Depressant replaces mechanical method for removing blockage

A viscosity depressant proved effective for replacing the time consuming mechanical methods for removing heavy oil blockages during the drilling of wells in the Tarim basin of China. The fracture cavernous Ordovician carbonate reservoir in Lunxi oil field in the Tarim basin is a multilayered structure with well-developed fractures or fissures in each layer, containing a highly viscous crude oil. Analysis shows that in Lunxi oil field, mud loss, well kicks, and stuck drilling tools occurred 14 times in 18 oil wells during 199T2005, with a drilling time loss of 873 hr. The drilling crew rotated the pipe to unfreeze the sticking and continued drilling until no mud circulation returned to the surface at 2330. The standpipe pressure (SSP) with the blocked annulus was 17 MPa. problems. The two wells, AA45 and AA701, had boreholes nearly in gage and experience no drilling pipe sticking induced by heavy oil blockage.