Using 4C to characterize lithologies and fluids in clastic reservoirs

Abstract

Multicomponent seismic has been around for a long time without gaining widespread acceptance. The potential benefits of having both compressional ( P -wave) and shear ( S -wave) information have never been disputed, but the cost of acquiring and processing the large data volumes has been high and the quality of the S -wave data has sometimes not met expectations. However, recent technological developments in the area of sources, sensors, telemetry, and data processing are making multicomponent data increasingly popular as a way to provide better quality data at lower cost. Although shear information can be accessed through the AVO response of the P -waves, the pure shear ( SS ) mode or the converted shear wave ( PS ) mode provide direct and more accurate information about the shear properties of the subsurface. Getting this improved information about the elastic properties of the subsurface is indeed one of the main reasons for acquiring multicomponent data. There are two major ways of acquiring multicomponent seismic data. Land multicomponent seismic is typically acquired using dedicated vertically and horizontally polarized traction sources to generate downgoing P - and S -wave modes. The seismic can then be recorded as three-component (3-C) or nine-component (9-C) data sets. The latter involves three consecutive 3-C recordings of direct and converted modes by activating each dedicated source mode in turn (i.e., vertical followed by in-line and cross-line horizontal components). Marine multicomponent data, known as 4-C, is acquired using the traditional air-gun sources to generate a pressure wave ( PP ), but the receivers are on the seafloor to record the 3-D vector field. The fourth component is a hydrophone recording the pressure field just like ordinary seismic streamers. By placing three-component geophones on the seafloor, converted shear waves, known as the PS mode, can also be recorded. A propagating wave front will, in addition to …