Abstract: Drilling practice and study show that the surge and swab pressures (SSP) caused by running or pulling a pipe in the wellbore are one of the important causes leading to lost circulation,kicks and other wellbore accidents in the process of oil drilling.So the accurate determination of SSP is the key to controlling pressure balance, preventing possible accidents and thus suc-
ceeding in balanced drilling. With the increasingly widespread use of slim and horizontal hole (SAHH) drilling technology,new methods of determining SSP are urgently needed. This paper presents a new calculation model, in which the rheology of drilling fluid is described by H-B model, to determine the SSP
of SAHHs. A comparison between the test data and predicted results indicates that the model is reliable and has a high level of accuracy, and thus can be used in the design and operation of SAHH.

Key words: surge and swab pressure, slim hole, horizontal hole