Recording Boat OBC Subsurface Source Boat Ocean floor Sea level Layer 2 Layer 1 63 Journal of Mining and Geology Vol. 43(1) 2007, pp. 63 – 69 1116-2775 © Nigerian Mining and Geosciences Society (NMGS) - Printed in Nigeria Introduction This paper presents an overview of a standard ocean bottom cable (OBC) seismic technology, a marine seismic data acquisition system that has now been introduced into Nigeria by one of the major multinational companies. This technology is compared with the normal marine seismic data acquisition system using a towed streamer. This is to demonstrate the superiority of the OBC to the traditional streamer method and to show the virtually unlimited advantages of this new method. The OBC data acquisition and processing stages and the concept of multi-sensors, are also discussed. Application of ocean bottom cable as a new tool in offshore 3-D seismic data acquisition C.C. UGBOR, K.M. ONUOHA and L.I. MAMAH Department of Geology, University of Nigeria, Nsukka Abstract The ocean bottom cable (OBC) seismic technology involves the deployment of some multi-sensor cables on the ocean floor to record both the velocity and pressure signals of seismic waves. The OBC method has advantage for obtaining coverage in congested producing fields clustered with platforms, pipelines and drilling rigs. In shallow waters, lakes, bays and rivers where towed source vessel operations are difficult or impossible, the OBC method comes in handy, offering a range of benefits including higher signal bandwidth, high spatial resolution, low noise, minimum down-time, design flexibility and improved near surface resolution. Dynamically positioned recording vessels are connected to several kilometers of cables deployed along pre- determined lines on the ocean floor. Strapped to the cable at regular increments are multi-component (4C) receivers or dual sensors (2C) which detect seismic signals reflected from the subsurface formations. These signals are filtered, amplified, and digitised in remote electronic modules along the cables and telemetered via the cable to a recording vessel. OBC surveys were recently introduced into 3D seismic operations in offshore Niger Delta, Nigeria. The OBC seismic technology is a special type of marine seismic acquisition which involves the laying of the receiver cables on the ocean floor, the multi-component sensors of the receivers being composed of a coupling of a hydrophone and three geophones (Rigsby, et al., 1987; Cafarelli, 1995). Fig. 1 shows a typical OBC arrangement on the ocean floor. During OBC operations, one of the operating vessels, e.g. the recording boat, may be anchored along the line, or be dynamically positioned. With an anchored vessel, it is possible for the anchor to get tangled up and damage the jumper cables. Dynamic positioning, although more Fig. 1. A typical ocean bottom cable operation with vessel afloat and receiver lines on the ocean floor