Text 4 Discovering the underground structure (6300)

1. Learn the words and word combinations before reading:

pattern - ['pxtn]– образец, пример, структура, форма

density -['densiti] - распределение определенного количества чего-либо на единицу площади, объема, длины, и т.д.; плотность, удельный вес

altitude - ['xltitHd] - высота, высокие места, высота над уровнем моря

subsurface picture – подповерхностная картина

delineation wells - [di"lini'eiSqn] - описательная скважина

geometric frame­work – геометрическая структура

spatial elements - ['speiSql] - пространственные элементы

slicing – нарезание

validate - ['vxlideit] - подтверждать

laterally – горизонтально

selected event – выделенная волна

travel time – время пробега

resolution – разрешение, разрешающая способность

strong acoustic impedance [im'pJdqns] contrast – сильный контраст акустического сопротивления

acquisition configuration – конфигурация сбора, приема

downhole hardware - аппаратное обеспечение скважины

2. Read and translate the text:

Large-scale geological structures that might hold oil or gas reservoirs are invariably located beneath non-productive rocks, and in addition this is often below the sea. Geophysical methods can penetrate them to produce a picture of the pattern of the hidden rocks. Relatively inexpensive gravity and geomagnetic surveys can identify potentially oil-bearing sedimentary basins, but costly seismic surveys are essential to discover oil and gas bearing structures.

Sedimentary rocks are generally of low density and poorly magnetic, and are often underlain by strongly magnetic, dense basement rocks. By measuring 'anomalies' or variations from the regional average, a three-dimensional picture can be calculated. Modern gravity surveys show a generalised picture of the sedimentary basins. Recently, high resolution aero-magnetic surveys flown by specially equipped aircraft at 70 - 100m altitude show fault traces and near surface volcanic rocks.

Initially 3D seismic surveys were used over the relatively small areas of the oil and gas fields where a more detailed subsurface picture was needed to help improve the position of production wells, and so enable the fields to be drained with maximum efficiency. Nowadays 3 D seismic surveys are used for more detailed information about the rock layers, to plan and mon­itor the development and production of a field. The seismic information is integrated with well logs, pres­sure tests, cores, and other engineering/geoscience data from the discovery and delineation wells to formulate an initial field development plan. As more wells are drilled, logged, and tested, and production histories are recorded, the interpretation of the 3-D data volume is revised and refined to take advantage of the new information. Aspects of the interpretation that were initially ambiguous become clear as an under­standing of the field builds, and inferences from the seismic data become more detailed and reliable. The 3-D data volume evolves into a continuously utilized and updated management tool that impacts reservoir planning and evaluation for years after the seismic survey was originally acquired.