The great Tancheng earthquake of M81/2 occurred in 1668 was the largest seismic event ever recorded in history in eastern China. This study determines the fault geometry of this earthquake by inverting seismological ...The great Tancheng earthquake of M81/2 occurred in 1668 was the largest seismic event ever recorded in history in eastern China. This study determines the fault geometry of this earthquake by inverting seismological data of present-day moderate-small earthquakes in the focal area. We relocated those earthquakes with the double-difference method and found focal mechanism solutions using gird test method. The inversion results are as follows: the strike is 21.6°, the dip angle is 89.5°, the slip angle is 170°, the fault length is about 160 km, the lower-boundary depth is about 32 km and the buried depth of upper boundary is about 4 km. This shows that the seismic fault is a NNE-trending upright right-lateral strike-slip fault and has cut through the crust. Moreover, the surface seismic fault, intensity distribution of the earthquake, earthquake-depth distribution and seismic-wave velocity profile in the focal area all verified our study result.展开更多
The Yanchang Formation Chang 7 oil-bearing layer of the Ordos Basin is important in China for producing shale oil.The present-day in situ stress state is of practical implications for the exploration and development o...The Yanchang Formation Chang 7 oil-bearing layer of the Ordos Basin is important in China for producing shale oil.The present-day in situ stress state is of practical implications for the exploration and development of shale oil;however,few studies are focused on stress distributions within the Chang 7 reservoir.In this study,the present-day in situ stress distribution within the Chang 7 reservoir was predicted using the combined spring model based on well logs and measured stress data.The results indicate that stress magnitudes increase with burial depth within the Chang 7 reservoir.Overall,the horizontal maximum principal stress(SHmax),horizontal minimum principal stress(Shmin) and vertical stress(Sv) follow the relationship of Sv≥SHmax>Shmin,indicating a dominant normal faulting stress regime within the Chang 7 reservoir of Ordos Basin.Laterally,high stress values are mainly distributed in the northwestern parts of the studied region,while low stress values are found in the southeastern parts.Factors influencing stress distributions are also analyzed.Stress magnitudes within the Chang 7 reservoir show a positive linear relationship with burial depth.A larger value of Young's modulus results in higher stress magnitudes,and the differential horizontal stress becomes higher when the rock Young's modulus grows larger.展开更多
Previous studies have postulated the contribution of present-day low-total organic carbon (TOC) marine carbonate source rocks to oil accumulations in the Tabei Uplift, Tarim Basin, China. However, not all present-da...Previous studies have postulated the contribution of present-day low-total organic carbon (TOC) marine carbonate source rocks to oil accumulations in the Tabei Uplift, Tarim Basin, China. However, not all present-day low-TOC carbonates have generated and expelled hydrocarbons; therefore, to distinguish the source rocks that have already expelled sufficient hydrocarbons from those not expelled hydrocarbons, is crucial in source rock evaluation and resource assessment in the Tabei Uplift. Mass balance can be used to identify modern low-TOC carbonates resulting from hydrocarbon expulsion. However, the process is quite complicated, requiring many parameters and coefficients and thus also a massive data source. In this paper, we provide a quick and cost effective method for identifying carbonate source rock with present-day low TOC, using widely available Rock-Eval data. First, we identify present-day low-TOC carbonate source rocks in typical wells according to the mass balance approach. Second, we build an optimal model to evaluate source rocks from the analysis of the rocks' characteristics and their influencing factors, reported as positive or negative values of a dimensionless index of Rock-Eval data (IR). Positive IR corresponds to those samples which have expelled hydrocarbons. The optimal model optimizes complicated calculations and simulation processes; thus it could be widely applicable and competitive in the evaluation of present-day low TOC carbonates. By applying the model to the Rock-Eval dataset of the Tabei Uplift, we identify present-day iow-TOC carbonate source rocks and primarily evaluate the contribution equivalent of 11.87×10^9 t oil.展开更多
This study attempts to acquire information on tectonic activity in western China from land surface temperature (LST) field data. On the basis of the established relationship between heat and strain, we analyzed the ...This study attempts to acquire information on tectonic activity in western China from land surface temperature (LST) field data. On the basis of the established relationship between heat and strain, we analyzed the LSTdistribution in western China using the satellite data product MODIS/Terra. Our results show that: 1. There are departures from annual changes of LSTin some areas, and that these changes are associated with the activity of some active tectonic zones. 2. When annual-change background values caused by climate factors are removed, the long-period component (LSTLow) of temperature residual (AT) of the LSTis able to serve as an indicator for tectonic activity. We have found that a major earthquake can produce different effects on the/ST fields of surrounding areas. These effects are characterized by both rises and drops in temperature. For example, there was a noteworthy temperature decline associated with the Sumatran M9 earthquake of 2004 in the Bayan Har-Songpan block of central Tibetan Plateau. 3. On the other hand, the LST field of a single area may respond differently to major shocks occurring in different areas in the regions surrounding China. For instance, the Kun- lun M 8.1 event made the LSTon the Longmen Mountains fault zone increase, whereas the Zaisan Lake M 7.9 quake of 2003, and the Sumatran M 9 event of 2004, caused decreases in the same area's LST. 4. The variations of land surface temperature (LST) over time are different in different tectonic areas. These phenomena may provide clues for the study of tectonic deformation processes. On the basis of these phenomena, we use a combi- nation of temperature data obtained at varied depths, regional seismicity and strain results obtained with GPS measurements, to test the information related to tectonic activity derived from variations of the LST field, and discuss its implications to the creation of models of regional tectonic deformation.展开更多
Knowledge of the present-day in-situ stress distribution is greatly import-ant for better understanding of conventional and unconventional hydro-carbon reservoirs in many aspects,e.g,reservoir management,wellbore stab...Knowledge of the present-day in-situ stress distribution is greatly import-ant for better understanding of conventional and unconventional hydro-carbon reservoirs in many aspects,e.g,reservoir management,wellbore stability asssment,etc.In tectonically stable regions,the present-day in-situ stress field in terms of stress distribution is 1argely controlled by lithological changes,which can be predicted through|a numerical simulation method incorporating specific mechanical properties of the subsurface reservoir.In this study,a workflow was presented to predict the present-day in-situ stress field based on the finite element method(FEM).Sequentially,it consists of:i)building a three-dimensional(3D)geometric framework,i)creating a 3D petrophysical parameter field,11)integrating the geometric framework with petrophysical parameters,iv)setting up a 3D heterogeneous geomechanical model,and finally,v)calculating the present-day in-situ stress distribution and calibrating the prediction with measured stress data,e.g.,results from the extended leak-off tests(XLOTs).The approach was sucessfully applied to the Block W in Ordos Basin of central China.The results indicated that the workflow and models presented in this study could be used as an effective tool to provide insights into stress perturbations in subsurface reservoirs and geological references for subsequent analysis.展开更多
The study evaluates the factors confronting the present-day construction practices in South-East Nigeria. Being a survey research, questionnaires containing information relating to factors/challenges affecting constru...The study evaluates the factors confronting the present-day construction practices in South-East Nigeria. Being a survey research, questionnaires containing information relating to factors/challenges affecting construction practices were randomly administered to selected construction practitioners in South-Eastern States of Nigeria. Accordingly, a total of 240 questionnaires were administered to the selected respondents while 160 copies were completed, returned and found useful. Thus, giving a response rate of 66.67%. Data collected were analysed and presented using percentages, mean scores, principal and factor analysis, z-test and tables. The study found that the core factors that constrain present-day construction in the study area are issues related to inadequate/dearth of technical and managerial expertise, corruption and poor project planning and control;which significantly affect operational effectiveness of the construction industry in the study area. Therefore, the study concluded by recommending that thorough capacity building through training or retraining programme which should centre on areas of the issues identified should be religiously pursued in the study area.展开更多
Velocity field of China continent constrained by Global Positioning System (GPS) reveals both continuous and block-like styles of deformation. Continuous deformation commonly characterizes actively deforming mountain ...Velocity field of China continent constrained by Global Positioning System (GPS) reveals both continuous and block-like styles of deformation. Continuous deformation commonly characterizes actively deforming mountain ranges such as the Tianshan Mountain, Qilian Mountain, and Tibet. The block-like movement often represents deformation in the tectonically stable regions such as Ordos, South China and Tarim blocks. GPS measurements indicate 5.1±2.5 mm/a left-lateral strike-slip rate along the Altun fault. Eastward convergence along the Longmenshan fault is less than 6.7±3.0 mm/a. South China moves 11-14 mm/a eastward compared with the stable Eurasia. These low slip rates do not imply rapid eastward extrusion of China continent predicted by the model of 'continental extrusion'. It appears that 'crustal thickening' model more properly describes both continuous and block-like styles of deformation in China continent.展开更多
The Puguang (普光) gas field is the largest gas field found in marine carbonate in China. The Puguang gas field experienced complicated evolution history from paleo-oil pool to gas pool. The purpose of this article ...The Puguang (普光) gas field is the largest gas field found in marine carbonate in China. The Puguang gas field experienced complicated evolution history from paleo-oil pool to gas pool. The purpose of this article is to reveal the evolution history of Puguang gas field through systematic study on the relationship between paleo-oil-water contact (POWC) and present-day gas-water contact (PGWC). POWC was recognized by observing the change of relative content of residual solid bitumen in the cores, and PGWC was observed using log and drilling stem test data. Two types of relationship between POWC and PGWC were observed in the Puguang gas field: POWC is above PGWC, and POWC is below PGWC. The former is normal as oil cracking may cause gas-water contact to move downward. The latter can be interpreted by lateral gas re-migration and re-accumulation caused by changes in structural configuration. The relationship between POWC and PGWC suggests that during oil charge, the southwestern and northwestern parts of the Puguang gas field were structurally lower than the northeastern and southeastern parts. Thrusting from Xuefengshan (雪峰山) since Yanshanian movement and from Dabashan (大巴山) since Himalayan movement resulted in the relative uplift of the southwestern and northwestern parts of the Puguang structure, which significantly changed the structural configuration. Based on the paleo-structure discussed in this article, the most probable migration directions of paleo-oil were from the northwest to the southeast and from the southwest to the northeast. Consequently, the evolution history of the Puguang gas field can be divided into three stages, namely,oil charging (200-170 Ma), cracking oil to gas (155-120 Ma), and gas pool adjustment (12-0 Ma).展开更多
Hydrocarbon expulsion occurs only when pore fluid pressure due to hydrocarbon generation in source rock exceeds the force against migration in the adjacent carrier beds.Taking the Middle-Upper Ordovician carbonate sou...Hydrocarbon expulsion occurs only when pore fluid pressure due to hydrocarbon generation in source rock exceeds the force against migration in the adjacent carrier beds.Taking the Middle-Upper Ordovician carbonate source rock of Tarim Basin in China as an example,this paper proposes a method that identifies effective carbonate source rock based on the principles of mass balance.Data from the Well YW2 indicate that the Middle Ordovician Yijianfang Formation contains effective carbonate source rocks with low present-day TOC.Geological and geochemical analysis suggests that the hydrocarbons in the carbonate interval are likely self-generated and retained.Regular steranes from GC-MS analysis of oil extracts in this interval display similar features to those of the crude oil samples in Tabei area,indicating that the crude oil probably was migrated from the effective source rocks.By applying to other wells in the basin,the identified effective carbonate source rocks and non-source rock carbonates can be effectively identified and consistent with the actual exploration results,validating the method.Considering the contribution from the identified effective source rocks with low present-day TOC(TOC_(pd))is considered,the long-standing puzzle between the proved 3 P oil reserves and estimated resources in the basin can be reasonably explained.展开更多
Based on the geodetic data taken from the National GPS Network established by China Climbing Program 'Investigation of Crust Motion and Geodynamics in Modern Time', we derived the movement velocities of the GP...Based on the geodetic data taken from the National GPS Network established by China Climbing Program 'Investigation of Crust Motion and Geodynamics in Modern Time', we derived the movement velocities of the GPS sites.In terms of the power series expansion of a rotation function for horizontal velocities on a spherical surface proposed by Hames and Holt (1993), we computed the horizontal velocity and strain-rate field.We preliminarilystudied the appearances and characteristics of the present-day crustal movement and deformation in the Chinesemainland with the computed results. The researches demonstrated (1)The present-day crustal movement anddeformation in the Chinese mainland are being jointly controlled by indian, Pacific and Philippines Ocean Platesand Siberia-Mongolia block, and these three large plates and block form a situation of triparite confrontation, butIndian Plate seems to play a leading role;(2) The North-South Earthquake Zone plays an important adjustment rolein the present-day crustal movement and deformation process. displaying clear characteristics of demarcation lineof tectonics in large areas, (3)There seems to be another adjustment zone along the latitude line approximate N35,but its characteristics are less obvious than that of the former; (4) Dynamic actions of these three large plates andblock on the Chinese mainland are dynamic stable; appearing in stable push-press velocities. These results aregenerally accorded with the results determined from geology, geophysics, and seismology. By the contrast withseismicities. if appears preliminarily that there is some corresponding relation between intense shear st fain zoneand future strong seismicity area. but this problem needs further examination of earthquake examples.展开更多
Background: In the contxt of ecosystem management, the present study aims to compare the natural and the present-day forested landscapes of a large territory in Quebec(Canada). Using contemporary and long-term fire cy...Background: In the contxt of ecosystem management, the present study aims to compare the natural and the present-day forested landscapes of a large territory in Quebec(Canada). Using contemporary and long-term fire cycles, each natural forst landscape is defined according to the variability of its structure and composition, and compared to the present-day landscape. This analysis was conducted to address the question of whether human activities have moved these ecosystems outside the range of natural landscape variability.Methods: The study encompassed a forested area of 175 000 km2 divided into 14 landscapes. Using a framework that integrates fire cycles, age structure and forest dynamics, we characterized the forest composition and age structures that resulted from three historical fire cycles(110,140, and 180 years) representative of the boreal forest of eastern Canada. The modeled natural landscapes were compared with present-day landscapes in regard to the proportion of old-growth forests(landscape level) and the proportion of late-successional forest stands(landscape level and potential vegetation type).Results: Four landscapes(39%) remain within their natural range of variability. In contrast, nine landscapes(54%)show a large gap between natural and present-day landscapes. These nine are located in the southern portion of the study area, and are mainly associated with Abies-Betula vegetation where human activities have contributed to a strong increase in the proportion of Populus tremuloides stands(early-successional stages) and a decrease of oldgrowth forest stands(more than 100 years old). A single landscape(7%), substantially changed from its potential natural state, is a candidate for adaptive-based management.Conclusion: Comparison of corresponding natural(reference conditions) and present-day landscapes showed that ten landscapes reflecting an important shift in forest composition and age structure could be considered beyond the range of their natural variability. The description of a landscape's natural variability at the scale of several millennia can be considered a moving benchmark that can be re-evaluated in the context of climate change.Focusing on regional landscape characteristics and long-term natural variability of vegetation and forest age structure represents a step forward in methodology for defining reference conditions and following shifts in landscape over time.展开更多
Based on GPS data from 1991- 2004 and the least-squares collocation method,we analyze the crustal deformation in the Chinese mainland. The results show that the first-order crustal deformation is unchanged in differen...Based on GPS data from 1991- 2004 and the least-squares collocation method,we analyze the crustal deformation in the Chinese mainland. The results show that the first-order crustal deformation is unchanged in different periods in the Chinese mainland,which reflects the background of regional tectonic activity. The strain rate is much higher in Western China,especially in the Qinghai-Tibetan Plateau and Sichuan-Yunnan area. The variations in different periods are related with seismicity of strong earthquakes during the same time. The GPS data after 2004 shows the post-seismic deformation of the 2001 Kunlun Mountains M S8. 1 earthquake.展开更多
The continually-discovered large volumes of marine hydrocarbons indicate a huge exploration potential within the carbonate rocks of Ordovician in the Tarim Basin,northwestern China.The Middle-Upper Ordovician(O2+3)car...The continually-discovered large volumes of marine hydrocarbons indicate a huge exploration potential within the carbonate rocks of Ordovician in the Tarim Basin,northwestern China.The Middle-Upper Ordovician(O2+3)carbonate source rocks are at a highly mature stage.These rocks presently contain a low amount of total organic carbon(TOC_(pd)≤0.5%)(TOC_(pd) means the present-day TOC).A mass balance approach is used to identify the source rocks that have expelled hydrocarbons.The characteristics and origin of hydrocarbon expulsion from low-TOC_(pd) source rocks are studied,which are significant for oil exploration in the basin.The results showed that a low-TOC_(pd) O2+3 source rock having expelled hydrocarbons was type I and had a very narrow oil window.With a high rock maturity and a high original TOC(TOCo)value exceeding 1%,nearly 80%of the generated hydrocarbons were expelled.The content of gammacerane and C28 steranes in the oil and source rock extracts were relatively lean,with a V-shaped distribution of regular steranes,suggesting a possible genetic relation between the low-TOC_(pd) source rocks and the marine oil in the Tabei area.Hydrogenrich planktonic algae or acritarchs were the main hydrocarbon parent materials,distributed in the subsiding platform-slope facies.Organic matter was preserved under reducing conditions,and source rocks were formed with a favorable kerogen type and a moderate hydrocarbon generation potential.This study illustrates the hydrocarbon expulsion of low TOC_(pd) source rocks in northern Tarim Basin,which is greatly significant for analyzing the genesis of marine crude oil in Tarim Basin,and evaluating the distribution of marine source rocks.This research method is theoretically significant for oil and gas exploration in the same type of highlymature carbonate paleobasins.展开更多
Legend says that Genghis Khan's dying wish was to exterminate the Tangut Empire in China's northwest. Today, the lost empire presents historians a unique challenge in trying to reconstruct its history, languag...Legend says that Genghis Khan's dying wish was to exterminate the Tangut Empire in China's northwest. Today, the lost empire presents historians a unique challenge in trying to reconstruct its history, language, and the mystery of its total annihilation展开更多
基金supported by the National Natural Science Foundation of China(No.90814002)the Natural Science Foundation of Shandong Province(No.Y2005E02)
文摘The great Tancheng earthquake of M81/2 occurred in 1668 was the largest seismic event ever recorded in history in eastern China. This study determines the fault geometry of this earthquake by inverting seismological data of present-day moderate-small earthquakes in the focal area. We relocated those earthquakes with the double-difference method and found focal mechanism solutions using gird test method. The inversion results are as follows: the strike is 21.6°, the dip angle is 89.5°, the slip angle is 170°, the fault length is about 160 km, the lower-boundary depth is about 32 km and the buried depth of upper boundary is about 4 km. This shows that the seismic fault is a NNE-trending upright right-lateral strike-slip fault and has cut through the crust. Moreover, the surface seismic fault, intensity distribution of the earthquake, earthquake-depth distribution and seismic-wave velocity profile in the focal area all verified our study result.
基金financial supports are from the National Natural Science Foundation of China (41702130 and 41971335)China Postdoctoral Science Foundation (2017T100419 and 2019M660269)Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)。
文摘The Yanchang Formation Chang 7 oil-bearing layer of the Ordos Basin is important in China for producing shale oil.The present-day in situ stress state is of practical implications for the exploration and development of shale oil;however,few studies are focused on stress distributions within the Chang 7 reservoir.In this study,the present-day in situ stress distribution within the Chang 7 reservoir was predicted using the combined spring model based on well logs and measured stress data.The results indicate that stress magnitudes increase with burial depth within the Chang 7 reservoir.Overall,the horizontal maximum principal stress(SHmax),horizontal minimum principal stress(Shmin) and vertical stress(Sv) follow the relationship of Sv≥SHmax>Shmin,indicating a dominant normal faulting stress regime within the Chang 7 reservoir of Ordos Basin.Laterally,high stress values are mainly distributed in the northwestern parts of the studied region,while low stress values are found in the southeastern parts.Factors influencing stress distributions are also analyzed.Stress magnitudes within the Chang 7 reservoir show a positive linear relationship with burial depth.A larger value of Young's modulus results in higher stress magnitudes,and the differential horizontal stress becomes higher when the rock Young's modulus grows larger.
基金supported by the China Postdoctoral Science Foundation (grant No. 2017M611108)the National Science and Technology Major Project of China (grant No. 2016ZX05006006-001)the National Basic Research Program of China (grant Nos. 2011CB2011-02 and 2014CB239100)
文摘Previous studies have postulated the contribution of present-day low-total organic carbon (TOC) marine carbonate source rocks to oil accumulations in the Tabei Uplift, Tarim Basin, China. However, not all present-day low-TOC carbonates have generated and expelled hydrocarbons; therefore, to distinguish the source rocks that have already expelled sufficient hydrocarbons from those not expelled hydrocarbons, is crucial in source rock evaluation and resource assessment in the Tabei Uplift. Mass balance can be used to identify modern low-TOC carbonates resulting from hydrocarbon expulsion. However, the process is quite complicated, requiring many parameters and coefficients and thus also a massive data source. In this paper, we provide a quick and cost effective method for identifying carbonate source rock with present-day low TOC, using widely available Rock-Eval data. First, we identify present-day low-TOC carbonate source rocks in typical wells according to the mass balance approach. Second, we build an optimal model to evaluate source rocks from the analysis of the rocks' characteristics and their influencing factors, reported as positive or negative values of a dimensionless index of Rock-Eval data (IR). Positive IR corresponds to those samples which have expelled hydrocarbons. The optimal model optimizes complicated calculations and simulation processes; thus it could be widely applicable and competitive in the evaluation of present-day low TOC carbonates. By applying the model to the Rock-Eval dataset of the Tabei Uplift, we identify present-day iow-TOC carbonate source rocks and primarily evaluate the contribution equivalent of 11.87×10^9 t oil.
基金supported by the Chinese National Natural Science Foundation(40872129,40902095,40572125)special funds provided for the earthquake community science by Ministry of Science and Technology(20080811)
文摘This study attempts to acquire information on tectonic activity in western China from land surface temperature (LST) field data. On the basis of the established relationship between heat and strain, we analyzed the LSTdistribution in western China using the satellite data product MODIS/Terra. Our results show that: 1. There are departures from annual changes of LSTin some areas, and that these changes are associated with the activity of some active tectonic zones. 2. When annual-change background values caused by climate factors are removed, the long-period component (LSTLow) of temperature residual (AT) of the LSTis able to serve as an indicator for tectonic activity. We have found that a major earthquake can produce different effects on the/ST fields of surrounding areas. These effects are characterized by both rises and drops in temperature. For example, there was a noteworthy temperature decline associated with the Sumatran M9 earthquake of 2004 in the Bayan Har-Songpan block of central Tibetan Plateau. 3. On the other hand, the LST field of a single area may respond differently to major shocks occurring in different areas in the regions surrounding China. For instance, the Kun- lun M 8.1 event made the LSTon the Longmen Mountains fault zone increase, whereas the Zaisan Lake M 7.9 quake of 2003, and the Sumatran M 9 event of 2004, caused decreases in the same area's LST. 4. The variations of land surface temperature (LST) over time are different in different tectonic areas. These phenomena may provide clues for the study of tectonic deformation processes. On the basis of these phenomena, we use a combi- nation of temperature data obtained at varied depths, regional seismicity and strain results obtained with GPS measurements, to test the information related to tectonic activity derived from variations of the LST field, and discuss its implications to the creation of models of regional tectonic deformation.
文摘Knowledge of the present-day in-situ stress distribution is greatly import-ant for better understanding of conventional and unconventional hydro-carbon reservoirs in many aspects,e.g,reservoir management,wellbore stability asssment,etc.In tectonically stable regions,the present-day in-situ stress field in terms of stress distribution is 1argely controlled by lithological changes,which can be predicted through|a numerical simulation method incorporating specific mechanical properties of the subsurface reservoir.In this study,a workflow was presented to predict the present-day in-situ stress field based on the finite element method(FEM).Sequentially,it consists of:i)building a three-dimensional(3D)geometric framework,i)creating a 3D petrophysical parameter field,11)integrating the geometric framework with petrophysical parameters,iv)setting up a 3D heterogeneous geomechanical model,and finally,v)calculating the present-day in-situ stress distribution and calibrating the prediction with measured stress data,e.g.,results from the extended leak-off tests(XLOTs).The approach was sucessfully applied to the Block W in Ordos Basin of central China.The results indicated that the workflow and models presented in this study could be used as an effective tool to provide insights into stress perturbations in subsurface reservoirs and geological references for subsequent analysis.
文摘The study evaluates the factors confronting the present-day construction practices in South-East Nigeria. Being a survey research, questionnaires containing information relating to factors/challenges affecting construction practices were randomly administered to selected construction practitioners in South-Eastern States of Nigeria. Accordingly, a total of 240 questionnaires were administered to the selected respondents while 160 copies were completed, returned and found useful. Thus, giving a response rate of 66.67%. Data collected were analysed and presented using percentages, mean scores, principal and factor analysis, z-test and tables. The study found that the core factors that constrain present-day construction in the study area are issues related to inadequate/dearth of technical and managerial expertise, corruption and poor project planning and control;which significantly affect operational effectiveness of the construction industry in the study area. Therefore, the study concluded by recommending that thorough capacity building through training or retraining programme which should centre on areas of the issues identified should be religiously pursued in the study area.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 49825104) National Key Basic Research Program (Grant No. 19980407), National Climbing Project and National Major Scientific Infrastructure Program, and National S
文摘Velocity field of China continent constrained by Global Positioning System (GPS) reveals both continuous and block-like styles of deformation. Continuous deformation commonly characterizes actively deforming mountain ranges such as the Tianshan Mountain, Qilian Mountain, and Tibet. The block-like movement often represents deformation in the tectonically stable regions such as Ordos, South China and Tarim blocks. GPS measurements indicate 5.1±2.5 mm/a left-lateral strike-slip rate along the Altun fault. Eastward convergence along the Longmenshan fault is less than 6.7±3.0 mm/a. South China moves 11-14 mm/a eastward compared with the stable Eurasia. These low slip rates do not imply rapid eastward extrusion of China continent predicted by the model of 'continental extrusion'. It appears that 'crustal thickening' model more properly describes both continuous and block-like styles of deformation in China continent.
基金supported by the National Basic Research Program of China (No. 2005CB422105)the National NaturalScience Foundation of China (No. 40772089)
文摘The Puguang (普光) gas field is the largest gas field found in marine carbonate in China. The Puguang gas field experienced complicated evolution history from paleo-oil pool to gas pool. The purpose of this article is to reveal the evolution history of Puguang gas field through systematic study on the relationship between paleo-oil-water contact (POWC) and present-day gas-water contact (PGWC). POWC was recognized by observing the change of relative content of residual solid bitumen in the cores, and PGWC was observed using log and drilling stem test data. Two types of relationship between POWC and PGWC were observed in the Puguang gas field: POWC is above PGWC, and POWC is below PGWC. The former is normal as oil cracking may cause gas-water contact to move downward. The latter can be interpreted by lateral gas re-migration and re-accumulation caused by changes in structural configuration. The relationship between POWC and PGWC suggests that during oil charge, the southwestern and northwestern parts of the Puguang gas field were structurally lower than the northeastern and southeastern parts. Thrusting from Xuefengshan (雪峰山) since Yanshanian movement and from Dabashan (大巴山) since Himalayan movement resulted in the relative uplift of the southwestern and northwestern parts of the Puguang structure, which significantly changed the structural configuration. Based on the paleo-structure discussed in this article, the most probable migration directions of paleo-oil were from the northwest to the southeast and from the southwest to the northeast. Consequently, the evolution history of the Puguang gas field can be divided into three stages, namely,oil charging (200-170 Ma), cracking oil to gas (155-120 Ma), and gas pool adjustment (12-0 Ma).
基金financially supported by the Science Foundation of China University of Petroleum,Beijing(Grant No.2462020BJRC005)the Joint Funds of National Natural Science Foundation of China(Grant No.U19B6003-02)。
文摘Hydrocarbon expulsion occurs only when pore fluid pressure due to hydrocarbon generation in source rock exceeds the force against migration in the adjacent carrier beds.Taking the Middle-Upper Ordovician carbonate source rock of Tarim Basin in China as an example,this paper proposes a method that identifies effective carbonate source rock based on the principles of mass balance.Data from the Well YW2 indicate that the Middle Ordovician Yijianfang Formation contains effective carbonate source rocks with low present-day TOC.Geological and geochemical analysis suggests that the hydrocarbons in the carbonate interval are likely self-generated and retained.Regular steranes from GC-MS analysis of oil extracts in this interval display similar features to those of the crude oil samples in Tabei area,indicating that the crude oil probably was migrated from the effective source rocks.By applying to other wells in the basin,the identified effective carbonate source rocks and non-source rock carbonates can be effectively identified and consistent with the actual exploration results,validating the method.Considering the contribution from the identified effective source rocks with low present-day TOC(TOC_(pd))is considered,the long-standing puzzle between the proved 3 P oil reserves and estimated resources in the basin can be reasonably explained.
文摘Based on the geodetic data taken from the National GPS Network established by China Climbing Program 'Investigation of Crust Motion and Geodynamics in Modern Time', we derived the movement velocities of the GPS sites.In terms of the power series expansion of a rotation function for horizontal velocities on a spherical surface proposed by Hames and Holt (1993), we computed the horizontal velocity and strain-rate field.We preliminarilystudied the appearances and characteristics of the present-day crustal movement and deformation in the Chinesemainland with the computed results. The researches demonstrated (1)The present-day crustal movement anddeformation in the Chinese mainland are being jointly controlled by indian, Pacific and Philippines Ocean Platesand Siberia-Mongolia block, and these three large plates and block form a situation of triparite confrontation, butIndian Plate seems to play a leading role;(2) The North-South Earthquake Zone plays an important adjustment rolein the present-day crustal movement and deformation process. displaying clear characteristics of demarcation lineof tectonics in large areas, (3)There seems to be another adjustment zone along the latitude line approximate N35,but its characteristics are less obvious than that of the former; (4) Dynamic actions of these three large plates andblock on the Chinese mainland are dynamic stable; appearing in stable push-press velocities. These results aregenerally accorded with the results determined from geology, geophysics, and seismology. By the contrast withseismicities. if appears preliminarily that there is some corresponding relation between intense shear st fain zoneand future strong seismicity area. but this problem needs further examination of earthquake examples.
基金funded by the Ministère des Forêts,de la Faune et des Parcs du Québec(MFFP).The funds were used mainly for the salary of the authors working for the MFFP
文摘Background: In the contxt of ecosystem management, the present study aims to compare the natural and the present-day forested landscapes of a large territory in Quebec(Canada). Using contemporary and long-term fire cycles, each natural forst landscape is defined according to the variability of its structure and composition, and compared to the present-day landscape. This analysis was conducted to address the question of whether human activities have moved these ecosystems outside the range of natural landscape variability.Methods: The study encompassed a forested area of 175 000 km2 divided into 14 landscapes. Using a framework that integrates fire cycles, age structure and forest dynamics, we characterized the forest composition and age structures that resulted from three historical fire cycles(110,140, and 180 years) representative of the boreal forest of eastern Canada. The modeled natural landscapes were compared with present-day landscapes in regard to the proportion of old-growth forests(landscape level) and the proportion of late-successional forest stands(landscape level and potential vegetation type).Results: Four landscapes(39%) remain within their natural range of variability. In contrast, nine landscapes(54%)show a large gap between natural and present-day landscapes. These nine are located in the southern portion of the study area, and are mainly associated with Abies-Betula vegetation where human activities have contributed to a strong increase in the proportion of Populus tremuloides stands(early-successional stages) and a decrease of oldgrowth forest stands(more than 100 years old). A single landscape(7%), substantially changed from its potential natural state, is a candidate for adaptive-based management.Conclusion: Comparison of corresponding natural(reference conditions) and present-day landscapes showed that ten landscapes reflecting an important shift in forest composition and age structure could be considered beyond the range of their natural variability. The description of a landscape's natural variability at the scale of several millennia can be considered a moving benchmark that can be re-evaluated in the context of climate change.Focusing on regional landscape characteristics and long-term natural variability of vegetation and forest age structure represents a step forward in methodology for defining reference conditions and following shifts in landscape over time.
基金funded by the Science and Technology Support Program(2012BAK19B01)Natural Science Foundation of China(41104057,41104058)the special project of basic scientific research of Institute of Earthquake Science,China Earthquake Administration(2012IES0405,2012IES0406)
文摘Based on GPS data from 1991- 2004 and the least-squares collocation method,we analyze the crustal deformation in the Chinese mainland. The results show that the first-order crustal deformation is unchanged in different periods in the Chinese mainland,which reflects the background of regional tectonic activity. The strain rate is much higher in Western China,especially in the Qinghai-Tibetan Plateau and Sichuan-Yunnan area. The variations in different periods are related with seismicity of strong earthquakes during the same time. The GPS data after 2004 shows the post-seismic deformation of the 2001 Kunlun Mountains M S8. 1 earthquake.
基金supported by the Joint Funds of National Natural Science Foundation of China(Grant number U19B6003-02-04)the CNPC Science and Technology Major Project of the Fourteenth Five-Year Plan(Grant number 2021DJ0101)the Science Foundation of China University of Petroleum(Beijing)(Grant number 2462022YXZZ007).
文摘The continually-discovered large volumes of marine hydrocarbons indicate a huge exploration potential within the carbonate rocks of Ordovician in the Tarim Basin,northwestern China.The Middle-Upper Ordovician(O2+3)carbonate source rocks are at a highly mature stage.These rocks presently contain a low amount of total organic carbon(TOC_(pd)≤0.5%)(TOC_(pd) means the present-day TOC).A mass balance approach is used to identify the source rocks that have expelled hydrocarbons.The characteristics and origin of hydrocarbon expulsion from low-TOC_(pd) source rocks are studied,which are significant for oil exploration in the basin.The results showed that a low-TOC_(pd) O2+3 source rock having expelled hydrocarbons was type I and had a very narrow oil window.With a high rock maturity and a high original TOC(TOCo)value exceeding 1%,nearly 80%of the generated hydrocarbons were expelled.The content of gammacerane and C28 steranes in the oil and source rock extracts were relatively lean,with a V-shaped distribution of regular steranes,suggesting a possible genetic relation between the low-TOC_(pd) source rocks and the marine oil in the Tabei area.Hydrogenrich planktonic algae or acritarchs were the main hydrocarbon parent materials,distributed in the subsiding platform-slope facies.Organic matter was preserved under reducing conditions,and source rocks were formed with a favorable kerogen type and a moderate hydrocarbon generation potential.This study illustrates the hydrocarbon expulsion of low TOC_(pd) source rocks in northern Tarim Basin,which is greatly significant for analyzing the genesis of marine crude oil in Tarim Basin,and evaluating the distribution of marine source rocks.This research method is theoretically significant for oil and gas exploration in the same type of highlymature carbonate paleobasins.
文摘Legend says that Genghis Khan's dying wish was to exterminate the Tangut Empire in China's northwest. Today, the lost empire presents historians a unique challenge in trying to reconstruct its history, language, and the mystery of its total annihilation