| 1. |
- Ask, Maria
(författare)
-
In situ stress from breakouts in the Danish sector of the North Sea
- 1997
-
Ingår i: Marine and Petroleum Geology. - 0264-8172 .- 1873-4073. ; 14:3, s. 231-243
-
Tidskriftsartikel (refereegranskat)abstract
- Borehole breakouts from 26 wells situated in the Danish Central Graben and one well situated in the northwestern section of the Ringkobing-Fyn High have been studied. The data provide information on the orientation of the contemporary principal horizontal stresses down to depths of 4.7 km. Statistics were used to obtain a mean azimuth of breakouts for each well, and each individual breakout was weighted by its length. Data quality of breakouts is assigned according to the World Stress Map quality ranking scheme. The breakout data reveal that SH orientations in the Danish Central Graben are extremely scattered; no regional trend in mean SH orientation can be identified as a result of the large standard deviation (±77°). Similar scatterings of SH orientations have been reported from adjacent regions of the North Sea. The results indicate that the state of stress in the sedimentary cover of the Danish Central Graben is influenced by a local stress generating mechanism rather than platewide stress transmissions mechanisms. Three units with different states of stress have been identified and found to correspond somewhat with the lithostratigraphic divisions of the Post Chalk Group, Chalk Group and Pre Chalk Group.
|
|
| 2. |
- Koyi, Hemin, et al.
(författare)
-
The influence of basement fault on the development of salt structures in the Danish Basin.
- 1993
-
Ingår i: Marine and Petroleum Geology. - 0264-8172 .- 1873-4073. ; 10:2, s. 82-94
-
Tidskriftsartikel (refereegranskat)abstract
- Scaled centrifuged models based on interpreted seismic profiles were used to simulate the salt structures in the Danish Basin. The models consisted of a viscous layer simulating rock salt, overlain by layers of cohesive sand that mimic brittle failure in natural overburdens. Model results support the hypothesis that basement faults trigger the growth of many salt diapirs in the Danish Basin. In plan view, model diapirs are localized as buoyant walls along faults in the overburden which collapsed due to basement fault movement. With further burial, single diapirs rose from these buoyant walls. Some of the diapirs surfaced through the faulted overburden, a few were trapped beneath the competent ‘Cretaceous’ units and others were starved due to lack of supply from below. In section, model diapirs were asymmetric and were rooted on the tip of the faults or located on the rotated footwall blocks. Model diapirs not located over faults were triggered by differential loading and collapsing of overburden layers due to basement block rotation. Models show that the presence of fewer salt structures in the northern than the southern part of the basin is due to differential subsidence and flow of buoyant material from north to south, where they rise diapirically. In the model, the pressure due to loading by overburden layers changed from 1.3 × 102 Pa in the south to 2.3 × 102 Pa in the northern part of the basin. In general, the model results illustrate that basement faults influence diapirs by accumulating buoyant material in half-grabens and introducing a slope and steps at the base of the buoyant layer, weakening its overburden and causing differential loading and compaction. The spreading overhangs of salt diapirs beneath the Cretaceous chalk in the Danish Basin would seal any potential pre-Cretaceous reservoir rocks.
|
|
| 3. |
- Abdelmaksoud, Ahmed, et al.
(författare)
-
Petroleum system of the fold-and-thrust belt of the United Arab Emirates : New insights based on 1D and 2D basin modeling
- 2023
-
Ingår i: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 158
-
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.
|
|
| 4. |
- Ali Kalefa El-ghali, Mohamed, et al.
(författare)
-
Diagenetic alterations related to marine transgression and regression in fluvial deltaic and shallow marine sandstones of the Triassic Buntsandstein and Keuper formations, the Paris Basin, France
- 2009
-
Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 26:3, s. 289-309
-
Tidskriftsartikel (refereegranskat)abstract
- The distribution of diagenetic alterations in Triassic fluvio-deltaic, quartzarenitic to sublitharenitic, lowstand systems tract (LST) sandstones of the Grès á Voltzia Formation, anastomosing fluvial, quartzarenitic transgressive systems tract (TST) sandstones of the Grès á Roseaux Formation, and shallow marine, quartzarenitic to sublitharenitic, TST sandstones of the Grès Coquiller Formation, the Paris Basin (France), can be linked to transgression and regression events, and thus to the sequence stratigraphic context. Near-surface eogenetic alterations, which display a fairly systematic link to the depositional facies and sequence stratigraphic framework, include: (i) cementation by meteoric water calcite (δ18O=−8.9‰ and δ13C=−9.1‰) in the fluvio-deltaic, LST sandstones, (ii) cementation by mixed marine–meteoric calcite (δ18O=−5.3‰ to −2.6‰ and δ13C=−3.9‰ to −1.3‰) and dolomite (δ18O=−4.6‰ to −2.6‰ and δ13C=−2.9‰ to −2.3‰) in the foreshore, TST sandstones and below parasequence boundaries (PB), and transgressive surface (TS), and in the shoreface, TST sandstones below maximum flooding surfaces (MFS), being facilitated by the presence of carbonate bioclasts, (iii) dissolution of detrital silicates and precipitation of K-feldspar overgrowths and kaolinite, particularly in the fluvio-deltaic, LST sandstones owing to effective meteoric water circulation, and (vi) formation of autochthonous glauconite, which is increases in abundance towards the top of the fluvio-deltaic, LST sandstones, and along TS, and in the shoreface, TST sandstones, by alteration of micas owing to the flux of seawaters into the sandstones during transgression, whereas parautochthonous glauconite is restricted to the TS sandstones owing to marine reworking. Mesogenetic alterations, which include cementation by quartz overgrowths and illite, display fairly systematic link to fluvio-deltaic, LST sandstones. This study has revealed that linking of diagenesis to transgression and regression events enables a better understanding of the parameters that control the spatial and temporal distribution of diagenetic alterations in sandstones and of their impact on reservoir quality evolution.
|
|
| 5. |
- Almeida, Nazare da Silva, et al.
(författare)
-
Incubation experiments to constrain the production of methane and carbon dioxide in organic-rich shales of the Permian Irati Formation, Parana Basin
- 2020
-
Ingår i: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 112
-
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.
|
|
| 6. |
- Braga, R., et al.
(författare)
-
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
-
Ingår i: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 112, s. 1-15
-
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.
|
|
| 7. |
- Carrillo, Emilio, et al.
(författare)
-
Structural significance of an evaporite formation with lateral stratigraphic heterogeneities (Southeastern Pyrenean Basin, NE Spain)
- 2017
-
Ingår i: Marine and Petroleum Geology. - : Elsevier. - 0264-8172 .- 1873-4073. ; 86, s. 1310-1326
-
Tidskriftsartikel (refereegranskat)abstract
- We run a series of analogue models to study the effect of stratigraphic heterogeneities of an evaporite formation on thin-skinned deformation of the Southeastern Pyrenean Basin (SPB; NE Spain). This basin is characterized by the existence of evaporites, deposited during the Early-Middle Eocene with lateral variations in thickness and lithological composition. These evaporites are distributed in three lithostratigraphic units, known as Serrat Evaporites, Vallfogona and Beuda Gypsum formations and acted as decollement levels, during compressional deformation in the Lutetian. In addition to analogue modeling, we have used field data, detailed geological mapping and key cross-sections supported by seismic and well data to build a new structural interpretation for the SPB. In this interpretation, it is recognized that the basal and upper parts of the Serrat Evaporites acted as the main decollement levels of the so-called Cadi thrust sheet and Serrat unit. A balanced restoration of the basin indicates that thrust faults nucleated at the stratigraphic transition of the Serrat Evaporites (zone with lateral variations of thickness and lithological composition), characterized by a wedge of anhydrite and shale. The analogue models were setup based on information extracted from cross-sections, built in two sectors with different lithology and stratigraphy of the evaporites, and the restored section of the SPB. In these models, deformation preferentially concentrated in areas where thickness change, defined by wedges of the ductile materials, was inbuilt. Based on the structural interpretation and model results, a kinematic evolution of the SPB is proposed. The kinematic model is characterized by the generation of out-of-sequence structures developed due to lateral stratigraphic variations of the Serrat Evaporites. The present work shows a good example of the role of stratigraphic heterogeneities of an evaporite formation which acts as decollement level on structural deformation in a fold-thrust belt. The results of this work have implications for hydrocarbon exploration and are relevant for studying structural geometry and mechanics in shortened evaporite basins. (C) 2017 Elsevier Ltd. All rights reserved.
|
|
| 8. |
- Chuvilin, E., et al.
(författare)
-
In-situ temperatures and thermal properties of the East Siberian Arctic shelf sediments : Key input for understanding the dynamics of subsea permafrost
- 2022
-
Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 138
-
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.
|
|
| 9. |
|
|
| 10. |
- El-Ghali, M. A. K., et al.
(författare)
-
Distribution of carbonate cements within depositional facies and sequence stratigraphic framework of shoreface and deltaic arenites, Lower Miocene, the Gulf of Suez rift, Egypt
- 2013
-
Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 45, s. 267-280
-
Tidskriftsartikel (refereegranskat)abstract
- This study aims to unravel the spatial and temporal distribution of diagenetic alterations of the Mheiherrat Member, the Rudeis Formation (lower Miocene) of the Gulf of Suez rift, Egypt within depositional fades and sequence stratigraphy. The Mheiherrat member is represented by shoreface calcarenites and hybrid arenites (transgressive and highstand systems tracts; TST and HST; respectively) and deltaic rudites and coarse-grained calcarenites and hybrid arenites (lowstand systems tracts; LST). Petrographic, stable O- and C-isotopes, mineral chemical and geochemical analyses have revealed that the arenites are pervasively cemented by eogenetic carbonates and, to small extent, by zeolite and pyrite as well as by telogenetic palygorskite. The shoreface TST and HST calcarenites and hybrid arenites were dominantly cemented by microcrystalline grain-rimming and inter- and intragranular pore-filling calcite (delta O-13(V-PDB) = -3.6 parts per thousand to -0.3 parts per thousand and delta C-13(V-PDB) = -2.3 parts per thousand to -0.7 parts per thousand) and rhombic dolomite (delta C-13(V-PDB) = -3.9 parts per thousand to +0.9 parts per thousand and delta C-13(V-PDB) = -2.5 parts per thousand to -0.7 parts per thousand). These cements are interpreted to be formed by marine to brackish waters with delta O-13(V-SMOW) -1.2 parts per thousand to +3.2 parts per thousand, at temperature of 20-55 degrees C. The deltaic LST coarse-grained calcarenites and hybrid arenites were dominantly cemented by coarse-crystalline, inter- and intragranular pore-filling calcite (delta O-13(V-PDB) -4.4 parts per thousand to -2.3% and delta C-13(V-PDB) = -2.8 parts per thousand. to -1.3 parts per thousand.), which are interpreted to have precipitated from pore waters with delta O-13(V-SWOM) +3.5 parts per thousand. to +5.5 parts per thousand, at temperatures of greater than 55 degrees C. Such pervasive cementation by carbonates is attributed to the occurrence of abundant intrabasinal carbonate grains. The carbonate cement texture is suggested to be controlled by changes in pore-water chemistry owing to transgression and regression events. This case study revealed that better understanding of factors controlling the extent and textural habits of carbonate cements can be achieved when it is linked with depositional facies and sequence stratigraphy.
|
|
