Table of Content

20 December 2016, Volume 22 Issue 4

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An Improved Thermodynamic Model for Calculating Solubility of the CO2-CH4-N2-C2H6-H2S Gas Mixture in Water

ZHANG Lu, SUN Rui*

2016, 22(4):  589. 

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This study extends the solubility model developed by Duan and coworkers for pure CO2, CH4, C2H6, and H2S to the
CO2-CH4-N2-C2H6-H2S gas mixture. The DMW92 equation of state (EOS) was extended to the CO2-CH4-N2-C2H6-H2S gas mixture by evaluation of interaction parameters between dissimilar molecule pairs from experimental VLE or PVTx data of binary gas mixtures. The extended DMW92 EOS was used in this model to calculate fugacity coefficients of components in gas mixture. The Pitzer model was used to calculate activity coefficients of gas dissolved in aqueous solutions. Solubility parameters determined by Duan and coworkers for pure CO2, CH4, C2H6 and H2S were followed and solubility parameters for pure N2 were determined in this study. Because this model contains no parameters evaluated from solubility data of gas mixtures, it is predictive for solubility of gas mixtures. Comparison with experimental data available shows that this model can predict solubility of CO2-CH4-N2-C2H6-H2S gas mixtures in aqueous solutions with high accuracy over a wide P-T range (For CO2 and CH4 dominant gas mixtures, the P-T range of this model is from 273 to 523 K and from 0 to 2000×105 Pa). Calculations of this model indicate that the solubility of CO2 decreases with adding small percentage of CH4, N2 or H2S. The homogenization pressure of CO2-H2O-NaCl fluid inclusions will increase with adding CH4. The computer program based on this model can be obtained from the corresponding author.

Trace Element Geochemical Characteristics of Gypsum and Its Gypsum and Significance from the Luotang Depression in
Xinjiang Basin, Jiangxi

ZHU Zhijun, GUO Fusheng, QIU Anqing

2016, 22(4):  598. 

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Dark red mudstone interbedded gypsum of late Cretaceous was developed in the Luotang depression in Xinjiang Basin,
Jiangxi. Gypsum trace element geochemical characteristics provide ways to decipher the depositional environment, together with well log data. This study shows that: (1) Gypsum was mainly developed in the second, third, and fourth section in Zhoutian Formation, which consists of gypsum-bearing calcium mudstone and muddy gypsum rock and a small amount of (hard) gypsum rocks; (2) Trace normalized patterns show that gypsum and wall rocks were terrigenous rather than deep brine sources; (3) Gypsum was developed in shallow water and deep water in early and late stage, respectively. It was probably located at the edge of basin in early stage, intercalated with purple calcareous mudstone tuberculosis gypsolith. It was mainly distributed in the central basin with gypsum rock and dark mudstonedeposition in the late stage，forming rhythmic salt layers. From the edge to the center of the basin, it was deposited as typical evaporite sequence from carbonate rocks togypsolith.

Geochronology, Geochemical Characteristics, and Genesis of Trachyte in Datan Basin, Northern Hebei

XIA Yingbing，WU Jianhua，JIANG Shan，WU Rengui1，LIU Shuai

2016, 22(4):  608. 

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Datan volcanic basin in Fengning is located in the zone of the northern North China Block, south of Xar Moron river fault
zone, west of the Yan-Liao polymetallic (Mo-U-Ag-Pb-Zn), and southwest of the Gu(yuan)-Hong(shanzi) uranium belts. It is adjacent to the Guyuan basin where there is a large Zhangmajing U-Mo deposit. The rhyolite-trachyte rock assemblage of Zhangjiakou was formed in the Datan volcanic basin and is the main wall rock of hydrothermal-type uranium deposit. The zircon SHRIMP U-Pb dating of trachyte yields an age of 140.3 ± 1.4 Ma (2σ, MSWD=1.09), which represents the emplacement age of the trachyte, and suggests that it was formed in the early Early Cretaceous. Trachyte contains high content of SiO2, K2O+Na2O ratio , SiO2=61.6%~63.1% , K2O+ Na2O=9.28%~10.2%, and falls in shoshonite series range of the K2O-SiO2 diagram and in alkaline series trachyte or dacite range of the TAS diagram. With the result of the CIPW and the content of Q =12.9%~18.4% (less than 20%), it belongs to the typical trachyte. Trachyte has high content of rare earth elements, enriched in light rare earth and the non-obvious negative Eu anomaly, ΣREE=(279~ 318)×10-6, δEu=0.77~0.88. The results show the right-leaning enrichment in light rare earth type with a high pressure type trachyte
characteristics of rare earth elements, enrichment in large ion lithophile element (K, Rb, Ba, Pb) and high field strength elements (Zr、 Y), and loss of these elements(Nb, Ta, Zr, Ti ). The Ti/Zr (8.40~14.72),Nb/Ta(14.07~15.26) ratio is low and Rb/Sr(0.95~1.60) ratio is high with high Sr-Ba dacite-rhyolite the characteristics of trace elements; High (87Sr/86Sr)i(0.7077~0.7096), lower εNd(t)(-12.09~-10.67), the larger TDM2(1796~1911Ma), lower (206Pb/204Pb)t(16.92~17.04), (207Pb/204Pb)t(15.39~15.42),（208Pb/204Pb)t(37.58~37.67). In the (87Sr/ 86Sr)i -t/Ga and (208Pb/204Pb)t-( 206Pb/204Pb)t diagram, it is located between the lower crust and the mantle, and is close to the EMⅠ enriched mantle. In the εNd(t)-(87Sr/86Sr)i diagram, it is located within EMⅠenriched mantle evolution line and Hannuoba two-pyroxenne grain xenoliths area. So the trachyte in the Datan basin can be explained by a two-stage model: In the paleoproterozoic, EMⅠenriched
mantle magma and a small part of the partial melting of ancient crust material were mixed and formed the young crust. In the early Early Cretaceous, the magma from partial melting of the young and thickened lower crust erupted and formed trachyte.

Diversity and Vertical Distribution of Culturable Sulfate-reducing Bacteria in Coastal Mangrove Swamps from Hainan Island, China

DING Hai, YAO Suping, LIU Guijian, Liu Changhong

2016, 22(4):  621. 

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Utilizing an anaerobic method of isolating microorganisms, we identified and cultured a total of 11 strains of anaerobic
sulfate-reducing bacteria (SRB) from sediment samples collected from 1.2 m-deep mangrove swamps in Hainan. These SRB were classified into 6 genera based on their morphology that was observed under a microscopy and through sequence analysis of their 16S ribosomal DNA (16S rDNA). These include three reported genera: Bacillus, Vibrio, and Clostridium. They also include three newly discovered genera: Burkholderia, Shewanella, and Marinobacterium. The minimum rate of sulfate reduction of these bacteria was 14.71%, and the maximum rate was 56.78%. Moreover, all the 11 strains were able to reduce sulfur S6+ to S2-, which was subsequently bound with iron (Fe2+) to produce black iron (II) monosulfide (FeS) precipitate. FeS precipitate is the precursor of pyrite. The population of SRB in the mangrove swamps decreased with depth. Geochemical analysis of the sediments reveal that the oxidation and reduction interface was located at interface of sediment and water (0 cm), and the periodic input of oxygen partially inhibited the growth of SRB. In contrast, as the depth of sediment increased (10-40 cm), an adequate supply of organic matter, a near-neutral pH, and an enhanced anaerobic environment led to a significant increase in both the number of SRB strains and the population of SRB. However, at depths greater than 60 cm, the total organic carbon (TOC) content in the sediment decreased, which reduced the carbon source available for microorganisms. In addition, both a significant reduction in pH levels and significant increases in sodium cation (Na+ ) and calcium cation (Ca2+) concentrations inhibited SRB growth, greatly decreasing the number of SRB strains and the total SRB population in the deep sediments. The geochemical characteristics of the sediments were the main factors affecting vertical distribution of SRB species in the mangrove swamp samples.

Sr-Nd Isotopic Compositions and Provenance of Materials at Liangzhu Culture Sites: Implications for the Lost Ancient Civilization

JI Xiang, WU Weihua, CHEN Minghui, WANG Ningyuan, LIU Bin, XU Shijin, YANG Jiedo

2016, 22(4):  631. 

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Liangzhu Culture is an important culture in the late neolithic age and has a significant connection to the origin of the Chinese
civilization. The archaeological site of Liangzhu ancient city located in Pinyao, Hangzhou, represents the crown of Liangzhu
development. Wecollected soil samples from the Liangzhu cultural layer, the overlying silty soil and the sediments of surrounding rivers and the Qiantang River, measuring and analyzing their Sr-Nd isotopic compositions. Comparing variations between the silty soil and the soil of the Liangzhu cultural layer, together with some recent studies of the sediments of the Yangtze River and the East China Sea, we infer that the silty soil may be a mixture of sediments from the East China Sea and the Qiantang River. Therefore, transgression during that period may result in the collapse of the LiangzhuCulture.

Performance of Thermally Activated Colloidal Pyrite in Removal of Cadmiun(Ⅱ) in Acid Solution

ZHU Yuke, LI Ping, LIU Haibo, YANG Yan, CHEN Tianhu*

2016, 22(4):  638. 

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The thermally activated colloidal pyrite was characterized by XRD and SEM. The effect of solution pH, dissolved oxygen，
and thermal activation temperatures on the performance of thermally activated colloidal pyrite on removal of Cd(Ⅱ) from aqueous solution were systematically studied. The reactive kinetics and the mechanism of the adsorption of Cd(Ⅱ) on thermally activated colloidal pyrite were also discussed. Colloidal pyrite was decomposed into Porous Monoclinic Pyrrhotite (PMPyr) after thermal activation at 650℃ for 5 minutes in a muffle furnace (nitrogen atmosphere). The removal efficiency of Cd(Ⅱ) by PMPyr in the solution of no dissolved oxy gen was above 88% at pH 2~6, suggesting that the removal efficiency of Cd(II) was less affected by pH. Moreover, surface oxidation of PMPyr could restrain the interaction between PMPyr and Cd( Ⅱ). The kinetic adsorption process was well described by pseudo-second-order model with high correlation coefficient (R2> 0.9992). The influence of pH and change of concentration of Fe (Ⅱ) and SO42- showed that the adsorption of Cd(Ⅱ) on PMPyr was mainly dominated by ion exchange and surface complexation.

Development and Distribution Characteristics of Tectonic Fractures in Kuqa Depression

YU Xuan, HOU Guiting, NENG Yuan, LI Jie, WEI Hongxing

2016, 22(4):  644. 

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The structural fracture development characteristics of Kuqa depression in Tarim Basin are comprehensively analyzed in
light of the outcrop, core and log data. The characteristics of fractures we overserved consist of properties, attitude, density, intensity, aperture, and filling. The tectonic fractures in this area are mainly the medium-high dip angle shear fractures and include three groups of fractures extending mostly in the N-S direction. The aperture of most outcrop and core fractures is 0~5mm and 0~1mm, respectively. The majority of fractures is unfilled or half-filled, and the filling is mainly calcite. The distribution of each parameter of fracture shows regularity in E-W and N-S direction, respectively. Laterally, the Lower Cretaceous fracture development area is mainly distributed in the Kelasu-Yiqikelike structural belt. Vertically, the fractures are well developed in the Lower Jurassic Ahe Formation in the east Kuqa depression, and the Lower Cretaceous Bashijiqike Formation in the west Kuqa depression. Overall, the structural fracture is very well developed in the Kuche depression, which is beneficial to the improvement of porosity and permeability of tight reservoir, and is also beneficial to the formation of fractured hydrocarbon reservoirs.

The Mesozoic Tectonic Palaeogeographic Analysis in Kuqa Depression of Tarim Basin

YU Haibo, QI Jiafu, YANG Xianzhang, LIU Qiyao, CAO Shujuan, FAN Sheng, SUN Tong,

2016, 22(4):  657. 

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Using the regional geological, seismic, and well data, this paper investigates the Mesozoic basin structure and tectonic style,
Mesozoic original thickness of strata and depositional system, paleo-uplift topography, and regional tectonic evolution in Kuqa
depression. Subsequently the paleogeography of the Mesozoic basin is reconstructed and factors of basin prototypes in Kuqa depression are analyzed. The residual Mesozoic strata in Kuqa depression show that the geological structure becomes thinner from the north to the south, and is stripped in the north and overlapped in the south. The northern part is marked by a large angular unconformity on Hercynian fold belt of south Tianshan, and the southern part shows a gentle angular unconformity on Cambrian or Ordovician. The basement faults have movements along with the WenSu-XiQiu-YaHa palaeohighs in the southern edge. The alluvial fan and braided river delta were developed in the northern monoclinal belt, and the deep-lake facies was developed in Crassus structural belt. Along with the southern palaeohighs were the gentle slope delta and a shallow lake. The Mesozoic prototype basin of Kuqa depression belongs to the transitional zone of Hercynian orogenic belt in southern Tianshan and the Tarim craton. The isostasy may be the main factor on the passive margin of the subsidence of Mesozoic basin. During the expansion of the Southern Tianshan Ocean, the southern palaeohighs were on the passive margin of Tarim cratonic platform. When the southern Tianshan ocean closed, the southern palaeohighswerelocatedonaupliftedbeltoftheforeland.Basementfaultsweredevelopedwithfaultblockshavingdifferentmovementsand
the southern palaeohighs were inherited in the Mesozoic. In the late Cenozoic, the southern palaeohighs experienced compressional deformationassociated with the up lift of new Tianshan,and then became the frontal thrust deformation of orogenicwedge in the new Tianshan.

Tectonic Evolution and Petroleum Accumulation in Zhuangxi Buried-hill, Jiyang Depression

SUN Yaoting，XU Shouyu，LIU Jing，LI Yulan，LI Hui

2016, 22(4):  670. 

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Zhuangxi Buried-hill is one of the most tectonically complicated regions in Jiyang Depression. It experienced multiphase
tectonism with good prospects for oil and gas exploration and development. However, its tectonic evolution has not been studied in detail, impeding the exploration and development work. Here we study the tectonic evolution of Zhuangxi Buried-hill by the method of cross-section balancing on the basis of regional tectonic evolution analysis. Results indicate that Zhuangxi Buried-hill was controlled by the cratonic tectonic setting after the North China continental core formation in Archaean to Mesoproterozoic and was mainly carbonate-based deposition conditions in the early Paleozoic. Zhuangxi Buried-hill experienced three evolutionary stages: the Indosinian folding related uplift, the Yanshanian fault block uplifting, that the Himalayan tectonic uplifting and burial. Bedrock strata underwent two episodes of weak compressional tectonism in Indosinian and late Yanshanian. The present fold is a rolling anticline formed in Himalayan. Zhuangxi Buried-hill is a lower compression-arch fold Buried-hill. The reservoirs in the Zhuangxi Buried-hill are mainly composed of Cambrian-Ordovician carbonate rocks in lower Paleozoic, the tectonic evolution controlled distribution of reservoirs in the Zhuangxi Buried-hill. The reservoir type is dominated by fault karst zone and fracture, followed by the weathering crust karst belt, mainly formed within the fractured Buried-hill reservoirs. The oil and gas of Zhuangxi Buried-hill came from source rocks of the lower part of the third member of Paleogene Shahejie Formation, and then migrated through the Zhuangnan fault to Zhuangxi Buried-hill and formed reservoirs. There are two kinds of accumulation models in Zhuangxi Buried-hill: compression-arch-fold type and compression-tension-block type. The compression-arch-fold accumulation is mainly distributed in the western limb of the anticline. The
compression-tension-block accumulation is mainly distributed in the anticline axis region where the stress is most concentrated, and it is the main type of high-yield reservoirs.

Shale Gas Occurrence Characteristics and Exploration Significance of WX2 Well in the Northeast Chongqing

FU Changqing, ZHU Yanming, CHEN Shangbin, LIANG Feng

2016, 22(4):  689. 

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To study the shale gas occurrence characteristics of the Longmaxi Formation in northeast Chongqing, the isothermal
adsorption data under high temperature and high pressure and porosity data under burden pressure of the well WX2 shale were analyzed. According to the principle of minimum error, we have chosen a suitable adsorption model for the study area. Based on the relationship between porosity and effective stress, the free gas model is established. In addition, comprehensive analysis of the characteristics of adsorption gas, free gas, and changes in total gas with the buried depth was conducted. The results show that excess adsorption quantity of well WX2 shale increased first and then decreased under different temperatures with an increasing pressure. The maximum adsorption capacity decreased gradually as the temperature increased. After correction, the absolute adsorption quantity shows a rapid increase first and then a slow increase with increasing pressures. As the absolute adsorption data can be fitted with D-A model with the minimum average error, it can represent the real adsorption process of shale in the study area. Pores and micro-cracks of shale samples will gradually close during pressurization, and reopen during depressurization. This process will cause irreversible damage by plastic deformation, but irreversible damage accounts for small proportion. Porosities of samples from different directions have a negative exponent relationship with effective stress. Parallel samples of lamina-rich shales have greater initial porosity and
stronger pore stress sensitivity than the vertical samples. Shale gas occurrence characteristic is comprehensively controlled by reservoir characteristics, adsorption capacity, reservoir temperature, and reservoir pressure. Among them, temperature has the negative effects on adsorption gas content and free gas content, and the reservoir pressure has the positive effect. The adsorption gas content, free gas content and total content increases first then decreases. Adsorption gas content and free gas content are mainly controlled by temperature and reservoir pressure, respectively. In addition, relative abundance of adsorption gas and free gas will change near the critical depth, and this will be of great importance for evaluating shale gas enrichment.

The Influence of Shale Sedimentary Environments on Oil and Gas Potential: Examples from China and North America

ZHAI Zheng, WANG Xuejun, LI Zheng, LI Juyuan, LIU Qing

2016, 22(4):  690. 

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Shale oil and gas are currently attracting global oil and gas exploration and research interest, however, their potential
evaluation is considered as the main difficulty. The article examines four shale formation in China and North America including Green River Formation lacustrine shale and Niobrara Formation inland marine shale in North America, Longmaxi Formation marine shale and Jiyang lacustrine shale in China. It is found that sedimentary environments are closely related to shale oil and gas potential. Therefore, the shale oil and gas potential can be evaluated by shale sedimentary environment. The four formations shales from China and North America were characterized trace elemental analysis, biomarker compounds, X-ray computed tomography (X-CT) and X-ray diffraction (XRD). Results show that the four formation shales have certain reducing sedimentary environment and high paleoproductivity in Green River formation and Niobrara formation in North America, as well as Longmaxi Formation and shale in Jiyang Depression. As the Niobrara formation shale has dysoxic-suboxic conditions, it has massive layers, lower fracture structure, the lowest organic content and reservoir volume in the four formation shales. The Longmaxi Formation shale is mainly composed of siliceous with high organic content, and the reservoir has more large pore and certain fracture structure, which can be attributed to anoxic marine sedimentary environment. Shales of Green River formations and Jiyang depression have saline source rocks with anoxicsedimentary environment. Shales of the two formations have relatively high organic abundance. Meanwhile, continuous laminae can be clearly seen and the rock is dominated by brittle mineral with abundant fractures. Thus, it can be speculated that shale with an anoxic environment has excellent exploration prospect.

Carbon and Oxygen Isotopic Composition and Uranium Mineralization Significance of Calcite of Zhiluo Formation Uranium-bearing Sandstones in Dongsheng Area

TANG Chao, SIMA Xianzhang, ZHU Qiang, FENG Xiaoxi, CHEN Yin, CHEN Lulu, LIU Xiao

2016, 22(4):  698. 

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Calcite is an important cement type of Zhiluo Formation uranium-bearing sandstones in Dongsheng area, and the carbonation
is closely related to the uranium mineralization. Based on petrographic，mineralogical, carbon and oxygen isotope analysis of calcite cements, the composition, precipitation mechanism, and uranium mineralization significance of carbon and oxygen isotope of calcite were researched in the study area. The results show that sandstones include feldspathic lithic sandstone, lithic sandstone and quartz sandstone, and clay minerals are mainly composed of smectite, illite, kaolinite and chlorite and iron-containing calcite, followed by iron calcite, as the main types of carbonate cements. The δ13CV-PDB is -15.7‰~-1.6‰with an average of -9.08‰. The δ18OV-PDB is -15.6‰ ~-10‰ with an average of -12.4‰ . The results indicate that the formation of calcite is related to the organic acid decarboxylation and the carbon source is organic carbon. Analyses of carbon and oxygen isotopic results reveal that the composition of isotope composition has characteristics of sealed atmospheric precipitation and the heavier isotope composition reflects the participation of deep low-temperature thermal fluid with oil and rich-gas during the process of diagenetic mineralization. The comprehensive analysis indicated that calcite in Zhiluo Formation sandstones of Dongsheng area was a result of interaction of surface water and deep oil and gas. Early organic prompted feldspathic matrix particle dissolution and the quartz grains overgrowth edge was formed, along with kaolinite precipitation. Later, with a large number of hydrocarbons injected into sandstones, diagenetic metallogenic
environment changed from acidic to basic and the reducibility is enhanced. The combination of CO2, Ca2+, and Fe2+ in medium water formed the iron calcite and precipitated in all kinds of primary and secondary pores. The uranium migration and precipitation during the whole process, which indicate the formation of uranium deposits, was a result of interaction of surface water and deep oil and gas.

Fracture Combination Patterns and Distribution of Ultra-deep Reservoirs beneath Salt in the Kelasu Structural Belt

ZHOU Lu，LEI Ganglin，ZHOU Peng，WANG Wei，ZHANG Xing，SHI Chaoqun，WANG Zhenhong，ZHAN

2016, 22(4):  707. 

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The ultra-deep reservoirs beneath salt in the Kelasu structural belt belong to low porosity and fractured sandstone reservoir.
Tectonic fractures are common in this area and show a complex distribution pattern. These widely distributed tectonic fractures have large influence on single-well production of Kelasu structural belt. At present, research on reservoir fracture in this area is mainly focused on description, characterization, and prediction of fractures. However, due to low resolution of seismic data, limited core data and uncertainties in interpretation of images of well logging, the study of is limited. Only some statistical data such as fracture density and fracture opening are applied in the process of hydrocarbon exploration. Outcrop, core, and well logging data were used. In this study, research on reservoir fracture and combinations of fractures is carried out in this area. It is found that there are primary and secondary cracks. The scale of main cracks is larger than that of the secondary cracks. The primary cracks are generally perpendicular to the strata, and are mostly tension cracks or tension-shear cracks. The secondary cracks are generally associated the main cracks. There are many different contacts between the cracks, mainly in“T”,“λ”,“V”,“y”, and“τ”shapes. According to the distribution of contacts between cracks, four combination modes of reservoir cracks have been established in this area including“parallel mode”,“broom like
mode”,“adjust mode”,“echelon mode”. Together with the tectonic process of the formation of faulted anticline and the difference between crack combinations, three types of genetic regions of crack combination have been identified, i.e., are tectonically transitional region, folding-related area, and fault formation area, corresponding to the first, second, and third category of high yield wells,respectively.

The Method for TOC Content Evaluation in Shale Reservoirs Based on Improved Rain Forest Fuzzy Neural Network Model

ZHU Linqi, ZHANG Chong*, WEI Yang, GUO Cong, ZHOU Xueqing, CHEN Yulong

2016, 22(4):  716. 

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The accuracy of evaluating total organic carbon in shale reservoirs is limited by using conventional logging curves because of
their insufficient generalization ability and requirement of a large number of samples. In view of these problems, neural network algorithm was improved to improve the prediction ability of the model. The cellular neural network structure was optimized by using a fuzzy system to enhance its logical reasoning ability and to improve its sensitivity to fuzzy data. The rain forest algorithm, which can effectively avoid the virtual collision, was selected, and its defect of slow convergence in the late learning was overcome. The initial weight value and threshold value of the network were optimized by the improved rain forest optimization algorithm to prevent the network from resulting in local minimum, which can improve the accuracy and generalization ability of the model. Based on the analysis of the physical meaning of the characteristic curve, the density log curves and the natural gamma ray spectrum logging curves were chosen as the input to the network and the total organic carbon content was used as the output. Through the network learning of 70 core samples and the prediction of 26 core samples, the role of the improved rain forest algorithm and fuzzy logic is proved. The superiority of the new network model is demonstrated. The result shows that the relative regressional error of the new model is reduced from 23.189% to 17.185%, and the relative prediction error is reduced from 52.421% to 15.158%, which means that the prediction is in accordance with the real situation of formation. From the above, we learn that the new model has better learning ability and generalization ability. The new model is more suitable for logging evaluation of total organic matter content in shale reservoirs.

Study on Distributed Monitoring Method of Deep Foundation Pit Retaining Pile Based on the Brillouin Optical Time Domain Technology

SUO Wenbin, CHENG Gang, LU Yi, SUN Yijie, SHI Bin

2016, 22(4):  724. 

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Retaining pile is a key part of bracing and retaining structures which directly affect the stability of deep foundation pit.
Therefore, it is important to monitor the strain and stress state of a retaining pile. In this paper, the single-ended detecting distributed optical fiber sensing technology based on the Brillouin Optical Time-Domain Reflectometer (BOTDR) was used for monitoring the deformation of a PHC type retaining pile in a deep foundation pit. The monitoring method was described and its effectiveness was well verified in a deep foundation pit in Nanjing. The results indicate that the BOTDR-based method is feasible to make a fully-distributed monitoring of the retaining pile in the deep foundation pit. It is expected to be a novel way for monitoring deep foundation pit.

Comparison of Two-dimensional and Three-dimensional Simulations of DNAPL Migration in Saturated Porous Media

MI Dong, FAN Hao, LUO Xiaoyong, ZHENG Fei, SHI Xiaoqing, WU Jichun

2016, 22(4):  733. 

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The cChange in the spatial dimension of heterogeneous media significantly influences the migration and distribution of
Dense Non-Aqueous Phase Liquid (DNAPL). Based on the Markov Chain transition probability model, we generate stochastic
permeability fields and take a fully account of horizontal spatial continuity, asymmetry, and anisotropy of heterogeneous media. By simulating the migration and distribution of DNAPL in heterogeneous media with TMVOC-MP, we investigate the effects of horizontal spatial continuity, reduced dimensionality, and lateral migration on the migration and distribution of DNAPL. Numerical analysis reveals that a better horizontal spatial continuity results in a larger horizontal pollution scope and a smaller vertical migration extent of DNAPL. Compared with the behavior in the three-dimensional model, DNAPL distributes in a larger scope in the horizontal direction, accumulates more on the low-permeability lenses, and is mostly in a pool state in the two-dimensional model. Lateral migration process can reduce the impact of heterogeneity of a single plane on the DNAPL migration. So it is necessary to use the threedimensional model in practical applications instead of two-dimensional model.

Features and Mechanisms of Earth Fissures Induced Groundwater Withdrawal in China

WANG Yiwei，YE Shujun，YU Jun，GONG Xulong

2016, 22(4):  741. 

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Excessive exploitation of groundwater in China has induced serious earth fissure hazards, which can cause significant
damage and heavy economic losses, and has received significant attention. In recent decades, mechanisms of earth fissures induced by groundwater withdrawal have been studied by researchers worldwide and many remarkable achievements have been accomplished. The results of previous studies were analyzed in this article firstly and then the mechanisms of earth fissure induced by excessive exploitation of groundwater were summarized and categorized as differential subsidence, horizontal tensile strain, and Four Earth Fissure Formation Conceptual Models. Then the distribution of earth fissures, development features and mechanisms of earth fissures in three regions (i.e., the Fenwei Basin, North China Plain and Su-Xi-Chang in China) where typical“groundwater-withdraw-induced” fissures developed, were elaborated, and a typical earth fissure was chosen to analyze its cause. Results indicate that earth fissures in the Fenwei Basin and North China Plain were mainly caused by pre-existing faults and excessively ground water exploitation, while the fissures in the Su-Xi-Chang region were generally induced by a“bedrock ridge”below the aquifer and excessively ground water exploitation.Differentialcompactionandhorizontalstrainmechanismscausingthedevelopmentofsuchearthfissureswerethenexplained.