Hydrocarbon Leakage Research Articles

THE MATHEMATICAL MODELLING METHODS APPLYING TO ESTIMATE THE PIPELINES TECHNICAL STATE AND ENVIRONMENT SITUATION

In the context of providing trouble-free operation of oil and gas pipelines and preventing possible negative impacts on the environment, the issues of constructing an integrated mathematical model for assessing the technical condition of pipelines and the impact of emergency situations on the state of the environment in the course of hydrocarbon leakage are considered. The model of the evaluation of the stress-strain state of the pipeline according to the data on the displacement of surface points for the above ground and underground sections is given by constructing the law of motion of the site by known displacements of a certain set of surface points using assumptions about the type of deformation of the sections and reproduction of the deformations and stresses tensors components on the basis of different models of deformed solid body.
 The specified model does not require information on the whole complex of forces and loads acting on the investigated object during operation. The flow model has been refined in a pipeline with a violation of its tightness by recording a special type of boundary conditions for a Navier-Stokes equation system in a two-dimensional formulation and developing an original method for its solution on the basis of the finite difference method. In the article the stability conditions of the proposed numerical schemes on basis of the spectral sign of stability are presented. In order to assess possible negative impacts on the environment, a model of propagation of matter at its leakage from the pipeline was developed by solving two-dimensional diffusion equations taking into account the variables and different types of boundary conditions that take into account the number of sources of pollution and their intensity. The results of computations based on computational algorithms implemented by these models and graphic material illustrating these calculations are presented, peculiarities of distribution of harmful substances in the environment near the pipeline are analyzed. Directions of further researches for successful practical realization of the offered models are established.

Simulações da migração de plumas dissolvidas de compostos BTEX geradas por LNAPL trapeado

O vazamento acidental de hidrocarbonetos é um cenário comum de contaminação subsuperficial. Uma vez liberado, o hidrocarboneto migra até atingir as vizinhanças da zona saturada, onde se acumula. Em razão da flutuação do nível d’água, o LNAPL (light non-aqueous phase) é redistribuído e trapeado na zona saturada. O LNAPL trapeado é responsável pela liberação de benzeno, tolueno, etilbenzeno e xilenos (BTEX) para a água, gerando plumas de fase dissolvida desses compostos. Essas plumas variam em dimensão e concentração ao longo do tempo, em resposta à depleção dos compostos BTEX na área-fonte. Para representar esta condição é proposta uma metodologia que combina o uso dos aplicativos MODFLOW, para simulações de fluxo, EXHAURIS, para simulação da transferência de massa e MT3DMS, para simulação do transporte de solutos. As simulações realizadas reproduziram o comportamento das plumas dissolvidas de benzeno e etilbenzeno geradas a partir da dissolução do querosene de aviação. Os resultados indicam que a pluma de benzeno se extingue dentro de um período de 10 anos, enquanto o etilbenzeno persiste por mais de 20 anos. Tal diferença está associada à menor fração molar e à maior solubilidade do benzeno em relação ao etilbenzeno. Os testes indicam que a metodologia proposta é uma alternativa promissora para previsões do comportamento de plumas dissolvidas ao longo do tempo, contemplando a condição de depleção da área-fonte.

Preliminary Study on Electrical Properties of Hydrocarbon-Contaminated Soils at an Artisanal Oil Field in Central Java, Indonesia

Investigation on hydrocarbon-contaminated soils at artisanal or traditional oil fields is a challenging task since the choice of an appropriate non-hazardous method is a must. Currently, the ground penetrating radar (GPR) method is widely accepted to apply in such a case. In this study we propose an alternative method in analyzing hydrocarbon leakage absorbed by soil. For years, local people operate this artisanal oil field and they often pour in the unused oil waste into the ground. Discrete measurements of electrical conductivity of core samples were conducted using Decagon EM 50 instrument. The samples were taken from an artisanal oil field near a state-owned oil field located in Central Java. The hydrocarbon-contaminated soils were compared to those taken from uncontaminated soils in the same area. Depth of the coring is 70 cm and it was sampled at every 5 cm to obtain its conductivity values. The natural-uncontaminated soils showed a maximum value of 0.65 dS/cm at 22 cm deep whereas the maximum conductivity value of the contaminated soil samples is 1.4 dS/cm at 31 cm deep. The results of this study indicate that the electrical conductivity values of the contaminated soils increase in contrast to what is expected where the introduction of hydrocarbon into soil will tend to decrease its electrical conductivity value since hydrocarbon is highly resistive. These results suggest that biodegradation may have been occurring in the contaminated soils for a considerably length of time

Burial and exhumation history controls on shale compaction and thermal maturity along the Norwegian North Sea basin margin areas

Abstract The North Sea area has been subjected to significant erosion and subsequent deposition of sediments in the basin margin and deeper basin areas, respectively, during the late Neogene. A large amount of Cretaceous-early Quaternary sediments have been removed below the angular unconformity along the west and southwest coast of Norway and deposited in the huge North Sea Fan at the mouth of the Norwegian Channel. At the same time, a considerable thickness of early Quaternary-Paleocene sediments was also eroded towards the east in the central North Sea and subsequently deposited in the deeper basin areas to the west. This study seeks to estimate exhumation from compaction and thermal maturity based techniques by using sonic velocities of shales/carbonates and vitrinite reflectance data in a large number of boreholes in the central, eastern and northern North Sea. The results indicate no or minor exhumation in the Central Graben and flanking high areas, whereas more than ∼1 km sediments are eroded in the basin margin areas towards the Norwegian coast. More than ∼500 m sediments are eroded in the Egersund Basin and Stord Basin areas. A similarity of exhumation estimates from the Early Cretaceous-Early Miocene shales and Late Cretaceous-Early Paleocene carbonates indicates maximum burial sometime after the Early Miocene in most of the central and northern North Sea areas. However, the maximum burial throughout the North Sea Basin may be diachronous. Seismostratigraphic analysis indicates maximum burial sometime during the Oligocene in the Sorgenfrei-Tornquist Zone area in the eastern North Sea. Maximum burial in the Norwegian-Danish Basin varies from Miocene-Pliocene in eastern parts to early Pleistocene in western parts, whereas sediments are currently at their maximum burial in the Central Graben and southern Viking Graben areas. Restoration of surface elevations to their original position before the onset of erosion indicated large subaerially exposed areas in the Norwegian-Danish Basin and along the southwest coast of Norway. This is also supported by predominantly coastal and/or deltaic environments in the Norwegian-Danish Basin area during the late Neogene. These subaerially exposed areas may be linked to the regional tilting and erosion of the basin margin areas to the east and progressive basinward migration of deposition centres to the west since the Oligocene. The exhumation had significant effects on the petroleum system in the basin margin areas by cooling down the source rock. However, the deeper burial of sediments may also have changed the rheological properties of sediments from more ductile to brittle due to compaction and diagenetic processes which makes them more failure prone during exhumation leading to hydrocarbon leakage or seal failure in case of CO2 injection.

Fracture Fillings and Implication of Fluid Activities in Volcanic Rocks: Dixi Area in Kelameili Gas Field, Junggar Basin, Northwestern China

The Carboniferous Batamayineishan Formation of the Kelameili Gas Field is a specific weathered crust-related volcanic reservoir that has a significant production rate in the Junggar Basin, Northwestern China, attributed to debatable processes of fluid evolution. The results suggest that various types of fluids occurring in volcanic rocks lead to the filling of quartz and calcite in fractures and their associated alteration haloes. The silica that formed quartz veins was mainly derived from deep hydrothermal fluids, while the carbon dioxide that formed calcite veins originated from sources characterized by mixing and alteration of deep hydrothermal and hydrocarbon fluids. Siliceous hydrothermal fluids rich in sulphur dioxide and other volatile components were driven by a pressure gradient and buoyancy, and circulated both laterally and vertically along the fractures, forming quartz veins and tension fractures under different temperature conditions. Moreover, changes in salinity, pressure, and carbon dioxide of deep fluids, varying from acidic to weakly alkaline, resulted in earlier calcite precipitation in contraction fractures and weathered fractures. Tectonic uplift resulted in the long-term exposure of volcanic rocks, where fresh water mixed with the partially alkaline fluid escaping the basin to form calcite cements, thus retaining the characteristics of a seepage environment in the weathered fractures. Structural fractures occurred due to tectonic movements during the burial period. Filling and leakage of hydrocarbons caused pore fluids to convert from acidic to alkaline, precipitating late sparry calcite in dissolution fractures. Late hydrothermal fluid metasomatism, brought about by infiltration into the permeable zone, caused partial dissolution of local calcite along cleavage cracks.

Formation of linear planform chimneys controlled by preferential hydrocarbon leakage and anisotropic stresses in faulted fine-grained sediments, offshore Angola

Abstract. A new type of gas chimney exhibiting an unconventional linear planform is found. These chimneys are termed Linear Chimneys, which have been observed in 3-D seismic data offshore of Angola. Linear Chimneys occur parallel to adjacent faults, often within preferentially oriented tier-bound fault networks of diagenetic origin (also known as anisotropic polygonal faults, PFs), in salt-deformational domains. These anisotropic PFs are parallel to salt-tectonic-related structures, indicating their submission to horizontal stress perturbations generated by the latter. Only in areas with these anisotropic PF arrangements do chimneys and their associated gas-related structures, such as methane-derived authigenic carbonates and pockmarks, have linear planforms. In areas with the classic isotropic polygonal fault arrangements, the stress state is isotropic, and gas expulsion structures of the same range of sizes exhibit circular geometry. These events indicate that chimney's linear planform is heavily influenced by stress anisotropy around faults. The initiation of polygonal faulting occurred 40 to 80 m below the present day seafloor and predates Linear Chimney formation. The majority of Linear Chimneys nucleated in the lower part of the PF tier below the impermeable portion of fault planes and a regional impermeable barrier within the PF tier. The existence of polygonal fault-bound traps in the lower part of the PF tier is evidenced by PF cells filled with gas. These PF gas traps restricted the leakage points of overpressured gas-charged fluids along the lower portion of PFs, hence controlling the nucleation sites of chimneys. Gas expulsion along the lower portion of PFs preconfigured the spatial organisation of chimneys. Anisotropic stress conditions surrounding tectonic and anisotropic polygonal faults coupled with the impermeability of PFs determined the directions of long-term gas migration and linear geometries of chimneys. Methane-related carbonates that precipitated above Linear Chimneys inherited the same linear planform geometry, and both structures record the timing of gas leakage and palaeo-stress state; thus, they can be used as a tool to reconstruct orientations of stress in sedimentary successions. This study demonstrates that overpressure hydrocarbon migration via hydrofracturing may be energetically more favourable than migration along pre-existing faults.

Toward one-meter resolution in 3D seismic

High-resolution 3D (HR3D) seismic data are important for hydrocarbon exploration of shallow reservoirs, site characterization, and geohazard assessments. The goal of this contribution is to identify and quantify the parameters to increase the resolution of HR3D seismic data to meter scale. The main acquisition parameters controlling the resolution of the collected data are the spectrum of the seismic source, source-receiver offset range, and trace density. An evolution to one-meter-scale resolution of 3D seismic will rely on combining a reproducible seismic source with high frequencies up to at least 600 Hz, a high uniform trace density of more than 4 million traces per square kilometer, and an offset range shorter than approximately 200 m. The resulting 3D seismic data volume will reach meter-scale resolution for water and target depths of less than 600 m. The proposed HR3D system will be suitable for 3D and 4D characterization of seabed properties and shallow stratigraphy, the identification of geohazards and hydrocarbon leakage, and monitoring the environmental impact of offshore activities. The P-Cable 3D system is an excellent starting point for achieving one-meter-scale resolution due to its flexible and tight meter-scale shot and receiver spacing.

Determination of changes in leaf and canopy spectra of plants grown in soils contaminated with petroleum hydrocarbons

Changes in vegetation near pipelines are symptomatic of petroleum hydrocarbon leakages, particularly diesel and gasoline, which are fuels regularly transported onshore. The investigation of such changes in leaf and canopy spectra of vegetation grown on contaminated soils is the goal of this work. A real scale experiment was installed in an area of 2000 m2. Two planting plots were firstly contaminated on a controlled style with diesel (6.25 L/m3 soil) and gasoline (8.33 L/m3 soil). A third plot was used as a control and preserved with no contaminants. Subsequently, maize, brachiaria and perennial soybean were planted on all plots. Visible and infrared spectral measurements of leaf and canopy targets were taken, respectively, between 28–184 days and 49–203 days after planting. The spectra of contaminated plants were compared to those of healthy plants. Significant differences were observed in the chlorophyll absorption feature and red edge position both at the canopy level. Narrowband spectral indices highlighted differences predominantly in plants affected by gasoline. The evident changes in the canopy spectra show that the hydrocarbons damaged the canopy structure extensively. The spectral patterns revealed here have important implications for detecting and monitoring areas likely contaminated with liquid HCs using hyperspectral remote sensing.

A natural gas hydrate system on the Exmouth Plateau (NW shelf of Australia) sourced by thermogenic hydrocarbon leakage

Abstract The identification of natural gas hydrates and shallow free gas in sedimentary basins is critical for understanding the organic carbon cycle dynamics in the shallow geosphere, as well as for geohazard studies related to the development of commercial hydrocarbon fields. In this study, we report for the first time the evidence for the potential occurrence of a natural gas hydrate system along the continental margin of Australia, on the Exmouth Plateau (NW Shelf). By the use of high-quality 3D seismic data, calibrated by downhole data from ODP and industry boreholes, we interpret a series of shallow high-amplitude anomalies, including patchy bottom-simulating reflections, as the seismic expression of localised accumulations of free gas beneath the base of hydrate stability, and overlying high-saturation hydrates or authigenic carbonates. The hydrate-bearing reservoir is constituted by Neogene and Quaternary fine-grained carbonate nannofossil and foraminifera-rich oozes. The patchy distribution of the shallow free gas and hydrate accumulations, which reflects the geometry of deeper fault blocks, is hypothesised to result from the leakage of thermogenic gas from deeper reservoirs. The interpretation of a thermogenic origin for the hydrate-forming gases is supported by (1) the existence in the study area of several thermogenic gas discoveries within Late Triassic reservoirs, (2) seismic evidence of cross-stratal and stratal pathways for migrating gases in the overburden, (3) the presence of free gas accumulations at depths intermediate between the deep reservoirs and shallow gas hydrate systems, and (4) geochemical and lithological evidence that the conditions which favour the generation of shallow microbial gas are not present in the area. The acquisition of downhole log and sample data through the observed seismic amplitude anomalies is necessary to test the interpretations and hypotheses presented in this manuscript.

Downslope-shifting pockmarks: interplay between hydrocarbon leakage, sedimentations, currents and slope’s topography

Pockmarks in Pliocene-Quaternary continental slope deposits offshore Angola show features related to: (1) fluid leakage craters that formed repeatedly, (2) authigenic methane-derived carbonates that indicate the (former) presence of hydrocarbons and (3) erosional–depositional structures that are clearly related to current activity. Depending on topography, the pockmarks show differing development: “Advancing Pockmarks” preferentially developed on regional slopes or inclined topography (> 2.5°–3°). They arranged in a chain-like pattern and mimic the outline of buried turbidite channels below. These pockmarks and their infill migrated downslope in response to shifting vents. “Nested Pockmarks” occur in gently sloping areas (< 2°). Their isolated conical infill records slope-parallel migration within a specific depth range pointing to the influence of contour currents. Both pockmark types are long-lived and they record preferential fluid migration along specific pathways, which developed at the downcurrent sidewalls of pockmarks due to flow separation initiating “cavity flow” within the pockmarks. The durable specific migration paths include pockmark sidewalls, vertically stacked erosional-interface of sediment waves, or entire pockmark bodies. The vertical extent of both pockmark types from End Miocene to the present-day seafloor documents various intensities of episodic fluid bursts followed by periods of quiescence and fill.

Modelling and simulation of oil spills in coastal waters

Over the years many navigation incidents took place in coastal areas or in ports. As a result of these incidents (collision between vessels, groundings, flooding, etc.) many wrecks remained. Due to the inability of authorities to manage these situations, or the lack of interest for the repercussions that may occur in such an incident, many problems may arise in medium and long term. The impact on the environment and local economy may prove to be important if no pollution measures are taken in order to prevent ecological disasters. In this paper the case of a sunken vessel in the Romanian Black Sea coastal area, in terms of management of a possible leakage of hydrocarbons, is analysed. The method used in the paper allows the modelling and simulation of oil products spreading, through specialized software solutions, thus providing the authorities with a starting point in managing the response to the emergency situation.

Analysis of Pre-Darcy flow for different liquids and gases

Fluid flow in porous media is extensively associated with Darcy's law. Deviations from Darcy's law and its limitations result in modifications known as non-Darcy flow at high velocity and Pre-Darcy flow at low velocity. In this paper, experiments were conducted to explore significance of departure from linearity at low fluid velocity (Pre-Darcy flow) in porous media. Effect of different liquid and gas types on the onset of Pre-Darcy flow were studied for water, condensate, n-hexane and n-heptane as liquid phase and CH4, CO2 and N2 as gas phase. Superficial velocity versus pressure gradient was measured and different onset values were reported. The minimum observed Darcy velocity was 0.189 × 10−05 m/s, below which Pre-Darcy flow prevails. Analysis was performed in terms of friction factor and Reynolds number for different particle size of 0.15, 0.25 and 0.3 mm. Pre-Darcy, Darcy and Non-Darcy flow regimes were observed and characterized in terms of Re√k, Red and Rep. The range of Reynolds number were reported for different flow regimes, different particle sizes and different types of liquids. For the case of condensate in 0.15 mm sand pack, Pre-Darcy flow was observed in the range of Re√k < 2.81 × 10−06, Red < 0.0014 and Rep < 0.0005. In addition to new liquids and gases that are investigated in this study, one of the differences between this study and previous ones, is investigation the relevance of Pre-Darcy flow to fluid properties in addition to rock properties for wide ranges of liquids and gases. The existence of Pre-Darcy flow means that, there is unknown opportunities for improved oil recovery in petroleum reservoirs. Also, accurate emission velocity is effective for reduction of soil pollution by hydrocarbon leakage. This velocity can be corrected by considering Pre-Darcy flow.

An overlooked play? Structure, stratigraphy and hydrocarbon prospectivity of the Carboniferous in the East Irish Sea–North Channel basin complex

Abstract Seismic mapping of key Paleozoic surfaces in the East Irish Sea–North Channel region has been incorporated into a review of hydrocarbon prospectivity. The major Carboniferous basinal and inversion elements are identified, allowing an assessment of the principal kitchens for hydrocarbon generation and possible migration paths. A Carboniferous tilt-block is identified beneath the central part of the (Permian–Mesozoic) East Irish Sea Basin (EISB), bounded by carbonate platforms to the south and north. The importance of the Bowland Shale Formation as the key source rock is reaffirmed, the Pennine Coal Measures having been extensively excised following Variscan inversion and pre-Permian erosion. Peak generation from the Bowland source coincided with maximum burial of the system in late Jurassic–early Cretaceous time. Multiphase Variscan inversion generated numerous structural traps whose potential remains underexplored. Leakage of hydrocarbons from these into the overlying Triassic Ormskirk Sandstone reservoirs is likely to have occurred on a number of occasions, but currently unknown is how much resource remains in place below the Base Permian Unconformity. Poor permeability in the Pennsylvanian strata beneath the Triassic fields is a significant risk; the same may not be true in the less deeply buried marginal areas of the EISB, where additional potential plays are present in Mississippian carbonate platforms and latest Pennsylvanian clastic sedimentary rocks. Outside the EISB, the North Channel, Solway and Peel basins also contain Devonian and/or Carboniferous rocks. There have, however, been no discoveries, largely a consequence of the absence of a high-quality source rock and a regional seal comparable to the Mercia Mudstone Group and Permian evaporites of the Cumbrian Coast Group in the EISB.

Integrated Consequence Modelling for Fire Radiation and Combustion Product Toxicity in offshore Petroleum Platform using Risk Based Approach

The processing area of offshore platform has high probability of leakage of hydrocarbons. Liquefied Natural Gas (LNG) is one of the most common hydrocarbon produced in offshore platforms. Leakage of LNG can cause pool fire, jet fire, flash fire or fire ball. Thermal radiations due to fire is the major source of damage to workers on board. But due to fire, various combustion product toxic gases are also produced that have both acute and chronic health effects. These toxic gases can cause incapacitation, increased heart rate, vomiting and even death. Predicting the human injury due to thermal radiations and concentration of toxic gases are the key issues. A risk based approach takes in to consideration the duration a worker spent on different location of offshore platform and also it has the additive ability to evaluate overall risk due to fire radiation and toxic gases. Grid based approach helps in better visualization of risk posed by fire radiation and combustion product toxic gases at different locations of platform. The current study proposed an integrated consequence modelling approach for fire and combustion product toxic gases using risk based and grid based approaches. The integrated accident is modelled using Computational Fluid Dynamics (CFD) code Fire Dynamics Simulator (FDS). The results showed that risk posed by thermal radiation is confined on sub cellar deck (lower deck) but estimated risk due to combustion product gas (carbon monoxide) on cellar deck (upper deck) has significant value that needs to be considered. The current approach would be useful for emergency preparedness plans and safety measures designs for offshore platforms.

3D seismic analysis of the AK Fault, Orange Basin, South Africa: Implications for hydrocarbon leakage and offshore neotectonics

A high-resolution 3D reflection seismic dataset was used to achieve a detailed description of the half-graben bounded AK Fault in the Ibhubesi gas field of the offshore Orange Basin. Seismic analysis of the fault involved the combination of both the conventional seismic interpretation and seismic attributes. The main objective of the study was to provide insights into hydrocarbon leakage and neotectonic activity along the west coast shelf of South Africa. The AK Fault is among the several half-graben bounded faults that formed in the Late Jurassic to Early Cretaceous during the separation of the South American and the African continents. The AK Fault consists of five seismically detectable segments, whose evolution reflects characteristics of both the “coherent” and the “isolated” end-members model of segmented fault origin. Diapiric structures that are direct indicators of vertical fluid movement were also observed along the AK Fault system, providing evidence of significant roles that the fault plays in promoting the vertical migration of hydrocarbon in the Orange Basin. Recent reactivation of the fault has also occurred along an oblique extensional regime that is dominated by normal dip-slip faulting, with minor shear components along the tips.

Enhanced subsea leakage detection with broadband active acoustic sensor system

For field re-activation, improved/enhanced oil recovery through injection of gas in reservoirs, and geological storage of CO2 (carbon dioxide), robust barriers must be provided and confirmed to avoid leakage. Natural seeps from the sea floor represents an additional challenge, as many detection systems will misinterpret them as an infrastructure leakage. Active acoustics (backscattering) has been successfully used for detection of even moderate underwater hydrocarbon gas releases at long ranges, using, e.g., scientific echosounders. However, CO2 leakage behavior is particularly complex and operations in cold and deep waters make such leakages difficult to detect with active acoustics, due to its behavior and low acoustic impedance in liquid phase. Methodology for detecting CO2 even in liquid phase is a prerequisite for many deep water operations, and at present no adequate technology exists for this purpose. In order to design an active acoustic system that can detect subsea leakage of hydrocarbons and CO2 in liquid phase, the behavior and backscattering by droplets as a function of environmental parameters and acoustic frequency is simulated. Theoretical backscattering is further compared with in situ acoustic and optical measurements of CO2, CH4 (methane), and air, released and measured at depths from 1300m to surface, using a custom built gas release and measurement frame.

Coupled stratigraphic and fault seal modelling used to describe trap integrity in the frontier Bight Basin, Australia

Top seals and faults represent key risks to trap integrity and therefore preservation of hydrocarbons in the frontier Ceduna Sub-basin, offshore Southern Australia. Due to a paucity of well data in the basin, to provide constraint to the stratigraphic distribution of the prospective Cretaceous deltaic and marine sequences, stratigraphic forward modelling was utilised to create facies, grain size and Vshale volumes. These modelled Vshale volumes were subsequently used to investigate the structural control(s) on potential hydrocarbon leakage and migration within key stratigraphic sequences in the sub-basin.A set of coarse (20 km horizontal resolution), large scale (1100 × 600 km) stratigraphic forward models simulated the deposition of Late Jurassic to Tertiary stratigraphic sequences in the sub-basin with an initial 1 Ma interval. Smaller (80 × 60 km), finer scale (0.5 km horizontal resolution, 200 ka interval), models focussing on the Tiger and Hammerhead Supersequences over the Trim 3D seismic survey were used to investigate fault seal and top seal frameworks, using shale gouge ratio and silt and shale thicknesses from Vshale volume. Four stratigraphic forward models were produced to match a range of estimates of Vshale derived from the Gnarlyknots-1A well, the only well penetrating the central Ceduna Sub-basin. These stratigraphies were in turn integrated into a geological model interpreted from the Trim 3D seismic survey creating a geocellular model to test potential migration and trapping scenarios for potential hydrocarbons generated in the sub-basin.Fault and top seal models from the most likely scenario suggest (i) restricted potential for structural trapping near the base of the Tiger Supersequence, (ii) the possible presence of a regional migration pathway associated with sandy shoreface deposits at the transition between the Tiger and Hammerhead Supersequences, and (iii) the association of intraformational top seals and increasing fault seal potential in the deltaic sediments of the Hammerhead Supersequence feasibly resulting in a series of stacked structural traps.

Acoustic waves in fluid-solid nested cylindrically layered structures: Theoretical investigation

Understanding the complex elastic-wave physics prevalent in fluid-elastic cylindrically-layered structures is of importance in many NDE fields, and most pertinently in the domain of well integrity evaluation in the oil and gas industry. Well construction requires lowering steel casings into the hole and cementing them to the wellbore as well as to each other so as to provide mechanical support and enable control over the channeling of the produced fluids—thus preventing unwanted leakage of hydrocarbons to the surface or shallow aquifers. Evaluating whether cement has cured and sealed the desired annuli between casing strings and between the outer string and rock formation is important to ascertain before putting the well in production. In this talk, we establish a mathematical framework to analyze the guided wave fields in a dual-string system embedded in infinite media—a configuration that is of great significance in oil field. We introduce a novel Sweeping Frequency Finite Element Modeling (SFFEM) method to investigate the dispersions and modal characteristics of the complex propagating signals synthesized over an axial array of receivers. The SFFEM provides for a flexible framework to study the modal sensitivities in a multi-string system with arbitrary eccentricity, azimuthal heterogeneities, and partial bonded interfaces.

Influence on moisture and hydrocarbons on conversion rate of tritium in catalytic reactors of fusion-DEMO detritiation system

ABSTRACTThoughtful consideration of abnormal events such as fire is required to design and qualify a detritiation system (DS) of a nuclear fusion facility. Since conversion of tritium to tritiated vapor over catalyst is the key process of the DS, it is indispensable to evaluate the effect of excess moisture and hydrocarbons produced by combustion of cables on tritium conversion rate considering fire events. We conducted demonstration tests on tritium conversion under the following representative conditions: (I) leakage of tritium, (II) leakage of tritium plus moisture, and (III) leakage of tritium plus hydrocarbons. Detritiation behavior in the simulated room was assessed, and the amount of catalyst to fulfill the requirement on tritium conversion rate was evaluated. The dominant parameters for detritiation are the concentration of hydrogen in air and catalyst temperature. The tritium in the simulated room was decreased for condition (I) following ventilation theory. An initial reduction in conversion rate was measured for condition (II). To recover the reduction smoothly, it is suggested to optimize the power of preheater. An increase in catalyst temperature by heat of reaction of hydrocarbon combustion was evaluated for condition (III). The heat balance of catalytic reactor is a point to be carefully investigated to avoid runaway of catalyst temperature.

Role of Faults in Hydrocarbon Leakage in the Hammerfest Basin, SW Barents Sea: Insights from Seismic Data and Numerical Modelling

Hydrocarbon prospectivity in the Greater Barents Sea remains enigmatic as gas discoveries have dominated over oil in the past three decades. Numerous hydrocarbon-related fluid flow anomalies in the area indicate leakage and redistribution of petroleum in the subsurface. Many questions remain unanswered regarding the geological driving factors for leakage from the reservoirs and the response of deep petroleum reservoirs to the Cenozoic exhumation and the Pliocene-Pleistocene glaciations. Based on 2D and 3D seismic data interpretation, we constructed a basin-scale regional 3D petroleum systems model for the Hammerfest Basin (1 km × 1 km grid spacing). A higher resolution model (200 m × 200 m grid spacing) for the Snøhvit and Albatross fields was then nested in the regional model to further our understanding of the subsurface development over geological time. We tested the sensitivity of the modeled petroleum leakage by including and varying fault properties as a function of burial and erosion, namely fault capillary entry pressures and permeability during glacial cycles. In this study, we find that the greatest mass lost from the Jurassic reservoirs occurs during ice unloading, which accounts for a 60%–80% reduction of initial accumulated mass in the reservoirs. Subsequent leakage events show a stepwise decrease of 7%–25% of the remaining mass from the reservoirs. The latest episode of hydrocarbon leakage occurred following the Last Glacial Maximum (LGM) when differential loading of Quaternary strata resulted in reservoir tilt and spill. The first modeled hydrocarbon leakage event coincides with a major fluid venting episode at the time of a major Upper Regional angular Unconformity (URU, ~0.8 Ma), evidenced by an abundance of pockmarks at this stratigraphic interval. Our modelling results show that leakage along the faults bounding the reservoir is the dominant mechanism for hydrocarbon leakage and is in agreement with observed shallow gas leakage indicators of gas chimneys, pockmarks and fluid escape pipes. We propose a conceptual model where leaked thermogenic gases from the reservoir were also locked in gas hydrate deposits beneath the base of the glacier during glaciations of the Hammerfest Basin and decomposed rapidly during subsequent deglaciation, forming pockmarks and fluid escape pipes. This is the first study to our knowledge to integrate petroleum systems modelling with seismic mapping of hydrocarbon leakage indicators for a holistic numerical model of the subsurface geology, thus closing the gap between the seismic mapping of fluid flow events and the geological history of the area.