Method of Calculating Secondary Porosity of Reef Limestone Reservoir by Casting Thin Section Calibrating Nuclear Magnetic T 2 Spectrum

Secondary pores are the main reservoir space and transportation channel of oil and gas in reef limestone reservoir. At present, the main method of calculating secondary porosity is restricted by the morphological characteristics of porosity spectrum, regional artificial influence, and accuracy of calculation. We present a new method for calculating secondary porosity of reef limestone reservoir by the nuclear magnetic resonance T 2 spectrum which is calibrated by casting thin section. We begin with analyzing and determining the high correlation between the surface porosity of casting thin section and the total porosity. The objective is confirming the feasibility of the method of calculating secondary porosity by using thin-section information calibrate. Then, we use the surface porosity of thin section as the calibrating data and find the T 2 relaxation time corresponding to the best correlation between the secondary porosity and the secondary surface porosity of casting thin section, that is, the T 2 cutoff value of secondary porosity, through the Monte Carlo method. Finally, we calculate the secondary porosity by using the functional relationship between the secondary surface porosity and the surface porosity. The statistical analysis shows that the method of calculating secondary porosity effectively improves the calculation accuracy of secondary porosity. The secondary porosity calculation results have a high correlation with the reservoir productivity.

Microfacies and biostratigraphy of an Upper Triassic Dachstein limestone fore-reef block in the Jurassic Sirogojno carbonate-clastic Mélange (Zlatibor Mt., SW Serbia)

In the late Middle to early Late Jurassic carbonate-clastic Sirogojno M?lange in the Zlatibor Mountain there is one roughly 35 m thick overturned block with an intact Late Triassic fore-reefal Dachstein Limestone succession that was studied here for its biostratigraphic age, faunal content and microfacies characteristics. The succession starts with coarse-grained rudstones followed by meter-sized reefal blocks intercalated in partly layered resedimented grainstones and packstones with abundant reef-building organisms like calcareous sponges, corals and encrusting organisms. Inside this part of the succession open-marine influenced layers are rare. The succession continues with a partly turbiditic sequence and chaotic rudstones, densely packed with reef-derived material like broken reef-building organisms and shallow-water material like gastropods, bivalves and foraminifers. Grainstones with clear open-marine influence (e.g., thin-shelled bivalves, crinoids, conodonts) appear in between those rudstones, in cases lumachelle layers consisting of halobiids were deposited. To the end of the succession some layers show turbiditic bedding with mixed shallow- water and deep-marine grains and organisms, i.e. filaments and crinoids. On base of conodonts, foraminifers, calcareous algae, holothurians and halobiids throughout the whole studied succession, a Middle Norian (Alaunian) to Rhaetian 1, most probably a Late Norian (Sevatian) age can be assigned to this forereefal Dachstein Limestone succession, with a similar sedimentation pattern like Late Triassic Dachstein fore-reef limestone facies, e.g., in the Northern Calcareous Alps or the eastern Southern Alps. The study of this block in the Sirogojno M?lange closes an important gap in knowledge about the extent, facies and stratigraphy of the Dachstein Carbonate Platform evolution in the Dinarides.

LARGE FORAMINIFERA FROM LIMESTONE IN THE RAJAMANDALA FORMATION, SUKABUMI, WEST JAVA

Rajamandala Formation is a limestone reef formation that is exposed in the Rajamandala – Sukabumi area, West Java. Different from those in the Rajamandala area, this formation which is located in the Sukabumi area is still rarely analyzed, especially from its large foraminifera. This study aims to assess the content, age, and depositional environment of reef limestone from the Rajamandala Formation based on large foraminifera. Research method was carried out in several stages. Sampling was done by spot sampling as many as 6 samples. Then, thin section observations was carried out using Olympus CX-22 binocular microscope. Finally, age and environmental analysis were carried out using basic biostratigraphic methods and cluster analysis based on the fossil content of large foraminifera. Result, the limestone reefs of Rajamandala Formation in Sukabumi area have varied material content. These rock ages were found to be in the Late Oligocene range (Chattian). This rock depositional environment is in shallow marine environment which is divided into 3 main clusters. The first cluster is dominated by Austrotrilina and Borelis which shows the Backreef shelf environment. The second cluster is dominated by Heterostegina and Cycloclypeus which shows the Forereef shelf environment. Finally, the third cluster is dominated by all large foraminifera representing the Reef environment. When compared with previous studies, the limestone of Rajamandala Formation in Sukabumi and Rajamandala areas has the same age and depositional environment.

Karakteristik Alterasi dan Mineralisasi Tipe Epitermal Daerah Gunung Budheg dan Sekitarnya, Tulungagung, Jawa Timur

ABSTRAK Penemuan bongkah-bongkah vuggy quartz di sekitar Desa Pojok, daerah Gunung Budheg, Tulungagung, Jawa Timur, mengindikasikan adanya proses endapan mineral di daerah tersebut. Tujuan penelitian ini adalah untuk membahas lebih detail karakteristik alterasi dan mineralisasi serta tipe endapan mineral di daerah penelitian. Metode penelitian berupa pengamatan lapangan dilengkapi dengan analisis laboratorium petrografi, X-ray Difraction (XRD) dan mineragrafi. Satuan batuan di daerah penelitian tersusun atas enam satuan litologi yaitu satuan intrusi dasit, satuan lava andesit, satuan breksi andesit, satuan breksi polimik, satuan batugamping terumbu dan aluvium. Tipe alterasi di daerah penelitian adalah alterasi profilitik, argilik, argilik lanjut, dan silisifikasi. Alterasi profilitik dicirikan oleh melimpahnya mineral klorit. Alterasi argilik dicirikan dengan melimpahnya mineral kaolin, sementara argilik lanjut dicirikan oleh hadirnya mineral kaolinit dan alunit. Alterasi silisifikasi yang dicirikan oleh melimpahnya mineral kuarsa. Mineral logam yang ditemukan di daerah penelitian didominasi oleh kelompok mineral sulfida seperti kovelit, kalkosit, enargit, kalkopirit, pirit, dan jarosit. Emas native ditemukan berasosiasi dengan enargit. Sistem endapan mineral pada daerah penelitian merupakan sistem epitermal sulfidasi tinggi dicirikan oleh kuarsa berongga (vuggy quartz) yang termineralisasi dan kehadiran mineral kaolin sebagai mineral hasil alterasi.ABSTRACT The discovery of vuggy quartz boulders around Pojok Village, Gunung Budheg area, Tulungagung, East Java, indicates the presence of mineral deposits process in this area. This study aims to discuss detailed characteristics of alteration and mineralization as well as mineral deposits type in the study area. The research methods are field observations completed with petrography, X-ray Diffraction (XRD), and mineragraphy laboratory analysis. The rock unit in the study area consists of six lithology units, a dacitic intrusion, andesitic lava, andesitic breccia, poly-mix breccia, reef limestone, and alluvium. The study area's alteration types are profilitic alteration, argillic alteration, advanced argillic, and silicification alteration. The profilitic alteration characterized by the abundance of chlorite minerals. The argillic alteration characterized by the abundance of kaolin minerals, while the advanced argillic alteration by the presence of kaolinite and alunite minerals. The silicification alteration characterized by abundance quartz minerals. The metallic minerals dominated in the area are sulfide minerals such as covellite, chalcocite, enargite, chalcopyrite, pyrite, and jarosite. The native gold found in an association with enargite. The study area's mineral deposit system is an epithermal high sulfidation system characterized by mineralized vuggy quartz and the presence of kaolinite mineral as an alteration mineral.

Échaillon stone from France: a Global Heritage Stone Resource proposal

AbstractÉchaillon stone, a Mesozoic platform limestone from SE France, is proposed as a Global Heritage Stone Resource. The Échaillon stone quarries are located at the western termination of the Alps, near the city of Grenoble. Stone from the main Échaillon quarries is an Upper Jurassic to Berriasian bioclastic near-reef limestone, renowned for its two characteristic white and pink colours. Two ancillary quarries nearby, the Lignet and Rovon quarries, provided the Lower Cretaceous (Barremian to Aptian) Yellow Échaillon stone, of lagoonal origin. Échaillon stone's unique characteristics, resistance to weathering and high aesthetic values made it a prized building and ornamental material used in many significant historical buildings in Europe, North Africa and the USA. Although the first use of Échaillon stone in buildings dates from the Gallo-Roman period, the industrial use ranges from the mid-nineteenth century, during the heyday of the Beaux-Arts architecture period in France, to the mid-twentieth century. The reputation of Échaillon stone was bolstered by world-renowned architects, sculptors and artists who used it for historical building ornament and sculptures. By the turn of the twentieth century, production started to decline and it ceased by the middle of that century.