| Cementing operation is an important link to oil-gas well construction，and that is alsoclosely related with the oil rational development and long-term production. Now, most of theoil fields in china evaluate cementing quality by acoustic amplitude log.In the process of sound waves，as the different absorption capacity of acoustic wave fordifferent medium，acoustic amplitude value which obtained from acoustic amplitude log isaffected by many factors. This led to the acoustic amplitude logging curve reflects often notonly the cementing quality，but also includes other factors. The affect of these factors onacoustic logging curve will often impact the accuracy of the cementing quality evaluate. Inthis paper，the microannulus parameters are selected to study it’s influence extent for acousticamplitude logging.In this paper，the calculating model of microannulus size is established, and throughcalculating the microannulus size of the model, the change of the microannulus size whichare produced by casing internal pressure will not cause the free flow of fluid in the annulus，not impact on cementing of cementing quality. In this paper, through analyzing the acousticpropagation path, mechanism of acoustic propagation in medium is researched，in view ofacoustic amplitude logging problem，the model of layered medium is established，expressionof relative acoustic intensity in each interface in this two conditions is deduced, and theacoustic ratio of the existence of the micro-annulus to good cement that got from receiver isobtained, through this expression to quantify the impact of the acoustic logging curve to themicroannulus amplitude. Through the calculation of example found when the medium ofmicroannulus is water, the acoustic amplitude was46.6%higher, when the microannulus ismud, the acoustic amplitude was30%higher than good cement condition. Mud and cementsheath impacts the microannulus influence extent: the smaller acoustic impedance of the mud,the more the effect of the microannulus on the acoustic amplitude log; the smaller acousticimpedance of the cement sheath, the less the effect of the microannulus on the acousticamplitude log. The correction factor of micro-annulus of acoustic logging curve is proposed,to improve the cementing quality evaluation precision. Calculated microannulus influenceextent for an actual example, and amend the affect of microannulus for using acoustic loggingcurve to evaluate cement job quality. |
