Study On Sealing Technology Of Shale Micro - Nano - Hole

In the process of drilling horizontal wells in shale formation, Wellbore instability is a difficult problem during drilling operation, as the water sensitivity is not strong in original shale. Shale stability can be achieved by plugging micro and nano aperture,preventing the penetrating of filtrate and minimizing effect of the hydration or the capillary force. Therefore, blocking efficiently has become the hotspot when using water-based drilling fluid in shale, which is also the main content of this paper.Based on the domestic and foreign plugging technology and shale wellbore stability technique research of drilling fluid,researches on the optimization of shale plugging effect evaluation method and plugging agent have been carried out in this paper.Taking the ideal filling and packing as the theoretical basis, according to the influence of conditions including clay content, barite content, particle size in proper proportions, dispersion,structured polymer, temperature,rolling and other factors on the permeability of the mud cake, the final permeability of mud cake reaches4.78X10-4mD. The study established a simulation of shale (ultra low permeability10-3～10-4mD) nano micron pore, crack closure method, evaluation standard screen plugging agent, the plugging mechanism and analysis. Adding nanometer blocking agent optimization of the drilling fluid system (YFD-1), reduce the cake permeability (blocking effect) and the degree of incremental collapse pressure of shale is one one corresponding relation. Cake permeability decreased more, better sealing effect, the smaller the collapse pressure increment. To further validate the mud cake permeability using standard10-4mD as the "core" simulation of nano-micron pores and slits ultra low porosity and low permeability shale formation plugging evaluation method is feasible.On the basis of the geological characteristics of shale of Yanchang oilfield, the zwitterionic polymer drilling fluid system for continental shale gas of Yanchang oilfield has been established.The system captured the merits such as strong inhibition, good sealing performance, good lubricity, rheology and filtration of good soil, anti invasion and anti calcium ability strong salt resistance after adding nanometer blocking agent.