Quantitative assessment of natural and anthropogenic land subsidence in oil and gas productive areas: issues and prospects in Italy.

Transcription

1 Quantitative assessment of natural and anthropogenic land subsidence in oil and gas productive areas: issues and prospects in Italy Valerio Comerci

2 All information are publicly available at:

3 Environmental Impact Assessment In Italy, a Technical Committee for Environmental Impact Assessment is appointed by decree of the Minister for the Environment and the Protection of the Territory and the Sea Since 2008, ISPRA gives support to the Technical Committee for EIA

4 Po Adriatic Sea

5 The only morphologies found in the study area correspond to ancient paleochannels and dune bars (Bondesan, 1985), and artificial river banks bordering watercourses or reclaimed areas. The stratigraphy shows the alternating and interdigitation of continental lithologies (paleochannels, dune bar) with marine lithologies (sands, silts, clays). The lithology of the dunes is predominantly sandy while the paleochannels are filled by a clay lithology Comacchio lagoon Average height between -2.5 m and -3 m Surficial stratigraphy of reclaimed land: 0-0,50 m: soil 0,50 1,60-6,00m: dark peat clay deposits, typical of fluvial-lacustrine facies, with abundant shell remains 1,60-6,00 11,50m: sandy deposits with peat levels and shell levels 11,50 16,00m: compacted silty clay 16,00 20,00m: silty sand deposits

6 Agosta Lithological map

7 Well Agosta. 2,253 m deep (-1,989.7 m a.s.l.) In the first 1000 m sandy deposits with silt/clay intercalations (Asti sands - Emiliano Romagnolo Supersyntem).

8 2 layers of Pliocene Sandy formations (Porto Garibaldi and Porto Corsini) mineralized with methane gas Estimated production: 453,4 Mm3 by 2 strings. Lifetime: at least 13 years Production started in 1971 Stopped from 2004 to wells deep 2,900 3,800 m for 13 production strings Closing date: 2027

9 The two reservoir are considered hydraulically separated. Two separate fluid dynamic studies (3D Eclipse model) were performed. Geomechanical modeling using finite element method 74 layers. Bedrock is the top of carbonatic rocks deep between 4,000 and 7,500 m Mesh of the Finite element method used in the ISAMGEO elasto-plastic model for the fields of Dosso and Agosta.

10 Results of simulations: Subsidence induced by Dosso+Agosta, at Dosso and Agosta for different uniaxial compressibility Dosso started in 1971 Agosta supposed start Dosso supposed closure Agosta supposed closure Subsidence induced only by Agosta, at Agosta

11 Control points Comparison with available data The results of the simulation were compared with the measured data available for the study area. This comparison was made only with reference to the Cm Med scenario (for Agosta). The comparison between measured and computed data requires that the first is cleaned from subsidence components not attributable to gas extraction (in this case the only extraction from the Dosso field). There is uncertainty about the value of the subsidence non-attributable to gas extraction, which is itself composed by compaction and oxidation of surface sediments (rich in organic matter), any water extraction component, and a deep tectonic component. The oil Company assumed that the average subsidence component not attributable to gas extraction was, for the whole area under examination, -5 mm / year. This value was chosen on the basis of recent integrated analyzes of the various historical available measurements

12 Teatini et al., 2005 AGOSTA Simeoni et al., 2007 used InSAR data, calibrated with geometric levelling data, to estimate the absolute velocities in the southern border of the Valli di Comacchio ERS Asc Bitelli et al Map of the displacement rates (mm/year) obtained by PSI on ERS-1/2 ( ) images Land subsidence rate (mm/year) in the Ravenna Municipality over the period. Can be considered as a quite reliable representation of the Natural land subsidence Natural and anthropic Subsidence can be estimated about - 5 mm / year RADARSAT-1 Asc Factors that likely contribute to the observed land displacements over the period.

13 Reprocessing with SqueeSAR technique: ERS and RADARSAT, Asc + Desc ERS1-2: RADARSAT-1: RADARSAT-1:

14 Area for comparison between Oil Company and ARPA results Comparison of analyzed InSAR data by the oil Company and by ARPA for the area of Dosso degli Angeli

15 RER, ARPAE : Vertical Velocity maps Geometric levelling RER, ARPAE, : Vertical Velocity maps PSInSAR ENVISAT Asc+Desc RADARSAT-1 Asc Calibrated with geometric levelling data

16 RER, ARPAE, 2012: vertical ground velocity map (1:250,000) Based on SqueeSAR elaboration of RADARSAT-1 Asc images, calibrated with 16 CGPS Stations (Bitelli et al., 2015)

17 62% of the territory: no variation 35% of the territory: reduction of subsidence 3% of the territory: increase of subsidence Map of variations of vertical velocities from to

18 Asc+Desc Desc Vertical velocities Asc+Desc Asc+Desc Differences from 5 to 10 mm/yr Vertical velocities Asc+Desc Asc Differences up to 10 mm/yr In some case more Vertical velocities Smarlacca CGPS Good agreement (not calibrated)

19 Calibration with the Smarlacca CGPS The Smarlacca CGPS is subject to control and certification by the University of Bologna Smarlacca CGPS mm/a The average Vertical velocity of the points falling within the radius of 150m is mm / year. In order to achieve absolute velocity, mm/year was added to the vertical velocity dataset. The average of the points falling within 150 m indicates a value of mm / year.

20 Asc Asc+Desc Vertical velocities Smarlacca CGPS mm/a Calibrated Differences up to 5 mm/yr Results for Dosso For points falling within the Dosso field, for a distance of less than 150 m radius from the Smarlacca CGPS, the average velocities are as follows: : - 8 mm/year : - 8 mm/year (calibrated with Smarlacca CGPS) : - 6 mm/year (calibrated with Smarlacca CGPS)

21 SqueeSAR elaboration of CSK data for the period

22 Calibration with Smarlacca CGPS and check with Spinaroni CGPS Smarlacca CGPS mm/yr R: 100 m

23 Calibrated velocities are quite in agreement with the velocity registered by Spinaroni CGPS SqueeSAR CSK calibrated vertical component

24 The average vertical velocity of the PS / DS at the Agosta field is about -4 mm / year

25 The average velocity is about -5.5 mm / year.

26 In the simulation of the geomechanical model, the oil company assumed that the average subsidence component not attributable to gas extraction was, for the whole area under examination, -5 mm/year The value of -5 mm/year has been subtracted from measured data in the control points (geometric levelling, GPS and InSAR), in order to obtain the part attributable to gas extraction Comparison of measured subsidence, after taking away the non-gas components (-5 mm / year), and the result of the simulation at the Smarlacca GPS station and at two leveling benchmarks Comparison of InSAR data for the five control points, after taking away the non-gas component, and result of the simulation at the same points (black line).

27 Simulation of subsidence induced by Agosta + Dosso production At Agosta 2030: 17 cm Anthropogenic cm Natural (5 mm/yr x 13 years) Simulation of subsidence induced only by Agosta production 2030: 15 cm Anthropogenic cm Natural

28 In the province of Ferrara, for more than 60% of the surface, there is a decrease in the lowering, which averages around 2 mm / year. In essence, the entire territory is free from significant land subsidence. Approaching the Po Delta, we notice a slight accentuation of the phenomenon of a few mm / year. Agosta RER, ARPAE, 2012: vertical ground velocity map of the coastal area (1:100,000)

29 SqueeSAR elaboration of 16/01/ /05/2011 RadarSat-1 Ascending images 16 permanent GPS stations belonging to three different geodetic infrastructures: IGS- EUREF (3); RING-INGV (4); FOGER Foundation of quantity surveyors (10)

30 6 GPS Stations used for calibration 6 years PS/DS velocities trend is in agreement with BOLG GPS trend

31 Estimated differences between SqueeSAR data and the 6 permanent GPS stations These differences were minimized by a calibration procedure that consisted in removing a velocity component due to orbital errors The average deformation velocities of SqueeSAR data were referred to the absolute reference system of the GPS stations

32 Successively, the vertical motion velocities of additional 10 GPS stations were used as check points with respect to the calibration result. The GPS velocities were subtracted from the velocities of the PS/DS targets in the period the SAR velocity is derived from the weighted average of such points for the period considered (the weight is proportional to the coherence of the single target) the average residual is mm/yr, standard deviation 1.39 mm/yr

33 Statistical procedures have been applied in order to remove outliers with anomalous velocity Example of a group of outliers due to the anomalous movement of an infrastructure Analysis of the outliers

34 ARPAE -2 mm/yr mm/yr Oil Company

35 vertical motion velocity map Agosta Dosso SqueeSAR analysis of RADARSAT Asc images, calibrated with 16 GPS stations

36 - Different measuring techniques for different periods: geometric levelling, GPS, InSAR - Different InSAR data stacks analysed, different geometries used - Different reference benchmarks - Different GPS networks analysed, different methods of calibration A difference of 2-5 mm/yr in the estimation of subsidence not induced by gas extraction, even if small in absolute, in relation to the working life of a gas extraction plant, may be relevant. (In the best case the measurement techniques have standard deviation +/- 1.5 mm / yr. But just this inaccuracy, on a ten-year production, can cause an estimation error of the impact of several centimeters!) As regards the EIA, the decision is being prepared by the Ministry of the Environment

37 The Italian Space Economy Strategic Plan In agreement with the Space Strategy for Europe, at National level, a Space Economy Strategic Plan has been defined with the aim to specify the operative strategic lines that will enable Italy to transform the national space sector into one of the driving forces behind the country's growth. Space Economy is the value chain that, starting from the research, development and realization of the enabling space infrastructure, called "Upstream", comes to the production of "enabled" products and services, called "Downstream" (environmental monitoring services, weather forecast, etc.). Six National strategic operative lines are designed. Among them the Mirror Copernicus, the national program in support of Copernicus. National Satellite Telecommunications Program (SATCOM); National Support Program to Galileo (Mirror Galileo); National Program for the Galileo PRS Infrastructure; Copernicus Support National Program (Mirror Copernicus); SST Support Program; Space technologies and exploration development program.

38 Through the Public-Private Partnerships, which associate the productive and industrial system with the research system and the national actors of the Space policies (ASI, CNR, ISPRA, Department of Civil Protection, Ministry of Defence, etc.), the financial availability of 1 billion euros (half public and half private) was created, for the 6 strategic lines. The Mirror Copernicus program, composed by a set of National Operational Infrastructures, is the main investment (500 M ) within the National Strategic Plan The signing of financing contracts is expected by the end of the year. In this framework, ISPRA worked on the definition of an Italian PS Journal, designed as a Mirror Copernicus Downstream service. SNPA ISPRA, in its twofold role of coordinator of the Italian National System for Environmental Protection (SNPA) and of the National Board of Regional Geological Surveys (TNSG), collected the user needs and requirements expressed by the regional authorities (Environmental Agencies and Geological Surveys), in order to design the service TNSG PS Journal Italia

39 One of the needs that the service will try to answer is that of Calibration of PS-DS data. GNSS Regional public stations 860 Regional stations public + private + IGM (geodetic/geodynamic networks), INGV (RING network), ISPRA (geodetic data), INOGS (geodetic network), ASI (high precision geodetic network), etc. The Italian Space Economy Plan offers the opportunity to structure an integrated GPS network specifically dedicated to calibrating PS / DS data