The dense geometry of a 3D VSP survey which was carried out in an oilfield located in the Emirate of Abu Dhabi, United Arab Emirates, enables us to perform high resolution azimuthal study of seismic wave attenuation, in order to investigate a fractured reservoir in the oilfield. We obtained the orientation of fractures in three reservoir units by using the concept suggesting that the strike direction of fractures corresponds to the azimuth of the minimum attenuation . We defined as the azimuth of the minimum attenuation that we estimated at several azimuths and offsets by using the spectral ratio method. The rose diagrams gathering obtained at several offsets, are in agreement with those gathering the strike direction of open and cemented fractures, obtained from cores interpretation. This is due to the fact that the attenuation is caused by a combination of scattering and fluid-related mechanisms. It is physical evidence that fractures, regardless their type, are an important source of scattering mechanism, and also of fluid-related mechanisms if they are open. Another way to define is by using a cosine least square fitting of azimuthal variation of the relative attenuation , that we estimated at several azimuths and offsets by using a modified spectral ratio method. In this case, the rose diagrams gathering defined at several offsets, are in agreement with those gathering strike direction of open fractures obtained from cores and Full-bore Formation Microimager interpretation. This agreement is due to the fact that the cosine least square fitting is based on the squirt flow mechanism that is caused by fluid movement between grain pores and fractures. Accordingly, comparison between the rose diagrams of estimated by using the two approaches, can be a good way to separate between open and cemented fractures. Such, finding is very interesting for petroleum industry and can help in Enhanced Oil Recovery (EOR) studies.
Presentation Date: Monday, September 16, 2019
Session Start Time: 1:50 PM
Presentation Time: 3:55 PM
Presentation Type: Oral