Comprehensive Reservoir Characterization "From Inside and Out" Using High-Fidelity Coupling Techniques and Point Receivers
Authors: Fageraas Bjarte , Behn Phil , Tessman Jon , Williams Marty 
Published: October 2008

Abstract
Permanent ocean-bottom systems have been much discussed over the recent past, but little has been done to prove their value. Image quality, reliability and cost have been issues, especially when compared to traditional streamer acquisition. New sensor technology and processing techniques hold promise for improving reservoir image quality that may justify permanent 4C systems on the ocean bottom and down-hole. Material improvements in vector fidelity from MEMS (Micro-Electro-Mechanical Systems) seismic sensors and innovative sensor de-coupling techniques are showing promising early results. The sensor and de-coupling technique has resulted in data with both lower and higher frequencies than traditional systems and has materially reduced cross-talk onto incorrectchannels. Further engineering assessments show that existing subsea infrastructure technology can serve to provide power and telemetry for these systems enabling long tie-backs and providing reduced cost and improved reliability.

Reservoir characterization and monitoring with 4 Dand four component (4C) seismic
During the past ten years, there has been a dramatic increase in geoscientists' demand for direct access to reservoir properties in order to reduce field development costs and improve development economics. Historically, coarse spatial reservoir models derived from high-resolution borehole-based measurements (logs, pressure, temperature, etc) have limited identification of and access to these properties. To increase accuracy and spatial resolution, it is common to condition property distributions within the models on seismic attributes, thereby providing more integrated and accurate reservoir characterizations.
In the development of reservoir characterization models, geoscientists use the available data to solve for various rock properties. Often, the number of known variables is significantly fewer than desired, requiring assumptions that are sensitive to seismic acquisition and processing parameters. The addition of another measurement, in this case shear wave information, enables more accurate determination of reservoir rock and fluid properties and helps to reduce some of the assumptions required with p-wave only data. As fields mature and enter secondary and tertiary recovery, the need to monitor dynamic reservoir processes such as water floods increases. Close monitoring of these processes enables more accurate prediction of undesirable effects such as water break through.

Streamer-based 4D
Many large, integrated reservoir studies and reservoirsimulations originated in the North Sea where 3D, streameracquired seismic data are both abundant and of reasonably high quality. These surveys are acquired with sophisticated vessels equipped with eight or more streamers, each up to twelve kilometers in length and consisting of a thousand or more channels. Such systems acquire vast amounts of seismic data in a very efficient and cost-effective manner. Streamerbased 4D surveys have successfully identified undrained reservoir segments and are generally agreed to be responsible for incremental production of tens of thousands of barrels per day in the North Sea. 4C / 4D Recently, certain classes of acquisition problems have required the use of ocean bottom seismic (OBS) arrays. These systems commonly consist of a hydrophone and either a single conventional geophone (2C) or a set of three geophones arranged in a mutually orthogonal configuration (4C). The use of both hydrophones and geophones allows the suppression of water borne multiples.