PDF(Pubmed)
Abstract：
Exxon Neftegas Ltd. (ENL) carried out three 4D seismic surveys during the summer of 2015. Seismic operations in two of these fields (Odoptu and Chayvo) ensonified the nearshore feeding area of Korean-Okhotsk (western) gray whales (Eschrichtius robustus), potentially disturbing feeding activities. Following model-based optimization of the source design to minimize its lateral acoustic footprint, pre-season modeling was used to compute the acoustic exposure along each survey line. Real-time acoustic data facilitated implementation of mitigation measures aimed to minimize disturbance of whales. Acoustic data originated from underwater recorders deployed on the seafloor. Two complementary approaches were used to transmit recorded sound data to a computer housed at the Central Post (CP), where decisions regarding mitigation shut downs were made. In the first approach, a limited bandwidth (2-2000 Hz) sampling of the data was transmitted via cable to a surface buoy, which relayed these data to a shore station up to 15 km away via digital VHF telemetry. At the shore station, acoustic impulses from the seismic surveys were processed to compute impulse characteristics in the form of estimates of sound exposure level and peak sound pressure level, as well as one-minute-average 1/3-octave power spectral density coefficients, which were then transmitted to the CP via the internet. In the second, the pulse characteristics were computed through algorithms running on an onboard processor in each recorder\'s surface buoy and sent directly to the CP computer via an Iridium satellite uplink. Both methods of data transfer proved viable, but Iridium transmission achieved the goal without the need for any shore based relay stations and is therefore more operationally efficient than VHF transmission. At the CP, analysts used the real-time acoustic data to calibrate and adjust the output of pre-season acoustical model runs. The acoustic footprint for the active seismic source, advancing synchronously with the motion of the seismic vessel and changing as the sound propagation environment changed, was computed from the calibrated and adjusted model output and integrated through the software Pythagoras with locations of gray whales provided by shore-based observers. This enabled analysts to require air gun array shutdowns before whales were exposed to mean square sound pressure levels greater than the behavioral response threshold of 163 dB re 1 μPa2. The method described here provides a realistic means of mitigating the possible effects of air guns at a behavioral response level, whereas most seismic surveys rely on pre-established mitigation radii to manage the risk of injury to a whale.
摘要：
ExxonNeftegasLtd.（ENL）在2015年夏季进行了三次4D地震勘测。其中两个油田（Odoptu和Chayvo）的地震作业使韩国-鄂霍次克（西部）灰鲸（Eschrichtiusrobustus）的近岸觅食区变得更加活跃，可能令人不安的喂养活动。在基于模型的源设计优化以最小化其横向声学足迹之后，季前建模用于计算沿每条测量线的声暴露。实时声学数据促进了旨在最大程度地减少鲸鱼干扰的缓解措施的实施。声学数据来自部署在海底的水下记录器。使用两种互补的方法将录制的声音数据传输到位于中央哨所（CP）的计算机，在那里做出了关于缓解关闭的决定。在第一种方法中，通过电缆将有限带宽（2-2000Hz）的数据采样传输到表面浮标，通过数字VHF遥测将这些数据中继到15公里外的岸上站。在岸上车站，对地震勘探的声脉冲进行了处理，以估计声暴露水平和峰值声压级的形式计算脉冲特性，以及一分钟平均1/3倍频程功率谱密度系数，然后通过互联网传输到CP。在第二个，脉冲特征是通过在每个记录仪的表面浮标中的机载处理器上运行的算法计算的，并通过铱卫星上行链路直接发送到CP计算机。两种数据传输方法都被证明是可行的，但是铱传输实现了目标，而无需任何岸基中继站，因此比VHF传输更有效。在CP,分析人员使用实时声学数据来校准和调整季前声学模型运行的输出。活动震源的声学足迹，与地震船的运动同步前进，并随着声音传播环境的变化而变化，根据校准和调整后的模型输出进行计算，并通过软件毕达哥拉斯与岸基观察者提供的灰鲸位置进行集成。这使分析师能够在鲸鱼暴露于大于163dBre1μPa2的行为响应阈值的均方声压级之前要求气枪阵列关闭。这里描述的方法提供了一种在行为响应水平上减轻气枪可能影响的现实手段，而大多数地震调查依赖于预先建立的缓解半径来管理鲸鱼受伤的风险。
