Structural analysis and seismic stratigraphy for delineation of Neoproterozoic-Cambrian petroleum system in central and eastern part of Bikaner–Nagaur basin, India

Bikaner–Nagaur basin is located in the northwestern part of India and lies on the rising flank of Punjab platform of Middle Indus basin in Pakistan. Existence of Neoproterozoic-Cambrian petroleum system was confirmed by the exploration activities in the western periphery of the basin, whereas vast areas of central and eastern parts remain unexplored. Knowledge of petroleum system in this unexplored part of the basin is limited due to non-availability of data. Recently, 2525 line km of regional 2D seismic data acquired for the first time by Government of India under National Seismic Program (NSP) unlocks the opportunity for comprehensive understanding of subsurface geology in unexplored part of the basin. Present work aims to interpret recently acquired 2D seismic data and integrate with available surface (outcrop) data, gravity and well data (drilled in western part of basin) for unfolding the petroleum system elements, structural configurations and stratigraphic features in the hitherto central-eastern part of the basin. Two Neoproterozoic-Cambrian hydrocarbon plays: (1) Jodhpur and (2) overlying Bilara/Hanseran Evaporite Group (HEG) were envisaged. Both the plays depicted distinctive seismic characteristics, structural alignment and distribution of reservoir, source and seal. Fluvio-deltaic sandstone within Jodhpur group and shallow marine fractured dolomites within Bilara/HEG showed potential reservoir characteristics whereas organic rich laminated dolomites, stromatolites and argillaceous litho-units within Bilara/HEG group have been predicted as prospective source. The Halite layers within HEG group were considered as effective regional seals. Fault bounded anticlinal structures associated with Cambrian compression have been identified as the main entrapment for hydrocarbon accumulation. The basin witnessed long tectonostratigraphic history with two major compressional phases Structures formed by Cambrian compression are likely to be charged as the time of source maturity and peak expulsion was later, during early Mesozoic period. Overall, the study indicates new opportunities and potential accumulation of hydrocarbon in the unexplored part of the basin.

Geology and Geothermal Setting of Tompaso Geothermal System, Indonesia, with Comparisons of Andesite Alteration Patterns with Wairakei, New Zealand

<p>Tompaso geothermal system is a typical volcanic arc geothermal system in North Sulawesi, Indonesia. Although situated close to the Tondano caldera, subsurface lithologies and structures do not show any evidence for caldera-related features and the system is inferred to be related to the andesitic Soputan volcano. The subsurface geology of Tompaso consists of Tuff B unit, Rhyolite unit, Andesite B unit, Pitchstone unit, Pyroclastic Breccia unit,Andesite A unit, Pumice unit, and Tuff A unit, respectively, from the oldest penetrated unit. The silicic Pitchstone and Rhyolite units are presumed to be sourced from the same magma chamber. Petrological and mineralogical observations using binocular and petrographic microscopy, short-wave infrared (SWIR) analysis, and back-scattered electron (BSE) imaging combined with energy dispersive X-ray spectroscopy (EDS) have been applied to cuttings and limited core material from three boreholes: LHD-26, LHD-27, and LHD-32. Age dating has not been undertaken and, thus, conclusions on correlations between subsurface geology inferred here with surface formation groupings from previous works cannot be drawn. Tompaso geothermal system is characterised primarily by variations in the fracturing within the reservoir. Secondary mineralogy and the structure of present-day temperature of the system suggest that the movement of hydrothermal fluids at Tompaso is controlled by faults: the Soputan, Tempang, and A-A’ faults, the last defined for the first time in this thesis. Soputan Fault controls the outflow of the system. On the other hand, the influence of Tempang and A-A’ faults is dominant only in the upper portion of the system. The A-A’ fault likely acts as a channel for cooler meteoric surface water, while the Tempang Fault is inferred to have experienced self-sealing and appears to be an impermeable structure in the system. The self-sealing process of the Tempang Fault and/or the introduction of meteoric water through the A-A’ fault may be related to the cooling of the northern and western part of the system. The challenges in identifying protoliths in active geothermal areas is addressed here through studies of the influence of andesite textures on the preferences of hydrothermal alteration processes. Wairakei andesites were chosen for comparison to Tompaso andesites, especially because of its different geological setting and geothermal reservoir structure. The results suggest that mineral composition and arrangement affect the preference of hydrothermal alteration on andesites.</p>

Geology and Geothermal Setting of Tompaso Geothermal System, Indonesia, with Comparisons of Andesite Alteration Patterns with Wairakei, New Zealand

<p>Tompaso geothermal system is a typical volcanic arc geothermal system in North Sulawesi, Indonesia. Although situated close to the Tondano caldera, subsurface lithologies and structures do not show any evidence for caldera-related features and the system is inferred to be related to the andesitic Soputan volcano. The subsurface geology of Tompaso consists of Tuff B unit, Rhyolite unit, Andesite B unit, Pitchstone unit, Pyroclastic Breccia unit,Andesite A unit, Pumice unit, and Tuff A unit, respectively, from the oldest penetrated unit. The silicic Pitchstone and Rhyolite units are presumed to be sourced from the same magma chamber. Petrological and mineralogical observations using binocular and petrographic microscopy, short-wave infrared (SWIR) analysis, and back-scattered electron (BSE) imaging combined with energy dispersive X-ray spectroscopy (EDS) have been applied to cuttings and limited core material from three boreholes: LHD-26, LHD-27, and LHD-32. Age dating has not been undertaken and, thus, conclusions on correlations between subsurface geology inferred here with surface formation groupings from previous works cannot be drawn. Tompaso geothermal system is characterised primarily by variations in the fracturing within the reservoir. Secondary mineralogy and the structure of present-day temperature of the system suggest that the movement of hydrothermal fluids at Tompaso is controlled by faults: the Soputan, Tempang, and A-A’ faults, the last defined for the first time in this thesis. Soputan Fault controls the outflow of the system. On the other hand, the influence of Tempang and A-A’ faults is dominant only in the upper portion of the system. The A-A’ fault likely acts as a channel for cooler meteoric surface water, while the Tempang Fault is inferred to have experienced self-sealing and appears to be an impermeable structure in the system. The self-sealing process of the Tempang Fault and/or the introduction of meteoric water through the A-A’ fault may be related to the cooling of the northern and western part of the system. The challenges in identifying protoliths in active geothermal areas is addressed here through studies of the influence of andesite textures on the preferences of hydrothermal alteration processes. Wairakei andesites were chosen for comparison to Tompaso andesites, especially because of its different geological setting and geothermal reservoir structure. The results suggest that mineral composition and arrangement affect the preference of hydrothermal alteration on andesites.</p>

2D Seismic Reflection Study of Mishrif and Yamama Formations in East Nasiriya Area, Southern Iraq

The structural division and stratigraphic estimation of the perceptible geological basin are the most important for oil and gas exploration. This study attempts to obtain subsurface geology in parts of east Nasiriya, southern Iraq using of seismic data and some adjacent well information for structural and stratigraphic interpretation. To achieve this goal, 2D seismic data in SEG-Y format were used with velocity and logging data. The seismic profile is then interpreted as a two-dimensional (time domain and depth domain) contour map, which is represented as a real subsurface geology. Reflectors from the Mishrif and Yamama Formations (Cretaceous period) were detected. According to the structural interpretation of the selected reflectors, TWT maps of the horizon were prepared, and depth maps were drawn, which show some noses structures in the study area. The seismic interpretation in this area confirmed the existence of certain stratigraphic features in the studied strata. Some distribution mounds and flat spots were also observed which similar to the characteristics of the Nasiriya oil field stratigraphic features that are the considered as hydrocarbon indicators.

Vertical Electrical Sounding (VES) investigation for road failure along Mekelle – Abi-Adi road segment, northern Ethiopia

Roads constructed along the mountainous terrains of Ethiopia are susceptible to landslides mostly during rainy season. Mekelle – Abi Adi road is one of the economically important road corridors that connects many towns with Mekelle city. However, the asphalt road segment is heavily affected by quasi-translational type of landslide which hinders traffic flow of the area. Vertical electrical sounding (VES) method was applied to investigate subsurface geology of the road failure along Mekelle – Abi-Adi asphalt road, northern Ethiopia. The geo-electric section result revealed that the shallow subsurface geology of the site is characterized by four distinct geological formations, from top to bottom are: shale, shale-limestone intercalation, limestone and shale-gypsum units. The subgrade of the failed road section is shale unit which is overlain by jointed sandstone unit. The sandstone unit serves as a recharge zone to the bottom shale layer by percolating water via sub-base fill materials which in turn blocks vertical percolation and promote seepage force to the overlying soil mass. Hence, the road failure in the study area seems to be caused due to the development of pore water pressure in the shale layer which soaked water during heavy rainfall. The recommended remedial method for the road failure is re-designing of the affected route from chainage 48 km+850 m to 49 km+250 m towards the northwest of the study area and excavates the top 6 m shale unit.

Subsurface Geology and Hydrothermal Alteration of The Patuha Geothermal Field, West Java: A Progress Report

Patuha geothermal field is one of the geothermal fields in West Java. Developed by PT Geo Dipa Energi (Persero) since 2014, the geothermal field produced electricity, with installed capacity amounted to 55 MWe. Patuha geothermal system is vapour-dominated system. The geothermal manifestations are located at approximately 2,100 m asl. The Patuha field consists of three main upflow zones, namely Kawah Putih, Kawah Ciwidey, and Kawah Cibuni. This study analyzed the drill cuttings from 3 wells as the primary data with total depths ranging from 1,581 to 2,166 m with the well’s highest stable temperatures measured of ±230°C. The three wells selected for this research—PPL 02, PPL 04, and PPL 07—were analyzed to describe the rock properties and estimate the prospect areas of present-day geothermal exploration in Patuha. The objective of this paper is to develop a better understanding of the subsurface geology and its correlation to the dynamic processes (i.e., hydrothermal alteration) in Patuha geothermal field. The hydrothermal minerals are formed by near-neutral pH fluids and are characterized by quartz, calcite, clays (smectite, illite, chlorite), wairakite, epidote, and actinolite. The existence of acidic fluids is evident by the formation of acidic hydrothermal minerals e.g., anhydrite at various depth of the studied wells, particularly at PPL 07 which is located around Sugihmukti-Urug area. Moreover, the previous studies by Reyes (1990), Layman and Soemarinda (2003), Rachmawati et al. (2016), Elfina (2017) on hydrothermal minerals, geothermal manifestation characteristics, fluid geochemistry, and conceptual model are adapted to improve the analysis and interpretation of this paper.

Determination of Leachate Plume Migrations from Selected Cemeteries in Benin-City Metropolis using Integrated Physicochemical and Geophysical Methods

Environmental geo-forensics which involves an integrated suite of geochemical and geophysical techniques was used to detect and evaluate contaminant plume migrations from three cemeteries (names of the cemeteries are; First, second and third cemeteries, all in Benin City) within Benin-City metropolis, South-South Nigeria. The study aimed at determining the risks to groundwater and soil by assessing the rate of leachate plume migrations on the study area. The Very Low Frequency-Electromagnetic (VLF-EM) surveys revealed locations of conductive bodies. The Electrical Resistivity Imaging (ERI) surveys showed patterns and resistivity values indicating the presence of leachate plumes around second and third cemeteries, and no presence of leachate around first cemetery. Soil samples from shallow depths within the vicinities of the cemeteries revealed pollution which had probably migrated from the study area. The surface and subsurface soil investigations showed pure laterites which is impervious to fluid flow. Generally, many depressions were identified within the study area, although migration rate is low because it is controlled mainly by the subsurface geology. A time lapse study showed contaminant migration rates of 41.6 cm/month and 51.7 cm/month in the horizontal directions in the second and third cemeteries respectively and 19.2 cm/month in the vertical directions for both (second and third) cemeteries. Also, the arrival time of migrating plumes in laterite layer under was estimated to be 4 years. This investigation demonstrates the suitability of environmental and criminal geo-forensics for identification and evaluation of electrically conductive contaminant plumes, and also to monitor the plume as it travels within the subsurface.