Three-dimensional structural models,evolution and petroleum geological significances of transtensional faults in the Ziyang area,central Sichuan Basin,SW China

With drilling and seismic data of Transtensional(strike-slip)Fault System in the Ziyang area of the central Sichuan Basin,SW China plane-section integrated structural interpretation,3-D fault framework model building,fault throw analyzing,and balanced profile restoration,it is pointed out that the transtensional fault system in the Ziyang 3-D seismic survey consists of the northeast-trending F_(I)19 and F_(I)20 fault zones dominated by extensional deformation,as well as 3 sets of northwest-trending en echelon normal faults experienced dextral shear deformation.Among them,the F_(I)19 and F_(I)20 fault zones cut through the Neoproterozoic to Lower Triassic Jialingjiang Formation,presenting a 3-D structure of an“S”-shaped ribbon.And before Permian and during the Early Triassic,the F_(I)19 and F_(I)20 fault zones underwent at least two periods of structural superimposition.Besides,the 3 sets of northwest-trending en echelon normal faults are composed of small normal faults arranged in pairs,with opposite dip directions and partially left-stepped arrangement.And before Permian,they had formed almost,restricting the eastward growth and propagation of the F_(I)19 fault zone.The F_(I)19 and F_(I)20 fault zones communicate multiple sets of source rocks and reservoirs from deep to shallow,and the timing of fault activity matches well with oil and gas generation peaks.If there were favorable Cambrian-Triassic sedimentary facies and reservoirs developing on the local anticlinal belts of both sides of the F_(I)19 and F_(I)20 fault zones,the major reservoirs in this area are expected to achieve breakthroughs in oil and gas exploration.

Characteristics and main controlling factors of intra-platform shoal thin-layer dolomite reservoirs:A case study of Middle Permian Qixia Formation in Gaoshiti-Moxi area of Sichuan Basin,SW China

Based on the study of the distribution of intra-platform shoals and the characteristics of dolomite reservoirs in the Middle Permian Qixia Formation in the Gaoshiti–Moxi area of the Sichuan Basin,SW China,the controlling factors of reservoir development were analyzed,and the formation model of“intra-platform shoal thin-layer dolomite reservoir”was established.The Qixia Formation is a regressive cycle from bottom to top,in which the first member(Qi1 Member)develops low-energy open sea microfacies,and the second member(Qi2 Member)evolves into intra-platform shoal and inter-shoal sea with decreases in sea level.The intra-platform shoal is mainly distributed near the top of two secondary shallowing cycles of the Qi2 Member.The most important reservoir rock of the Qixia Formation is thin-layer fractured-vuggy dolomite,followed by vuggy dolomite.The semi-filled saddle dolomite is common in fracture-vug,and intercrystalline pores and residual dissolution pores combined with fractures to form the effective pore-fracture network.Based on the coupling analysis of sedimentary and diagenesis characteristics,the reservoir formation model of“pre-depositional micro-paleogeomorphology controlling shoal,sedimentary shoal controlling dolomite,penecontemporaneous dolomite benefiting preservation of pores,and late hydrothermal action effectively improving reservoir quality”was systematically established.The“first-order high zone”micro-paleogeomorphology before the deposition of the Qixia Formation controlled the development of large area of intra-platform shoals in Gaoshiti area during the deposition of the Qi2 Member.Shoal facies is the basic condition of early dolomitization,and the distribution range of intra-platform shoal and dolomite reservoir is highly consistent.The grain limestone of shoal facies is transformed by two stages of dolomitization.The penecontemporaneous dolomitization is conducive to the preservation of primary pores and secondary dissolved pores.The burial hydrothermal fluid enters the early dolomite body along the fractures associated with the Emeishan basalt event,makes it recrystallized into medium–coarse crystal dolomite.With the intercrystalline pores and the residual vugs after the hydrothermal dissolution along the fractures,the high-quality intra-platform shoal-type thin-layer dolomite reservoirs are formed.The establishment of this reservoir formation model can provide important theoretical support for the sustainable development of Permian gas reservoirs in the Sichuan Basin.

Tectonic Evolution of the Middle Frontal Area of the Longmen Mountain Thrust Belt,Western Sichuan Basin,China

By analyzing the balanced cross sections and subsidence history of the Longmen Mountain thrust belt, China, we concluded that it had experienced five tectonic stages： （1） the formation stage （T3x） of the miniature of Longmen Mountain, early Indosinian movement, and Anxian tectonic movement created the Longmen Mountain; （2） the stable tectonic stage （J1） where weaker tectonic movement resulted in the Longmen Mountain thrust belt being slightly uplifted and slightly subsiding the foreland basin; （3） the intense tectonic stage （J2-3）, namely the early Yanshan movement; （4） continuous tectonic movement （K-E）, namely the late Yanshan movement and early Himalayan movement; and （5） the formation of Longmen Mountain （N-Q）, namely the late Himalayan movement. During those tectonic deformation stages, the Anxian movement and Himalayan movement played important roles in the Longmen Mountain＇s formation. The Himalayan movement affected Longmen Mountain the most; the strata thrust intensively and were eroded severely. There are some klippes in the middle part of the Longmen Mountain thrust belt because a few nappes were pushed southeastward in later tectonic deformation.

Study on rain-runoff process in the peripheral mountainous area of the Sichuan Basin

Studies on rain-runoff process in the peripheral mountainous area of the Sichuan Basin, which is regarded as a key ecological shelter, will contribute to flood control and environmental protection for the Upper Yang-tze River Basin. In two typical catchments-the Fujiang River Catchment and the Wujiang River Catchment, rainfall simulations have been conducted to study the rain-runoff processes of yellow soil and limestone soil in three types of land use-forestland, farmland and grassland. Results showed that (1) within the same rainfall process, overland flow occurs first on farmland, then on grassland, and finally on forestland; (2) soil surface coverage has a great impact on the occurrence and amount of overland flow. The runoff amount can increase 2-4 times after the coverage is removed;(3) the infiltration before the occurrence of overland flow will decrease because of higher gravel contents of soil, but it takes no effect on infiltration once overland flow becomes stable; (4) the runoff coefficient of the limestone soil forestland is greater than that of the yellow soil forest land, but less than that of the farmland; (5) three empirical infiltration models, including Horton' model, Kostiakov' model, and modified Kostiakov' model, were compared by using the observed results under rainfall simulation. The results showed that the Kostiakov' model performed better than both the Horton' model and modified Kostiakov model. According to the results of this research, the Kostiakov's model can be used to simulate rainfall infiltration when water erosion is modeled in the peripheral mountainous area of the Sichuan Basin.

Structural attributes,evolution and petroleum geological significances of the Tongnan negative structure in the central Sichuan Basin,SW China

The Tongnan secondary negative structure in central Sichuan Basin has controls and influences on the structural framework and petroleum geological conditions in the Gaoshiti-Moxi area.To clarify the controls and influences,the deformation characteristics,structural attributes and evolution process of the Tongnan negative structure were investigated through a series of qualitative and quantitative methods such as balanced profile restoration,area-depth-strain(ADS)analysis,and structural geometric forward numerical simulation,after comprehensive structural interpretation of high-precision 3D seismic data.The results are obtained in three aspects.First,above and below the P/AnP(Permian/pre-Permian)unconformity,the Tongnan negative structure demonstrates vertical differential structural deformation.It experiences two stages of structural stacking and reworking:extensional depression(from the Sinian Dengying Formation to the Permian),and compressional syncline deformation(after the Jurassic).The multi-phase trishear deformation of the preexisting deep normal faults dominated the extensional depression.The primary depression episodes occurred in the periods from the end of Late Proterozoic to the deposition of the 1st–2nd members of the Dengying Formation,and from the deposition of Lower Cambrian Longwangmiao Formation–Middle–Upper Cambrian until the Ordovician.Second,the multi-stage evolution process of the Tongnan negative structure controlled the oil and gas migration and adjustment and present-day differential gas and water distribution between the Tongnan negative structure and the Gaoshiti and Moxi-Longnüsi structural highs.Third,the Ordovician,which is limitedly distributed in the Tongnan negative structure and is truncated by the P/AnP unconformity on the top,has basic geological conditions for the formation of weathering karst carbonate reservoirs.It is a new petroleum target deserving attention.

Development Phases and Mechanisms of Tectonic Fractures in the Longmaxi Formation Shale of the Dingshan Area in Southeast Sichuan Basin, China

Shale gas has currently attracted much attention during oil and gas exploration and development. Fractures in shale have an important influence on the enrichment and preservation of shale gas. This work studied the developmental period and formation mechanism of tectonic fractures in the Longmaxi Formation shale in the Dingshan area of southeastern Sichuan Basin based on extensive observations of outcrops and cores, rock acoustic emission(Kaiser) experiments, homogenization temperature of fracture fill inclusions, apatite fission track, thermal burial history. The research shows that the fracture types of the Longmaxi Formation include tectonic fractures, diagenetic fractures and horizontal slip fractures. The main types are tectonic high-angle shear and horizontal slip fractures, with small openings, large spacing, low densities, and high degrees of filling. Six dominant directions of the fractures after correction by plane included NWW, nearly SN, NNW, NEE, nearly EW and NW. The analysis of field fracture stage and fracture system of the borehole suggests that the fractures in the Longmaxi Formation could be paired with two sets of plane X-shaped conjugate shear fractures, i.e., profile X-shaped conjugate shear fractures and extension fractures. The combination of qualitative geological analysis and quantitative experimental testing techniques indicates that the tectonic fractures in the Longmaxi Formation have undergone three periods of tectonic movement, namely mid-late Yanshanian movement(82–71.1 Ma), late Yanshanian and middle Himalaya movements(71.1–22.3 Ma), and the late Himalayan movement(22.3–0 Ma). The middle-late period of the Yanshanian movement and end of the Yanshanian movement-middle period of the Himalayan movement were the main fractureforming periods. The fractures were mostly filled with minerals, such as calcite and siliceous. The homogenization temperature of fracture fill inclusions was high, and the paleo-stress value was large; the tectonic movement from the late to present period was mainly a slight transformation and superposition of existing fractures and tectonic systems. Based on the principle of tectonic analysis and theory of geomechanics, we clarified the mechanism of the fractures in the Longmaxi Formation, and established the genetic model of the Longmaxi Formation. The research on the qualitative and quantitative techniques of the fracture-phase study could be effectively used to analyze the causes of the marine shale gas fractures in the Sichuan Basin. The research findings and results provide important references and technical support for further exploration and development of marine shale gas in South China.

Source Rock and Cap Rock Controls on the Upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation Shale Gas Accumulation in the Sichuan Basin and its Peripheral Areas

Objective The Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation is one of the priority interval for shale gas exploration in the Sichuan Basin and its peripheral areas, and commercial shale gas has been discovered from this interval in Jiaoshiba, Changning and Weiyuan shale gas fields in Sichuan Province. However, there is no significant discovery in other parts of the basin due to the different quality of black shale and the differences of tectonic evolution. Based on the progress of shale gas geological theory and exploration discoveries, as well as the theory of ＂source rock and cap rock controls on hydrocarbon accumulation＂, of the Upper Ordovician the main controlling factors Wufeng Formation-Lower Silurian Longmaxi Formation shale gas enrichment in the Sichuan Basin and its peripheral areas were analyzed, and the source rock and cap rock controls on the shale gas were also discussed. The results can provide new insights for the next shale gas exploration in this area.

Study of temperature and precipitation change in upstream mountain area of the Hexi inland river basin since 1960s

All rivers in the Hexi inland region of Gansu Province, China, originate from the northern slope of the Qilian Mountains. They are located in the southern portion of the region and respectively belong to the three large river systems from east to west, the Shiyang, Heihe and Shule river basins. These rivers are supplied by precipitation, snowmelt and ice-melt runoff from the Qilian Mountain area. Therefore, changes of precipitation and temperature in the upstream watersheds of these rivers have an important effect on changes of mountainous runoff and reasonable utilization of water resources in this region. For this reason, the Qilian Mountain area, upstream watersheds and runoff forming areas of these rivers are chosen as the study area. The change characteristics and variation trend of temperature and precipitation in this area under the backdrop of global warming axe analyzed based on observa- tional data of relational weather and hydrologic stations in the area. Results show that temperatures in the upriver mountain areas of these three large river basins have been increasing, although the increasing degree is differentially affected by global warming. The rising extent of annual and seasonal temperatures in the upstream mountain area of the Shule river basin located in the west- em Qilian Mountains, were all largest over the past 50 years. Precipitation in the upstream mountain areas of Hexi region＇ three river basins located respectively in the western, middle and eastern Qilian Mountains have been presenting an increasing trend to varying degrees as a whole for more than 50 years. This means that climate in the upstream mountain areas of Hexi region＇ three river basins are becoming increasingly warmer and moister over the past 50 years, which will be very good for the ecological en- vironment and agricultural production in the region.

Biostratigraphy and reservoir characteristics of the Ordovician Wufeng Formation-Silurian Longmaxi Formation shale in the Sichuan Basin and its surrounding areas,China

Through graptolite identification in profiles,graptolite zone division,contour map compilation,and analysis of mineral composition,TOC content,lamina distribution features of shale samples,the biostratigraphic and reservoir characteristics of Ordovician Wufeng Formation-Silurian Longmaxi Formation in the Sichuan Basin and its peripheral are sorted out.There are 4 graptolite zones(WF1 to WF4)in Wufeng Formation and 9(LM1 to LM9)in Longmaxi Formation,and the different graptolite zones can be calibrated by lithology and electrical property.The shale layers of these graptolite zones have two depocenters in the southwest and northeast,and differ in mineral composition,TOC,and lamina types.Among them,the graptolite zones of lower WF2 and WF4 are organic matter-poor massive hybrid shale,the upper part of WF1-WF2 and WF3 have horizontal bedding hybrid shale with organic matter,the LM1-LM4 mainly consist of organic-rich siliceous shale with horizontal bedding,and the LM5-LM9 graptolite zones consist of organic-lean hybrid shale with horizontal bedding.The mineral composition,TOC and lamina types of shale depend on the paleo-climate,paleo-water oxidation-reduction conditions,and paleo-sedimentation rate during its deposition.Deposited in oxygen-rich warm water,the lower parts of WF1 and WF2 graptolite zones have massive bedding,low TOC and silicon content.Deposited in cooler and oxygen-rich water,the WF4 has massive bedding,high calcium content and low TOC.Deposited in anoxic water with low rate,the upper part of WF2,WF3,and LM1-LM4 are composed of organic rich siliceous shale with horizontal bedding and high proportion of silt laminae.Deposited in oxygen rich water at a high rate,the graptolite zones LM5-LM9 have low contents of organic matter and siliceous content and high proportions of silt lamina.

Sequence Stratigraphy and Sedimentary Facies of Feixianguan Formation in the Kaijiang-Liangping Area of Sichuan Basin, China

The Feixianguan formation in the Kaijiang-Liangping basin has been the focus of extensive research on multiple aspects. Based on field survey, core observation, laboratory analysis and seismic data interpretation, the sequence stratigraphy and sedimentary facies of the Kaijiang-Liangping area are studied. Four sequence boundaries and three maximum flooding surfaces of the Feixianguan formation are detected in this area. Three third-order sequences are identified as first sequence (SQ1), the second sequence (SQ2), and the third sequence (SQ3) in which SQ1 corresponds to the member 1 of the Feixianguan formation, SQ2 corresponds to the member 2, and SQ3 corresponds to the member 3 and member 4. Member 1, 2, 3 and 4 are lithologic sections divided by predecessors. On the basis of this sequence division and their sedimentary marks, the facies of the Feixianguan formation can be divided into open platform and evaporate platform categories. The open platform is composed of three subfacies identified as platform bank or basin marginal bank, interbank, and platform basin. Thus, a sedimentary evolution model is established. According to the sedimentary and seismic characteristics of the Kaijiang-Liangping area, we determine that two oolitic bank models, the aggradation model and the progradation model, are developed in this area. The aggradation model is developed in the Longgang region, which includes the basin marginal bank as a favorable exploring zone. The progradation model is developed in the Jiulongshan and Longhui areas, besides the basin marginal bank, the favorable exploration zones also include the oolitic bank developing areas of the inner basin.

Reservoir characteristics and genetic differences between the second and fourth members of Sinian Dengying Formation in northern Sichuan Basin and its surrounding areas

This study investigated the characteristics and genesis of reservoirs in the 2^(nd) and 4^(th) members of Sinian Dengying Formation in northern Sichuan and its surrounding areas, on the basis of outcrop, drilling cores and thin section observation and geochemical analysis. The reservoirs of 2^(nd) member are distributed in the middle part of the stratum. The reservoir quality is controlled by supergene karst and the distribution of mound-shoal complex. The bedded elongated isolated algal framework solution-cave and the residual "grape-lace" cave, which are partially filled with multi-stage dolosparite, constituted the main reservoir space of the 2^(nd) member. There is no asphalt distribution in the pores. The pore connectivity is poor, and the porosity and permeability of the reservoir is relatively low. The reservoirs of 4^(th) member were distributed in the upper and top part of the stratum. The reservoir quality is controlled by burial dissolution and the distribution of mound-shoal complex. The bedded algal framework solution-pores or caves, intercrystalline pores and intercrystalline dissolved pores constituted the main reservoir space of the 4^(th) member. It's partially filled with asphalt and quartz, without any dolosparite fillings in the pores and caves. The pore connectivity is good. Most of the 4^(th) member reservoirs had medium-low porosity and low permeability, and, locally, medium-high porosity and medium permeability. Affected by the development of mound-shoal complex and heterogeneous dissolution, the platform margin along Ningqiang, Guangyuan, Jiange and Langzhong is the most favorable region for reservoir development. Deep buried Dengying Formation in the guangyuan and langzhong areas should be the most important hydrocarbon target for the future exploration.

Response of glacier area variation to climate change in the Kaidu-Kongque river basin,Southern Tianshan Mountains during the last 20 years

Glaciers are crucial water resources for arid inland rivers in Northwest China.In recent decades,glaciers are largely experiencing shrinkage under the climate-warming scenario,thereby exerting tremendous influences on regional water resources.The primary role of understudying watershed scale glacier changes under changing climatic conditions is to ensure sustainable utilization of regional water resources,to prevent and mitigate glacier-related disasters.This study maps the current(2020)distribution of glacier boundaries across the Kaidu-Kongque river basin,south slope of Tianshan Mountains,and monitors the spatial evolution of glaciers over five time periods from 2000-2020 through thresholded band ratios approach,using 25 Landsat images at 30 m resolution.In addition,this study attempts to understand the role of climate characteristics for variable response of glacier area.The results show that the total area of glaciers was 398.21 km^(2)in 2020.The glaciers retreated by about 1.17 km^(2)/a(0.26%/a)from 2000 to 2020.The glaciers were reducing at a significantly rapid rate between 2000 and 2005,a slow rate from 2005 to 2015,and an accelerated rate during 2015-2020.The meteorological data shows slight increasing trends of mean annual temperature(0.02℃/a)and annual precipitation(2.07 mm/a).The correlation analysis demonstrates that the role of temperature presents more significant correlation with glacier recession than precipitation.There is a temporal hysteresis in the response of glacier change to climate change.Increasing trend of temperature in summer proves to be the driving force behind the Kaidu-Kongque basin glacier recession during the recent 20 years.

Sequence sedimentary evolution and reservoir distribution in the third and fourth members of Sinian Dengying Formation,Gaomo area,Sichuan Basin,SW China

Based on comprehensive analysis of cores,thin sections,logging and seismic data,the sequence stratigraphy and sedimentary evolution of the third and fourth members of Sinian Dengying Formation(Deng 3 and Deng 4 members for short)in the Gaomo area of Sichuan Basin were investigated,and the favorable zones for reservoir development in the Deng 3 Member and Deng 4 Member were predicted.(1)Two Type I and one Type II sequence boundaries are identified in the Deng 3 and Deng 4 members.Based on the identified sequence boundaries,the Deng 3 and Deng 4 members can be divided into two third order sequences SQ3 and SQ4,which are well-developed,isochronal and traceable in this area;the SQ3 thins from west to the east,and the SQ4 thins from northwest to southeast.(2)The sedimentary environment from the depositional period of SQ3 to SQ4 has experienced the evolution from mixed platform to rimmed platform,and the platform rimmed system on the west side is characterized by the development of platform margin microbial mound and grain shoal assemblages.The intraplatform area is a restricted platform facies composed of a variety of dolomites,and there are local micro-geomorphic highlands of different scales and scattered intraplatform mounds and shoals.(3)The Deng 4 Member reservoirs,with obvious facies-controlled characteristic,are mainly distributed in the upper part of high-frequency upward shallow cycle and the high-stand systems tract of the third-order sequence vertically,and are more developed in the platform margin belt than in the intraplatform belt,and more developed in the Gaoshiti platform margin belt than in the west Suining platform margin belt on the plane.(4)Three types of favorable reservoir zones of Deng 4 Member have been finely delineated with 3D seismic data;among them,the mound and shoal facies zones developed in the ancient highlands of the intraplatform are the first choice for the next exploration and development of the Deng 4 Member.

The Quantitative Analysis of Land Use Structure Characteristics of County in Mountainous Areas in Sichuan Province of China——A Case Study of Rong County

Based on the data concerning detailed survey on land in the year 2009 and land change in the year 2010 in Rong County,a mountainous region of Sichuan Province,by using quantitative geographical model,we conduct quantitative analysis of the status quo of land use in Rong County in terms of land use diversification,land use centralization,land use combination type,land use geographic significance and comprehensive use degree of land use.The results show some characteristics as follows.Firstly,land use in study area displays prominent characteristic of diversification;there is a high degree of completeness land use type;there is a great similarity among towns.Secondly,there is limited combination number of land use type;mostly the combination number of the towns is 2-3;the holistic function of regional land is fragile;the proportion of farmland areas is big,reaching 40.09%;the land use type of 21 towns is farmland.Thirdly,the towns with prominent characteristic of diversification of land use in Rong County,have low degree of centralization of land use and relatively big combination number of land use type,and vice versa.Fourthly,the type and quantity of agricultural land resources with geographical significance are relatively complete with nothing missing;it abounds in untapped land,but the overall index values of land use are all smaller than 300,with low overall use degree of land.

Characteristics and main controlling factors of reservoirs in the fourth member of Sinian Dengying Formation in Yuanba and its peripheral area, northeastern Sichuan Basin, SW China

Based on the abundant outcrops and 3 D seismic data in Yuanba and its surrounding areas in northeastern Sichuan Basin,the characteristics,main controlling factors and development regularities of reservoirs in the fourth member of Sinian Dengying Formation(shortened as Deng 4 Member)were analyzed comprehensively.The results show that the reservoirs were mainly developed in microbial dolomite associated with the microbial mound and dolarenite associated with grain beach,and had intergranular dissolution pores,inter-frame dissolution pores and karst caves as main storage space.The reservoirs were large in scale and strong in heterogeneity.The analysis of the reservoir genetic mechanisms shows that the reservoirs in the fourth member of Dengying Formation were the products of karstification on mound-beach facies deposited in the second episode of Tongwan movement.The karstification had the marks of eogenetic karstification such as granophyric karst system and half-dissociation zone.The reservoirs were controlled by the sedimentary facies belt,the mound beach facies was the decisive factor in reservoir development.Further analysis indicates that the Yuanba area had a geological background of well-developed platform margin mound beach facies,so mound beach bodies can be taken as a favorable exploration target.

Characterization of favorable lithofacies in tight sandstone reservoirs and its significance for gas exploration and exploitation: A case study of the 2nd Member of Triassic Xujiahe Formation in the Xinchang area, Sichuan Basin

By using core,logging curves,and experiment data,favorable lithofacies types in the 2 nd Member of Triassic Xujiahe Formation in the Xinchang area,Sichuan Basin were classified,standard of the favorable lithofacies was established,planar distribution regularities of the favorable lithofacies were identified,and forming mechanisms of the favorable lithofacies and their control effect on production were examined.(1)The 2 nd Member of Xujiahe Formation has twelve types of lithofacies,among which multiple layer medium-coarse grain sandstone lithofacies,parallel bedding medium-coarse grain sandstone lithofacies,massive bedding medium-coarse grain sandstone lithofacies,inclined bedding medium-coarse grain sandstone lithofacies,and charcoal-bearing medium-coarse grain sandstone lithofacies with better physical properties and higher gas content are favorable lithofacies;they feature low gamma,low neutron porosity,low resistivity,and high acoustic travel time on logging curves.(2)The sedimentary process controls spatial distribution of sand bodies which are the material basis of the favorable lithofacies;post diagenetic fluids would differentially reconstruct the favorable lithofacies;tectonic activities and abnormal formation pressure made strata slide along the weakness plane,giving rise to fractures in different types of rocks,which can enhance the reservoir permeability significantly.(3)The development degree of favorable lithofacies is a major factor affecting stable production of gas well.

Influence of the Kunlun Mountain M_S8.1 Earthquake on Horizontal Crustal Deformation in the Sichuan and Yunnan Area

In order to track the space-time variation of regional strain field holistically(in a large scale) and to describe the regional movement field more objectively,the paper uses a nonlinear continuous strain model focused on extracting medium-low frequency strain information on the basis of a region with no rotation.According to the repeated measurements(1999～2001～2004) from GPS monitoring stations in the Sichuan and Yunnan area obtained by the Project of "China Crust Movement Measuring Network",and with the movement of 1999～2001(stage deformation background) as the basic reference,we separated the main influencing factors of the Kunlun Mountain M-S8.1 earthquake in 2001 from the data of 2001 and 2004,and the results indicate:(1) the Kunlun Mountain M-S8.1 earthquake has a discriminating effect on the Sichuan and Yunnan area,moreover,the deformation mode and background had not only certain similitude but also some diversity;(2) The movement field before the earthquake was very ordinal,while after the earthquake,order and disorder existed simultaneously in the displacement field;The displacement quantities of GPS monitoring stations were generally several millimeters;(3) The principal strain field before earthquake was basically tensile in an approximate EW direction and compressive in the SN direction,and tension was predominant.After the earthquake,the principal strain field in the Sichuan area was compressive in the EW direction and tensile in the SN direction,and the compression was predominant.In the Yunnan area,it was tensional in the NE direction and compressive in the NW direction,and tension was predominant;(4) The surficial strain before the earthquake was dominated by superficial expansion,the contractive area being located basically in the east boundary of Sichuan and Yunnan block and its neighborhood.After the earthquake,the Sichuan area was surface contractive(the further north,the greater it was),and south of it was an area of superficial expansion.Generally speaking,the Kunlun Mountain M-S8.1 earthquake played an active role in the accumulation of energy in the Sichuan and Yunnan area.Special attention shall be focused on the segment of Xichang-Dongchuan and its neighborhood.

^(137)Cs and^(210)Pb_(ex) as Soil Erosion Tracers in the Hilly Sichuan Basin and the Three Gorges Area of China

Accelerated soil erosion and land degradation represent major environmental problems for agricultural lands.Reliable information on the rates of soil loss is urgently needed.The traditional techniques for documenting rates of soil loss may meet this need,but face many limitations.The fallout radionuclides,especially 137 Cs and 210 Pb ex,are increasingly used as effective tracers to quantify soil erosion rates,and they represent a valuable complement to the existing classical methods.This paper aims to introduce the basis for assessing soil erosion rates on cultivated and uncultivated slopes by using 137 Cs and 210 Pb ex measurements,to compare the 137 Cs and 210 Pb ex reference inventories,and to report several case studies undertaken in the hilly area of Sichuan Basin and the Three Gorges area of China.

Characteristic of Gravity and Magnetic Anomalies in the Daba Shan and the Sichuan basin, China: Implication for Architecture of the Daba Shan

The Dabashan nappe structural belt links the Hannan block to the west with the Huangling block to the east between Yangxian and Xiangfan. The Dabashan arc-shaped fold belt formed during late Jurassic and was superposed on earlier Triassic folds. To achieve an improved understanding of the deep tectonics of the Dabashan nappe structural belt, we processed and interpreted the gravity and magnetic data for this area using new deep reflection seismic and other geophysical data as constraints. The results show that the Sichuan basin and Daba Mountains lie between the Longmenshan and Wulingshan gravity gradient belts. The positive magnetic anomalies around Nanchong-Tongjiang-Wanyuan-Langao and around Shizhu result from the crystalline basement. Modeling of the gravity and magnetic anomalies in the Daba Mountains and the Sichuan basin shows that the crystalline basement around Nanchong-Tongjiang-Wanyuan-Langao extends to the northeast underneath the Wafangdian fault near Ziyang. The magnetic field boundary in the Zhenba-Wanyuan-Chengkou-Zhenping area is the major boundary of the Dabashan nappe thrusting above the Sichuan Basin. This boundary might be the demarcation between the south Dabashan and the north Dabashan structural elements. The low gravity anomaly between Tongjiang and Chengkou might be partly caused by thickened lower crust. The local low gravity anomaly to the south of Chengkou-Wanyuan might result from Mesozoic strata of low density in the Dabashan foreland depression area.

Evaluation Methods of Profitable Tight Oil Reservoir of Lacustrine Coquina: A Case Study of Da'anzhai Member of Jurassic in the Sichuan Basin

Based on core observation,cast and fluorescent thin sections,FESEM and ESEM,coquina in Da'anzhai Member of Jurassic in Sichuan Basin were examined systematically.Together with production data and logging evaluation,a method for lacustrine coquina evaluation based on geological theory was established up.In the article,two aspects of the study were elaborated,characteristics of favorable reservoirs,and a"five-step"evaluation method for favorable coquina reservoir.According to the correlation between porosity and production data,porosity is not effective in finding high quality coquina reservoir of this area.Whereas micro research of reservoir samples from a high productivity well revealed that sparry coquina is the best lithofacies,with the most developed micro storage space of various kinds.After the favorable reservoir was sorted out,a five-step method evaluating the coquina reservoir was worked out.Correlation ofGR value and rock types suggests that GR<30 API is an effective evaluation parameter in identifying profitable reservoir lithofacies.Meanwhile,the combination of profitable reservoir rock thickness and production data revealed that the reservoirs with the highest potentiality are those with thickness of 3-18 m.Fractures are more developed in faults,folds and structural noses in the study area.Organic acid is discharged massively before the peak of hydrocarbon generation,leading to the formation of dissolution pores in the reservoir.The evaluation of organic acid was made by using the source rock indexes.After evaluating the four factors,and compiling their distribution maps,the maps were overlapped to predict favorable reservoir zones,and 7 first class and 9 second class favorable zones of coquina were picked out.