Petrophysical and petrographic characteristics of Barail Sandstone of the Surma Basin, Bangladesh

The Barail sandstone in the Surma Basin is a medium- to coarse-grained pinkish-colored rock exposed near the northeastern margin of Bangladesh. In this study, we evaluated the reservoir quality of the Barail sandstone based on its petrophysical and petrographic characteristics. Petrophysical analyses of outcropped samples showed that sandstones are made up of 16.48% porosity and 132.48 mD permeability. Sandstone density ranges from 1.94 g/cm3 to 2.37 g/cm3, with a mean value of 2.12 g/cm3, shown as moderately compacted sandstone. Integrated data such as bulk density, porosity, permeability, Rock Quality Index (RQI), Normalized Porosity Index (NPI), Flow Zone Indicator (FZI), compressive strength, etc. with their relationships indicate that Barail sandstone owing characters to become a good petroleum reservoir. The rock samples consisted mainly of quartz with an insignificant amount of rock fragments and plagioclase feldspar and are categorized as sub-arkose to sub-litharenite. The rock samples also contains lithic (andesine, microcline, muscovite, biotite, etc.) of granitic and gneissic fabric and some volcanic product like aguite, albite, andesine, garnet, spinel and ulvo-spinel indicating the source of nearby orogeny. The euhedral to subhedral shape of the quartz grain in a porphyritic texture, moderately sorted with a smaller amount of clay minerals indicating the moderately mature rock type. The iron oxide border around the quartz grain also indicates that the Barail sandstone was deposited under dry climatic condition.

Aplikasi Metode Geolistrik untuk Pendugaan Air Bawah Tanah Desa Karanganyar Kecamatan Bantaran Kabupaten Probolinggo Jawa Timur

Desa Karanganyar, Kecamatan Bantaran, Kabupaten Probolinggo merupakan salah satu daerah kekeringan. Daerah ini tersusun oleh lapisan produk Gunungapi Tengger yang terdiri dari tuff, breksi gunungapi, lava, dan lahar. Kondisi tersebut memungkinkan daerah tersebut mengalami krisis akan air tanah karena lapisan produk gunungapi memiliki karakteristik impermiabel atau kedap air. Untuk itu diperlukan penelusuran mengenai informasi dasar tentang letak keberadaan air tanah dengan cara survey geofisika menggunakan metode geolistrik resistivitas. Penelitian ini bertujuan untuk mengkaji potensi keberadaan air tanah di lokasi penelitian dan mengetahui kondisi litologi bawah permukaan dengan metode geolistrik tahanan jenis menggunakan konfigurasi Wenner dan Schlumberger. Berdasarkan hasil penelitian diketahui litologi penyusun di daerah pengukuran berupa batuan vulkanik (lempung tuffan, tuff, lahar tuffan, breksi, dan lava). Batuan yang berpotensi mengandung akuifer yaitu batuan lahar tuffan. Batuan lahar tuffan tersebar di ketiga titik pengukuran sehingga ketiga titik tersebut memiliki potensi akuifer. Pada titik KRA-1 akuifer yang dapat dijumpai diduga terdapat pada kedalaman 37,1 – 102,3 meter dengan nilai resistivitas 60,3 – 171,5 ohm meter, titik KRA-2 pada kedalaman 92,8 – 143,9 meter dengan nilai resistivitas 50,2 – 62,9 ohm meter, dan titik KRA-3 pada kedalaman 63,4 – 133,15 meter dengan nilai resistivitas 62,6 – 119,5 ohm meter.Kata Kunci: Karanganyar; Bantaran; Probolinggo; geolistrik; akuifer ABSTRACT Karanganyar Village, Bantaran District, Probolinggo Regency is one of the drought areas. This area is composed of layers of Tengger Volcano products consisting of tuff, volcanic breccias, lava, and lava. These conditions allow the area to experience a crisis of groundwater because the volcanic product layer has impermiable or waterproof characteristics. For this reason it is necessary to search for basic information about the location of the presence of groundwater by geophysical survey using the resistivity geoelectric method. This study aims to examine the potential presence of groundwater in the study site and determine the conditions of subsurface lithology with the geoelectric resistivity method using the Wenner and Schlumberger configurations. Based on the research results, it is known that the lithology of the constituents in the measurement area is volcanic rock (tuffan clay, tuff, lava tuffan, breccia, and lava). Rocks that have the potential to contain aquifers are tuffan lava rocks. Tuffan lava rocks are scattered in all three measurement points so that all three points have an aquifer potential. At the point of KRA-1 aquifer that can be found is suspected to be at a depth of 37.1 - 102.3 meters with a resistivity value of 60.3 - 171.5 ohm meters, a KRA-2 point at a depth of 92.8 - 143.9 meters with a value of resistivity 50.2 - 62.9 ohm meters, and KRA-3 points at depths of 63.4 - 133.15 meters with resistivity values of 62.6 - 119.5 ohm meter.

Geoelectricity Data Analysis For Identification The Aquifer Configuration In Bandorasawetan, Cilimus, Kuningan, West Java Province

Indonesian water consumption is influenced by the people growth. One of Water consumption fulfilment by groundwater aquifer. Bandorasawetan is one of the areas which predicted have proper potential due to located in East of Mt. Ceremai that predicted recharge area. Based on regional geological data, Bandorasawetan is an undifferentiated young volcanic product which consists of lava, breccia, lapilli, and tuffaceous sand. Geophysics method for groundwater prediction is 2-D geoelectrical with Wenner – Schlumberger configuration. The result of acquisition is obtained resistivity value from 0 - >1000 Ohm. m. Interpretation from data distribution is consist of two resistivity range that describes lithology on the research area, such as: 0 – 150 Ohm.m contributed as aquiqlud with tuffaceous sand lithology and > 150 Ohm.m interpreted as volcanic breccia lithology. Volcanic breccia has a role as aquifer in study area, the conclusion is distribution of resistivity value with range > 150 Ohm.m be the reference to developing groundwater resource in study area. Depth of aquifer is varying, deeper to the east. In Line – 1, depth of the aquifer is 48 meters and in Line – 2, depth of aquifer be 60 meters.