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3D Seismic Inversion 1* 0D-S Holding A/S mm A Company in the 0degaard & Danneskiold-Samsoe Group Report 97.487 A/jEX- dK~ " <9x5'(?(5x 3D Seismic Inversion Energistyrelsen Amaliegade 44 DK-1256 Kpbenhavn K Denmark March 1997 iBsrammoN or tub document ts unlimith) Prepared by Klaus Bolding Rasmussen 0D-S Holding A/S, Copenhagen, Denmark Jacob M0rch Pedersen 0D-S Holding A/S, Copenhagen, Denmark Serge Gluck Compagnie Generale de Geophysique, Massy, France Emmanuelle Juve Compagnie Generale de Geophysique, Massy, France DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document Contents Page Dansk sammendrag......................................................................................................................3 1. 3-D seismic inversion............................................................................................................. 4 1.1 New products onthe world market.........................................................................4 1.2 Seismic inversion......................................................................................................4 1.3 Applications of inversion......................................................................................... 5 2. The Measurements................................................................................................................. 7 2.1 Seismic data.............................................................................................................. 7 2.2 The well data............................................................................................................. 7 2.2.1 Deviated wells........................................................................................... 8 3. Wavelet..................................................................................................................................... 8 3.1 Wavelet estimation....................................................................................................9 3.1.1 Wavelet methods.......................................................................................9 3.1.2 Deviated wells......................................................................................... 12 4. The inversion.......................................................................................................................... 13 4.1 Method..................................................................................................................... 13 4.2 Parameterisation...................................................................................................... 14 4.3 Objective function...................................................................................................14 4.4 Global search............................................................................................................16 4.5 The spectral content of the seismic data related to the inverted seismic traces 16 4.5.1 Initial model / a priori model................................................................. 16 4.6 The results................................................................................................................19 4.7 Uncertainties.............................................................................................................19 5. Reservoir description............................................................................................................ 21 6. The future............................................................................................................................... 24 Acknowledgements....................................................................................................................25 References...................................................................................................................................26 2 Dansk sammendrag Denne rapport praesenterer resultateme af EF-93 forskningsprojektet "3-D inversion af seismiske data". Arbejdet er udfprt af 0D-S Holding A/S i samarbejde med det franske firma Compagnie Generale de Gdophysique (CGG). Projektet bar f&et stptte af EU under Joule- programmet, under hvilket det indgik i et stprre projekt udfprt af en raekke europaeiske universiteter og forskningscentre: Imperial College, London, UK (projektleder); Birkbeck College, London, UK; Hamburg Universitat, Hamborg, Tyskland; Institut Francais du Petrole, Paris, Frankrig; Observatorio Geoflsico Sperimentale di Trieste, Trieste, Italien samt olieselskabeme Norsk Hydro, Norge; BP, UK og Amoco, UK. I projektet er der udviklet en ny 3D inversionsmetode, der benytter en global optimeringsteknik til at s0ge efter den bedste undergrundsmodel. Metodens succes skyldes denne avancerede spgestrategi kombineret med en unik parameterisering af inversionsproblemet. Parameteriseringen g0r, at det er muligt at anvende global optimering, uden at regnetiden for inversionsmetoden bliver urimelig lang. Metoden er under projektforlpbet blevet kommercialiseret, og den bruges allerede som konsulentydelse. Denne konsulentydelse giver arbejde til et betydeligt antal geologer og geofysikere bos 0D-S Holding A/S i forbindelse med 3D inversion for olieselskaber i hele verden. Desuden er der foreg&et et software udviklingsarbejde under EFP-94. 0D-S forventer sig meget af 3D inversionsmarkedet fremover, bade hvad angSr konsulentarbejde og software. Af den grand Abnes der kontor i Houston, Texas ca. 1. maj 1997. Det EFP-93 projekt, som er beskrevet i denne rapport og i rapporten "ISIS Global Inversion of 3-D Land Seismic Data", 0DS rapport 95.391 af Lars S. Hansen, bar sAledes vaeret bAde en videnskabelig og kommerciel succes, som vil danne basis for det videre geofysiske udviklingsarbejde i 0D-S Holding mange ar frem. Jacob M0rch Pedersen, Projektleder 1. 3-D seismic inversion 1.1 New products on the world market The research results from the 3D inversion have been made into products already available on the market. The new products are used both within the EU and in the rest of the world. The two partners in the 3D inversion project have launched two different products onto the market; 0D- S Holding A/S (0DS) has introduced ISIS and Compagnie Generale de Geophysique (CGG) has introduced TDROV. Both products use global optimisation in the 3D seismic inversion. The two products have been very well received by oil companies, and global inversion is increasingly used for seismic inversion on the European market. There is also a significant worldwide export market. These two products are the only commercial products utilising global optimisation for seismic inversion, giving EU a significant advance internationally. 0DS is a small enterprise (SME) and the research results have already lead to several new jobs and the market is rapidly growing. 1.2 Seismic inversion Seismic data is a very important contribution to oil and gas exploration and optimisation of oil and gas exploitation. Drillings give direct and detailed information about reservoir properties and content, but they are expensive and cover only a small area. Seismic data on the other hand is relatively inexpensive and covers a large area. The drawbacks are that seismic is a remote sensing with limited resolution and it is the changes in acoustic impedance that give rise to the signal, with acoustic impedance being only an indirect reservoir parameter. The present research project is focused on utilising the information in the seismic data and combing it with other sources of information such as the well log measurements from the bore holes. When oil companies want to perform detailed stratigraphic interpretation of fully processed post stack seismic data, it becomes more and more natural to include seismic inversion and thereby transform the seismic data to acoustic impedance. The acoustic impedance field produced by these methods is meant to help stratigraphic interpretation and reservoir characterisation since: a. it is less oscillatory than the initial seismic data (impedance vs. reflectivity), b. it is more directly correlatable to well log data for lateral prediction of lithology, porosity and fluid content, and c. it produces a high resolution layer framework whose strata are deformed in order to become conformable to seismic reflectors. Since the transformation of seismic data to impedance is non-unique, some a priori information has to be introduced in order to sample only the acoustic impedance solutions which are geologically realistic. The seismic response of the impedance model is compared with the real 4 EH seismic data in a volumetric fashion by measuring the error along the mobile impedance model interfaces. The resulting misfit is minimised in order to maximise a probability function of the impedance model parameters. By doing so, the impedance model interfaces tend to orient themselves conformably to the seismic reflectors, thereby averaging out the random seismic noise, and reinforcing laterally weak, but coherent events. This feature contributes to thin layer detection/resolution. More generally, 3D seismic amplitudes may be distorted as a result of poor 3D spatial sampling/binning and a possible low signal-to-noise ratio. These data problems are addressed through 3D inverse modelling coupled to sparse model parameterisation and relevant a priori information. 1.3 Applications of inversion Inversion can be applied from the first seismic data are collected in the oil/gas exploration to exploitation with the seismic
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