一种适用于超高温超高压塑性泥岩的V形齿PDC钻头

A V-cutter PDC bit suitable for ultra-HTHP plastic mudstones

高密度钻井液静液柱压力和深部围压对近井区域形成的压持效应导致近井底区域泥岩呈现强硬塑性力学特征,钻头难以吃入、钻速较慢,同时还有可能因此诱发其他井下复杂情况,增加了钻完井成本。为了给深部塑性地层个性化PDC钻头的研制提供理论与技术支撑,以南海西部莺琼盆地超高温高压巨厚泥岩为例,基于塑性泥岩的岩石力学实验,选择D-P岩石强度准则并确定了本构模型力学参数,并据此进行了PDC钻头齿组切削泥岩的数值模拟。研究结果表明:①通过对比V形齿齿组、脊形齿齿组和平面齿齿组破碎泥岩的力学机理,V形齿齿组较脊形齿齿组和平面齿齿组对该塑性泥岩攻击性更强、破碎效率更高;②在保证钻头抗磨性能的前提下,采用较小的后倾角和较大的齿组间距能够在高温高压塑性泥岩中取得更高的破岩效率;③研制出的V形齿个性化PDC钻头在现场应用中平均机械钻速为20.99 m/h,约为邻井常规PDC钻头的2.52倍,大幅度提升了该层段的机械钻速,出井钻头基体完整,内外锥部分均未出现明显严重破坏,仍可以继续使用。结论认为,该研究成果为莺琼盆地深部塑性泥岩层的高效钻井提供了理论与技术支撑。

Due to the pressure holding effect generated near the wellbore by hydrostatic column pressure and deep confining pressure of high-density drilling fluid,the mechanical characteristics of strong plasticity appear in the mudstone near the bottom hole,which makes it difficult for the bit to penetrate in the strata and slows down the rate of penetration(ROP).Moreover,it may induce other downhole troubles so as to increase the drilling and completion costs.In order to provide theoretical and technical support for the research and development of an individualized PDC bit suitable for deep plastic strata,this paper takes the massive mudstone of ultra high temperature and high pressure(HTHP)in the Yingqiong Basin of western South China Sea as an example to select the D-P criterion and determine the mechanical parameters of constitutive model based on the rock mechanical experiment of plastic mudstone.Then,the cutter group of PDC bit cutting mudstone was numerically simulated.And the following research results were obtained.First,it is shown by comparing the mechanical mechanism of V-shaped,ridge and plane cutter groups to break mudstone that the V-shaped cutter group is more aggressive to the plastic mudstone and has a higher breaking efficiency than the ridge cutter group and the plane cutter group.Second,on the premise of ensuring bit's anti-wear performance,the application of smaller back rake angle and larger cutter group spacing can provide higher rock breaking efficiencies in HTHP plastic mudstone.Third,when the newly developed V-cutter individualized PDC bit is applied on site,the average ROP is up to 20.99 m/h,about 2.52 times that of the conventional PDC bit in the adjacent well.Obviously,the ROP in this interval is improved greatly.When the bit is pulled out of the hole,its matrix is complete,and the inner and outer cone parts are not seriously damaged,so it could still be used.In conclusion,the research results can provide theoretical and technical support for the efficient drilling in the deep plastic mudstone of the Yingqiong Basin.