Relation between seismic source parameters and mechanical properties of rocks: A case study     

Bruno Feignier  Jean-Robert Grasso 《Pure and Applied Geophysics》1991,137(3):175-199

This study attempts to determine the relation between source parameters and mechanical properties of the rock matrix in which the microseismic events occur. For this purpose, accurate geological, mechanical and seismological data were acquired on a gas field experiencing induced seismicity due to its reservoir pressure drop. More than 30 deep boreholes (depth greater than 4 km) are concentrated in a 10×10×5 km volume, providing core samples for both geological and mechanical assessment. In this study, we focus on induced seismic events recorded by the local seismic network, over a three-year-long period. Characteristics of the seismic sources were obtained using spectral analysis and a dynamic model of failure. Results point out correlation between physical parameters of the seismic sources and the geomechanical properties of the rocks involved. Maximal static stress drops are found to be associated with the mechanical strength of the geological strata where the rupture occurs. The fracture size, using a circular model of failure, is also found to be dependent on the geomechanical setting. It is found that the size of the seismic fractures is dependent on the layer thickness and the prefracturation of the medium, both factors influencing the extension of preexisting discontinuities. The parameters of the seismic sources also show important changes when the gas reservoir is reached. The reservoir unit experienced a 45 MPa pore fluid pressure drop over a period of 20 years.  相似文献   

Cookeite LiAl4(Si3Al)O10(OH)8: Experimental study and thermodynamical analysis of its compatibility relations in the Li2O−Al2O3−SiO2−H2O system     

Olivier Vidal  Bruno Goffé 《Contributions to Mineralogy and Petrology》1991,108(1-2):72-81

Three reactions limiting the stability field of the di-trioctahedral chlorite cookeite in the presence of quartz, in the system Li₂O−Al₂O₃−SiO₂−H₂O (LASH) have been reversed in the range 290–480°C, 0.8–14 kbar, using natural material close to the end member composition. Combining our results with known and estimated thermodynamic properties of the other minerals belonging to the LASH system, the enthalpy (-8512200 J/mol) and the entropy (504.8 J/mol^*K) of cookeite are calculated by a feasible solution space approach. The knowledge of these values allowed us to draw the first P−T phase diagram involving both the hydrated Li-aluminosilicates cookeite and bikitaite, which is applicable to a large variety of natural rock systems. The low thermal extent of the stability field of cookeite+quartz (260–480°C) makes cookeite a valuable indicator of low temperature conditions within a wide range of pressure (1–14 kbar).  相似文献   

Single-crystal infrared reflectivity of pure Mg2SiO2 forsterite and (Mg0.86,Fe0.14)2SiO4 olivine     

Bruno Reynard 《Physics and Chemistry of Minerals》1991,18(1):19-25

New polarized infrared reflectance spectra of pure synthetic forsterite and natural Fo₈₆-olivine have been recorded from 5000 to 100cm^-1. Out of the 35 expected infrared active modes, 33 have been observed (8 B_1u, 12 B_2u, 13 B_3u). The observed frequency shift from pure forsterite to Fo₈₆-olivine is consistent with the higher mass of the substituted iron. The substitution of only 14% of iron also reduces the overal far-infrared reflectivity of olivine as compared to pure forsterite. Several discrepancies associated with previous studies of forsterite are explained by our investigation. We suggest that some of the previous investigations were complicated by polarization mixing.  相似文献   

Measuring molecular variation in zooplankton populations: DNA extraction from smallDaphnia species     

Mona A. Mort  Bruno Streit 《Aquatic Sciences - Research Across Boundaries》1992,54(1):77-84

We present methods developed for the small-sizedDaphnia species,D. galeata, D. hyalina, D. cucullata, and their hybrids, which facilitate the use of DNA variation in population studies. Described are large-scale production of material from single genotypes ofDaphnia and subsequent extraction of total DNA. The average DNA yields ranged between 6 µg per gram wet weight (D. cucullata) and 12 µg per gram wet weight (D. galeata). For comparison, the large-sized speciesD. pulex was tested and yielded an average of 28 µg DNA per gram wet weight. The DNA isolated in this manner lends itself well to molecular genetic techniques suited for population studies.Reprint requests to B. Streit.  相似文献   

Seismicity induced by gas production: II. Lithology correlated events,induced stresses and deformation     

Jean-Robert Grasso  Bruno Feignier 《Pure and Applied Geophysics》1990,134(3):427-450

A 3D relocation technique permits precise locations of induced earthquakes. Geostatistical processing using the data of 87 boreholes provides the basis of a precise 3D structure, with a dome geometry. Conventional laboratory mechanical tests performed on deep rock samples (1000 m to 5000 m) define the rock properties at depths similar to those of the seismic events (1<M _L<4.2) that range from 1 to 7 km.In the studied period, most (85%), of the events were located above the gas reservoir, with very few located in the reservoir itself. Because the production parameters (50 MPa depletion of the gas pressure reservoir) are homogeneous throughout the gas field, the lateral inhomogeneity of the seismic rupture locations are a consequence of variations in the rheological response of the dome to the deformation induced by gas production.Here a ratio of two is found between the elastic modulus of the seismic rock matrix and the elastic modulus of the aseismic rock matrix. The contrast in strength is at least as great, if not greater. Repeated measured surface deformations involve the whole structure. Spatial and temporal deformations indicate that aseismic deformation is quantitatively the main process of this structural deformation. The heterogeneous stress pattern inferred fromP-axes of induced earthquakes disagrees with the tectonic regional stress field. The radial distribution ofP-axes towards the gas reservoir probably reflects the production induced deformation. The inferred deformation of the dome occurs in response to weak induced stresses.  相似文献   

Seismicity induced by gas production: I. Correlation of focal mechanisms and dome structure     

Bruno Feignier  Jean-Robert Grasso 《Pure and Applied Geophysics》1990,134(3):405-426

From August 1976 to June 1979, more than 220 seismic events were recorded by a 7-station network operating over an active gas field in France. 120 earthquakes with magnitudes greater than 1.0 were selected for a detailed study in order to understand the seismic response to a decrease in the gas reservoir pressure of 50 MPa. Composite focal mechanisms were determined for these events. We found that where preexisting fractures were known from well-logs, faults with the most favorable orientation were reactivated. In the part of the gas field where no preexisting faults were known, orientation of the fracture planes was close to the orientations of stratigraphic interfaces.Our kinematic model, constrained by the distribution of the earthquakes and their focal mechanisms, consists of the downward dropping of a block located close to the top of the gas field. The main faults, as defined by the spatial density of the seismic activity, define the limits of this block. The displacements observed along these faults can be either normal or reverse mechanism, dependent on the preexisting orientation of each fault. Another important result is the evidence that the depletion of the gas reservoir exerts the major influence on local seismic displacements, obscuring the effect of regional setting.  相似文献   

Al-Si ordering in Sr-feldspar SrAl2Si2O8: IR,TEM and single-crystal XRD evidences     

P. Benna  M. Tribaudino  E. Bruno 《Physics and Chemistry of Minerals》1995,22(6):343-350

Al-Si ordering in Sr-feldspar has been followed by isothermal annealing, starting from a disordered metastable configuration. Ordering could not be followed by changes in the spontaneous strain as cell parameters did not show significant changes with thermal treatment from 0.016 h to 452 h at T=1350° C, while, on the contrary, significant changes in IR spectra are observed. A single crystal obtained from melt (Q _od 0) has been progressively heated up to 678 h at T=1350° C and the relevant structural refinements enabled to monitor changes in degree of Al-Si order up to Q_od = 0.86. In isothermal treatment for Sr-feldspar it is observed a significantly lower Q _od than in anorthite after the same annealing time. TEM observation has shown in Sr-feldspar, also for shortest annealing, b type reflections, while in anorthite, in the same conditions, e type reflections have been observed (Carpenter 1991a). In the first stages of ordering b APDs sized 100 Å (at T=1350° C, 0.33 h) have been observed in Sr-feldspar; APD coarsening occurs with an activation energy of 120±7 kcal mol^-1, not significantly different from anorthite. The ordering process seems to be a slower process in Sr-feldspar than in anorthite, even though data from longer annealing suggest that the Q _od close to the equilibrium is the same in Sr and Ca-feldspar (Q _od = 0.86 at T=1350° C).  相似文献   

Limnogeology of Laguna Miscanti: evidence for mid to late Holocene moisture changes in the Atacama Altiplano (Northern Chile)   总被引：1，自引：0，他引：1  

Blas L. Valero-Garcés  Martin Grosjean  Antje Schwalb  Mebus Geyh  Bruno Messerli  Kerry Kelts 《Journal of Paleolimnology》1996,16(1):1-21

Sedimentological, mineralogical and geochemical analyses of sediment cores from 9 m-deep, saline Laguna Miscanti, Chile (23 ° 44S, 67 °46W, 4140 m a.s.l.) together with high-resolution seismic profiles provide a mid to late Holocene time series of regional environmental change in the Atacama Altiplano constrained by ²¹⁰Pb and conventional ¹⁴C dating. The mid Holocene was the most arid interval since the last glacial maximum, as documented by subaerial exposure and formation of hardgrounds on a playa surface. Extremely low lake levels during the mid Holocene appear consistent with lower effective moisture recorded at other sites along the Altiplano and in the Amazon Basin. Termination of this arid period represented a major shift in the regional environmental dynamics and inaugurated modern atmospheric conditions. The cores show a progressive upward increase in effective moisture interrupted by numerous century-scale drier periods of various intensities and durations that characterize a fluctuating late Holocene climate. In spite of chronological uncertainties, the major environmental changes seem to correlate with the available paleorecords from the region providing a coherent account of effective moisture variability in the tropical highlands of South America.This is the 16th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest for these papers.  相似文献   

Late-glacial and early Holocene lake sediments,ground-water formation and climate in the Atacama Altiplano 22–24°S     

Martin Grosjean  Mebus A. Geyh  Bruno Messerli  Ueli Schotterer 《Journal of Paleolimnology》1995,14(3):241-252

Precipitation rates in the Atacama Altiplano 22–24°S were 400–500 mm yr^–1 during late glacial and early Holocene times as opposed to 200 mm yr^–1 today. This humid phase (Tauca phase) was likely due to strengthened tropical (monsoonal) circulation, which brought continental moisture to the Atacama Altiplano. The lake level of Laguna Lejía (23°30S, 4350 m) at that time was up to 25 m higher than it is today. Mg/Ca and Sr/Ca data from lake sediments show that, what today is a highly saline lake was a freshwater lake at that time. Seasonally-laminated calcareous sediments were deposited between 13 500 and <10 400 yr B.P. indicating the maximum of the humid phase. Climatic changes in the past are important for current groundwater resources.¹⁴C and³H data from lake-, ground- and well water suggest that modern groundwater formation (i.e. water <40 years) in the Altiplano is very limited under current arid conditions. We conclude that significant amounts of the water resources in this area originated during the time of the late-glacial and early Holocene humid climate. Tritium data from snow samples show that the moisture in the Altiplano at 22–24°S is mainly of continental origin, whereas precipitation from the westerlies hardly contributes to the water supply in this area. This precipitation pattern matches the paleodata, and we suggest that current precipitation formation may provide an analogue framework for late-glacial circulation in this area.This is the 3rd in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers.  相似文献   

Review: The state-of-art of sparse channel models and their applicability to performance assessment of radioactive waste repositories in fractured crystalline formations     

Bruno Figueiredo  Chin-Fu Tsang  Auli Niemi  Georg Lindgren 《Hydrogeology Journal》2016,24(7):1607-1622

Laboratory and field experiments done on fractured rock show that flow and solute transport often occur along flow channels. ‘Sparse channels’ refers to the case where these channels are characterised by flow in long flow paths separated from each other by large spacings relative to the size of flow domain. A literature study is presented that brings together information useful to assess whether a sparse-channel network concept is an appropriate representation of the flow system in tight fractured rock of low transmissivity, such as that around a nuclear waste repository in deep crystalline rocks. A number of observations are made in this review. First, conventional fracture network models may lead to inaccurate results for flow and solute transport in tight fractured rocks. Secondly, a flow dimension of 1, as determined by the analysis of pressure data in well testing, may be indicative of channelised flow, but such interpretation is not unique or definitive. Thirdly, in sparse channels, the percolation may be more influenced by the fracture shape than the fracture size and orientation but further studies are needed. Fourthly, the migration of radionuclides from a waste canister in a repository to the biosphere may be strongly influenced by the type of model used (e.g. discrete fracture network, channel model). Fifthly, the determination of appropriateness of representing an in situ flow system by a sparse-channel network model needs parameters usually neglected in site characterisation, such as the density of channels or fracture intersections.  相似文献