Characteristics,classification and ordination of riparian plant communities in the Three-Gorges areas

Sixteen different vegetation types of grassland and shrubland were selected to study the component and diversity of plant species of riparian plant communities along main channel in the Three-Gorges areas. Species richness (s), Simpson index (D), and Shannon-Weiner index (H) were used to study the biodiversity and the hierarchical classification was carried out by the methods of TWINSPAN and DCA ordination. The results showed that the components of flora were complex and dominated by the temperate type in the riparian plant communities. Species diversity was not different between the communities, but Shannon-Weiner indexes of different layers in some grassland were significantly different. TWINSPAN and DCA indicated that riparian plant communities distributed along the gradient of moisture.

Three-Gorges Reservoir Area on the Yangtze River Faced with Risk of Induced Destructive Earthquakes

The Three-Gorge Water Conservancy Project on the Yangtze River started to impound water by locking gates on June 1, 2003. A swarm of more than 2000 small earthquakes suddenly occurred densely along the river section in Xinling Town north of Badong, Hubei Province, on June 7. This caused grave concern in the following years, but, with the completion of the second- and third-phase engineering construction, the water level in the reservoir will rise up to 156 m and 175 m respectively, no matter whether it can induce larger and stronger earthquakes. After an analysis of the distribution of active faults in the eastern part of the reservoir area, their intersections and capability to generate earthquakes from a seismo-tectonic viewpoint, we consider that after the reservoir impounding, two potential focal zones existing in Badong and Zigui counties may generate M 5.5 earthquake, the seismic intensity of which may reach Ⅷ. It will induce landslide bodies in the reservoir area to be reactivated and slide. The evidence is the large-scale landslide occurring on the Shazhenxi Creek river in Zigui County on June 12, 2003.

Application of fluid modulus inversion to complex lithology reservoirs in deep-water areas

It has been a challenge to distinguish between seismic anomalies caused by complex lithology and hydrocarbon reservoirs using conventional fluid identification techniques,leading to difficulties in accurately predicting hydrocarbon-bearing properties and determining oil-water contacts in reservoirs.In this study,we built a petrophysical model tailored to the deep-water area of the Baiyun Sag in the eastern South China Sea based on seismic data and explored the feasibility of the tri-parameter direct inversion method in the fluid identification of complex lithology reservoirs,offering a more precise alternative to conventional techniques.Our research found that the fluid modulus can successfully eliminate seismic amplitude anomalies caused by lithological variations.Furthermore,the seismic databased direct inversion for fluid modulus can remove the cumulative errors caused by indirect inversion and the influence of porosity.We discovered that traditional methods using seismic amplitude anomalies were ineffective in detecting fluids,determining gas-water contacts,or delineating high-quality reservoirs.However,the fluid factor Kf,derived from solid-liquid decoupling,proved to be sensitive to the identification of hydrocarbon-bearing properties,distinguishing between high-quality and poor-quality gas zones.Our findings confirm the value of the fluid modulus in fluid identification and demonstrate that the tri-parameter direct inversion method can significantly enhance hydrocarbon exploration in deep-water areas,reducing associated risks.

Electrical structure identification of deep shale gas reservoir in complex structural area using wide field electromagnetic method

To fully exploit the technical advantages of the large-depth and high-precision artificial source electromagnetic method in the complex structure area of southern Sichuan and compensate for the shortcomings of the conventional electromagnetic method in exploration depth,precision,and accuracy,the large-depth and high-precision wide field electromagnetic method is applied to the complex structure test area of the Luochang syncline and Yuhe nose anticline in the southern Sichuan.The advantages of the wide field electromagnetic method in detecting deep,low-resistivity thin layers are demonstrated.First,on the basis of the analysis of physical property data,a geological–geoelectric model is established in the test area,and the wide field electromagnetic method is numerically simulated to analyze and evaluate the response characteristics of deep thin shale gas layers on wide field electromagnetic curves.Second,a wide field electromagnetic test is conducted in the complex structure area of southern Sichuan.After data processing and inversion imaging,apparent resistivity logging data are used for calibration to develop an apparent resistivity interpretation model suitable for the test area.On the basis of the results,the characteristics of the electrical structure change in the shallow longitudinal formation of 6 km are implemented,and the transverse electrical distribution characteristics of the deep shale gas layer are delineated.In the prediction area near the well,the subsequent data verification shows that the apparent resistivity obtained using the inversion of the wide field electromagnetic method is consistent with the trend of apparent resistivity revealed by logging,which proves that this method can effectively identify the weak response characteristics of deep shale gas formations in complex structural areas.This experiment,it is shown shows that the wide field electromagnetic method with a large depth and high precision can effectively characterize the electrical characteristics of deep,low-resistivity thin layers in complex structural areas,and a new set of low-cost evaluation technologies for shale gas target layers based on the wide field electromagnetic method is explored.

Benefit evaluation of the Three-Gorges Reservoir migration by an assessment index model based on analytic hierarchy process

An assessment index model was established to evaulate the benefit of the Three-Gorges Reservoir migration through the analytical hierarchy process. Totally 43 indicators were selected to assess the impact of migration on the economic, social and ecological environmental aspects of the migration communities, with the data of the indicators of the years 1992, 1998, 2002 which represented the period of premigration, the end of the first phase migration and the end of the second phase migration, respectively. The evaluation matrix is sufficiently consistent, with a consistency ratio CR equal to 0.086 3. The assessment turned out a benefit value for the economic subsystem in the year 2004 larger than triple the value in the year 1992, indicating a remarkable economic growth in the Reservoir area. The constantly increasing value for the social subsystem reflects the stable social situations. There is a slight decline in the assessment outcome of the ecological subsystem for the year 1998, which implies enviromental conservation was given insufficient importance during that period. On the whole, the implementation of the migration project is favorable to the Reservoir region, as confirmed by the stably increasing overall evaluation value from 42.22% in 1992 to 68.81% in 2002. However, there is still much room to improve from the status quo to the target criteria.

Characteristics and influencing mechanisms of production-living-ecological space dynamics in the Three Gorges Reservoir Area(TGRA),Chongqing,China

The Three Gorges Reservoir Area(TGRA)is an important ecological barrier in the Yangtze River Basin,China.Therefore,it is of great importance to understand the spatio-temporal variation and the driving factors of production-living-ecological spaces for sustainable and high-quality development in the TGRA.This study investigated the dynamic variation of production-living-ecological spaces in the TGRA by employing land use data in 2000,2005,2010,2015,and 2018,and detected the influencing factors by using the Geographic detector(GeoDetector).Results implied that the structure and dynamic trajectories of production-living-ecological spaces in the TGRA varied in both horizontal and vertical directions,and the study area was dominated by ecological space.A spatial orientation towards the northeast was detected in the evolution of production-living-ecological spaces during 2000-2018.In terms of quantity,the transition from ecological space(grassland and woodland)to agriculture land accounted for the largest proportion from 2000 to 2018.However,the reverse transition from agriculture land to ecological space has increased since 2000 with the efforts of“Grain for Green”.In terms of temporal scale,there was a fluctuating trend in production space with the continuous expansion of living space,while ecological space showed an inverted U-shaped trend during 2000-2018.The dynamic pattern of production-living-ecological spaces in the TGRA was influenced by both physical and socio-economic variables as basic determinants and dominant driving factors,respectively.Finally,the harmonization and protection of production-living-ecological spaces still require policy-makers’efforts.This work may have potential in advancing our understanding about land use conflicts,and provide a reference for rational layout of spatial functions and the realization of sustainable development in the TGRA.

Runoff Characteristics of Different Stands in Dongjiang Lake Reservoir Area

Different forest stands in the Dongjiang Lake Reservoir area of Zixing were selected as the research objects to study the characteristics of runoff generation in different forest stands.The results showed that there was no significant difference in annual runoff among M3,M1,and M5,and no significant difference between each forest stand and the control.The order was M3(22.75 mm)>M1(21.77 mm)>M5(20.14 mm).Forest vegetation generates less runoff through vegetation restoration compared to the control,indicating that forest vegetation reconstruction and restoration are beneficial for soil and water conservation.

Baoziwan-Majiashan Area of Jiyuan Oilfield Analysis of Reservoir Characteristics and Main Control Factors in Long 4 5 Section

Based on the sheet, scanning electron microscope and high pressure mercury analysis method, this paper takes Jiyuan oilfield-Ma Jia mountain district 4 5 sandstone reservoir as the research object, from the reservoir petrology, pore type and porosity, permeability, the system analyzed the reservoir characteristics and its control factors. The results show that the sandstone in the 4 5 section of Baoziwan-Majiashan area of Jiyuan oilfield is fine in size and high in filling content. The pore types were dominated by intergranular pores and dissolved pores, with a low face rate. The reservoir property is relatively poor, with mean porosity of 11.11% and mean permeability of 1.16 × 10−3 µm2. In the low porous, low otonic background, the development of relatively high pore hypertonic areas. Compaction and cementation should play a destructive role in reservoir properties, and dissolution should play a positive role in reservoir properties. Compaction adjusts the migration of clay minerals and miscellaneous bases in the original sediment in the study area, greatly reducing the porosity and permeability of the reservoir;the development of the cement cement, carbonate cementation and some quartz secondary compounds reduces the storage space;the dissolution effect, especially the secondary dissolution pores of the reservoir, which obviously improves the properties of the reservoir.

Evaluation of Chang 2 Reservoir in Zichang Area, Ordos Basin

In this paper, the Chang 2 reservoir in Zichang Area of Ordos Basin, the second largest sedimentary basin in China, is classified and evaluated by using logging and core data, thin section identification and electron microscopy. The main sedimentary microfacies of Chang 213 is braided river delta sedimentary system in geological history, and there are three main sedimentary microfacies types: swamp microfacies, distributary channel microfacies and natural embankment microfacies on land. The heterogeneity in the study area is as follows: Chang 212 formation has the strongest heterogeneity, followed by Chang 211 formation with strong heterogeneity, and finally Chang 213 formation with medium heterogeneity. The reservoirs of Chang 2 member in the study area are dominated by IIIa, IIb and IIIb, and the reservoirs are mainly composed of ultra-low porosity and low permeability reservoirs and low porosity and low permeability reservoirs.

Water Environment Pollution in Three-Gorge Reservoir Area and Treatment Technology

After the erection of Three-Gorge Reservoir, the water environment in the reservoir area will be turned into water bodies like lakes, and the self-clarification ability of water will also be much slower than ever. Now, the quality of water in most segments in upper reaches of Yangtze River cannot meet the requirements of l-ll class Environment Quality Standard (GHZB1-1999). In Yangtze River, dialing River and Wujiang River, the main indexes such as colon bacillus, nonionic ammonia, chemical oxygen demand (COD), petroleum, phenol, total phosphorus (TP), heavy metal, etc., have exceeded the standard limits. The water bodies of the reservoir area are facing serious risk of eutrophicationm. To solve that problem, a countermea-sure of multi-spot diverted treatment and separate discharge is recommended. For doing this, lots of small-scale wastewater treatment facilities employing updated activated sludge treatment technologies are to be set up. Up to now, a number of sewage treatment technologies to control eutrophication of water have been developed, which include processes of sequencing batch activated sludge (SBR), absorbing bio-degradation (AB), oxidation channel, package intermittent aeration system (PIAS), intermittent cycle extended aeration system (ICEAS), UNITANK and so on. The Effective one to be applied in the reservoir area should convey the requirements of ecological agriculture, forestry and urban planning, and be accompanied by legal support for appropriate exploitation of natural resources.

Climate Characteristics in Three Gorges Reservoir Area after Water Storage and Its Impact on the Production Potential

Based on the meteorological data from 33 stations of Three Gorges Reservoir from 1960 to 2008,climate yield of rice,corn and winter wheat and the changes of climatic potential productivity after water storage in Three Gorges Reservoir were calculated by the dynamic statistic model of crop growth.The results showed that the temperature in Three Gorges Reservoir was fluctuant decreased before late 1980s,and warmed rapidly after the late 1980s.The precipitation had little change before the late 1990s and had a slight decrease after the late 1990s.Sunshine hours were more in 1960s and 1970s,and then it changed little after 1980s.After water storage,the temperature increased in Three Gorges Reservoir as a whole.The precipitation decreased in the south of Three Gorges Reservoir,while it increased in the northwest of Three Gorges Reservoir.The sunshine hours were reduced except that in the vicinity of Dianjiang.After water storage,climatic potential productivity of rice decreased in the northwest and the northeast,while it increased in the south of Three Gorges Reservoir.The climatic potential productivity of corn decreased in the northeast and the southwest,but increased in the rest of Three Gorges Reservoir.The climatic potential productivity of winter wheat increased almost in total.

Geological Features and Reservoiring Mode of Shale Gas Reservoirs in Longmaxi Formation of the Jiaoshiba Area

This study is based on the sedimentation conditions, organic geochemistry, storage spaces, physical properties, lithology and gas content of the shale gas reservoirs in Longmaxi Formation of the Jiaoshiba area and the gas accumulation mode is summarized and then compared with that in northern America. The shale gas reservoirs in the Longmaxi Formation in Jiaoshiba have good geological conditions, great thickness of quality shales, high organic content, high gas content, good physical properties, suitable depth, good preservation conditions and good reservoir types. The quality shales at the bottom of the deep shelf are the main target interval for shale gas exploration and development. Shale gas in the Longmaxi Formation has undergone three main reservoiring stages：the early stage of hydrocarbon generation and compaction when shale gas reservoirs were first formed; the middle stage of deep burial and large-scale hydrocarbon generation, which caused the enrichment of reservoirs with shale gas; the late stage of uplift, erosion and fracture development when shale gas reservoirs were finally formed.

Characteristics of Tight Sandstone Reservoirs and Controls of Reservoir Quality: A Case Study of He 8 Sandstones in the Linxing Area, Eastern Ordos Basin, China

Determining the process of densification and tectonic evolution of tight sandstone can help to understand the distribution of reservoirs and find relatively high-permeability areas.Based on integrated approaches of thin section,scanning electron microscopy(SEM),cathode luminescence(CL),nuclear magnetic resonance(NMR),X-ray diffraction(XRD),N2 porosity and permeability,micro-resistivity imaging log(MIL)and three-dimensional seismic data analysis,this work discussed the reservoir characteristics of the member 8 of the Permian Xiashihezi Formation(He 8 sandstones)in the Linxing area of eastern Ordos Basin,determined the factors affecting reservoir quality,and revealed the formation mechanism of relatively high-permeability areas.The results show that the He 8 sandstones in the Linxing area are mainly composed of feldspathic litharenites,and are typical tight sandstones(with porosity<10%and permeability<1 mD accounting for 80.3%of the total samples).Rapid burial is the main reason for reservoir densification,which resulted in 61%loss of the primary porosity.In this process,quartz protected the original porosity by resisting compaction.The cementation(including carbonate,clay mineral and siliceous cementation)further densified the sandstone reservoirs,reducing the primary porosity with an average value of 28%.The calcite formed in the eodiagenesis occupied intergranular pores and affected the formation of the secondary pores by preventing the later fluid intrusion,and the Fe-calcite formed in the mesodiagenetic stage densified the sandstones further by filling the residual intergranular pores.The clay minerals show negative effects on reservoir quality,however,the chlorite coatings protected the original porosity by preventing the overgrowth of quartz.The dissolution of feldspars provides extensive intergranular pores which constitute the main pore type,and improves the reservoir quality.The tectonic movements play an important role in improving the reservoir quality.The current tectonic traces of the study area are mainly controlled by the Himalayan movement,and the high-permeability reservoirs are mainly distributed in the anticline areas.Additionally,the improvement degree(by tectonic movements)of reservoir quality is partly controlled by the original composition of the sandstones.Thus,the selection of potential tight gas well locations in the study area should be focused on the anticline areas with relatively good original reservoir quality.And the phenomena can be referenced for other fluvial tight sandstone basins worldwide.

Reductions in non-point source pollution through different management practices for an agricultural watershed in the Three Gorges Reservoir Area

Non-point source water pollution generated by agricultural production is considered a major environmental issue in the Three Gorges Reservoir Area （TGRA） of China. The Annualised Agricultural Non-Point Source Pollution （AnnAGNPS） model was selected to assess the impact of the application of various management treats, including seven crops, five fertilizer levels and three-group management practice scenarios, on water quality from Heigou River Watershed in TGRA. The scenario subsets include conservation tillage practice （CTP）, conservation reserve program （CRP） and conversion of cropland into forestland program （CCFP）. Results indicated that tea can not be replaced by other crops because comparatively tea resulted in a higher sediment yield. CTP with no-tillage was more effective to reduce sediment yield, but could increased nutrient loss. CRP reduced sediment yield significantly, but slightly benefited on nutrient loss. CCFP reduced not only sediment yield but also the nutrient loss significantly. The conversion of cropland with a slope greater than 10° into forestland was found to be the best scenario as the sediment yield export is less than 5 tons/ha and nutrient loss is within the permissible limit.

Effect of nitrogen and phosphorus on the water quality in the Three Gorges Reservoir Area during and after its construction

A survey concerning the concentration of the nutrients in the Three Gorges Reservoir Area was carried out. This paper presents the parameters(NO 3 - N, NO 2 - N, Kjeldahl N, non ionic ammonia, P PO 4 and TP) determined at 16 sampling sites from 1997 to 1999 The dominant soluble nitrogen form was NO 3 - N followed by Kjeldahl N, NO 2 - N and non ionic ammonia. Mean values of NO 3 - N, NO 2 - N, Kjeldahl N and non ionic ammonia ranged from 0 50 to 2 37 mg/L, 0 022 to 0 084 mg/L, 0 33 to 0 99 mg/L and 0 007 to 0 092 mg/L respectively. Mean values of P PO 4 at most sampling sites were higher than 0 1 mg/L for subject to eutrophication. The major factors influencing the concentrations of N and P might be agricultural runoff, municipal and industrial effluents. In addition, 6 kinds of soil were sampled at the area where would inundated after the dam completed. Two approaches were adopted to simulate the N and P release from the inundated soils. The results showed that the soils would release nitrogen and phosphorus to the overlying water when the soils were inundated. The characteristics of soil affected the equilibrium concentrations of N and P between the soil and the overlying water.

Changes in cultivated land patterns and driving forces in the Three Gorges Reservoir area, China, from 1992 to 2015

Changes of cultivated land patterns caused by major water conservation projects are rarely reported. We selected the Three Gorges Reservoir area in China to study the change in area and landscape pattern of the cultivated land in the head,central, and tail areas of the reservoir that took place between 1992 and 2015;we then studied the spatial distribution of the cultivated land in the three parts of the reservoir;finally, we studied the driving forces behind the changes in the cultivated land. The results derived are as follows.(1) During the construction of the Three Gorges Project(TGP, 1992–2015), the area of cultivated land around the reservoir decreased by30.23 million ha. This reduction occurred in phases:the most severe change in cultivated land occurred during the later stage of the project(2002–2010);only 0.62 million ha of cultivated land did not change between 1992 and 2015.(2) Spatial pattern analysis showed that the cultivated land in the three parts of the reservoir changed from a northern distribution to a southern distribution;thus, the area of cultivated land in the north decreased over the time period. The area of cultivated land in the head and tail areas decreased by varying degrees, while it increased in the central area over the 23 years, indicating that the change in cultivated land showed regional differences.(3) The TGP, the policy of reverting farmland to forest,and urbanization were the main driving factors for the change of cultivated land, but there were differences in their impacts at different stages.(4) According to the patch dynamics of the land cover change, the degree of change gradually intensified during the early and later stages of the project and then stabilized during the operational period. Our research provides scientific support for the protection of cultivated land resources and food security in the reservoir area and for the coordination of social and economic development, which is of great significance to sustainable development in the reservoir area.

Conflict between wild boars(Sus scrofa) and farmers:distribution, impacts,and suggestions for management of wild boars in the Three Gorges Reservoir Area

Economic losses caused by wild boars(Sus scrofa)continue to increase in the Three Gorges Reservoir Area.We selected 206 farmers in Wuqiaohe Basin as survey respondents using random stratified sampling.The distribution and impacts of wild boars were examined using a questionnaire survey and spatial analysis.The results showed that:(1)The density of farmer settlements is low and most peasants’households are located on the forest edge.Due to large-scale labor migration,a high proportion of farmland(25.85%)has been abandoned and an even higher proportion of farmland(40.48%)has been returned to forest.(2)The probability of wild boar damage to peasant households was 67.96%.Yields of corn and sweet potato decreased by 24.87%and 28.24%,respectively,with a total economic loss of approximately 2,590,100 RMB/yr in the Wuqiaohe basin.Sixty-five percent of the affected cultivatedlands were located within approximately 150 m of the forest edges.(3)The wild boar damage coefficient was significantly and negatively correlated with the distance between the peasants’household and the forest edge,the density of the settlements,and the area of cultivated land.The wild boar damage coefficient shows a significant positive correlation with the area of farmland returned to forest.(4)The damage activity caused by wild boars began to occur7-8 years ago,and the destruction has been more frequently and seriously observed in the last 4-5 years.(5)We make suggestions for wild boar control and management measures including developing a compensation policy.The compensation standard is related to the land area returning from farmland to forests and the actual cultivated land area.

Geochemical studies of the Silurian oil reservoir in the Well Shun-9 prospect area, Tarim Basin, NW China

Commercial oil flow has been obtained from the sandstone reservoir of the Lower Silurian Kelpintag Formation in the Well Shun-9 prospect area.In the present studies,10 Silurian oil and oil sand samples from six wells in the area were analyzed for their molecular and carbon isotopic compositions,oil alteration（biodegradation）,oil source rock correlation and oil reservoir filling direction.All the Silurian oils and oil sands are characterized by low Pr/Ph and C21/C23 tricyclic terpane（〈1.0） ratios,＂V＂-pattern C27-C29 steranes distribution,low C28-sterane and triaromatic dinosterane abundances and light δ13C values,which can be correlated well with the carbonate source rock of the O3 l Lianglitage Formation.Different oil biodegradation levels have also been confirmed for the different oils/oil sands intervals.With the S1k2 seal,oils and oil sands from the S1k1 interval of the Kelpintag Formation have only suffered light biodegradation as confirmed by the presence of ＂UCM＂ and absence of 25-norhopanes,whereas the S1k3-1 oil sands were heavily biodegraded（proved by the presence of 25-norhopanes） due to the lack of the S1k2 seal,which suggests a significant role of the S1k2 seal in the protection of the Silurian oil reservoir.Based on the Ts/（Ts＋Tm） and 4-/1-MDBT ratios as reservoir filling tracers,a general oil filling direction from NW to SE has been also estimated for the Silurian oil reservoir in the Well Shun-9 prospect area.

Land Use of the Three Gorges Reservoir Area and the Effect on Its Landscape Pattern in the Recent 50 Years

The paper makes detailed analysis on the changing processes of the main types of land use in Three Gorges Reservoir Area through the techniques of RS （Remote Sense） and GIS （Geography Information System）. Based on the theory of landscape ecology, many types of landscape pattern indexes are calculated and made correlation analysis. The results indicate that： in 1995 the ecological environment of Three Gorges Reservoir Area was the most vulnerable in the recent 50 years, but resumed in 2002; the landscape pattern diversity index, fractal dimension index and fragmentation index has close correlation with the area of land use/cover change （LUCC）. The research also releases that the increase of the cultivated land, grassland and construction land deteriorates the landscape ecological pattern, while the increase of forest land area will help restore the landscape ecological pattern to its original state. The rapid change of grassland is an important index of the change of landscape pattern, because it has the most effect on change of landscape pattern index.

Distribution of gas hydrate reservoir in the first production test region of the Shenhu area,South China Sea

In May and July of 2017,China Geological Survey (CGS),and Guangzhou Marine Geological Survey (GMGS)carried out a production test of gas hydrate in the Shenhu area of the South China Sea and acquired a breakthrough of two months continuous gas production and nearly 3.1×10^5 m^3 of production. The gas hydrate reservoir in the Shenhu area of China,is mainly composed of fine-grained clay silt with low permeability,and very difficult for exploitation,which is very different from those discovered in the USA,and Canada (both are conglomerate),Japan (generally, coarse sand)and India (fracture-filled gas hydrate).Based on 3D seismic data preserved-amplitude processing and fine imaging,combined with logging-while-drilling (LWD)and core analysis data,this paper discusses the identification and reservoir characterization of gas hydrate orebodies in the Shenhu production test area.We also describe the distribution characteristics of the gas hydrate deposits and provided reliable data support for the optimization of the production well location.Through BSR feature recognition,seismic attribute analysis, model based seismic inversion and gas hydrate reservoir characterization,this paper describes two relatively independent gas hydrate orebodies in the Shenhu area,which are distributed in the north-south strip and tend to be thicker in the middle and thinner at the edge.The effective thickness of one orebody is bigger but the distribution area is relatively small.The model calculation results show that the distribution area of the gas hydrate orebody controlled by W 18/W 19 is about 11.24 km^2,with an average thickness of 19 m and a maximum thickness of 39 m,and the distribution area of the gas hydrate orebody controlled by W11/W17 is about 6.42 km^2,with an average thickness of 26 m and a maximum thickness of 90 m.