Pyrolytic and provenance evaluation of organic matter from the tertiary niger delta basin, nigeria: implication on hydrocarbon generation.

The present work deals with evaluation of organic matter based on detailed Rock-Eval pyrolysis techniques studies to evaluate hydrocarbon generation potential of source rocks by collecting twenty- nine shale samples from well cuttings in the Tertiary Formations of the Niger Delta, Nigeria. The values of vitrinite reflectance (0.57–0.74%Ro) and maximum (Tmax: 420–445°C) confirmed that samples are at early maturity to matured stage enough to generate liquid and gaseous hydrocarbon. The cross-plot between hydrogen index (HI) and oxygen index (OI) atomic ratio indicates that samples were predominant in the bituminous rank and having kerogen Type III makes it suitable for hydrocarbon generation. Rock-Eval pyrolysis analysis (Types II-III and Type III kerogen) on shale samples from the Niger Delta reveals organic matter of predominantly terrestrial origin based on type III kerogen. The organic matter (OM) assemblages suggests a marine setting but dominated by terrestrial inputs likely related to fluvial processes which is function of most delta system. Based on high total organic carbon (TOC) value of 5.42wt% and Type III kerogen made the shale an excellent source rock, with gas-prone kerogen. The high OI, low total sulphur (TS) suggests terrestrially derived OM and deposition in an oxic and dysoxic shallow marine environment. In addition, HI and Tmax values describe the samples as a characteristic Type III dominant kerogen and potential to generate oil and gases while the Tmax, consistently indicate an immature to mature on the shale organic matter

The velocity field of baryonic gas in the universe

The dynamic evolution of the baryonic intergalactic medium (IGM) caused by the underlying dark matter gravity is governed by the Navier-Stokes equations in which many cooling and heating processes are involved. However, it has long been recognized that the growth mode dynamics of cosmic matter clustering can be sketched by a random force driven Burgers' equation if cooling and heating are ignored. Just how well the dynamics of the IGM can be described as a Burgers fluid has not been fully investigated probably because cooling and heating are essential for a detailed understanding of the IGM. Using IGM samples produced by a cosmological hydrodynamic simulation in which heating and cooling processes are properly accounted for, we show that the IGM velocity field in the nonlinear regime shows the features of a Burgers fluid, that is, when the Reynolds number is high, the velocity field consists of an ensemble of shocks. Consequently, (1) the IGM velocity $v$ is generally smaller than that of dark matter; (2) for the smoothed field, the IGM velocity shows tight correlation with dark matter given by $v \simeq s v_{dm}$, with $s<1$, such that the lower the redshift, the smaller $s$; (3) the velocity PDFs are asymmetric between acceleration and deceleration events; (4) the PDF of velocity difference $\Delta v=v(x+r)-v(x)$ satisfies the scaling relation for a Burgers fluid, i.e., $P(\Delta v)=(1 r^y)F(\Delta v/r^y)$. We find the scaling function and parameters for the IGM which are applicable to the entire scale range of the samples (0.26 - 8 h$^{-1}$ Mpc). These properties show that the similarity mapping between the IGM and dark matter is violated on scales much larger than the Jeans length of the IGM.Comment: 14 pages, 10 jpg-figures, accepted for publication in the Astrophysical Journal. References adde

Numerical Simulations of Highly Porous Dust Aggregates in the Low-Velocity Collision Regime

A highly favoured mechanism of planetesimal formation is collisional growth. Single dust grains, which follow gas flows in the protoplanetary disc, hit each other, stick due to van der Waals forces and form fluffy aggregates up to centimetre size. The mechanism of further growth is unclear since the outcome of aggregate collisions in the relevant velocity and size regime cannot be investigated in the laboratory under protoplanetary disc conditions. Realistic statistics of the result of dust aggregate collisions beyond decimetre size is missing for a deeper understanding of planetary growth. Joining experimental and numerical efforts we want to calibrate and validate a computer program that is capable of a correct simulation of the macroscopic behaviour of highly porous dust aggregates. After testing its numerical limitations thoroughly we will check the program especially for a realistic reproduction of various benchmark experiments. We adopt the smooth particle hydrodynamics (SPH) numerical scheme with extensions for the simulation of solid bodies and a modified version of the Sirono porosity model. Experimentally measured macroscopic material properties of silica dust are implemented. We calibrate and test for the compressive strength relation and the bulk modulus. SPH has already proven to be a suitable tool to simulate collisions at rather high velocities. In this work we demonstrate that its area of application can not only be extended to low-velocity experiments and collisions. It can also be used to simulate the behaviour of highly porous objects in this velocity regime to a very high accuracy.The result of the calibration process in this work is an SPH code that can be utilised to investigate the collisional outcome of porous dust in the low-velocity regime.Comment: accepted by Astronomy & Astrophysic

The Statistical Discrepancy between the IGM and Dark Matter Fields: One-Point Statistics

We investigate the relationship between the mass and velocity fields of the intergalactic medium (IGM) and dark matter. Although the evolution of the IGM is dynamically governed by the gravity of the underlying dark matter field, some statistical properties of the IGM inevitably decouple from those of the dark matter once the nonlinearity of the dynamical equations and the stochastic nature of the field is considered. With simulation samples produced by a hybrid cosmological hydrodynamic/N-body code, which is effective in capturing shocks and complicated structures with high precision, we find that the one-point distributions of the IGM field are systematically different from that of dark matter as follows: 1.) the one-point distribution of the IGM peculiar velocity field is exponential at least at redshifts less than 2, while the dark matter velocity field is close to a Gaussian field; 2.) although the one-point distributions of the IGM and dark matter are similar, the point-by-point correlation between the IGM and dark matter density fields significantly differs on all scales and redshifts analyzed; 3.) the one-point density distributions of the difference between IGM and dark matter fields are highly non-Gaussian and long tailed. These discrepancies violate the similarity between the IGM and dark matter and cannot be explained simply as Jeans smoothing of the IGM. However, these statistical discrepancies are consistent with the fluids described by stochastic-force driven nonlinear dynamics.Comment: Accepted in Astrophysical Journal Supplement Serie

High-resolution regional gravity field recovery from Poisson wavelets using heterogeneous observational techniques

2016-2017 > Academic research: refereed > Publication in refereed journal201804_a bcmaVersion of RecordPublishe

Seasonal glacier and snow loading in Svalbard recovered from geodetic observations

We processed time-series from seven Global Navigation Satellite System (GNSS) stations and one Very Long Baseline Interferometry (VLBI) station in Svalbard. The goal was to capture the seasonal vertical displacements caused by elastic response of variable mass load due to ice and snow accumulation. We found that estimates of the annual signal in different GNSS solutions disagree by more than 3 mm which makes geophysical interpretation of raw GNSS time-series problematic. To overcome this problem, we have used an enhanced Common Mode (CM) filtering technique. The time-series are differentiated by the time-series from remote station BJOS with known mass loading signals removed a priori. Using this technique, we have achieved a substantial reduction of the differences between the GNSS solutions. We have computed mass loading time-series from a regional Climatic Mass Balance (CMB) and snow model that provides the amount of water equivalent at a 1 km resolution with a time step of 7 d. We found that the entire vertical loading signal is present in data of two totally independent techniques at a statistically significant level of 95 per cent. This allowed us to conclude that the remaining errors in vertical signal derived from the CMB model are less than 0.2 mm at that significance level. Refining the land water storage loading model with a CMB model resulted in a reduction of the annual amplitude from 2.1 to 1.1 mm in the CM filtered time-series, while it had only a marginal impact on raw time-series. This provides a strong evidence that CM filtering is essential for revealing local periodic signals when a millimetre level of accuracy is required