Hydraulic Effects of Shales in Fluvial-Deltaic Deposits: Ground-Penetrating Radar, Outcrop Observations, Geostatistics, and Three-Dimensional Flow Modeling for the Ferron Sandstone, Utah

Ground-penetrating radar (GPR) surveys, outcrop measurements, and cores provide a high-resolution 3D geologic model to investigate the hydraulic effects of shales in marine-influenced lower delta-plain distributary channel deposits within the Cretaceous-age Ferron Sandstone at Corbula Gulch in central Utah, USA. Shale statistics are computed from outcrop observations. Although slight anisotropy was observed in mean length and variogram ranges parallel and perpendicular to pale of low , the anisotropy is not statistically significant and the estimated mean length is 5.4 m. Truncated Gaussian simulation was used to create maps of shales that are placed on variably dipping stratigraphic surfaces interpreted from high-resolution 3D GPR surveys, outcrop interpretations, and boreholes. Sandstone permeability is estimated from radar responses calibrated to permeability measurements from core samples. Experimentally designed flow simulations examine the effects of variogram range, shale coverage fraction, and trends in shale coverage on predicted upscaled permeability, breakthrough time, and sweep efficiency. Approximately 1500 flow simulations examine three different geologic models, flow in the 3 coordinate directions, 16 geostatistical parameter combinations, and 10 realizations for each model. ANOVA and response models computed from the flow simulations demonstrate that shales decrease sweep, recovery, and permeability, especially in the vertical direction. The effect on horizontal flow is smaller. Flow predictions for ideal tracer displacements at Corbula Gulch are sensitive to shale-coverage fraction, but are relatively insensitive to twofold variations in variogram range or to vertical trends in shale coverage. Although the hydraulic effects of shale are statistically significant, the changes in flow responses rarely exceed 20%. As a result, it may be reasonable to use simple models when incorporating analogous shales into models of reservoirs or aquifers.     

A New Method for Estimating Lengths for Partially Exposed Features

Length distributions from sedimentary bodies can be measured in outcrop. A common feature in many outcrops is the occurrence of partially exposed bodies, i.e., sedimentary bodies that are cut by either one or both edges of the outcrop. Ignoring these partials while establishing a length distribution leads to a bias toward the smaller length classes. This is because larger bodies have a larger probability to occur as partials than smaller bodies. We present a new method for estimating the expected complete length for a partially exposed feature, based on the theory of conditional probability. The method is demonstrated and tested on a sandstone outcrop exhibiting over 200 interbedded thin silt/shale streaks. It is shown that the method can significantly enlarge both the size and the representativeness of length distributions.     

Architecture of a tide-influenced river delta in the Frontier Formation of central Wyoming, USA

The Frewens sandstone is composed of two elongate tide-influenced sandstone bodies that are positioned directly above and slightly landward of a more wave-influenced lobate sandstone. The 20-km-long, 3-km-wide Frewens sandstone bodies coarsen upwards and fine away from their axes, have gradational bases and margins and have eroded tops abruptly overlain by marine shales. These sandstones are superbly exposed in large cliffs on the banks of the South Fork of the Powder River in central Wyoming, USA. The deposits change upwards from thinly interbedded sandstones and mudstones to metre-thick heterolithic cross-strata and, finally, to metres-thick sandstone-dominated cross-strata. There is abundant evidence for tidal modulation of depositional flows; however, palaeocurrents were strongly ebb-dominated and nearly parallel the trend of sandstone-body elongation. Detailed mapping of stratal geometry and facies across these exposures shows a complex internal architecture. Large-scale bedding units within sandstone bodies are defined by alternations in facies, bed thickness and the abundance of shales. Such bedsets are inclined (5°–15°) in walls oriented parallel to palaeoflow and gradually decrease in dip over hundreds of metres as they extend from the sandstone-dominated deposits higher in a sandstone body to muddier deposits lower in the body. Where viewed perpendicular to palaeoflow, bedsets are 100-metre-wide lenses that shingle off the sandstone-body axis towards its margins. The sandstone bodies are interpreted as sand ridge deposits formed on the shoreface of a tide-influenced river delta. Metres-thick cross-strata in the upper parts of sandstone bodies resemble deposits of bars (sandwaves) formed where tidal currents moved across shallows and the tops of tidal ridges. Heterolithic deposits lower in sandstone bodies record fluctuating currents caused by ebb and flood tides and varying river discharge. Erosion surfaces capping sandstone bodies record tidal ravinement. The tidal ridges were abandoned following transgression and covered with marine mud as waters deepened.     

Coastal geology and revised stratigraphy of the Brega area,northeastern Libya

While describing the geology of the Brega area, NE Libya, the Brega Sandstone Bed of Pliocene age was established as a new stratigraphic unit in this part of Libya (Kumar, 2014). New field data from the western regions of Brega especially along the Brega Area One beach provides some new significant geological information. New outcrops of the Brega Sandstone Bed and Ajdabiya Formation are described. A new hitherto unknown outcrop of beachrocks is also described. Based on these outcrops and their stratigraphic relationships, a new stratigraphy for the Brega area is proposed. The new outcrop of the Brega Sandstone Bed is much larger and is exposed along the sea coast. It is of grayish yellow to brown color and intensely bioturbated, and unlike the outcrops of this stratigraphic unit in the Brega Area Two, this outcrop shows distinct bedding planes that dip 15° to 20°E to ESE. A new outcrop of Pleistocene Ajdabiya Formation was observed in close vicinity of the newly observed outcrop of the Brega Sandstone Bed. There is an unconformable contact between the Ajdabiya Formation and underlying Brega Sandstone Bed. A new outcrop of beachrocks was observed on the southwestern end of the Brega Area One beach. These rocks are very hard, of gray to dark gray color, and are characterized by numerous circular to sub-circular holes of various diameter and depth; these are filled by floating crude oil that is derived from leakages and spills of crude oil pumped into ships for export from the Brega Port. These rocks are mostly unfossiliferous but at places, fossil corals and gastropods were noted. Presence of corals is problematic because there are no coral reefs offshore Braga or in the nearby waters of the Mediterranean Sea. It is possible that the fossil corals from Libya could have been eroded and transported by wind and water during the past and transported to the beaches of Brega. Ultimately, these corals along with calcareous beach sand were lithified by calcium carbonate and became parts of beachrocks. The gastropods found in the beachrocks are local shallow marine inhabitants, and they can be observed on the surface of the Brega Sandstone Bed as well as in the recent sediments.     

Geology of the Devonian black shales of the Appalachian Basin

Black shales of Devonian age in the Appalachian Basin are a unique rock sequence. The high content of organic matter, which imparts the characteristic lithology, has for years attracted considerable interest in the shales as a possible source of energy. The recent energy shortage prompted the U.S. Department of Energy through the Eastern Gas Shales Project of the Morgantown Energy Technology Center to underwrite a research program to determine the geologic, geochemical, and structural characteristics of the Devonian black shales in order to enhance the recovery of gas from the shales. Geologic studies by Federal and State agencies and academic institutions produced a regional stratigraphic network that correlates the 15 ft black shale sequence in Tennessee with 3000 ft of interbedded black and gray shales in central New York. These studies correlate the classic Devonian black shale sequence in New York with the Ohio Shale of Ohio and Kentucky and the Chattanooga Shale of Tennessee and southwestern Virginia. Biostratigraphic and lithostratigraphic markers in conjunction with gamma-ray logs facilitated long-range correlations within the Appalachian Basin. Basinwide correlations, including the subsurface rocks, provided a basis for determining the areal distribution and thickness of the important black shale units. The organic carbon content of the dark shales generally increases from east to west across the basin and is sufficient to qualify as a hydrocarbon source rock. Significant structural features that involve the black shale and their hydrocarbon potential are the Rome trough, Kentucky River and Irvine-Paint Creek fault zone, and regional decollements and ramp zones.     

China Shale Gas Reservoir Types and Its Controlling Factors

Shale gas is an important unconventional natural gas. This paper classified shale into three types, which are marine, marine-continental transitional and continental facies shales, and summarized strata, distributions and reservoir features of the three kinds of shales. Marine face shale usually occurs in large scale and great thickness, and has widespread distributions; transitional face shale has the characteristics of thin layers, large multiple thickness and frequent interbedding, while the distribution of terrestrial face shale is relative narrow. Different shale reservoirs have similarities in gas compositions, occurrence states, gas origins. But they also differ in thickness, distributions and rock associations, etc., because of different sedimentary environments. Comparing reservoir characteristics of Chinese and American shale, organic matter abundance, maturity and types control the gas generation; mineral compositions and structures, organic matter maturity and types, pore and fracture structures, gas occurrence and migration characteristics, burial depth, and effective thickness control the shale gas accumulation.     

Geochemical signatures for the grain size variation in the siliciclastics of Kaimur Group,Vindhyan Supergroup from Markundi ghat,Sonbhadra district, (U.P.), India

The chemical composition of siliciclastics from Mesoproterozoic Kaimur Group, Vindhyan Supergroup have been investigated to determine and appraise the influence of the weathering, hydraulic sorting and recycling processes upon source rock signature. The studies pertaining to the relationship between major, trace and REE and the grain size variation were carried out along Markundi ghat section, Sonbhadra district, Son valley. Upper Kaimur Group has been divided into three principal formations-the uppermost-Dhandraul quartzites, Scarp sandstone and Bijaigarh shales. Petrographically, they range from quartz arenite, sublitharenite, subfeldspathic arenite to pyritiferous shale. The elemental enrichment, except for SiO₂, is in the following order-Bijaigarh Shale > Scarp Sandstone ≫ Dhandraul Sandstone.     

四川盆地南部下寒武统筇竹寺组页岩沉积微相研究

页岩气是我国未来一个重要的且比较现实的非常规油气资源,加强该领域的基础研究对页岩气油气成藏理论创新、页岩气开采技术运用和资源量的准确计算都非常必要.因此,本文运用野外露头资料、钻取岩芯和测井资料,以及页岩有机地球化学分析化验结果等大量第一手资料,通过详细分析四川盆地南部下寒武统筇竹寺组页岩沉积微相特征及其含气性特征,并结合研究区沉积相标志和测井相特征,明确指出泥质深水陆棚微相是四川盆地南部下寒武统筇竹寺组优质页岩最有利沉积微相带.     

Subaerial weathering of sedimentary organic matter

Small diameter core samples were taken from outcrops of the Permian Phosphoria Formation and the Cretaceous Pierre Shale of the Western United States to determine the effects of weathering on organic matter in shale outcrops. While the Pierre Shale core showed no evidence of weathering, the Phosphoria Formation showed significant reduction of overall organic content and pronounced changes in organic composition over the near-surface interval of the core. Total organic carbon is lower by as much as 60% over the upper 2 ft of the core. Chloroform-soluble organic matter and total hydrocarbon (C₁₅₊) concentrations are 50% lower over this same interval. The ratio of saturated to aromatic hydrocarbons decreases steadily with core depth over the upper 2.6 ft of the core. Aromatic hydrocarbons are enriched in the stable carbon-13 isotope by an average of 1.7%. over this same interval. Shallow core samples also show a loss of n-paraffins relative to branched/cyclic compounds in the saturated C¹⁵⁺ fraction.Although the extent of weathering is variable, certain characteristic effects are recognizable and can be applied to the interpretation of outcrop data in organic geochemical studies.     

Study of mechanical properties of Vindhayan shaly rocks at elevated temperature

Shale is an important rock due to its suitability for different engineering and scientific applications. Elevated temperature may cause major deformation or damage in shale rock and it may be of irreversible in nature. Such damage have adverse effect on the physicomechnical properties of shale rock. The uniaxial compressive strength and tensile strength of two shales (upper Vindhyan basin, India) have been estimated at elevated temperature using point load strength index method. The rock samples have been analyzed at various temperatures starting from room temperature to 900 °C. The effect of elevated temperature on the physicomechanical properties and their influence on the uniaxial compressive strength has been studied in detail. Damage induced, in both shale have been estimated using compressional wave velocity. The analysis of the experimental result shows that the uniaxial compressive strength decreases from 63.45 to 18.45 MPa and 60.94 to 22.22 MPa, for Jhiri and Ganurgarh shale respectively. Tensile strength of shales have been also estimated. The value of tensile strength decreases from 3.65 to 1.05 MPa and 3.46 to 1.26 MPa respectively for Jhiri and Ganurgarh shale. Multivariate regression analysis has been carried out to obtain the correlation between physicomechanical properties and uniaxial compressive strength of Jhiri and Ganurgarh shale.     

湖北当阳复向斜北部页岩气地质评价与有利区优选

以露头、钻井、地震等资料为基础,对湖北当阳复向斜北部上奥陶统五峰组—下志留统龙马溪组页岩气成藏条件和勘探潜力展开评价。研究表明,当阳复向斜五峰组—龙马溪组具备良好的页岩气成藏地质条件:五峰组—龙马溪组沉积期以深水陆棚沉积环境为主,页岩广泛发育,优质页岩层厚度约50 m;有机质类型为Ⅱ_2型,有机碳含量一般大于2%,有机质成熟度R_o在3.0%左右,已进入过成熟阶段;页岩中的矿物以石英和黏土为主,有利于后期压裂改造和吸附气的大量富集;储层具有低孔特低渗特征;当阳复向斜构造简单,区域上盖层连续分布,保存条件较好。通过地质评价和资源量计算,当阳复向斜页岩气资源量较为丰富,优选巡检—溪前向斜带和龙坪—肖堰—栗溪背斜带为页岩气勘探有利区。     

Subsurface lithofacies analysis of the Fluvial Early Permian Warchha Sandstone, Potwar Basin, Pakistan

The Early Permian Warchha Sandstone is well preserved in subsurface in the Potwar Basin and the Punjab Plain of Pakistan. However, this succession is only exposed in the Salt Range, and within this region, only a modest number of the many outcrops are of sufficient quality to enable the preparation of lateral and vertical log profiles. From the subsurface, data from five wells drilled in the Salt Range and Potwar Basin have been analysed. Although they are of restricted coverage, these subsurface data — which take the form of gamma ray logs and well cuttings — provide a valuable addition to the outcrop dataset of the Warchha Sandstone as they provide useful information about vertical textural changes, type and thickness of bedding and the nature of sandbody contacts with underlying strata. Overall, the Warchha Sandstone succession is composed of repeated fining-upwards cycles indicative of a meandering fluvial succession. Sub-components of each cycle are themselves classified into six subsurface sedimentary facies. Through comparison with outcropping parts of the succession, the origin and significance of these subsurface facies can be related to specific architectural elements within the meandering fluvial system responsible for generating the Warchha Sandstone succession.     

Tectonic and Topographic Framework of Political Division

Boundaries between the various topographic, geologic, and socio-political entities that span the Earths continental surfaces are determined by a myriad of complexly interrelated natural and/or cultural factors. Areas of large river basins, of lithologic units on geologic maps, and of nations exhibit size frequency distributions that are closely approximated by density functions in which diameters of individual areas are distributed exponentially. As such, size distributions of each type of surface unit are closely modeled as randomly delimited areas. In other words, if one were to walk in a straight line across any particular continent, each step along that transect would embody some random continuous probability of passing out of a major drainage basin, or out of an area of more or less homogeneous rock type, or from one country to another. Moreover, this simple truism gives rise to area frequency distributions for large river basin or outcrop or nation area that are primarily dependent on the number of basins or outcrops or countries that exist across that particular landmass. As a consequence, the size frequencies of these areal units can be closely predicted knowing only the total area under consideration and the number of drainage basins, outcrop areas, or nations that exist within the area. The similarity between area frequencies of large river basins and rock types and nations suggests a nontrivial component of geologic influence on the partitioning of continental surfaces into major political divisions, and implies that cultural and economic factors, which serve to divide and unite political entities, do so within a geological framework.     

Cross polarization magic-angle spinning 13C NMR spectra of oil shales

Cross plarization magic-angle spinning ¹³C NMR spectra have been obtained on oil shales representing a variety of geologic ages, origins, depositional environments, and source locations. The spectra show variations in the aliphatic and aromatic carbon distributions of the oil shales and reveal correlations between aliphatic carbon contents and potential shale oil yields. Hints of additional fine structure are present in the spectra of some samples, and examples are given of the spectral resolution that may be obtainable on other solid samples of geochemical interest.     

中国页岩气开发的实质性突破

页岩气是指吸附在页岩中的天然气或自生自储在页岩纳米孔隙中连续聚集的天然气。新世纪以来,美国发生的页岩气革命影响了世界油气资源格局; 中国的非常规油气储存量非常可观,是世界上具有页岩气可采储量最大的国家; 但页岩气地质条件、水平钻井、分段压裂等技术储备和页岩气管理经验等还面临很大挑战。近年来,中国大力推进页岩气的开发利用,中石化、中石油和延长油田三家公司在示范区块开发的成功,以及短时间内在勘探开发方面取得的技术突破,标志着中国页岩气的开发已取得了实质性突破。但中国今后是否采取页岩气开发对多元资本开放的模式,还需要进一步研讨。     

Adsorption of pyridine by combusted oil shale

Large volumes of solid waste material will be produced during the commercial production of shale oil. An alternative to the disposal of the solid waste product is utilization. One potential use of spent oil shale is for the stabilization of hazardous organic compounds. The objective of this study was to examine the adsorption of pyridine, commonly found in oil shale process water, by spent oil shale. The adsorption of pyridine by fresh and weathered samples of combusted New Albany Shale and Green River Formation oil shale was examined. In general, pyridine adsorption can be classified as L-type and the isotherms modeled with the Langmuir and Freundlich equations. For the combusted New Albany Shale, weathering reduced the predicted pyridine adsorption maximum and increased the amount of pyridine adsorbed at low solution concentrations. For the combusted Green River Formation oil shales, weathering increased the predicted pyridine adsorption maximum. The pyridine adsorption isotherms were similar to those produced for a combusted Australian oil shale. Although adsorption can be mathematically described by empirical models, the reduction in solution concentrations of pyridine was generally less than 10 mg/l at an initial concentration of 100 mg/l. Clearly, the observed reduction in solution pyridine concentrations does not sufficiently justify using spent oil shale as a stabilizing medium. However, data in the literature suggest that other organic compounds can be effectively removed from solution by spent oil shale and that adsorption is dependent on process conditions and organic compound type.     

页岩油分类与评价

页岩油是以游离(含凝析态)、吸附及溶解(可溶解于天然气、干酪根和残余水等)态等多种方式赋存于有效生烃泥页岩地层层系中且具有勘探开发意义的非气态烃类。根据泥页岩地层中所含烃类相态、成因机理及勘探开发等特点,将页岩类油气划分为页岩气和页岩油等两类八种。结合页岩油特点,指出了我国页岩油形成条件和分布规律,即规模分布的有效生烃泥页岩、形成于深水-半深水相的富有机质泥页岩、较高的有机质丰度和适当的热演化程度以及较好的基质物性条件等是页岩油形成的主要条件。建立了中国陆相断陷湖盆页岩油发育模式,指出概率体积法可以作为页岩油资源评价的主要方法,提出了页岩油远景区、有利区及目标区优选的参数体系和标准。作为非常规油气能源的主要类型之一,页岩油将会对我国能源结构产生重要影响。     

页岩沉积环境对其油气潜力的影响:以中国和北美对比研究为例

页岩油气是当前全球油气勘探和研究的热点,但其潜力评价一直是难点。该文以中国和北美的四套典型页岩为例,包括北美湖相Green River组、内陆海相Niobrara组、中国环境来评价相龙马溪组和济阳坳陷湖相页岩,发现页岩沉积环境与其油气潜力具有密切关系,因此可通过分析发现这四套页岩的沉积环境都具有页岩沉积环境评价其页岩油气潜力。通过微量元素、生物标志化合物、扫描电镜、X-CT和X射线衍射等方法,发现这四套页岩都具有一定的还原性和较高的生产力,且具有差异性。内陆海相Niobrara组页岩具有弱还原的沉积环境,在四套页岩中有机碳含量较低,呈块状沉积构造,裂缝与微裂缝较少,储集空间相对有限。焦石坝海相龙马溪组页岩为还原的沉积环境,岩石以富含有机质的硅质岩为主,可观察到大量的大孔隙与少量的微裂缝。Green River页岩和济阳坳陷页岩形成于陆相咸化的强还原沉积环境,有机碳含量高,页岩以纹层状结构为主,岩石组成脆性矿物含量高,含有大量的裂缝。可见,具有强还原沉积环境的页岩通常具有较好的勘探前景。     

页岩油气富集的主控因素及误辩:以美国、阿根廷和中国典型页岩为例

页岩气富集不均匀,无论对于不同页岩油气藏还是同一页岩油气藏不同地方,产量都是有高有低.有必要系统分析和对比全球不同页岩油气的地质、石油系统与油气富集的关系,总结页岩油气富集的主控因素,从而采取合理的勘探和开发技术.以美国、阿根廷和中国典型页岩为例,基于野外和岩心观察、样品属性测试分析、储层表征、石油系统分析及油气测试,探究了页岩油气富集的主控因素及存在的认识误区.结果表明,富含有机质和脆性矿物的页岩主要分布于远离造山带物源的非深水的沉积和构造背景,富含石英和高伽马页岩并非判断优质储层的矿物和岩石物理标准,优质碳酸盐页岩应以富含碳酸盐和低伽马值为标准.页岩油气藏实际是细粒富含有机质的自生自储或与富含有机质烃源岩相邻的贫有机质细粒沉积储层.天然裂缝对页岩油气富集具有有利和不利的双重作用.因此,页岩油气富集同时受到沉积和构造环境、岩相及矿物组成、天然裂缝的耦合影响,且对不同沉积盆地、不同属性页岩的影响差异明显.      

川南下志留统龙马溪组页岩岩相表征

页岩岩相表征是页岩气地质评价和选层、选区的基础性研究工作。本文以露头和钻井资料为基础,依据岩矿、薄片、地化和测井资料,建立了海相页岩岩相划分方法,对川南上奥陶统五峰组下志留统龙马溪组主要岩相进行了精细表征,并形成4点认识：(1)应用岩石矿物三端员法+沉积微相划分页岩岩相类型及其组合,是开展海相页岩岩相表征的有效方法;(2)川南五峰组龙马溪组页岩发育6种岩相类型和3种典型岩相组合,其中硅质页岩和钙质硅质混合页岩是(半)深水环境的特有岩相,黏土质页岩和黏土质钙质混合页岩是半深水浅水环境的主要岩相,黏土质硅质混合页岩是浅水深水环境下的共有岩相;(3)随着水体由深变浅和水动力条件逐渐增强以及陆源物质输入量增大,不同成因岩相组合的页岩矿物成分、基质组构、古生物和有机质富集程度、测井响应等基本特征均发生重大变化;(4)受海平面变化控制,主力产层为深水陆棚沉积的硅质页岩、钙质硅质混合页岩和黏土质硅质混合页岩组合,产层顶板为半深水浅水陆棚沉积的黏土质页岩、黏土质硅质混合页岩和黏土质钙质混合页岩组合;前者因富含硅质和有机质,具有良好的脆性和物性,是形成页岩气产层的优质岩相;后者因富含黏土和贫有机质,脆性和渗透性差,是形成页岩气藏区域封盖层的优质岩相;两者自下而上构成良好的自封自储型储盖组合。