Controlling effects of cap rocks on the formation of deep geothermal resources

Cap rocks with high thermal insulation are important for deep geothermal systems at a depth of 3000‒6000 m.Based on the deep geothermal geological conditions in the Fujian-Guangdong-Hainan area of South China,this study established an ideal geological model of reservoir-cap rock assemblages and simulated the geothermal field distribution of cap rocks of different thicknesses and thermal conductivity.The simulation results show that the vertical geothermal temperature distribution in an uplifted area of a depression was present as inverted mirror reflections relative to the elevated area of the basement.Specifically,the isotherms above the elevated area are convex in shape,while those below the elevated area are concave.There is a temperature equilibrium line between the convex and concave isotherms.The heat flow moves from the depressed area to the uplifted area below the temperature equilibrium line and migrates in an opposite direction above the line.On this base,this study conducted the inversion of geothermal temperature fields in typical areas with thin,moderately thick,and thick cap rocks.The results indicate that,at the depth of 3000e6000 m,areas with thin cap rocks(igneous rock zone in the coastal area of Fujian)mainly host moderate-to low-temperature hydrothermal resources;areas with moderately thick cap rocks(Yuezhong Depression)have the geothermal temperature ranging between 100℃and 200℃and may develop moderate-to high-temperature hydrothermal resources and hot dry rocks(HDRs),with the former superimposing on the latter;and areas with thick cap rocks(onshore Beibuwan Basin)have a geothermal temperature of 120‒220℃,and contains mainly moderate-to high-temperature hydrothermal resources and HDRs.Therefore,it is recommended that the evaluation,exploitation,and utilization of deep geothermal resources be carried out according to the burial depth of the temperature equilibrium line and the specific demand for geothermal resources.

Seasonality regulates the effects of resource addition on plant diversity and ecosystem functioning in semi-arid grassland

Aims Seasonal variations in species richness,aboveground net primary productivity(ANPP)and stability under resource enrichment are frequently ignored.This study explores how the impacts of resource enrichment on species richness,ANPP and stability vary among seasons in semi-arid grasslands.Methods We conducted a 3-year experiment in an Inner Mongolia grassland to determine the effects of resource input(water[W],nitrogen[N])on species richness,community ANPP and stability using seasonal sampling during the growing season(2013–2015).Structural equation modeling(SEM)was used to examine the relative importance of resource input on community stability via mechanistic pathways in each month and the whole growing season.Important Findings Resource inputs did not affect community ANPP in May and June,while N and/or NW enhanced ANPP in July and August.Resource inputs generally did not affect species richness,asynchrony or community stability in most of the time.Positive responses of perennial bunchgrasses(PB)to N and/or NW treatments contributed to the increased community ANPP in July and August.Species asynchrony may be the major mechanism contributing to community stability in May and June and the entire growing season,and PB stability is potentially the primary factor controlling community stability in July and August under resource enrichment.Our results indicate that season and resource availability could interact to regulate species richness,community ANPP and stability in semi-arid grasslands.These findings have important implications for management practices in semi-arid grasslands in order to mitigate the impact of land use and global change.

New advances in the assessment of tight oil resource in China

The research on tight oil becomes another hotspot in the field of unconventional oil and gas after the boom of shale gas.The global recoverable resources of tight oil are estimated to be around 47.3×10^(9)t.In recent years,significant progress has been made in the technologies of tight oil exploration and development in North America,thus stimulating the dramatic increase of tight oil production.Meanwhile,China has also acquired remarkable achievements in tight oil exploration.Mature assessment methods have been established for tight oil resources by the US,generally dominated by analogy and statistical methods with their own advantages and disadvantages as well as applicable conditions.In China,improvement of resource evaluation techniques becomes an urgent issue in increasing tight oil reserve and production.This study mainly discusses the resource evaluation methods and resource enrichment characteristics of tight oil.Seven kinds of assessment methods in three categories(i.e.,analogy,statistical and genetic method)and evaluation parameters have been preliminary established,and are specifically applied in the Sichuan,Ordos,Songliao,Junggar,Bohai Bay and other tight oil basins through the newly hierarchical resource abundance analogy method,the estimated ultimate recovery(EUR)analogy method and the small-cell volumetric method.The preliminary evaluation results reveal that China has great potential in tight oil resource,and the geological resources amount to 20×10^(9)t,providing a resource base for large-scale development.