ANALYSIS OF MAIN FACTORS AFFECTED PENETRATION RATE OF DEEP AND ULTRADEEP WELLS

Resulted from unknown geology in deep and ultradeep wells and inaccurate geological prediction, numerous problems encountered during drilling have caused significant decline of penetration rate. The analysis of main factors affected penetration rate in deep and ultradeep wells indicates that:1. the problems resulted from geologic factors and improper wellbore structure affect penetration rate; 2. less choice in available structure and type of large size home made bits precludes from adapting to lithology variation in the deep inter-vals; 3. inadequate mechanlcal power for rock breaking; 4. inadequate hydraulics to remove bottomhole cutting completely; 5. it is force to fan the bottom with less weight on bit for de-viation control in devi8tlon prone area; 6. poor dril1ing fluid property and inadequate borehole cleaning cause wellbore problems; 7. the tight and hard plastic shale in deep formation is dif-fi cult to drilling, resulting in low penetration rateI 8. the drilling equipment for slim hole is not completed, affecting the penetration of deep slim hole.