Modelización de la inundación química de yacimientos petrolíferos

Se desarrollan dos modelos que predicen el petróleo recuperable mediante la inyección de sustancias químicas. Ambos consideran dos fases (acuosa u oleosa) y tres componentes (agua, petróleo y especie química). El flujo es horizontal, unidimensional e incompresible. La roca tiene propiedades uniformes y puede adsorber la sustancia química. Se supone equilibrio termodinámico a través de las fases. La dispersión y los gradientes de presión capilar son despreciables y además la composición de inyección es constante. Los modelos están gobernados por un sistema de ecuaciones diferenciales parciales no lineales: la ecuación de continuidad de cada componente y la ecuación de Darcy para el flujo bifásico. En el modelo más riguroso se resuelve el sistema de ecuaciones aplicando una técnica en diferencias finitas. En el modelo más simple se adicionan restricciones con el objeto de hallar soluciones analíticas. El objetivo de este trabajo es analizar la utilidad y las limitaciones del modelo simple. Se concluye que si bien las restricciones adicionadas no responden a la realidad, el modelo simple es capaz de representar los mecanismos físicos de desplazamientos más importantes y permite obtener una primera aproximación del petróleo recuperable que es el valor máximo de la recuperación verdadera.Peer Reviewe

Simulación numérica del flujo unidimensional de un gas real a través de un medio poroso

Se resuelve la ecuación diferencial de difusión para un gas real en un reservorio poroso e isotérmico. Este problema está representado por una ecuación diferencial no lineal. Esta se resuelve utilizando y comparando dos aproximaciones en diferencias finitas: 1.- Esquema explícito en transmisibilidades e implícito en presiones. 2.- Esquema implícito en transmisibilidades y presiones. Ambos esquemas se resuelven iterando sobre sus coeficientes variables; además se emplea el método de Newton-Raphson generalizado. Las resoluciones se comparan entre sí y con una solución analítica hallada por W.E. Culham et al. [1]. También se comparan los resultados numéricos con mediciones de una experiencia de laboratorio presentada por G.H. Bruce et al. [2]. Finalmente se analiza la influencia de la variación de las propiedades del gas con la presión, de la porosidad y permeabilidad sobre los perfiles de presión, de la porosidad y permeabilidad sobre los perfiles de presión, utilizando datos de un yacimiento de gas real hidrocarburo [3]. SUMMARY The differential equation for the difusión of real gas in a porous and isotermic medium, is solved. This process is represented by non linear differential equation. Two finite difference approximations have been applied and compared: 1.- Explicit in transmissibilities and implicit pressures. 2.- Implicit in transmissibilities and pressures. Both approximations have been solved by iteration on the variable coefficients, and also using the generalized method of Newton-Raphson. The results have been compared among them and with an analytic solution n obtained by W.E. Culham et al. [1]. Besides, the numerical solutions have also been compared among with laboratory results presented by G.H. Bruce et al. [2]. Finally, the influence of the variation of gas properties, porosity and permeability upon the calculated pressure is analyzed with data of a real hydrocarbon gas reservoir [3].Peer Reviewe

Effects of glycine supplementation at varying levels of methionine and cystine on the growth performance of broilers fed reduced crude protein diets

Two experiments were conducted to investigate gly addition to reduced crude protein corn-soybean meal (C-SBM) diets with varying levels of TSAA achieved by varying Met and Cys. The experiments were conducted with female Ross 708 broilers in brooder batteries from 0 to 18 d posthatching. Treatments had 6 replicates with 6 broilers/pen. Diets in all experiments were fed without or with gly supplementation to contain 2.32% total gly + Ser. All diets were C-SBM based and formulated to contained 1.27% standardized ileal digestible Lys supplemented with 0.20% Lys (0.394% Lys·SO4) and to meet or exceed the requirement of all nutrients except Met and Cys where appropriate. Experiment 1 consisted of 8 dietary treatments. Three ratios of Met to Cys (60:40, 50:50, and 40:60) were used on a mole for mole basis to achieve 0.063 mol of TSAA/kg of feed and a positive control with Met:Cys of 50:50 at 0.76 TSAA:Lys. glycine supplementation did not affect ADg or ADFI; however, g:F was increased (P = 0.003) with gly supplementation. An increase in Cys and a decrease in Met resulted in a decrease (P = 0.028) in ADg but had no effect on ADFI or g:F. In experiment 2, Met was kept constant at a marginal level of 0.45% and Cys was increased in 0.05% increments from 0.35 to 0.50%. glycine supplementation had no main effect on ADg, ADFI, or g:F; however, gly increased g:F at the lower levels of Cys but not at the higher levels (gly × Cys, P = 0.031). A linear decrease (P = 0.071) was found in ADFI with increasing Cys supplementation. These data indicate that gly increased g:F in female broilers fed suboptimal levels of Met and Cys but not at Cys levels at or above the requirement. This implies that the synthesis of Cys accounts for a portion of the increased g:F observed from gly supplementation in female broilers fed reduced CP C-SBM diets. © 2011 Poultry Science Association Inc

Influencia de la permeabilidad vertical en el flujo de petróleo hacia un pozo productor

Se describe el flujo bidimensional de petróleo a través de un reservorio heterogéneo mediante una ecuación parabólica en derivadas parciales, que es una extensión de la denominada ecuación de difusividad. Este modelo tiene interés práctico en ingeniería de reservorios: se utiliza para predecir la producción de un pozo de petróleo y también en la interpretación de ensayos de presión en pozos. La solución numérica de dicha ecuación se obtiene mediante una familia de esquemas de diferencias finitas que dependen de un parámetro 8, O 5 8 5 1. Una técnica basada en la expansión en serie de Taylor de funciones matriciales (TSMF) es usada para resolver el sistema de ecuaciones lineales resultante. El simulador numérico descrito se aplica para estudiar el comportamiento de reservorios de dos capas con valores típicos de permeabilidad vertical iguales o menores que los de permeabilidad horizontal. Específicamente, para un pozo de petróleo que produce a caudal constante, se analiza la influencia de la permeabilidad vertical en las respuestas de presión y caudal de cada capa. Se concluye que la permeabilidad vertical influye en las respuestas de presión y caudal a tiempos cortos e intermedios, por lo que debería ser tenida en cuenta tanto en el diseño como en la interpretación de los ensayos de presión en pozos.Peer Reviewe

Effects of body size on estimation of mammalian area requirements.

Accurately quantifying species' area requirements is a prerequisite for effective area-based conservation. This typically involves collecting tracking data on species of interest and then conducting home range analyses. Problematically, autocorrelation in tracking data can result in space needs being severely underestimated. Based on the previous work, we hypothesized the magnitude of underestimation varies with body mass, a relationship that could have serious conservation implications. To evaluate this hypothesis for terrestrial mammals, we estimated home-range areas with global positioning system (GPS) locations from 757 individuals across 61 globally distributed mammalian species with body masses ranging from 0.4 to 4000 kg. We then applied blockcross validation to quantify bias in empirical home range estimates. Area requirements of mammals 1, meaning the scaling of the relationship changedsubstantially at the upper end of the mass spectrum

Moving in the anthropocene: global reductions in terrestrial mammalian movements

Animal movement is fundamental for ecosystem functioning and species survival, yet the effects of the anthropogenic footprint on animal movements have not been estimated across species. Using a unique GPS-tracking database of 803 individuals across 57 species, we found that movements of mammals in areas with a comparatively high human footprint were on average one-half to one-third the extent of their movements in areas with a low human footprint. We attribute this reduction to behavioral changes of individual animals and to the exclusion of species with long-range movements from areas with higher human impact. Global loss of vagility alters a key ecological trait of animals that affects not only population persistence but also ecosystem processes such as predator-prey interactions, nutrient cycling, and disease transmission

Effects of body size on estimation of mammalian area requirements

Accurately quantifying species’ area requirements is a prerequisite for effective area‐based conservation. This typically involves collecting tracking data on species of interest and then conducting home‐range analyses. Problematically, autocorrelation in tracking data can result in space needs being severely underestimated. Based on previous work, we hypothesized the magnitude of underestimation varies with body mass, a relationship that could have serious conservation implications. To evaluate this hypothesis for terrestrial mammals, we estimated home‐range areas with GPS locations from 757 individuals across 61 globally distributed mammalian species with body masses ranging from 0.4 to 4,000 kg. We then applied block cross‐validation to quantify bias in empirical home‐range estimates. Area requirements of mammals 1, meaning the scaling of the relationship changed substantially at the upper end of the mass spectrum

One-Dimensional Modelling of Polymer Flood Performance. Analytical and Graphical Solutions

A graphical method for simulating linear polymer flooding is proposed. The method is based upon the analytical solution of Darcy's law and continuity equation which describe the two-phase, one-dimensional, incompressible flow of oil and polymer solution through the reservoir rock. Continuous polymer injection and polymer slug injection are considered. Several physical mechanisms determining microscopic displacement efficiency are taken into account: resistance factor, residual resistance factor, retention composed by adsorption and mechanical entrapment, and inaccessible pore volume. Other properties are not considered: mixing and dispersion, shear and thermal degradation. This analytical-graphical model closely reproduces linear laboratory oil displacement experiments. Consequently, it can be used by the Field Engineer to rapidly estimate the additional oil recoverable by a linear polymer flood

Aplicación del método inverso al análisis de ensayos de pozos petrolíferos

Se estiman parámetros característicos de un reservorio petrolíefro ajustando un modelo matemático a mediciones de presión realizadas durante un ensayo de pozo. Para lograrlo se utilizan técnicas de optimización cnon restricciones físicas en las variables. El modelo matemático usado es la ecuación de difusión, que rige el flujo radial de petróleo hacia el pozo productor en un reservorio isótropo, homogéneo y acotado. Se analizan tres ejemplos de ensayos de pozos en producción (presión en disminución). El objetivo de los dos primeros ejemplos es comparar cuatro técnicas de optimización: Davidson-Fletcher-Powell (DFP), Fletcher-Reeves (FR), Aproximaciones Quasi-Newton para el problema de mínimos cuadrados (AQN) y Levenberg-Marquardt (LM). Los parámetros buscados son porosidad y permeabilidad. Aplicando cualquiera de los cuatro métodos se obtienen valores óptimos únicos de dichos parámetros, pero el que presenta el mejor comportamiento es AQN. Entonces, esta técnica se aplica a un tercer ejemplo: un ensayo de caída de presión realizado en un pozo fracturado hidraúlicamente. También se obtienen valores óptimos únicos de los parámetros , que en este caso son permeabilidad, factor de daño y radio de drenaje; y se los compara con los proporcionados por los métodos gráficos tradicionales presentados por Matthews and Russell. SUMMARY Reservoir parameters are estimated by matching a mathematical model to pressure measurements taken during an oil well test. multivariate optimization techniques with physically realistic constraints on the parameters are used in order to obtain the best match. The mathematical model is the diffusivity equation which rules the single-phase radial flow of oil in an isotropic, homogeneous and bounded reservoir. Three examples of draw-down tests are shown. The purpose of the first two examples is to compare four optimization techniques: Davidson-Fletcher-Powell (DFP), Fletcher-Reeves (FR), Quasi-Newton Approximationfor the Least-Squares Problem (AQN) and Levenberg-Marquardt (LM) methods. Permeability and porosity are the parameters to be determined. The application of any of the four methods leads to unique values of optimal parameters, although AQN shows the best behavior finding the optimum. Therefore, this technique is applied in the third example which is an extended draw-down test runon a hydraulically fractured well to estimate the size of the oil accumulation. A unique ste of optimal parameters. permeability, skin factor and drainage radius is found. These parameters are compared with the results obtained by applying the traditional graphical methods presented by Matthews and Russell.Peer Reviewe