砂岩侵入体的形成机制分析*

砂岩侵入体是指深水沉积砂体受到外界的触发,并在一定条件下形成超压,致使上覆弱渗透性沉积物等围岩发生破裂,砂体以流化和液化的形式向周围沉积物产生侵入。砂岩侵入体的形成过程为形成超压、盖层破裂、产生液化和流化、发生侵入。差异压实、地震引发的液化、流体的加入和压力传递等多种因素都可以使砂岩中形成超压,当地层压力达到并超过破裂压力时,发生水力破裂,或地震引起上覆地层破裂,超压砂岩发生流化,侵入到低渗透围岩中。大量未固结的深水沉积砂岩、低-非渗透层的快速覆盖、形成超压的机制和触发事件是砂岩发生侵入的必备条件。     

Crustal Stress in the northern North Sea as inferred from borehole breakouts and earthquake focal mechanisms

The regional stress field in the northern North Sea (offshore western Norway) has been studied through the acquisition and analysis of directions of maximum horizontal compression (_H) as extracted from borehole breakouts and from earthquake focal mechanism solutions.
The results indicate that the regional stress field is dominated by NW-SE compression, with good consistency between shallow borehole breakouts (2–5 km depth) and deeper earthquakes (10–25 km depth). The broad spatial consistency in stress direction indicates that the main stress field is related to factors of primarily plate tectonic origin, and the results are in good agreement with the western Europe trend found in earlier investigations.
The Tampen Spur region in the northern North Sea has been subjected to particularly complex deformation, with two dominating fault directions trending NW-SE and NE-SW. From Tampen Spur in the west to the Sogn graben in the east an anomalous stress field is indicated, with NE-SW oriented maximum horizontal compressions. This anomaly is clearly seen both in the borehole breakout data and in the earthquake data. Possible sources for this anomaly are discussed, and include postglacial uplift and/or lateral variations in the physical properties of the crust.     

砂岩侵入体系模拟及形成机理分析

砂岩侵入体系是一种普遍的地质现象,近些年来越来越受到地学界的重视,但对其形成机理探讨较少。作者及研究团队通过设计一套室内模拟实验装置,来简化模拟3层地层结构中砂岩侵入体系的形成和演化过程。在之前模拟实验(实验变量为顶层沉积物的厚度、进水管的结构)结果的基础上,进一步考察了地形坡度对实验结果的影响,并对砂岩侵入体系的形成机理进行了分析。实验过程中,共观察到7种不同形态不同样式的管道,并对实验过程中压力变化进行了测试。对实验结果分析认为:盖层厚度越大,压力下降的速度越慢,越不利于压力的释放;随着实验的继续进行,砂岩侵入体最终会转化为砂岩喷出体并喷出地表;不稳定的地形有利于触发疏松沉积物发生变形。实验表明,超压是砂岩侵入体发生的最重要条件之一, 沉积盆地中的压实不均衡和生烃作用是可独立产生大规模超压的2种主要机制。     

Clastic injectites,internal structures and flow regime during injection: The Sea Lion Injectite System,North Falkland Basin

This paper details and describes a suite of 143 sub-seismic-scale clastic injectites encountered within the early Cretaceous, early post-rift of the deep-lacustrine North Falkland Basin. The injectites, referred to here as the Sea Lion Injectite System, are encountered below, above and in between the hydrocarbon-bearing, deep-lacustrine turbidite sandstones of the Bleaker 30, Sea Lion North, Sea Lion, Casper and Beverley fans. Sedimentary structures are documented within the injectites including: planar laminations, mud-clast imbrication and clast alignment. Clasts align along centimetre-scale foresets formed through ripple-scale bedform migration in a hydraulically-open fracture. The style of flow within the injectite system is interpreted as initially through fluid turbulence during an open fracture phase, which was followed by a later stage where laminar flow dominated, most likely during the closing phase of the fracture system. The host rocks display evidence for ductile deformation, which along with ptygmatic folding of dykes and internally injected mud-clasts, suggests a period of injection into relatively uncompacted sediments. Evidence for brittle fracturing, in the form of stepped margins may be indicative of a separate phase of emplacement into more-compacted sediments. This variability in deformation styles is related to multi-phased injection episodes into host strata at different stages of consolidation and lithification at shallow burial depths. Injectites have been identified in four stratigraphic groupings: above the Bleaker 30 Fan and within/above the Sea Lion North Fan; within the hydrocarbon-bearing Sea Lion Fan; overlying the Sea Lion Fan; and above/below the hydrocarbon-bearing Casper and Beverley fans. This spatial association with the hydrocarbon-bearing fans of the North Falkland Basin is important, considering the ability of injectite networks to form effective fluid-flow conduits in the subsurface. Consequently, the findings of this study will improve the characterization of sub-seismic scale injectites (and therefore fluid conduits) within otherwise impermeable strata.     

An experimental investigation of gravity-driven shale tectonics in progradational delta

Many deltas exhibit gravitational deformation of their sedimentary cover. In these systems, the décollement layers do not always consist of rock salt but sometimes of overpressured shale. Unlike salt, the efficiency of detachment in shale depends on the magnitude of fluid overpressures and it varies through time and space, as rapid sedimentary burial progrades into deeper water. As a result, the gravity deformational domains are progressively translated seaward. Sandbox models involving high air pore pressures were used to simulate such gravity-driven shale tectonics in prograding deltas. Models were built with sand of various permeabilities and air was injected to simulate the mechanical effects of fluid overpressure. Our apparatus for the injection of air allowed us to control subsurface pressures in space and time during the experiments, and it was used to simulate the advance of the front of the overpressured domain during the sedimentary progradation. In our models, sand kept obeying a frictional behavior, for medium to high pore pressures, and the detachment appeared as very thin shear bands. Compressional belts that formed during the experiment were dominated by asymmetric basinward-verging fore-thrusts, as is often observed in deep-water, shale-detached foldbelts. Where the value of fluid pressures approached that of the lithostatic stress, sand was fluidized, resulting in ductile strains analogous to what occurs in highly overpressured mobile shale. During progradation, ancient buried thrustbelts were reactivated, thereby controlling later extension. During the experiments, sand volcanoes, analogous to mud volcanoes, formed in relation with tectonic structures. Some of them developed near normal faults but many of them formed directly above old buried thrusts.     

http://www.sciencedirect.com/science/article/pii/S1674987111000764

The Jinding Zn-Pb deposit has been generally considered to have formed from circulating basinal fluids in a relatively passive way,with fluid flow being controlled by structures and sedimentary facies,similar to many other sediments-hosted base metal deposits.However,several recent studies have revealed the presence of sand injection structures,intrusive breccias,and hydraulic fractures in the open pit of the Jinding deposit and suggested that the deposit was formed from explosive release of overpres-sured fluids.This study reports new observations of fluid overpressure-related structures from underground workings(Paomaping and Fengzishan).which show clearer crosscutting relationships than in the open pit.The observed structures include:I) sand(±rock fragment) dikes injecting into fractures in solidified rocks:2) sand(±rock fragment) bodies intruding into unconsolidated or semi-consolidated sediments;3) disintegrated semi-consolidated sand bodies;and 4) veins and breccias formed from hydraulic fracturing of solidified rocks followed by cementation of hydrothermal minerals.The development of ore minerals(sphalerite) in the cement of the various clastic injection and hydraulic fractures indicate that these structures were formed at the same time as mineralization.The development of hydraulic fractures and breccias with random orientation indicates small differential stress during mineralization,which is different from the stress field with strong horizontal shortening prior to mineralization. Fluid flow velocity may have been up to more than 11 m/s based on calculations from the size of the fragments in the clastic dikes.The clastic injection and hydraulic fracturing structures are interpreted to have formed from explosive release of overpressured fluids,which may have been related to either magmatic intrusions at depth or seismic activities that episodically tapped an overpressured fluid reservoir.Because the clastic injection and hydraulic structures are genetically linked with the mineralizing fluid source,they can be used as a guide for mineral exploration.     

Submarine landslide identified in MD179 cores,off-Joetsu area,eastern margin of the Sea of Japan

Gas hydrate is exposed on the sea floor and is buried in shallow sediments in the off-Joetsu area at the eastern margin of the Sea of Japan. Sediment cores recovered from topographic highs of the Joetsu Knoll and Umitaka Spur show pockmarks and mounds formed by gas hydrate dissociation, but those from the Un-named ridge have no such topographic features. All topographic highs and pockmarks mainly comprise bioturbated layers interbedded with thinly laminated (TL) layers, which are common Sea of Japan sediments. Recovered sediments are, however, mostly disturbed by submarine landslides, showing tilted horizons, faults, slump folds, and breccia, except that from the Un-named ridge. The timing of events is well constrained by identification of the number of TL layers in some sediment cores. Landslides occurred both during the cold glacial period of the late MIS3 to the last glacial maximum (LGM) and during the warm interglacial period of the post-LGM. All were caused by the explosive rise of gas hydrate formed at very shallow depths of the sea bottom by the supply of gas from the depth of the gas hydrate stability zone through gas chimney passages developed under the pockmarks. Seismic activity demands consideration as a factor because the off-Joetsu area is tectonically active.     

Convolute lamination in modern sands of the estuary of the Oosterschelde,the Netherlands,formed as the result of entrapped air*

Soft-sediment deformation structures similar to convolute lamination were found at the sandy rim of an intertidal shoal in the Oosterschelde estuary, the Netherlands. Abundant air filled cavities within upward penetrated domes suggest that reversed density stratification resulting from trapped air in some sand layers plays a role in the deformational process. Field observations show that air-filled cavities are formed within fine-grained sand; at rising tide the ground water level does not rise quickly enough to replace the interstitial air before flood water covers the sediment surface. Thus, air is trapped in the sand between the ground water level and the sediment-water interface. Because of the weight of the overlying water column and the slow downward movement of water due to capillary action, the entrapped air is compressed and eventually may attain a pressure which enables it to lift the overlying sediment. At this time bubbles are formed, often to a depth of 20 cm. Observation and experiments show that, in layers of fine sand, bubbles develop preferentially in better sorted and coarser zones. This is probably because capillary forces are greater in finer-grained and less sorted sand. Thus, water will penetrate by preference into the latter, pressing the interstitial air into the better sorted and coarser sand. The high content of air cavities in certain layers then provides the density instability responsible for the deformational process leading to the formation of convolute lamination. In the intertidal zone this appears to be a slow process that covers a number of ebb and flood cycles. Convolute lamination has been described from a number of ancient sandstones that are thought to have been deposited in shallow water, near-shore environments. In many of these cases sand size compares with that found in the Oosterschelde. Air entrapment might have played a role in the formation of certain of these occurrences of convolute lamination.     

Shear zones in porous sand: Insights from ring-shear experiments and naturally deformed sandstones

In a high-resolution small-scale seismic experiment we investigated the shallow structure of the Wadi Araba fault (WAF), the principal fault strand of the Dead Sea Transform System between the Gulf of Aqaba/Eilat and the Dead Sea. The experiment consisted of 8 sub-parallel 1 km long seismic lines crossing the WAF. The recording station spacing was 5 m and the source point distance was 20 m. The first break tomography yields insight into the fault structure down to a depth of about 200 m. The velocity structure varies from one section to the other which were 1 to 2 km apart, but destinct velocity variations along the fault are visible between several profiles. The reflection seismic images show positive flower structures and indications for different sedimentary layers at the two sides of the main fault. Often the superficial sedimentary layers are bent upward close to the WAF. Our results indicate that this section of the fault (at shallow depths) is characterized by a transpressional regime. We detected a 100 to 300 m wide heterogeneous zone of deformed and displaced material which, however, is not characterized by low seismic velocities at a larger scale. At greater depth the geophysical images indicate a blocked cross-fault structure. The structure revealed, fault cores not wider than 10 m, are consistent with scaling from wear mechanics and with the low loading to healing ratio anticipated for the fault.     

Linear Elastic and Cohesive Fracture Analysis to Model Hydraulic Fracture in Brittle and Ductile Rocks

Hydraulic fracturing technology is being widely used within the oil and gas industry for both waste injection and unconventional gas production wells. It is essential to predict the behavior of hydraulic fractures accurately based on understanding the fundamental mechanism(s). The prevailing approach for hydraulic fracture modeling continues to rely on computational methods based on Linear Elastic Fracture Mechanics (LEFM). Generally, these methods give reasonable predictions for hard rock hydraulic fracture processes, but still have inherent limitations, especially when fluid injection is performed in soft rock/sand or other non-conventional formations. These methods typically give very conservative predictions on fracture geometry and inaccurate estimation of required fracture pressure. One of the reasons the LEFM-based methods fail to give accurate predictions for these materials is that the fracture process zone ahead of the crack tip and softening effect should not be neglected in ductile rock fracture analysis. A 3D pore pressure cohesive zone model has been developed and applied to predict hydraulic fracturing under fluid injection. The cohesive zone method is a numerical tool developed to model crack initiation and growth in quasi-brittle materials considering the material softening effect. The pore pressure cohesive zone model has been applied to investigate the hydraulic fracture with different rock properties. The hydraulic fracture predictions of a three-layer water injection case have been compared using the pore pressure cohesive zone model with revised parameters, LEFM-based pseudo 3D model, a Perkins-Kern–Nordgren (PKN) model, and an analytical solution. Based on the size of the fracture process zone and its effect on crack extension in ductile rock, the fundamental mechanical difference of LEFM and cohesive fracture mechanics-based methods is discussed. An effective fracture toughness method has been proposed to consider the fracture process zone effect on the ductile rock fracture.     

Time evolution of hydraulic and electrokinetic parameters around the Nojima fault, Japan, estimated by an electrokinetic method

The Nojima Fault Zone Probe was designed to study the properties and healing processes of the Nojima fault, which is the surface fault rupture of the Hyogo-ken Nanbu earthquake (M7.2) of 1995 (1995 Kobe earthquake). In this project, water injection experiments were conducted in a borehole of 1800 m depth at the Nojima fault. We set up electrodes around the borehole and observed self-potential variations to investigate the magnitude of electrokinetic and hydraulic parameters around the Nojima fault zone. In the 1997 experiment, self-potential variations were in the range of a few to about 20 mV across 320–450 m electrode dipoles with hydraulic pressure variations from 3.5 to 4 MPa. In the 2000 experiment, self-potential variations were in the range of a few to about 85 mV across 160–260 m electrode dipoles with the hydraulic pressure variations from 3 to 4.5 MPa. In the 2003 experiment, self-potential variations were in the range of a few to about 30 mV across 20–80 m electrode dipoles with hydraulic pressure of 4 MPa. These observed self-potential variations were explained well with an electrokinetic effect due to the underground flow of the injected water. From the observed results, we estimated that the ratio of hydraulic parameters (permeability, porosity, and tortuosity) to electrokinetic parameters (zeta potential and dielectric constant) decreased approximately 40% during eight years after the earthquake. This result suggests that the healing process around the fault zone progress.     

Evaluation of heterogeneity and field-scale groundwater flow regime in a leaky till aquitard

Recent work in southern Ontario, Canada, demonstrates anomalously high vertical groundwater flow velocities (>1 m/year) through a thick (as much as 60 m), sandy silt till aquitard (Northern till), previously assumed to be of very low permeability (hydraulic conductivity <10^–10 m/s). Rapid recharge is attributed to the presence of fractures and sedimentary heterogeneities within the till, but the field-scale flow regime is poorly understood. This study identifies the nature of physical groundwater pathways through the till and provides estimates of the associated groundwater fluxes. The aquitard groundwater flow system is characterized by integrating details of the outcrop and subsurface sedimentary characteristics of the till with field-based hydrogeologic investigation and numerical modeling. Outcrop and subsurface data identify a composite internal aquitard stratigraphy consisting of tabular till beds (till elements) separated by laterally continuous sheet-like sands and gravels (interbeds) and boulder pavements. Individual till elements contain sedimentary heterogeneities, including discontinuous sand and gravel lenses, vertical sand dikes, and zones of horizontal and vertical fractures. Hydrogeologic field investigations indicate a three-layer aquitard flow system, consisting of upper and lower zones of more hydraulically active and heterogeneous till separated by a middle unit of relatively lower hydraulic conductivity. Groundwater pathways and fluxes in the till were evaluated using a two-dimensional aquitard/aquifer flow model which indicates a step-wise flow mechanism whereby groundwater moves alternately downward along vertical pathways (fractures, sedimentary dikes) and laterally along horizontal sand interbeds within the till. This model is consistent with observed hydraulic-head and isotope profiles, and the presence of tritiated pore waters at various depths throughout the till. Simulations suggest that a bulk aquitard vertical hydraulic conductivity on the order of 1×10^–9 m/s is required to reproduce observed hydraulic-head and tritium profiles. Electronic Publication     

砂岩侵入体系物理模拟实验

近十年来,从露头、地震、岩心和测井曲线等资料中识别出了越来越多的砂岩侵入体。这些砂岩侵入体对油气勘探和开发既有正面影响,也有负面影响,但由于其发育过程和分布的复杂性,使得对于其成因机制和形成过程探讨较少。笔者建立了一套模拟砂岩侵入体系的实验装置,并设计了完整的实验程序,以模拟砂岩侵入体的形成过程,并探索其形成机理。在此基础上,进行了5组实验,分析了顶层沉积物厚度和进水管结构对砂岩侵入体形成的影响。通过对实验结果进行冷冻、切片和照相,将砂岩侵入体的形成过程分为5个阶段,并借助软件对每次实验的模型进行了三维重构,以期为更好地分析砂岩侵入体系的形成机理提供实验基础。     

基于零厚度内聚力单元的水力裂缝随机扩展方法研究

为有效模拟裂缝性页岩储层中水力裂缝随机扩展过程,基于单元节点的拓扑数据结构,利用网格节点分裂方式,建立了一种基于有限元网格嵌入零厚度内聚力单元的水力裂缝随机扩展新方法。利用KGD模型解析解和2种室内试验,验证了新方法的准确性和有效性。同时,通过数值算例研究了水平地应力差和储层非均质性对水力裂缝随机扩展过程的影响。研究表明:(1)该方法弥补了ABAQUS平台内置的内聚力单元无法有效模拟水力裂缝随机扩展的不足;(2)在较高水平地应力差下页岩储层非均质性越强,与水力裂缝相交的高角度天然裂缝越容易开启。所建方法能准确地描述复杂水力裂缝的随机扩展行为,可为裂缝性页岩储层的数值模拟提供新手段。     

Detection of concealed Cu–Zn massive sulfide mineralization below eolian sand and a calcrete cover in the eastern part of the Namaqua Metamorphic Province, South Africa

The regolith studied here is located at the defunct Areachap mine and the newly discovered Kantienpan Cu–Zn volcanic-hosted massive sulfide (VHMS) deposit, located in the Areachap Group of the eastern part of Mesoproterozoic Namaqua Metamorphic Province. This area is highly prospective for further VHMS discoveries. Paleo and recent weathering of the upper most parts of massive sulfide deposits led to the formation of a gossan zone. Due to semi-arid climatic conditions during the late Cretaceous, affecting the African Land surface, the lowermost units of the Kalahari Group and the underlying floor rocks were calcretized. An approximately 6 m thick calcrete layer formed above the gossan zone and this was later covered by eolian Kalahari sand. Samples were collected from the eolian sand cover in the study areas to determine the best analytical method that would enable recognition of the concealed ore deposits and detect the widest secondary dispersion halo.Mobile metal ions from the finest fraction of the eolian sand samples (< 75 μm) were extracted with a NH₄EDTA (EDTA) solution. The solution was analysed for Cu, Zn, Pb and Mn by inductively coupled plasma mass spectrometry (ICP-MS). The same grainsize fraction of the original samples was also analysed for comparison purposes by means of X-ray fluorescence (XRF).Results indicate that the ore zone in both areas may be recognized by both partial and total analyses of the eolian sand samples collected, although the calcrete layer, below the sand cover, acts as a partial geochemical barrier. The recognition of the ore zone depends on the regolith forming processes and the thickness of the eolian sand cover. In the Areachap area, with a relatively thick sand cover (in excess of 1 m) above the calcrete layer, the detectable geochemical halo is related to the distribution of the mobile metal ions, and partial extraction (EDTA solution) results define a larger dispersion halo than that, that could be detected by total analysis (XRF). Whereas, in the Kantienpan area with a very thin sand cover (< 50 cm) dispersion appears to be related more to the secondary redistribution of gossaniferous clasts released by recent weathering out of the calcrete, than to dispersion of mobile metal ions on the surface of sand particles. In this area, the XRF results reveal a wider dispersion of the elements of interest.     

鄂尔多斯盆地北部塔巴庙地区上古生界致密砂岩气藏天然裂缝形成机理浅析

鄂尔多斯盆地北部塔巴庙地区上古生界致密砂岩气藏的低孔、低压、低渗特点给开发带来了相当大的难度.天然裂缝的存在对致密砂岩气藏经济开发意义重大,致密砂岩中裂缝发育层段往往是天然气富集区,天然裂缝能大大改善致密砂岩储层渗透性,研究其发育状况及分布规律对储层压裂改造及水平井开发技术的实施具有积极的指导意义.塔巴庙地区位于鄂尔多斯盆地北部伊陕斜坡构造带上,构造平缓,地层倾角仅1°左右,一般认为不具备裂缝发育条件,然而大量岩心观察、薄片分析、物性测试、测井及试井资料证实,研究区的确不同程度地发育垂直裂缝和高角度裂缝.对裂缝的形态、产状、密度及裂缝分布范围研究后认为,天然裂缝主要是在区域应力、差异压实和异常高流体压力综合作用下形成的,断裂作用不是该区裂缝发育的主导因素.      

X-ray CT and hydraulic evidence for a relationship between fracture conductivity and adjacent matrix porosity

Multi-phase flow in fractured rocks plays an important role in any hydrocarbon recovery process, be it for environmental remediation or natural oil and gas extraction. Fractures may form the primary production conduits, and the mass transport at the fracture interfaces with the matrix determines the effectiveness of extraction processes. This paper presents specific evidence for a relationship between fracture apertures and the porosity of the adjoining perpendicular layers in Berea sandstone samples. Measurements of fracture apertures were done with high-resolution Micro-Computed Tomography (MCT) with a voxel resolution of about 0.05 mm in three dimensions. Multi-phase fluid flow experiments were done using a medical CT scanner with a voxel resolution of about 1.00 × 0.25 × 0.25 mm. MCT evidence shows a correlation between aperture and the porosity of the intersected layers. The comparison was made by generating two-dimensional maps of matrix porosity and CT values adjacent to the fracture and of the corresponding fracture apertures. High-porosity layers are lined up with large fracture apertures. Multi-phase fluid experiments provided hydraulic evidence that the high-porosity layers have high permeability. Oil injection into a water-saturated sample was tracked by a sequence of transverse scans near the downstream tip of a fracture. The hydraulic evidence from the two-phase flow experiments also confirms high permeability in fracture strips adjacent to high-porosity and high-permeability layers. The reasons for the relationship between fracture aperture and the properties of the adjacent layers are not fully understood. Some explanation for the physical and hydraulic observations rests in the method of fracturing, fracture propagation, and the lithological characteristics of the rock.     

Submarine exhalative gold mineralization at the London-Virginia Mine,Buckingham County,Virginia

Low grade submarine exhalative gold mineralization occurs at the London-Virginia deposit in central Virginia Piedmont. The deposit consists of a series of localized but conformable units — basal garnetiferous-chlorite schist, magnetite schist, quartz-muscovite schist, ferruginous quartzite, and chlorite-biotite schist — which represent a mixture of submarine epiclastic volcanic debris and exhalative chemical sediments. Finely disseminated gold occurs dispersed with minor amounts of pyrite, sphalerite, chalcopyrite, galena, and tennantite in the ferruginous quartzite and quartz-muscovite schist. The deposit is believed to have formed by processes analogous to those currently active in the Atlantis II Deep of the Red Sea. Silicarich, hypersaline brines discharged through fractures in the sea floor and ponded in a local basin. Epiosodic influx of clastic debris and extensive deposition of hydrothermal silica diluted the concentration of sulfides and gold to produce a low-grade, siliceous mineralized zone. Emanation from the exhalative vent was terminated when the basin was capped by a lava flow. Subsequent regional greenschist grade metamorphism has recrystallized the silica into a granular quartzite and produced minor remobilization of the gold and sulfides.     

Flow patterns, sedimentation and deposit architecture under a hydraulic jump on a non-eroding bed: defining hydraulic-jump unit bars

This paper presents results from two flume runs of an ongoing series examining flow structure, sediment transport and deposition in hydraulic jumps. It concludes in the presentation of a model for the development of sedimentary architecture, considered characteristic of a hydraulic jump over a non-eroding bed. In Run 1, a hydraulic jump was formed in sediment-free water over the solid plane sloping flume floor. Ultrasonic Doppler velocity profilers recorded the flow structure within the hydraulic jump in fine detail. Run 2 had identical initial flow conditions and a near-steady addition of sand, which formed beds with two distinct characteristics: a laterally extensive, basal, wedge-shaped massive sand bed overlain by cross-laminated sand beds. Each cross-laminated bed recorded the initiation and growth of a single surface feature, here defined as a hydraulic-jump unit bar . A small massive sand mound formed on the flume floor and grew upstream and downstream without migrating to form a unit bar. In the upstream portion of the unit bar, sand finer than the bulk load formed a set of laminae dipping upstream. This set passed downstream through the small volume of massive sand into a foreset, which was initially relatively coarse-grained and became finer-grained downstream. This downstream-fining coincided with cessation of the growth of the upstream-dipping cross-set. At intervals, a new bed feature developed above and upstream of the preceding hydraulic-jump unit bar and grew in the same way, with the foreset climbing the older unit bar. The composite architecture of the superimposed unit bars formed a fanning, climbing coset above the massive wedge, defined as one unit: a hydraulic-jump bar complex .     

基于体素模型的砂岩侵入体三维重建

砂岩侵入体是由沉积后的砂岩再活动并侵入到周围地层中形成的一种特殊砂体。为了研究其演化过程,设计了砂岩侵入体形成过程的模拟实验。针对实验结果,提出了基于体素模型法和Petrel软件的三维重建方法:在实验切片的基础上,对所得到的实验照片进行预处理,将其转化为Petrel软件能够识别的Gslib格式的数据体,再使用克里金插值算法进行模拟。结果表明,克里金算法可以很好地再现砂岩侵入体的外部形态,多组切片的特征参数统计可以定量地刻画出侵入体的形态,以期为实际岩性油气藏中的规模预测提供理论指导。