| The geological conditions of the marine strata are complex as there are fault develop-ment,serious formation crushing,narrow pressure window and so on.Lost circulation often occurs because of the high density and viscosity of the drilling fluid or cement slurry.There are many issues on the relatively simplex plugging agent at present,such as there are mis-match between a bridge plugging agent and leakage layer,and the poor stability of high water loss plugging agent,and the expensive cost on chemical plugging and the difficulty to control the expansion time,and the incompatibility of cement slurry plugging and drilling fluid,and the inconvenience of the operation and so on.The purpose of this paper is to develop a high efficiency plugging technology for fractured strata,to explore the mechanism of hydration and hardening,to lay the theoretical foundation for engineering application,mainly researches as the following:(1)Curing agent is selected from metallurgical industry waste granulated blast furnace slag,in advantage of the use of its potential gel characteristics to achieve plugging fluid hardening.Slag composition and structure are the basis of hydration reaction.The struc-ture of the slag composition is observed by X-ray diffraction,nuclear magnetic resonance,high resolution transmission electron microscopy.The results show that the slag composi-tion is composed of amorphous phase,mixed with a certain amount of microcrystalline,and contains a small amount of CaO,SiO2 and various aluminosilicate crystal mixture;the Si in the slag is mainly silicon tetrahedron,which exists in the form of orthosilicic acid,disilicic acid and a small amount of frame structure;Al part of the form of four coordination,a part of A1 in the form of five coordination,more Al in the form of six coordination;O mostly exists in the form of bridge oxygen,and a small part in the form of non-bridge oxygen.(2)The rheological properties of the plugging fluid directly affect the flow resistance in the leakage layer.In this paper,it is tested that the effect of fluidity and composition of the base mud on the rheological parameters.Based on this paper,the working mechanism of ac-tivator on the rheology is studied.The results show that the concentration of solid particles leads to the change of the rheology of the fluid as well as the quantities of bentonites and polymeric materials in the base mud.So the rheology of the fluid can be adjusted according to their influence characteristics.(3)The key to the success of the plugging is the formation of a slug,effectively pre-venting the pressure in the well from passing to the crack tip.The sclerosis of slag material requires the excitation of alkali metal compounds,different alkaline medium has different hardening performance,and it must be studied by hydration hardening mechanism.The physical and chemical characteristics of the mineral components,the structure and the activa-tor of the slag material are clarified,and the influencing factors and reaction characteristics can be evaluated to provide the technical route and theoretical guidance for the application of the solidified body.The results show that the activation effect of Na2SiO3·9H2O,NaOH and Na2CO3 is from high to low.The activation of alkali-activated slag is to break the Si-O bond of partially disilicic acid into orthosilicic acid,the more[Si04]4-the lower the degree of polymerization of structure proportion in the slag,the higher the strength of solidified body;Na2CO3,Na2SiO3·9H2O due to the low hydrolysis to produce OH-concentration,in addition to the Si-O bond rupture,still can increase the degree of polymerization;Curing temperature increasing,alkali slag hydration products structure does not change obviously.(4)When a single kind of alkali metal compounds is used to excite the slag,there is a problem that the effect of the low temperature is low and the strength of the solidified body is low.Based on the evaluation of the thermodynamic characteristics of hydration reaction,the influence of the activator on the hydration characteristics of the hardened body was discussed,and principle of exciting agent distribution is determined.The results show that the plugging fluid system should achieve better development of 30? curing intensity,and it is necessary to maintain the proper concentration of OH-in the whole reaction process.And there was a better result if[Si04]4-exists.(5)The slag solidified body tends to crack itself at high temperatures,hindering its widespread use as a structural material.Based on the study of the structure and force of the slag solidified body,the microstructure of the mineral composition,by means of Micro-CT nondestructive testing methods,the hydration reaction process and the microstructure of the hydration product have been investigated,and the reasons of cracking of solidified body have been analyzed.It is found that the mineral components and alternating thermal stress in the slag hydration products can induce the micro-cracks in the solidified body.The air intro-duced during the slurry preparation has promoted the further extension of the cracks.(6)In order to meet the needs of different depths,the study on the development of different density plugging fluid strength is studied.The results show that the low temperature and low density system have better early strength of the slurry when using three kinds of ac-tivator to stir the system,.When there are high slag content and high temperature under the maintenance,good result can be got using single stimulant.(7)The results of the study Chongqing gas in Northeast Sichuan and other serious failure wells in the successful industrial experiments to improve the plugging efficiency,re-ducing the number of operations,saving drilling fluid and cement consumption,reducing the cost of plugging operations,forming a plugging new technologySlag as building materials accessories are mainly used for the production of high-strength special cement,the preparation of low hydration heat dam cement to prevent hardening cracking,the waste drilling fluid for surface curing,but all low temperature appli-cation environment.At home and abroad in the 1990s had tried conventional density MTC cementing technology,but because of low strength of this system whose density is 1.3g/cm3,and the happens of solid cracking when temperature is high,difficult to replace cement mate-rials,resulting in the new technology "flash in the pan".The researches of this paper will show the broad application prospects for the integration of slag material self-condensation,drilling fluid condensation,annular mud cake and replacement channeling. |
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