Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
1999-06-16
2001-04-17
McElheny, Jr., Donald E. (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
Reexamination Certificate
active
06219620
ABSTRACT:
This application is the U.S. national phase application of PCT International Application No. PCT/GB97/02924 filed 23 Oct. 1997.
This invention relates to seismic acquisition using geophones.
It is well known to conduct a geophysical survey of a land area by using an array of geophones in conjunction with either a succession of explosions or a continuous vibration applied to the ground by a vibratory apparatus.
Although the results obtained are valuable, conventional techniques are logistically slow, labour intensive, and costly. It is necessary to deploy a large number of geophones on a grid which has been previously surveyed. Each geophone string is individually wired to a central control unit. As the survey progresses, geophones in the rear must be disconnected, repositioned at the front, and reconnected. This procedure is extremely laborious, and the complexity of the connections gives a high probability of error. The scale of the problem will be understood when it is realised that a typical 3D seismic array involves up to 750 km of cabling.
An object of the present invention is to provide a means to simplify these procedures, and thus to reduce the time and cost of the survey by a significant factor.
Accordingly, the invention from one aspect provides a seismic acquisition system comprising a multiplicity of a geophone units which, in use, are arranged in an array across a survey terrain; each geophone unit comprising means for deriving digital data representative of seismic movement of the earth's surface at the geophone location, and wireless telemetry means adapted to receive command signals from a central control and to transmit said digital data to the central control on command.
In a preferred form of the invention, the terrain is divided into a number of cells each of which contains a number of geophone units and a cell access node. The geophone units in a given cell communicate with the respective cell access node using wireless telemetry at a given frequency, with different frequencies used in adjacent cells.
The cell access nodes may communicate with the central control by radio, or by cable or fibre optic link.
The communication within each cell is preferably high frequency (most preferably 2.4 GHz band) low power. This permits a limited number of frequencies to be re-used across the terrain.
The means for deriving said digital data may comprise an analog geophone measuring velocity, coupled to an analog-to-digital converter.
Each of the geophone units is preferably provided with a memory for short term storage of said data, and for permanent storage of a unique code identifying that geophone unit.
Preferably, each of the geophone units has a preamplifier and preamplifier control means remotely operable from the central control. The preamplifier control means may be operable to control the gain and/or an operating time window of the preamplifier as a function of the distance of that geophone unit from the location of the seismic signal source being monitored, and/or as a function of time.
Each of the geophone units may additionally have its unique code physically embodied internally or externally, or electronically tagged on a microprocessor forming part of the geophone unit, or as an external display for example in the form of a machine readable bar code, all of which can be read by wireless method using existing hardware.
The wireless telemetry means is preferably digital, and may comprise a dedicated wireless system, or may be provided by a cellular wireless system.
From another aspect, the invention provides a method of conducting a seismic survey in which a number of geophone units are positioned in an array across a terrain of interest, a seismic signal (or a series of seismic signals) is generated to produce seismic data collected by the geophone units, the data for each geophone unit is stored at the geophone unit, and said data is transferred to a central location using wireless telemetry, at the same time or at a later time.
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Hamilton David James
Park William Pentland
Sandham William Alan
Smith John Grant Flavell
Whelan John Christopher
McElheny Jr. Donald E.
Ratner & Prestia
Vibration Technology Limited
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