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.