Contribution of Seismic and Acoustic Methods to Reservoir Model Building

Abstract

The seismic reflection method has the advantage of providing a picture of the subsurface in three dimensions (3D) with a regular grid. In high resolution seismic surveys, the size of the grid cell is of the order of tens of meters for horizontal distances, and of several meters for vertical distances. The initial success of the seismic reflection method was solely linked to structural interpretation: it only recognized geometric shapes, regardless of the content. Stratigraphic interpretation permitted a deeper understanding of seismic data. To be validated, seismic data must be tied to wells. The tying and calibration of seismic data are carried out with the use of geophysical measurements in wells. Well measurements are seismic data such as vertical seismic profiles (VSP) with a resolution comparable to that of seismic reflection and log data with a vertical resolution ranging from tens of centimetres to several meters. Acoustic logs establish the link between seismic data (surface and wells) and other logs. The acoustic log has the vertical resolution of the other logs (electric, nuclear, etc) but obeys the same propagation laws as the seismic methods, although it operates in a different frequency bandwidth. The purpose of this chapter is to show the contribution of seismic and acoustic methods to reservoir model building. After a description of the geophysical methods (acoustic logging and reflection seismics), we show, with field examples, how the geophysical data have been recorded and processed to estimate porosity and hydraulic conductivity of the studied geological formations.