Synthesis Of Shale Inhibitors And Evaluation Of Their Effects In Extending Water-based Drilling Fluids In Shale Gas Wells

Water-based drilling fluid is a more economic and environmental technology in the development of shale gas,and how to solve the problem of shale borehole wall instability is the key factor in water-based drilling fluid technology can be widely used in the shale gas development.Shale samples in the research object comes from YanChang area,by means of X-ray diffraction,scanning electron microscopy(sem)the lithology and mineral composition of the shale samples were analyzed,and the mechanism of sidewall instability was discussed in this paper.The results shows that the shale in YanChang has a high amount of clay minerals and large cation exchange capacity which make it has a strong hydration ability,at the same time the shale is density and has mang micro cracks,bond between shale is fragile,these make it much easy to lead to borehole wall issues.Mechanical-chemical coupling effect is obvious,only fully inhibit the hydration of clay and effectively plug the fracture can solve the problem of borehole wall.According to the mechanism treatment agent in drilling fluid and molecular design mechanism,using N,N-dimethyl acrylamide(DMAM),Dimethyl allyl ammonium chloride(DMDAAC)and sodium p-styrenesulfonate(SSS)synthesized a kind of amphoteric ion polymer PDMS for the first time,the synthesis conditions were studied,the molecular weight was tested by gel permeation chromatography,and its structures have been characterized by infrared spectroscopic analysis and nuclear magnetic resonance(NMR).Through the experiments of rock rolling recovery rate and inflation rate,the inhibition effect of PDMS in the mud was evaluated,and by thermogravimetric analysis the influence of temperature on PDMS was studied,the results showed that PDMS has a strong inhibitory and has a certain ability to resist temperature under 300℃.By the studys of PDMS’s influence on clay particle size,clay Zeta potential and the influence on clay crystal layer spacing,the inhibition mechanism of PDMS was studied.lt shows that PDMS can be adsorpted on the surface of clay and compress the electric double layer on the surface,it can partly get into the clay crystal layer and inhibit clay hydration.Through the optimization of drilling fluid,the formula of water-based drilling fluid system with PDMS as inhibitors was established and its performance was evaluated,the results showed that this formula has good rheological property and strong inhibitory and good sealing ability,through the collapse pressure test that the system’s influence on rock collapse pressure is small,the collapse pressure increment is small,which indicate that the formula can be applied to shale gas well drilling practice in yancahng area.