Seismic Method for Exploration Oil and Gas Reservoirs

Abstract

In general, Reservoir Exploration is considered the first step to detect the structures geology (Reservoirs) that contain hydrocarbons and known if this structures (Reservoirs) are economic or noneconomic by several methods and calculations. As it known the geophysical exploration project normally follows a sequence of activities starting with field work and ending up with production of the subsurface geological model of the project area. An exploration project passes through a sequence of three phases, normally executed in sequence. The starting phase of a survey is collecting the field raw data through standard field procedures by which the geophysical measured values are recorded, usually on magnetic tapes. After completing the acquisition work, the recorded data are passed on to a processing center where it is subjected to certain processing steps for purpose of certain corrections and enhancing of the geophysical signal. The third and last phase of the project is to interpret the final processed data to extract the subsurface geological model of the area under exploration. Actually, the main exploration methods employing geophysical principles are: (Seismic, Gravity, Magnetic, Electrical, Radioactivity, Electromagnetic). Seismic method is considered by far the most widely applied method in the exploration of oil and gas deposits. Gravity, magnetic, electrical, and radioactivity methods provide support data in the oil exploration and also applied as the main tools for other mineral exploration. Geophysical techniques which are using the Earth geophysical potential fields (as gravity and magnetic fields) are often called (Potential Methods). As it known the seismic survey or seismic method is the modern and best method for exploration of the reservoir but it is expensive method, this method is based on generating seismic waves by a mechanical energy (Energy produced by instrument such as a seismic vibrator (on land) or an air gun (in water)) at a point on, or just below, the ground surface and recording the arrival at another surface point of the reflected (or refracted) waves. From the travel-time measurements of these waves and wave motion-velocity, the structural variation of subsurface geological layers are mapped. Under favorable conditions, study of the seismic wavelet can provide information on the stratigraphic nature and hydrocarbon contents of the traversed rocks. The raw seismic data (normally recorded on magnetic tapes), are passed through a sequence of processing steps followed by a set of certain interpretation procedures in order to obtain the final result, which is a model of the subsurface geological structure. Actually, there are two main techniques involved by the seismic method; the reflection and the refraction methods. The term AVO (Amplitude Variation with Offset), or AVA (Amplitude Variation with angle of incidence) is considered to be one of the effective tools used in direct hydrocarbon detection exploration. It can be used to explore reservoir and subsurface geological conditions, since it can give indications on lithological changes, reservoir conditions, and presence of high-pressure gas zones. Another significant application of the concept is determination of boundary outlines and areal extensions of hydrocarbon reservoirs. Improved accuracy in interpretation is achieved when supported with additional geological and geophysical information.

So, it concludes the seismic method is the most widely applied method in the exploration of oil and gas reservoir, detect lateral and vertical variation in velocity, produce detailed images of the subsurface, used to map stratigraphic units, sometimes direct hydrocarbon detection is possible. Also, AVO analysis is widely used in hydrocarbon detection, lithology identification, and fluid parameter analysis, due to the fact that seismic amplitudes at layer boundaries are affected by the variations of the physical properties just above and below the boundaries.

Copyright 2022, IFEDC Organizing Committee

This paper was prepared for presentation at the 2022 International Field Exploration and Development Conference in Xi’an, China, 16–18 November 2022.

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