The Evaluation Method And Optimization Of Shale Nano-micron Plugging Agent

As an unconventional energy source,shale gas has been paid more and more attention due to its high gas content,stable gas production rate and long production cycle.Due to the development of natural micro-fractures,the shale is mainly composed of clay minerals in the Yi/Meng mixed layer,which is brittle and has developed bedding.During drilling,the shale cleavage and pore pressure near the borehole wall are increased due to the invasion of drilling fluid filtrate,which leads to wellbore instability.Therefore,this paper has carried on the Shale nano-micron pore gap plugging evaluation method and the shale pore gap size matching nano-micron plugging agent research and development,so as to solve the problem of shale gas drilling wellbore instability.In this paper,the mechanism of Shale wellbore instability,plugging theory and research status of nano-micron plugging agents were investigated.In this paper,the wellbore instability in shale is analyzed,and it is concluded that the drilling fluid plugging ability is an important factor in addition to the mechanical effect,finally,combined with the physical and chemical properties of Shale,it is concluded that the size of solid particles in oil-based drilling fluid is too large to effectively seal the nano-micron pores of Shale,the size mismatch of the particles causes the drilling fluid filtrate to invade the Shale mixing zone and cause the wellbore to collapse.In this paper,two kinds of nanoscale plugging agents NA-1 and NA-2 were synthesized by semi-continuous seed emulsion method and batch method respectively,which were composed of inorganic silicon dioxide and organic acrylate.The optimal synthesis temperature of NA-1 is 79?,p H is 6,drop rate is 0.3g/min,D₉₀value of NA-1 particle size distribution is 0.1305?m,and the optimal synthesis temperature of NA-2 is 80?,Ph is 6,the drop rate was 0.3g/min,and the D₉₀value of NA-1 particle size distribution is 0.1482?m.The effects of nano-micron materials on the rheology,lubricity and HTHP loss of oil-based drilling fluids are evaluated,and a low permeability core displacement method is established to evaluate the plugging ability of oil-based drilling fluids,the results showed that the plugging efficiency reached84.18%,and the breakthrough pressure exceeded 35 MPa,and the plugging efficiency was close to 100%after NA-1 treatment.The strong plugging oil-based drilling fluid formed by this plugging agent has been successfully applied in well Ning 209H19-5 with regular well diameter,no block dropping during drilling in horizontal section,and no downhole accident occurred when the Rotary steering is taken out safely.It is expected to be popularized and applied in this area.