Exploratory Factor Analysis of Wireline Logs Using a Float-Encoded Genetic Algorithm

In the paper, a novel inversion approach is used for the solution of the problem of factor analysis. The float-encoded genetic algorithm as a global optimization method is implemented to extract factor variables using open-hole logging data. The suggested statistical workflow is used to give a reliable estimate for not only the factors but also the related petrophysical properties in hydrocarbon formations. In the first step, the factor loadings and scores are estimated by Jöreskog’s fast approximate method, which are gradually improved by the genetic algorithm. The forward problem is solved to calculate wireline logs directly from the factor scores. In each generation, the observed and calculated well logs are compared to update the factor population. During the genetic algorithm run, the average fitness of factor populations is maximized to give the best fit between the observed and theoretical data. By using the empirical relation between the first factor and formation shaliness, the shale volume is estimated along the borehole. Permeability as a derived quantity also correlates with the first factor, which allows its determination from an independent source. The estimation results agree well with those of independent deterministic modeling and core measurements. Case studies from Hungary and the USA demonstrate the feasibility of the global optimization based factor analysis, which provides a useful tool for improved reservoir characterization.     

Prévision rapide de l''extension d''une pollution dans quelques cas d''écoulement et de mode d''injection

The relationship between maximum concentration and longitudinal distance, independent of time, can determine the size of the area to be contaminated, under well-defined conditions of injection and flow in a saturated medium. The envelope curve for maximal concentrations is easily obtained as a function of the axial distance in non-dimensional variables in the cases of one- and two-dimensional uniform flow, as well as in those of radially symmetric converging or diverging flow.

Graphs providing relations between dimensionless variables (as described in the text) are given for the following cases:

1. (1) uniform flow with instantaneous discharge of a pollutant; measurement downstream of the injection point, no transverse dispersion;

2. (2) uniform flow with continuous injection of a pollutant; measurement downstream of the injection point, influence of transverse dispersion included;

3. (3) convergent radial flow towards a well; pollution caused by an instantaneous pointsource at some distance; and

4. (4) divergent radial flow from an injection point; pollution caused by instantaneous injection of a pollutant.

Résumé

L'expression de la concentration maximale en fonction de la distance et indépendamment du temps permet de déterminer l'extension d'une zone susceptible d'être contaminée lors de conditions bien définies d'injection d'un produit dangereux et d'écoulement en milieu saturé. La courbe enveloppe des maxima de concentration en fonction de la distance axiale est facilement exprimable sous forme adimensionnelle (abaques) dans le cas d'écoulements uniformes mono- et bi-dimensionnels (réponse dans l'axe), comme dans ceux d'écoulements purement cylindriques convergent ou divergent.     

Boundary-layer ozone depletion as seen in the Norwegian Arctic in spring

Several years of measurements of ozone, hydrocarbons, sulphate and meteorological parameters from Spitsbergen in the Norwegian Arctic are presented. Most of the measurements were taken on the Zeppelin Mountain at an altitude of 474 m a.s.l. The focus is the episodes of ozone depletion in the lower troposphere in spring, which are studied in a climatological way. Episodes of very low ozone concentrations are a common feature on the Zeppelin Mountain in spring. The low ozone episodes were observed from late March to the beginning of June. When the effect of transport direction was subtracted, the frequenty of the low ozone episodes was found to peak in the beginning of May, possibly reflecting the seasonal cycle in the actual depletion process. Analyses based on trajectory calculations show that most of the episodes occurred when the air masses were transported from W-N. Ozone soundings show that the ozone depletion may extend from the surface and up to 3–4 km altitude. The episodes were associated with a cold boundary layer beneath a thermally stable layer, suppressing mixing with the free troposphere. The concentration of several individual hydrocarbons was much lower during episodes of low ozone than for the average conditions. The change in concentration ratio between the hydrocarbons was in qualitative agreement with oxidation of hydrocarbons by Br and Cl atoms rather than by OH radicals.     

Atmospheric concentrations of nonmethane hydrocarbons at a North European coastal site

Two years of individual nonmethane hydrocarbon (NMHC) measurements at a rural site close to the south coast of Norway show that there was a distinct annual cycle with a late winter maximum and late summer minimum in the slowly reacting NMHCs acetylene, ethane, propane and i- and n-butane. The average January—March concentrations were a factor 2–4 higher than the July-September concentrations. Also ethene, propene and the pentanes show a similar annual cycle, but the individual scatter in the measurements in particular of propene, is large. The highest concentrations of NMHC were found in winter for easterly transport on a regional scale (out to 1500 km from the site), and for southeasterly transport in the summer.     

An evaluation of conditioning data for solute transport prediction

The large and diverse body of subsurface characterization data generated at a field research site near Oyster, Virginia, provides a unique opportunity to test the impact of conditioning data of various types on predictions of flow and transport. Bromide breakthrough curves (BTCs) were measured during a forced-gradient local-scale injection experiment conducted in 1999. Observed BTCs are available at 140 sampling points in a three-dimensional array within the transport domain. A detailed three-dimensional numerical model is used to simulate breakthrough curves at the same locations as the observed BTCs under varying assumptions regarding the character of hydraulic conductivity spatial distributions, and variable amounts and types of conditioning data. We present comparative results of six cases ranging from simple (deterministic homogeneous models) to complex (stochastic indicator simulation conditioned to cross-borehole geophysical observations). Quantitative measures of model goodness-of-fit are presented. The results show that conditioning to a large number of small-scale measurements does not significantly improve model predictions, and may lead to biased or overly confident predictions. However, conditioning to geophysical interpretations with larger spatial support significantly improves the accuracy and precision of model predictions. In all cases, the effects of model error appear to be significant in relation to parameter uncertainty.