气体钻井预弯曲钟摆钻具控斜的动力学行为

Dynamic behaviors of deviation control of the prebent pendulum BHA in gas drilling

井斜控制困难一直都是制约气体钻井技术发展的难题之一。为此,在研究带预弯结构的井底光钻铤钻具组合(BHA)动力学行为的基础上,基于拉格朗日方程建立了预弯钟摆BHA的非线性动力学模型,由简支梁静态模型求取钻头上的动态侧向力,进而设计、评价不同结构的预弯钟摆BHA在气体钻井中的控斜能力,并进行了现场验证。研究结果表明:①合理的预弯钟摆BHA在气体钻井中可以提供较大的动态降斜力,从而发挥出很好的降斜效果,当预弯短接弯角为0.75°时,BHA形心运动的最大半径较小,说明0.75°的弯角时BHA具有最佳的稳定性;②当钻头与近钻头稳定器之间为两根钻铤时,BHA的运动稳定性大幅提高,基本上处于井眼中心,这对于井眼质量控制十分有益;③所设计的预弯钟摆BHA在现场应用中能够较好的控制气体钻井井斜。结论认为,预弯钟摆BHA的动力学控制方程能够很好地描述预弯结构的运动特征,所设计的预弯钟摆BHA不仅适用于常规地层,而且在非均质性较强的砾石层钻井中控斜效果也同样显著;该研究成果对于气体钻井低成本控斜技术发展具有很好的推动作用。

Deviation control is always one of the difficulties that restrict the development of gas drilling technology. In this paper, the dynamic behavior of the bottomhole assembly with the prebent structure (i.e., prebent BHA) was studied. Then, the nonlinear dynamic model of prebent BHA was established based on the Lagrange equation and the dynamic lateral force on the bit was calculated in the simple- beam quasi-static model. Finally, the deviation control capacity of prebent BHA with different structures in gas drilling was designed, evaluated and verified on site. And the following research results were obtained. First, the reasonable prebent pendulum BHA can provide higher dynamic deviation decreasing capacity in gas drilling so as to realize good deviation decreasing effect. When the bend angle of the prebent nipple is 0.75°, the maximum radius of BHA centroid movement is smaller, which indicates that BHA stability is optimum at the bend angle of 0.75°. Second, when there are two drill collars between the bit and the near-bit stabilizer, BHA's motion stability is improved significantly and it is basically located at the center of the borehole, which is quite beneficial for wellbore quality control. Third, during the field application, the prebent pendulum BHA designed in this paper can well control the well deviation in gas drilling. In conclusion, the dynamic control equation of prebent pendulum BHA can describe the motion characteristics of prebent structures, and the prebent pendulum BHA designed in this paper is not only applicable to conventional strata, but also presents a remarkable deviation control effect in the drilling of gravel strata with stronger heterogeneity. The research results promote the development of the low-cost deviation control technologies in gas drilling.