Study On Bit Type Series Individual Design For Complex Deep Wells In Qinghai Oilfield

Dongping,Niudong,Zhahaquan block have been discovered in Qaidam Basin in recent years.The depth of most wells in Qinghai oilfield is in the range of 3500⁴000m.Variety of strata were drilled and the lithology and anti-drilling characteristic of formation is complex in three block.Bedrocks in the bottom mostly are igneous and metamorphic rocks,which have high strength,poor drillability and high abrasive property.Besides,the complexity of formation and unreasonable bit selection lead to the drill bit and the formation being drilled does not match,resulting in low drilling rate and short bit life.For that reason,the prediction of igneous anti-drillability and bit selection method were studied.Igneous rock samples acoustic characteristics and mechanical parameters were measured through laboratory core test.By comparison,find that predicting igneous anti-drillability by the anti-drillability parameter prediction model of sedimentary is unaccurate.Through mathematical statistical analysis methods,the anti-drillability parameter prediction model of igneous rock was established.Because of the complexity of formation and variety of anti-drillability parameter and uncertainty of well section,the lithology,drillability value,abrasiveness index and heterogeneity is chosen as formation characteristic parameters.The drilling formations and bits are classified by C-mens clustering method.The best bit is chosen from each type of formation,then the strata-bit standard mode was established.The pre-drilling formation can classified by K-NN pattern recognition method.Finally,the bit selection method based on pattern recognition was established.Based on drilling history data of Dongping,Niudong and Zhahaquan block,the strata-bit standard mode was established and applied in Zhahaquan block.Field application shows that the average amount of single well bit from the previous 11 down to 5;the average rate increased from 6.16m/h to 8.9m/h,increased by 44.4%,while the drilling rate increased from 3.86m/h to 5.03m/h,increased by 36.7%in the N₁ layer under 3000m depth.The drill bit recommended by this method match with formation.The footage and drilling rate of bit has been improved significantly.