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921.
922.
Optimal filtering high-resolution seismic reflection data using a weighted-mode empirical mode decomposition operator 总被引:2,自引:0,他引:2
Leonardo Macelloni Bradley Matthew Battista Camelia Cristina Knapp 《Journal of Applied Geophysics》2011,75(4):603-614
Gas-hydrate related processes in deep-water marine settings exist on spatial scales that challenge conventional seismic reflection profiling to successfully image them. The conventional approach to acoustic identification of buried hydrates is to use advanced, cost-prohibitive survey techniques and highly customized software to define subsurface structure wherein compositional changes may be modeled and/or interpreted. This study adopts a different approach derived from recent theoretical advancements in signal processing. The method consists in optimal filtering high resolution, single-channel seismic reflection data using the Empirical Mode Decomposition (EMD). The time series is decomposed in sub-components and the noisy portions are suppressed adopting the technique that we referred as Weighted Mode(s) EMD. The optimal filtering greatly improves the resolution and fidelity of the seismic data set.High Resolution single channel seismic profiles, acquired over a carbonate\hydrates site in the northern Gulf of Mexico, manipulated in such way, show a complex, shallow subsurface, and suggest potential evidence for buried gas hydrates. 相似文献
923.
924.
Relative permeability of CBM reservoirs: Controls on curve shape 总被引:1,自引:0,他引:1
C.R. Clarkson M. Rahmanian A. Kantzas K. Morad 《International Journal of Coal Geology》2011,88(4):204
Relative permeability to gas and water for 2-phase flow coalbed methane (CBM) reservoirs has long been known to exhibit a strong control on (gas and water) production profile characteristics. Despite its important control on both primary and enhanced recovery of CBM for coal seams that have not been fully dewatered, relative permeability in coal has received little attention in the literature in the past decade. There are few published laboratory-derived curves; these studies and their resulting data represent a small subset of the commercial CBM reservoirs and do not allow for a systematic investigation of the physical controls on relative permeability curve shape. Other methods for estimation of relative permeability curves include derivation from simulation history-matching, and production data analysis. Both of these methods will yield pseudo-relative permeability curves whose shapes could be affected by several dynamic CBM reservoir and operating characteristics.The purpose of the current work is to perform a systematic investigation of the controls on CBM relative permeability curve shape, including non-static fracture permeability and porosity, multi-layer effects and transient flow. To derive the relative permeability curves, effective permeability to gas and water are obtained from flow equations, flow rates and pressure data. Simulated cases are analyzed so that derived and input curves may be compared allowing for investigation of CBM reservoir properties on curve shape. One set of relative permeability curves that were input into the simulator were obtained from pore-scale modeling. Field cases from two basins are also examined and controls on derived relative permeability curve shape inferred. The results of this work should be useful for future CBM development and greenhouse gas sequestration studies, and it is hoped that it will spark additional research of this critical CBM flow property. 相似文献
925.
Sorption of methane on lignite from Polish deposits 总被引:1,自引:0,他引:1
Coal samples from Miocene lignite deposits (ortholignite—ECE-UN 2002) in Belchatow, Adamow, Konin and Turow (Poland) were analyzed to determine the relationships between coal properties and gas capacity.Investigations presented here addressed the occurrence of methane sorbet in lignite deposits within Poland's largest penetrated lignite deposits (e.g., Belchatow, Adamow, Turow and Konin).Lignite samples collected from surface mines were detritic coal with variable contents of xylites. The highest level of xylites (up to 25 vol.%) was found in carbon samples taken from the Belchatow deposit. Samples from other mines contained no more than 10 vol.% xylites. Petrographic compositions were dominated by huminite group macerals (73-88 vol.%) with atrinite, densinite and texto-ulminite, a porous form of ulminite; inertinite groups were less important components (4-8 vol.%).Isotherms were determined for methane sorption at 298 K with test pressure ranges below 1.2 MPa. At a pressure of 1.0 MPa, the largest gas capacity of approximately 1.7 [dm3 STP/kg] was found in the sample from Belchatow. This result may have been attributable to differences in the porosity of the samples; the porosity of the sample from Belchatow was twice as high as the porosities of the other coal samples. This variation in porosity resulted from the lithologic and maceral composition of the coal sample that contained substantial quantities of porous textinite and texto-ulminite.The thermal sorption equation was used to determine the limiting values of isosteric enthalpy of sorption, which suggested weak interactions between methane and the lignite matrix. The residual gas capacity of the tested samples was also determined.All samples exhibited a high residual methane-bearing capacity, which may not only cause methane to be released from coal at a pressure of 1 bar but also may pose a gas risk during mining operations. 相似文献
926.
水力封堵型煤层气藏判识条件分析 总被引:1,自引:0,他引:1
从宏观和微观两个方面分析了不同条件下煤层气的赋存特征,总结出水力封堵型煤层气藏的判识条件。研究表明,宏观上,可以通过煤储层边界的物理性质进行判识,在煤储层与地下水连通的基础上,分析断层、岩性、地下水三者之间的组合对水力封堵型煤层气藏赋存所起的作用,将水力封堵型煤层气藏划分为地层-水力封堵型、开放性断层-水力封堵型、封闭性断层-水力封堵型、岩性-水力封堵型、开放性断层-岩性-水力封堵型五种类型;微观上,主要通过煤储层流体的化学性质来判识,包括水的矿化度、水化学类型、甲烷碳同位素等三个方面,通常水力封堵型煤层气藏的地层水矿化度低于1 000mg/L,甲烷碳同位素较轻,且水化学类型为NaHCO3型、Na2SO4型或为NaHCO3和Na2SO4混合型。 相似文献
927.
We have implemented a 2-dimensional numerical model for simulating gas hydrate and free gas accumulation in marine sediments. The starting equations are those of the conservation of the transport of momentum, energy, and mass, as well as those of the thermodynamics of methane hydrate stability and methane solubility in the pore-fluid. These constitutive equations are then integrated into a finite element in space, finite-difference in time scheme. We are then able to examine the formation and distribution of methane hydrate and free gas in a simple geologic framework, with respect to the geothermal heat flow, fluid flow, the methane in-situ production and basal flux. Three simulations are performed, leading to the build up of hydrate emplacements largely linear through time. Models act primarily as free gas accumulators and are relatively inefficient with respect to hydrate emplacements: 26–33% of formed methane are converted to hydrate. Seepage of methane across the sea-floor is negligible for fluid flow below 2. 10−11 kg/m2/s. At 5.625 10−11 kg/m2/s however, 9.7% of the formed methane seeps out of the model. Moreover, along strike variation arising in the 2-dimensional model are outlined. In the absence of focused flow, the thermodynamics of hydrate accumulation are primarily one-dimensional. However, changes in free methane compressibility (density) and methane solubility (the intrinsic dissolved methane flux) subtlety impact on the formation of a free gas zone and the distribution of the hydrate emplacements in our 2-dimensional simulations. 相似文献
928.
揭示台风对湿地土壤甲烷产生的影响对全球气候变化研究具有重要意义。采用厌氧培养法对闽江河口芦苇湿地土壤受台风影响下的甲烷产生潜力(J)进行模拟实验。研究结果表明:受台风的影响,甲烷产生潜力经历了升高—下降—稳定—下降4个阶段;花枯落物输入与根、茎、叶枯落物输入后芦苇湿地土壤甲烷产生潜力差异极显著(P〈0.01);台风影响... 相似文献
929.
K.-Y. Wang J. A. Pyle D. E. Shallcross D. J. Larry 《Journal of Atmospheric Chemistry》2001,38(1):31-71
In part two of this series of papers on the IMS model, we present the chemistry reaction mechanism usedand compare modelled CH4, CO, and O3 witha dataset of annual surface measurements. The modelled monthly and 24-hour mean tropospheric OH concentrationsrange between 5–22 × 105 moleculescm–3, indicating an annualaveraged OH concentration of about 10 × 105 moleculescm–3. This valueis close to the estimated 9.7 ± 0.6 × 105 moleculescm–3 calculated fromthe reaction of CH3CCl3 with OH radicals.Comparison with CH4 generally shows good agreementbetween model and measurements, except for the site at Barrow where modelledwetland emission in the summer could be a factor 3 too high.For CO, the pronounced seasonality shown in the measurements is generally reproduced by the model; however, the modelled concentrations are lower thanthe measurements. This discrepancy may due to lower the CO emission,especially from biomass burning,used in the model compared with other studies.For O3, good agreement between the model and measurements is seenat locations which are away from industrial regions. The maximum discrepancies between modelled results and measurementsat tropical and remote marine sites is about 5–10 ppbv,while the discrepancies canexceed 30 ppbv in the industrial regions.Comparisons in rural areas at European and American continental sites arehighly influenced by the local photochemicalproduction, which is difficult to model with a coarse global CTM.The very large variations of O3 at these locations vary from about15–25 ppbv in Januaryto 55–65 ppbv in July–August. The observed annual O3amplitude isabout 40 ppbv compared with about 20 ppbv in the model. An overall comparison of modelled O3 with measurements shows thatthe O3seasonal surface cycle is generally governed bythe relative importance of two key mechanisms that drivea springtime ozone maximum and asummertime ozone maximum. 相似文献
930.
Global distribution of natural freshwater wetlands and rice paddies,their net primary productivity,seasonality and possible methane emissions 总被引:18,自引:0,他引:18
A global data set on the geographic distribution and seasonality of freshwater wetlands and rice paddies has been compiled, comprising information at a spatial resolution of 2.5° by latitude and 5° by longitude. Global coverage of these wetlands total 5.7×106 km2 and 1.3×106 km2, respectively. Natural wetlands have been grouped into six categories following common terminology, i.e. bog, fen, swamp, marsh, floodplain, and shallow lake. Net primary productivity (NPP) of natural wetlands is estimated to be in the range of 4–9×1015 g dry matter per year. Rice paddies have an NPP of about 1.4×1015 g y–1. Extrapolation of measured CH4 emissions in individual ecosystems lead to global methane emission estimates of 40–160 Teragram (1 Tg=1012 g) from natural wetlands and 60–140 Tg from rice paddies per year. The mean emission of 170–200 Tg may come in about equal proportions from natural wetlands and paddies. Major source regions are located in the subtropics between 20 and 30° N, the tropics between 0 and 10° S, and the temperate-boreal region between 50 and 70° N. Emissions are highly seasonal, maximizing during summer in both hemispheres. The wide range of possible CH4 emissions shows the large uncertainties associated with the extrapolation of measured flux rates to global scale. More investigations into ecophysiological principals of methane emissions is warranted to arrive at better source estimates. 相似文献