csem - eni 0407

882019 CSEM - ENI 0407

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Index Table of contents

Integrating Potential Methods in EampPGeophysics Enirsquos Experience and Vision

P E Flores

Eni EampP Division Via Emilia 1 20097 S Donato Mil Italy - Geophysical Services Mngr

Summary

The history of potential methods in Eni dates back from 1929 just a few years after the companyrsquos

foundation Even the advent of digital and later 3D seismic did not discourage the acquisition

processing and interpretation of grav-mag data as testified by more than 300000 gravimetric stations

acquired over the whole Italian territory In the 90rsquos magneto-telluric methods (MT) have been

successfully applied especially in complex geological settings and Eni pioneered the first marine MT

acquisition More recently Eni has decided to invest in marine controlled source electromagneticforeseeing a bright future for this technique One of the greatest challenges ahead of us is the

harmonization of the various potential methods seismic well data and geologic knowledge in order

not only to reduce drastically the exploration risks but also to optimize the reservoir studies This can

possibly be achieved by joint multidimensional inversion techniques

Introduction

Potential field methods have historically played a role in oil and gas exploration at the basin scale or

where seismic reflection techniques have poor resolution (fi sub-salt sub-basalt or thrust belt areas)

After the advent of 3D seismic potential methods appeared on the verge of a downfall This triggered

a series of RampD projects inside the oil companies and contractors that has led to a great improvement

of the field tools operations and processing software This has been coupled by a decrease of

acquisition processing and interpretation costs Moreover the methods can be easily used inenvironmentally sensitive areas where seismic is not allowed to operate The disadvantage of

potential methods as compared to seismic has always been the lower resolution but the new

technologies (eg microgravity high resolution aeromagnetic and their gradients) are trying to

overcome this limitation with a certain degree of success Moreover recent developments in Controlled

Source Electromagnetic methods (CSEM) have added a promising new geophysical tool which can

complement traditional seismic methods by detecting non-seismic direct hydrocarbon indications

Past

The history of potential methods in Agip (now Eni EampP Division) dates back to 1929 3 years after

Agiprsquos foundation when the Geophysical Section was created and two gravimetric crews were set up

utilizing Eoumltvoumls Torsion Balances These instruments invented in 1888 had been used with a certain

degree of success in oil exploration in Checoslovakia and Germany right after the first world war andlater in Texas (1924)

In 1934 two crews equipped with magnetic variometers were sent to Dehalak Kebir Island (Eritrea)

and then to Etiopia for the first magnetometric surveys Two other crews were operating in Italy with

Schmidt variometers together with two geoelectric crews

After WW2 there was a surge of interest in Grav-Mag encouraged also by the improvement of the

instruments capable now of being used both in the onshore and offshore environment and airborne

The decision in the late 70rsquos of dismissing all geophysical crews did not affect Agiprsquos interest in these

methods as testified for example by the fact that the whole Italian territory was completely surveyed

(more than 300000 gravimetric stations)

EGM 2007 International WorkshopInnovation in EM Grav and Mag Methodsa new Perspective for Exploration

Capri Italy April 15 ndash 18 2007

882019 CSEM - ENI 0407


Eni has been a pioneer company in application of electromagnetic methods It applied both natural

source and active source based methodologies with increasing attention to the second category

starting from 2003

In the period from 1990 to 2002 magneto-telluric (MT) data have been acquired mainly on land with

the purpose of improving geophysical interpretation in complex geological settings Many hundreds of

MT receivers have been deployed in thrust belt regions in order to provide additional geophysical

information to be integrated with seismic and gravity data Intensive applications have been performed

in the Southern and Central Apennines (Italy) and in Sicily MT methods have been applied alsooffshore in the Sicily channel in the Gulf of Mexico and in the North Sea It is worth mentioning that

in 1994 Agip first experimented the Marine Magneto-telluric technique and acquired the first survey

offshore Sicily

In the years 1998-2000 a dedicated experiment of quantitative integration of MT gravity and seismic

data has been successfully performed The ESIT (Enhance Seismic In Thrust belts) in joint venture

with Shell Italia (formerly Enterprise Oil) and partially funded by the European Union provided a

valuable multiple data set consisting of MT gravity reflection and refraction seismic The application

of cooperative inversion approaches has confirmed the high potential of non-seismic information

especially when it is adequately integrated with seismic

In the late lsquo90rsquos Agip also explored the possibility of using gravity gradient data by the acquisition of

3DFTG (3D Full Tensor Gravity Gradient) In the early 2000rsquos the new HRAM (High Resolution

AeroMagnetic) surveys allowed the preparation of the new Carta Magnetica drsquoItalia (2004) More than

320000 km of flown profiles were acquired from the lsquo70rsquos

The advent of the first dedicated workstations in the 90rsquos triggered Agip interest a great effort was

devoted to the design and implementation of sophisticated software for the processing reprocessing

enhancement filtering and modelling of 2D 25D and 3D gravimetric and magnetic data

Present

In the years 2000 Eni devoted many efforts to consolidating the activities of modelling and

enhancement of anomalies for their interpretative resolution through RampD projects As a result

applications were developed for converting conventional gravimetric data into GGT (Gravity Gradient

Tensor) data 3D depth estimate (Euler deconvolution) of gravimetric and tensor data separation of

shallow and deep effects with the Multiscale Derivative Analysis (MDA) identification of specificamplitudes with the Wavelet Analysis (without frequency filtering) The dedicated software

commercial and proprietary is now running on dedicated Linux platforms

In the same research project new algorithms for the modelling and inversion of gravity magnetic and

full tensor data have been developed and successfully tested over many parts of the world (Figure 1)

At present Eni is very much interested in the full exploitation of non-seismic methods and their

quantitative integration with seismic applications

The results of a research project focused on quantitative integration of seismic and non-seismic data

are coming to light In fact one of the main results was the development of an innovative algorithm of

joint inversion of reflection and refracted travel times with MT and gravity data A multi-parametric

model is produced iteration after iteration and at the same time the seismic imaging improvement is

guaranteed through pre-stack depth migration using the updated velocity field

Great interest is also devoted to marine Controlled Source Electromagnetic methods (CSEM) BothRampD projects and real applications are increasing in numbers year after year Eni is member of the

main EM research consortia guided by the major research institutes and service companies It has

increased the budget for internal RampD projects and developed proprietary algorithms and codes for

modelling inversion and interpretation of CSEM data Eni has recently acquired new data in Norway

Nigeria and Egypt obtaining very significant contributions to the evaluation of prospect exploration

risk



882019 CSEM - ENI 0407


Figure 1 Example of integration seismic gravity MMT and TZZ

The recent reorganisation of the Eni geophysical services has again seen the creation of a dedicated

department in charge of all potential methods studies with the ability to follow the entire workflow of

these activities from survey feasibility and design through acquisition processing and interpretation

of results

Future

The advent of faster and more flexible hardware is going to affect the time dedicated to data

reprocessing and modelling This will require a substantial improvement of the recognition and

separation of anomalies of the depth estimate through the acquisition of gradient data (gravimetric

and magnetic)

The acquisition technology of Marine Controlled Source EM (CSEM) is now commercially available

The CSEM methodology is essentially based on the mapping of the electric resistivity of structures in

the subsurface from few meters below the sea bottom down to various kilometres The resulting data

can be used to interpret direct hydrocarbon indicators (DHI) possibly together with seismic indicators

This implies a better definition of the reservoirs and a substantial reduction of the exploration risk Eni

is engaged in an effort of combining all geophysical methods seismic grav-mag and electromagnetic

in a single phase of multi-dimensional inversion The target is quite ambitious but we are confident

that it can be achieved in a reasonable time frame

The most used approaches for inverting potential field data usually are not able to incorporate all

geological and petrophysical information in a 3D model that can be profitably used by geologists andengineers Integrated inversion techniques have to be designed in order to avoid the typical non

uniqueness problem This implies the incorporation of all available constraints (seismic well markers

wireline logs petrophysics) in order to correctly model the earth interior The integrated inversion of

gravimetric magnetic MT EM and seismic data is the great frontier area awaiting us in the very near

future The proper definition of the geological model must contain not only the elastic properties but

also the electromagnetic and gravimetric (density) Eni is very interested in integrated inversion and is

already working on this subject as testified by the papers scheduled for presentation at this workshop



882019 CSEM - ENI 0407


Figure 2 Pioneering EM in the lsquo90rsquos

Conclusions

Eni started its geophysical activities in 1929 with the torsion balance that measures a gravity gradient

and we have arrived today at measuring MGG a gravity gradient that means ldquoback to the futurerdquo

This is not just a simple joke but signifies that the potential methods do have a great potential for

future development since theory and practice have not been fully exploited over the many years since

they were first developed largely due to the domination of seismic methods

We should also be aware that no single discipline is going to give the answer to the geological model

and great efforts need to be made in the integration phase typically all along the life cycle of dataacquisition processing and interpretation Only the joint exploitation of all geophysical data seismic

gravity magnetic and electromagnetic is able to provide a geologically consistent and quantitatively

robust earth model



882019 CSEM - ENI 0407


Eni has been a pioneer company in application of electromagnetic methods It applied both natural

source and active source based methodologies with increasing attention to the second category

starting from 2003

In the period from 1990 to 2002 magneto-telluric (MT) data have been acquired mainly on land with

the purpose of improving geophysical interpretation in complex geological settings Many hundreds of

MT receivers have been deployed in thrust belt regions in order to provide additional geophysical

information to be integrated with seismic and gravity data Intensive applications have been performed

in the Southern and Central Apennines (Italy) and in Sicily MT methods have been applied alsooffshore in the Sicily channel in the Gulf of Mexico and in the North Sea It is worth mentioning that

in 1994 Agip first experimented the Marine Magneto-telluric technique and acquired the first survey

offshore Sicily

In the years 1998-2000 a dedicated experiment of quantitative integration of MT gravity and seismic

data has been successfully performed The ESIT (Enhance Seismic In Thrust belts) in joint venture

with Shell Italia (formerly Enterprise Oil) and partially funded by the European Union provided a

valuable multiple data set consisting of MT gravity reflection and refraction seismic The application

of cooperative inversion approaches has confirmed the high potential of non-seismic information

especially when it is adequately integrated with seismic

In the late lsquo90rsquos Agip also explored the possibility of using gravity gradient data by the acquisition of

3DFTG (3D Full Tensor Gravity Gradient) In the early 2000rsquos the new HRAM (High Resolution

AeroMagnetic) surveys allowed the preparation of the new Carta Magnetica drsquoItalia (2004) More than

320000 km of flown profiles were acquired from the lsquo70rsquos

The advent of the first dedicated workstations in the 90rsquos triggered Agip interest a great effort was

devoted to the design and implementation of sophisticated software for the processing reprocessing

enhancement filtering and modelling of 2D 25D and 3D gravimetric and magnetic data

Present

In the years 2000 Eni devoted many efforts to consolidating the activities of modelling and

enhancement of anomalies for their interpretative resolution through RampD projects As a result

applications were developed for converting conventional gravimetric data into GGT (Gravity Gradient

Tensor) data 3D depth estimate (Euler deconvolution) of gravimetric and tensor data separation of

shallow and deep effects with the Multiscale Derivative Analysis (MDA) identification of specificamplitudes with the Wavelet Analysis (without frequency filtering) The dedicated software

commercial and proprietary is now running on dedicated Linux platforms

In the same research project new algorithms for the modelling and inversion of gravity magnetic and

full tensor data have been developed and successfully tested over many parts of the world (Figure 1)

At present Eni is very much interested in the full exploitation of non-seismic methods and their

quantitative integration with seismic applications

The results of a research project focused on quantitative integration of seismic and non-seismic data

are coming to light In fact one of the main results was the development of an innovative algorithm of

joint inversion of reflection and refracted travel times with MT and gravity data A multi-parametric

model is produced iteration after iteration and at the same time the seismic imaging improvement is

guaranteed through pre-stack depth migration using the updated velocity field

Great interest is also devoted to marine Controlled Source Electromagnetic methods (CSEM) BothRampD projects and real applications are increasing in numbers year after year Eni is member of the

main EM research consortia guided by the major research institutes and service companies It has

increased the budget for internal RampD projects and developed proprietary algorithms and codes for

modelling inversion and interpretation of CSEM data Eni has recently acquired new data in Norway

Nigeria and Egypt obtaining very significant contributions to the evaluation of prospect exploration

risk



882019 CSEM - ENI 0407






of results

Future




and magnetic)



















882019 CSEM - ENI 0407



Conclusions









robust earth model



882019 CSEM - ENI 0407






of results

Future




and magnetic)



















882019 CSEM - ENI 0407



Conclusions









robust earth model



882019 CSEM - ENI 0407



Conclusions









robust earth model



csem - eni 0407

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