小井眼环空压耗的室内试验研究

小井眼环空水力学与常规井区别很大。在室内小井眼环空实验架上对小井眼环空压力损失进行了试验研究。模拟环空钻井液返速、钻柱旋转速度、钻柱偏心弯曲程度、钻井液性能和钻具接头等对压耗的影响,取得上千组试验数据。试验结果表明:随环空返速增加,小井眼环空压耗增加很快;在转速较低时随转速增加压耗反而有所下降,但下降幅度很小,在转速较高时钻柱旋转时压耗的影响很大;随偏心度增大,环空压耗降低;随环空间隙减小,压耗对钻柱旋转变得更为敏感;随钻井液幂律流性指数增加,环空压力损耗增大;随宾汉塑性粘度增加,环空压耗增加;随钻井液密度增加,环空压耗增大;钻具接头对小井眼环空压耗的影响很显著。

LABORATORY STUDY ON PRESSURE IN ANNULAR OF SLIM HOLE

The hydraulics in annular of a slim hole differs greatly with that of a conven- tional borehole. An experimental study on pressure loss in annular of a slim hole was con-ducted with a test rack of annular in slim hole in laboratory. About one thousand sets of data were acquired through simulating the effects upon pressure loss from return velocity of drilling fluid in annular, rotation speed of drill string, eccentric buckling of drill string, drilling fluid property, tool joints and so on. The test results show that the pressure loss in annular of a slim hole increases rapidly as the return velocity in annular increases; but the pressure loss decreases with a small decline as rotation speed increases at a lower rotation speed, and the rotation of drill string affects greatly on the pressure loss at a higher rotation speed; the pressure loss decreases as the eccentricity increases; the pressure loss become more susceptible to rotation of drill string as the annular space gets smaller; the pressure loss in annular increases as the power law flow exponent of drilling fluid increases; the pres-sure loss in annular increases as Bingham plastic viscosity increases; the pressure loss in an-nular increase as the density of drilling fluid increases; and the effect of tool joints on the pressure loss in annular of a slim hole is remarkable.