油气井固井水泥混浆段声学特性分析

套管、水泥环、地层3介质的声学特性是影响声波水泥胶结测井结果的关键因素。井下水泥环形成后,分为纯水泥段和水泥浆与隔离液或钻井液的混浆段。以油气井水泥混浆段为主要研究对象,提出利用超声波测试与孔隙度测试等为实验手段,分析了混浆段的声学特性及其形成机理。结果表明:水泥浆含量越低,混浆段凝固时间越长,抗压强度值越小,孔隙度越高,声阻抗值越小,从而CBL声幅曲线值越高;相同测试条件下,相同体积比的水泥浆与钻井液混浆水泥石的孔隙度高于水泥浆与隔离液混浆水泥石的孔隙度,这是前者声速值低于后者声速值的本质因素之一;GYW201隔离液除能更好地改善第一界面与第二界面实际固井质量外,还能得到更好的CBL声幅曲线,具有较好的工程应用前景;掌握混浆段凝固特性、强度特性、声学特性可对工程测井时间的确定和CBL声幅曲线的水泥环声阻抗校正以及固井质量的精细评价提供参考。

Acoustical behaviors of cemented slurry/spacer/drilling fluid section in oil/gas wells

The acoustical behaviors of casing, cement sheath and formation are the key elements affecting the acoustic cement bond log (CBL) results. The cement sheath will include pure cement section and commingled cement slurry/space/drilling fluid section after the cement is set. Taking the commingled section as the study object, using ultra acoustic testing and porosity testing as the experimental methods, we analyze its acoustical behaviors and development mechanism. The results show that the lower the slurry content, the longer the commingled section needs to be set, the smaller the compressive strength, the higher the porosity, and the smaller the acoustic impedance, which will be ultimately reflected by a high acoustic amplitude on the CBL curve. Under the same testing conditions, the porosity of the cement slurry/drilling fluid section is higher than that of the cement slurry/spacer fluid section with the same volumetric ratio, which is one of the essential reasons why the sound velocity in the former is lower than that in the latter. It is also found that besides a better bond quality between the first and the second interface, a better CBL curve will be also achieved by use of the GYW201 spacer, which is proved to have a promising future in field application. A better understanding of the cement setting behavior, the strength behavior and the acoustical behavior of the commingled slurry section will help determine the logging time, correct the acoustic impedance of the cement sheath on the CBL curve, and evaluate the cementing quality exactly.