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Lausanne, Switzerland

Lee S.H.,Chevron | Jensen C.,Chevron | Lunati I.,UNIL
ECMOR 2012 - 13th European Conference on the Mathematics of Oil Recovery | Year: 2012

Shale gas production is effectively enhanced by multi-staged hydraulic fracturing from horizontal wells. The characteristics of the generated fracture networks are crucial to estimating shale gas production rate and consequently determine the economics of shale gas projects. The location and geometry of hydraulic fractures are reasonably well known; whereas the secondary fractures, generated during the fracturing process, are numerous and can only be described by a stochastic framework. We thus propose three groups of fractures to be modeled: (1) hydraulic fractures whose location and geometry can be deterministically approximated, (2) smaller induced/natural fracture subset connected between hydraulic fractures, and (3) disconnected small scale (natural or induced) fractures. As the permeability contrast between fractures and micro or nano pores in shale is very large, the gas production rate will be controlled by the diffusion process that feeds gas from shale to fracture networks and by the pressure-drop propagation mechanism in the formation. The transport of gas from micro or nano pores to the fracture network comprises two mechanisms: (1) molecular (or density) diffusion and (2) convective flow due to gas compressibility. We derive a simple numerical solution for the advection/diffusion equation, coupled with statistical distribution of micro and nano pores. Source


Menichelli E.,Nofima Materials AS | Menichelli E.,Norwegian University of Life Sciences | Olsen N.V.,Nofima Materials AS | Meyer C.,UNIL | Naes T.,Nofima Materials AS
Food Quality and Preference | Year: 2012

This paper proposes a methodology for combining extrinsic and intrinsic attributes in consumer testing of food products. The paper attempts to focalize on the main sensory drivers of liking or choice probability and their interaction with additional information, and to investigate effects related to the population as well as how consumers differ in their assessments. Two different data analysis approaches are considered and compared on choice probability data from a consumer study of orange juice. One of the methods is based on mixed model ANOVA of individual differences, the other approach is based on fuzzy clustering related to regression residuals. The main results show that extrinsic consumer attributes are easily and efficiently related to the sensory properties of products, allowing for interactions. The methodology estimates population or segment means and gives an overview of individual differences in choice intent or liking. © 2011 Elsevier Ltd. Source


Neves P.,UNIL | Neuffer N.,Service des Urgences | Yersin B.,Service des Urgences
Revue Medicale Suisse | Year: 2011

Alcohol abuse causes numerous medical and social problems. In spite of the decrease of the global consumption of alcohol per capita in Switzerland during the last years, the cases of massive alcoholic poisoning seem increasing in emergency departments. Very few data is available at the moment on this phenomenon. The present article focuses on this problem within the framework of the emergency department of the CHUV. It aims at bringing to light on the sociodemographic and medical characteristics, as well as on the characteristics of the stay of these patients who are admitted with such a problem, to have a global vision of this phenomenon. Source


Lee S.H.,Chevron | Jensen C.L.,Chevron | Lunati I.,UNIL
Society of Petroleum Engineers - SPE Reservoir Simulation Symposium 2015 | Year: 2015

Gas flow through fractured nano-porous shale formations is complicated by a hierarchy of structural features and fluid transport mechanisms. Structural features include tight porous rock with a variety of fractures. Gas transport mechanisms include self diffusion, Knudsen diffusion, advection, gas expansion, adsorption, and slippage effects at the pore walls. In nanopores, as encountered in tight shale gas reservoirs, the effects of diffusion can overcome advection and should be included in reservoir flow calculations. As the permeability of shale is very low, conventional reservoir simulation modeling and production estimation methods, which are designed for fluid-flow processes dominated by viscous forces, may not be reliable to predict the reservoir production rate. We present a pore-based mechanistic model (the Bundle of Dual-Tube Model, BoDTM), which includes complex gas dynamics in fractured nano- porous shale formations. The pore-based model provides a quick and reliable means for modeling tight rock gas flow that includes known and uncertain reservoir properties, such as rock permeability, diffusion, pore volume, pore throat size, rock tortuosity and fracture characteristics. Gas flow is modeled in the shale matrix and production rate is estimated with a simple bundle of dual-tubes. Each dual-tube idealizes a gas pathway formed by pore bulbs and throats and is characterized by two diameters (a conductive diameter and a storage diameter) and one length. The two diameters permit modeling slow recovery of large gas volumes; the tube length takes into account the pathway length from the matrix into the fracture network, which is the length that controls the travel time and the production rate. To construct the BoDTM, a statistical estimate of the fracture-network and shale-matrix parameters is necessary. Production rate is controlled by flow from the tight shale rock matrix (which has the largest storage capacity but the lowest diffusivity) into the fracture network, and we assume that gas in the fractures is produced instantaneously. Applying statistical distribution functions, we examine the effect of model input properties on gas production. By applying the BoDTM to field data from the Bamett and Fayetteville Plays, we demonstrate that the model provides a means to quickly assess gas production rates from shale formations. Copyright © 2015 Society of Petroleum Engineers. Source


Olsen N.V.,430 As | Menichelli E.,430 As | Menichelli E.,Norwegian University of Life Sciences | Meyer C.,UNIL | Naes T.,430 As
Appetite | Year: 2011

The objective of this article is to compare product quality and brand choice for private labels (PL) and national brands (NB). Over the past two decades, PL have gained larger and larger share of grocery sales, and nowadays PL play a crucial part in the European food retail sector. Since it is stated that most PL have moved on from being mostly low cost me-too products to become also premium products, we want to investigate if objective and perceived quality of PL fits the quality of NB. Four hypotheses are stated and tested on orange juice data from Norway. A trained sensory panel and consumers (n= 105) evaluated six juice samples that vary according to three factors. These factors were (1) Brand (PL and NB), (2) Treatment (Gentle heat treatment and Pasteurized) and (3) Pulp (with and without). Principal component analysis, two-way ANOVA, and PLS regression were conducted, and the results indicate that variation in quality exists both among PL and NB, there is a large discrepancy between blind liking and brand choice, and that consumers with a positive attitude towards PL are more likely to choose a PL instead of a NB. © 2011 Elsevier Ltd. Source

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