Passive seismic emission tomography: The dynamics of a reservoir.

2003年，英国石油公司在北海瓦尔霍尔油田上方的海底安装了密集的地震记录设备。近2500个最先进的地震仪连接到120公里的电缆，覆盖45平方公里的区域，并连接到一个记录平台。该装置是世界上第一个此类装置，耗资近4500万美元。这种永久性监测允许在油田寿命期间（因此称为油田寿命地震或LoFS）定期采集船载地震勘测（所谓的4D地震）。由于每次测量都是相同的，因此数据可以用于非常准确地监测储层的变化，例如，由于生产而导致的石油迁移。多组分传感器也可用于记录不太传统的数据。例如，在北海的这一部分，剪切波在通过位于储层上方的气体云成像时比传统的第一次到达的P波要好得多。这种监测油田的新方法极大地改善了油藏管理和生产率，并降低了长期成本。即使在没有进行有源（气枪）船舶调查的情况下，传感器也会持续记录。因此，利用这些数据研究地下小地震有很大的潜力。这种微地震事件是有用的，因为它们提供关于区域构造和生产相关力的信息。它们提供有关断层位置和流体运移的信息，这些信息对生产非常重要。此外，这样的应力释放可能导致井故障（钻孔崩落），这每年花费工业数十亿英镑并且可能是相当危险的。我们建议通过开发复杂的成像技术来研究这些微地震，这种技术将使用像眼睛一样的传感器，可以从不同的方向观察地球。虽然这些地震非常小（它们释放的能量与折断铅笔大致相同），但由于如此大量的数据所提供的冗余，它们可以被准确地定位和研究。我们可以使用常规地震学的标准技术来推断断层面的方向和储层中的应力场。另一个协同作用来自BP手头关于该领域的详细信息（例如，速度结构）。我们将与英国石油公司的工作人员密切合作，并将被允许使用他们的大规模计算集群来处理数据。我们是第一批被允许查看这个令人兴奋的数据集的组织之一，该项目将产生备受瞩目的结果。这是一个独特而及时的机会。

In 2003 BP installed a dense array of seimic recording equipment on the sea bottom above the Vallhall oil field in the North Sea. Nearly 2500 state-of-the-art seismometers were attached to 120 km of cables that cover a 45 square km area and are connected to a recording platform. The installation is the first of its kind anywhere in the world and cost nearly US$45million. Such permanent monitoring allows the acquisition of ship-borne seismic surveys at regular intervals in time (so-called 4D seismics) for the life of the field (hence the name Life of Field Seismic or LoFS). Because the surveys are identical each time the data can be used to very accurately monitor changes in the reservoir, for example, the migration of oil due to production. The multicomponent sensors can also be used to record less conventional data. For example, in this part of the North Sea shear-waves are much better than the conventional first arriving P-waves at imaging through the cloud of gas that lies above the reservoir. This new way of monitoring an oil field has dramatically improved reservoir management and productivity, and reduce costs in the long term. The sensors are continuously recording, even when active-source (airguns) ship surveys are not being conducted. Thus there is great untapped potential in using these data to study small earthquakes in the subsurface. Such microseismic events are useful because they provide information about regional tectonics and production related forces. They provide information about fault locations and fluid migration, knowledge of which are of great importance to production. Furthermore, such stress releases can lead to well failure (borehole breakout), which costs the industry billions of pounds each year and can be quite dangerous. We are proposing a study of these micro-earthquakes by developing sophisticated imaging techniques that will use the sensors like eyes that can look in different directions into the Earth. Whilst these earthquakes a very small (they release roughly the same amount of energy as breaking a pencil) they can be accurately located and studied because of the redundancies afforded by such an immense amount of data. We can use standard techniques from conventional earthquake seismology to infer the orientation of fault planes and the stress field in the reservoir. A further synergy comes from the detailed information about the field that BP has at hand (e.g., velocity structure). We will work closely with BP staff and will be allowed to use their massive computing clusters to process the data. We are one of the very first organisations being allowed to look at this exciting dataset and the project will produce high-profile results. This is a unique and timely opportunity.