Wellbore Stabilization Technology of Oil-based Drilling Fluid in Long Horizontal Section of Shale Gas in Changning Block,Sichuan Basin
The shale gas reservoir in Changning block of Sichuan Basin has entered the vertical and three-dimensional development stage,and complex accidents such as wall collapse and pipe sticking occurred frequently in Longyi 14 Sub-bed,Longmaxi Formation,Changning Block.Therefore,based on X-ray diffraction and scanning electron microscopy,the mineral composition and microstructure characteristics of the Longyi14 small layer rock sample were determined,and the mechanism of wellbore instability in this block was revealed.Graphene nanosheets and multistage micron rigid plugging agents were used to optimize the plugging performance of the drilling fluid in the field,and the inhibition of drilling fluid was enhanced by increasing the oil-water ratio and CaCl2 solution concentration.Finally,a strong plugging and strong inhibition anti-collapsing drilling fluid system was established.After the drilling fluid system was applied in the field,there were no complex accidents such as frequent pump pressure increase,top drive clogging and sticking caused by falling blocks.All the friction coefficients were in the medium to low value range,and the average borehole diameter expansion rate in the horizontal section was 4.07%.It shows that the oil-based drilling fluid can effectively strengthen the borehole and reduce friction and drag,and can solve the borehole instability problem of Longmaxi formation shale horizontal well in Changning block.
shale gasborehole stabilityoil-based drilling fluidmicro-nano plugginghorizontal well
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