Pore-scale analyses of heterogeneity and representative elementary volume for unconventional shale rocks using statistical tools

We express our appreciations to the Petroleum Technology Development Fund, Nigeria (PTDF), for funding this work.Peer reviewedPublisher PD

Data Analysis and Neuro-Fuzzy Technique for EOR Screening : Application in Angolan Oilfields

This study is sponsored by the Angolan National Oil Company (Sonangol EP) and the authors are grateful for their support and the permission to use the data and publish this manuscriptPeer reviewedPublisher PD

Simulation of pore-scale flow using finite element-methods

I present a new finite element (FE) simulation method to simulate pore-scale flow. Within the pore-space, I solve a simplified form of the incompressible Navier-Stoke’s equation, yielding the velocity field in a two-step solution approach. First, Poisson’s equation is solved with homogeneous boundary conditions, and then the pore pressure is computed and the velocity field obtained for no slip conditions at the grain boundaries. From the computed velocity field I estimate the effective permeability of porous media samples characterized by thin section micrographs, micro-CT scans and synthetically generated grain packings. This two-step process is much simpler than solving the full Navier Stokes equation and therefore provides the opportunity to study pore geometries with hundreds of thousands of pores in a computationally more cost effective manner than solving the full Navier-Stoke’s equation. My numerical model is verified with an analytical solution and validated on samples whose permeabilities and porosities had been measured in laboratory experiments (Akanji and Matthai, 2010). Comparisons were also made with Stokes solver, published experimental, approximate and exact permeability data. Starting with a numerically constructed synthetic grain packings, I also investigated the extent to which the details of pore micro-structure affect the hydraulic permeability (Garcia et al., 2009). I then estimate the hydraulic anisotropy of unconsolidated granular packings. With the future aim to simulate multiphase flow within the pore-space, I also compute the radii and derive capillary pressure from the Young-Laplace equation (Akanji and Matthai,2010

Studies on the biology of dipterous stem-boring larvae in grasses

Imperial Users onl

Multi-Index Monte Carlo: When Sparsity Meets Sampling

We propose and analyze a novel Multi-Index Monte Carlo (MIMC) method for weak approximation of stochastic models that are described in terms of differential equations either driven by random measures or with random coefficients. The MIMC method is both a stochastic version of the combination technique introduced by Zenger, Griebel and collaborators and an extension of the Multilevel Monte Carlo (MLMC) method first described by Heinrich and Giles. Inspired by Giles's seminal work, we use in MIMC high-order mixed differences instead of using first-order differences as in MLMC to reduce the variance of the hierarchical differences dramatically. This in turn yields new and improved complexity results, which are natural generalizations of Giles's MLMC analysis and which increase the domain of the problem parameters for which we achieve the optimal convergence, $\mathcal{O}(\text{TOL}^{-2}).$ Moreover, in MIMC, the rate of increase of required memory with respect to $\text{TOL}$ is independent of the number of directions up to a logarithmic term which allows far more accurate solutions to be calculated for higher dimensions than what is possible when using MLMC. We motivate the setting of MIMC by first focusing on a simple full tensor index set. We then propose a systematic construction of optimal sets of indices for MIMC based on properly defined profits that in turn depend on the average cost per sample and the corresponding weak error and variance. Under standard assumptions on the convergence rates of the weak error, variance and work per sample, the optimal index set turns out to be the total degree (TD) type. In some cases, using optimal index sets, MIMC achieves a better rate for the computational complexity than the corresponding rate when using full tensor index sets..

Current and Future Implications of the Coups for Women in Fiji

The impact on women of the two military coups in Fiji is the focus of this paper. Essentially, the coups have simultaneously generated new problems for women while reinforcing the existing economic, ideological, and polit-ical conditions that sustained and reproduced women's unequal position in Fiji society. Undoubtedly, the coups have had profound effects on women-some blatant and obvious, others more subtle. As a direct result of the coups, women's economic position has wors-ened, their political activity has suffered a major setback, and they are confronted by increased violence and additional constraints on their phys-ical and social space. Any gains women had made in the previous decade are fast disappearing, and prospects for future advancement are severely threatened. The heightened political momentum of the women's move-ment immediately prior to the coup has been disrupted and is suffering from an increased workload for the leaders as well as the constraints of operating in a repressive political climate. In this paper I explore some of the obvious and not-so-obvious ramifi-cations of the coups for women in Fiji. To illustrate the various implica-tions, the paper is divided into three sections: the economic impact, the social impact, and the impact on the women's movement. Where appropriate, the different impacts on ethnic Fijian and Indo-Fijian women are highlighted, but in general my comments apply to most women in Fiji. THE ECONOMIC IMPACT ON WOMEN In the postcoup period, Fiji suffered major economic decline as the direct result of the coups. The downturn in the economy has created immens

Quality Assessment of Some Groundwater Samples in Ogbomoso Metropolis, Southwest Nigeria

This study examines the physico-chemical and microbiological attributes of water samples obtained from ten boreholes that were sampled twice a month for a period of five months. The physico-chemical attributes revealed that the ammonia, manganese, nitrate, nitrite, fluoride, chloride contents, conductivity and total dissolved solids were below the permissible levels. However, total alkalinity and total hardness values of some water samples were higher than the permissible levels, while all the water samples had BOD and COD values that were higher than the permissible levels. The pH of water samples ranged from 5.8-6.9, showing that only two samples fell within the permissible levels. Similarly, the temperature ranged from 31.5-35.4 oC, with only two samples having values that fell within the permissible levels. The microbial quality of the water samples indicates extensive microbial contamination involving heterotrophic bacteria, coliforms, yeasts/molds, staphylococci, and Shigella. However, Salmonella was not isolated in this study. Bacterial isolates such as Proteus, Escherichia, Shigella, Streptococcus, Staphylococcus, Bacillus, Pseudomonas, Enterobacter, and Klebsiella with multiple-drug resistance ranging from 2-8 were encountered. The safety of the borehole water can be enhanced through regular cleaning, disinfection of storage tanks and further treatment by end-users to ensure the potability of water. This study provides baseline data with regard to the quality of underground water within Ogbomoso metropolis, Nigeria. Keywords: ground water, boreholes, microbiology, physico-chemical attributes, antibiotic resistanc

Syndromic surveillance: A necessary public health tool

AbstractOf late much has been said about emerging infectious diseases and the threat of bioterrorism. The focus has been on continuous public health surveillance for early detection of outbreaks and potential threats. Preparedness is the way forward and relevant institutions and organizations need to make the necessary investments early. Familiarity, good coordination, active participation and a change of mindset amongst personnel is crucial to make the system work. We also share a general approach to using electronic Emergency Department data for syndromic surveillance