Slim hole drilling technology used to deepen the ultra-deep well Jianmen-1

Upon the fourth spud-in of the well Jianmen-1,serious and complicated downhole problems occurred in drilling with a 215.9 mm bit.The casing program had to be changed,and the production casing was run ahead of the schedule.The length of the 149.2 mm hole was thus largely increased.So the geologic challenges to be solved before the fourth spud-in were left over to the slim drilling stage.Basically the deepening slim hole is hard to drill,and extremely harder in drilling ultra-deep wells.Therefore for the deepening slim hole drilling on the well Jianmen-1 with the total depth of 7009 m and the slim hole length of 2005.43 m,we adopted technical measures as follows:①to change the poly-sulphonated drilling fluid gradually with the MEG drilling fluid;②to optimize bit selection and drilling parameters;③to use top-drive system;④to adopt composite drill string with the 127mm S135 18° drill pipe at the top,and the 88.9 mm S135 18° drill pipe at the bottom.The drilling work was carried out safely and smoothly,thus valuable experiences have been gained in slim hole drilling.