基于振动实测的非均质地层钻头失效分析与对策

四川盆地作为国内页岩气开发的重点区域,通过近几年的不断攻关和实践,机械钻速得到了提高,但由于受地层复杂、可钻性差、非均质性强等地质因素的影响,导致井下钻柱系统不良振动剧烈,容易出现钻头损坏严重、钻速较低等问题,严重影响了钻井时效。为了解决上述难题,以该盆地涪陵工区上二叠统龙潭组—中二叠统茅口组为例,采用井下振动高频测量工具的实测手段,测量了钻头—钻柱系统的动态振动加速度参数,结合地层的岩性和矿物组分分析,研究钻头失效原因与对策,并开展了现场试验。研究结果表明:①在非均质地层中钻进的钻头—钻柱系统产生了大于40 m/s~2的高幅值瞬时冲击振动,高幅值的瞬时冲击是导致钻头先期失效的主要原因;②提出了抑制高幅值的瞬时冲击振动采用"减振+增压"工具组合和避免井下工具共振的钻井参数;③采用钻井新参数的试验井比邻井的高幅值瞬时振动降低了17%,单只钻头进尺增加24%,钻头工作环境得到了较大的改善,钻头使用数量减少。结论认为,该研究成果能够有效地改善钻头—钻柱系统的振动状态,有利于达成延长钻头使用寿命的目标。

Analysis of and countermeasure for bit failures in heterogeneous strata based on vibration measurement

In the Sichuan Basin, an important area of shale gas development in China, the rate of penetration (ROP) has been improved after constant researches and practices in recent years. Under the effect of geological factors of complex harsh strata (e.g. poor drillability and strong heterogeneity), however, the improper vibration of a downhole drilling string system is violent and serious bit damage and low ROP tend to occur easily, so the drilling time efficiency will be seriously impacted. In order to solve these problems, this paper took the Upper Permian Longtan Formation–Middle Permian Maokou Formation in the Fuling working area of the Sichuan Basin as an example. The dynamic vibration acceleration parameters of a drilling bit–string system were measured using the high-frequency downhole vibration measurement tool. Then, combined with the analysis on the lithology and the mineral component of the strata, the causes of and countermeasures for bit failures were studied. Finally, field experiments were carried out. And the following research results were obtained. First, in drilling the heterogeneous strata, the drilling bit–string system generates a high-amplitude instantaneous shock vibration greater than 40 m/s2, which is just the main reason for early bit failures. Second, the "vibration damping + pressure boost" drilling assembly is recommended for inhibiting the high-amplitude instantaneous shock vibration, so are the drilling parameters for avoiding tool resonance. Third, compared with a neighboring well, the test well adopting the new drilling parameters is 17% lower in the high-amplitude instantaneous shock and 24% higher in the single-bit footage. And thus the operation environment of the drilling bit is improved and the number of used drilling bits is decreased. In conclusion, the research results can effectively improve the vibration state of a drilling bit–string system and is conducive to reaching the target of extending the service life of a drilling bit.