| In conventional drilling operations,the solid particles in the drilling fluid will form a layer of mud cake with uneven thickness on the sidewall rock by deposition,adsorption and filtration during the cycle.The mud cake is loose and porous and is easy to be dissolved by formation fluids(water,oil and gas).This leads to the failure of the second interface of cementing,which seriously affects the exploitation of oil and gas.In conventional cementing operations,physical flushing and chemical removal of mud cake are usually used,but these cleaning are not thorough.In this paper,based on the idea of solidifying mud cake,blast furnace slag(BFS)and carboxyl styrene butadiene latex(XSBRI)were selected as mud cake cementing agent.through a series of modern analysis and testing techniques,the solidification cementation performance and mechanism of mud cake rock interface were studied.The results are as follows:The analysis of the physical and chemical properties of the two binders shows that BFS has potential activity and can destroy its vitreous structure under the action of alkali activator,and the released active substances can react with each other to form gels with certain mechanical strength.XSBRI latex is often used in the toughening of cement stone.The hydroxyl and carboxyl groups on its surface can react with metal cations in the system to form a macromolecular network interwoven structure,which enhances the mechanical properties of the system.The test of the rheological properties of the two kinds of cementing agents shows that they will not affect the fluidity of the drilling fluid in the process of use.These results show that BFS and XSBRI can be applied to the solidification process of mud cake,and provide a theoretical basis for the solidification and cementation of mud cake rock.The compressive strength tests of mud cake under different experimental conditions show that the mechanical properties of mud cake develop well at 60～90℃,and the compressive strength increases with the extension of curing time of mud cake.At the same time,the compound use of BFS and XSBRI as mud cake curing agent can obviously increase the compressive strength of mud cake.The mixed use of XSBRI and BFS at low concentration has a certain synergistic effect on the strength of mud cake,but when the concentration of XSBRI is too high,it will weaken the relationship between hydration products and clay particles,and reduce the strength of mud cake,but the higher the content of BFS,the greater the strength of mud cake.The modern analysis and test of FTIR,XRD,TG and SEM-EDS showed that BFS and XSBRI successfully modified the mud cake and both participated in the solidification process of the mud cake to form hydration products,which connected,filled and covered the cracks,pores and surfaces of the mud cake rock in a network.It is the formation of these hydration products and the interaction among polymers,hydration products and clay particles that improve the cementation strength of the interface between mud cake and mud cake rock.The solidification and cementation mechanism of mud cake rock is analyzed systematically.the study shows that BFS decomposes and releases a large number of active substances under the action of alkali activator.when a part of Ca2+migrates to the rock surface due to the same ion effect,it will first be adsorbed on the surface of rock particles,so that the active material can occur hydration reaction at the interface between mud cake and rock.XSBRI latex further covers the interface between mud cake and rock and reacts with Ca2+,Al3+,Mg2+and their hydration products to form a three-dimensional network structure.On the other hand,the three-dimensional network structure formed by BFS and XSBRI latex and hydration products and the network wrapping,covering and pore filling formed by hydration products can reflect and absorb some of the forces in the breaking process of mud cake,improve the cementation strength of the interface between mud cake and mud cake rock,and realize the integration of mud cake rock.Through the optimization,compounding and evaluation of other functional auxiliaries commonly used in drilling fluid,a set of cementing agent drilling fluid system with good comprehensive performance was established:4%bentonite+8%BFS+1%XSBRI+2%SPNH+0.4%FA367+0.5%graphite+barite powder.After testing the comprehensive properties of the drilling fluid,the results show that the drilling fluid system not only realizes the solidification and cementation of mud cake rock,but also has excellent rheological properties,filtrate loss reduction,temperature and salt tolerance. |
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