Study On Water-based Drilling Fluid System For New Type Of High Efficiency Shale Gas

Shale gas,as a national emerging strategic industry,has been developed on a preliminary scale in Fuling,Changning-Weiyuan and Zhaotong shale fields.At present,oil based drilling fluid is mainly used in the horizontal section of shale gas drilling.However,with the enforcement of environmental laws and regulations and the awareness of environmental protection deeply rooted in people,shale gas water based drilling fluid has gradually become the focus of attention.When shale gas horizontal wells are drilled with conventional water-based drilling fluid,the use of conventional water-based drilling fluids is seriously restricted because of its insufficient inhibition,poor plugging performance and insufficient lubricity.Therefore,it is necessary to study the water based drilling fluid system of shale gas,so as to be suitable for horizontal shale drilling and make the development of shale gas more safe,high quality and high efficiency.In this paper,the development of shale gas development and shale gas base drilling fluid at home and abroad are analyzed.In view of the environmental problems of oil based drilling fluid and the shortage of KCl polymer anti collapse drilling fluid in the mud shale horizontal well drilling in the block of Fuling Jiao Shi dam area,I selected outcrop shale of Longmaxi-Wufeng formation of Fuling Jiaoshiba as the research object,and carried out the research of new high efficient water-based drilling fluid inhibitor,filtration plugging agent and lubricant,etc,and selected and evaluated the new type of high efficiency water-based drilling fluid.According to the mechanism of inhibition,filtrate loss and lubrication,compared with the current inhibitors used in shale gas water based drilling fluid,KCl and HCOONa as inhibitors,CMC-LV as a stabilizer and AB-201 as a high temperature stabilizer,a new type of high efficient water based drilling fluid system has been developed through a large number of experimental studies.System formulation:water+0.6%bentonite+1%NaOH+0.8%HZ-01（CMC-LV）+5%HW-01（AB-201）+5%HZ-02（SMP-II）+7%HJ-01（JNJS）+6%HR-01（JNJS）+2%HR-03（YH-8）+8%HR-02（anti-card lubricants）+2%emulsifier+2%superfineCaCO₃+12%KCl+11%HCOONa+barite.The results show that the system can meet the requirements of shale gas horizontal well drilling in terms of inhibition,plugging and lubricity.The inhibition effect of the system is similar to that of oil-base drilling fluid,and is superior to that of conventional water-based drilling fluid.The expansion rate and rolling recovery of Longmaxi-Wufeng outcrop shale are 5.12%and 100%respectively;A strong plugging system combined with"rigid particle plastic particle"has the same plugging effect as oil based drilling fluid and is superior to conventional water-based drilling fluid.The loss of water at room temperature and middle pressure is even lower than that of oil based drilling fluid,in which FL_API is 1.4 ml,FL_HTHP is 4.2 ml,and mud cake is thin and compact;The lubricating effect of high efficiency lubricant composed of anti-card lubricant and emulsifier is better than that of conventional water-based drilling fluid.The friction coefficient of the system is 0.14.The results show that the system has good aggravation performance,anti-fouling performance and thermal stability on the basis of strong inhibition,strong plugging and good lubricity.The system has good rheological and filtration properties at the density range of 1.2g/cm³、1.35g/cm³、1.5g/cm³、1.7g/cm³,and the slurry performance is stable.When the system density is 1.5g/cm³,the AV is 66mPa·S、PV is 58 mPa·S、YP is 8.2Pa、FL_API is 1.4ml、FL_HTHP is 4.8ml;After the 8%NaCl and 8%cuttings were invaded,the rheological properties and filtration properties of the system had no obvious change,but still had good rheological properties and filtration properties;And the viscosity of the system decreased slightly after aging at 130℃,and the water loss did not change obviously,still maintain good rheological and filtration performance.The results show that the new high efficiency water-based drilling fluid not only solves the environmental protection problem of oil based drilling fluid in horizontal shale formation drilling,but also overcomes the shortage of conventional water-based drilling fluid.Moreover,it can meet the requirements of horizontal shale formation drilling and provide regional environmental security for shale gas development.