论文详情
根据采集方式的不同,随钻地震技术可分为钻头随钻地震和随钻VSP。钻头随钻地震采用钻头破岩时的振动作为震源,能量较弱,信噪比低,在深井、高斜度井、水平井、大位移井、使用PDC钻头、钻遇软岩层等情况下震源信号不佳,近年来应用逐渐减少。而在钻头上方安装水力脉冲冲击器使井底产生脉冲冲击和瞬时负压的方式,可增加震源信号的强度,提高随钻地震信号的信噪比。随钻VSP采用海面气枪震源或地面可控震源、炸药激发,井下地震检波器接收,泥浆脉冲遥测系统实时传输校验炮、初至波数据,实时更新随钻速度、压力模型,提高成像精度。与常规电缆VSP相比,随钻VSP在钻井过程的自然间隙,例如连接钻杆的过程中进行采集,不干扰钻井过程,避免电缆VSP在水平井、高斜度井等的操作风险,降低钻井成本。目前,随钻VSP技术日趋成熟,可实现钻头前准确的速度预测、地层压力预测和精细构造成像,从而预见性地指导钻井过程。针对新探区、钻前地层压力预测风险较大的地区、非常规油气藏、常规电缆VSP部署风险大的地区、复杂油气藏等在高精度构造成像、准确地层压力预测等方面的需求,开展随钻VSP技术应用研究具有现实意义,可降低钻井风险和成本,提高油气勘探开发效益。
Seismic while drilling (SWD) can be divided into two categories,which are drill-bit SWD and vertical seismic profiling (VSP) while drilling respectively in terms of acquisition geometry.Drill-bit SWD takes drill-bit vibrations as source,which leads to low source energy and low SNR.Its application effects are unsatisfactory in deep,high deviated,horizontal,or extended-reach wells and wells drilling with polycrystalline diamond compact (PDC) drill-bit or encountering soft formations,which results in less application in recent years.Downhole impulse percussion and instantaneous negative pressure generated by the hydraulic impulse impactor installed above the drill bit can enhance the intensity of source signal and therefore the SNR of SWD data is improved.VSP while drilling takes air gun in the sea or surface vibroseis or dynamite in land as source.Some downhole geophones and hydrophones record and a high speed mud pulse telemetry system transmits seismic data,checkshots and first arrivals in real time in order to update interval velocity model and pressure model,improving imaging accuracy.Compared with conventional wireline VSP,VSP while drilling are conducted during natural pauses of drilling process.For instance,data acquisition is carried out during pipe connection times without interfering with drilling process,which avoids operational risks,reduces nonproductive time and drilling costs.VSP while drilling becomes mature internationally,and can accurately predict velocity,pore pressure and elaborately image structures before drill-bit and guides drilling process such as drilling trajectory optimization,casing point location determination,mud weight optimization,etc.Aiming at the requirement of high precision structural imaging and accurate pore pressure prediction for new exploration areas,unconventional reservoirs,complex reservoirs and areas with high risk of pore pressure prediction and VSP operation etc.,we suggest conducting VSP while drilling in above areas in order to reduce drilling risk,costs and improve benefit of oil and gas exploration and development.