高温损伤岩石高压CO_(2)射流PDC齿联合破岩研究

High-Temperature Treated Rock Breaking Study of PDC Teeth Assisting with High Pressure CO_(2) Jetting

欠平衡气体相比传统钻井液钻井技术,可提高机械钻速、减少和避免井漏和压差卡钻事故的发生。欠平衡钻井的井筒多相流及控压钻井工艺研究较为完善,但是围绕油气井欠平衡钻井中的CO_(2)气体射流-PDC齿联合破碎高温岩石问题尚不明确。通过单轴压缩与巴西劈裂试验测试高温损伤后岩石力学特性,然后在高压CO_(2)射流-PDC齿切削破岩试验破岩系统上进行联合破碎高温损伤后岩石试验,研究其破岩规律与切削力变化。力学特性测试试验结果表明,随加热温度的增大,砂岩加热后抗拉强度先减小后陡增,抗压强度先减小再增大。切削力与岩石力学参数相关性分析显示,岩石弹性模量与切削力关联度较强。联合破碎岩石的试验结果表明,高压CO_(2)射流能对岩石进行预打击,且射流强化齿前岩屑运移和齿后岩屑的排出,显著降低切削齿阻力,降低破碎岩石所需的切削力。进一步研究岩石加热温度、射流压力和喷嘴直径等工况参数的影响,当流体压力、喷嘴直径、射流温度分别为20 MPa、2 mm、45℃时,射流对砂岩的打击、携岩效果良好,切削力小,有利于破岩。本研究对指导高温井气体钻井技术和配套钻头研发具有重要指导意义。

Oil and gas resources in deep and ultra-deep strata are taking up an increasing proportion in China's energy development.Underbalanced gas or foam drilling has a better effect,but the problem of rock breakage after high temperature damage in drilling around deep oil and gas wells is particularly prominent.In order to analyze the cutting force of high-temperature rock broken by CO_(2) gas jet and PDC teeth in high-temperature well,the mechanical properties of rock after high-temperature damage were tested by uniaxial compression and Brazil splitting test.The rock test after high temperature damage was carried out on the rock breaking system of high pressure CO_(2) jet and PDC gear cutting.The test results of mechanical properties show that with the increase of heating temperature,the tensile strength of sandstone decreases first and then increases sharply,and the compressive strength decreases first and then increases.The correlation analysis between cutting force and rock mechanical parameters shows that the elastic modulus of rock has strong correlation with cutting force.Combined with the experimental results of rock crushing,it is shown that the high pressure CO_(2) jet can pre-strike the rock,and the jet can enhance the cuttings migration before the tooth and the cuttings discharge behind the tooth,which can significantly reduce the resistance of the cutter and reduce the cutting force required for rock crushing.Further study rocks heating temperature,nozzle diameter and jet pressure condition parameters,when the fluid pressure,nozzle diameter and jetting temperature are 20 MPa,2 mm and 45 ℃,respectively,the jet has good impact on sandstone and rock carrying effect,and the cutting force is small,which is conductive to rock breaking.This study has important guiding significance for guiding the gas drilling technology of high temperature wells and the research and development of matching bits.