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 E&P, Milan, Italy

DMMMSADepartment of Mathematical

Methods and Models for Scientific Applications

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

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

The Lombardia fieldLocation 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

The Lombardia fieldProduction 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Primary production started from pool C in 1981 with 2.7 GSm3 withdrawn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

Analysis and management toolsPSInSAR 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

Analysis and management toolsPSInSAR 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)

Analysis and management toolsFluid-dynamic and geomechanical computational models

Water dynamics in the connected aquifer is predicted by coupling a 3D FE groundwater flow simulator calibrated over the primary production period 1981-1986

Gas/water dynamics in the reservoir is predicted by the multi-phase flow simulator Eclipse calibrated over the 1981-2007 period

Analysis and management toolsFluid-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: =Eh/Ev, =Gh/Gv, h, v and s=cM,I/cM,II

UGS activity in the Lombardia fieldGeomechanical 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

• = 3.0 and = 1.0

• h = 0.15 and v = 0.25

• s = 4.0

UGS activity in the Lombardia fieldGeomechanical response

Measured (from PSInSAR) and simulated vertical and horizontal displacements from April 2006 to November 2006

Maximum vertical displacement simulated over the reservoir

Future UGS scenariosPore 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

Future UGS scenariosLand 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 (< 10-5 m/m)

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

DMMMSADepartment of Mathematical

Methods and Models for Scientific Applications

Thank you for your attention