| The salt lake mining areas in the Qaidam Basin mainly represented by Qarhan Salt Lake are the main production areas for the development and utilization of salt lake mineral resources in China.Qarhan Salt Lake is the largest production base of potash,magnesium and lithium salt in China at present due to its early development and large scale.With the large-scale continuous exploitation of the Qarhan Salt Lake in recent three decades,the technology of mining and utilization of underground brine-based salt mine resources has been increasingly enhanced,as well as annual output scale of salt mine resources.However,at the same time,the recoverable reserves of underground liquid mineral resources are also decreasing,and the mining environment is becoming increasingly severe.Therefore,the bottleneck of the development and utilization of salt mines has changed from production to salt exploitation.How to determine the occurrence status and spatial distribution characteristics of underground brine,improve the efficiency of resource exploitation,reduce the cost,and make groundwater recharge plan to increase the recoverable reserves of salt mines has gradually become an important problem to be solved in large-scale sustainable development and utiliza t io n of salt lake resources.This paper takes the spatial occurrence characteristics of underground brine as the research target,selects the northwest of Dabson Salt Lake in the middle of Qarhan Salt Lake as research area,and the surface nuclear magnetic resonance water exploratio n and groundwater simulation are carried out to study the occurrence and change characteristics of the underground brine in the work area..The mainly work is as follows:1)Surface NMR(Nuclear Magnetic Resonance)water finding technology is the only non-invasive geophysical method for direct water finding currently,which can accurately detect the burial depth,thickness,water content of the aquifer and important hydrogeological parameters such as permeability coefficient and porosity in the survey area.The underground brine in the study area has good stratification,and is far away from industrial facilities and residential areas.The electromagnet ic interference in the measurement area is relatively smal,which is a better area to implement surface NMR water finding work.The latest model of the Surface NMR water finder produced by the American Vista Clara company was used to carry out detection work in the research area.The information of the distribution of formation water content in the study area was investigated by setting up a total of 20 measuring points with two crosses in eastwest and north-south.2)The groundwater information obtained from the survey is usual y instantaneous state information.Groundwater simulation technology can be used to study the large-scale dynamic change trend in the survey area and understand the occurrence state change characteristics of groundwater.As an open source software for groundwater simulation,OGS(OpenGeoSys)is a more promising groundwater simulation software than commercial software,which can simulate the complex coupling process of multiple physical fields(including heat,hydrology,physics and Chemistry).The OGS software was used to carry out numerical simula t io n calculations on the occurrence status of underground brine in the research area,and various situations were set up to deeply understand the changing characteristics of the underground brine occurrence status in the research area.According to the application of the two research methods in the study area,the following preliminary results were obtained:(1)The inversion results of NMR detection data show that the total underground water content in the study area is generally low,with a maximum water content of about 0.7% and an average water content of about 0.4%.By comparing the detection results with buried depths of adjacent boreholes,it is shown that the water content and the stratum interface have a better consistency at the shal ow surface and the detection accuracy is higher.(2)The two-dimensional simulation results of OGS show that the origina l groundwater level will decrease as the pumping process continues.According to the actual conditions of the study area,there are brine mining channels in the north-northwest direction at the north and south ends of the survey area,and there is an abandoned brine mining channel in the center of research area.This shows that the brine in the shal ow part of the study area is likely to be exhausted when using the abandoned brine extraction channel.At the same time,with the use of the brine extraction channels at the north and south ends,it is difficult to supply water in the shallow part of the study area,resulting in low water content in the shal ow part.In addition,the plane water content distribution results obtained by accumulating the measured water content results at the detection depth have characteristics consistent with the north-north-we st brine picking channels.The overall trend of north-east-east to south-west-west gradually decreases,and the abnormal characteristics of small water content in the center coincide with the abandoned karst site,which is in line with the expectations of actual water content distribution and consistent with the detection results.(3)The OGS simulation results show that the influence width of brine mining channels on underground brine is generally 3.4km to 5.0km.(4)Three-dimensional simulation results show that there are obvious differe nces between the two modes of well mining and channel mining.1)In the well mining mode,the groundwater level in the stratum around the wellbore decreases rapidly,which has a destructive effect on the groundwater,but the influence range is relatively smal;2)In the channel mining mode,the groundwater head fal ing speed of the surrounding stratum is significantly lower than that of the underground mining head in the well mining mode which is due to seepage of channel.The water surface is significa nt ly larger than that of the well,which leads to the extension of the area of influence to the channel's distribution space.It can be seen that under the same pumping volume and pumping time,the influence of canal mining on regional formation head drop is lower than that of well mining.The preliminary conclusions obtained in this paper indicate that the detection results of the NMR method in the dry salt flat area have higher detection accuracy and formation resolution.However,due to the low water content in the dry salt flat area,it is difficult to obtain a more obvious detection effect.Due to the strong conductivity of brine,the adaptive correction of nuclear magnetic resonance methods needs further study.The OGS simulation results have initially verified the accuracy of the NMR detection results,and also found out the spatial distribution of the underground brine layer in the brine mining area.The combination of the two research results can provide more information for the brine occurrence and exploitation process,which is helpful for provide relevant scientific support for the reasonable exploitation of salt lake resources. |
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