| The tuff of Lancang Laochang Lead Mine is a kind of high expansion and fast collapse tuff, it brought difficulty to production. On this engineering background, and based on the tuff occurrence and the summary of the main engineering geological problems, use the representativable tuff samples of the ore-bearing bed, expansion and collapse mechanism of the tuff are systematicly discussed mainly from these ways:The tuff’s microstructure and it’s changes, the chemical reactions and it’s principle, the material factors, anti-sloughing drilling fluid and it’s mechanism, etc. And impactful anti-sloughing drilling fluid is gained.(1)Based the analysis of granularity, pore, fracture, etc. mainly used the scanning electron microscope to observe. By contrast the structure changes of dry tuff, slow water absorbed tuff and quick absorbed water tuff samples, the changes of tuff’s microscopic structure were studied, the changes of pore and fracture when meeting water were discussed, and, such problems as how the water flow in the tuff and the capillary force model are researched too. Also, the micro mechanical problems discussed by establishing the model and formula. Microstructural studies show that:Tuff granularity is not uniform, relatively in small particles, but dense hard big blocks are contained, it has great effect to drill stick. Tuff have lots of pores and cracks. When free expand, the tiny pore and fracture increased, and the permeability increased too. Under pressure and in the closed space, expansion made the pore and fracture smaller and more uniform, permeability be reduced. In the expansion process,water flow in tuff is as follows:Under the capillary force, water along the cracks and pores quickly spread into the tuff, when it come into the lamellar structure, a lot of new micro pores and cracks come into being, it provide new channels for further water infiltration. For the distance between pieces is tiny, so the capillary force of the sheet structure is very strong, it led to widespread and strong water absorption. After water absorption, the inserted water layer and the curling sheet made the distance increased and generated lots of pores and cracks. So, it is considered that the widespread water layer insert and hydrophilic sheet structure curling after absorbed water is one of the main reasons of Lancang tuff’s expansion and collapse.(2)Use the variety of experimental contrast datum of a variety of means such as X fluorescence, X diffraction and electron probe, the material factors of Lancang tuff’s expansion&collapse mechanism are studied from the expansion aspect and from collapse aspect separately. When study the expansion, firstly, use X fluorescence and XRD test the water-sensitive mineral components, Then, in order to confirm the expansion material, electron probe is used to detect the typical structure of expansion part which obtained from scanning electron microscope observation. In the study of collapse, a series of dissolution and anti collapse experiments were designed under incremental time, ICP-AES was used to detect the dissolved ions concentration. First step, get the possible dissolved material which may lead the tuff to collapse, then the saturation solution of those possible ions were used in anti-collapse experiment to affirm, and the functional material were obtained. Material factors research results show that:The minerals cause of Lancang Laochang tuff’s rapid expansion is the tuff have lots of clay minerals, mainly constituted by kaolinite, quickly water absorption of lamellar or sheet structure kaolinite leads to quickly expansion and quickly collapse, and the hydrophilic polar mineral is swelling factor which can not be ignored. When water absorbed into tuff, it is an important reason that the fast salt dissolution make tuff expansion and reduce tuff strength. Chemical hydrate crystalline exists in always wet underground and can cause certain tuff expansion, but it forms slowly, and expansion caused by hydrate crystallinity is not universal, so it is not the main reason of fast tuff expansion. The dissolving of soluble material in tuff plays a very important role to Lancang Laochang tuff’s collapse, the dissolution of Na+and K+are the important material factors of tuff decomposition and collapse.(3)Through the chemical reaction characteristics and principles of tuff reacting to acid, alkali, salt solution and organic reagent, tuff expansion collapse mechanism were discussed from chemical reaction and dissolution side. Respectively, groping chemical experiment and salt direction experimental study were carried out. It has been known that the tuff is relatively stable in saturated NaCl solution or in saturated KBr saturated solution. Bases on these experimental results, NaCl saturated drilling fluid system is selected for drilling fluid formulation adaptable research and optimize research,and the effective anti-sloughing drilling fluid formulation components have been obtained. Using the formulation, stability of tuff is improved from2minutes in water to above15days. In chemical study, the inhibition of saturated brine to the dissolution of tuff has been experimentalized and analyzed too, and the anti-collapse function of anion has been discussed also. Research results show that:There’s closely relativity between the tuff collapse and the ion dissolution, the saturated NaCl solution can block the ion dissolution of tuff, then can prevent the tuff collapse. From the drilling fluid component adaptable study, it is know that the NaOH and the soluble amylum based saturated NaCl solution have significant inhibitory effect to the tuff collapse. And from the study on the optimization of the drilling fluid component, it is know that using the local tuff filtrate as the base liquid of drilling fluid can improve the anti-collapse properties of the drilling fluid, so bentonite is needed, additives which ant salt crystallization should not be used. The role of anion can not be ignored, to prevent Lancang tuff’s collapse, the anion should use the halogen anion Cl-or Br-.(4)The researches of anti-sloughing mechanisms of the drilling fluid, are the collapse mechanisms studied by anti-sloughing mechanisms, are necessary and effective. The detection of dissolved ions according to the increased solute sequence of drilling fluid formula, is the supplement of the material factor of tuff’s collapse mechanism. Tuff’s stability state and dissolved ion detection of the drilling fluid related chemical solution, is the quantitative research of the qualitative chemical phenomena.The anti-sloughing mechanism of the drilling fluid to Lancang Laochang Lead Mine is studied from two aspects of each component:the water resistance effect and the dissolution resistance effect of drilling fluid. Researches show that:Soluble starch flocculate along the tuff crack and surface, has strong blocking effect, and can provide crystal base to NaCl; saturated NaCl solution has effects of crystallization blockage and hinder tuff soluble dissolution; NaOH has certain help for flocculation, can enhance NaCl crystallization rate and prevent soluble dissolution,and colloid such as Fe(OH)2can form with NaOH too; tuff filtrate can increase the ions concentration of the drilling fluid, those just as same as the soluble ions of tuff, then it can reduce dissolution rate of tuff sidewall’s material, and the tuff filtrate can provide nucleus to NaCl crystallization. The sidewall covered by moist mixed film formed by starch flocculation, NaCl crystal colloid, and bentonite,the mixed film block up water immersion into tuff greatly, the water isolation ability is the important anti-collapse reason of the drilling fluid. High concentrations tuff filtrate+saturated brine solution+NaOH has preliminary block effect to the dissolution of soluble in tuff, flocculation, crystallization and film covering lead the dissolution been further prevented, the drilling fluid has strong dissolution inhibitor ability is also the important reason of anti collapse.(5) The chemical reaction principle of tuff was comprehensively studied, and stressed the causes of tuffs different stability in the water, saturated NaCl solution and alkaline saturated NaCl solution. Firstly, by experiment, the quantity of three kinds of liquid absorbed into tuff and the state of tuff were identified. Then, the viscosity, interfacial viscosity, electric double layer effect and end surface electric double layer based on adsorption effect were researched, it is the study of the interaction principle of saturated NaCl solution-tuff liquid. Through the integrated application of various theories, the shortcomings of single theory cannot explain a variety of chemical phenomena of tuff was overcame, it provides further theoretical basis for drilling fluid anti-sloughing application. Researches show that:The interfacial viscosity played a role of inhibiting alkaline NaCl solution to go into the tuff’s micro layer. Adsorptions of end surface electric double layer have the overall effects on blocking solution into tuff, but ion adsorptions can make the saturated solution to be unsaturated, and then free water come into being, the increased free water can weak the blocking effect. Due to the strongly ion adsorption effect of the end surface of the clay in tuff, the adsorption capacity is greater than the capillary pressure, so,the saturated NaCl solution is difficult to enter the micro layer, but the adsorption of weakly sorption ion Na+is not sufficient to produce lots of free water. For strong sorption ions such as Fe3+, by strong adsorption, the saturated solution is made unsaturated, so free water emerged, for binding force is small, distal free water and can not overcome the capillary pressure and then entered the tuffs micro pieces; the enter of water into the tuffs micro pieces increased the distance between the pieces, so the double layer effect were weakened, which made the ions contained solution get into the micro pieces, it is why tuff rapid collapse in the saturated solution of strong sorption ions. NaOH is a kind of surfactant to increase the tuff-water interfacial tension. Also, NaOH and kaolinite’s H+are bond by hydrogen, it made interfacial viscosity increased on the tuff surface, and then made tuff end surface adsorption stronger. NaOH also increased Na+concentration, and it’s colloidal formation effect made viscosity increased. When satisfied "End surface electrical double layer force+Interfacial viscosity resistance+Electrolyte ion binding force> Capillary pressure", the liquid can not enter into the tuff; on the contrary, can enter tuff. By comprehensive analysis results, it further explains the anti-collapse principle of formula drilling fluid, and the anti-sloughing drilling fluid formulation been further optimized. The addition of KCl and NaBr, can further reduce free water in drilling fluid, strengthen the binding of the end electric double layer charge to the liquid, it can make the tuff more stable. |
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