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1.
The present study extends the numerical manifold method to investigate the effective permeability coefficient (keff) of soil–rock mixtures. The influence of rock content, rock size, rock shape, and rock blocks' major axis direction on keff is studied. The results show the following: (1) keff decreases as the rock content increases; (2) the influence of rock size on keff can be neglected if other parameters are fixed; (3) the values of keff are nearly the same if rock blocks are in circular or regular hexagon shapes; and (4) the major axis direction of rock blocks has some influence on keff. 相似文献
2.
This paper describes the geomechanical back-analysis of the flexural failure of an overhanging limestone slab (volume = 68 m3) that collapsed on 26/01/1999 on the abandoned Cellina Valley state road SS 251 (western Friuli, NE Italy). The survey carried out on site examining the contact surfaces between the block and the slope has ascertained that the rock slab was connected to the stable rock mass by means of a single great rock bridge. The detailed reconstruction of the slab geometry and of the actual restraint conditions acting before the rockfall permitted an estimation of the stress state by using a 3D finite element code (Strand7). The finite element numerical model, referred to the restrained cross-section measured on site (Ares = 2.82 m2), gives a maximum value of σt = 5.19 MPa for the tensile stress, which is in good agreement with the estimated value for the characteristic strength mobilized at rupture by the intact rock material (T0 = 3.5–5.5 MPa). Considerably lower maximum tensile stress (σt = 2.25 MPa), smaller than one half, is obtained if the whole contact surface is assumed as resisting surface (Ares = 10.50 m2) and the rock bridge is neglected. 相似文献
3.
Estimation of Rock Cuttability from Shore Hardness and Compressive Strength Properties 总被引：6，自引：1，他引：6
Summary Shore hardness has been used to estimate some mechanical and physical properties of rocks for many years. This study differs
from previous studies in a way that it is directly oriented to rock cuttability. Two Shore hardness values (SH
1 andSH
2) and a coefficient of deformation value (K) have been measured for 30 different rock samples. In the first stage of the study, optimum specific energy values for 16
different rock samples obtained from full-scale cutting tests were correlated with the Shore hardness values of the same rock
samples changingSH
1 values from 9 to 66 andSH
2 values from 25 to 83, with deformation coefficient values changing from 26 to 195. In the second stage, the performance of
a roadheader used in the Kü?üksu (Istanbul) tunnel was recorded in detail and the instantaneous cutting rate of the machine
was determined. Then, the relationship between Shore hardness values, deformation coefficient and the instantaneous cutting
rate of the machine was determined for different formations encountered. It is concluded that there is a relationship between
Shore hardness values, optimum specific energy and compressive strength, which may be used to estimate the rock cuttability
and the instantaneous cutting rates of roadheaders within certain limits of reliability. 相似文献
4.
5.
An Experimental Damage Model and Its Application to the Evaluation of the Excavation Damage Zone 总被引：1，自引：2，他引：1
Summary. An experimental damage model, which can simulate both post-peak and pre-peak damage characteristics of rock by assuming distinct
elastic constants in each damage level, was proposed. Each damage level was identified by two successive threshold values
of major principal stresses, which could be determined from uniaxial and triaxial compression tests and measurement of acoustic
emissions. Elastic constants pertaining to each damage level were expressed in terms of confining pressure (minor principal
stress) by regression equations of the experimental data. Post-peak behavior was simulated by selecting suitable values of
the Hoek-Brown constants m
r
and s
r
for post-failure. The proposed experimental model was implemented into FLAC by writing a FISH function. The parametric studies on Hoek-Brown constants for post-peak behavior revealed that peak strength depends greatly
more on s
r
than m
r
, and post-peak slopes of stress–strain curves depend mainly on m
r
.
Together with the elastic and elasto-plastic models, the nonlinear-brittle-plastic damage model derived from experiments was
applied to the evaluation of an excavation damage zone around a highly-stressed circular tunnel for the purpose of checking
the performance of the model. Of the three models, the nonlinear-brittle-plastic damage model gave the largest extent of disturbed
zones and displacements around the tunnel. The damage zone predicted by the nonlinear-brittle-plastic model became larger
as the magnitudes and the stress differences of in-situ stresses increased. Consequently, taking the damage model into account
in the stability analysis of hard rock tunnels may be appropriate for conservative design of a highly stressed tunnel. 相似文献
6.
The exhumation mechanism of high‐pressure (HP) and ultrahigh‐pressure (UHP) eclogites formed by the subduction of oceanic crust (hereafter referred to as oceanic eclogites) is one of the primary uncertainties associated with the subduction factory. The phase relations and densities of eclogites with MORB compositions are modelled using thermodynamic calculations over a P–T range of 1–4 GPa and 400–800 °C, respectively, in the NCKFMASHTO (Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3) system. Our modelling suggests that the mineral assemblages, mineral proportions and density of oceanic crust subducted along a cold P–T path are quite different from those of crust subducted along a warm P–T path, and that the density of oceanic eclogites is largely controlled by the stability of low‐density hydrous minerals, such as lawsonite, chlorite, glaucophane and talc. Along a cold subduction P–T path with a geotherm of ~6 °C km?1, lawsonite is always present at 1.1 to >4.0 GPa, and chlorite, glaucophane and talc can be stable at pressures of up to 2.3, 2.6 and 3.6 GPa respectively. Along such a P–T path, the density of subducted oceanic crust is always lower than that of the surrounding mantle at depths shallower than 110–120 km (< 3.3–3.6 GPa). However, along a warm subduction P–T path with a geotherm of ~10 °C km?1, the P–T path is outside the stability field of lawsonite, and the hydrous minerals of chlorite, epidote and amphibole break down completely into dry dense minerals at relatively lower pressures of 1.5, 1.85 and 1.9 GPa respectively. Along such a warm subduction P–T path, the subducted oceanic crust becomes denser than the surrounding mantle at depths >60 km (>1.8 GPa). Oceanic eclogites with high H2O content, oxygen fugacity, bulk‐rock XMg [ = MgO/(MgO + FeO)], XAl [ = Al2O3/(Al2O3 + MgO + FeO)] and low XCa [ = CaO/(CaO + MgO + FeO + Na2O)] are likely suitable for exhumation, which is consistent with the bulk‐rock compositions of the natural oceanic eclogites on the Earth's surface. On the basis of natural observations and our calculations, it is suggested that beyond depths around 110–120 km oceanic eclogites are not light enough and/or there are no blueschists to compensate the negative buoyancy of the oceanic crust, therefore explaining the lack of oceanic eclogites returned from ultradeep mantle (>120 km) to the Earth's surface. The exhumed light–cold–hydrous oceanic eclogites may have decoupled from the top part of the sinking slab at shallow depths in the forearc region and are exhumed inside the serpentinized subduction channel, whereas the dense–hot–dry eclogites may be retained in the sinking slab and recycled into deeper mantle. 相似文献
7.
The rate of a high-pressure phase transition increases exponentially with temperature (T) and overpressure or pressure beyond equilibrium (ΔP). It is also greatly promoted by introducing shear stress, diminishing grain size, and adding water or other catalysts to the reactants. For an isothermal and isobaric transition with no compositional change, if steady state of nucleation on grain surfaces is attained, the rate equation can be expressed: (1) before site saturation by: X = 1 − exp(−Kt4), where
and (2) after site saturation by: X = 1 − exp(−K′T), where
, where X is volume fraction of completion of transformation, t is time, and the C's are characteristic constants. C1 and C9 are functions of grain size, C3 and C6 are functions of shear stress. All the C's are almost independent of temperature and pressure. Thus, if X as a function of T, ΔP, and t over a narrow P-T range can be experimentally determined, the C's can be calculated and the effect of grain size and shear stress on the rate of transformation can be evaluated. The isothermal and isobaric rate equations for a given composition, shear stress, and grain size are then experimentally determinable. The non-isothermal and non-isobaric rate equation can be calculated from the isothermal and isobaric ones if the rate of penetration into the metastability field is known. The important feature of the kinetics of high-pressure phase transitions predicted by these rate equations is that for a given rate of penetration into the metastability field, there can be defined a characteristic temperature, Tch, below which the rate of the transition is virtually zero no matter how metastable the material is. For the olivine → spinel transition in the mantle, this characteristic temperature may be as high as 700° C. Thus, in a fast moving downgoing slab, the temperature at its cold center may remain below Tch even down to depths in excess of 600 km, thereby greatly depressing the olivine—spinel phase boundary.At an early stage in the development of a downgoing slab, the plunging speed is slow. This allows the interior of the slab to heat up and the olivine → spinel transition to proceed rapidly and near equilibrium. As a result, the olivine—spinel phase boundary in the slab will be distorted upwards. The rising of the denser spinel phase then provides an additional driving force which accelerates the plate. Since the upper portion of the slab is pulled from below and the lower portion pushed from above, earthquakes of down-dip extension will occur in the upper mantle while those of down-dip compression will originate in the transition zone. Because the transformation occurs close to equilibrium, there will be an aseismic region separating the two seismic zones. When the plate velocity exceeds a certain limit, the temperature in the cold interior becomes low enough to depress the olivine → spinel transition. The phase boundary is then distorted downwards. The buoyant force thereby created will reduce the driving force, and the plunging speed of the plate will approach a steady state. In addition, the buoyant force will compress the slab from below and result in earthquakes of down-dip compression throughout the length of the slab. Now the olivine → spinel transition is so far from equilibrium that the reaction becomes implosive. A rise in frequency of deep earthquakes towards the implosion region in the lower transition zone is thus predicted. Therefore, as well as stabilizing the plate velocity, the olivine → spinel transition may also control earthquake distributions throughout the downgoing slab. 相似文献
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8.
9.
Fault plane processes and mesoscopic structure of a strong-type seismogenic fault in tonalites (Adamello batholith, Southern Alps) 总被引：3，自引：3，他引：3
The Gole Larghe Fault is an exhumed paleoseismic fault crosscutting the Adamello tonalites (Italian Southern Alps). Ambient conditions of faulting were 9–11 km in depth and 250–300 °C. In the study area the fault accommodates 1100 m of dextral strike-slip over a fault thickness of 550 m. Displacement is partitioned into three hierarchically different sets of discrete subparallel cataclastic horizons (faults1–2–3). Fault displacement is in the range of few centimeters (faults3) to a maximum of a few tens of meters in major faults1. Faults1–2 nucleated on pre-existing joints, whereas faults3 are newly generated fractures produced during slip along faults1–2. Each fault within the Gole Larghe Fault records the same evolution with development of indurated cataclasites precursory to pseudotachylyte production. Pseudotachylytes are usually generated at the host rock/cataclasite boundary and within cataclasites the mean clast size decreases getting closer to pseudotachylyte fault veins. Pseudotachylytes and cataclasites have a similar chemical composition which is enriched in Loss On Ignition, K, Rb, Ba, U and Fe3+ compared to host rock.We envision two models for the evolution of the Gole Larghe Fault. In both models synkinematic fluid–rock interaction along a fault causes fault hardening by precipitation of abundant K-feldspar+epidote (and minor chlorite) in the cataclasite matrix conducive to final production of pseudotachylyte. In the first model, induration occurs progressively by differential precipitation related to fabric evolution in cataclasites. In the second model, induration occurs abruptly dependent on the development of full connectivity within the fault network and to fluid reservoir. Whatever the model, the Gole Larghe Fault represents a strong fault, where hardening processes resulted in a low displacement/fault thickness ratio and contrast with many mature weak faults where localized repeated seismic slip along the same weak horizons yields high displacement/fault thickness ratios. 相似文献
10.
The method of stress characteristics has been used for computing the ultimate bearing capacity of strip and circular footings placed on rock mass. The modified Hoek‐and‐Brown failure criterion has been used. Both smooth and rough footing‐rock interfaces have been modeled. The bearing capacity has been expressed in terms of nondimensional factors Nσ0 and Nσ, corresponding to rock mass with (1) γ = 0 and (2) γ ≠ 0, respectively. The numerical results have been presented as a function of different input parameters needed to define the Hoek‐and‐Brown criterion. Slip line patterns and the pressure distribution along the footing base have also been examined. The results are found to compare generally well with the reported solutions. 相似文献
11.
Numerical modeling of thermal structure, circulation of H2O, and magmatism–metamorphism in subduction zones: Implications for evolution of arcs 总被引：2，自引：2，他引：0
Numerical models on thermal structure, convective flow of solid, generation and transportation of H2O-rich fluid in subduction zones are consolidated to have a comprehensive view of the subduction zone processes: heat balance, circulation of H2O magmatism–metamorphism, growth of arcs and continental margins. A large scale convection model with steady subduction of a cold old slab (130 Myr old) predicts rapid ( 100 Myr) cooling of subduction zones, resulting in cessation of magmatism. The model also predicts that the mantle temperature beneath arcs and continental margins is greatly affected by the effective temperature of the subducting slab, i.e., the age of the subducting slab. If subduction of a young hot slab, including ridge subduction, occurs every 60 to 120 Myr as is suggested for eastern Asia, the average temperature beneath arcs is increased by about 300 °C, which may explain the long-lasting magmatism in eastern Asia. Associated with subduction of young slabs and ridges, thermal structure and circulation of H2O are greatly modified to cause a transition from (1) normal arc magmatism, (2) forearc mantle melting, to (3) slab melting to produce a significant amount (100 km3) of granitic melts, associated with both high-P/T and low-P/T type metamorphism. The last stage of (3) can result in formation of a granitic batholith belt and a paired metamorphic belts. Synthesis of the numerical models and observations suggest that episodic subduction of young slabs and ridges can explain heat source for generating a large amount of granitic magmas of batholiths, synchronous formation of batholith and regional metamorphic belts, and P–T conditions of the paired metamorphism. Even the high-P/T metamorphism requires an elevated geothermal structure in the forearc region, associated with ridge subduction. Although the emplacement of the batholiths and the regional metamorphic belts, and the mass balance in subduction zones are not well constrained at present, the episodic event associated with ridge subduction is thought to be essential for net growth of arcs and continental margins, as well as for the long-term heat balance in subduction zones. 相似文献
12.
一种常见的岩体结构——板裂结构及其力学模型 总被引：7，自引：0，他引：7
岩体结构观念的提出对岩体工程地质和岩体力学的研究具有重要意义。岩体结构类型划分方案已经提出了许多,已有的岩体结构划分原则主要是岩体破碎程度。谷德振、孙玉科等曾提出过岩体结构基本单元是:结构面和结构体。1977年底谷德振教授曾提出过,碎碎带应作为一种岩体结构单元问题,没有引起人们的重视。 相似文献
13.
The development of thermodynamic models for tonalitic melt and the updated clinopyroxene and amphibole models now allow the use of phase equilibrium modelling to estimate P–T conditions and melt production for anatectic mafic and intermediate rock types at high‐T conditions. The Permian mid‐lower crustal section of the Ivrea Zone preserves a metamorphic field gradient from mid amphibolite facies to granulite facies, and thus records the onset of partial melting in metabasic rocks. Interlayered metabasic and metapelitic rocks allows the direct comparison of P–T estimates and partial melting between both rock types with the same metamorphic evolution. Pseudosections for metabasic compositions calculated in the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O (NCKFMASHTO) system are presented and compared with those of metapelitic rocks calculated with consistent end‐member data and a–x models. The results presented in this study show that P–T conditions obtained by phase equilibria modelling of both metabasic and metapelitic rocks give consistent results within uncertainties, allowing integration of results obtained for both rock types. In combination, the calculations for both metabasic and metapelitic rocks allows an updated and more precisely constrained metamorphic field gradient for Val Strona di Omegna to be defined. The new field gradient has a slightly lower dP/dT which is in better agreement with the onset of crustal thinning of the Adriatic margin during the Permian inferred in recent studies. 相似文献
14.
S. Najmedin Almasi Raheb Bagherpour Reza Mikaeil Yilmaz Ozcelik Hamid Kalhori 《Geotechnical and Geological Engineering》2017,35(4):1311-1326
One of the key parameters that affect the selection of equipment and the cost estimation of dimension stone quarries is the rock cutting rate or production rate. In this study, the M5P tree algorithm is used to determine the relationship between the hard rock sawability and its factors especially the physical and mechanical characteristics of rock. To achieve the research goal, a variety of eleven types of hard dimension stone were selected and nine major physical and mechanical characteristics of rock including uniaxial compressive strength, Young’s modulus, Brazilian tensile strength, equivalent quarts content, grain size, Mohs hardness, point load test, density and P-wave velocity of these samples were evaluated. The cutting rate of diamond wire for all of the Workpiece was measured at different pullback amperage with a fully instrumented cutting platform in laboratory. All operational parameters of cutting process were entirely controlled. Thus, a database containing 99 datasets was provided and it has been used for analyses. The obtained results from the pruned and unpruned tree models showed a significant relationship between cutting rate and its factors. In the end, the results of M5P tree method were compared with statistical analyses (i.e., linear and nonlinear regression). The coefficient of determination be equal with 0.92, 0.86, 0.77 and 0.63 for unpruned tree, pruned tree, linear and nonlinear regression method respectively. This comparison showed that the both method of M5P tree technique have a better performance in predicting the cutting rate rather than the statistical regression methods. 相似文献
15.
XIONG Xiao ZHU Laimin LI Ben ZHANG Guowei GONG Hujun ZHENG Jun JIANG Hang 《《地质学报》英文版》2015,89(6):1926-1946
Precise in situ zircon U-Pb dating and Lu–Hf isotopic measurement using an LA-ICP-MS system, whole-rock major and trace element geochemistry and Sr–Nd isotope geochemistry were conducted on the volcanic host rocks of the Tongyu copper deposit on the basis of further understanding of its geological characteristics. Three zircon samples from the volcanic host rocks yielded 206Pb/238 U weighted average ages ranging from 436±4 Ma to 440±5 Ma, which are statistically indistinguishable and coeval with the ca. 440 Ma northward subduction event of the Paleo-Qinling oceanic slab. The volcanic host rocks were products of magmatic differentiation that evolved from basalt to andesite to dacite to rhyolite, forming an integrated tholeiitic island arc volcanic rock suite. The primitive mantle-normalized trace element patterns for most samples show characteristics of island arc volcanic rocks, such as relative enrichment of LILE(e.g. Th, U, Pb and La) and depletion of HFSE(e.g. Nb, Ta, Ti, Zr and Hf). Discrimination diagrams of Ta/Yb vs Th/Yb, Ta vs Th, Yb vs Th/Ta, Ta/Hf vs Th/Hf, Hf/3 vs Th vs Nb/16, La vs La/Nb and Nb vs Nb/Th all suggest that both the volcanic host rocks from the Tongyu copper deposit and the volcanic rocks from the regional Xieyuguan Group were formed in an island arc environment related to subduction of an oceanic slab. Values of ISr(0.703457 to 0.708218) and εNd(t)(-2 to 5.8) indicate that the source materials of volcanic rocks from the Tongyu copper deposit and the Xieyuguan Group originated from the metasomatised mantle wedge with possible crustal material assimilation. Most of the volcanic rock samples show good agreement with the values of typical island arc volcanic rocks in the ISr-εNd(t) diagram. The involvement of crustal-derived material in the magma of the volcanic rocks from the Tongyu copper deposit was also reflected in the zircon εHf(t) values, which range from-3.08 to 10.7, and the existence of inherited ancient xenocrystic zircon cores(2616±39 Ma and 1297±22 Ma). The mineralization of the Tongyu copper deposit shows syn-volcanic characteristics such as layered orebodies interbedded with the volcanic rock strata, thus, the zircon U-Pb age of the volcanic host rocks can approximately represent the mineralization age of the Tongyu copper deposit. Both the Meigou pluton and the volcanic host rocks were formed during the ca. 440 Ma northward subduction of the Paleo-Qinling Ocean when high oxygen fugacity aqueous hydrothermal fluid released by dehydration of the slab and the overlying sediments fluxed into the mantle wedge, triggered partial melting of the mantle wedge, and activated and extracted Cu and other ore-forming elements. The magma and ore-bearing fluid upwelled and erupted, and consequently formed the island arc volcanic rock suite and the Tongyu VHMS-type copper deposit. 相似文献
16.
Amin Jamshidi Mashalah Khamehchiyan Reza Zarei Sahamieh 《Geomechanics and Geoengineering》2016,11(1):13-19
Estimation of uniaxial compressive strength (UCS) by P-wave velocity (VP) is of great interest to geotechnical engineers in various design projects. The specimen diameter size is one of the main factors that influence rock parameters such as UCS and VP. In this study, the diameter size of specimens that effect UCS and VP is investigated. Moreover, the correlation between UCS and VP are examined via empirical analysis. For this purpose, 15 travertine samples were collected and core specimens with a diameters size of 38, 44, 54, 64 and 74 mm were prepared. Then, uniaxial compressive strength and P-wave velocity tests were conducted according to the procedure suggested by ISRM (1981). It is concluded that the diameter size of the specimen has a significant effect on UCS and VP. Moreover, it was found that the best correlation between relevant parameters obtained for the specimen diameter of 38 mm. 相似文献
17.
Rock glaciers are an end unit of the coarse debris system that links frost weathering and rockfall to debris transport in mountainous environments. By examining topographic and climatic controls on creep, a better understanding of rock glacier formation and evolution could be obtained. A series of statistical tests were run comparing contributing area parameters (width, length, area, slope, headwall height, etc.) and rock glacier variables (width, length, area, thickness, slope, creep and temperature) in the Front Range of Colorado. Results showed that rock glacier width had the strongest correlation with contributing area width due to an abundance of lobate rock glaciers (r = 0.78). Rock glacier area and contributing area size were also related (r = 0.74), but are also a function of talus production factors. Mean surface velocity appears to be better correlated with thickness (r = 0.58) and length (r = 0.62), rather than slope (r = 0.33). Mean annual air temperature had a stronger exponential relationship with maximum velocities (r = 0.76) compared to mean annual velocity (r = 0.60). Front Range rock glacier velocities tend to decrease with warming, suggesting that the volume of ice and debris, rates of shear in plastic layers, or melt water may have a greater influence on deformation. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
18.
The prediction of production rate in ornamental stones sawing is very important in cost estimation and process planning of the rock sawing plants. The main aim of this paper is finding a mathematical correlation between production rate and rock brittleness indexes. The utilized data have been collected from several stone factories in Iran. Seventeen different granite and carbonate rocks have been experienced sawing conditions with large-diameter circular saws. The laboratory tests such as uniaxial compressive strength and tensile strength, were carried out on the rock samples which were collected from these factories. The ratio of compressive strength to tensile strength (B 1), the ratio of compressive strength minus tensile strength to compressive strength plus tensile strength (B 2), and the area under the line of compressive strength and the line of tensile strength (B 3) were used as brittleness indexes in this study. Then, the relationships between these brittleness indexes and production rate were investigated by using a regression analysis. The results show that, there is not a good relationship between the production rate and B 1 and B 2. However, the production rate correlates with B 3 very well. Therefore, there is a reliable prediction for ornamental stones production based on B 3 as a brittleness indexes. 相似文献
19.
Interaction between slab-derived melt and mantle peridotite and the role of slab melt as a metasomatizing agent in the sub-arc mantle is being increasingly recognized. Adakite, the slab melt erupted on the surface, usually exhibits anomalously high MgO, CaO, Cr and Ni contents that indicate interaction with mantle peridotitite. Here we note that Cenozoic adakites have Na2O contents below 5.8 wt.% with ∼95% samples lower than 5.0 wt.%, and are generally depleted in this component relative to experimental basalt partial melts (mostly beyond 5.0 wt.% and up to 9.0 wt.% Na2O) produced under 1.5-3.0 GPa conditions that are most relevant to adakite production. We interpret the adakite Na depletion to be also a consequence of the melt / rock reaction that takes place within the hot mantle wedge. During ascent and reaction with mantle peridotite, primary adakite melts gain mantle components MgO, CaO, Cr and Ni but lose Na2O, SiO2 and perhaps K2O to the mantle, leading to Na-rich mantle metasomatism. Selective assimilation of predominately mantle clinopyroxene, some spinel and minor olivine at high T/P has been considered to be an important process in producing high-Mg adakites from primary low-Mg slab melts [Killian, R., Stern, C. R., 2002. Constraints on the interaction between slab melts and the mantle wedge from adakitic glass in peridotite xenoliths. Eur. J. Mineral. 14, 25-36]. In such a process, Na depletion in the assimilated melt is the result of dilution due to the increase in melt mass. Phase relationships in the reaction system siliceous melt + peridotite and quantitative calculation suggest that assimilation of mantle clinopyroxene, olivine and spinel and fractional crystallization of sodic amphibole and orthopyroxene, under conditions of moderate T/P and increasing melt mass, is also an important process that modifies the composition of adakites and causes the Na depletion. 相似文献
20.
Birger Dahl Jrgen Bojesen-Koefoed Anders Holm Holger Justwan Egil Rasmussen Erik Thomsen 《Organic Geochemistry》2004,35(11-12):1461
A simple method for application in source potential mapping is used to assess the original oil and gas potentials in source rock horizons based upon Rock-Eval potential (S2) and total organic carbon (TOC) values. The method assumes that kerogens consist of mixtures of end-members with assigned hydrogen index values. Based on suggested algorithms, the average amounts of oil-prone, gas-prone and inert organic material over source rock intervals are determined in TOC units. The method uses regression lines from plots of remaining hydrocarbon potentials (S2) versus total organic carbon (TOC), and “quick-look” transparent overlays are used to read the appropriate kerogen mixture.Mineral matrix effects during pyrolysis, when strong, can cause erroneous results. This effect which occurs for oil-prone kerogens and adsorptive minerals can cause problems particularly for lean samples (S2 = 0–3 mg HC/g rock) whilst the errors for richer samples are less.The method is applied on three sections of Upper Jurassic organic-rich rocks from the Danish North Sea sector, which are at different maturity stages. One of these sections is dominated by gas-prone material, one is dominated by oil-prone material and the third section contains a mixture of oil- and gas-prone material.The method has been compared with other methods that split kerogens in oil and gas generating potential and has given reasonable results.Experience using the method and a presented example suggest that sedimentological, system tract information may be derived from S2 to TOC cross-plots. A constructed modelling example suggests that the end-member concept used in this approach may be used in forward type source rock prediction models when combined with sedimentological models. The resulting S2–TOC plots can be used in order to check the forward modelling results against observed values. 相似文献