| 1. |
- Abdelmaksoud, Ahmed, et al.
(författare)
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Petroleum system of the fold-and-thrust belt of the United Arab Emirates : New insights based on 1D and 2D basin modeling
- 2023
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Ingår i: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 158
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Tidskriftsartikel (refereegranskat)abstract
- The hydrocarbon potential of the fold-and-thrust belt (FTB) in the United Arab Emirates (UAE)-Oman mountains has received limited attention to date, leading to a poor understanding of the petroleum systems in this region. Despite the existence of hydrocarbon fields within the FTB, the source rock potential has not been adequately studied. This study aims to address this knowledge gap using 1D and 2D basin modeling approaches to evaluate the petroleum system of the FTB. In addition, gas chromatographs are also used to correlate hydrocarbon occurrences with their source rock. This study's findings identify the Silurian, Upper Cretaceous, Paleocene-Eocene, and Oligocene formations as the primary source rocks in the study area. Silurian shales, encountered in a well in the northern UAE, are currently considered overmature. The Cenozoic source rocks exhibit a spectrum of Total Organic Carbon (TOC) content, ranging from less than 1 to as high as 2 wt%, leading to variable degrees of expulsion efficiency. The maturity of these rocks varies based on their position in relation to the FTB and foredeep, with increasing maturity towards the north. The Upper Cretaceous sequences display low TOC and Hydrogen Index, indicating very low expulsion efficiency. The present-day distribution of maturity is largely influenced by Late Cretaceous and Oligocene-Miocene compressional events that affected the northern and northeastern Arabian Plate. This analysis shows that hydrocarbon expulsion from the Silurian source rocks was initiated during the Middle-Late Jurassic. These hydrocarbons are presumed to have migrated through Upper Permian, Jurassic, and Lower and middle Cretaceous reservoirs. Westward hydrocarbon migration, towards a regional bulge, may have also occurred following compressional events that resulted in lithospheric flexure and formation of the foreland basin. Notably, certain exceptions to migration towards the bulge include structural entrapment of hydrocarbons beneath the main frontal thrust zone of FTB and some structural traps beneath the Lower Fiqa Formation.
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| 2. |
- Almeida, Nazare da Silva, et al.
(författare)
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Incubation experiments to constrain the production of methane and carbon dioxide in organic-rich shales of the Permian Irati Formation, Parana Basin
- 2020
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Ingår i: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 112
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Tidskriftsartikel (refereegranskat)abstract
- The Permian Irati Formation in Brazil hosts organic-rich shales and heavy hydrocarbons suitable for biogenic production of methane (CH4) and carbon dioxide (CO2). In this study, shale samples from the irati Formation were used in laboratory incubation experiments performed under different temperatures (22 degrees C, 50 degrees C, 70 degrees C and 80 degrees C) to evaluate the generation of CH4 and CO2 under thermal conditions compatible with biodegradation in shallow gas systems (< 80 degrees C). Despite our laboratory experiments do not represent natural subsurface temperature conditions, it is observed that the concentrations of CH4 and CO2 increase when shale samples are incubated under temperature higher than 22 degrees C. Samples incubated at 80 degrees C presented a maximum CH4 yield of 2.45 ml/t.d (milliliter per ton of shale per day) compared to 0,49 ml/t.d at 22 degrees C, 1.75 ml/t.d at 50 degrees C and 2.09 ml/t.d at 70 degrees C. The same trend of increasing production rates with higher temperatures was observed for CO2, with maximum potential production observed under a laboratory temperature of 80 degrees C, reaching 23.47 ml/t.d. Stable carbon isotopes (delta C-13) on CH4 and CO2 suggest a mixture of thermogenic and secondary microbial gas. However, the measured CH4 and CO2 can be generated through methanogenic degradation of heavy hydrocarbons present in the studied shales, difficulting the use of carbon isotope composition to discriminate between biogenic and thermogenic gases. The studied shale samples showed significant differences in CH4 and CO2 production rates, which are possibly related to the major elements composition of the mineral matrix. Higher CH4 and CO2 production rates occurred in samples with higher amount of sulfur. Besides sulfur, we highlight that others soluble elements in the mineral matrix, such as Ca and Mg, can play an important role for the generation of biogenic CH4 and CO2. The present work intends to alert for the importance of thermal conditions as well as the geochemical composition of the mineral matrix to build conceptual models about shallow gas systems, acting on organic-rich shales in sedimentary basins.
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| 3. |
- Braga, R., et al.
(författare)
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Modelling methane hydrate stability changes and gas release due to seasonal oscillations in bottom water temperatures on the Rio Grande cone, offshore southern Brazil
- 2020
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Ingår i: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 112, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- The stability of methane hydrates on continental margins worldwide is sensitive to changes in temperature and pressure conditions. It has been shown how gradual increases in bottom water temperatures due to ocean warming over post-glacial timescales can destabilize shallow oceanic hydrate deposits, causing their dissociation and gas release into the ocean. However, bottom water temperatures (BWT) may also vary significantly over much shorter timescales, including due to seasonal temperature oscillations of the ocean bottom currents. In this study, we investigate how a shallow methane hydrate deposit responds to seasonal BWT oscillations with an amplitude of up to 1.5 °C. We use the TOUGH + HYDRATE code to model changes in the methane hydrate stability zone (MHSZ) using data from the Rio Grande Cone, in the South Atlantic Ocean off the Brazilian coast. In all the cases studied, BWT oscillations resulted in significant gaseous methane fluxes into the ocean for up to 10 years, followed by a short period of small fluxes of gaseous methane into the ocean, until they stopped completely. On the other hand, aqueous methane was released into the ocean during the 100 years simulated, for all the cases studied. During the temperature oscillations, the MHSZ recedes continuously both horizontally and, in a smaller scale, vertically, until a permanent and a seasonal region in MHSZ are defined. Sensitivity tests were carried out for parameters of porosity, thermal conductivity and initial hydrate saturation, which were shown to play an important role on the volume of methane released into the ocean and on the time interval in which such release occurs. Overall, the results indicate that in a system with no gas recharge from the bottom, seasonal temperature oscillations alone cannot account for long-term gas release into the ocean.
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| 4. |
- Chuvilin, E., et al.
(författare)
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In-situ temperatures and thermal properties of the East Siberian Arctic shelf sediments : Key input for understanding the dynamics of subsea permafrost
- 2022
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Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 138
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Tidskriftsartikel (refereegranskat)abstract
- Significant reserves of methane (CH4) are held in the Arctic shelf, but the release of CH4 to the overlying ocean and, subsequently, to the atmosphere has been believed to be restricted by impermeable subsea permafrost, which has sealed the upper sediment layers for thousands of years. Our studies demonstrate progressive degradation of subsea permafrost which controls the scales of CH4 release from the sediment into the water-atmospheric system. Thus, new knowledge about the thermal state of subsea permafrost is crucial for better understanding of the permafrost -hydrate system and associated CH4 release from the East Siberian Arctic Shelf (ESAS) – the broadest and shallowest shelf in the World Ocean, which contains about 80% of subsea permafrost and giant pools of hydrates. Meanwhile, the ESAS, still presents large knowledge gaps in many aspects, especially with respect to subsea permafrost distribution and physical properties of bottom sediments. New field data show that the ESAS has an unfrozen (ice-free) upper sediment layer, which in-situ temperature is −1.0 to −1.8 °C and 0.6оС above the freezing point. On one hand, these cold temperature patterns may be related to the presence of subsea permafrost, which currently primarily occurs in the part of the ESAS that is shallower than 100 m, while ice-bearing sediments may also exist locally under deeper water in the Laptev Sea. On the other hand, the negative bottom sediment temperatures of −1.8 °C measured on the Laptev Sea continental slope sediments underlying water columns as deep as down to 330 m may result from dissociation of gas hydrates or possibly from dense water cascading down from the shelf. In contrast, data collected on recent expeditions in the northern Laptev shelf, zones of warmer bottom temperatures are coinciding with methane seeps, likely induced by seismic and tectonic activity in the area. These warm temperatures are not seen in the East Siberian Sea area, not even in areas of methane seeps, yet with little seismic activity.The thermal conductivity and heat capacity of bottom sediments recorded in the database of thermal parameters for the ESAS areas mainly depend on their lithification degree (density or porosity), moisture content, and particle size distribution. The thermal conductivity and heat capacity average about 1.0 W/(m·K) and 2900 kJ/(m3·K), with ±20% and ±10% variance, respectively, in all sampled Arctic sediments to a sub-bottom interval of 0–0.5 m.
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| 5. |
- Fan, Ke, et al.
(författare)
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Sacrificial W Facilitates Self-Reconstruction with Abundant Active Sites for Water Oxidation
- 2022
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Ingår i: Marine and Petroleum Geology. - : Wiley. - 0264-8172 .- 1873-4073. ; 138
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Tidskriftsartikel (refereegranskat)abstract
- Water oxidation is an important reaction for multiple renewable energy conversion and storage-related devices and technologies. High-performance and stable electrocatalysts for the oxygen evolution reaction (OER) are urgently required. Bimetallic (oxy)hydroxides have been widely used in alkaline OER as electrocatalysts, but their activity is still not satisfactory due to insufficient active sites. In this research, A unique and efficient approach of sacrificial W to prepare CoFe (oxy)hydroxides with abundant active species for OER is presented. Multiple ex situ and operando/in situ characterizations have validated the self-reconstruction of the as-prepared CoFeW sulfides to CoFe (oxy) hydroxides in alkaline OER with synchronous W etching. Experiments and theoretical calculations show that the sacrificial W in this process induces metal cation vacancies, which facilitates the in situ transformation of the intermediate metal hydroxide to CoFe-OOH with more high-valence Co(III), thus creating abundant active species for OER. The Co(III)-rich environment endows the in situ formed CoFe oxyhydroxide with high catalytic activity for OER on a simple flat glassy carbon electrode, outperforming those not treated by the sacrificial W procedure. This research demonstrates the influence of etching W on the electrocatalytic performance, and provides a low-cost means to improve the active sites of the in situ self-reconstructed bimetallic oxyhydroxides for OER.
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| 6. |
- Hong, Wei-Li, et al.
(författare)
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Interactions between deep formation fluid and gas hydrate dynamics inferred from pore fluid geochemistry at active pockmarks of the Vestnesa Ridge, west Svalbard margin
- 2021
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Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 127
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Tidskriftsartikel (refereegranskat)abstract
- Seafloor seepage sites along the Vestnesa Ridge off west-Svalbard have been, for decades, a natural laboratory for the studies of fluid flow and gas hydrate dynamics along passive continental margins. The lack of ground truth evidence for fluid composition and gas hydrate abundance deep in the sediment sequence however prohibits us from further assessing the current model of pockmark evolution from the region. A MARUM-MeBo 70 drilling cruise in 2016 aims to advance our understanding of the system by recovering sediments tens of meters below seafloor from two active pockmarks along Vestnesa Ridge. We report pore fluid composition data focusing on dissolved chloride, stable isotopes of water (delta O-18 and delta D), and the isotopic composition of dissolved boron (delta B-11). From one of the seepage sites, we detect a saline formation water with two layers where gas hydrates were recovered. This saline formation pore fluid is characterized by elevated chloride concentrations (up to 616 mM), high B/Cl ratios (9 x 10(-4) mol/mol), high delta O-18 and delta D isotopic signatures (+0.6 parts per thousand and +3.8 parts per thousand, respectively) and low 811B signatures (+35.0 parts per thousand), which collectively hint to a high temperature modification at great depths. Based on the dissolved chloride concentration profiles, we estimated up to 47% of pore space occupied by gas hydrate in the sediments shallower than 11.5 mbsf. The observation of bubble fabric in the recovered gas hydrates suggests formation during past periods of intensive gaseous methane seepage. The presence of these gas hydrates without associated positive anomalies in dissolved chloride concentrations however suggests that the decomposition of gas hydrate is as fast as its formation. Such a state of gas hydrates can be attributed to a relatively low methane supply transported by the saline formation water at present. Our findings based on pore fluid composition corroborate previous inferences along Vestnesa Ridge that fluids sustaining seepage have migrated from great depths and that the variable gaseous and aqueous phases through the gas hydrate stability zone control the distributions of authigenic carbonates and gas hydrates.
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| 7. |
- Jia, Yunzhong, et al.
(författare)
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Laboratory geomechanical and petrophysical characterization of Longmaxi shale properties in Lower Silurian Formation, China
- 2021
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Ingår i: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 124
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Tidskriftsartikel (refereegranskat)abstract
- The Lower Silurian Longmaxi formation is one of the most promising shale gas reservoirs in China. A comprehensive understanding of the shale geomechanical and petrophysical properties is crucial for the successful exploration and extraction of shale gas. We select four representative locations to acquire Longmaxi formation shale samples for the laboratory experiments, to investigate the geomechanical and petrophysical properties through a series of X-ray diffraction (XRD), scanning electron microscope (SEM), uniaxial compression, triaxial compression, tensile strength, and fracture toughness measurements. Laboratory results indicate that: (1) The quartz is the dominant mineral, and phyllosilicate mineral contents vary largelly from 7.30% to 47.80% in Longmaxi shale, which enables a higher brittleness index and fracbility. SEM results show that the high gas storage potential and well micro-fractures development of Longmaxi shale rocks. (2) The phyllosilicate content is vital in determining the uniaxial compressive strength, triaxial strength and elastic properties due to its weaker mechanical properties than tectosilicate minerals; (3) Fracture toughness of Longmaxi shale are relatively higher than shale formations in the USA, which indicate a higher potential to form fracture networks during hydraulic fracturing operations. (4) The anisotropy affects Longmaxi shale mechanical properities extensively due to the high-density bedding planes, which may further influence the fracture network formation during hydraulic fracturing operations. Our results revealed significant non-linear mechanical response as a consequence of shale fabric and mineralogy, which provides necessary information for the in-situ hydraulic fracturing and wellbore stability application during shale gas development in Longmaxi shale formation.
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| 8. |
- Misra, Satabdi, et al.
(författare)
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Multi-proxy approach on the hydrocarbon generation perspective of Barjora Basin, India
- 2020
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Ingår i: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 112
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Tidskriftsartikel (refereegranskat)abstract
- Barjora Basin in India is a small basin characterized by a high organic richness of early mature nature. The present study aims to find the source of organic matter (OM) and hydrocarbon generation potential of Barjora Basin. Systematically collected coal and shale samples from R-II seam of the basin were used for proximate and ultimate analyses, Rock Eval pyrolysis along with total organic carbon (TOC) content, organo-micropetrographic framework, thermal maturity, carbon isotopic signature, biomarker composition, functional group studies and estimation of relative aliphaticity and aromaticity through Fourier Transform infrared spectroscopy (FTIR). The novelty of the present work lies in the application of multiple proxies such as stable isotope ratio of organic carbon (delta C-13), biomarker signatures, thermal maturity parameters, organo-micropetrography and estimation and quantification of functional groups for palaeoenvironmental reconstruction and to assess the hydrocarbon productivity of the basin. A dominant terrestrial OM input in Barjora Basin is indicated by the TOC to total nitrogen ratio (C/N), delta C-13 and biomarker compositions. High gelification index (GI), tissue preservation index (TPI), and carbon preference index (CPI) values indicate that coals are deposited in wet swamp forest regime under high rainwater conditions and shales are formed in upper delta plain regime under high groundwater activity. In addition, large liptinite content, TPI and GI designate short transportation of the OM before burial leading to organic richness of the Barjora Basin. Moreover, high liptinite content, type II-III admixed kerogen input, S-2/S-3 ratio, TPI and index for hydrocarbon generation (I-HG) signify higher potential of the basin for hydrocarbon generation.
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| 9. |
- Breitfeld, H. T., et al.
(författare)
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The onshore West Baram Delta deposits: Provenance and drainage in the Middle Miocene to Pliocene in NW Borneo and comparison to the Champion Delta
- 2023
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Ingår i: Marine and Petroleum Geology. - 0264-8172. ; 158
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Tidskriftsartikel (refereegranskat)abstract
- The Baram Delta province in NW Borneo forms a major hydrocarbon reservoir offshore northern Sarawak and Brunei. The delta sequence is thereby subdivided into the West Baram delta to the south and the Champion delta to the north. Onshore are the remains of the Neogene delta deposits exposed and provide the possibility to study the equivalent offshore successions in outcrop. This study focuses on the Neogene West Baram delta successions which were studied for sedimentological facies and provenance characteristics. The successions consist of the Lambir, Miri, Tukau, and the enigmatic southern Lambir/Belait-Sarawak formations. Deposition took place in various mixed-energy delta environments between the Langhian and early Pliocene. The sediments are all quartzrich and heavy minerals are dominated by ultra-stable zircon, rutile and tourmaline. Dominant detrital zircon age clusters are in the Early Cretaceous and Permian-Triassic. Based on light mineral petrography, heavy mineral assemblages, and detrital zircon U-Pb geochronology, all formations are interpreted as derived from multirecycled sources, likely the underlying Paleogene Rajang Group turbidites and the Oligocene to Lower Miocene Nyalau-Tatau delta deposits. Additionally, literature data of the Champion Delta and one sample from Labuan analysed for provenance in this study are used to demonstrate that the Champion Delta can be distinguished from the West Baram Delta by having higher chrome spinel and garnet contents and slightly different detrital zircon age populations. The Champion Delta deposits are interpreted as sourced by recycling of the Crocker Formation and older turbidites (e.g., Sapulut Formation) with potentially input from ultra-mafic basement rocks of Sabah.
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| 10. |
- Mangione, A., et al.
(författare)
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Estimation of pre-dolomitisation porosity and permeability of a nummulitic carbonate reservoir rock using the Multi-Component Architecture Method (MCAM)
- 2021
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Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172. ; 132
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Tidskriftsartikel (refereegranskat)abstract
- The fossiliferous Eocene carbonate reservoir interval of the offshore Hasdrubal Field has a diagenetic history in which dolomitisation of micrite-rich facies has significantly enhanced reservoir quality. Using published information on the diagenetic evolution, digital textural representations of the limestones and dolostones are created using the Multi-Component Architecture Method (MCAM). This technique allows integration of images at different length scales (e.g., SEM, micro-/nano- XRT) which provide different forms of information about the pre-dolomitisation rock, including textural and compositional factors, and the arrangements of preserved components. These digital representations of the dolostones, together with their now completely overprinted precursor micritic limestones, permit exploration of the impact on porosity and permeability of uncemented, partly cemented and biomoulds Nummulites, their number per unit volume, and their orientation (i.e., uniformly or randomly orientated) allowing investigation of the petrophysical consequences of different distributions, orientations and abundances of the matrix and fossiliferous components. Viable diagenetic pathways, which were identified by thin section analysis as well as data available in the literature, are linked to petrophysical property evolution. In this way MCAM permits investigation of earlier stages of the diagenetic processes which were overprinted by later diagenetic processes.
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