New Marine Towed-streamer Acquisition Technology
Authors: Ozdemir Kemal , Vassallo Massimiliano , Eggenberger Kurt , Zeroug Smaine , Robertsson Johan O. , Ozbek Ali , van Manen Dirk-Jan 
Published: May 2013

Two of the main limiting factors in seismic resolution for marine towed-streamer acquisition are the ghost effect and sparse crossline sampling of the streamers. The ghost is the reflection from the sea surface that interferes constructively or destructively with the primary reflections, reducing the seismic bandwidth at the low and high ends of the spectrum. Acquisition and processing solutions to address the receiver ghost problem were introduced in early 1980s and again in the last five years; these are:Slant streamer (Ray and Moore, 1982)Over/under streamers (Sønneland, et al., 1986)Hydrophone-vertical geophone streamers (Carlson, et al., 2007)Variable receiver depth acquisition and processing (Soubaras, 2010; Moldoveanu, et al., 2012)

These solutions address only the temporal resolution by attenuating the receiver notch. A new towed-streamer technology based on multimeasurement acquisition was introduced in 2012 that addresses both temporal and spatial resolution.

The concept of multimeasurement towed streamers was introduced by Robertsson et al. (2008). The system measures pressure with hydrophones and particle acceleration in crossline and vertical directions with accelerometers. As the pressure gradient can be derived from acceleration, the multimeasurement streamers provide measurements of pressure and gradient of pressure in two directions. Based on these measurements, wavefield separation of upgoing and downgoing components can be performed simultaneously with crossline wavefield reconstruction (Özbek et al., 2010). The multimeasurement system enables one to calculate the 3D upgoing wavefield at any desired position within the spread, for instance, a densely sampled grid of 6.25 m × 6.25 m, and this allows improving not only the temporal bandwidth, but also the spatial bandwidth. Multisensor streamers can be deployed at larger depths and this improves low-frequency content, signal-to-noise ratio due to reduced swell noise, and acquisition efficiency. Operational efficiency can be further improved by using multimeasurement towed-streamer data to detect and eliminate seismic interferences (Vassallo et al., 2012). Seismic modeling and feasibility studies were conducted to prove that this new marine acquisition technology performs as expected, and commercial seismic surveying has already been performed with the new system.

Introduction

Conventional towed marine seismic data acquisition systems capable of measuring the pressure wavefield associated with seismic source-driven subsurface scattering have provided for an effective method of acquiring high volumes of subsurface data offshore. However, due to logistical and cost constraints, these systems can be deployed to acquire only a limited number of parallel lines (i.e., streamers) that are coarsely spaced in the crossline direction: streamers are towed typically with crossline spacing of 75-100 m, resulting in coarse wavefield sampling that contrasts with the adequate (non-aliasing) wavefield sampling of 6.25 m implemented along the streamers (inline). They consequently do not adequately capture the full spatial bandwidth of the subsurface-scattered wavefield, leading to limitations in accurately imaging the subsurface.