Hasil Pencarian  ::  Simpan CSV :: Kembali

"Andesitic and basaltic lavas are the main product of the upper Miocene volcanic activities in Lubuk Sikaping region. They posses vesicular and amygdales structure, dark grey to black in colour, highly porphyritic in texture composed of plagioclase, clinopyroxene, orthopyroxene, olivine (in basalt only) and minor hornblende, magnetite and ilmenite. They (basalt and andesite) mostly fall within the calc-alkaline series on the AFM. The basalt and andesite are not primary magma since they have low Mg# and Ni contents. The lavas resemble the typical of arc setting with Nb through on the spider-diagram patterns, enrichment in large ion lithophile elements and light rare earth elements relative to high field strength elements and heavy rare earth element. They are co-magmatic as shown by the REE pattern. The lavas have high concentration of Ba, Sr, La, Rb and Ce, Zr, Th and U, and high Ba/La ratio which indicating an involvement subducted sediment in their generation. The lava from Lubuk Sikaping is product of Maninjau Crater eruption in Upper Miocene. This lava was uplifted and exposed on high level topography for a few million years, and then superimposed by a high-K calcalkaline volcanic of mainly rhyolitic tuff as a result of the reactivation of the Maninjau Crater in Pleistocene."

"

---

ABSTRACTThis book provides a comprehensive introduction to the field of geochemistry. The book first lays out the 'geochemical toolbox': the basic principles and techniques of modern geochemistry, beginning with a review of thermodynamics and kinetics as they apply to the Earth and its environs. These basic concepts are then applied to understanding processes in aqueous systems and the behavior of trace elements in magmatic systems. Subsequent chapters introduce radiogenic and stable isotope geochemistry and illustrate their application to such diverse topics as determining geologic time, ancient climates, and the diets of prehistoric peoples. The focus then broadens to the formation of the solar system, the Earth, and the elements themselves. Then the composition of the Earth itself becomes the topic, examining the composition of the core, the mantle, and the crust and exploring how this structure originated. A final chapter covers organic chemistry, including the origin of fossil fuels and the carbon cycle's role in controlling Earth's climate, both in the geologic past and the rapidly changing present.Geochemistry is essential reading for all earth science students, as well as for researchers and applied scientists who require an introduction to the essential theory of geochemistry, and a survey of its applications in the earth and environmental sciences.Additional resources can be found at."

"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.

---

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."

"Gunung Api Krakatau merupakan salah satu gunung api aktif yang terbagi menjadi tiga periode letusan. Aktivitas vulkanik yang terjadi setelah letusan pembentuk kaldera pertama (diperkirakan sekitar abad ke-5) hingga letusan pembentuk kaldera kedua pada tahun 1883 termasuk dalam periode Krakatau Muda. Penelitian pada produk sebelum 1883 dilakukan pada lokasi penelitian Danan dan Pulau Rakata dengan total sampel berjumlah empat. Aktivitas vulkanisme yang terjadi pada 1883 membentuk kaldera dan mengakibatkan hilangnya Pulau Perbuatan dan sebagian Danan, sehingga penelitian pada produk sebelum 1883 terbilang sangat terbatas. Penelitian ini dilakukan melalui pendekatan petrologi, petrografi dan analisis geokimia dan kaitannya pada proses magmatisme periode Krakatau Muda. Periode Krakatau Muda menunjukkan karakteristik batuan berkomposisi mafik hingga felsik dengan jenis batuan basaltik hingga dasitik, dengan analisis geokimia batuan menunjukkan afinitas magma dalam seri kalk-alkali dan toleiitik, serta seri magma sub-alkali dengan seri K rendah hingga sedang dan evolusi magma yang berasal dari island arc. Analisis kimia mineral menunjukkan proses magmatisme yang terjadi di Krakatau Muda dipengaruhi oleh proses kristalisasi fraksional dan pencampuran magma dari terbentuknya mikro-tekstur zonasi dan glomerokris pada plagioklas.

---

Mount Krakatoa is one of the active volcanoes that can be divided into three eruption periods. The volcanic activity that occurred after the first caldera-forming eruption (estimated around the 5th century) until the eruption forming the second caldera in 1883 is part of the Young Krakatau period. Research on products from before 1883 was conducted at the Danan research location and Rakata Island with a total of four samples. The volcanic activity in 1883 formed a caldera and caused the disappearance of Perbuatan Island and parts of Danan, so that research on volcanic products before 1883 are quite limited. This study was conducted using petrology, petrography, and geochemical analysis approaches, focusing on the magmatic processes of the Young Krakatoa period. The Young Krakatoa period is characterized by rocks with compositions ranging from mafic to felsic, including basaltic to dacitic rocks. Geochemical analysis of the rocks indicates a magma affinity within the calcalkaline and tholeiitic series, as well as a sub-alkaline magma series with low to medium potassium series and magma evolution originating from an island arc. Geochemical analysis of minerals shows that the magmatic processes in Young Krakatoa were influenced by fractional crystallization and magma mixing, as evidenced by the formation of microtextures, zonation, and glomerocrysts in plagioclase."