PDC混合布齿钻头破碎非均质花岗岩数值模拟

Numerical simulation of breaking heterogeneous granite with PDC mixed-tooth bits

非常规油气资源所处地层复杂,开采难度大,钻井过程中钻遇地层密实度高,对钻头性能提出了更高要求。普通PDC钻头主要依靠切削齿剪切破碎岩石,攻击性弱,不仅导致钻头寿命和破岩效率严重下降,而且增加了钻井成本。为探究混合布齿PDC钻头的破岩机理和效果,提升PDC钻头破岩效率和寿命,建立了非均质花岗岩模型,使用有限元方法对比了斧形、三棱形和圆形PDC齿混合布齿的破岩效果,优选了最佳布齿方案,并使用响应面法优化了齿间距,对前后排齿不同高度差情况下的钻头破岩效果及规律进行了分析,最后结合钻头的现场应用对比分析了混合布齿、斧形齿和三棱形齿PDC钻头的破岩过程。研究结果表明:①斧形齿攻击性强,有利于吃入岩石,适用于刀翼前排,而三棱形齿更稳定,适用于刀翼后排;②混合布齿最佳方案为前排斧形齿,后排三棱形齿与斧形齿交替布置,后排齿距离前排齿的最佳横向距离为10.0 mm、10.1 mm,最佳纵向距离均为7.0 mm;③前排齿破岩后能释放岩石内应力,便于后排齿的破岩,但产生的应力区域有限,建议前后排齿高度差不超过1 mm;④围压条件下按照最佳方案布齿的PDC钻头相较于单斧形齿和三棱形齿的PDC钻头,钻井进尺分别提升了21.4%和44.1%。结论认为,混合布齿钻头兼具高破岩效率和稳定性,在深部和难钻地层具有较好的钻进效果,具有良好的现场推广应用价值。

Unconventional oil and gas resources have complicated stratigraphic conditions,which bring great difficulties to their exploitation.In the process of exploiting unconventional oil and gas resources,the encountered dense strata have stricter requirement for the performance of drill bit.Conventional PDC bit mainly makes use of cutting teeth to cut and break rocks,producing weak aggressiveness,which not only decreases its lifespan and rock breaking efficiency greatly,but also increases drilling costs.To clarify the rock breaking mechanisms and effects of the PDC mixed-tooth bit and improve its rock breaking efficiency and lifespan,this paper establishes a heterogeneous granite model,compares the rock breaking effects of mixed cutter arrangement of axe-shaped,triangular,and circular PDC cutters using the finite element method,and selects the optimal cutter arrangement scheme.Then,the space between cutters is optimized using the response surface method,and the rock breaking effects and patterns of bits with different height differences between the front and rear rows of cutters are analyzed.Finally,the rock breaking processes of PDC bits with mixed cutters,axe-shaped cutters,and triangular cutters are comparatively analyzed based on field application.And the following research results are obtained.First,axe-shaped cutters possess stronger aggressiveness,facilitating the penetration into rocks,so they shall be arranged in the front row of the blade,while triangular cutters are more stable,so they are applicable in the rear row.Second,the optimal mixed cutter layout consists of axe-shaped cutters in the front row and triangular cutters alternating with axe-shaped cutters in the rear row.The optimal lateral distance from the rear-row triangular and axe-shaped cutters to the front-row axe-shaped cutters are 10.0 mm and 10.1 mm,respectively,and the optimal longitudinal distance is 7.0 mm.Third,after the rock breaking of the front-row cutters,the stress inside the rock can be released,which facilitates the rear-row cutters to break rocks,but the generated stress zone is limited,so it is recommended to keep the height difference between the front and the rear rows of cutters within 1 mm.Fourth,compared with the PDC bits with only axeshaped cutters or triangular cutters,the PDC bit with the optimal mixed cutter arrangement increase the drilling footage by 21.4%and 44.1%,respectively under confining pressure.In conclusion,the drill bit with mixed cutter arrangement can achieve a high rock breaking efficiency and stability and realize a favorable drilling effect in deep and hard-to-be-drilled strata,so it is worth promoting and applying practically.