Seismic Exploration Methods Research Articles

Seismic exploration method and apparatus for canceling interference from seismic vibration source

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Method for seismic exploration by vertical seismic profiling and installation for its implementation

A seismic exploration method is disclosed for filtering the signals produced by a detector placed at different depths in a well in response to an emission of acoustic waves from a source on the surface: the signals comprising downgoing wave components and upgoing wave components. The filtering consists in sampling from among the N signals to be processed a group of n signals s 1 . . . s n detected at respective levels x 1 . . . x n , in determining the propagation time t k of the acoustic waves from the level x 1 to each level x k , in both advancing and delaying the signals s k by the time t k in relation to s 1 , in adjusting the signals for the effects of the acoustic impedance of the formation, in combining s 1 and the signals s k thus shifted and adjusted to obtain a sum z 1 ', in calculating a sum y 1 ' of s 1 and of the thus delayed and adjusted signals s k , and in generating a signal u 1 * ', defined as an optimum estimation of the upgoing wave component, from the sums y 1 ' and z 1 '.

The polarisation method of seismic exploration

The effectiveness and the costs of geological exploration, primarily of that for oil and gas are, to a considerable extent, determined by the effectiveness of seismic exploration. Over 90% of the increase in the established reserves of oil and gas has been obtained in areas prepared for drilling with the aid of seismic exploration methods.

Seismic exploration with simulated plane waves

A method of seismic exploration by which substantially plane or substantially cylindrical seismic energy waves are simulated by combining reflectional signal traces of conventional spherical seismic waves. Seismic sources and receivers are established in sets at positions such that at least one of the sets includes a plurality of positions spaced over an extent of the area being explored having either one or two dimensions which are large relative to a seismic energy wavelength. Seismic energy is imparted into the earth from the sources and signals are generated in response to seismic energy received at the receivers. The generated signals are then combined into a form simulating the reflection response of the earth to seismic energy having a substantially continuous wavefront in either one dimension, simulating a cylindrical seismic energy wave, or two dimensions, simulating a plane seismic wave.

Sandstone and limestone porosity determination from shear and compressional wave velocity

Recent and ongoing development of seismic petroleum exploration methods for generating and recording shear waves requires companion efforts to extract useful information from these data. Data exami...

Seismic exploration method using a rotating eccentric weight seismic source

First Page

Seismic exploration method

A seismic exploration method in which a coded energy signal is generated and transmitted into the earth, the seismic energy reflected from within the earth is sensed and sampled to form a raw trace, the raw trace is crosscorrelated with a record of the coded energy signal, and a predictive operator derived from the autocorrelation function of the coded energy signal is subtractively applied to the crosscorrelated trace to remove correlation residuals, and thereby produce a high quality processed trace. Geophysical principles are used to interpret the processed trace and identify subterranean mineral deposits of interest. Based on this interpretation at least one well is drilled to further explore and/or develop the mineral deposits of interest.

Seismic method

The fifty years from 1930 to 1980 almost completely cover the entire history of the reflection seismograph exploration industry. During its growth from infancy to maturity there have been many major technological breakthroughs and innumerable evolutionary advances. At the conclusion of any time period, there is a tendency to believe that the peak has been reached, only to see significant breakthroughs which start a whole new round of amazing developments. So it is today with a veritable explosion of channel capacity in the recording systems and three‐dimensional surveys finally just becoming a practical reality. The prospects for major improvements in the resolving power of the seismic exploration method have probably never been better.

Bidirectional seismic array and method of seismic exploration

An improved seismic array and method of seismic exploration are provided which have the capability to supply data to separate recording stations simultaneously. The seismic array has a plurality of seismic detector connection points, and a seismic detector is located at each seismic detector connection point. The outputs of the seismic detectors are electrically isolated from each other, and weighting may be applied to the output of each seismic detector in the array. Two signal-carrying media are also provided in the array, and the weighted outputs of the seismic detectors are conveyed to the first end of the array over one signal-carrying medium and to the second end of the array over the second signal-carrying medium. A Chebychev weighted array is achieved by a proper selection of weighting.

Geophysics as an Engineering Tool

JPT Forum articles are limited to 1,500 words including 250 words per table or figure, or a maximum of two pages in JPT. A Forum articles may present preliminary results or conclusions continuing investigation that present preliminary results or conclusions continuing investigation that the author wishes to publish before completing a full study; it may impart general technical information that does not warrant publication as a full-length paper. All Forum articles are subject to approval by an editorial committee. Letters to the editor are published under Dialog, and may cover technical or nontechnical topics. SPE-AIME reserves the right to edit letters for style and content. Engineers, geologists, and petrophysicists often practice their professions in isolation, considering each activity a separate science. This is not always intentional, but limited time and resources accentuate the effect by narrowing the scope of activity and investigation. The professional engineer is inquisitive by nature and probes professional engineer is inquisitive by nature and probes other fields, but in geophysics, for example, the rate of change is so rapid that even specialists cannot maintain reasonable knowledge of the state of the art. Yet, knowledge of new developments in other fields is fundamental because a technique effective in one field often can be adapted for another. For instance, one successful method of seismic exploration was adapted from radar techniques. Petroleum engineers and exploration geophysicists draw freely from each other's disciplines. One recent technological transfer, not yet widely available, is the adaptation of the geophysical gravimeter to borehole logging. A gravimeter measures changes in density, so it can be used to locate subsurface structures or salt domes. A gravimeter has been designed to fit into a logging sonde and to withstand extreme pressure and temperature encountered at depth. In the sonde, the apparatus is oriented to measure lateral expression of gravity, and thus can measure the relative density of rock surrounding the borehole. Casing in the hole, which precludes valid readings on many types of logs, merely applies a small constant shift to measurements, making the gravimeter equally effective in cased or uncased holes. Porous formations, particularly when filled with gas, are usually less dense than surrounding rock and cause reduced gravity readings. Therefore, the device is well adapted for detecting porosity, even behind casing. The device cannot operate continuously because acceleration and gravity are related functionally; it must be stationed at each level to be measured. Hence, conventional logging is faster, but for many applications the device can be targeted for a relatively narrow zone of interest. Another new geophysical development is related to digital computing. Seismic surveys are interpreted in terms of structure. Although potential reservoirs may be located this way, little important information about the nature of the rock (lithology, porosity, and permeability) can be gathered by surface-based techniques without first drilling a borehole. Amplitude of a signal returning to the surface from a given reflector, when compensated for transmission losses, is a direct function of the velocity change across the boundary it maps. Until recently, little attention was paid to the strength of the returning reflection because it paid to the strength of the returning reflection because it could not be measured reliably, but now it is possible to measure it with reasonable precision. The first application of this new information was rather simple. Average velocity through porous rock filled with liquid will decrease if the fluid is replaced by gas. If a continuous reservoir bed, normally containing water (or oil), crosses a trap where gas replaces the fluid in the pore space, the sudden change in velocity through the reservoir rock results in a changed velocity contrast across the boundary between the reservoir rock and adjoining formation. This, in turn, changes the amplitude of the reflection, often by a readily measured amount. The resulting amplitude change, termed a bright spot, is used to indicate gas directly. Unfortunately, other changes in lithology produce similar effects. For example, a coal seam produces a response similar to gas-filled porosity. These failures do not discredit the method, but merely show that at best geophysical surveys indicate subsurface conditions imperfectly. P. 1627

How Operational Gaming can Help with the Introduction of a New Technology

This paper describes the OR contribution to the problems related to the introduction of seismic exploration methods into the coal industry. The OR team were able to adapt a well-established operational gaming technique to determine the situations in which seismic exploration is worthwhile and assist in the design of the seismic survey itself.

SIGNAL ENHANCEMENT OF VIBRATORY SOURCE DATA IN THE PRESENCE OF ATTENUATION*

AbstractAmplitude spectra of input FM signals used in the vibratory source method of seismic exploration often show undesirable oscillations near the initial and terminal frequencies. These oscillations have an effect on the correlation background and distort the output signal. Considerable improvement in reducing the amplitude of these oscillations is obtained using a proper taper fuction. Attention is given to the relation between the tapering time and bandwidth of the spectrum.Analyses of the spectra of the received data from vibratory sources show considerable attenuation in comparison with the original field sweep. Since the matched filtering process will result in a series of waveforms which have the shape of the autocorrelation of the input signal, consideration is given to the autocorrelation function and its zero‐lag coefficient of the FM signal in the presence of attenuation. A method has been developed which compensates for the attenuation and recovers the distortion of waveforms when the received data is correlated.The design of a waveform shaping filter for vibratory source data is given to reduce the influence of phase distortion on the received waveforms as well as to increase S/N ratio resolution. Parameters used for this filter are based on the properties of the FM signal and its autocorrelation function.Several examples from field data are presented to illustrate the methods. The results indicate that the use of the above techniques yields sections with good frequency resolution and improved S/N ratio.

Yesterday, Today, and Tomorrow in Seismic Exploration: ABSTRACT

ABSTRACT The science of seismic exploration has successfully passed the birth of the digital revolution, and in its youthful presence we envision a significant improvement in its future resolving power through an expansion of the geologic information generated from reflection data. In the early stages of this revolution the signal/noise ratio was improved, largely because the use of high-speed computers made the common-depth-point shooting techniques, the repetitive use of low energy, non-dynamite (low noise) sources, and various signal-processing techniques practical. The net gain to the interpreter has been a much improved seismic record section (in time or depth), from which, as in predigital days, he usually develops only a geometric configuration description. The recorded data, however, contain information about the type of rocks through which the energy has propagated. Extraction of this information, for example, in the form of velocity and attenuation variations, will permit lithologic identification. To measure the resolving power of the seismic exploration method, one needs to evaluate the simple equation: geometric configuration plus lithologic distribution equals geologic section.

RESEARCH AND PROGRESS IN EXPLORATION

This is a general review of new developments in geophysical exploration in 1957. In the Eastern Hemisphere, the strong emphasis on the use of refined seismograph techniques in virgin territories despite extreme operating problems is a development of primary importance. In mining geophysics a new Swedish development employs a rotary electromagnetic field and two‐plane operation to improve substantially the economy and effectiveness of reconnaissance for conductive ore‐bodies. In the United States new developments include work on a method of seismic exploration using continuous waves rather than pulses, the incorporation of transistors into seismic units, a trend toward simplified equipment for plotting seismic record sections, an electrical prospecting method which permits detection of near surface structures in water‐covered areas, and the increased use of continuous velocity logs. Other developments have occurred in the field of chemical logging, including the use of mass spectrometers, infrared analyzers, and gas chromatographic columns. Academic research into techniques for dating feldspar‐bearing rocks has advanced spectacularly. It is now possible to obtain dates on certain kinds of rocks extending from a few thousand years to a few billion years in age.

Seismic Model Study

A method has been developed for studying seismic sound pulses in reduced scale models which simulate geophysical seismic exploration methods. Use is made of a tank of water for transmission of the acoustic wave from a source to a faulted limestone stratum and return to a pressure sensitive receiver. Results obtained demonstrating the geometric aspects of the propagation, reflection, refraction, and diffraction of sound pulses are described and illustrated on accompanying plates.

Seismic Sounding of Shallow Depths

After a short review of the development of ≥artificial seismology≤ a description is given of the modern field procedure when using the seismic refraction method for measuring of small depths, of the order of only a few meters. A small portable instrument equipment used for this purpose is described. The theoretical and physical basis for the seismic exploration method is briefly discussed, and by an example it is shown that laboratory tests on rock samples can be used to calculate the transmission velocity of seismic waves. Some examples are given on the use of the seismic refraction method for civil engineering work. It is also related how the small portable instrument equipment previously described was used to measure the thickness of a glacier by means of the seismic reflection method. Repeated reflections (reverberations) were obtained and the smallest depth accurately determined in this way was 96 m.

New Method of Seismic Exploration - From, 'Science,' November 19, 1948

New Method of Seismic Exploration - From, 'Science,' November 19, 1948

Developments in Texas Panhandle in 1947

The Panhandle district includes the 25 northwestern counties in Texas. Ten of these counties produce oil or gas. There was an increase in drilling in 1947 as compared with 1946. In 1947 429 wells were completed. Of these 240 were oil wells, 178 were gas wells, and 22 were dry and abandoned. No new fields or producing formations were discovered. However, the Phillips Petroleum Company's Elton No. 1 in west-central Hansford County was temporarily abandoned after swabbing 22 barrels of oil and 215 barrels of water in 24 hours from 6,138-6,165 feet, a Pennsylvanian granite wash zone. In 1947 the Panhandle field produced 29.8 million barrels of oil, approximately equalling the 1946 oil production. Gas production was 834.76 billion cubic feet. Two exploratory wells, the Phillips Petroleum Company's Virginia No. 1 in Hansford County and the Union Producing Company's Glenn No. 1 in Collingsworth County were drilled to the granite. The areas of intense leasing were Castro County in the southwest part of the district, and Wheeler, Hemphill, Roberts, and Lipscomb counties in the northeast part of the district. Geophysical operations were concentrated in these areas. There was an increase in seismic and core-drill exploration methods over previous years.

Bibliography of Seismology

THE present number of this important bibliography (13, No. 11, January to June, 1942), published at the Dominion Observatory at Ottawa by Ernest A. Hodgson with the assistance of four collaborators, maintains its previous high standard. There are seventy-seven items culled from world-wide sources covering topics from the strength of rock materials to world structure. Many items concern patents for geophysical prospecting such as item 5326, Williams, P. S., “ Seismic Exploration Method”, U.S. Patent 2,253,358, Aug. 19, 1941, and Beers, R. F., “ Means for Analysing and Determining Geologic Strata”, U.S. Patent 2,249,108, July 15, 1941. Items from NATURE and Science News Letter are included. There has been some discussion recently concerning the geology of the beds of the oceans especially near shore-lines. This enhanced interest is mirrored in item 5313, Jones, O. T., “Continental Slopes and Shelves”, Geographical Journal, 97, No. 2, 80-99 (London, Feb., 1941) ; and in item 5341, Shepard, Francis P., and Emery, K. O., “Submarine Topography off the California Coast”, Geological Society of America Special Publications, No. 31, 171 pp., 4 charts, 18 pi., 42 fig. (New York, 1941). Reginald A. Daly made a contribution to NATURE concerning “Glaciation and Submarine Valleys” on Feb. 7, 1942 (pp. 156-60), item 5291.

Applications of Geophysics in War: ABSTRACT

War-time applications of geophysics come under the heading of military operations and location of essential minerals. In the combat zone, sound ranging helps to locate hostile guns and to adjust friendly artillery. Listening devices determine the approach of submarines or airplanes. Buried munition dumps, shells, and bombs can be located by radio detection devices. Vessels at sea may establish their position by radio-acoustic ranging. Planning of fortifications and harbors and location of construction materials will be aided by seismic refraction, electrical resistivity, and dynamic ground testing. The same methods are applicable to problems involving the construction of railroads, highways, bridges, tunnels, and munitions plants. For the last, added protection is possibl by static-ground-resistance investigations. Salvage operations, location of shipwrecks and practice weapons, are aided by echo-sounding and radio methods. In the second group, geophysics is concerned with the location of water, fuels, and strategic minerals. Water may be found under favorable conditions by electrical and seismic methods, and water wells may be tested by electrical logging. Geophysical foundation investigations are applicable in irrigation, flood-control, and power projects. Magnetic, gravimetric, seismic-reflection, and electrical well-logging methods occupy a prominent place in oil exploration. Coal and lignite deposits may be mapped by geophysical methods. Magnetic, electrical, gravimetric, and seismic exploration methods are now used in a systematic government-sponsored exploration program to uncover vitally needed deposits of bauxite, chromite, manganese, mercury, nickel, tin, and tungsten. End_of_Article - Last_Page 903------------