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"Perubahan sifat-sifat batuan seperti porositas, densitas, saturasi dan lain-lain terefleksikan oleh perubahan impedansi seismik. Seperti diketahui, inversi seismik memungkinkan kita untuk mencari korelasinya pada domain impedansi, yang secara unik sering mencirikan perubahan sifat-sifat batuan. Namun demikian, analisa dari seismic inversi full stack gelombang-P membawa kita pada kesimpulan yang membingungkan pada banyak situasi explorasi.Dengan melakukan inversi simultan, kita diarahkan pada interpretasi hasil inversi yang lebih pasti dimana kita dapat mengestimasi densitas, impedansi P dan S yang memberikan respon yang cukup berbeda dalam memisahkan pengaruh lithology dan fluida. Dengan menggunakan konsep matematika inversi AVO, inversi simultan menggunakan data partial angle stack yang kemudian diinversikan secara bersamaan menggunakan wavelet yang di extract dari setiap offset.Kemudian dengan mengkombinasikan parameter-parameter ini dengan teknik analisa rock physics yang dapat digunakan sebagai alat untuk memprediksi distribusi lithology, porositas dan saturasi.Kemudian parameter-parameter ini juga dapat ditransformasikan menjadi Lambda-Rho yang dapat digunakan sebagai indikator kandungan fluida di pori batuan. Akhirnya dengan menganalisa peta distribusi sifat batuan yang di overlay dengan peta struktur dan sumur produksi, kita dapat mengidentifikasi area potensial untuk strategi pengembangan lebih lanjut untuk mengoptimalkan pengurasan hidrokarbon pada area studi.

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The change of lateral rock properties such as porosity, density, fluid saturation etc are reflected in seismic impedance changing. It is known widely that seismic inversion allows us for correlation investigation in the impedance domain which often highlights uniquely the change of rock properties. However the analysis of the early P-wave fullstack seismic inversion data alone can lead to ambiguous conclusions in many exploration situations.

Answering this problem, performing simultaneous inversion will bring us to a less ambiguous interpretation of our inversion results in which we are able to estimate Density, P and S-impedance which have sufficiently different response to discriminate fluid and lithology effects. Utilizing the mathematical concept of AVO inversion, simultaneous inversion use partial angle stack data which can be inverted simultaneously using wavelet extracted from each offset.

Later, these parameters combined with rock physics technique analysis can be used as a tool to predict sand, porosity and saturation distribution. Also, they can be transformed to Lambda-Rho (λρ) that is used for pore fluid content indicator. Finally by analyzing the rock properties distribution map overlaid by structure map and producer well, we can identify the potential area for further development strategy to optimize the hydrocarbon recovery of the study area."

"ABSTRACTUG Massive formation is the main reservoir of Javaz field, oil and gasproducing field, situated in West Natuna Basin. The use of acoustic impedance (PImpedance)only to characterize reservoir hydrocarbon in this field will lead us intolarge uncertainty. Therefore, to overcome that issue, Seismic Simultaneous Inversionmethod is used at Javaz field within UG Massive formation interval. This method isapplied as an alternative method to predict the pore gas (Lambda-Rho) and porositydistribution, using partial post stack 3D seismic data which are invertedsimultaneously; then Javaz-4 well data which will be used as a reference well forpredicting reservoir properties in other wells at Javaz field.Seismic Simultaneous Inversion method resulted Javaz-3 well has similarreservoir properties as studied in Javaz-4 well. However, Javaz-1A and Javaz-2showed different result caused by large uncertainty in seismic resolution (poor qualityseismic data). Porosity and pore gas prediction suggested around 20 to 30 percent and13 to 18 GPa*g/cc respectively, throughout the field. Hence, this method could beused as an alternative to predict UG Massive reservoir properties in Javaz field awayfrom the wells, and it could be applied to the same field with large uncertainty.

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ABSTRAKFormasi UG Massive merupakan reservoar utama pada lapangan Javaz,lapangan ini memproduksi minyak dan gas dan berada pada cekungan Natuna Barat.Study yang dilakukan untuk mengkarakterisasi reservoir hydrocarbon pada lapanganini jika hanya menggunakan akustik impedance (P-Impedance) saja akanmenimbulkan ketidakpastian, untuk mengatasi hal ini maka metode Seismicsimultaneous inversion digunakan pada lapangan Javaz dengan target formasi UGMassive. Metode ini digunakan sebagai alternative untuk memprediksi sebaran poregas (Lambd-Rho) dan porositas, dengan menggunakan partial post stack 3D seismicdata yang di inversikan secara bersamaan dan satu sumur (Javaz-4) data yangdigunakan sebagai kontrol untuk kemudian dijadikan acuan dalam memprediksikarakter reservoir para area sumur lainnya.Dengan menggunakan metode Seismic simultaneous inversion ini, makadidapatkan hasil prediksi karakter reservoir pada sumur Javaz-3 yang memilikikarakter mendekati sumur Javaz-4 pada formasi utama, namun tidak demikian untuksumur Javaz-2 dan Javaz-1A. Untuk perkiraan sebaran porositas maupun pore gasdidapatkan hasil yang cukup baik, dengan nilai porositas berkisar antara 20% hingga30% dan pore gas (Lambda-Rho) yang berkisar antara 13 (GPa*g/cc) hingga 18(GPa*g/cc). Dari hasil study ini maka dapat disimpulkan bahwa metode ini dapatdigunakan sebagai alternative untuk memprediksi karakter reservoar pada formasiUG Massive."

"Perubahan impedansi seismik memberikan petunjuk adanya perubahan sifat-sifat batuan, seperti porositas, densitas, saturasi dan lain-lain. Dengan inversi seismik kita dapat membuat korelasi pada domain impedansi berdasarkan perubahan sifat-sifat batuannya. Namun demikian, analisa seismik inversi dengan full stack gelombang-P memberikan kesimpulan yang terlalu umum, masih mengandung multi interpretasi pada kondisi eksplorasi tertentu. Melalui inversi simultan, kita mendapatkan kesimpulan yang lebih pasti dimana kita dapat mengestimasi densitas, impedansi P dan impedansi S, dimana masing-masing memberikan respon yang cukup berbeda dalam memisahkan pengaruh lithology dan fluida. Proses inversi simultan menggunakan data partial angle stack, yang kemudian wavelet yang diekstrak dari setiap offset diinversikan secara bersamaan. Dari hasil inversi simultan diatas, selanjutnya dengan teknik analisa rock physics kita dapat memprediksi distribusi lithology, porosity dan kandungan hidrokarbon (gas). Proses selanjutnya dengan mentransformasikan hasil inversi menjadi Lambda-Rho (λρ) dapat digunakan untuk memperkuat argumentasi adanya indikator kandungan fluida di pori batuan. Akhirnya dengan melakukan analisa peta distribusi sifat batuan yang di overlay dengan peta struktur dan sumur produksi, kita dapat mengidentifikasi area potensial untuk strategi pengembangan lebih lanjut untuk mengoptimalkan pengurasan hidrokarbon pada area studi.

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The change of seismic's impedance giving clues that there is change of lateral rock properties such as porosity, density, fluid saturation etc. Seismic inversion allows us to make correlation in the impedance domain based on the change of rock properties. However the analysis of the early P-wave fullstack seismic inversion data alone can lead to ambiguous conclusions in many exploration conditions.

By performing simultaneous inversion will bring us to a less ambiguous interpretation of our inversion results in which we are able to estimate Density, Pimpedance and S-impedance which they are giving different response to discriminate fluid and lithology effects. Simultaneous inversion process uses partial angle stack data which can be inverted simultaneously using wavelet extracted from each offset.

Based on result above, using further rock physics technique analysis we can predict sand, porosity and hydrocarbon content distribution. Further process, the result can be transformed to Lambda-Rho (λρ) that can be used for pore fluid content indicator.

Finally by analyzing the rock properties distribution map overlaid by structure map and producer well, we can identify the potential area for further development strategy to optimize the hydrocarbon recovery of the study area."

"Di lapangan AA, metoda seismik inversi digunakan untuk menghasilkan volume akustik impedansi. Hasil dari metode ini tidak hanya menghasilkan resolusi yang lebih baik untuk interpretasi struktur yang lebih akurat , tetapi juga memberikan pengertian lebih baik tentang prediksi sifat-sifat fluida dan resrevoar. Seismik inversi AVO merobah seismik data menjadi P-impedansi (hasil dari densitas dan kecepatan gelombang-P), S-impedansi (hasil dari densitas dan kecepatan gelombang-S), dan densitas (ρ) yang menjadikan pemisahan fluida dan litologi menjadi lebih baik. Sebelum membahas AVO inversi, reservoar fisika batuan dianalisa untuk tujuan Fluid Replacement Modeling (FRM). Melalui FRM, dilakukan pertukaran fluida menggunakan persamaan Biot Gassmann untuk mengetahui pengaruh fluida pada sifat-sifat elastik batuan. Awalnya, Vp, Vs, ρ dan Sw dari suatu fluida harus diketahui. Kemudian, hasil analisa dibawa memalui perbandingan antara sumur seismogram sintesa dari fluida yang berbeda atau sifat-sifat batuan dengan data seismik menggunakan hasil ekstraksi wavelet. Perbedaan fluida dengan perbedaan sifat-sifat batuan menunjukkan perbedaan respons amplitudo dan karakternya. Hasil studi ini diharapkan memperkuat interpretasi seismik untuk pemisahan fluida dan litologi. Selanjutnya, melalui studi diharapkan dapat digunakan untuk mengoptimalkan produksi oil dan gas dan di lapangan AA.

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At AA Field, we applied seismic AVO inversion methods to generate acoustic impedance volume. The results of this approach provide not only better resolution for more accurate structural interpretations, but also allow us to perform better fluids and reservoir properties predictions. Seismic AVO inversion transforms seismic data into P-impedance (product of density and P-wave velocity), S-impedance (product of density and S-wave velocity), and density (ρ) for better discrimination on fluid and lithology effects. Prior to AVO Inversion, rock physics of the reservoir were analyzed for Fluid Replacement Modeling (FRM) purposes. Through this FRM, we employed Biot Gassmann fluid substitution to investigate fluid effects on rocks elastic properties. Initially, we setup input logs of Vp, Vs, ρ, and fluid saturation (Sw) with known fluid type. Later on the workflow, analysis was carried-out through comparison between well synthetic seismogram of different fluids or rock properties with seismic data using extracted wavelet. Different fluid with different rock properties exhibit different amplitude responses and characters. This study has enhanced our seismic interpretation for fluid and lithology discriminations. Furthermore, this study can be used for optimization of oil and gas productions at AA Field."

"Metodologi inversi simultan telah dilakukan untuk mendelineasi dan menkarakterisasi reservoir utama pada lapangan “R”, Cekungan Kutei, Indonesia, hasil dari inversi simultan adalah attribute karakter batuan (Vsh,Porositas dan Saturasi air). Namun, hasil yang kita dapatkan pada target sekunder banyak ambigu dan tidak bisa digunakan oleh Interpreter untuk memperbarui moldel bumi. Oleh karena itu, Proses inversi simultan Akan kembali dilakukan menggunakan kontrol sumur yang tersedia untuk reservoir tersebut tetapi dengan wavelet yang berbeda dengan inversi yang pretama. Wavelet yang diekstrak dikontrol oleh jendela waktu antara tiap horizon. Inversi simultan kedua dilakukan dengan menggunakan wavelet yang difokuskan pada Horizon atas dan bawah dari reservoir sekunder. Tujuan dari proyek ini adalah untuk membangun volum karakteristik batuan (Vsh, Porositas dan Saturasi) untuk reservoir sekunder yang dapat digunakan oleh interpreter untuk memperbarui model statis bumi saat ini . Sifat batuan akan diperkirakan dari produk inversi simultan (P-Impedance, S-Impedansi dan rasio VpVs).

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Simultaneous inversion methodology has been done to delineate and characterize the primary reservoir at R field, Kutei Basin, Indonesia, resulting rock properties attributes (Vsh, Porosity and Saturation) derived from seismic inversion result. However, the result on the secondary target was ambiguous and can’t be used by interpreter to update the earth model. This study focuses on characterizing the reservoir at the secondary target. Therefore, simultaneous inversion process will be re-run using wells control that was available for this particular reservoir but with a different wavelet that was extracted. Wavelets that are extracted are controlled by the time window between the horizons. The second simultaneous done was using a wavelet that was focused on the top and bottom horizon of the secondary reservoir.

The objectives of this project are to build rock properties volume ( Vsh, Porosity and Saturation) for secondary reservoirs only that can be used by interpreter to update current static earth model. Those rock properties volumes will be estimated from simultaneous inversion products (P-Impedance, S-Impedance and VpVs ratio)."

"[ABSTRAKLapangan XXX merupakan lapangan minyak di cekungan Natuna Baratdengan reservoir utama berupa reservoir batu pasir. Ketebalan reservoir padalapangan ini sangat bervariasi sehingga hasil inversi hanya dapat memetakanketebalan reservoir yang mendekati ketebalan tuning.Berdasarkan uji sensitifitas, parameter AI di setiap sumur tidak dapatmembedakan hidrokarbon, sehingga parameter akustik saja tidak dapat diaplikasikandalam karakterisasi reservoir lapangan ini. Namun ketika parameter densitas terpisahdengan parameter kecepatan P, sebaran hidrokarbon dapat dibedakan dengan baik.Kecepatan S tidak tersedia di semua sumur padahal data ini sangat diperlukanuntuk melakukan pengolahan data dengan metode inversi simultan. Oleh karena ituakan dilakukan beberapa estimasi untuk mendapatkan data kecepatan S antara laindengan metode castagna, metode gassmann, metode parsial, metode Xu-White danmetode Lee. Data kecepatan S yang dipakai adalah kecepatan S terbaik yangdiperoleh dari metode Xu White dikarenakan hasil log poisson’s rationya palingmendekati tren kurva saturasi air. Selain itu aspek rasio batuan yangmempertimbangkan nilai porositas dan volume clay, serta kontrol kualitas Vp modeldari metode Xu-White memiliki rasio error minimum jika dibandingkan dengan nilaiVp dari data log.Metode inversi simultan dengan data pre-stack atau partial stackmemungkinkan dilakukannya prediksi parameter Impedansi P, Impedansi S, dandensitas dari data seismik. Selain itu meode inversi simultan dapat dipergunakanmulti wavelet dalam pengolahan datanya. Hasil penampang inversi yang diperolehmenunjukkan bahwa inverse densitas dapat menjelaskan letak sebaran batuanreservoir dan fluida berdasarkan cut off sensitifitas yakni nilai dibawah 2,26 gr/cc.

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ABSTRACTfield is an oil field in West Natuna Basin with sandstone reservoir asprimary target. There was varying reservoir thickness, so the inversion method thatcould only be applied to map reservoir thickness, which close to tuning thickness.Based on sensitivity analysis, Acoustic Impedance parameters couldn’tindicate hydrocarbon appearance for each well, so Acoustic Impedance cannot beapplied for reservoir characterization in this field. Density versus AcousticImpedance could map hydrocarbon appearance.Shear velocity weren’t available where those data was needed for runningsimultaneous inversion method. Predicting velocity shear would be carried out byusing several method such as Castagna, Gassmann, Parsial, Xu-White, and Lee. Thebest estimated velocity shear would be used for inversion, The best estimated shearvelocity from Xu-White method because Xu-White’s poisson ratio log presentssimilar trend with water saturation log (Sw). Moreover, Xu-White’s ratio aspect isalso considering porosity and clay volume value. Based on quality control result, Vpmodel of Xu-White had minimum error ratio compared to Vp from log.Simultaneous inversion with pre-stack and parsial stack data what can be usedfor predicting P-Impedance, S-Impedance, and density from seismic data. Otherwise,this method is also used not only for single wavelet but also multi wavelet. Theinversion result from this study can mapping out the hydrocarbon appearance forreservoir target based on cut off value from sensitivity test of less than 2,26 gr/cc.;X field is an oil field in West Natuna Basin with sandstone reservoir asprimary target. There was varying reservoir thickness, so the inversion method thatcould only be applied to map reservoir thickness, which close to tuning thickness.Based on sensitivity analysis, Acoustic Impedance parameters couldn’tindicate hydrocarbon appearance for each well, so Acoustic Impedance cannot beapplied for reservoir characterization in this field. Density versus AcousticImpedance could map hydrocarbon appearance.Shear velocity weren’t available where those data was needed for runningsimultaneous inversion method. Predicting velocity shear would be carried out byusing several method such as Castagna, Gassmann, Parsial, Xu-White, and Lee. Thebest estimated velocity shear would be used for inversion, The best estimated shearvelocity from Xu-White method because Xu-White’s poisson ratio log presentssimilar trend with water saturation log (Sw). Moreover, Xu-White’s ratio aspect isalso considering porosity and clay volume value. Based on quality control result, Vpmodel of Xu-White had minimum error ratio compared to Vp from log.Simultaneous inversion with pre-stack and parsial stack data what can be usedfor predicting P-Impedance, S-Impedance, and density from seismic data. Otherwise,this method is also used not only for single wavelet but also multi wavelet. Theinversion result from this study can mapping out the hydrocarbon appearance forreservoir target based on cut off value from sensitivity test of less than 2,26 gr/cc., X field is an oil field in West Natuna Basin with sandstone reservoir asprimary target. There was varying reservoir thickness, so the inversion method thatcould only be applied to map reservoir thickness, which close to tuning thickness.Based on sensitivity analysis, Acoustic Impedance parameters couldn’tindicate hydrocarbon appearance for each well, so Acoustic Impedance cannot beapplied for reservoir characterization in this field. Density versus AcousticImpedance could map hydrocarbon appearance.Shear velocity weren’t available where those data was needed for runningsimultaneous inversion method. Predicting velocity shear would be carried out byusing several method such as Castagna, Gassmann, Parsial, Xu-White, and Lee. Thebest estimated velocity shear would be used for inversion, The best estimated shearvelocity from Xu-White method because Xu-White’s poisson ratio log presentssimilar trend with water saturation log (Sw). Moreover, Xu-White’s ratio aspect isalso considering porosity and clay volume value. Based on quality control result, Vpmodel of Xu-White had minimum error ratio compared to Vp from log.Simultaneous inversion with pre-stack and parsial stack data what can be usedfor predicting P-Impedance, S-Impedance, and density from seismic data. Otherwise,this method is also used not only for single wavelet but also multi wavelet. Theinversion result from this study can mapping out the hydrocarbon appearance forreservoir target based on cut off value from sensitivity test of less than 2,26 gr/cc.]"

"[ABSTRAKLapangan XXX merupakan lapangan minyak di cekungan Natuna Baratdengan reservoir utama berupa reservoir batu pasir. Ketebalan reservoir padalapangan ini sangat bervariasi sehingga hasil inversi hanya dapat memetakanketebalan reservoir yang mendekati ketebalan tuning.Berdasarkan uji sensitifitas, parameter AI di setiap sumur tidak dapatmembedakan hidrokarbon, sehingga parameter akustik saja tidak dapat diaplikasikandalam karakterisasi reservoir lapangan ini. Namun ketika parameter densitas terpisahdengan parameter kecepatan P, sebaran hidrokarbon dapat dibedakan dengan baik.Kecepatan S tidak tersedia di semua sumur padahal data ini sangat diperlukanuntuk melakukan pengolahan data dengan metode inversi simultan. Oleh karena ituakan dilakukan beberapa estimasi untuk mendapatkan data kecepatan S antara laindengan metode castagna, metode gassmann, metode parsial, metode Xu-White danmetode Lee. Data kecepatan S yang dipakai adalah kecepatan S terbaik yangdiperoleh dari metode Xu White dikarenakan hasil log poisson?s rationya palingmendekati tren kurva saturasi air. Selain itu aspek rasio batuan yangmempertimbangkan nilai porositas dan volume clay, serta kontrol kualitas Vp modeldari metode Xu-White memiliki rasio error minimum jika dibandingkan dengan nilaiVp dari data log.Metode inversi simultan dengan data pre-stack atau partial stackmemungkinkan dilakukannya prediksi parameter Impedansi P, Impedansi S, dandensitas dari data seismik. Selain itu meode inversi simultan dapat dipergunakanmulti wavelet dalam pengolahan datanya. Hasil penampang inversi yang diperolehmenunjukkan bahwa inverse densitas dapat menjelaskan letak sebaran batuanreservoir dan fluida berdasarkan cut off sensitifitas yakni nilai dibawah 2,26 gr/cc.

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ABSTRACTX field is an oil field in West Natuna Basin with sandstone reservoir asprimary target. There was varying reservoir thickness, so the inversion method thatcould only be applied to map reservoir thickness, which close to tuning thickness.Based on sensitivity analysis, Acoustic Impedance parameters couldn?tindicate hydrocarbon appearance for each well, so Acoustic Impedance cannot beapplied for reservoir characterization in this field. Density versus AcousticImpedance could map hydrocarbon appearance.Shear velocity weren?t available where those data was needed for runningsimultaneous inversion method. Predicting velocity shear would be carried out byusing several method such as Castagna, Gassmann, Parsial, Xu-White, and Lee. Thebest estimated velocity shear would be used for inversion, The best estimated shearvelocity from Xu-White method because Xu-White?s poisson ratio log presentssimilar trend with water saturation log (Sw). Moreover, Xu-White?s ratio aspect isalso considering porosity and clay volume value. Based on quality control result, Vpmodel of Xu-White had minimum error ratio compared to Vp from log.Simultaneous inversion with pre-stack and parsial stack data what can be usedfor predicting P-Impedance, S-Impedance, and density from seismic data. Otherwise,this method is also used not only for single wavelet but also multi wavelet. Theinversion result from this study can mapping out the hydrocarbon appearance forreservoir target based on cut off value from sensitivity test of less than 2,26 gr/cc.;X field is an oil field in West Natuna Basin with sandstone reservoir asprimary target. There was varying reservoir thickness, so the inversion method thatcould only be applied to map reservoir thickness, which close to tuning thickness.Based on sensitivity analysis, Acoustic Impedance parameters couldn?tindicate hydrocarbon appearance for each well, so Acoustic Impedance cannot beapplied for reservoir characterization in this field. Density versus AcousticImpedance could map hydrocarbon appearance.Shear velocity weren?t available where those data was needed for runningsimultaneous inversion method. Predicting velocity shear would be carried out byusing several method such as Castagna, Gassmann, Parsial, Xu-White, and Lee. Thebest estimated velocity shear would be used for inversion, The best estimated shearvelocity from Xu-White method because Xu-White?s poisson ratio log presentssimilar trend with water saturation log (Sw). Moreover, Xu-White?s ratio aspect isalso considering porosity and clay volume value. Based on quality control result, Vpmodel of Xu-White had minimum error ratio compared to Vp from log.Simultaneous inversion with pre-stack and parsial stack data what can be usedfor predicting P-Impedance, S-Impedance, and density from seismic data. Otherwise,this method is also used not only for single wavelet but also multi wavelet. Theinversion result from this study can mapping out the hydrocarbon appearance forreservoir target based on cut off value from sensitivity test of less than 2,26 gr/cc., X field is an oil field in West Natuna Basin with sandstone reservoir asprimary target. There was varying reservoir thickness, so the inversion method thatcould only be applied to map reservoir thickness, which close to tuning thickness.Based on sensitivity analysis, Acoustic Impedance parameters couldn’tindicate hydrocarbon appearance for each well, so Acoustic Impedance cannot beapplied for reservoir characterization in this field. Density versus AcousticImpedance could map hydrocarbon appearance.Shear velocity weren’t available where those data was needed for runningsimultaneous inversion method. Predicting velocity shear would be carried out byusing several method such as Castagna, Gassmann, Parsial, Xu-White, and Lee. Thebest estimated velocity shear would be used for inversion, The best estimated shearvelocity from Xu-White method because Xu-White’s poisson ratio log presentssimilar trend with water saturation log (Sw). Moreover, Xu-White’s ratio aspect isalso considering porosity and clay volume value. Based on quality control result, Vpmodel of Xu-White had minimum error ratio compared to Vp from log.Simultaneous inversion with pre-stack and parsial stack data what can be usedfor predicting P-Impedance, S-Impedance, and density from seismic data. Otherwise,this method is also used not only for single wavelet but also multi wavelet. Theinversion result from this study can mapping out the hydrocarbon appearance forreservoir target based on cut off value from sensitivity test of less than 2,26 gr/cc.]"

"West Natuna Barat merupakan cekungan yang memiliki lingkungan fluvial dengan reservoir berupa bed-sand berselingan dengan shale dan shaly-sand. Metode inversi dilakukan dengan Seismic Colored Inversion yang akan memberikan hasil yang kuat untuk melihat fitur geologi berupa kanal pasir menerus yang memiliki nilai Impedansi Akustik rendah pada zona-zona yang menarik. Pengirisan dilakukan pada horizon A1, saluran pasir dengan nilai AI berkisar antara 12.000 hingga 15.500 ((ft/s)*(g/cc) tersebar di tengah zona penelitian ke arah timur. , alur pasir dengan AI berkisar antara 16.000 sampai 17.800 ((ft/s)*(g/cc)) tersebar di daerah tengah zona penelitian sekitar U1 sampai U3, juga terlihat di timur laut zona penelitian. Pada hasil slicing horizon C1, ditemukan saluran pasir dengan nilai AI berkisar antara 18.000 sampai dengan 19.000 ((ft/s)*(g/cc)) di daerah tengah zona penelitian dekat sumur U1 sampai U3.

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The West Natuna Basin is a basin that has a fluvial environment with a reservoir in the form of bed-sand alternating with shale and shaly-sand. The inversion method is carried out with Seismic Colored Inversion which will give strong results to see geological features in the form of continuous sand canals that have low Acoustic Impedance values ​​in interesting zones. The slicing was carried out on the A1 horizon, a sand channel with AI values ​​ranging from 12,000 to 15,500 ((ft/s)*(g/cc) spread in the center of the study zone to the east. , sand grooves with AI ranging from 16,000 to 17,800 ((ft) /s)*(g/cc)) is spread in the central area of ​​the study zone around U1 to U3, also seen in the northeast of the study zone. In the results of the slicing horizon C1, sand channels were found with AI values ​​ranging from 18,000 to 19,000 ((ft /s)*(g/cc)) in the center of the study zone near wells U1 to U3."

"Inversi seismik konvensional yang menghasilkan penampang impedansi akustik kini terbatas dalam mengidentifikasi litologi. Telah dilakukan inversi prestack yakni simultaneous inversion yang mampu memprediksi tidak hanya parameter impedansi akustik, tetapi juga impedansi shear, dan densitas untuk mengatasi hal tersebut. Dengan memperoleh ketiga parameter tersebut, akan dapat diperoleh paramater lame berupa lamda-rho dan mu-rho yang lebih sensitif terhadap litologi dan fluida untuk mempertajam indentifikasi litologi maupun fluida reservoar. Inversi simultan, yang bertujuan mengkarakterisasi reservoar batupasir dan penyebaran gas ini, dilakukan pada kasus Lapangan ?C‟ yang terletak di Cekungan Natuna Barat. Inversi dilakukan pada data angle stack baik itu near angle stack (5o-15o), mid angle stack (15o-25o), dan far angle stack (25o-35o) dengan dua kontrol sumur yakni sumur CS-1 dan CSR-3. Inversi yang dilakukan juga meliputi analisis lambda-rho dan mu-rho yang diturunkan dari parameter impedansi akustik dan impedansi shear. Hasil yang diperoleh adalah penyebaran reservoar batupasir dapat diprediksi dengan menggunkan parameter impedansi shear dan mu-rho dengan cut off impedansi shear ± 3300 m/s*g/cc dan cut off mu-rho ± 11 GPa*g/cc sementara keberadaan gas dapat diprediksi dengan menggunakan parameter lambda-rho dan VpVs ratio dengan cut off lambda-rho ± 11 - 20 GPa*g/cc dan cut off VpVs ratio ± 1.8. Dengan demikian, reservoar batupasir dapat diperkirakan terletak di sekitar inversion anticline dengan pola pengendapan channel yang berada di sebelah tenggara daerah penelitian.

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Conventional seismic inversion that produces cross-sectional acoustic impendance is limited in identifying lithology. Prestack inversion i.e.simultaneous inversion that is capable of predicting not only acoustic impedance parameter, but also the shear impedance and density has been applied to solve that problem. By obtaining these three parameters, we can get the parameters of lambda-rho and mu-rho that are more sensitive to lithology and fluid to sharpen the identification of lithology and fluid reservoir.

Simultaneous inversion, that aims to characterize the sandstone reservoir and the distribution of gas, done in the case of ?C‟ Field located in the West Natuna Basin. Inversion performed on the data near angle stack (5o-15o), mid angle stack (15o-25o), and far angle stack (25o-35o) with two control wells CS-1 and CSR-3. Inversion carried out also includes the analysis of lambda-rho and mu-rho derived from the acoustic impedance and shear impedance.

The obtained results are the distribution of sandstone reservoir can be predicted using the parameter of shear impedance and mu-rho with shear impedance cut off ± 3300 m/s*g/cc & mu-rho cut off ± 11 GPa*g/cc while the presence of gas can be predicted by using the parameter of lambda-rho and VpVs ratio with lambda-rho cut off ± 11 - 20 GPa*g/cc & VpVs ratio cut off ± 1.8. Thus, estimated sandstone reservoir is located around inversion anticline with the channel deposition in the southeast area of research."

"ABSTRAK

Integrasi pemodelan isi fluida dan analisis seismik AVO untuk memetakan reservoar gas Globigerina limestone melalui simultaneous pre stack inversion telah dilakukan pada Cekungan Jawa Timur, Selat Madura. Penelitian ini memanfaatkan pemodelan ke belakang atau lebih dikenal sebagai inversion modelling. Tujuan dari penelitian ini adalah untuk menggambarkan penyebaran reservoar gas dari Globigerina limestone sehingga hasil analisis kuantitatifnya dapat dijadikan sebagai rujukan didalam pemboran sumur berikutnya. Penelitian diawali dengan pembuatan low frequency model yang optimum yaitu dengan mengintegrasikan pemodelan isi fluida dan analisis seismik AVO. Integrasi keduanya diperlukan mengingat target penelitian banyak terpengaruh oleh zona gas dangkal yang mengakibatkan terdistorsinya puncak dan dasar dari struktur reservoar targetnya. Data penelitian terdiri dari data seismik tiga dimensi (3D) seluas 320km² dengan kerapatan bin size 18.75m x 12.5m disertai dengan dua data sumur. Hasil dari crossplot menunjukan bahwa litologi target reservoar dapat dibedakan dengan litologi non reservoar melalui log Vp dan Vs. Hasil dari crossplot antara impedansi P dan Vp/Vs dapat menunjukkan bagaimana kualitas reservoar gas pada struktur F dan struktur H. Nilai cut-off pada crossplot utama yaitu antara impedansi P dan Vp/Vs adalah sebesar 2.400 - 5.500 gr/cc*m/s dan 2,0 - 2,1 pada rasio cepat rambat gelombang. Hasil dari optimasi low frequency model menunjukkan bahwa pada struktur G, yang merupakan target pemboran berikutnya, respon impedansi P dan Vp/Vs nya analog terhadap kedua struktur F dan H. Hal ini menunjukkan bahwa melalui integrasi pemodelan isi fluida dan analisis seismik AVO, low frequency model dapat dioptimasikan sehingga metode simultaneous seismic inversion mampu memetakan zona-zona reservoar gas lainnya.

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ABSTRACT

Integration of fluid replacement modelling and seismic AVO analysis towards simultaneous seismic inversion had been done to delineate the distribution of Globigerina limestone gas reservoir in Madura Strait, East Java Basin. This study was using backward modelling or well known as inversion modelling to finish the quantitative analysis. The purpose of the study is to map the distribution of Globigerina limestone gas reservoir so that in the end the final result will be used as a guidance to drill the next exploration well. It started with an optimized low frequency model building by integrating fluid replacement modelling and seismic AVO analysis. By integrating these two methods, the distorted reservoir top structure and bottom can be compensated and the low frequency model will be optimized. The availability of the data includes 3D seismic data with acquisition bin size 18.75m x 12.5m, area of 320km², with two well logs. The crossplot result showed that the reservoir and non-reservoir lithology can be distinguished by Vp and Vs log. By analysing the acoustic impedance together with Vp/Vs, the character of gas reservoir at surrounding F and H structures can also be delineated. The main cutoff for acoustic impedance and Vp/Vs were 2,400 - 5,500 gr/cc*m/s and 2.0 - 2.1. The final optimizing result of low frequency model showed that the target G structure, which will be the next exploration target, showed an analogue response with its neighbour F and H structures. It is concluded that by integrating both two methods, fluid replacement modelling and AVO seismic analysis, the optimizing of low frequency model can be achieved and the simultaneous seismic inversion can successfully map other gas reservoir.

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