On estimating the earthquake-induced changes in hydrogeological properties of the Choshuishi Alluvial Fan, Taiwan     

Kuo-Chin Hsu  Chih-Chiu Tung 《Hydrogeology Journal》2005,13(3):467-480

The hydrological response of the Choshuishi alluvial fan to the 1999 Chi-Chi earthquake shows that the earthquake did impact the aquifer. The possible earthquake-induced changes in hydrogeological properties were investigated in this study. First, contour maps of the hydrologic anomaly, seismic factors, and vertical ground-surface displacement were compared qualitatively. Bulls eye patterns were found on the contour maps of hydraulic conductivity, coseismic groundwater-level change and vertical ground-surface displacement but did not occur with other seismic factors. The more permeable zones of the aquifer were found to coincide with the locations of greater vertical ground-surface displacement and coseismic groundwater-level change in the 1999 Chi-Chi earthquake. This indicates that the change of the hydrogeologic properties of Choshuishi alluvial fan due to the 1999 Chi-Chi earthquake may have mainly occurred in the highly permeable zones. Fractal, cross semivariogram and cross correlogram analyses were performed to quantitatively measure the persistency, variability and similarity, respectively, of spatial hydrologic response, seismic factors and hydraulic conductivity. The groundwater-level change, earthquake intensity, and vertical ground-surface displacement were found to show antipersistent tendencies while other factors showed the opposite. Higher correlations were found between hydraulic conductivity and groundwater-level change in aquifers 2–1 and 2–2, and between hydraulic conductivity and vertical ground-surface displacement in aquifer 3. Changes in porosities and hydraulic conductivity were evaluated in the main aquifers of the Choshuishi alluvial fan based on the data of hydrologic anomaly and the vertical ground-surface displacement. While both approaches show that the 1999 Chi-Chi earthquake has impacted the Choshuishi alluvial fan by reducing its porosity and hydraulic conductivity, these changes were not significant relative to natural variation in hydraulic conductivity.This revised version was published in May 2005 with correction to the rubric.  相似文献   

Permeability and degassing of dome lavas undergoing rapid decompression: An experimental determination   总被引：1，自引：1，他引：0  

Sebastian Mueller  Oleg Melnik  Oliver Spieler  Bettina Scheu  Donald B. Dingwell 《Bulletin of Volcanology》2005,67(6):526-538

The gas permeability of volcanic rocks may influence various eruptive processes. The transition from a quiescent degassing dome to rock failure (fragmentation) may, for example, be controlled by the rocks permeability, in as much as it affects the speed by which a gas overpressure in vesicles is reduced in response to decompression. Using a modified shock-tube-based fragmentation bomb (Alidibirov and Dingwell 1996a,b; Spieler et al. 2003a), we have measured unsteady-state permeability at a high initial pressure differential. Following sudden decompression above the rock cylinder, pressurized gas flows through the sample. Two pressure transducers record the pressure signals above and below the sample. A transient 1D filtration code has been developed to calculate permeability using the experimental decay curve of the lower pressure transducer. Additionally an analytical steady-state method to achieve permeability is presented as an alternative to swiftly predict the sample permeability in a sufficiently precise manner. Over 100 permeability measurements have been performed on samples covering a wide range of porosity. The results show a general positive relationship between porosity and permeability with a high data scatter. Our preferred interpretation of the results is a combination of two different, but overlapping effects. We propose that at low porosities, gas escape occurs predominantly through microcracks or elongated micropores and therefore could be described by simplified forms of Kozeny–Carman relations (Carman 1956) and fracture flow models. At higher porosities, the influence of vesicles becomes progressively stronger as they form an increasingly connected network. Therefore, a model based on the percolation theory of fully penetrable spheres is used, as a first approximation, to describe the permeability-porosity trend. In the data acquired to date it is evident, that in addition to the porosity control, the samples bubble size, shape and distribution strongly influence the permeability. This leads to a range of permeability values up to 2.5 orders of magnitude at a given porosity.  相似文献   

Relationships between porosity,organic matter,and mineral matter in mature organic-rich marine mudstones of the Belle Fourche and Second White Specks formations in Alberta,Canada     

《Marine and Petroleum Geology》2014

This study presents approaches for evaluating hybrid source rock/reservoirs within tight-rock petroleum systems. The emerging hybrid source rock/reservoir shale play in the Upper Cretaceous Second White Specks and Belle Fourche formations in central Alberta, Canada is used as an example to evaluate organic and inorganic compositions and their relationships to pore characteristics. Nineteen samples from a 77.5 m-long core were analyzed using organic petrography, organic geochemistry, several methods of pore characterization, and X-ray powder diffraction (XRD). The lower part of the studied section includes quartz- and clay-rich mudrocks of the Belle Fourche Formation with low carbonate content, whereas the upper portion contains calcareous mudrocks of the Second White Specks Formation. Strata are mineralogically composed of quartz plus albite (18–56 wt. %), carbonates (calcite, dolomite, ankerite; 1–65 wt. %), clays (illite, kaolinite, chlorite; 15–46 wt. %), and pyrite (2–12 wt. %). Petrographic examinations document that organic matter represents marine Type II kerogen partly biodegraded with limited terrestrial input. Vitrinite reflectance R_o (0.74–0.87%), T_max values (438–446 °C) and biomarkers indicate mid-maturity within the oil window. The relatively poor remaining hydrocarbon potential, expressed as an S2 value between 2.1 and 6.5 mg HC/g rock, may result from an estimated 60–83% of the original kerogen having been converted to hydrocarbons, with the bulk having migrated to adjacent sandstone reservoirs. However, the present-day remaining total organic carbon TOC_pd content remains relatively high (1.7–3.6 wt. %), compared with the estimated original TOC_o of 2.4–5.0 wt. %. The calculated transformation ratio of 60–83% suggests that the remaining 17–40 wt. % of kerogen is able to generate more hydrocarbons. The studied section is a tight reservoir with an average Swanson permeability of 3.37·10⁻⁵ mD (measured on two samples) and total porosity between 1.7 and 5.0 vol. % (3 vol. % on average). The upper part of the sandy Belle Fourche Formation, with slightly elevated porosity values (3.5–5 vol. %), likely represents the interval with the best reservoir properties in the studied core interval. Total pore volume ranges between 0.0065 and 0.0200 cm³/g (measured by a combination of helium pycnometry and mercury immersion). Mesopores (2–50 nm ∅) are the most abundant pores and occupy 34–67% of total porosity or a volume of 0.0030–0.0081 cm³/g. In comparison, micropores (<2 nm ∅) cover a wide range from 6 to 60% (volume 0.0007–0.0053 cm³/g), and macropores (>50 nm ∅) reach up to 57% with the exception of some samples failing to indicate the presence of this pore fraction (volume 0.0000–0.0107 cm³/g). Macroporosity is mostly responsible for variations in total porosity, as suggested by macroporosity's strongest correlation with total porosity within the section. The relatively narrow ranges of TOC and minerals contents among measured samples limit our ability to further deconvolute factors that influence changes in total porosity and pore size distribution.  相似文献   

Physical properties of sediment from the Mount Elbert Gas Hydrate Stratigraphic Test Well, Alaska North Slope   总被引：1，自引：0，他引：1  

William Winters  Michael WalkerRobert Hunter  Timothy CollettRay Boswell  Kelly RoseWilliam Waite  Marta TorresShirish Patil  Abhijit Dandekar 《Marine and Petroleum Geology》2011,28(2):361-380

This study characterizes cored and logged sedimentary strata from the February 2007 BP Exploration Alaska, Department of Energy, U.S. Geological Survey (BPXA-DOE-USGS) Mount Elbert Gas Hydrate Stratigraphic Test Well on the Alaska North Slope (ANS). The physical-properties program analyzed core samples recovered from the well, and in conjunction with downhole geophysical logs, produced an extensive dataset including grain size, water content, porosity, grain density, bulk density, permeability, X-ray diffraction (XRD) mineralogy, nuclear magnetic resonance (NMR), and petrography.This study documents the physical property interrelationships in the well and demonstrates their correlation with the occurrence of gas hydrate. Gas hydrate (GH) occurs in three unconsolidated, coarse silt to fine sand intervals within the Paleocene and Eocene beds of the Sagavanirktok Formation: Unit D-GH (614.4 m-627.9 m); unit C-GH1 (649.8 m-660.8 m); and unit C-GH2 (663.2 m-666.3 m). These intervals are overlain by fine to coarse silt intervals with greater clay content. A deeper interval (unit B) is similar lithologically to the gas-hydrate-bearing strata; however, it is water-saturated and contains no hydrate.In this system it appears that high sediment permeability (k) is critical to the formation of concentrated hydrate deposits. Intervals D-GH and C-GH1 have average “plug” intrinsic permeability to nitrogen values of 1700 mD and 675 mD, respectively. These values are in strong contrast with those of the overlying, gas-hydrate-free sediments, which have k values of 5.7 mD and 49 mD, respectively, and thus would have provided effective seals to trap free gas. The relation between permeability and porosity critically influences the occurrence of GH. For example, an average increase of 4% in porosity increases permeability by an order of magnitude, but the presence of a second fluid (e.g., methane from dissociating gas hydrate) in the reservoir reduces permeability by more than an order of magnitude.  相似文献   

Porosity preservation due to grain coating illite/smectite: Evidence from Buchan Formation (Upper Devonian) of the Ardmore Field,UK North Sea     

Longxun Tang  Jon Gluyas  Stuart Jones 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(2):202-214

The Buchan Formation sandstone reservoirs from the Ardmore Field in the UK Central North Sea are fluvial-aeolian deposits and provide examples of porosity preservation in deeply-buried reservoirs (2.7–3.2?km) caused by grain-coating illite/smectite (I/S). Here, high reservoir quality commonly correlates with the occurrence of grain-coating I/S and consequent inhibition of quartz cementation in the aeolian dune and interdune sandstones. Porosity is lower in fluvial sandstones lacking grain coating I/S but with intense quartz overgrowths. We propose that the presence of I/S reflects concentration of the smectitic-rich clay bearing water which would have been the deposits of the interdune and/or distal sector of fluvial distributary system, and were introduced into aeolian deposits by mechanical infiltration. Petrographic relationships indicate that these coatings grew mainly before the mechanical compaction as the clays occur at grain contacts. The use of empirical model suggested that about 6–7% porosity have been preserved. The burial-thermal history of the Ardmore area contributed to the high quality reservoir because throughout much of the time since deposition, the Devonian sandstones have been little buried. Only from the Palaeogene the reservoir temperatures exceeded about 70?°C and rapidly buried to today’s maximum depth, which have minimized the negative effect generally ascribed to smectitic clays on reservoir quality. The circumstances of porosity preservation shown in this study may be unusual, but nonetheless have profound consequences for exploration. It is possible to identify new Buchan Formation prospects in areas hitherto dismissed because they were generally assumed to be poor reservoir.  相似文献   

Grain boundary dissolution porosity in quartzofeldspathic ultramylonites: Implications for permeability enhancement and weakening of mid-crustal shear zones     

《Journal of Structural Geology》2013

Quartzofeldspathic ultramylonites from the Alpine Fault Zone, one of the world's major, active plate boundary-scale fault zones have quartz crystallographic preferred orientations (CPO) and abundant low-angle (<10° misorientation) boundaries, typical microstructures for dislocation creep-dominated deformation. Geometrically necessary dislocation density estimates indicate mean dislocation densities of ∼10⁹ cm⁻². A significant proportion (∼30%) of grain boundaries (>10° misorientation) are decorated by faceted pores, commonly with uniformly-oriented pyramidal shapes. Only grain boundaries with >10° misorientation angles in polymineralic aggregates are decorated by pores. Mean grain boundary pore densities are ∼5 × 10⁸ cm⁻². Grain boundary pores are dissolution pits generated during syn-deformational transient grain boundary permeability, nucleating on dislocation traces at dilatant grain boundary interfaces. They have not been removed by subsequent grain boundary closure or annealing. Pore decoration could have led to grain boundary pinning, triggering a switch in the dominant deformation mechanism to grain boundary sliding, which is supported by evidence of CPO destruction in matrix quartz. Pore-decorated grain boundaries have significantly reduced surface area available for adhesion and cohesion, which would reduce the tensile and shear strength of grain boundaries, and hence, the bulk rock. Grain boundary decoration also significantly decreased the mean distance between pores, potentially facilitating dynamic permeability. Consequently, these microstructures provide a new explanation for strain weakening and evidence of fluid flow along grain boundaries in mylonites at mid-crustal conditions.  相似文献   

子长油田安定区长6储层砂岩成岩作用及对孔隙影响     

唐建云  王永东  陈玉宝 《地下水》2014,(5)

根据砂岩薄片、铸体薄片、扫描电镜、X-衍射等分析,对子长油田安定区块长6储层砂体的岩石学特征、成岩作用进行了研究。结果表明：研究区长6储层储集砂体成分主要由长石质岩屑砂岩和岩屑质长石砂岩组成,砂岩具成分成熟度较低、分选性较好、磨圆度较差的特点,其成岩作用处于晚成岩 A 期。早期的压实作用及胶结作用是使原生孔隙遭受破坏的主要因素,而溶蚀作用是形成次生孔隙的主要因素。  相似文献   

：~orous-grain-upper-boundary model and its application to Tarim Basin carbonates     

Guo Yu-Qian  Ma Hong-Da  Shi Kai-Bo  Cao Hong  Huang Lu-Zhong  Yao Feng-Chang  Hu Tian-Yue 《应用地球物理》2013,(4):411-422,511

Most of the carbonates in the Tarim Basin in northwest China are low-porosity and low-permeability rocks. Owing to the complexity of porosity in carbonates, conventional rock- physics models do not describe the relation between velocity and porosity for the Tarim Basin carbonates well. We propose the porous-grain-upper-boundary （PGU） model for estimating the relation between velocity and porosity for low-porosity carbonates. In this model, the carbonate sediments are treated as packed media of porous elastic grains, and the carbonate pores are divided into isolated and connected pores The PGU model is modified from the porous-grain-stiff-sand （PGST） model by replacing the critical porosity with the more practical isolated porosity. In the implementation, the effective elastic constants of the porous grains are calculated by using the differential effective medium （DEM） model. Then, the elastic constants of connected porous grains in dry rocks are calculated by using the modified upper Hashin-Shtrikman bound. The application to the Tarim carbonates shows that relative to other conventional effective medium models the PGU model matches the well log data well.  相似文献   

Impact of sedimentology and diagenesis on the petrophysical properties of a tight oolitic carbonate reservoir. The case of the Oolithe Blanche Formation (Bathonian,Paris Basin,France)     

《Marine and Petroleum Geology》2013

The Oolithe Blanche Formation was studied in three quarries, located at the south-eastern edge of the Paris Basin (France). Heterogeneities in reservoir properties were assessed through a sedimentological, diagenetic and petrophysical study. The relationships between depositional settings, diagenesis and petrophysical properties were analysed using detailed petrographic studies, image analysis, Nano CT-scans and petrophysical measurements.The carbonate reservoir pore network is mainly controlled by intraparticle microporosity which ensures the connectivity with interparticle meso- and macroporosity.Early cementation vs. early compaction processes (mainly grain interpenetration) may have considerable influence on fluid-flow properties and parameters such as permeability, acoustic velocities and tortuosity. Better reservoir properties are found when compaction processes begin before cementation.From statistical analyses, e.g. Principal Component Analysis and Linear Discriminant Analysis, a sedimentological/diagenetic and petrophysical model is proposed that is in a good agreement with the geological model developed from field work.  相似文献   

油砂组分遥感光谱响应特征及意义          下载免费PDF全文

尤金凤  邢立新  潘军  单玄龙  樊瑞雪 《地球物理学报》2016,59(8):3068-3078

基于油砂组分的吸收光谱物理响应机理,通过对比矿物基团平均吸收深度,建立主要蚀变矿物ASTER多光谱遥感数据异常提取模式以识别油砂分布.研究表明,与传统的烃类微渗漏遥感研究手段相比,该模式可以更有效地指示油砂的分布.利用油砂组分基团光谱平均吸收深度与孔隙度及渗透率进行相关分析,研究了油砂光谱与所处地质背景环境中储层物性之间的关联关系.结果表明,表征粘土矿物含量的粘土基团吸收深度与孔渗值呈负相关关系,指示含油性的烃类基团吸收深度与孔渗值呈显著正相关关系.  相似文献