Geophysical surveys are frequently applied in mining prospection to detect the presence and volume of ore bodies of different nature.Particularly,in gypsum ore bodies exploitation,electrical resistivity measurements a...Geophysical surveys are frequently applied in mining prospection to detect the presence and volume of ore bodies of different nature.Particularly,in gypsum ore bodies exploitation,electrical resistivity measurements are usually the most used methodology.However,it has been observed that different electrical resistivity values can be obtained depending on geometrical features and composition of gypsum.Indeed,electrical resistivity of gypsum rocks depends on several parameters,such as gypsum purity,nature of secondary minerals,porosity,saturation and interstitial fluid properties.Saturation and hydrogeological setting,in particular,were recognized as the most influencing parameters.Hydrogeological conditions of gypsum rock masses are also very relevant for exploitability,safety conditions and economic feasibility and should be accurately known during the prospection and planning phases of the quarries.In this work,a relationship between electrical resistivity and saturation degree of gypsum is proposed.The possibility to estimate gypsum porosity with the use of this relationship is also investigated.The reliability of laboratory measurements is finally verified in comparison with field and modelled resistivity data.The reported results underline the potentiality of the proposed approach to obtain a reliable characterization of the studied ore body.展开更多
The stability of underground abandoned gypsum mines is dependent on the gypsum pillar's strength,and most abandoned mines are in a fully saturated condition. Moisture affects the strength of gypsum and is therefor...The stability of underground abandoned gypsum mines is dependent on the gypsum pillar's strength,and most abandoned mines are in a fully saturated condition. Moisture affects the strength of gypsum and is therefore commonly measured when testing rock strength. For most rocks, this is a simple task of weighing the rock's mass before and after oven-heating at a specified temperature and duration. For natural gypsum, however, this is not a straightforward process. Heating natural gypsum can result in dehydration and transformation of gypsum to hemihydrate and anhydrite, thus changing the physical characteristics of the gypsum such as its particle density which in turn affects the moisture content and strength measurements. To prevent transformation when determining the moisture content of gypsum,the American Society for Testing Materials(ASTM) recommends lowering the drying temperature from 110℃ to 60℃ . To investigate the temperature at which gypsum transforms to hemihydrate, we used a helium pycnometer to measure the particle densities of gypsum, hemihydrate and anhydrite. In this research, we suggest that a higher drying temperature of 80℃ can be used for drying gypsum without transforming gypsum to hemihydrate. Further, preparing saturated samples for mechanical testing,which is required in stability analyses of abandoned mines, is challenging due to the dissolution of gypsum when placed in water. To address this problem, we investigated the following methods to saturate gypsum cores taking into account the solubility of gypsum:(1) water immersion,(2) vacuum saturation, and(3) improved vacuum saturation. The research indicates that all the three methods are acceptable but they should be conducted using a saturated gypsum-water solution to minimize dissolution. Further, the research found that the improved vacuum saturation method saturated the test samples within 24 h, while duration of 30 h was required for the other two methods.展开更多
Regarding to the problem on the reservoir-cap rock assemblage evaluation in the carbonate-evaporite paragenesis system,this study examined the dolomite and reservoirs genesis and the characteristics of reservoir-cap r...Regarding to the problem on the reservoir-cap rock assemblage evaluation in the carbonate-evaporite paragenesis system,this study examined the dolomite and reservoirs genesis and the characteristics of reservoir-cap rock assemblage.Based on the literature research of the global carbonate reservoirs and the case study on four profiles of carbonate-evaporite succession,together with geological and experimental work,three aspects of understandings are achieved.(1)Lithology of carbonate-evaporite paragenesis system is mainly composed of microbial limestone/bioclastic limestone,microbial dolomite,gypsum dolomite and gypsum salt rock deposited sequentially under the climatic conditions from humid to arid,and vice versa,and an abrupt climate change event would lead to the lack of one or more rock types.(2)There developed two kinds of dolomite(precipitation and metasomatism)and three kinds of reservoirs in the carbonate-evaporite system;and the carbon dioxide and organic acid generated during early microorganism degradation and late microbial dolomite pyrolysis process,and early dolomitization are the main factors affecting the development of microbial dolomite reservoirs with good quality.(3)In theory,there are 14 types of reservoir-cap rock assemblages of six categories in the carbonate-evaporite system,but oil and gas discoveries are mainly in four types of reservoir-cap rock assemblages,namely"microbial limestone/bioclastic limestone–microbial dolomite–gypsum dolomite–gypsum salt rock","microbial limestone/bioclastic limestone–gypsum salt rock","microbial dolomite–gypsum dolomite–gypsum salt rock"and"gypsum dolomite–microbial dolomite–tight carbonate or clastic rock".These four kinds of reservoir-cap rock assemblages should be related with the climate change rules in the geologic history,and have good exploration prospects.展开更多
文摘Geophysical surveys are frequently applied in mining prospection to detect the presence and volume of ore bodies of different nature.Particularly,in gypsum ore bodies exploitation,electrical resistivity measurements are usually the most used methodology.However,it has been observed that different electrical resistivity values can be obtained depending on geometrical features and composition of gypsum.Indeed,electrical resistivity of gypsum rocks depends on several parameters,such as gypsum purity,nature of secondary minerals,porosity,saturation and interstitial fluid properties.Saturation and hydrogeological setting,in particular,were recognized as the most influencing parameters.Hydrogeological conditions of gypsum rock masses are also very relevant for exploitability,safety conditions and economic feasibility and should be accurately known during the prospection and planning phases of the quarries.In this work,a relationship between electrical resistivity and saturation degree of gypsum is proposed.The possibility to estimate gypsum porosity with the use of this relationship is also investigated.The reliability of laboratory measurements is finally verified in comparison with field and modelled resistivity data.The reported results underline the potentiality of the proposed approach to obtain a reliable characterization of the studied ore body.
文摘The stability of underground abandoned gypsum mines is dependent on the gypsum pillar's strength,and most abandoned mines are in a fully saturated condition. Moisture affects the strength of gypsum and is therefore commonly measured when testing rock strength. For most rocks, this is a simple task of weighing the rock's mass before and after oven-heating at a specified temperature and duration. For natural gypsum, however, this is not a straightforward process. Heating natural gypsum can result in dehydration and transformation of gypsum to hemihydrate and anhydrite, thus changing the physical characteristics of the gypsum such as its particle density which in turn affects the moisture content and strength measurements. To prevent transformation when determining the moisture content of gypsum,the American Society for Testing Materials(ASTM) recommends lowering the drying temperature from 110℃ to 60℃ . To investigate the temperature at which gypsum transforms to hemihydrate, we used a helium pycnometer to measure the particle densities of gypsum, hemihydrate and anhydrite. In this research, we suggest that a higher drying temperature of 80℃ can be used for drying gypsum without transforming gypsum to hemihydrate. Further, preparing saturated samples for mechanical testing,which is required in stability analyses of abandoned mines, is challenging due to the dissolution of gypsum when placed in water. To address this problem, we investigated the following methods to saturate gypsum cores taking into account the solubility of gypsum:(1) water immersion,(2) vacuum saturation, and(3) improved vacuum saturation. The research indicates that all the three methods are acceptable but they should be conducted using a saturated gypsum-water solution to minimize dissolution. Further, the research found that the improved vacuum saturation method saturated the test samples within 24 h, while duration of 30 h was required for the other two methods.
基金Supported by the China National Science and Technology Major Project(2016ZX05004-002).
文摘Regarding to the problem on the reservoir-cap rock assemblage evaluation in the carbonate-evaporite paragenesis system,this study examined the dolomite and reservoirs genesis and the characteristics of reservoir-cap rock assemblage.Based on the literature research of the global carbonate reservoirs and the case study on four profiles of carbonate-evaporite succession,together with geological and experimental work,three aspects of understandings are achieved.(1)Lithology of carbonate-evaporite paragenesis system is mainly composed of microbial limestone/bioclastic limestone,microbial dolomite,gypsum dolomite and gypsum salt rock deposited sequentially under the climatic conditions from humid to arid,and vice versa,and an abrupt climate change event would lead to the lack of one or more rock types.(2)There developed two kinds of dolomite(precipitation and metasomatism)and three kinds of reservoirs in the carbonate-evaporite system;and the carbon dioxide and organic acid generated during early microorganism degradation and late microbial dolomite pyrolysis process,and early dolomitization are the main factors affecting the development of microbial dolomite reservoirs with good quality.(3)In theory,there are 14 types of reservoir-cap rock assemblages of six categories in the carbonate-evaporite system,but oil and gas discoveries are mainly in four types of reservoir-cap rock assemblages,namely"microbial limestone/bioclastic limestone–microbial dolomite–gypsum dolomite–gypsum salt rock","microbial limestone/bioclastic limestone–gypsum salt rock","microbial dolomite–gypsum dolomite–gypsum salt rock"and"gypsum dolomite–microbial dolomite–tight carbonate or clastic rock".These four kinds of reservoir-cap rock assemblages should be related with the climate change rules in the geologic history,and have good exploration prospects.
