Evaluation of the Performance of Time-Series Sentinel-1 Data for Discriminating Rock Units

The potential use of time-series Sentinel-1 synthetic aperture radar (SAR) data for rock unit discrimination has never been explored in previous studies. Here, we employed time-series Sentinel-1 data to discriminate Dananhu formation, Xinjiang group, Granite, Wusu group, Xishanyao formation, and Diorite in Xinjiang, China. Firstly, the temporal variation of the backscatter metrics (backscatter coefficient and coherence) from April to October derived from Sentinel-1, was analyzed. Then, the significant differences of the time-series SAR metrics among different rock units were checked using the Kruskal–Wallis rank sum test and Tukey’s honest significant difference test. Finally, random forest models were used to discriminate rock units. As for the input features, there were four groups: (1) time-series backscatter metrics, (2) single-date backscatter metrics, (3) time-series backscatter metrics at VV, and (4) VH channel. In each feature group, there were three sub-groups: backscatter coefficient, coherence, and combined use of backscatter coefficient and coherence. Our results showed that time-series Sentinel-1 data could improve the discrimination accuracy by roughly 9% (from 55.4% to 64.4%), compared to single-date Sentinel-1 data. Both VV and VH polarization provided comparable results. Coherence complements the backscatter coefficient when discriminating rock units. Among the six rock units, the Granite and Xinjiang group can be better differentiated than the other four rock units. Though the result still leaves space for improvement, this study further demonstrates the great potential of time-series Sentinel-1 data for rock unit discrimination.

Petrophysical Core-Based Zonation of An Oil Field In The Bredasdorp Basin South Africa

This study aims to generate rock units based on core permeability and porosity of an oil field in the Bredasdorp Basin offshore South Africa. In this study, we identified and classified lithofacies based on sedimentology reports in conjunction with well logs. Lucia's petrophysical classification method is used to classify rocks into three classes. Results revealed three lithofacies as A(sandstone, coarse to medium-grained), B (fine to medium-grained sandstone), and C (carbonaceous claystone, finely laminated with siltstone). Lithofacies A is the best reservoir quality and corresponds to class 1, while lithofacies B and C correspond to class 2 and 3, which are good and poor reservoir quality rock, respectively. An integrated reservoir zonation for the rocks is based on four different zonation methods (Flow Zone indicator (FZI), Winland r35, Hydraulic conductivity (HC), and Stratigraphy modified Lorenz plot (SMLP)). Four flow zones were identified as high(HFZ), moderate (MFZ), Low (LFZ), and tight (TFZ), respectively. The HFZ is the best reservoir quality composed of a megaporous rock unit, with an average FZI value between 5 to 10µm, and HC from 40 to 120 mD/v3, ranked as very good. The most prolific flow units (HFZ and MFZ zones) form more than 75 % of each well's flow capacities. The TFZ is the most reduced rock quality composed of impervious and nanoporous rock. There appears to be a slight increase of illite in the tight and low zones that block pore throats, thereby decreasing permeability. Therefore, illite has a dominant effect on flow zones. Quartz is the dominant framework grain, and siderite is the dominant cement that affects flow zones. This study has demonstrated a robust approach to delineate flow units in an oilfield. A novel sandstone reservoir zonation classification criteria developed from this study can be applied to other datasets of sandstone reservoirs with confidence.

PENENTUAN LOKASI TITIK BOR AIR TANAH BERDASARKAN METODE TAHANAN JENIS 2D DI DESA SUBUR MAKMUR KABUPATEN KOTABARU, KALIMANTAN SELATAN

Subur Makmur Village is an area where the availability of clean water is difficult, especially during the dry season. One of the sources of water that can be used by the villagers is groundwater. However, to obtain groundwater, it is necessary to drill wells and investigate the aquifer layer first. This study aims to obtain an overview of the subsurface layers based on the resistivity properties of the rock, so that the aquifer layer can be identified and can determine the exact location of the drill point in the prospective aquifer position that may be encountered. The geoelectric method is the most efficient method for detecting aquifer layers. It uses two types of configurations, namely, the Wenner and Wenner-Schlumberger configurations where the number of geoelectric paths is one path. The length of the track used is 540 meters, the number of electrodes is 28 with the spacing between the electrodes is 20 meters. The resistivity cross section for both configurations, obtained resistivity values of 11 - 140 Ohm meters. Composed of 2 (two) rock units, namely graywacke sandstone rock units. Consists of graywacke sandstones with claystone inserts. Density value ≥ 40 Ohm meter. Hydraulic properties, small porosity, small permeability, the potential for groundwater in this unit is small. The position of this unit is at a depth of 40 m. In the cross section, the resistivity is yellow - red. The second rock unit comprising this trajectory is the alteration claystone unit consisting of claystone containing bolders of sandstone / igneous rock. Resistivity value ≤ 40 Ohm meter. The position of this unit is on the Surface to a depth of 40 m. Hydraulic properties, large porosity with very small permeability, the potential for groundwater is very small. In the cross section of this unit resistivity are colored dark blue, blue and green. From the resistivity cross section, it can be determined the position of the borehole which is effectively located in the length range of the trajectory between 360 - 420 meters. Keywords: subur makmur, groundwater, wenner, wenner-schlumberger

Petrographic Studies of Rocks around Arum and Its Environs, North Central Nigeria

A detailed geological mapping of the area around Arum and environs part of Kurra sheet 189 SW was carried out on the scale of 1: 12, 500. Geologic field mapping and petrographic study (both megascopic and microscopic) were the methodology used. The geologic mapping of the area identified four rock units which are; granite, porphyritic granite, granitic gneiss and Porphyroblastic gneiss. These rock types were distributed such that the granite at the north-eastern part covered about 25%, the north –western portion was occupied by the porphyritic granite which occupied the largest portion of about 30% of the area. The third rock unit is the granitic gneiss which covered only about 20%. The fourth (last) and the oldest rock unit is the Porphyroblastic gneiss covering about 25% of the total area at the south-eastern corner. Megascopic and microscopic study revealed that the rocks in the area comprised of minerals such as; quartz, biotite, muscovite, microcline, feldspar, hornblende, garnet, etc. Structures that were clearly evident in the area included fault, foliation, joints, and veins. Structural analysis showed that their rose diagrams proved a NW-SE, NNE-SSW and NE-SW trends to be dominant.

Geomechanical characterization of a heterogenous rock mass using geological and laboratory test results: a case study of the Niobec Mine, Quebec (Canada)

To conduct a successful geomechanical characterization of rock masses, an appropriate interpretation of lithological heterogeneity should be attained by considering both the geological and geomechanical data. In order to clarify the reliability and applicability of geological surveys for rock mechanics purposes, a geomechanical characterization study is conducted on the heterogeneous rock mass of Niobec Mine (Quebec, Canada), by considering the characteristics of its various identified lithological units. The results of previous field and laboratory test campaigns were used to quantify the variability associated to intact rock geomechanical parameters for the different present lithological units. The interpretation of geomechanical similarities between the lithological units resulted in determination of three main rock units (carbonatite, syenite, and carbonatite-syenite units). Geomechanical parameters of these rock units and their associated variabilities are utilized for stochastic estimation of geomechanical parameters of the heterogeneous rock mass using the Monte Carlo Simulation method. A comparison is also made between the results of probabilistic and deterministic analyses to highlight the presence of intrinsic variability associated with the heterogeneous rock mass properties. The results indicated that, for the case of Niobec Mine, the carbonatite-syenite rock unit could be considered as a valid representative of the entire rock mass geology since it offers an appropriate geomechanical approximation of all the present lithological units at the mine site, in terms of both the magnitude and dispersion of the strength and deformability parameters. Article Highlights Evaluating the reliability and applicability of geological survey outcomes for rock mechanics purposes. A geomechanical characterization study is conducted on the heterogeneous rock mass by considering the various identified rock lithotypes. The geomechanical parameters of intact units and their associated variabilities are used to stochastically estimate the geomechanical parameters of the heterogeneous rock mass by employing the Monte Carlo Simulation. A comparison is also made between the results of probabilistic and deterministic geomechanical analyses. The results indicate that, in the case of Niobec Mine, the combined syenite-carbonatite rock unit could be considered as a valid representative of the entire rock mass.

New insights into the formation and emplacement of impact melt rocks within the Chicxulub impact structure, following the 2016 IODP-ICDP Expedition 364

This study presents petrographic and geochemical characterization of 46 pre-impact rocks and 32 impactites containing and/or representing impact melt rock from the peak ring of the Chicxulub impact structure (Yucatán, Mexico). The aims were both to investigate the components that potentially contributed to the impact melt (i.e., the pre-impact lithologies) and to better elucidate impact melt rock emplacement at Chicxulub. The impactites presented here are subdivided into two sample groups: the lower impact melt rock−bearing unit, which intrudes the peak ring at different intervals, and the upper impact melt rock unit, which overlies the peak ring. The geochemical characterization of five identified pre-impact lithologies (i.e., granitoid, dolerite, dacite, felsite, and limestone) was able to constrain the bulk geochemical composition of both impactite units. These pre-impact lithologies thus likely represent the main constituent lithologies that were involved in the formation of impact melt rock. In general, the composition of both impactite units can be explained by mixing of the primarily felsic and mafic lithologies, but with varying degrees of carbonate dilution. It is assumed that the two units were initially part of the same impact-produced melt, but discrete processes separated them during crater formation. The lower impact melt rock−bearing unit is interpreted to represent impact melt rock injected into the crystalline basement during the compression/excavation stage of cratering. These impact melt rock layers acted as delamination surfaces within the crystalline basement, accommodating its displacement during peak ring formation. This movement strongly comminuted the impact melt rock layers present in the peak ring structure. The composition of the upper impact melt rock unit was contingent on the entrainment of carbonate components and is interpreted to have stayed at the surface during crater development. Its formation was not finalized until the modification stage, when carbonate material would have reentered the crater.

BRUCS: a new system for classifying and naming mappable rock units

A new scheme is introduced for classifying and naming mappable rock bodies that lack primary stratification. In recognition of their distinctive geological characteristics, these ‘nonstratiform’ bodies are defined and classified according to their 3D form, spatial distribution and genetic relationships, in two hierarchical (parent-child) chains: one for intrusions and one for tectonometamorphic units. Geologically complex units, encompassing bodies of different genetic classes, are classified in a third chain reserved specifically for ‘mixed-class’ units. The new classification scheme is offered as an alternative to existing recommendations in the International Stratigraphic Guide and North American Stratigraphic Code, in which nonstratiform bodies are recognised and defined primarily by their lithological character. BRUCS (the BGS Rock Unit Classification System) combines the three new parent-child chains for nonstratiform units with the well-established chain for stratiform units (bed-member-formation-group-supergroup) to create a flexible, practical and effective solution for classifying and naming all mappable rock bodies. The taxonomic rigour of BRUCS means the considerable capabilities of modern digital systems for managing and communicating mapping data can be exploited fully.

Petrographic and mineralisation Potentials of Precambrian Pegmatities and associated rock units of Olode area, Southwestern Nigeria

The geology of the Olode area, south-western Nigeria was investigated petrographically and geochemically in order to elucidate the mineralisation potential of the rock units in the area. The area under study is generally underlain by granite gneiss, mica schist and pegmatites. Petrographical studies indicated prevalence of anhedral quartz (30 – 50%), plagioclase (14 – 20%), orthoclase (12 – 15%), muscovite (11 – 15%), tourmaline (6 – 10) and other minerals (8 – 11%) for the pegmatite. The high value of SiO2 and Al2O3 is consistent with the petrographical study. High values and wide range in Ba (34 – 737 ppm) and Zr (3.8 – 132.6 ppm) strongly support a mixture of igneous and sedimentaryThe bivariant plots of Rb vs K/Rb, Zn vs K/Rb and Th vs K/Rb indicated a partial series of fractionation, suggesting that the pegmatites are of rare element classes while granite gneiss and mica schist belong to the barren muscovite and rare element classes. This was supported by high ratios of K/Cs and K/Ba but low Th/U values indicating distinctively low rare metal mineralization. The plot of Na2O/Al2O3 vs K2O/Al2O3 revealed an igneous precursor for all the rock units. The negative Eu anomalies especially in the pegmatitic rock unit indicates fractionation and point toward a late metasomatic effect and their relatively weak negative Ce anomalies, also suggest their rare metal mineralization. The pegmatites, granite gneiss and mica schist of Olode area considered as barren as all the samples plotted below the Gordiyenkos and Beus’ line of mineralization.

WELL AND OUTCROP CORRELATION IN THE EASTERN PART OF AKIMEUGAH BASIN, PAPUA: MESOZOIC PLAY POTENTIAL

Mesozoic sediments are the main objective for hydrocarbon exploration in the eastern part of Akimeugah Basin, Papua. However, little information is currently available on paleogeography and subsurface distribution of the Mesozoic rock unit. This study analyzed Mesozoic rock unit from outcrops at Wamena and surrounding area to wells data in the eastern part of Akimeugah Basin, Papua. Outcrop and well correlation was made to interpret paleogeography of Mesozoic unit. This study was using existin 2D seismic and passive seismic tomography data to determine the distribution of Mesozoic rock unit in the subsurface and its hydrocarbon potential. The Mesozoic rock unit in the eastern part of Akimeugah Basin is divided into four formations based on their lithological characteristic. Respectively from old to young, Kopai, Woniwogi, Piniya and Ekmai Formation. The depositional environment of Mesozoic rock unit in the southern part of the study area is shore/tidal to shelf and basin fl oor in the northern part. Three Mesozoic potential plays in the studied area are divided into 1) Central Range Mountains thrust-fold belt play, 2) Akimeugah low land thrust-fold belt play and 3) Tanah Merah pinch-out play. The results presented in this paper are expected to be a guide for further hydrocarbon exploration in the study area. Mesozoic sediments are the main objective for hydrocarbon exploration in the eastern part of Akimeugah Basin, Papua. However, little information is currently available on paleogeography and subsurface distribution of the Mesozoic rock unit. This study analyzed Mesozoic rock unit from outcropsat Wamena and surrounding area to wells data in the eastern part of Akimeugah Basin, Papua. Outcrop and well correlation was made to interpret paleogeography of Mesozoic unit. This study was using existing 2D seismic and passive seismic tomography data to determine the distribution of Mesozoic rock unit in the subsurface and its hydrocarbon potential. The Mesozoic rock unit in the eastern part of Akimeugah Basin is divided into four formations based on their lithological characteristic. Respectively from old to young, Kopai, Woniwogi, Piniya and Ekmai Formation. The depositional environment of Mesozoic rock unit in the southern part of the study area is shore/tidal to shelf and basin fl oor in the northern part. Three Mesozoic potential plays in the studied area are divided into 1) Central Range Mountains thrust-fold belt