Seismic Data Analysis Techniques in Hydrocarbon Exploration

Enwenode Onajite

• Publisher: Elsevier
• Year: 2013
• ISBN:
  9780124200296
• Topic: Tecnologia e ingegneria
• Subtopic: Combustibili fossili

Seismic Data Analysis Techniques in Hydrocarbon Exploration explains the fundamental concepts and skills used to acquire seismic data in the oil industry and the step-by-step techniques necessary to extract the sections that trap hydrocarbons as well as seismic data interpretation skills.

It enhances the ability to interpret seismic data and use that data for basin evaluation, structural modeling of a fault, reservoir characterization, rock physics analysis, field development, and production studies.

Understanding and interpreting seismic data is critical to oil and gas exploration companies. Arming young geoscientists with a reference that covers the key principles of seismic data analysis will enhance their job knowledge, skills and performance. A fundamental grasp of seismic data enhances employability and aids scientists in functioning effectively when working with seismic data in industry.

• Edited by a team of petroleum geoscientists with more than 30 years of experience in hydrocarbon exploration and data analysis at O&G companies.
• More than 200 figures, photographs, and illustrations aid in the understanding of the fundamental concepts and techniques used to acquire seismic data
• Takes an easy-to-follow, step-by-step approach to presenting the techniques and skills used to extract the geologic sections from acquired seismic data.
• Enhances the geoscientist's effectiveness when using seismic data for field development and other exploration and production studies

II

Detailed Seismic Data Processing Techniques

Outline

Chapter 5 Understanding the Detail Seismic Processing Techniques Used to Convert the Acquired Seismic Data into the Geologic Section of the Earth

Chapter 6 Understanding CMP Binning and Sorting

Chapter 7 Understanding Deconvolution

Chapter 8 Understanding Sample Data

Chapter 9 Understanding NMO, Velocity Analysis DMO, and Stacking

Chapter 10 Understanding Multiple Reflections

Chapter 11 Understanding Residual Statics

Chapter 12 Understanding Seismic Migration

Chapter 5

Understanding the Detail Seismic Processing Techniques Used to Convert the Acquired Seismic Data into the Geologic Section of the Earth

Abstract

The purpose of seismic data processing is to convert the acquired seismic field data into the geologic section of the earth, with noise suppressed as much as possible. This chapter of “Seismic Data Analysis Techniques in Hydrocarbon Exploration” describes the initial data/information required to extract the subsurface image (geologic section of the earth) from the acquired seismic data and key seismic processing steps applied to improved the quality of the individual seismic trace in the recorded data. It explains automatic gain control (AGV), which is applied to stabilize/equalize the amplitude content of the seismic data in other to maximize the structural content. The chapter, also, describes how refraction statics correction is done in the oil industry, noise attenuation, and trace editing.

Keywords

Transcription; Observer log; Spherical divergence; AGC; Refraction statics; Static correction; Datum correction; Noise attenuation; Trace editing; Polarity reverser

Outline

What is Seismic Data Processing

Transcription

Observer Log

Spherical Divergence

Automatic Gain Control (AGC)

Refraction Statics

Statics Correction

Datum and Floating Datum

Noise Attenuation

Common Midpoint Stack

Trace Editing

Polarity Reversal

Soft Kick

Hard Kick

What is Seismic Data Processing

Seismic processing is the alteration of the acquired data to suppress noise, enhance the recorded seismic trace and migrate the seismic trace to its correct location in space and time. Processing steps include static corrections, deconvolution, normal moveout, velocities analysis, dip move-out, CMP/CDP stacking and migration, which can be performed before or after stacking.

The objective of seismic data processing is to remove all noise and distortions introduced by the seismic acquisition method and produce a seismic section as close as possible to the subsurface image of the earth that can be interpreted as shown in Figure 5.1.

Figure 5.1 Described the objective of seismic data processing. Source: www.geophysics.geoscienceworld.org.

The data/information required to extract the subsurface image (geologic section of the earth) from the acquired seismic data are as follows:

• Field seismic data in SEG-D format – it does not contain coordinate information of each shot and geophone group (channel).

• The (X, Y, Z) coordinates for each shot and geophone group and this is obtained using global positioning system (GPS). The GPS allows the surveyor to produce an accurate map showing every shot and geophone position in the surveyed area.
Note that wrong shot and geophone group coordinates will lead to mis-positioning and distortion of the final seismic image (migrated image).

• Accurate elevation information of every shot and geophone groups (for land data). The geophone group is also known as geophone station.

• Information on which geophone groups are “live“ for each shot.

Transcription

The acquired field data are stored in SEG-D or SEG-Y (if it has been processed in the field) format.

Transcription is the process whereby all of the field data are converted into the company’s internal storage format in the initial stage of seismic data processing.

If the data have been recorded in a multiplexed format (ordered by channel, not trace), then the computer must be able to read the entire field record in one go and then reorder it (de-multiplexed).

A field record consists of all trace samples recorded in a single shot. After de-multiplexing the geophysicists check to ensure that every trace of every shot has been read correctly.

Observer Log

The observer log contains information about the acquired seismic field data. The geophysicists usually compare the list of shots read from the tape against those listed in the observer logs. A field record number may be used which is designated to match the shot-point number and could get out of step.

A scan error may occur. A scan error is when one multiplex scan of the channels gets out of “sync”. This means that the shot will have to be omitted from any processing, but the geophysicists usually look at the data as soon as possible to confirm this. The geophysicist checks this initial stage to ensure that every trace of every shot has been read correctly.

Spherical Divergence

As the acoustic wave emitted by the seismic source travel through the subsurface, its energy expands in all direction like a sphere (Figure 5.2). All the energy initially contained in the seismic source is spread...