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Introduction

Geophysical business processes deal primarily with data and information created through seismic acquisition, processing and interpretation. Unexplored geographic areas are often targeted for preliminary stratigraphic evaluation using seismic data because seismic data provides reasonably broad aerial coverage at a relatively low cost. Certain types of seismic data may also be used to support detailed delineation of hydrocarbon reservoirs.

Seismic exploration programs are developed to evaluate and test geological hypothesis about stratigraphic structures in a project area. Once a geologist has developed a model for hydrocarbon entrapment in the project area, the geophysicist develops a program for acquiring seismic data that will further evaluate the trap. By measuring, recording and analyzing data generated during acquisition, the geophysicist can determine the depth and thickness of each relevant rock sequence.

Specialized contractors are hired to record seismic in the prospective area. Surface access permits are acquired from landowners; these permits detail rights to shoot seismic on the owner’s land and obligations that are incurred for compensation or reclamation. Survey teams lay out seismic surveys using the design plans specified by the geophysicist. Each plan is designed to provide optimal data quality in the area to be explored. Seismic exploration may be conducted on land, in transition zones, offshore or within well bores.

Land exploration is conducted using an energy source such as dynamite (in which shallow holes are drilled to accommodate dynamite charges that are detonated) or vibroseis (vibrator trucks are used to shake the ground and send sound waves into the subsurface). Marine seismic operations use specialized vessels that tow an energy source (air gun) and one or more marine cables (streamers) with water receivers (hydrophones).

Reflected and refracted energy signals are captured using geophone arrays laid out in geometric arrays called patches; a permanent record is created on digital media such as magnetic tape. Data reduction transforms the raw data into usable formats for subsequent processing. Analysis of reflection data yields estimates of transit time, velocity and elevation corrections; this information is used to improve the coherency and resolution of recordings.

Processed seismic trace data is given to the geophysicist who interprets the data in conjunction with other available data such as well logs, synthetics, gravity and magnetic data or velocity surveys. Based on these results, the geophysicist may choose to apply additional processing steps to the data or create an interpretation dataset consisting of time, amplitude or depth picks.

Interpreted results for many seismic sets are combined to create threedimensional representations of specific stratigraphic units; these results can be shown as isopach or isochron maps, or displayed using special three dimensional interpretation tools or even visualized using state of the art visualization tools.

If suitable stratigraphic structures are identified, expenditures may be authorized to acquire mineral and surface land rights, drill wells and continue the exploration cycle.

Each phase of the exploration life cycle is intensively data driven. Permanent records detailing the processes and technology applied, observations and results are retained. Suitable cataloguing practices must be employed to ensure that this data asset is managed for the future. Seismic data that is no longer useful to the originating company may ultimately be used as a negotiable asset and made available to other interested parties through a series of transactions and agreements.

Business Process Overview

Purpose

The Seismic Module provides a means of describing and managing information about seismic data. This data is created throughout its life cycle, from acquisition, processing and interpretation through disposition by sales or trades.

Description

The life cycle of seismic data, from inception to final disposition through destruction or disposition, is lengthy. Seismic data is often processed and reprocessed many times in order to extract maximum value from the data; it is treated as a valuable asset in data sales and trades and provides important information for the design of new seismic surveys. Each step in the life cycle is data intensive. Product generation and use of archived information at every stage mean that integration between seismic data and a records management store is a critical component of effective seismic data management.

Key Business Processes

Seismic Acquisition and Processing

Designing an effective seismic acquisition survey involves a great deal of research. Typically, it is necessary to gather samples of work previously done in the area to evaluate the success of historic surveys and determine whether a new survey is likely to produce useful results. An examination of existing corporate land positions, availability of new land rights, infrastructure support (such as pipelines, roads and processing facilities), budget considerations and environmental or cultural considerations will help managers and geophysicists determine how (or if) a survey should be conducted.

One or more recording crews will conduct the field survey. The field crew will create positional information for all field locations (shot and receiver), set up energy source locations and receiver positions and record the energy signatures generated by the seismic source. Detailed records are kept at each stage of this process. The field survey information, usually captured as bearings, azimuths and offsets, is converted to geographic locations (latitude and longitude) for mapping and calculating mis-ties.

Driller records contain detailed information about the condition of the subsurface where shot holes are drilled for use in near surface corrections. Shooter’s logs record details about the creation of the energy source and the observer’s logs capture information about where the actual acquisition varies from the nominal design parameters. These records would include details about offsets or skids created to avoid some environmental hazard, such as a creek, list test records and corrective action taken in the field. The location of each digital recording for each geophone group for each source is captured to assist in processing.

Pre-processing involves the preparation of data for input into a processing system. Quality control of field data, geometry, survey locations, and tape indexes are often included. Generally, this step is only done once, and the results stored for future use. Figure 3 illustrates the conversion of raw recorded data to usable processing traces.

Processing is an iterative process that may involve all or a portion of a line or 3D survey and which may combine 3D and 2D data or multiple 3D surveys. Prestack and post-stack processing may be repeated as many times as necessary or desired. The parameters, filters, and processes that may be applied are varied and complex. It is important for processors and interpreters to know exactly what was done to the data in what sequence. Figure 4 illustrates the sequence of processing events.

3D Seismic Data

Three-dimensional (3D) seismic recording is conducted in areas where it is desirable to obtain detailed subsurface horizon imagery, such as for reservoir analysis or marine exploration. Through specialized methods of acquisition, processing, and interpretation, a three dimensional image can be constructed in an area of interest according to detailed specifications.

Land based 3D acquisition employs a pattern of source lines and receiver lines, which are commonly either perpendicular or parallel to each other. As each energy source is activated, the seismic response is recorded by groups of geophones on several receiver lines, called a patch, as shown in Figure 5.

Marine based 3D acquisition may use one or more vessels; the primary or controlling vessel is called the master and subordinate vessels the slaves. The master vessel detonates the energy source and controls the recording of signal from streamers towed by all vessels. Typically each vessel tows between 2 and 10 steamer cables; each cable contains between 50 and 150 groups of geophones. Each shot is recorded simultaneously on all cables as the boat moves.

During pre-processing, positional data gathered in the field is used to compute a theoretical grid network called a binning grid. Every individual recorded seismic trace is assigned to one or more bins; the number of traces summed together at each bin is called the fold or coverage for that bin. The nominal average fold for the survey is part of the descriptive information for the survey. Summing all the traces assigned to each bin creates a single multi-fold trace that is used as input to subsequent seismic processing steps.

Other descriptive acquisition information includes details about the source and receiver setup, layout of source and receiver lines and navigation information such as master-slave vessel relationships and streamer layout for marine data.

Seisrecarray.JPG

Mapping and reporting for a 3D survey may relate to either the surface (field) positions or the subsurface bin grid and points. Regional maps may only show the perimeter of a 3D bin grid. Except for the three dimensional aspect and the large data volumes created, interpretation information for 3D surveys is similar in content to conventional 2D interpretation.

Bin coordinate data sets for 3D surveys can be extremely large if each bin center coordinate is explicitly stored. Various strategies for managing the data volume have been developed; data thinning, online bin calculation (using starting points, azimuth, and incremental distances) and off- or near-line data storage are some common methods.

Activities such as interpretation, processing, brokerage, or partnerships may involve only a portion of a 3D survey; a clear definition of which portion(s) of the survey are included is necessary to properly administer projects and agreements. The maps, reports, and other information or data that results from these activities will only pertain to the relevant portion of the survey.

Transactions, Agreements and Partnerships

Seismic data is an expensive and valuable asset; naturally a large industry has evolved that exploits this resource. Seismic brokers act as a liaison for buying and selling (or licensing) data. Companies that specialize in seismic acquisition create spec surveys and sell them to many buyers. Data management companies store and manage the paper and digital data that is created during the seismic life cycle.

Business agreements provide the foundation for cooperative ventures between E&P companies, software vendors and data providers. Most business agreements establish mechanisms for sharing costs, labor, responsibility, and profits for various aspects of the business. In the E&P industry, a single agreement can affect the disposition of land ownership, well or seismic rights, and production.

The business of Seismic Transactions in the E&P industry generates hundreds of millions of dollars every year. Seismic lines are bought, sold, traded, farmed in or out, or acquired through mergers and takeovers on a daily basis. Any E&P company can determine what data is available for purchase through information provided by data vendors in trade journals, public information sources, or through online or dial-up data access services provided by vendors. Many large companies also provide their own data sales services.

Agreements that affect seismic data may be set out before, during, or even years after the actual seismic acquisition. They may exist in perpetuity or for a defined length of time and may affect all or portions of a group of seismic lines. Depending on the terms of an individual agreement, parts of seismic lines may be included or excluded specifically or based on geographic area, a specified date interval, or by project, AFE, or processed or field data product.

Prior to a seismic data transaction (often called a sale), authorization from all data owners and partners must be obtained. For older data, obtaining authorization can be a very difficult task unless a good tracking system has been in place for many years; determining the current and past owners of seismic data can be difficult and complex.

With suitable authorization, data samples are made available for inspection. The data broker will provide the geophysicist with information about the seismic line, including nominal field parameters and a sample of a processed product. Based on the results of a quality inspection (called a QI), the requesting company may make an offer to purchase or license the seismic line.

Licensing agreements may define exactly what the licensee is permitted to do with the data acquired. Post stack processing may be allowed, but pre-stack processing prohibited. Many licensing agreements specify the disposition of licensed products after the primary term has expired; often these products must be returned to the owner or certified as destroyed.

SEISMIC

Contents

Introduction

Business Process Overview

Purpose

Description

Key Business Processes

Seismic Acquisition and Processing

3D Seismic Data

Transactions, Agreements and Partnerships

Tables

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