Borehole Seismic Technology For Reservoir Imaging
Authors: Justice J.H. 
Published: October 2008

ABSTRACT
Borehole seismic imaging technology is rapidly growing in interest and acceptance for use in detailed reservoir analysis. New types of tools developed specifically for borehole seismic use provide increased capabilities for conventional VSP surveys, but open the door to new seismic imaging technologies as well. These include interwell tomographic imaging, interwell reflection profiling and numerous single-well applications. Among the applications of the latter technology, salt flank imaging ranks high as an important future application, particularly in the offshore environment.
In addition, these technologies are finding growing importance in reservoir mapping and delineation and in fluid flow monitoring in EOR applications. When integrated with other widely used reservoir surveillance technologies, borehole seismic imaging technology promises to play an important future role in successful reservoir management both onshore and offshore.

INTRODUCTION
Over the past ten years or so, attention has been increasingly focused on the development of new seismic imaging technologies designed specifically for reservoir surveillance applications. Early work in this field was limited by the lack of tools suitable to support R&D efforts and by limited access to the borehole environment for testing and evaluating new ideas. Gradually, progress has been made in both areas and today new tools are beginning to be available which are suitable to the stringent requirements of borehole seismic imaging
Source, receiver, and recording technologies have all undergone simultaneous development. With support from several of the major oil companies, access to reservoirs has been possible and encouraging reports of success are beginning to be reported. Some of the important areas of application which are beginning to emerge include:Reservoir Delineation/MappingPorosity MappingFluid Saturation MappingFault/Fracture MappingBed ContinuityFluid Flow PathsEOR MonitoringSalt Flank ImagingGas Cap DynamicsGas/Oil Interface

DATA ACQUISITION
Many new tools have been developed, or are being developed for borehole seismic imaging applications. Seismic source tool technologies include:Air Gun (similar to marine)Chemical ExplosiveImplosivePiezoelectricMagnetostrictiveHydraulicSparker
These tools are typically designed to operate in standard cased holes, and in some cases operate from standard wire lines which are readily available. The tools are operated in such a way that there is minimal danger to casing or cement. Generally, energy output is low and bandwidth is high, resulting in good image resolution when high frequencies are not highly attenuated by the formation.
New receiver technologies are being designed so that multiple receiver modules can be operated simultaneously from a single wire line. These "multi-element" units can acquire large quantities of data in short periods of time. As a result, they offer anadvantage over conventional VSP tools, when used or VSP surveys. Some types of multi-element receiver tools in use today include:Digital Locking GeophonesAnalog Locking GeophonesHydrophones
The digital tools typically convert data to digital format down hole and transmit the data in multiplexed format to the surface recording unit.