钻井液流态对孔壁稳定性的影响

摘要

The borehole wall stability is closely related to drilling fluid flow pattern in sedimentary strata, this pa-per combined a 2386m salt drilling project in Yewu sag basin, conducted the experiment in different depth with different pump discharge and return velocity. The result shows: in water sensitive formation (clay, mudstone, sandy shale etc.) with shallow rock porosity and high plasticity index, in the drilling fluid laminar flow conditions, the maximum diameter shrinkage rate was 26.6%, in middle and deep formation, in the turbulent flow conditions, borehole shrinkage and oversized exit exist in same time. With the depth increased, diameter shrinkage rate tends to decrease; the ratio of oversized diameter increases with borehole depth. In mudstone formation, the maximum di-ameter oversized rate is up to 157.4%, in salt rock formation, the maximum diameter oversized rate is 225.7%. This paper aiming at these problems conducts the theoretical analysis and research, and gives the detail suggestions.%　　沉积地层中孔壁的稳定性与钻井液流态有着密切关系。结合河南叶舞凹陷盆地2386 m 盐矿钻探工程，采用不同的泵量和上返流速在不同孔段进行了钻探试验。试验和理论计算表明：在水敏性地层(黏土、泥岩、砂质泥岩等)浅层岩石孔隙率和塑性指数较高时，在钻井液层流流态情况下，主要以缩径为主，最大缩径率达26.6%；中部和深部同等地层，在紊流流态情况下，缩径和超径同时存在。其中，随着孔深的增加，缩径率呈减小趋势，超径率则有增大趋势，泥岩地层最大超径率达157.4%，盐岩地层超径率高达225.7%。