Rock-physics models of hydrate-bearing sediments in permafrost,Qilian Mountains,China

Rock-physics models are constructed for hydrate-bearing sediments in the Qilian Mountains permafrost region using the K–T equation model, and modes I and II of the effective medium model. The K–T equation models the seismic wave propagation in a two-phase medium to determine the elastic moduli of the composite medium. In the effective medium model, mode I, the hydrate is a component of the pore inclusions in mode I and in mode II it is a component of the matrix. First, the P-wave velocity, S-wave velocity, density, bulk modulus, and shear modulus of the sediment matrix are extracted from logging data.. Second, based on the physical properties of the main components of the sediments, rock-physics model is established using the K–T equation, and two additional rock-physics models are established assuming different hydrate-filling modes for the effective medium. The model and actual velocity data for the hydrate-bearing sediments are compared and it is found that the rock-physics model for the hydrate-filling mode II well reproduces the actual data.

Gas sand distribution prediction by prestack elastic inversion based on rock physics modeling and analysis

Seismic inversion is one of the most widely used technologies for reservoir prediction. Many good results have been obtained but sometimes it fails to differentiate the lithologies and identify the fluids. However, seismic prestack elastic inversion based on rock physics modeling and analysis introduced in this paper is a significant method that can help seismic inversion and interpretation reach a new quantitative （or semi-quantitative） level from traditional qualitative interpretation. By doing rock physics modeling and forward perturbation analysis, we can quantitatively analyze the essential relationships between rock properties and seismic responses and try to find the sensitive elastic properties to the lithology, porosity, fluid type, and reservoir saturation. Finally, standard rock physics templates （RPT） can be built for specific reservoirs to guide seismic inversion interpretation results for reservoir characterization and fluids identification purpose. The gas sand distribution results of the case study in this paper proves that this method has unparalleled advantages over traditional post-stack methods, by which we can perform reservoir characterization and seismic data interpretation more quantitatively and efficiently.

Controlled illumination and seismic acquisition geometry for target-oriented imaging

The conventional method of seismic data acquisition geometry design is based on the assumption of horizontal subsurface reflectors, which often is not suitable for complex structure. We start from a controlled illumination analysis and put forward a method of seismic survey geometry design for target-oriented imaging. The method needs a velocity model obtained by a preliminary seismic interpretation. The one-way Fourier finite-difference wave propagator is used to extrapolate plane wave sources on the target layer to the surface. By analyzing the wave energy distribution at the surface extrapolated from the target layer, the shot or receiver locations needed for target layer imaging can be determined. Numerical tests using the SEG-EAGE salt model suggest that this method is useful for confirming the special seismic acquisition geometry layout for target-oriented imaging.

A new type of fiber Bragg grating based seismic geophone

Aimed at the poor performance of conventional geophones in exploration for deeper and complex targets, we present the principle and theoretical design of a new geophone based on the optical fiber Bragg grating （FBG） sensing technology. The important parameters such as response functions are calculated theoretically. Because of the advantages of FBG sensing technology, the new FBG geophone has a high dynamic range of 94dB at （10-200 Hz）. This new generation of geophones will have wide use in seismic prospecting due to its higher sensitivity, lighter weight, and lower cost.

The Course of Time in the Cracking of Earth CrustCaused by Earthquake of Magnitude 8

The world,the continent and the large country at all times have similar distribution of intervals between recurrences of the great earthquakes,depending on the earthquake sequence. lt indicates that how the force source of world scale changes with time and space.

Ordovician limestone aquosity prediction using nonlinear seismic attributes:Case from the Xutuan coal mine

Ordovician limestone water is coal mines. In this paper, we analyze the the main source of water inrush in North China characteristic of three kinds of nonlinear seismic attributes, such as the largest lyapunov exponent,fractal dimension and entropy and introduce their calculation methods. Taking the 81st and 82nd coal districts in the Xutuan coal mine as examples, we extract the three seismic attributes based on the 3D prestack migration seismic data of this area, which can display the Ordovician limestone fracture distribution in the mine. We comprehensively analyzed the three nonlinear seismic attributes and compared the results with transient electromagnetic exploration results and determined the possible Ordovician limestone aquosity distribution. This demonstrated that the nonlinear seismic attributes technology is an effective approach to predict the aquosity of Ordovician limestone.

性感篮球

性感NBA,这竟然像一项很神圣的使命,足以让我们用一年的时间去踌躇。算不算过分?算不算狂野?算不算是一种盲目的殉道? 也许。

Rock skeleton models and seismic porosity inversion

By substituting rock skeleton modulus expressions into Gassmann approximate fluid equation, we obtain a seismic porosity inversion equation. However, conventional rock skeleton models and their expressions are quite different from each other, resuling in different seismic porosity inversion equations, potentially leading to difficulties in correctly applying them and evaluating their results. In response to this, a uniform relation with two adjusting parameters suitable for all rock skeleton models is established from an analysis and comparison of various conventional rock skeleton models and their expressions including the Eshelby-Walsh, Pride, Geertsma, Nur, Keys-Xu, and Krief models. By giving the two adjusting parameters specific values, different rock skeleton models with specific physical characteristics can be generated. This allows us to select the most appropriate rock skeleton model based on geological and geophysical conditions, and to develop more wise seismic porosity inversion. As an example of using this method for hydrocarbon prediction and fluid identification, we apply this improved porosity inversion, associated with rock physical data and well log data, to the ZJ basin. Research shows that the existence of an abundant hydrocarbon reservoir is dependent on a moderate porosity range, which means we can use the results of seismic porosity inversion to identify oil reservoirs and dry or water-saturated reservoirs. The seismic inversion results are closely correspond to well log porosity curves in the ZJ area, indicating that the uniform relations and inversion methods proposed in this paper are reliable and effective.

Brittleness index and seismic rock physics model for anisotropic tight-oil sandstone reservoirs

Brittleness analysis becomes important when looking for sweet spots in tightoil sandstone reservoirs. Hence, appropriate indices are required as accurate brittleness evaluation criteria. We construct a seismic rock physics model for tight-oil sandstone reservoirs with vertical fractures. Because of the complexities in lithology and pore structure and the anisotropic characteristics of tight-oil sandstone reservoirs, the proposed model is based on the solid components, pore connectivity, pore type, and fractures to better describe the sandstone reservoir microstructure. Using the model, we analyze the brittleness sensitivity of the elastic parameters in an anisotropic medium and establish a new brittleness index. We show the applicability of the proposed brittleness index for tight-oil sandstone reservoirs by considering the brittleness sensitivity, the rock physics response characteristics, and cross-plots. Compared with conventional brittleness indexes, the new brittleness index has high brittleness sensitivity and it is the highest in oil-bearing brittle zones with relatively high porosity. The results also suggest that the new brittleness index is much more sensitive to elastic properties variations, and thus can presumably better predict the brittleness characteristics of sweet spots in tight-oil sandstone reservoirs.

Shales in the Qiongzhusi and Wufeng–Longmaxi Formations:a rock-physics model and analysis of the effective pore aspect ratio

The shales of the Qiongzhusi Formation and Wufeng-Longmaxi Formations at Sichuan Basin and surrounding areas are presently the most important stratigraphic horizons for shale gas exploration and development in China. However, the regional characteristics of the seismic elastic properties need to be better determined. The ultrasonic velocities of shale samples were measured under dry conditions and the relations between elastic properties and petrology were systemically analyzed. The results suggest that 1） the effective porosity is positively correlated with clay content but negatively correlated with brittle minerals, 2） the dry shale matrix consists of clays, quartz, feldspars, and carbonates, and 3） organic matter and pyrite are in the pore spaces, weakly coupled with the shale matrix. Thus, by assuming that all connected pores are only present in the clay minerals and using the Gassmann substitution method to calculate the elastic effect of organic matter and pyrite in the pores, a relatively simple rock-physics model was constructed by combining the self-consistent approximation （SCA）, the differential effective medium （DEM）, and Gassmann＇s equation. In addition, the effective pore aspect ratio was adopted from the sample averages or estimated from the carbonate content. The proposed model was used to predict the P-wave velocities and generally matched the ultrasonic measurements very well.

Slope Debris Flows in the Wenchuan Earthquake Area

Avalanches and landslides,induced by the Wenchuan Earthquake on May 12,2008,resulted in a lot of disaggregated,solid material on slopes that could be readily mobilized as source material for debris flows.Rainstorms triggered numerous slope debris flows with great damage to highways and rivers over the subsequent two years.Slope debris flows(as opposed to channelized debris flows) are defined as phenomena in which high-concentration mixtures of debris and water flow down slopes for short distances to highways and river banks.Based on field investigations and measurements of 19 slope debris flows,their main characteristics and potential mitigation strategies were studied.High rainfall intensity is the main triggering factor.Critical rainfall intensities for simultaneous occurrence of single,several and numerous slope debris flow events were 20 mm/day,30mm/day,and 90 mm/day,respectively.Field investigations also revealed that slope debris flows consist of high concentrations of cobbles,boulders and gravel.They are two-phase debris flows.The liquid phase plays the role of lubrication instead of transporting medium.Solid particles collide with each other and consume a lot of energy.The velocities of slope debris flows are very low,and their transport distances are only several tens of meters.Slope debris flows may be controlled by construction of drainage systems and by reforestation.

Characteristics of viscous debris flow in a drainage channel with an energy dissipation structure

A new type of drainage channel with an energy dissipation structure has been proposed based on previous engineering experiences and practical requirements for hazard mitigation in earthquakeaffected areas.Experimental studies were performed to determine the characteristics of viscous debris flow in a drainage channel of this type with a slope of 15%.The velocity and depth of the viscous debris flow were measured,processed,and subsequently used to characterize the viscous debris flow in the drainage channel.Observations of this experiment showed that the surface of the viscous debris flow in a smooth drainage channel was smoother than that of a similar debris flow passing through the energy dissipation section in a channel of the new type studied here.However,the flow patterns in the two types of channels were similar at other points.These experimental results show that the depth of the viscous debris flow downstream of the energy dissipation structure increased gradually with the length of the energy dissipation structure.In addition,in the smooth channel,the viscous debris-flow velocity downstream of the energy dissipation structure decreased gradually with the length of the energy dissipation structure.Furthermore,theviscous debris-flow depth and velocity were slightly affected by variations in the width of the energy dissipation structure when the channel slope was 15%.Finally,the energy dissipation ratio increased gradually as the length and width of the energy dissipation structure increased;the maximum energy dissipation ratio observed was 62.9%(where B = 0.6m and L/w = 6.0).

Study on the Rainfall and Aftershock Threshold for Debris Flow of Post-earthquake

Due to the special condition of provenance and disaster environment after "5·12" Earthquake, the probability and conditions of the occurrence of gully debris flow change greatly after the event, which make it difficult to prevent disaster effectively. In this study the hydrological model of ground water table in loose sediment is established. According to infinite slope theory, the safety factor of deposits is defined as the ratio of resistance force to driving force. The starting condition of post-earthquake gully debris flow is clearly studied by analyzing the effects of rainfall intensity, seismic strength, slope gradient and mechanical properties on the balance of accumulation body. Then the formulas of rainfall and aftershock threshold for starting of gully debris flow are proposed, and an example is given to illustrate the effect of rainfall, aftershocks and their coupling action on a debris flow. The result shows the critical rainfall intensity decreases as the lateral seismic acceleration and channel gradient increases, while the critical intensity linearly increases as the friction angle increases.

Analysis on the Dynamical Process of Donghekou Rockslide-Debris Flow Triggered by 5.12 Wenchuan Earthquake

Among the geo-hazards caused by the great Wenchuan Earthquake, the rapid and long runout rockslide-debris flow is of primary concern due to the large volume of displaced material and the resultant catastrophic impacts to the landscape and socioeconomic structure. In order to analyze the dynamical process of this kind of geo-hazard, the Donghekou rockslide-debris flow is given as an example in this paper. This event, which killed 780 people, initiated at an elevation of 1300 m with a total long run-out distance of more than 2400 m. The slide mass is mainly composed of dolomite limestone and siliceous limestone of Sinian system, together with carbon slate and phyllite of Cambrian. During the processes from slide initiation to the final cessation of slide movement, five dynamic stages took place, here identified as the initiation stage, the acceleration of movement stage, the air-blast effect stage, the impact and redirection stage and the long runout slidematerial accumulation stage. Field investigations indicate that due to the effects of the earthquake, the dynamics of the Donghekou rockslide-debris flow are apparently controlled by geologic and tectonic conditions, the local geomorphological aspects of the terrain, and the microstructural and macroscopic mechanical properties of rocks which compose the slide mass. These three main factors which dictate the Donghekou rockslide-debris flow dynamics are discussed in detail in this paper, and significant results of field investigations and tests of materials are presented. The above dynamical processes are analyzed in this paper, and some useful conclusions have been gained.

Influences of the Wenchuan Earthquake on Sediment Supply of Debris Flows

The 5.12 Wenchuan Earthquake and the subsequent rainstorms induced a large number of landslides, which later were transformed into debris flows. To evaluate the effect of the earthquake on the sediment supply of debris flows, eight debris flow basins near Beichuan City, Sichuan Province, China were chosen as the study area. The area variations of the debris flow source after the Wenchuan Earthquake and the subsequent rainstorm are analyzed and discussed in this paper. Interpretations of aerial photographs (after the 5.12 Wenchuan Earthquake) and SPOT5 images (after the rainstorm event of September 24, 2008) as well as field investigations were compared to identify the transformation of landslide surface in the study area, indicating that the landslide area in the eight debris flow basins significantly increased. The loose sediment area on the channel bed increased after the rainstorm event. In order to estimate the relationship of the landslide area with the rainfall intensity in different return periods, a model proposed by Uchihugi was adopted. Results show that new landslide area induced by heavy rainfall with 50-year and 100-year return period will be 0.87 km2 and 1.67 km2, respectively. The study results show the Wenchuan earthquake had particular influences on subsequent rainfall-induced debris flow occurrence.

The seismic CT method in measuring rock bodies

The seismic computed tomography （CT） method is derived from the basic principles of X-ray section scanning first applied in medical science. The method records P-wave arrivals between shots and receivers in separate boreholes. Using the velocity information from 2D seismic P-wave arrival inversion, we can determine the distribution of velocity in rock and soil bodies. This paper introduces a practical case of using the seismic CT method for detecting the structure of the rocks for tunnel engineering and to utilize SIRT algorithms for doing first arrival time iterative inversion. Compared with other exploration methods, it is more efficient and accurate.

Experiment on Hydraulic Fracturing in Rock and Induced Earthquake

Experiment on rock hydraulic fracturing strength under different confining pressures was conducted on a series of test specimens with various pre-cracks prepared from 7 types of rock. Combining the data of an actual reservoir-induced earthquake with the experimental results of the contemporary tectonic stress field according to the theory of rock strength and the principle and method of rock fracture mechanics, the authors tentatively investigated the earthquakes induced by pore-water pressure in rock and obtained the initial results as follows: （1） One type of induced earthquake may occur in the case of larger tectonic stress on such weak planes that strike in similar orientation of principle tectonic compressional stress in the shallows of the rock mass; the pore-water pressure σp may generate tensile fracture on them and induce small earthquakes; （2） Two types of induced earthquake may occur in the case of larger tectonic stress, i.e.,① on such weakness planes that strike in similar orientation of principle tectonic compressional stress, σ1, in the shallows of the rockmass, the pore-water pressure, σp, may generate tensile fracture on them and induce small earthquakes; ② When the tectonic stress approximates the shear strength of the fracture, the pore-water pressure σp may reduce the normal stress, σn, on the fracture face causing failure of the originally stable fracture, producing gliding fracture and thus inducing an earthquake. σp may also increase the fracture depth, leading to an induced earthquake with the magnitude larger than the previous potential magnitude; （3） There is a depth limit for each type of rock mass, and no induced earthquake will occur beyond this limit.

Aseismic strengthening techniques of Chinese typical stele relics:A case study of Xi'an Beilin

In order to improve the seismic performance of Chinese traditional stele relics, a suitable aseismic strengthening method of Chinese traditional stele relics is proposed. Taking the typical stele relic in Xi＇an Beilin as an example, the on-site investigations were carried out to obtain the actual geometric size and damage state of the stele relic. Then, the structural performance of the stele relic was analyzed by the finite element software ANSYS. Finally, the two different aseismic strengthening methods of the traditional stele relic are proposed and comparatively analyzed. The results show that in addition to the common problems, such as weathering, and cracks, etc, earthquakes seriously threaten the structural safety of stele relics. Under the rarely-occurring earthquake of eight degree, the unstrengthened stele relic will be overturned, and many cracks will occur at the connection area of stele body and stele pedestal. When the stele relic is strengthened by the stainless angle steel strengthening method, the stele relic will not be overturned, but some cracks will occur at the connection area of stele body and stele pedestal. When the stele relic is strengthened by the base isolation strengthening method, the stele relic will not be overturned, and no cracks will occur at the connection area of stele body and stele pedestal. Therefore, the aseismic strengthening effect of the base isolation strengthening method is obviously better than that of the stainless angle steel strengthening method, and this method is a suitable aseismic strengthening method of Chinese traditional stele relics.

Seismic Signatures of Rock Pore Structure

Rock pore structure is one of the important parameters in controlling both seismic wave velocity and permeability in sandstones and carbonate rocks. For a given porosity of two similar rocks with different pore structures, their acoustic wave speeds can differ 2 km/s, and permeability can span nearly six orders of magnitude from 0.01 mD to 20 D in both sandstone and limestone. In this paper, we summarize a two-parameter elastic velocity model reduced from a general poroelastic theory, to characterize the effect of pore structures on seismic wave propagation. For a given mineralogy and fluid type of a reservoir, this velocity model is defined by porosity and a frame flexibility factor, which can be used in seismic inversion and reservoir characterization to improve estimation of porosity and reserves. The frame flexibility factor can be used for quantitative classification of rock pore structure types (PST) and may be related to pore connectivity and permeability, using both poststack and prestack seismic data. This study also helps explain why amplitude versus offset analysis (AVO) in some cases fails for the purpose of fluid detection: pore structure effect on seismic waves can mask all the fluid effects, especially in carbonate rocks.

On the initiation,movement and deposition of a large landslide in Maoxian County,China

At 5 am 24 th June 2017, a catastrophic landslide hit Xinmo Village, Maoxian County, Sichuan Province, China. The slide mass rushed down from an altitude of 3400 m and traveled 2700 m in a high velocity. The 13 million m^3 deposition buried the whole village and caused about 100 deaths. The source area of the landslide is located in a high steep slope, average slope angle is 40o and maximal angle is 65o. The strata are interbedded Triassic Zagunao Formation metamorphic sandstone and slate with the dip slope angle of 45°. Based on high-resolution satellite remote sensing image, UAV image, DEM data, and field investigation, failure mechanism, travel features, and deposit characteristics were analyzed. The results showed that this landslide was influenced by Songpinggou Fault zone. According to the topography before the failure, the landslide is located in the back scarp of an antecedent landslide induced by Diexi Earthquake in 1933. The bedding slope provided potential rupture surface. Historical seismic activities and long-term gravitational deformation caused rock mass accumulated damages. Weathering and precipitation weakened the rock mass and finally induced shearing and tension failure. A huge block detached from the top rock slope, pushed the past landslide deposits in the middle part, rushed out of the slope bottom in a high velocity and buried the Xinmo Village. The rapid movement entrained and brought the soil into the Songping Gully which recoiled with and bounced back from the opposite mountain.