2D seismic interpretation of Sawan gas field integrated with petrophysical analysis:A case study from Lower Indus Basin,Pakistan

The Lower Indus Basin is the leading hydrocarbon-bearing sedimentary basin in Pakistan.This study has been conducted on the Sawan gas field located in the Lower Indus Basin,adjacent to a few other wellknown gas fields of Pakistan like Kadanwari,Qadirpur,and Miano gas fields.This research aims to present the spatial distribution and reservoir potential of the productive zones of the Lower Goru Formation.The present study utilized various two-dimensional(2D)seismic lines and well-log data(Sawan-01 and Sawan-02)to investigate the structural and stratigraphic features of the area.The stratigraphic layers are mildly deepening in the southeast direction.The 2D seismic interpretation of the research area identifies the existence of extensional remanents,i.e.,normal faults.These extensional structures are associated with horst and graben geometry that acts as a trapping mechanism for hydrocarbons.Wireline logs are used to identify the reservoir's diverse lithology and petrophysical properties.Petrophysical results indicate fair to good effective porosities,low shale volume,and high hydrocarbon saturation(>55%),signifying good reservoir potential in C interval of the Lower Goru Formation.

Mineralogy and element geochemistry of the Sohnari rocks of Early Eocene Laki Formation in the Southern Indus Basin,Pakistan:Implications for paleoclimate,paleoweathering and paleoredox conditions

The Sohnari Member of the Early Eocene Laki Formation is massively deposited in the Southern Indus Basin of Pakistan and is considered a potential source rock to generate hydrocarbons.However,the detailed paleoclimatic,paleoweathering,and depositional conditions of the Sohnari Member have not been studied earlier.This research mainly discusses the detailed mineralogical(bulk and clay)and elemental geochemistry of the Laki Formation from two outcrop sections(Jhimpir and Lakhra)in the Southern Indus Basin,Pakistan.The bulk minerals,including quartz(low),hematite,calcite,halite,gypsum,and clay minerals such as kaolinite,chlorite,smectite and illite have been discussed here.These results demonstrate the paleo-environment of studied area was arid with enhanced saline and weak to strong oxidizing depositional conditions.The chemical index of alteration(CIA)values in Jhimpir and Lakhra sections are in the ranges of 41.30-97.93 and 22.30-96.19,respectively,indicating that the Sohnari sediments experienced weak to intense chemical weathering in the source area.The interpretation of the A-CN-K ternary diagram is consistent with the clay mineral contents in the studied sediments,which is characterized by the predominance of kaolinite,gibbsite and chlorite,demonstrating the weak to strong weathering state under warm and humid climatic conditions.The chemical indices such as Sr/Ba,δU,V/Cr,Ni/Co,and Cu/Zn,U/Th and Ba/Ga show that Sohnari rocks of Early Eocene Laki Formation underwent strong evaporation,oxic water column with warm to humid and minor contact of cold climatic conditions.Based on our present data,it can be concluded that the sediments of Sohnari Member of Laki Formation from Jhimpir and Lakhra areas of Southern Indus Basin in Pakistan are related to Indio-Eurasian collision and came from the Indian shield rocks that were deposited in a brackish water body with a minor contact of the freshwater oxidizing paleo-environment depositional conditions.

The occurrence of vanadium in nature:its biogeochemical cycling and relationship with organic matter—a case study of the Early Cambrian black rocks of the Niutitang Formation,western Hunan,China

Vanadium in the black rocks has economic and environmental impacts.In sediments,it is broadly disseminated as a multivalent metal element mainly sensitive to redox settings.Globally in petroleum,it is considered an abundant component.Vanadium is an essential tool to determine the relationship of the Earth with extra-terrestrial bodies.In the Yangtze region,the black rocks of the Early Cambrian Niutitang Formation are highly enriched in the concentration of V,Co,Ni and Mo.These sediments are comprised of a high total organic carbon content,and the average concentration of vanadium is over 240 ppm.Here we discuss the mechanisms and conditions that were responsible for the accumulation of vanadium in these black sediments in the Yangtze region.The oxygenated ocean water is favorable for the dissolved vanadate species Ⅴ(Ⅴ).Therefore,in oxic ocean-water,it can be reduced by organic matters or by H_(2)S to vanadyl ions Ⅴ(Ⅳ),which can facilely be adsorbed to the tiny particles and finally deposit into the sediments with the settling of the particles.The presence of V_(2)O_(3) in the Niutitang Formation indicates the isomorphism state of vanadium existence in the clay minerals.Clays and pyrite are the most favorable mineral for vanadium enrichment.However,it is suggested the quartz of non-biogenic origin might be unfavorable for vanadium enrichment.Vanadium is mainly derived from the diagenetic transformation of its precursor(porphyrin pigments and chlorophyll)from the organism.During the Early Cambrian period,the massive transgression in the sea level created a favorable environment for organisms to survive.Additionally,the hydrothermal activities brought massive nutrient supply in the form of vanadium and other metal elements from the deep Earth.These creatures consumed the vanadium-rich nutrients,which became a part of their bodies in the form of hard and soft parts.Later on,when these organisms died and were submerged in the sediments.After the diagenetic actions,this vanadium became a part of these black sediments along with organic carbon.Therefore,these black rocks in the Yangtze region are enriched in vanadium and organic carbon.It is suggested the various processes such as adsorption,complexation,and reductions are the main factors responsible for the precipitation of dissolved vanadium into the organically rich sediments.

Subsurface geological model of sedimentary and metasedimentary wedge from Mansehra to Battal based on gravity data,Hazara area,Pakistan

This study is aimed to delineate the subsurface structural elements using geophysical techniques in the Haraza area of Pakistan.We investigated the Oghi and Battal thrust faults,sedimentary and metasedimentary wedge,and the absolute crustal thickness based on terrestrial gravity data.Unlike seismic survey relying on wave propagation,magnetic survey is based on both attraction and repulsion,and electrical and electromagnetics on induction.The attractive gravity field produces relatively simpler patterns of anomalies,like a series of highs and lows over regions with undulating basements and buried structures.A qualitative interpretation of gravity data reveals a good deal of information.During the collision of Indian and Eurasian Plates,compressional structures were developed in the Lesser Himalayas or northwest of the Hazara Kashmir Syntaxis.The study mainly focuses on the western limb of the Hazara Kashmir Syntaxis.The regional and local Bouguer anomalies were incorporated to delineate the regional structural units.The gravity model is computed through geophysical technique along with profile A-A'from Mansehra to the Battal area that demarcates the blind Oghi Thrust and emergent Battal Thrust.Tanol Formation of Precambrian age demarcates the Oghi Thrust near Kotli Pine while the Battal Thrust is demarcated within the Mansehra Granite of Cambrian to Ordovician age near Battal.Along with the Battal Thrust,fault gouge and breccias have been observed during the field studies.The total thickness of the sedimentary/metasedimentary wedge in the Mansehra and Battal areas was estimated to be 13.6 km and 14.2 km.In comparison,the total thickness of crust in the Mansehra and Battal areas was 51.6 km and 52.2 km,respectively.

Geochemical Characterization of Organic Rich Black Rocks of the Niutitang Formation to Reconstruct the Paleoenvironmental Settings during Early Cambrian Period from Xiangxi Area,Western Hunan,China

The Niutitang Formation in the South China Block might be a source of hydrocarbon as it contains an enormous quantity of organic matter.Black rock of the Early Cambrian Niutitang Formation is widely distributed in the Yangtze region,but detailed geochemical understanding of it is still emerging.This research discusses the detailed geochemical characteristics of the Niutitang Formation to reconstruct the paleoenvironmental conditions,employing total organic carbon(TOC)content,major,trace,and rare earth element data.For this purpose,black rock specimens of the Niutitang Formation from two outcrop sections were utilized for geochemical characterization,and the results compared with another eight sections from the South China Block.The average total organic carbon in these sediments is significantly higher(5.80 wt.%).In the platform region,lower quantities of TOC indicate a poor potential to produce hydrocarbons.At the same time,significantly higher TOC is observed in the deep shelf and slope sediments,indicating a significant potential to produce hydrocarbons.The average Ce,Eu and Y anomalies from both Longbizui and Sancha sections studied are 0.74,0.86,1.77,1.07,and 1.19,1.30,respectively.The chemical index of alteration(CAI)throughout the Yangtze block is higher(averaging 71.32)than that of Post Archean Australian Shale(PAAS 69),indicating a moderately weathered source of the Niutitang Formation relative to PAAS.As the sediments are moderately weathered,this suggests these rocks might have been derived from felsic rocks,mainly granite-granodiorite.The normalization of REEs in the black rocks reveals a reduction of light REEs with increase in heavy REEs enrichment.Similarly,a positive Eu anomaly,negative Ce anomaly,and a moderate Y/Ho(34.61)are clues to a hybrid depositional mechanism associated with hydrothermal action and terrigenous input.These anomalies are also evidence of upwelling in the paleo-ocean and mixing of organic matter,which created anoxic bottom water during the deposition of the Niutitang Formation in the basin and upper oxic water conditions before deposition.The main controlling factors for the distribution of rare earth elements in these black rocks of the Niutitang Formation are pH,terrigenous input,source rock composition,tectonism,an upwelling mechanism,and hydrothermal activity.