Multicomponent 3-D characterization of a coalbed methane reservoir

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SITE 1NVESTIGATIONS:GEOPHYSICS

and even obstructs direct lithologic mapping. The Calanas area in southwest Spain includes all these properties and was selected for geologic investigation using a multiple-source remotely sensed dataset. (from Author)

Geophysical techniques 968185 Earth work ANON, Ground Engineering, 29(4), 1996, pp 18-28. This issue focuses on geophysics and its application to geotectmical engineering. Methods and practises are outlined, problems identified and solutions offered. A range of recent case studies include the use of resistivity imaging to detect cavities and subsidence features, the application of ground penetrating radar to site investigations, various use of tomographic techniques, geophysical techniques for the study of contaminated land, gravity surveys, magnetic mapping, seismic surveys and geophysical borehole logging. (S.E.Long) 968186 Application of ground geophysical data to uranium mineralization in the El-Missikat area, central Eastern Desert, Egypt E. M. Elkattan, H. M. Abdulhadi, S. I. Rabie & H. I. E. I&anein, Journal of African Earth Sciences, 22(l), 1996, pp - . The El-Missikat prospect lies in the Eastern Desert of Egypt, 85 km from Qena along the river Nile. The importance of the study area comes from previous studies which prove that the area has radioactive mineralization zones at the northeastern periphery of G. El-Missikat. The previous studies concluded that the radioactive mineralization was mostly associated with sulphides, especially at the reduction zones. These sulphides give a good response to electrical or electromagnetic techniques. Accordingly, the present study uses self potential, electrically induced polarization and horizontal loop electromagnetic surveys to explore the extension of the mineralization zones at the subsurface. (from Authors) 968187 Rovaniemen kaatopaikan geofysikaalinen ja geokemiailinen ymparistotutkimus (Enviromnental study of the refuse dump at Rovaniemi by geophysical and geochemical methods) P. Hannula & E. Lanne, Report of Investigation - Geological Survey of Finland, 128, 1995, 30 pp. From the airborne geophysical survey of the Rovaniemi region, a weak electrical conductivity anomaly was obtained that was associated with the anomaly of the Mantyvaara refuse dump, northwest of Rovaniemi. In order to explain the anomaly sources, electromagnetic, electric and seismic ground surveys were carried out in summer of 1993. Also geochemical samples were collected for the analyses of inorganic and organic substances. The results of the study indicate that the dump may be classified as a potential risk site from which leakage of harmful substances can be assumed. (from English summary) 968188 Multicomponent 3-D characterization of a coalbed methane reservoir E. L. Shuck, T. L. Davis & R. D. Benson, Geophysics, 61(2), 1996, pp 315-330. A multiwmponent 3-D seismic survey was acquired to aid in walbed methane reservoir characterization. Coalbed reservoir heterogeneities, including isolated pressure cells, zones of increased fracture density, and variable fracture directions, have heen interpreted through the analysis of the multicomponent data and integration with petrophysical and _ _ reservoir engineering studies. Strike-slip-faults have been identified bv structural interoretation of the seismic data. The analysis of-polarizations, &eltimes, and reflection amplitudes from the shear-wave seismic data has allowed the

identification of zones of variable fracture direction and fracture density. There is good agreement between stresses inferred from the structural interpretation and those indicated by the shear-wave polarizations. New methods have been developed for the statistical analysis of prestack shear-wave polarizations, poststack polarizations, and the accurate determination of traveltime anisotropy. Shear-wave anisotropy has been quantified over the reservoir zone using both traveltime and thin-bed reflection response with excellent agreement between the two methods. Crack densities wmputed from the anisotropy show two regions of high crack density. The potential for monitoring production of coalbed methane reservoirs using multiwmponent seismology is discussed. (from Authors) 968189 Survey boost from vertical thinking I. Essau, Offshore Engineer, February, 1996, pp 28-29. Describes vertical cable seismic (VCS) technology, originally developed for antisubmarine warfare, and its potential for offshore oil and gas exploration. It has been applied to Texaco’s Strathspey Field in the North Sea and is now being used on the deepwater Fuji discovery in the Gulf of Mexico. The technology offers significant advantages for imaging subsalt oil and gas prospects: it can be used with 3D pre-stack depth migration tools. Other advantages include the ability to work in rough seas and improved signal to noise ratio compared with conventional technology. It cannot, however, be used in shallow waters. (J.M.McLaughlin) 9681% Seismic reflection, borehole and outcrop geometry of late Wisconsin tills at a proposed landfill near Toronto, Ontario J. I. Boyce, N. Eyles & A. Pugin, Canadian Journal of Earth Sciences, 32(9), 1995, pp 1331-1334. Reports the results of a detailed shallow seismic reflection investigation of a proposed 275 ha landfill site 40 km northeast of Toronto, where previous hydrochemical analysis and hydrogeological monitoring identified rapid vertical recha@e 07 w&aminated surface waters through Late Wisconsin tills UD to 60 m thick. Seismic reflection nrofiles identify the pm&ice of well-defined reflectors within the Northern till, which are correlated in outcrop with laterally extensive erosion surfaces overlain by sheet-like sands and gravels, and boulder concentrations. Erosion surfaces and associated sediments provide potential ‘hydraulic windows’ for the movement of surface contaminants through the till into underlying aquifers. (from Authors) 968191 Impact of the seismic ‘while drBI.ing’ technique on exploration wells F. Miranda 8c 6 others, First Break, 14(2), 1996, pp 55-68. Vertical seismic profiles are an extremely effective seismic tool for surveying the area around a well. Conventional surveying techniques in which drilling is interrupted and a geophone is conveyed downhole, imply high costs and serious operating risks. Passive listening at the surface,‘which uses the noise produced by the bit during drilling as a seismic source for producing reciprocal VSPs, helps to overwme these ditliculties. The experimental system known as SEISBIT, designed and implemented by AGIP and OGS, allows acquisition and pre-processing of data directly in the field in order to obtain a dataset which can be urocessed bv means of standard VSP packages. The results-obtained during an operational test carried out for setting up the system, are described below. (from Authors) 968192 The use of surface waves in the determination of ground stiffness profiles M. C. Matthews, V. S. Hope & C. R. I. Clayton, Proceedings - ICE: Geotechnical Egineering, 119(2), 1996, pp 84-95. Increasing use is being made of seismic velocity measurements to ascertain the variation of stiffness with depth in the design