Characterization of fractured reservoirs using a consistent stiffness‐permeability model: focus on the effects of fracture aperture

In this paper we propose a method for the characterization of naturally fractured reservoirs by quantitative integration of seismic and production data. The method is based on a consistent theoretical frame work to model both effective hydraulic and elastic properties of fractured porous media and a (non‐linear) Bayesian method of inversion that provides information about uncertainties as well as mean (or maximum likelihood) values. We model a fractured reservoir as a porous medium containing a single set of vertical fractures characterized by an unknown fracture density, azimuthal orientation and aperture. We then look at the problem of fracture parameter estimation as a non‐linear inverse problem and try to estimate the unknown fracture parameters by joint inversion of seismic amplitude versus angle and azimuth data and dynamic production data. Once the fracture parameters have been estimated the corresponding effective stiffness and permeability tensors can be estimated using consistent models. A synthetic example is provided to clearly explain and test the workflow. It shows that seismic and production data complement each other, in the sense that the seismic data resolve a non‐uniqueness in the fracture orientation and the production data help to recover the true fracture aperture and permeability, because production data are more sensitive to the fracture aperture than the seismic data.     

Emotional and cognitive factors influencing flood preparedness in Dire Dawa town,Ethiopia

Traditional approaches to risk communication ignore the emotional, cognitive and social factors that interact to influence the meaning people attribute to hazards and protective actions. The aim of this study was to investigate the emotional and cognitive factors predicting preparedness intention and community’s preparedness for flood hazards. A cross-sectional study was conducted between June and July 2015, in Dire Dawa town, Ethiopia. Using stratified systematic random sampling, a structured questionnaire was administered to individuals aged 18 and over in 660 households. Data were analyzed using structural equation modeling (SEM) (STATA version 13.0). The study participants’ mean age was 34 years, ranging from 18 to 80 (SD?=?12) with equal gender balance. SEM analysis revealed that the total effects of preparedness intention (path coefficient (β)?=?0.202, 95% CI: [0.036, 0.369]), past flood disaster experience (β?=?0.034, 95% CI: [0.008, 0.061]), trust (β?=?0.100, 95% CI: [0.059, 0.142]), anxiety (β?=?0.026, 95% CI: [0.018, 0.034), positive outcome expectancy (β?=???0.139, 95% CI: [??0.253, ??0.026]), negative outcome expectancy (β?=?0.105, 95% CI: [0.062, 0.149]), perceived flood likelihood (β?=?0.049, 95% CI: [0.012, 0.086]) and consequence (β?=???0.040, 95% CI: [??0.077, ??0.003]) on community preparedness for flood hazards were statistically significant. The main implication of these findings is that people affected by hazard events in the past experience more anxiety and are more likely to participate in community preparedness activities than those who were not affected.     

Multivariate approach to estimate colour producing agents in Case 2 waters using first-derivative spectrophotometer data

The complex composition and distribution of colour producing agents (CPAs) in turbid aquatic environments such as the Western Basin of Lake Erie (WBLE) presents a challenge to the application of remote sensing data for differentiating among in-water constituents and estimating their concentrations independently. In this study, multivariate procedures are applied to lab-based spectrophotometer data to estimate the concentration of chlorophyll-a and suspended matters in the WBLE. Principal Component Analysis of first-derivative transformed hyper-spectral data from the spectrophotometer extracted three significant spectral components for each cruise, explaining up to 88% of the spectral variability. Spectral matching using reference spectra indicated that two of the extracted patterns represent signatures of in-water constituents that govern the optical properties of the WBLE, namely, cyanobacteria and diatoms associated with green algae. The spectrophotometer data clearly revealed known spectral features associated with phytoplankton, such as the absorption minima near 550 and 700 nm, which can be attributed to the minimum of absorption and fluorescence of chlorophyll-a, respectively. The method also extracted the absorption peaks due to chlorophyll-a, near 670 nm, and due to phycocyanin, near 620 nm. Principal component regression of chlorophyll-a on the PC scores indicated that 63.4% of variation of chlorophyll-a in the WBLE can be explained by two components. Factors 2 and 3 explain 60% of the joint spatiotemporal variability of suspended matters in the WBLE. The results illustrate the potential of multivariate technique applied to remote sensing data in isolating the patterns that represent constituents in turbid Case 2 waters.     

Geological and Geochemical Investigation of Three Ophiolite‐Hosted Manganese Prospects,Southeast of Birjand,South Khorasan,East of Iran

The studied ophiolite‐hosted manganese prospects are located in southeast of Birjand, South Khorasan, in the east of Iran. The manganese ores within the ophiolitic sequence in this region occur as small discrete patches, associated with radiolarian chert and shale. Manganese ores in the host rocks are recognizable as three distinct syngenetic, diagenetic, and epigenetic features. The syngenetic manganese ores occurred as bands associated with light‐red radiolarian chert. The diagenetic Mn ores occurred as lenses accompanied by dark‐red to brown radiolarian chert. The epigenetic Mn ores occurred as veins/veinlets within the green radiolarian shale. The major manganese ore minerals are pyrolusite, braunite, bixbyite, ramsdellite, and romanechite showing replacement, colloidal, and brecciated textures. The high mean values of Mn/Fe (15.32) and Si/Al (15.65), and the low mean concentration values of trace elements, such as Cu (85.9 ppm), Ni (249.9 ppm), and Zn (149 ppm), as well as the high concentration values of Si, Fe, Mn, Ba, Zn, Sr, and As in the studied manganese ores furnished sufficient evidence to postulate that the sea‐floor Mn‐rich hydrothermal exhalatives were chiefly responsible for the ore formation, and the hydrogenous processes had negligible role in generation of the ores. The further geological and geochemical evidence also revealed that the ores deposited on the upper parts of the ophiolitic sequence by submarine exhalatives. The intense hydrothermal activities caused leaching of elements such as Mn, Fe, Si, Ba, As and Sr from the basaltic lavas (spilites). After debouching of the sea‐floor exhalatives, these elements entered the sedimentary basin. The redox conditions were responsible for separation of Fe from Mn.     

Another look at the 1993 and 1995 Gulf of Aqaba earthquakes from the analysis of teleseismic waveforms

In this work we estimated the source process and the source parameters of the 1993 and 1995 Gulf of Aqaba earthquakes. To investigate the source process of both events, we inverted the teleseismic P- and SH-waveform data using an iterative technique in which the rupture is modeled as a series of point source subevents with varying mechanisms. The main source process of the 1993 event can be explained by two subevents with essentially the same mechanism. These two subevents had different focal depths. The second subevent was about 5 s later than the first one and about 70% of the moment rate released with the second one. The total rupture duration time was about 12 s. Our solution for the 1995 Gulf of Aqaba earthquake indicated that the event consists of three subevents with various fault geometries and about 60% of the moment released by the second subevent. The first subevent occurred at a depth of 13 km, and was followed after 9 s by the second one at a depth of 11 km; the third subevent, at a depth of 9 km occurred 19 s after the second one. The total duration of the earthquake rupture process was about 18.7 s. The obtained mechanisms for the 1993 and 1995 Gulf of Aqaba earthquakes are well correlated with the structural setting of the Gulf of Aqaba.     

Anisotropic permeability in fractured reservoirs from frequency‐dependent seismic Amplitude Versus Angle and Azimuth data

Attempts have previously been made to predict anisotropic permeability in fractured reservoirs from seismic Amplitude Versus Angle and Azimuth data on the basis of a consistent permeability‐stiffness model and the anisotropic Gassmann relations of Brown and Korringa. However, these attempts were not very successful, mainly because the effective stiffness tensor of a fractured porous medium under saturated (drained) conditions is much less sensitive to the aperture of the fractures than the corresponding permeability tensor. We here show that one can obtain information about the fracture aperture as well as the fracture density and orientation (which determines the effective permeability) from frequency‐dependent seismic Amplitude Versus Angle and Azimuth data. Our workflow is based on a unified stiffness‐permeability model, which takes into account seismic attenuation by wave‐induced fluid flow. Synthetic seismic Amplitude Versus Angle and Azimuth data are generated by using a combination of a dynamic effective medium theory with Rüger's approximations for PP reflection coefficients in Horizontally Transversely Isotropic media. A Monte Carlo method is used to perform a Bayesian inversion of these synthetic seismic Amplitude Versus Angle and Azimuth data with respect to the parameters of the fractures. An effective permeability model is then used to construct the corresponding probability density functions for the different components of the effective permeability constants. The results suggest that an improved characterization of fractured reservoirs can indeed be obtained from frequency‐dependent seismic Amplitude Versus Angle and Azimuth data, provided that a dynamic effective medium model is used in the inversion process and a priori information about the fracture length is available.