Innovative Drilling Fluid Design and Rigorous Pre-Well Planning Enable Success in an Extreme HTHP Well

摘要

Drilling in the Qiongdongnan Basin, offshore China’s HainanIsland Province, has often resulted in failure to reach desiredobjectives. Bottomhole temperatures up to 475°F, andpressures requiring mud weights up to 19.5 lbm/gal equivalent,place severe limitations on the performance of drilling fluidsand often contribute in failure to reach the desired drillingobjectives.Well Yacheng 21-1-4 was drilled in this basin with theCOSDC semi-submersible rig Nanhai V and was spudded on27th November 1998. TD of 5,250 meters was attained on 20thMay 1999 where the bottomhole static temperature was 414°Fand the pore pressure was 18.5 lbm/gal equivalent. Logs wererun to bottom without incident with no significant drilling fluidrelated problems and the primary drilling objectives achieved.The success is attributed to innovative, fit-for-purpose drillingfluids and rigorous pre-well planning over a 2-year period priorto the well commencing.The paper describes the holistic approach to drilling fluidengineering for extreme well conditions. The development ofinnovative drilling fluids specific to these well conditions, andthe rigorous laboratory testing necessary to generate detailedengineering guidelines, are described. Large-scale abrasion andpressure tests were also conducted. Modifications made to therig design facilitated the management of drilling fluidproperties at high density with high flow line temperatures. Aportable drilling fluids laboratory, staffed with trainedtechnicians, was installed on the rig to continually pilot testdrilling fluid samples and treatments under simulated downholeconditions. The importance of good communications andglobal technical support networks proved invaluable during thepre-well planning and for the execution phase of extreme hightemperature and high pressure wells drilling.