2013 Vol. 24, No. 6
The Longmenshan Range is a tectonically composite intracontinental orogen. Its structure, deformation and spatial evolution reflect multiple kinematic eposides and variable dynamics especially during Post-Middle to Post-Late Triassic time. Field work, lower-temperature thermochronological data and U-Pb detrital zircon ages indicate document down-dip zonation and along-strike segmentation demonstrated by significant differences in geological structure, intensity of deformation and deformation-involved strata, uplift and cooling processes. Low-temperature thermochronology and U-Pb detrital zircon ages reveal a period of tectonothermal quiescence with slow uplift and cooling during post Early Norian to Rhaetian orogeny, followed by rapid cooling and uplift during the Late Cenozoic accompanied by coeval southeastward thrusting and southwestward propagation of defromation. The Longmenshan Range formed by S-N striking compression exerted by the Qinling orogen, E-W striking compression by the Tibetan Plateau and SE-striking compression by the Yangtze Plate. We propose a southwestward propagation model for the Longmenshan Range based our observations of zonation, segmentation and composite evolutional processes during the Late Triassic superimposed by development of the differential uplift and cooling processes that shows southern segments of the Longmenshan Range during Post-Jurassic times.
Statistical study of analyses of water from 43 samples from geothermal wells, three groundwater wells, and one sample of local rainwater along with rainwater data from the Global Network of Isotopes in Precipitation has been used to identify the origin and evolution of geothermal water in the Niutuozhen (牛驼镇) geothermal field and estimate the renewability rate of its geothermal resource. The results show that the geothermal waters of the Jixianian Wumishanian dolomite reservoir and the Ordovician limestone reservoir are of Cl-Na type, the geothermal water of the Pliocene Minghuazhen (明化镇) Formation sandstone reservoir are Cl-Na type and HCO3-Na type and the groundwater of the Quaternary aquifer is HCO3-Na and HCO3-Na?Mg?Ca type. A linear relationship between silica concentration and temperature indicates that higher temperature probably enhances concentration of silica in Jixianian geothermal water. δ18O shift in Wumishanian geothermal water averaged 1.57‰, and was less than 1‰ in the other geothermal waters. The minimum and maximum 14C ages of Wumishanian geothermal water are 17 000 and 33 000 years from north to the south of the Niutuozhen geothermal field. Geothermal water and Quaternary groundwater belong to different groundwater systems with no hydraulic connections. Although the geothermal field receives some recharge from the Yanshan and Taihang mountains outside the northern and western boundaries of the geothermal field respectively, the renewability rate of geothermal water is on the scale of 10 000 years.
In the Early Ordovician Zhaogezhuang (赵各庄) Section of Tangshan (唐山), North China, the Yeli (冶里) Formation is composed of an entire third-order sequence, with facies ranging from the inner ramp restricted platform and open marine to the middle and even outer ramps. The Liangjiashan (亮甲山) Formation is dominated by highstand system tracts (HST) with predominantly inner ramp grain-shoal and lagoon facies. Analyzing the carbon and oxygen isotope during the whole-rock carbonate reveals the δ13C values in the Yeli Formation range from -7.11‰–0.76‰ (PDB), with the mean value at -2.98‰, while the δ18O values range of -9.09‰– -4.65‰ with the mean value at -6.12‰. The δ13C values in the Liangjiashan Formation range of -1.15‰–0.3‰, and the mean value of -0.57‰; the δ18O values are -8.76‰– -7.48‰, and the mean value is -8.06‰. The δ13C values in the Yeli Formation decrease, but at the bottom of the Liangjiashan Formation the values increase steadily. In the middle-upper formation, there is an extended fluctuation between 0– -1.00‰. The δ13C trend in the studied section is similar to that of the contemporary sections, except that it has much lower δ13C values and a more negative excursion. The correlation between the δ13C changes and the eustatic events, as well as the sedimentary facies, indicates that in the Tangshan area, the carbon isotope evolution can be attributabled to the processes of the eutrophic sea/oligotrophic sea, the seafloor organism-mediated oxidation in shallow water and the organic reduction after maximum flooding. The changes in the carbon isotope contents were primarily affected by the regional relative sea level changes. Compared to the other coeval data, the Early Ordovician of the Tang shan area is also severely depleted in 18O, with all of the δ18O sample values being below -5‰, except for one sample with a value of -4.65‰. With the ancient seawater having a δ18O value of -5.5‰ (SMOW), it is reasonable to delineate a temperature of less than 37 ℃.
In these years, with more and more volcanic oil and gas fields being discovered and developed, the volcanic rocks reveal a great petroleum potential in the eastern basins of China. There are five volcanic facies identified in the study area, which include volcanic conduit facies, explosive facies, effusive facies, extrusive facies, and volcanogenic sedimentary facies. The subaerial eruption usually happened in Mesozoic and Paleocene, and subaquatic eruption in Eocene. The upper subfacies and top autoclastic brecciation of effusive facies of subaquatic volcanic rocks and pyroclastic flow subfacies of explosive facies of subaerial volcanic rocks are the most favorable volcanic reservoirs. The intermittent belt formed between two times of volcanic eruptions is most effective for reservoirs both in subaquatic and subaerial volcanic rocks. Their main porosity types are interclast porosity, interflow laminar porosity, vesicular and gas pipes porosity, intercrystalline sieve of moldic porosity, secondary dissolution porosity, and tectonic fracture. Developed between preemplacement stage and final cooling, the primary porosity may lead to high porosity and permeability, and the secondary porosity usually developed upon them. The porosity of volcanic rocks was less influenced by the compaction and the burial depth.
Yinger (营尔) sag is the main petroleum generative sag in eastern Jiuquan (酒泉) Basin, and only the Changshaling (长沙岭) oil resource has been found after 60 years prospecting. Changshaling anticline crest zone was formed above the regional uplift, and was slightly affected by over thrust during Tertiary Period. The anticline crest was identified as a structural transposition zone. Based on analysis of seismic facies, logging facies and seismic inversion technique, it has been demonstrated that anticline crest zone conducts drainage entering basin and dominates sedimentary detritus further dispersing, and the anticline crest zone controls the distribution of sand bodies and the development of sedimentary system consequently. The sequence stratigraphic patterns of multi-step fault belt in Member 3 of Xiagou (下沟) Formation in Lower Cretaceous in the anticline crest zone is composed of the development of sedimentary facies in plan and distribution of multistep fault belt sand bodies in spatial. This research investigates the sand-control models and sequence patterns, and finally a model of reservoirs in anticline crest zone is identified.
Shale intercalations in salt deposits of the upper part of the third member of the Shahejie (沙河街) Formation (Es3) in the Liutun (柳屯) sag have industrial oil and gas potential. This article classifies and evaluates lithology, pore systems, porosity, permeability and pore characteristics using core logs, XRD, SEM, lab and log porosity data of shale reservoirs in the salt formation. The lithology of these reservoirs is complex as parts of complex salt rhythms composed of clastic, carbonate and evaporitic rocks. Their rigid minerals contents and total organic carbon are high, the organic type is good, and the maturity of organic matter ranges from medium to low. There are strong overpressures and natural hydraulic fractures. Organic matter pores and matrixrelated shale pores provide an appreciable part of the permeability. Different methods of measurement, sonic logging and equivalent cycle countingpoint are used to evaluate the different types of porosity and permeability. A preliminary evaluation of shale permeability has been made by using fracture data from cores and image logging, and it is considered that the organic nets composed of organic matter pores generated in the maturation stage of shale have greatly increased oil permeability. On the above basis, this article proposes classification criteria for the upper Es3 intersalt shale oil reservoirs to provide a foundation for evaluating other shale oil reservoirs in this area.
Hydrogeochemical investigations were carried out in the Datong (大同) Basin, northern China to understand the sources and mechanisms of fluoride enrichment in the groundwater. The results indicate that fluoride concentrations reached up to 7.2 mg/L, and the hydrochemical type changed from Ca-HCO3, Ca-Mg-HCO3 water in the recharge areas to Na-HCO3, Na-Mg-HCO3 in the flowthrough area and ultimately to Na-Cl-HCO3, Na-SO4-Cl and Na-Cl in the discharge areas. The total fluorine contents in the soils ranged between 277.6 and 1 292.5 mg/kg, which can provide large amounts of fluorine from fluorinebearing minerals, such as fluorite, biotite and amphibole. The concentration of watersoluble fluorine ranged from 3.9 to 49.9 mg/kg (mostly less than 1% of the total fluorine) in the soils and rocks that, may have released sufficient fluorine into the groundwater. The results of PHREEQC simulations indicate that most of the analyzed samples are undersaturated with respect to fluorite (CaF2) from the recharge area to the discharge area. The fluctuation of F concentration in the 11 months indicates that the seasonal variation and the agricultural activity also affect the fluoride content in the groundwater. Fluoride enrichment in groundwater is predominantly controlled by fluorite solubility, residence time, evapotranspiration intensity and seasonal variation in this arid and semi-arid area.
With the analysis of the element geochemistry characteristics, the ancient lake information evolution history of the argillaceous source rocks in Lucaogou (芦草沟) Formation in Sangonghe (三工河) area is reconstructed. According to the ancient lake information and total organic matter (TOC) characteristics of argillaceous source rocks, the study section is divided into 6 Subsections. Subsection I mainly developed low-quality source rocks. This is because of the arid climate, high salinity, low lake productivity, unstable preservation conditions in this Subsection. Subsection II mainly developed high-quality source rocks. This is because of the humid climate, low salinity, high lake productivity, stable preservation conditions in this Subsection. Though the paleoclimate was humid and preservation conditions were stable. Lake productivity and the water salinity changed frequently. So Subsection III mainly developed medium-quality source rocks. Because of the humid climate, high lake productivity, medium sedimentary rate and stable preservation conditions, high-quality source rocks were developed in Subsection IV. The preservation conditions were stable, but other ancient lake information changed frequently. Therefore, the quality of the formed source rocks in Subsection V was different. Subsection VI mainly developed high-quality source rocks because of the humid climate, medium sedimentary rate, high lake productivity, low salinity and good preservation conditions. In summary, the ancient lake information parameters and TOC characteristics of each Subsection are different from each other.
A surrogate model is introduced for identifying the optimal remediation strategy for Dense Non-Aqueous Phase Liquids (DNAPL)-contaminated aquifers. A Latin hypercube sampling (LHS) method was used to collect data in the feasible region for input variables. A surrogate model of the multiphase flow simulation model was developed using a radial basis function artificial neural network (RBFANN). The developed model was applied to a perchloroethylene (PCE)-contaminated aquifer remediation optimization problem. The relative errors of the average PCE removal rates between the surrogate model and simulation model for 10 validation samples were lower than 5%, which is high approximation accuracy. A comparison of the surrogate-based simulation optimization model and a conventional simulation optimization model indicated that RBFANN surrogate model developed in this paper considerably reduced the computational burden of simulation optimization processes.
The exploration level in the south of Lixian (蠡县) slope is relatively low that causes the hydrocarbon distribution pattern and hydrocarbon accumulation model of discovered reservoirs unclear. It was assumed that the hydrocarbon accumulation model was mainly “stepped-like” type, but this model is contradicted with newly discovered reservoirs. Through comprehensive study of faults activity stages and depositional system, it can be concluded that the late period developed and late period attenuation faults act as the vertical migration path, while connected sandbodies provide lateral migration path for oil and gas. Combining with the distribution of the known reservoirs and oil-source correlation, the hydrocarbon accumulation model in the south of Lixian slope is characterized by dual source rocks generating; connected sandbodies parallel transporting; shallow fault nose traps accumulating. This model reveals the direction and clue of the following exploration and development, which are based on shallow formation; finding subtle structure traps by fine seismic interpretation and accurate sedimentary microfacies characterization.
Two field surveys on the thickness of Hei Valley No. 8 Glacier (H8) on the southern slope of Mount Bogda in the Tianshan (天山) Mountains using ground-penetration radar (GPR) were carried out in August 2008 and September 2009. Comparisons of the observed change in glacier thickness using GPR and ablation stakes suggest that GPR observations have high accuracy. Thus, the thickness change for H8 during 2008–2009 was estimated using GPR data. Digital elevation models obtained from topographic maps and the Shuttle Radar Topography Mission were used to analyze ice-elevation changes of H8 between 1 969 and 2 000 m a.s.l.. The results show that H8 has continually thinned, and the thinning rate has increased gradually. The thinning of ablation areas of H8 increased from 0.42±0.56 m/a in 1969–2000 to 1.47±0.79 m/a in 2000–2008, and then accelerated to 1.92±0.98 m/a in 2008–2009. The retreat of the glacier terminus has had a similar pattern. The distribution of the temperateice zone of H8 as determined from GPR data also implies that H8 has experienced strong melting from 2008 to 2009, which indicates that temperature rises have not only enhanced glacial surface melting and prolonged melting periods, but also changed the englacial structure and increased the water content of glacier, both of which probably lead to the acceleration of glacial thinning.
It is important to explore active faults in urban areas and their surroundings for earthquake disaster mitigation. Satellite remote sensing techniques can play an important role in such active fault exploration. It can not only reveal the pattern of active faults and active tectonics on a macroscopic scale, but also monitor the occurrence, development and rules of temporal-spatial evolution of active faults. In this paper, we use the Hangzhou area as an example to introduce methods of extracting detailed active fault information when covered by thick unconsolidated Quaternary sediment, using image enhancement and image fusion etc. to improve the definition and precision of satellite images and presenting a three-dimensional (3D) image to illustrate tectono-geomorphic features along the relevant faults. We have also collected aeromagnetic anomaly data, shallow seismic exploration data and dating data, and carried out field surveys to validate the characteristics of active faults based on remote sensing images. The results revealed about the faults showed a high consistency with traditional geological knowledge, and demonstrate that it is feasible to explore active faults in a weakly active tectonic area by using satellite remote sensing techniques and contribute to large engineering projects and research on neotectonics.
Quantitative thickness estimation of thin-layer is a great challenge in seismic exploration, especially for thin-layer below tuning thickness. In this article, we analyzed the seismic response characteristics of rhythm and gradual type of thin-layer wedge models and presented a new method for thin-layer thickness estimation which uses relative peak frequency increment. This method can describe the peak frequency to thickness relationship of rhythm and gradual thin-layers in unified equation while the traditional methods using amplitude information cannot. What’s more, it won’t be influenced by the absolute value of thin-layer reflection coefficient and peak frequency of wavelet. The unified equations were presented which can be used for rhythm and gradual thin-layer thickness calculation. Model tests showed that the method we introduced has a high precision and it doesn’t need to determine the value of top or bottom reflection coefficient, so it has a more wide application in practice. The application of real data demonstrated that the relative peak frequency increment attribute can character the plane distribution feature and thickness characteristic of channel sand bodies very well.
The Gabon Coastal Basin is a typical saliferous basin located in the middle portion of the West African passive continental margin. Complex salt tectonics make sedimentary sequences and structural frameworks difficult to interpret and can lead to difficulties in construction of balanced cross-sections and reconstruction of basin evolutionary processes. Sedimentary facies and salt structural patterns displaying zonation are based on seismic reflection profiles and drilling data. Two near-vertical fault systems, NW-SE and NE-SW, caused basin to be subdivided E-W zoning and N-S partitioning. Scarp slopes and extension faults formed in the Hinge belt III zone where salt diapir piercement occurred and numbers of salt pillars, salt stocks and salt rollers developed under transtension of coupled near-orthogonal fault systems. The zone east of Hinge belt III is characterized by small-scale salt domes and salt pillows. To the west are large-scale salt walls and salt bulge anticlines caused by diapirism promoted by tension and torsion that also resulted in formation of numerous salt pillars, salt stocks and salt rollers. Our modeling of salt tectonic structures indicates that they were produced by plastic rheological deformation of salt under regional stress fields that varied during three distinct phases of extension, compression and re-activation. Hinge belt III was active from Coniacian to Early Eocene, which was a critical period of formation of salt structures when many extension-related salt structures formed and salt diapirism controlled the distribution of turbidite fans. Rootless extrusion-related salt stocks developed throughout the Late Eocene to Early Oligocene as a result of local ephemeral low-intensity tectonic inversion. Post Oligocene salt diapirism was weak and salt tectonics had a weak influence on sedimentation. Balanced cross-sections of two saliferous horizons crossing different tectonic units from east to west reveal that the basin tectonic evolution and sediment filling processes can be divided into three stages containing seven episodes of rifting, transition and drifting.
Based on comprehensive analysis of the drilling core, slice analysis, FMI image well logging and other well logging data, the features of the Carboniferous volcanic rocks fracture reservoirs in Hongshanzui (红山嘴) oilfield of Junggar Basin have been studied. According to contributing factor, the fracture reservoirs were divided into diagenetic fractures, tectonic fractures, weathered fractures and dissolving fractures. And the diagenetic fractures were further divided into three subclasses of condensation contraction fractures, intergravel fractures and intercrystal fractures. The fracture reservoirs were also divided into 4 categories, such as high-angle fractures, oblique fractures, mesh fractures and lowangle fractures according to fracture attitude. With the FMI image logging and other logging information, the scale logging by the core method was adopted, our study shows that the fracture of tuff was the most developed, and the fracture density can be reached 11.46 bar/m, followed by the lava, and the sedimentary rock fracture was the lowest level. The fractures thickness in the region of 300 m apart from weather crust was accounted for 80.3% of the total thickness. Because of image logging data is limited, the method of drilling wells trajectory to calculate the fracture trend was proposed. The fracture trend was divided into two groups NE and NW. The secondary porefracture forming and distribution were controlled by fracture system, formed the beneficial passage system of the oil and gas, the fracture system was the key factor in restricting oil and gas accumulation, and was crucial for the volcanic rocks reservoirs.
The degree-day factor (DDF) is a key parameter in the degree-day model, and the variations in DDF have the significant effects on the accuracy of glacier mass balance modeling. In this study, Glacier No. 1 at the headwaters of ürümqi (乌鲁木齐) River in China was selected, and the estimated DDF by stakes-observed mass balance and meteorological data from 1983–2006 was used to analyze the spatio-temporal variability of DDF and its influencing factors, such as climate condition, surface feature, and topography. Then, the ablations from the 1980s to 2000s were estimated using the degree-day model, and the ablation change from the 1980s to 2000s was divided into the changes caused by climate change and by the ice-surface feature. The following results were obtained: (1) The annual change in DDF for snow was not obvious, whereas that for ice increased, and the increasing trend on the lower glacier was more significant than that on the upper glacier because of decreased albedo caused by variations in ice-surface feature; (2) The DDF for ice clearly decreased with altitude by approximately 0.046 and 0.043 mm?℃-1?d-1?m-1 on the east and west branches, respectively, and the DDF of the west branch was obviously larger than that of the east branch in the same altitude belt; (3) the changes in mass balance in the summers from the 1980s to 2000s were -391 and -467 mm on the east and west branches, respectively. Among the total changes, the components directly caused by climate change were -193 and -198 mm, whereas those indirectly caused by ice-surface feature change were -198 and -269 mm on the east and west branches, respectively.
Successful exploration and development of shale-gas in the United States and Canada suggest a new solution to the energy problem in China. The Longmaxi (龙马溪) Formation in the Sichuan (四川) Basin is regarded as a strong potential play for shale-gas with the following significant features: (1) complex structural types caused by multiphase tectonic superposition and reconstruction; (2) varied slippage processes that enhance porosity and permeability; (3) high thermal maturation of organic matter (Ro>2.5%); (4) high brittle mineral contents; (5) high and constant thicknesses of shale horizons within the formation. Evaluation of shale-gas prospects in this area should consider not only hydrocarbon parameters, but also preservation conditions and structural stability. Data from several new exploration wells in the Sichuan Basin indicate that tectonically induced netshaped fractures effectively enhance shale reservoir properties. Structural types providing favorable storage conditions for shale-gas are described and evaluated. The highyielding shale gas reservoir shares the same characteristics of conventional gas reservoirs except for its consubstantial source rock and reservoir in South China.