Application Of Open Hole Acoustic Amplitude Measurements

Publication Rights Reserved This paper is to be presented at the 36th Annual Fall Meeting of the Society of Petroleum Engineers of AIME in Dallas October 8–11, 1961, and is considered the property of the Society of Petroleum Engineers. Permission to publish is hereby restricted to an abstract of not more than 300 words, with no illustrations, unless the paper is specifically released to the press by the Editor of JOURNAL OF PETROLEUM TECHNOLOGY or the Executive Secretary. Such abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in JOURNAL OF PETROLEUM TECHNOLOGY or SOCIETY OF PETROLEUM ENGINEERS JOURNAL is granted on request, providing proper credit is given that publication and the original presentation of the paper. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and considered for publication in one of the two SPE magazines with the paper. In acoustic velocity logging the phenomena of cycle skipping has been used to indicate the presence of fractures, etc. Since the cycle skips of interest are the result of attenuation of the acoustic signal, a measurement of formation amplitude is a more positive means for this purpose. In the field of acoustic bond logging the amplitude of the formation signal depends to a great extent upon the quality of bonding of cement to pipe and formation. By comparing the open hole acoustic amplitude to that in cased hole, the over-all effectiveness of the cement job may be more clearly distinguished. Test well data is included to show the degree of attenuation of the acoustic signal at solid, liquid interfaces as would be present in fractured formations. Field examples of this and other applications of amplitude measurement are included to illustrate the effectiveness of the application. Introduction In the past there has been some use of acoustic velocity logs for the location of natural formation fractures and shallow gas sands by the presence of cycle skips on the log. This cycle skipping is the result of the amplitude of the acoustic signal being reduced to the extent that the trigger skips over to a later pulse of the signal. In fractured formations this reduction in signal amplitude is caused by the large reflection of energy and lower transmission at any interface where there is a large density change such as from limestone to water or oil, thus there is a lower signal amplitude at the receiver than if the fractures were not present.