Seismic Estimation Research Paper

Chapter 2: VELOCITY REGIM

2-1Introduction

The seismic method represents one of the most important geophysical techniques for oil and gas exploration due to its high accuracy, high resolution, and deep penetration

The objective of seismic exploration to determine the depth of the target formations which carry hydrocarbons martial to be extracted by drilling ,seismic exploration use the sound wave shotted from the ground surface (source) to travel throw the earth layers and interact with its martial then reflected back to be recorded at other point (receiver) ,basically we measuring the required time to complete this period inside the earth and reflected back to recording device fig1

The basic technique of seismic exploration consists of generating

Generally, the near surface layer heterogenic with complex properties distribution and change rapidly in short distance which form the complexity to deal seismically with it. the abrupt vertical discontinuities in the elastic parameters, affect wave propagation velocity substantially, this variation in velocity could result in a static anomaly “pseudo anomaly”.

The complexity of the near surface in most land seismic surveys is a major limitation for imaging deeper reservoirs due to the rapid velocity change which consider the most effective factor in conversion of the time section obtained from the seismic survey to depth data valuable to use in exploration industry in commercial

The weathered layer has low velocity and large energy attenuation as a result of frictional losses in unconsolidated non-compacted material also, it is characterized by a significant absorption of the high frequencies so, it is known as LVL low Velocity Layer. Generally The low velocity layer LVL formed the near surface layer.it could be weathered un consolidated loose soil layer, buried valleys of the old delta below the surface with soft material or old channel of water path. The low velocity layer varies in thickness from ground surface up to several hundred feet in vertical direction, the weathered layer change laterally in short distance and not controlled by a specific grade but the lateral extension may affected by elevation level the higher elevation location may has the thinnest part of the weathered