The Shale Nano Water-based Drilling Fluid System In Jiaoshiba Area

There are abundant reserves in Jiaoshiba shale gas field which has cheerful prosp ect.However,accidents such as collapse and leakage always happened in filed.To mee t the demand for cost-effective drilling and environmental protection,a drilling fluid sys tem with strong inhibition and plugging shale formation effectively need to be develop ed.This is also the core content of the paper.Firstly,mechanism of borehole wall instability and the technical countermeasures of drilling fluid was studied according to basic geological conditions,composition and physical and chemical properties of rock in Longmaxi formation.It was found that the development of bedding and cracks by which aqueous phase can easily invade format ion is the main reason of water wedge and water-rock interaction.Then,the species and dosage of inhibitor were filtrated through cuttings roller recovery,line swelling,partic le size analysis,mud-making and mud ball soaking experiment.Thereout,inhibitory based drilling fluid system was established preliminarily.Based on the mechanism of agglom eration and dispersion of nanomaterials,three kinds of single-dose nanometer blocking agent were obtained by optimizing dispersal conditions.Meanwhile,a new method was built with existing equipment and common material at low cost and good repeatability.Two kinds of mixed nanometer blocking agent were choosed by this method including A(4%NCC40+3%NM80+0.6%polyacrylamide+0.8%WDG)and B(2%ND-1+3%NM80+0.6%polyacrylamide+0.8%WDG+0.5%calgon).Finally,the water-based drilling fluid system was eastablished after matching inhibit ory based drilling fluid system and mixed nanometer blocking agent as previously me ntioned.The formula of final system turned out to be:water+1.5%SM-1+0.5%FV-5+60%KCOOH+3.5%JT888+0.05%CaO+0.05%XY27+5%CaCO3+5%PEG+blocking agent A+2%RH-220.The system possessed strong inhibitory,good rheological properties,excellen t wall building properties.Furthermore,it was able to plug shale formation effectively w hile caused low increment of the collapse pressure.