抽吸式微取心PDC钻头的研究与应用

常规PDC钻头切削产生的粉状或片状岩屑颗粒不便于地质录井,对此提出了一种新型抽吸式微取心PDC钻头。该抽吸式微取心PDC钻头取消了常规PDC钻头心部的主切削齿,设置特殊的水力结构,使钻头心部在钻进过程中形成一定直径的竖直岩心并适时折断,通过负压抽吸作用将断的微岩心从钻头体内部流道带离井底。结合破岩仿真与液固两相流理论,研究了在岩心、岩屑与钻井液混合流动的流场中,射流喷嘴直径的大小对取心通道中抽吸效果的影响规律。数值模拟结果表明,对于拟定条件下钻头直径为215.9 mm的微取心PDC钻头,当射流喷嘴直径为8 mm时,从排心孔排出的岩心、岩屑和钻井液的质量较高,其负压腔的抽吸效果较好。室内及现场试验表明:采集的岩心以柱状为主,岩心完整性和采集率高;在磨溪111井位嘉陵江组二段3亚段至长兴组上部地层,获总进尺805.65 m,平均机械钻速为4.57 m/h,最高机械钻速可达7.4 m/h;该钻头在嘉陵江组二段3亚段至飞仙关组一段(总进尺742 m)的机械钻速比该区块同层位的其他常规PDC钻头高出了50%以上。

Research and application of suction-type micro coring PDC drill bit

The powder or schistose rock particles produced by the cutting of conventional PDC drill bit are not conductive to geological logging. Accordingly, a new suction-type micro coring PDC drill bit was presented. The new PDC drill bit removes the main cutters in the center of the PDC drill bit where vertical cores with a certain diameter are generated and then broken in a timely manner during drilling. Based on a special hydraulic design, under the action of negative pressure, the broken cores are sucked from the bottom of the well through the internal coring channel of the bit. Based on the theories of rock breaking simulation and liquid-solid two-phase flow, the influence laws of the jet nozzle diameter on the suction effect in core channel were studied in the field of mixed flows with cores, rock cuttings and drilling fluid. The numerical simulation results show that when the jet nozzle diameter of 8 mm is assembled in the micro coring PDC drill bit with 215.9 mm bit diameter under certain conditions, the mass of cores, rock cuttings and drilling fluid exhausted from discharge core hole is the highest, showing the optimal suction effect of negative pressure chamber. Indoor and field tests show that the collected cores are mainly columnar with high core integrity and collection rate. From Jiaer³ to the upper of Changxing at Well Moxi 111, the total footage is 805.65 m, the average rate of penetration is 4.57 m/h, the highest rate of penetration is 7.4 m/h and the rate of penetration from Jiaer³ to Feiyi (total footage of 742 m) is higher than other horizons in the same block by 50% and above.