Coalbody structure classification method based on dual-lateral and RXO crossplot analysis

According to the positive correlation of coal ash content and natural gamma, using a new coal core reposition method, which is ordered by global and local extreme, coal samples from medium-thickness seam are reasonably located. Inte- grated the data of coal macrostructure characteristics, coal petrography analysis and coal gas production test, it studies the rela- tionship between coalbody structure and amplitude variation of different well logging data, and the tectonic coal recognition method with well logging data in fresh-water mud invasion. The results show that： the anomalous response of natural gamma ray, neutron, density and apparent resistivity does not reflect the coalbody structure type. In fresh-water drilling mud invasion, using the crossplot technique of dual-lateral, RXO resistivity response and the coalbody structure can classify granulated coal accurately; the proposed method is of good practicability and high reliability.

Genesis of Kaolinite Deposits in the Jungar Coalfield,North China:Petrological,Mineralogical and Geochemical Evidence

Petrological,mineralogical and geochemical studies carried out on kaolinite deposits in Haerwusu surface mine,Jungar Coalfield,northern Ordos Basin,North China,define their characteristics,ore genesis and economic interest.Based on the crystalline size,two different types of kaolinite rocks,cryptocrystalline and grainy,were identified under the microscope.XRD data show that kaolinite is the predominant mineral,associated with boehmite,magnesite,anatase,pyrite,diaspore and calcite.However,high boehmite content(mean 70%)shows up in the middle layers.Kaolinite minerals present homogeneous shape and a good crystallinity(HI=0.96–1.26).Geochemical studies show that the SiO_(2)/Al_(2)O_(3)molar ratio of kaolinite is close to the theoretical value,and the contents of Na_(2)O,K_(2)O,CaO,Mg O are less,suggesting a strong chemical weathering environment.The REE and Eu anomalies show a close relationship between kaolinite and the Yinshan Oldland granite.A Ce anomaly reflects a continental sedimentary environment with shallow water.A temperature range of 26.7–34℃was calculated on the basis of the isotopic signatures(δ18O,δD)of the kaolinite rocks.All these data indicate that the formation of the kaolinite is caused mainly by the dissolution,coagulation,precipitation and recrystallization of aluminosilicate clastics in acidic conditions.The formation of boehmite in the middle layers indicates that the source rocks have changed.Boehmite is mainly formed by dehydration and compaction of an aluminum-rich colloid which transported into peat swamp during diagenesis.In addition,it formed by desiliconization of kaolinite under acidic conditions.Due to its high kaolinite content(up to 90%)and low iron mineral content(less than 1%),and good crystallinity,kaolinite deposits occurred at Haerwusu surface mine probably have great economical value in the future.

3D forward modeling and response characteristics of low-resistivity overburden of the CFS-PML absorbing boundary for ground-well transient electromagnetic method

This study used the stable and convergent Dufort-Frankel method to differentially discretize the diffusion equation of the ground-well transient electromagnetic secondary field.The absorption boundary condition of complex frequency-shifted perfectly matched layer(CFS-PML)was used for truncation so that the low-frequency electromagnetic wave can be better absorbed at the model boundary.A typical three-dimensional(3D)homogeneous half-space model was established and a low-resistivity cube model was analyzed under the half-space condition.The response patterns and drivers of the low-resistivity cube model were discussed under the influence of a low-resistivity overburden.The absorption boundary conditions of CFS-PML significantly affected the low-frequency electromagnetic waves.For a low-resistivity cube around the borehole,its response curve exhibited a single-peak,and the extreme point of the curve corresponded to the center of the low-resistivity body.When the low-resistivity cube was directly below the borehole,the response curve showed three extreme values(two high and one low),with the low corresponding to the center of the low-resistivity body.The total field response of the low-resistivity overburden was stronger than that of the uniform half-space model due to the low-resistivity shielding effect of electromagnetic waves.When the receiving-transmitting distance gradually increased,the effect of the low-resistivity overburden was gradually weakened,and the response of the low-resistivity cube was strengthened.It was affected by the ratio of the overburden resistivity to the resistivity of the low-resistivity body.

Feasibility of central loop TEM method for prospecting multilayer water-fi lled goaf

With deep mining of coal mines, prospecting multilayer water-filled goaf has become a new content that results from geophysical exploration in coalfields. The central loop transient electromagnetic （TEM） method is favorable for prospecting conductive layers because of the coupling relationship between its field structure and formation. However, the shielding effect of conductive overburden would not only require a longer observation time when prospecting the same depth but also weaken the anomalous response of underlying layers. Through direct time domain numerical simulation and horizontal layered earth forward modeling, this paper estimates the length of observation time required to prospect the target, and the distinguishable criterion of multilayer water-filled goal is presented with observation error according to the effect of noise on observation data. The observed emf curves from Dazigou Coal Mine, Shanxi Province can distinguish multilayer water-filled goaf. In quantitative inversion interpretation of observed curves, using electric logging data as initial parameters restrains the equivalence caused by coal formation thin layers. The deduced three-layer and two-layer water-filled goals are confirmed by the drilling hole. The result suggests that when observation time is long enough and with the anomalous situation of underlying layers being greater than the observation error, the use of the central loop TEM method to orosoect a multilaver water-filled goaf is feasible.

Pore Structure Characteristics of Taiyuan Formation Shale in Qinshui Basin

Qinshui Basin is located in the southeast of Shanxi Province, China. Taking the shale of Taiyuan Formation in Qinshui Basin as the research object, the study analyzed the pore size of the shale of Taiyuan formation in detail from micropore to macropore by the methods of mercury injection, liquid nitrogen analysis and combination of liquid nitrogen and mercury injection. The results show that: 1) the visible pores and macropores are poorly developed and distributed unevenly in the shale of Taiyuan formation, and the micropores are well developed in the shale, and there are more open pores in the pore diameter range, and the pore connectivity is good;2) the liquid nitrogen experiment shows that the pores of Taiyuan Shale are relatively developed between 15 nm and 20 nm, and the formation of hysteresis loop may be caused by some narrow slit pores with similar layered structure;3) the comprehensive analysis of liquid nitrogen and mercury injection experiments shows that the shale of the Taiyuan formation mainly develops micropores, the Mesopores is not developed, the pore volume at 10 - 100 nm is more developed than other parts, and the specific surface is mainly contributed by micropores, which can improve the efficiency of shale gas resolution;at the same time, it provides a channel for Shale gas migration, which is beneficial to the development of shale gas.

Gas-in-place and its influence factors of the upper Paleozoic coal-bearing shale in the Qinshui Basin, China

Coal-bearing shale shows great potential for unconventional gas resources in China, while its exploration and development have been challenging for a long time. Gas-in-place (GIP) is critical to shale gas evaluation, but the major factors controlling the GIP content of coal-bearing shale remain unclear. To address this issue, the coal-bearing shales of the upper Carboniferous-lower Permian Taiyuan and Shanxi formations in the Zuoquan Block, Qinshui Basin, China, were collected for GIP measurements and an integrated investigation, including organic geochemistry, inorganic mineral compositions, and pore characterizations, was carried out. Our results show that the GIP content of the studied shales displays relatively low values and wide variations, which range from 0.30 to 2.28 m^(3)/t. The GIP is dominated by desorbed gas and residual gas. Total organic carbon (TOC) contents of the studied shales vary from 0.92% to 16.91%, and inorganic minerals are dominated by clays that mainly consist of illite/smectite mixed layer (I/S) and kaolinite. Inorganic pores have been widely observed in the studied shales, while the organic matter-hosted pores are rarely found using SEM observations. Total porosity of the studied shales is primarily contributed by clay minerals, followed by organic matter and quartz. Weak positive relationships between the GIP content and pore structure parameters imply that the adsorption of methane to nanopores is relatively weak, which may be attributed to the hydrophilicity of clay-hosted pores. Moreover, hydrophobic organic pores are not well developed. Positive correlations between the GIP contents and contents of TOC, clays, and the I/S indicate that major factors influencing the GIP contents of the coal-bearing shales are clays (especially I/S) and TOC content. In summary, these findings would be very helpful to reveal the enrichment mechanism of coal-bearing shale gas and provide a scientific basis for the exploration and development of coal-bearing shale gas.