Search

This research was conducted using EEI inversion on seismic data in Z Field, Kutai Basin. The EEI inversion is effectively used to determine the reservoir distribution by eliminating the angle limit on the elastic impedance to the Chi angle so that it can be correlated with petrophysical parameters that are sensitive to lithology and fluids. The data used in this study are well data, checkshots, horizons, and partial-stack angle gather 3D seismic data. The data obtained is processed to obtain the target zone first based on log interpretation. Based on data processing, the target zone is obtained at 1513 m to 1531 m. Sensitivity analysis was conducted to determine the sensitive parameters, which can separate the lithology of the formation. In the sensitivity analysis, the most sensitive log to separate lithology is the Vp/VS log, which can separate sandstone, shale, and coal. Furthermore, the EEI inversion analysis was carried out to obtain the most suiTable model for the inversion, the Based Hard Constraint model was obtained with a correlation reaching 0.997 and an error value of 0.078. Based on the EEI inversion, the target zone in the Z-field at a depth of 1258 ms - 1269 ms with a sandstone reservoir in the EEI range of 6000 (m/s)(g/cc) - 7500 (m/s)(g/cc) which spreads from northeast to south. The distribution of the sandstone reservoir is surrounded by coal with a range of EEI 7500 (m/s)(g/cc) - 12000 (m/s)(g/cc), and also the distribution of shale in the EEI range of 7500(m/s)( g/cc) - 9200(m/s)(g/cc).

Volume magnetic susceptibility measurements have been widely used in numerous studies related to river sediment characterization. A study of the transport distance effect toward the frequency-dependent volume magnetic susceptibility is needed to identify the superparamagnetic grain behavior in river sediments. The purpose of this study is to identify the presence of superparamagnetic grains and to obtain the relation between transport distances and frequency-dependent volume magnetic susceptibility in river sediments. The sediment samples were taken and measured by using the Bartington MS2B Susceptibilitymeter at two different frequencies of 470 Hz and 4700 Hz. The measurement results show that the sediment transport distance is directly proportional to the frequency-dependent volume magnetic susceptibility. Superparamagnetic grain content is identified to tend to be higher as the distance of sediment transport increases.

Gravity survey is one of the passive geophysical techniques commonly used to delineate geological formations, especially in determining basement rock and the overlying deposit. Geologically, the study area is made up of thick quaternary alluvium deposited on top of the older basement rock. The Muda River basin constitutes, approximately, of more than 300 m of thick quaternary alluvium overlying the unknown basement rock type. Previous studies, including drilling and geo-electrical resistivity surveys, were conducted in the area but none of them managed to conclusively determine the basement rock type and depth precisely. Hence, a regional gravity survey was conducted to determine the thickness of the quaternary sediments prior to assessing the sustainability of the Muda River basin. Gravity readings were made at 347 gravity stations spaced at 3–5 km intervals using Scintrex CG-3 covering an area and a perimeter of 9000 km2 and 730 km, respectively. The gravity data were then conventionally reduced for drift, free air, latitude, Bouguer, and terrain corrections. These data were then consequently analyzed to generate Bouguer, regional and total horizontal derivative (THD) anomaly maps for qualitative and quantitative interpretations. The Bouguer gravity anomaly map shows low gravity values in the north-eastern part of the study area interpreted as representing the Main Range granitic body, while relatively higher gravity values observed in the south-western part are interpreted as representing sedimentary rocks of Semanggol and Mahang formations. Patterns observed in the THD anomaly and Euler deconvolution maps closely resembled the presence of structural features such as fault lineaments dominantly trending along NW-SE and NE-SW like the trends of topographic lineaments in the study area. Based on power spectral analysis of the gravity data, the average depth of shallow body, representing alluvium, and deep body, representing underlying rock formations, are 0.5 km and 1.2 km, respectively. The thickness of Quaternary sediment and the depth of sedimentary formation can be more precisely estimated by other geophysical techniques such as the seismic reflection survey.

Salah satu penyebab munculnya semburan lumpur Sidoarjo yang masih diperdebatkan hingga saat ini yaitu mengenai reaktivasi patahan watukosek. Studi yang telah dilakukan sebelumnya menunjukkan adanya manifestasi di permukaan akibat patahan watukosek, contohnya Tebing Watukosek dan pembelokan geomorfologi Kali Porong. Penelitian dengan menggunakan metode tahanan jenis dilakukan untuk memetakan patahan yang berada di daerah Kali Porong dan Patahan Watukosek. Lintasan yang digunakan memiliki bentangan 400m dengan arah Barat – Timur untuk memotong patahan yang berarah Barat Daya – Timur Laut dari Gunung Penanggungan menuju semburan lumpur Sidoarjo. Kedalaman pengukuran mencapai ±74.8m dengan anomali tahanan jenis terendah 1.05 Ohm.m hingga yang tertinggi 33.3 Ohm.m.

Sebuah kawasan yang memiliki aktivitas vulkanik, mempunyai potensi SDA yang dapat dimanfaatkan sebagai sumber energi panas bumi hingga cadangan hidrokarbon. Tujuan dari penelitian ini ialah untuk mengkarakterisasi fisis dan analisa hubungan antara parameter densitas, kecepatan Vp, atenuasi, dan resistivitas pada batuan vulkanik studi kasus Gunung Arjuno-Welirang. Penelitian diawali dengan pengambilan sampel di lapangan dan pembuatan coring batuan sehingga didapatkan 45 coring batuan, dari 16 sampel batuan, yang mewakili 6 satuan batuan, kemudian dilakukan pengukuran parameter resistivitas dengan metode konfigurasi axial resistivity, pengukuran densitas dengan prinsip Archimedes, dan pengukuran kecepatan Vp serta atenuasi dengan transmisi gelombang ultrasonik. Maka didapatkan hasil rentang parameter densitas batuan vulkanik Arjuno Welirang berkisar antar 2400 – 2900 kg/m3, sedangkan rentang resistivitas bervariasi dari 30-185 kOhm.m, kemudian rentang nilai kecepatan Vp bervariasi dari 5100-6700 m/s, dengan koefisien atenuasinya memiliki rentang 0.05–0.23x10-3dB/m, dimana nilai densitas akan berbanding lurus dengan kecepatan Vp, dan nilai resistivitas akan berbanding terbalik dengan densitas-kecepatan Vp. Berdasarkan analisa petrologi batuan vulkanik Arjuno-Welirang memiliki tipe intermediate-mafik dengan nama batuan dominasi andesit-basaltik dan basalt.