A Study On The Acoustic Field Characteristics Of Complex Wellbore Using High-Performance Computing

Acoustic logging can inverse wellbore structure and formation lithology by collecting full-waveform data in the wellbore.According to application scenarios,it can be divided into acoustic logging-while-drilling(ALWD),open-hole wireline acoustic logging,and cased-hole acoustic logging.With the development of electronic information technology,the development of acoustic logging tools by logging companies at home and abroad tends to be digital and accurate.New logging tools provide more information,but also increase the difficulty of data processing and interpretation.For example,the ALWD tool is difficult to be strictly centered due to gravity and collar movement,leading to measurement errors.An ultrasonic pitch-catch device can measure compress and shear velocity in the open hole with high resolution,but the relevant technical details need to be further studied.Ultrasonic flexural wave technology can excite Leaky-Lamb modes in the casing,which can detect multi-layer media parameters and evaluate cement bonding quality.However,due to the complex and changeable downhole environment,the current application effect of the technology is not ideal.Considering the above problems,the acoustic field of the complex wellbore is simulated by the finite-difference time-domain(FDTD)method,then its distribution characteristics and propagation laws were studied,which provides a theoretical reference for the optimization of tool design and data processing methods.The main research contents and conclusions are as follows:(1)The GPU parallel algorithm is used to accelerate the 2D and 3D numerical simulation of the wellbore acoustic field based on FDTD,and the algorithm verification and performance analysis are carried out.(2)The acoustic field of dipole ALWD is simulated respectively when the tool is centered and eccentric,and the characteristics of the acoustic field are analyzed qualitatively and quantitatively.It is pointed out that the tool eccentricity can be quantified by the characteristics of the dipole acoustic field.(3)The formation velocity in the open hole is measured by pitch-catch measurement with the oblique incidence of ultrasonic wave.The relative error index is used to evaluate the influence of formation parameters and tool parameters on acoustic velocity logging.The optimum incidence angle and spacing range are determined in the simulated environment.(4)The influence of cased well model parameters and tool position on pitch-catch measurement is studied.The results show that there is a negative linear relationship between the arrival time of the third interface echo(TIE)and annular thickness.The formation scattering dose not affect A₀,and affect P-P mode the least.The critical velocity to distinguish between fast and slow cement is between the phase velocity and group velocity of casing flexural wave.With the linear increase of the eccentricity of the tool,the arrival time of A₀ and TIE linearly decreases,and the amplitude of casing reflection decreases exponentially.Besides,tool tilt may introduce interference mode S₀ and even lead to failure of detection capability.