STUDIES ON SLANTING CONTROL FAST DRILLING BHA IN THE OVERTHRUST NAPPE FORMATION

Conventional pendulum drill-assembly is not efficient enough in drilling the over - thrust nappe formation which is slant and hard and causes such problems as bit jumping and drill tool friction; while only light WOB could be applied when drilling the hard formation which severely limits the penetration rate and adds up to the drilling cost. This paper focuses on the experimental application of several drill - assemblies when drilling the ?311 mm hole in the over- thrust nappe in Well Qiong-9, specifically these assemblies are angle-holding assembly with multiple stabilizers and MWD plus steerable drill, eccentric drill and suspended drilling. Results show that all the three assemblies can improve ROP by applying high WOB, however, hole deviation control remains a problem. Possible causes of poor deviation control are analyzed and eccentric drill should be used; it is also an ideal alternative to drill directional well and extended reach well by taking the advantage of the natural slanting tendency in such formation.