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1.
Microbial carbonates in Holocene beachrocks,Shuiweiling, Luhuitou Peninsula,Hainan Island 总被引：2，自引：0，他引：2
Two research methods, geomicrobiology and carbonate sedimentology, were adopted to study the microbial carbonates in the beachrocks, Shuiweiling, Luhuitou, Sanya City, Hainan Island. The results indicate that microbial carbonates occur in Shuiweiling beachrocks and cements related to microbial activitives are common. Microbial carbonates were mainly developed on the surfaces of coral skeletons and within the coral (fragments and shivers) skeletal cavities,and rarely grew in interspaces formed by coral and other biological detritus. The growth morphologies of microbial carbonates are various, including stromatolitic lamination, thin crusts, dome-like, and microbialites. Microbial carbonates commonly trap fine-sized bioclasts, contain tubular filaments, and show laminated growth striation. Microbial carbonates within the coral skeletal cavities are generally stromatolitic cone-shaped, with a random growth direction along the bearing of trend of cavities, showing distinct growth laminae and recognizable growth phases. It is a special growth pattern of crypt microbial carbonates. Microbial cements occur mainly in shape of needle cement, calcified filaments, microborings, and calcified framboidal spheres. The needle cement is the most common type. These microbial cements indicate that microbial activities and microbial carbonates played an important role in beachrock formation in which carbonates were dominant components and the climate of tropical ocean monsoon was influential. Such microbial carbonates and microbial cementation have not been reported here from beachrocks along the northern shorelines of the South China Sea. The results support a clear microbial origin for certain carbonate cements in beachrocks, confirm that microbial carbonates are a significant contributor to carbonate sedimentation, and widen the knowledge of beachrocks from a new field. 相似文献
2.
3.
Tyler G. Sproule Glenn A. Spinelli John L. Wilson Michael D. Fort Peter S. Mozley Jared Ciarico 《Ground water》2021,59(3):396-409
Fault zones are an important control on fluid flow, affecting groundwater supply, contaminant migration, and carbon storage. However, most models of fault seal do not consider fault zone cementation, despite the recognition that it is common and can dramatically reduce permeability. In order to study the field-scale hydrogeologic effects of fault zone cementation, we conducted a series of aquifer pumping tests in wells installed within tens of meters of the variably cemented Loma Blanca Fault, a normal fault in the Rio Grande Rift. In the southern half of the study area, the fault zone is cemented by calcite; the cemented zone is 2-8 m wide. In the center of the study area, the cemented fault zone is truncated at a buttress unconformity that laterally separates hydrostratigraphic units with a ∼40X difference in permeability. The fault zone north of the unconformity is not cemented. Constant rate pumping tests indicate that where the fault is cemented, it is a barrier to groundwater flow. This is an important demonstration that a fault with no clay in its core and similar sediment on both sides can be a barrier to groundwater flow by virtue of its cementation; most conceptual models for the hydrogeology of faults would predict that it would not be a barrier to groundwater flow. Additionally, the lateral permeability heterogeneity across the unconformity imposes another important control on the local flow field. This permeability discontinuity acts as either a no-flow boundary or a constant head boundary, depending on the location of pumping. 相似文献
4.
Koichiro Fujimoto Hidemi Tanaka Takayuki Higuchi Naoto Tomida Tomoyuki Ohtani Hisao Ito 《Island Arc》2001,10(3-4):401-410
Abstract Mineralogical and geochemical studies on the fault rocks from the Nojima–Hirabayashi borehole, south-west Japan, are performed to clarify the alteration and mass transfer in the Nojima Fault Zone at shallow depths. A complete sequence from the hornblende–biotite granodiorite protolith to the fault core can be observed without serious disorganization by surface weathering. The parts deeper than 426.2 m are in the fault zone where rocks have suffered fault-related deformation and alteration. Characteristic alteration minerals in the fault zone are smectite, zeolites (laumontite, stilbite), and carbonate minerals (calcite and siderite). It is inferred that laumontite veins formed at temperatures higher than approximately 100°C during the fault activity. A reverse component in the movement of the Nojima Fault influences the distribution of zeolites. Zeolite is the main sealing mineral in relatively deep parts, whereas carbonate is the main sealing mineral at shallower depths. Several shear zones are recognized in the fault zone. Intense alteration is localized in the gouge zones. Rock chemistry changes in a different manner between different shear zones in the fault zone. The main shear zone (MSZ), which corresponds to the core of the Nojima Fault, shows increased concentration of most elements except Si, Al, Na, and K. However, a lower shear zone (LSZ-2), which is characterized by intense alteration rather than cataclastic deformation, shows a decreased concentration of most elements including Ti and Zr. A simple volume change analysis based on Ti and Zr immobility, commonly used to examine the changes in fault rock chemistry, cannot account fully for the different behaviors of Ti and Zr among the two gouge zones. 相似文献
5.
We studied the fine-grained matrices (< 150 μm) of 14 gas-rich ordinary chondrite regolith breccias in an attempt to decipher the nature of the lithification process that converted loose regolith material into consolidated breccias. We find that there is a continuous gradation in matrix textures from nearly completely clastic (class A) to highly cemented (class C) breccias in which the remaining clasts are completely surrounded by interstitial, shock-melted material. We conclude that this interstitial material formed by shock melting in the porous regolith. In general, the abundances of solar-wind-implanted 4He and 20Ne are inversely correlated with the abundance of interstitial, shock-melted, feldspathic material. Chondrites with the highest abundance of interstitial, melted material (class C) experienced the highest shock pressures and temperatures and suffered the most extensive degassing. It is this interstitial, feldspathic melt that lithifies and cements the breccias together; those breccias with very little interstitial melt (class A) are the most porous and least consolidated. 相似文献
6.
为进一步探讨上地幔的高导层成因,了解碳酸盐在上地幔电性方面的作用并估算上地幔高导层的碳酸盐含量,本文对不同碳酸盐含量的橄榄岩及玄武岩样品在2~3 GPa、300~1300℃的条件下进行了电性实验研究.研究初步发现:碳酸盐熔体显著增强橄榄岩、玄武岩样品的导电能力;单纯用含硅酸盐熔体的橄榄岩或单纯用含水橄榄岩可能难以解释上地幔某些区域的异常高导现象;同样,单纯用碳酸盐化的橄榄岩可能也难以解释上地幔某些区域的高导现象;上地幔的高导区很可能是碳酸盐熔体、硅酸盐熔体及水的共存区域. 相似文献
7.
A. A. Sidorov 《Journal of Volcanology and Seismology》2008,2(3):143-148
Contrasting volcanism (rhyolite-basalt) is typical of volcanogenic ore-bearing zones. At the same time, it has not been considered correct to regard contrasting volcanism as an exploration criterion for such zones, since the basaltoid member of volcanism is frequently postmineral. However, there is sufficient reason to consider subvolcanic bodies of postmineral basaltoids as the latest (terminating) formations of an approaching front of basic magmas, which is the cause of upper crustal granitoid magmatism and hydrothermal anomalies. Naturally enough, all volcanism ceases after the basaltoid effusions, and the hydrothermal systems also gradually disappear. Relicts of these systems are frequently reliably identified as quartz carbonate geodes in basaltic andesite sheets and dikes. 相似文献
8.
Tanguy Robert Alain DassarguesSerge Brouyère Olivier KaufmannVincent Hallet Frédéric Nguyen 《Journal of Applied Geophysics》2011,75(1):42-53
ERT and SP investigations were conducted in carbonate rocks of the Dinant Synclinorium (Walloon Region of Belgium) to find suitable locations for new water wells in zones with little hydrogeological data. Since boreholes information needed to be representative of the area, large fractured zones were searched for the drillings. Large ERT profiles (320 to 640 m) allowed us to image the resistivity distribution of the first 60 m of the subsurface and to detect and characterize (in terms of direction, width and depth) fractured zones expected to be less resistive. Data errors, depth of investigation (DOI) indexes and sensitivity models were analyzed in order to avoid a misinterpretation of the resulting images. Self-potential measurements were performed along electrical profiles to complement our electrical results. Some negative anomalies possibly related to preferential flow pathways were detected. A drilling campaign was conducted according to geophysical results. ‘Ground truth’ geological data as well as pumping tests information gave us a way to assess the contribution of geophysics to a drilling program. We noticed that all the wells placed in low resistivity zones associated with SP anomalies provide very high yields and inversely, wells drilled in resistive zones or outside SP anomalies are limited in terms of capacity. An apparent coupling coefficient between SP signals and differences in hydraulic heads was also estimated in order to image the water table. 相似文献
9.
Augustus K. Armstrong Jacques R. Renault Robert L. Oscarson 《Journal of Volcanology and Geothermal Research》1995,67(1-3)
Continental Scientific Drilling Program (CSDP) drill hole VC-2B [total depth 1761.7 m (5780 ft); maximum temperature 295 °C] was continuously cored through the Sulphur Springs hydrothermal system in the western ring-fracture zone of the 1.14 Ma Valles caldera. Among other units, the hole penetrated 760.2 m (2494.1 ft) of Paleozoic carbonate and siliciclastic strata underlying caldera fill and precaldera volcanic and epiclastic rocks. Comparison of the VC-2B Paleozoic rocks with corresponding lithologies within and around the 32.1 Ma Socorro caldera, 192 km ( 119 miles) to the south-southwest, provides insight into the variability of alteration responses to similar caldera-related hydrothermal regimes.The Pennsylvanian Madera Limestone and Sandia Formation from VC-2B preserve many of the sedimentological and diagenetic features observed in these units on a regional basis and where unaffected by high temperatures or hydrothermal activity. Micrites in these formations in VC-2B are generally altered and mineralized only where fractured or brecciated, that is, where hydrothermal solutions could invade carbonate rocks which were otherwise essentially impermeable. Alteration intensity (and correspondingly inferred paleopermeability) is only slightly higher in carbonate packstones and grainstones, low to intermediate in siltstones and claystones, and high in poorly cemented sandstones. Hydrothermal fracture-filling phases in these rocks comprise sericite (and phengite), chlorite, allanite, apatite, an unidentified zeolite and sphene in various combinations, locally with sphalerite, galena, pyrite and chalcopyrite. Terrigenous feldspars and clays are commonly altered to chlorite and seriate, and euhedral anhydrite “porphyroblasts” with minor chlorite occur in Sandia Formation siltstone. Fossils are typically unaltered, but the walls of some colonial bryozoans in the Madera Limestone are altered to the assemblage chlorite-sericite-epidote-allanite. La, Ce and Nd are present in an unidentified hydrothermal mineral occurring throughout much of the VC-2B Pennsylvanian sequence.Carboniferous carbonate and siliciclastic formations within and around the Socorro caldera show a similar style of alteration and mineralization to their Valles caldera counterparts, but by contrast locally host commercial, caldera-related, base-metal sulfide deposits. As in the Valles rocks, mineralization and alteration in those of the Socorro caldera were strongly controlled by porosity. Unless disrupted by fractures, breccias, or karst cavities ( not identified in Valles caldera drill holes), the rocks remained relatively unaltered. Where these features allowed ingress of mineralizing hydrothermal solutions, base-metal sulfides and rare-earth-element-bearing minerals were precipitated. 相似文献
10.
Fernando Gázquez José María Calaforra Paolo Forti Heather Stoll Bassam Ghaleb Antonio Delgado‐Huertas 《地球表面变化过程与地形》2014,39(10):1345-1353
Speleothems are usually composed of thin layers of calcite (or aragonite). However, cemented detrital materials interlayered between laminae of speleothemic carbonate have been also observed in many caves. Flowstones comprising discontinuous carbonate layers form due to flowing water films, while flood events introduce fluviokarstic sediments in caves that, on occasion, are recorded as clayey layers inside flowstones and stalagmites. This record provides a potential means of understanding the frequency of palaeofloods using cave records. In this work, we investigate the origin of this type of detrital deposit in El Soplao Cave (Northern Spain). The age of the lowest aragonite layer of a flowstone reveals that the earliest flood period occurred before 500 ka, though most of the flowstone formed between 422 +69/‐43 ka and 400 +66/‐42 ka. This suggests that the cave was periodically affected by palaeoflood events that introduced detrital sediments from the surface as a result of occasional extreme rainfall events, especially at around 400 ka. The mineralogical data enable an evolutionary model for this flowstone to be generated based on the alternation of flood events with laminar flows and carbonate layers precipitation that can be extrapolated to other caves in which detrital sediments inside speleothems have been found. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
11.
Alla Shogenova Anne Kleesment Ann Hirt Enn Pirrus Toivo Kallaste Kazbulat Shogenov Rein Vaher 《Studia Geophysica et Geodaetica》2009,53(1):111-131
The formation of hematite and goethite concretions in different sedimentary rocks including sandstones is an important diagenetic
process in the geologic history of the Earth. Its interpretation can also contribute to understanding the diagenetic history
of Martian iron hydroxide concretions.
A case study of iron-rich concretions from Estonian Middle Devonian sandstones exposed in ancient river valleys in southeastern
Estonia was carried out based on the results of mineralogical, petrographical, geochemical, petrophysical and magnetic analyses.
It was found that the high Fe2O3(total) content (25.0–39.5%), high magnetic susceptibility, bulk and grain density, very low porosity, corrosion and fracturing
of the quartz grains of the platy iron concretions are in contrast with properties of the Devonian host sandstones. However
the ferrous iron content (measured as FeO) of iron-rich concretions was as low as in the other Devonian rocks, suggesting
an oxidizing environment and arid climate during the cementation by iron-hydroxides. The fracturing of quartz grains cemented
by iron hydroxides could take place at near-surface conditions including vadose and phreatic zones in arid climate with high
evaporation rates. Such climatic conditions have been reported for the Baltic region during Devonian, Upper Permian and Triassic
times.
We have found that goethite is prevalent in the cement, replacing clay and carbonate minerals. We assume that this iron-rich
cement is originated from the mobilization of iron in host sandstones by groundwater, associated with tectonic activity at
the end of the Middle Devonian, evidenced by fracturing in Devonian outcrops and caves. Although this mobilization could occur
under reducing conditions, precipitation of goethite and hematite for the cementation could take place in oxidizing environment
along bedding planes close to the surface during short sedimentation breaks. Another possible time for the formation of iron
concretions could be Permian, under the condition of both arid climate and tectonic activity. 相似文献
12.
The reservoir quality of Jurassic and Triassic fluvial and lacustrine-deltaic sandstones of the Yanchang Oil Field in the Ordos Basin is strongly influenced by the burial history and facies-related diagenetic events. The fluvial sandstones have a higher average porosity (14.8%) and a higher permeability (12.7×10?3 ?m2) than those of the deltaic sandstones (9.8% and 5.8 ×10?3 ?m2, respectively). The burial compaction, which resulted in 15% and 20% porosity loss for Jurassic and Triassic sandstones, respectively, is the main factor causing the loss of porosity both for the Jurassic and Triassic sandstones. Among the cements, carbonate is the main one that reduced the reservoir quality of the sandstones. The organic acidic fluid derived from organic matter in the source rocks, the inorganic fluid from rock-water reaction during the late diagenesis, and meteoric waters during the epidiagenesis resulted in the formation of dissolution porosity, which is the main reason for the enhancement of reservoir-quality. 相似文献
13.
Application of alternative digital rock physics methods in a real case study: a challenge between clean and cemented samples 
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下载免费PDF全文 Sadegh Karimpouli Sadegh Khoshlesan Erik H. Saenger Hamed Hooshmand Koochi 《Geophysical Prospecting》2018,66(4):767-783
High‐resolution three‐dimensional images are used in digital rock physics to numerically compute rock physical properties such as permeability and elastic moduli. These images are not widely available, and their preparation is both expensive and time consuming. All of these issues highlight the importance of alternative digital rock physics methods that are based on two‐dimensional images and use different approaches to compute effective properties of three‐dimensional samples. In addition, the scale of study in both standard and alternative digital rock physics is very small, which applications of its results are questionable at wells or reservoir scale. The aim of this study is to use two‐dimensional images and alternative digital rock physics techniques for computing seismic wave velocity and permeability, which are compared with well and laboratory data. For this purpose, data from one well in a reservoir located in the southwestern part of Iran are used. First, two clean (carbonate) and two cemented (limy sandstone) samples were collected from well cores at different depths. Then, two‐dimensional images by scanning electron microscope and conventional microscope were captured. In the next step, two alternative digital rock physics methods, namely, empirical relations and conditional reconstruction, have been employed to compute P‐wave velocity and permeability of a three‐dimensional medium. Results showed that, in clean (mono‐mineral) samples, velocity values were reasonably close to well data. However, permeability values are underestimated compared with laboratory data because laboratory data were obtained at ambient pressure, whereas alternative digital rock physics results are more representative of reservoir pressure conditions. Nevertheless, permeability–porosity trends are valid for both samples. In the case of cemented samples, a two‐scale procedure, along with a method for two‐scale computation and grain‐cement segmentation, is presented and developed. Results showed that P‐wave velocity is overestimated probably due to random sampling in this method. However, velocity–porosity trends are in agreement with well data. Moreover, permeability results obtained for cemented samples were also similar to those obtained for the clean samples. 相似文献
14.
Understanding the transport of chemical components in porous media is fundamentally important to many reservoir processes such as contaminant transport and reactive flows involved in CO2 sequestration. Carbonate rocks in particular present difficulties for pore-scale simulations because they contain large amounts of sub-micron porosity. In this work, we introduce a new hybrid simulation model to calculate hydrodynamic dispersion in pore-scale images of real porous media and use this to elucidate the origins and behaviour of stagnant zones arising in transport simulations using micro-CT images of carbonates. For this purpose a stochastic particle model for simulating the transport of a solute is coupled to a Lattice-Boltzmann algorithm to calculate the flow field. The particle method incorporates second order spatial and temporal resolution to resolve finer features of the domain. We demonstrate how dispersion coefficients can be accurately obtained in capillaries, where corresponding analytical solutions are available, even when these are resolved to just a few lattice units. Then we compute molecular displacement distributions for pore-spaces of varying complexity: a pack of beads; a Bentheimer sandstone; and a Portland carbonate. Our calculated propagator distributions are compared directly with recent experimental PFG-NMR propagator distributions (Scheven et al., 2005; Mitchell et al., 2008), the latter excluding spin relaxation mechanisms. We observe that the calculated transport propagators can be quantitatively compared with the experimental distribution, provided that spin relaxations in the experiment are excluded, and good agreement is found for both the sandstone and the carbonate. However, due to the absence of explicit micro-porosity from the carbonate pore space image used for flow field simulations we note that there are fundamental differences in the physical origins of the stagnant zones for micro-porous rocks between simulation and experiment. We show that for a given micro-CT image of a carbonate, small variations in the parameters chosen for the segmentation process lead to different amounts of stagnancy which diffuse away at different rates. Finally, we use a filtering method to show that this is due to the presence of spurious isolated pores which arise from the segmentation process and suggest an approach to overcome this limitation. 相似文献
15.
V. Rabemanana S. Violette G. de Marsily H. Robain B. Deffontaines P. Andrieux M. Bensimon A. Parriaux 《Journal of Hydrology》2005,310(1-4):143-156
This study assesses the causes of the high spatial variability of the mineral content of groundwater in crystalline bedrock of Southern Madagascar. Although many kilometres from the coast and at a mean altitude of 400 m a.s.l, wells drilled in this area produce water with electrical conductivities in the range of 300–30,000 μS cm−1 with a high spatial variability. Chemical and isotopic data are used to identify the processes involved in the groundwater mineralization. It is shown that the chemical composition of the groundwater in this region has its origin in (i) normal silicate and carbonate weathering reactions and (ii) input of marine salts, probably via rainfall recharge, modified by evapo-concentrative processes probably including precipitation and re-dissolution of secondary evaporites in the unsaturated zone. To obtain a better understanding of the spatial salinity distribution, well parameters such as yields, weathered zone thickness, weathered materials and morphological positions (upper slope, mid-slope, lower slope or valley bottom) are scrutinized.
A correlation was found between high salinity and low flow, shallow groundwater environments (flat hill tops, valley bottoms, weakly developed and clayey weathered zones) and between low salinity and high flow environments (granular, well-developed weathered zones and situation on valley slopes). 相似文献
16.
碳酸盐岩储层是南堡凹陷潜山重要的勘探领域,由于受到构造、岩性等多种因素的影响,常规储层预测难度大.本文提出相控储层预测方法,通过井上精细对比,确定南堡凹陷潜山碳酸盐岩储层的优势发育段,结合古地貌确定其有利分布相带,在有利相带约束下,优选出地震平均能量属性、曲率体属性、蚂蚁体属性和谱分解属性,融合这些属性,综合预测储层发育区.通过与已钻井的对比,储层发育区与钻井资料吻合度高,证实了该方法的有效性,同时为南堡凹陷潜山的展开勘探提供了参考. 相似文献
17.
The effect of low‐permeability fault zones on groundwater flow in a compartmentalized system. Experimental evidence from a carbonate aquifer (Southern Italy) 下载免费PDF全文
下载免费PDF全文 The hydrogeological behaviour of fault zones in carbonate aquifers is often neglected in conceptual and numerical models. Furthermore, no information is available regarding the relationships between piezometric levels when significant compartmentalization occurs due to the occurrence of low‐flow fault zones. The aim of this study was to refine the conceptualization of subsurface flow in faulted carbonate aquifers and to analyse relationships between sub‐basins within a compartmentalized aquifer system in Southern Italy. The interactions between compartments that straddle low‐flow faults were investigated over four hydrologic years using a statistical approach to compare (i) the hydraulic heads within two wells located up‐ and down‐gradient of tectonic discontinuities as well as (ii) the rainfall and piezometric levels. The results of this study suggest that a set of barriers exists between the wells, and, therefore, the total head loss observed between the wells (approximately 80 m) should be distributed across several aquitards, with one aquitard exhibiting a relatively high permeability or low degree of integrity. Due to slight differences in permeability, transient conditions in aquitards can occur over relatively short periods, which is in agreement with the results of the statistical data analysis. Consequently, rather than being caused by pure aquitards, aquifer system compartmentalization likely results from slight differences in the permeability between lower‐permeability fault zones and adjacent higher‐permeability protoliths. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
18.
James C. Adamski 《水文研究》2000,14(5):849-866
Geochemical data indicate that the Springfield Plateau aquifer, a carbonate aquifer of the Ozark Plateaus Province in central USA, has two distinct hydrochemical zones. Within each hydrochemical zone, water from springs is geochemically and isotopically different than water from wells. Geochemical data indicate that spring water generally interacts less with the surrounding rock and has a shorter residence time, probably as a result of flowing along discrete fractures and solution openings, than water from wells. Water type throughout most of the aquifer was calcium bicarbonate, indicating that carbonate‐rock dissolution is the primary geochemical process occurring in the aquifer. Concentrations of calcium, bicarbonate, dissolved oxygen and tritium indicate that most ground water in the aquifer recharged rapidly and is relatively young (less than 40 years). In general, field‐measured properties, concentrations of many chemical constituents, and calcite saturation indices were greater in samples from the northern part of the aquifer (hydrochemical zone A) than in samples from the southern part of the aquifer (hydrochemical zone B). Factors affecting differences in the geochemical composition of ground water between the two zones are difficult to identify, but could be related to differences in chert content and possibly primary porosity, solubility of the limestone, and amount and type of cementation between zone A than in zone B. In addition, specific conductance, pH, alkalinity, concentrations of many chemical constituents and calcite saturation indices were greater in samples from wells than in samples from springs in each hydrochemical zone. In contrast, concentrations of dissolved oxygen, nitrite plus nitrate, and chloride generally were greater in samples from springs than in samples from wells. Water from springs generally flows rapidly through large conduits with minimum water–rock interactions. Water from wells flow through small fractures, which restrict flow and increase water–rock interactions. As a result, springs tend to be more susceptible to surface contamination than wells. The results of this study have important implications for the geochemical and hydrogeological processes of similar carbonate aquifers in other geographical locations. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
19.
Paleokarst system development in the San Andres Formation, Permian Basin, revealed by seismic characterization 总被引：1，自引：0，他引：1
Paleokarst systems are one of the major factors resulting in carbonate reservoir heterogeneity and compartmentalization. Nevertheless, few effective workflows have been proposed to map the 3D distribution of such systems. We describe a detailed seismic characterization approach integrating core, well log and rock physics analysis, to reveal a complex subsurface paleokarst system in the San Andres Formation, Permian basin, West Texas. In the area of high volume production, the collapsed paleokarst system is characterized by irregularly developed crackle and fracture breccias, mosaic breccias and cave fillings in the Upper San Andres Formation, which are delineated using seismic acoustic impedance. Along the transition from platform to basin, the paleokarst system is marked by a linear collapse including sags and small vertical faults that are recognizable in seismic imaging. Production data indicates that tight paleokarst zones cause reservoir compartmentalization and influence fluid communication between wells. The complex paleokarst system development is explained using a carbonate platform hydrological model, an outcrop analogue similar to modern marine hydrological environments within carbonate islands. Our method of model development for complex subsurface paleokarst systems may be applicable to other paleoenvironments. 相似文献
20.
《中国科学:地球科学(英文版)》2015,(8)
Beef structures(bedding-parallel veins of fibrous calcite)are widespread within the Lower Triassic carbonate rocks in the Sichuan Basin of China,especially within clay-rich strata of low permeability.In the veins,fibrous calcite occurs in the outer zones,and coarse equant calcite in the inner zones.At least two generations of calcite crystallization took place during aqueous alteration,at the same time as deformation recorded by the calcite.The first-generation calcite fibers are at steep angles to the hydrocarbon-bearing host beds,and they grew vertically against the force of gravity at a time when the source rocks were maturing.Second-generation calcite occurs as coarse equant grains that sealed pores via localized fluid flow during horizontal tectonic compression,so that shear stresses acted at the fracture margins.Shearing of the host rock was accommodated in part by dissolution-precipitation creep(DPC),grain rotation,and grain slippage,recorded in crystallographic preferred orientations(CPOs)of the host calcite grains beside the crack walls.The beef veins formed during high pore-fluid overpressures along hydrofractures.We propose that the bedding-parallel veins with beef structures are evidence of a"crack-seal slip"fault valve process during hydrocarbon generation.The hydrocarbon-bearing calcite beef structure may be a good indicator of oil or gas migration,and of the flow direction of aqueous solutions. 相似文献