  the same basin in the framework of a
  transversally isotropic constitutive model
• This study can be viewed as a prototype
  application of a promising interdisciplinary
  approach integrating petroleum engineering,
  remote sensing and computer modeling for a
  complete geomechanical characterization and
  management of a UGS program

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DMMMSA Department of Mathematical Methods and
Models for Scientific Applications
Thank you for your attention