EQUIPMENT/ENGINEERING: Q-Marine debuts in North Sea; surveyor moves to equip fleet

Data from a Q-Marine 2D survey shot over the Diana field in the Gulf of Mexico last year delivered frequencies up to 110 Hz, compared with data from an earlier conventional survey with signals up to 60 Hz at the target depth.

WesternGeco is almost at the end of a first full season in the North Sea using its new Q-Marine seismic data acquisition and processing system, deployed from theGeco Topaz. The initial feedback from clients has been encouraging, justifying the faith that the company has displayed in the system throughout its long development.

The first customer for the system in the North Sea was BP. A 3D survey, which is expected to form the baseline for a repeat (4D) survey at some point in the future, was carried out over 200 sq km of ocean using six streamers, each extending 4.5 km behind the vessel. Although too early to make a definite judgment, the results obtained from the early data sets appear to bear out claims of improved clarity of the reservoir seismic images.

The company plans to fit Q-Marine technology to the rest of its fleet as vessels come in for service. The work takes a couple of weeks. The aim is to have two or three more Q-Marine vessels, in addition to theTopaz, operating in the Gulf of Mexico before the end of the year.

Data quality

A series of advances has been made in seismic and related data-processing technology over recent years. The development of 3D and then time-lapse (4D) seismic, plus the introduction of multicomponent surveys, are probably the most notable.

The extra information that these techniques are capable of producing is extremely valuable, since it enables operators to identify drilling targets and to position wells more accurately. However, in order to reap the benefits of the new techniques, improved quality seismic data is required. In practical terms, this means better signal-to-noise ratio over an extended range of frequencies.

WesternGeco worked toward this goal for some years, in an effort to overcome the three main barriers to acquiring high-quality seismic data:

• Variation in sound source and receiver characteristics
• Positioning errors associated with the receiver arrays
• Swell noise produced by wave action on the receivers.

Key features

Q-Marine is the result of the company's efforts. The overall design of the system is such that towed arrays with as many as 4,000 hydrophones attached to up to 20 streamers are possible, providing a maximum of 80,000 channels. The system incorporates a variety of innovative features that, when combined, provide a step-change in the quality of the data that can be collected, including:

• Improved source control
• Receiver sensitivity
• Accurate positioning
• Steerable streamers
• Unique single sensor recording.

Q-Marine is a calibrated single-sensor seismic acquisition system, purpose-built for reservoir applications. Full calibration allows the operator to correct for environmental and any system perturbations, thus delivering high quality data ideally suited to 4D baseline and repeat surveys. Single-sensor recording leads to an increase in the quality of the data and opens the door to a variety of high-end processing possibilities.