Abstract: A method is disclosed for processing seismic data. The method includes prestack depth migrating the seismic data to generate common image gathers using an initial velocity-depth model. Horizons in the migrated seismic data are selected. Residual migration velocity analysis in the depth-offset domain is performed with respect to each selected horizon, and the velocity-depth model is updated based on the residual migration velocity analysis.

Abstract: Methods are disclosed employing seismic waves having infrasonic frequencies in the range of about 0.1–20 Hz for generating electromagnetic waves of similar infrasonic frequency in hydrocarbon bearing subterranean formations located at depths up to about 5000 meters, said electromagnetic waves having sufficient voltage amplitudes for detection at the earth's surface. Also disclosed are seismic sources capable of generating infrasonic seismic waves of sufficient amplitude for generating electromagnetic waves in hydrocarbon bearing formations at depths up to 5000 meters, said electromagnetic waves having voltage amplitudes sufficient for detection at the earth's surface.

Abstract: Systems and methods provide for detection of one or more underground utilities. Radar waves and seismic waves of about the same wavelength are generated and communicated into a subsurface. Radar and seismic response signals resulting from communication of the radar and seismic waves into the subsurface are concurrently received. Data associated with the received radar and seismic response signals are stored. One or more underground utilities within the subsurface is/are detected using the stored data. The underground utilities may include metallic and non-metallic utilities.

Abstract: A method of diagnostics of oil-and-gas deposit for seismic survey on the basis of the complex of waves of the different types. It is performed by means of the insonification of the vicinity of the borehole by the seismic waves, the recording of the displacement vectors of the direct longtidunial and shear waves using the three-component seismic profiling in the investigated borehole, the data processing of the detailed profiling for the obtaining of the dynamical, rheological and absorbing parameters of the rock, and the geological interpretation of the above-mentioned parameters for the obtaining of the quantitative estimates of the reservoir and fluid-saturated properties of the rocks for each observation point lengthways depth of the borehole.

Abstract: A method is disclosed for determining a direction of a target formation with respect to an instrument in a wellbore. The target has an electrical conductivity different than earth formations surrounding the wellbore. The method includes inducing time varying electromagnetic fields in the formations surrounding the wellbore. The electromagnetic fields have at least some components along mutually orthogonal directions. Voltages induced by the time varying electromagnetic fields are detected. The detecting is performed to have at least some component along mutually orthogonal directions. The direction of the target is calculated from the detected voltages.

Abstract: A method for treating a hydrocarbon containing formation is described. The method may include providing heat from one or more heaters to at least a portion of the formation. At least one heater may be located in at least one wellbore in the formation. At least one wellbore may be sized, at least in part, based on a determination of formation expansion caused by heating of the formation so that formation expansion caused by heating of the formation is not sufficient to cause substantial deformation of one or more heaters in the sized wellbores. The ratio of the outside diameter of a heater to the inside diameter of a wellbore may be less than about 0.75. In certain embodiments, heat may transfer from the one or more heaters to a part of the formation. In some embodiments, a mixture may be produced from the formation.

Abstract: A method is provided for accurately determining the physical location of a deployed seismic geophone used in seismic investigations by using a portable navigational satellite receiver to obtain a set of navigational satellite measurements providing the position of the deployed geophone at the time of deployment of the geophone into the earth. A method is provided for automatically and accurately identifying and determining the physical location of a deployed geophone used in seismic investigations by using one or more portable navigational satellite receivers and an automatic geophone identification and tracking system at the time of geophone deployment.

Abstract: Electromechanical device for generating elastic waves in a material medium such as the subsoil in a frequency range where the wavelengths of the waves generated are great in view of the dimensions of the device, and method for implementing it.

Abstract: A method of evaluating a seismic survey to be carried out at a particular survey location comprises choosing an initial seismic surveying arrangement. One or more parameters of AVO (amplitude versus offset) uncertainty are then determined from the seismic surveying arrangement using a model of the earth's interior at the survey location. If the parameter(s) of AVO uncertainty are not acceptable the seismic surveying arrangement is changed, and the AVO uncertainty parameter(s) re-determined for the new acquisition geometry.

Abstract: A profiling system for obtaining a characterization of a medium under a surface. The profiling system comprising a plurality of system components exchanging messages through a communication interface. The system components comprise an energy impulse generator, a sensing assembly, and a user-computing interface. The generator, for transferring an energy pulse to the surface, comprises generator communication means for exchanging the messages with other system components. The sensing assembly includes sensors. Each one of the sensors comprises an accelerometer for detecting an acceleration on the surface resulting from the energy pulse and producing a signal representative of the acceleration. Each one of the sensors also comprises an interface communication means for transmitting the signal representative of the acceleration and exchanging messages with other system components through the communication interface.

Abstract: An energy impulse generator for transferring an energy pulse to a surface. The generator exchanges messages with a computing means through a communication interface. The generator comprises a housing. The generator further comprises an impact assembly movably mounted within the housing between at least a resting position, a latched position and an impact position. In the impact position, the impact assembly transfers the energy pulse to the surface. The generator also includes an energy storage means attached to the impact assembly. In the latched position, the energy storage means is capable of releasing a specified amount of energy to the impact assembly such that upon release of the specified amount of energy the impact assembly moves from the latched position to the impact position then returns to the resting position. The computing means controls the release of the specified amount of energy to the impact assembly.

Abstract: A sensor for detecting an acceleration on a surface. The sensor exchanging messages with a computing means through a communication interface. The sensor comprises an accelerometer for outputting a signal representative of the acceleration and an interface unit comprising a transmitting circuit. The interface unit receives the signal representative of the acceleration and modulates the same for transmission to the computing means.

Abstract: A system for detecting a subterranean reservoir or determining the nature of a subterranean reservoir 12 whose position and geometry is known from previous seismic surveys. An electromagnetic field 24, 25, 26, 27 is applied by a transmitter 18 on the seabed 14 and detected by antenna 21, 22, 23 also on the seabed 14. A refracted wave component is sought in the wave field response, to determine the nature of any reservoir present.

Abstract: Method, system, and apparatus for processing seismic data by means of a time-varying optimum offset concept capable of minimizing both complexity of a common midpoint stacking method and a depth distortion of a optimum offset method. Basic information regarding the seismic data acquired by a data acquisition device is received. The position of a trace window is determined according to a time or an offset of a seismic trace. Only the data included in the trace windows of the seismic traces are horizontally stacked. Since the time-varying optimum offset method, system, and apparatus for seismic reflection data do not need a process of more than ten steps or tests to determine optimum parameters at each step, which are required by the conventional common midpoint stacking method, the processing time and cost are greatly reduced.

Abstract: An enlarged computer graphic image of seismic data is displayed on a concave three-dimensional surface having a shape corresponding to the shape of selected data extracted from a three-dimensional seismic volume. Thus providing an enlarged image of a seismic surface where the data is spatially correct in three-dimensions, and which increases the ease with which interpreters can locate geological features such as horizons, faults, and channels.

Abstract: The general object of the present invention is to provide a method for determining and displaying the relative changes of elastic moduli and that of density of geologic formations and for utilizing these relative changes and plottings for gas/oil exploration, especially for direct gas and light oil detection. The said relative changes of elastic moduli are the relative change of Lame constant .DELTA..lambda./(.lambda.+2.mu.), the relative change of shear modulus .DELTA..mu./(.lambda.+2.mu.) and/or .DELTA..mu./[.kappa.+(4/3).mu.], the relative change of bulk modulus .DELTA..kappa./[.kappa.+(4/3).mu.]; and the relative change of density is .DELTA..rho./.rho..

Abstract: The method consists in building a common midpoint gather of seismic traces of which the CMP point is said given point, subjecting the traces of this gather to dynamic and/or static corrections, and characterized in that the gather associated with the given point (A) is built by recording four CMP sub-gathers associated with said given point along four angular directions (1 to 4) passing through said given point, and dynamic and/or static corrections are applied to each of the four CMP sub-gathers in order to determine, for each sub-gather, a value of the curvature and/or the velocity optimizing the energy of the trace stack of the corrected sub-gather concerned, the four values thus obtained representing the components of the stacking velocity field desired for each of the reflector elements corresponding to the given point, and characterized by a vertical propagation time t0 with reflection for zero offset.Application in particular to the exploration of a medium with a complex tectonics.

Abstract: A seismic vibrator system for imparting compressional and shear wave vibrations into the earth has an earth contacting base with a vertical post. A tubular hub is slidably received on the post in a piston/cylinder relationship. Spaced apart horizontal top and bottom plates are secured to the hub. A mass is slidably supported between the plates. Pistons interconnect the hub and the mass. Hydraulic energy is used to reciprocate the mass vertically on the post and horizontally between the plates.

Abstract: Monofrequency continuous wave signals of long duration are used as inputs form sources of known characteristics and location. These signals are reflected off subterranean features and serve to paint the features for display and evaluation. A primary feature is the use of continuous wave, long duration signals as opposed to the standard short pulse technique.

Abstract: The invention is a method for facilitating discrimination and identification of seismic or microseismic events by means of permanent pickups in an underground zone under development. The method comprises permanent installation of, in one or more wells, elastic wave receivers, geophones and hydrophones leaving the wells clear for development of the zone, at least one reference pickup with direct acoustic coupling with the technical zone development equipment (pickup pressed against a production string for example) for detection of events directly connected with the operation of the wells (valve opening and closure, etc.

Abstract: A method of producing images of the limits of a geologic reservoir from measurements of fluid pressure in a well controlled to produce from the reservoir at a constant flow rate. The measurements are taken over a period of time, which includes initiation of well flow and recorded in a plot of well pressure v. time. The method includes detecting abrupt changes in slope of the pressure v. time function, where each abrupt change signifies the arrival of a primary shock wave at a discrete section of a boundary limit of the reservoir; and calculating the minimum radial distance to the discrete section from the well bore as a function of wave travel time. The changes in the slope of the pressure v. time function are used to calculate the curvature of the boundary at the minimum radial distance.

Abstract: A method for seismic data interpretation for the purposes of identification of oil, gas and water accumulation locations and delineation of their contours uses a model of discrete media with inhomogeneous stresses. For a selected reflection horizon, the relative value of overall pressure gradient is calculated on the basis of instantaneous amplitudes and frequencies of seismic signals using a derived relationship between the reflection coefficients of elastic waves and the stress condition parameter. The calculation technique uses estimates of instantaneous amplitudes and frequencies smoothed over the entire seismic horizon or its fragment. A generalized model of normal (lithostatic) pressure is excluded, and the final interpreted parameters have the sense of relative estimates of anomalous pressure caused by basin dynamics.

Abstract: A method and system for simulating and optimizing land seismic survey operations. The method and system utilizes spatially referenced data and nonspatial data relevant to land seismic survey operations such as high resolution satellite and airborne imagery and uses discrete event information about land seismic survey operation to simulate a land seismic survey. The output of the simulation is a detailed list of survey events. Mathematical optimization techniques are used to enhance the efficiency of the survey execution via optimal route planning and optimal allocation of survey logistical components. The invention uses a discrete event simulator which is an object-oriented software program with survey geometry objects that represent the survey design, resources objects that represent resources needed to conduct survey operations and manager objects to coordinate the resource objects within the specified survey geometry.

Abstract: The present invention provides a method for interpreting shear-wave seismic data to detect fractures in the subsurface of the earths crust. Seismic shear waves are acquired along medium symmetry planes and their corresponding AVO intercepts and gradients are estimated. The resulting AVO attributes are combined using a weighted least squares solution to estimate the change in splitting parameter and fast shear velocity, which are diagnostic of the presence of fractures. The method is also useful in assessing the porosity of the subsurface. Knowledge of subsurface fracturing and porosity is useful in locating, for example, oil and gas wells.

Abstract: A discrete, minimally-equipped standard seismic calibration system is permanently installed over a subsurface reservoir structure that contains fluids of economic interest. Changes in the fluid content as a function of long-term time lapse may introduce changes in the acoustical characteristics of the reservoir rock layers, producing a corresponding change in the seismic signature recorded by the calibration system. The difference between two signatures over a selected time epoch defines a time-lapse calibration signature. The time lapse calibration signature can be applied to reduce the results of different conventional seismic data-acquisition systems of different vintages and technologies to a common standard.

Abstract: An unconstrained transformation filter operator that is efficient in terms of computer resources and that improves circularly symmetric migrated impulse response for steep dips. The filter operator combines selected desirable attributes of the more efficient McClellan transformation filter with selected desirable attributes of the more accurate Laplacian transformation filter. The novel filter operator is not constrained along the k.sub.x and k.sub.y spatial axes by the requirement that it equal cos (k). The transformation filter is averaged over all azimuths to improve its accuracy of response.

Abstract: An attenuator for use in attenuating tube waves in a borehole includes a body formed from a permeable material having a rigid matrix which can be saturated with fluid. In its simplest form, the attenuator is one or more cylindrical bodies as part of a borehole acoustic logging system. Alternatively, the shape, particularly at the end regions, can be modified to reduce the amount of reflection of tube waves in the borehole. Another attenuator includes a body for placement in a borehole formed from an attenuating material, the shape of the body being selected such that the change in impedance experienced by acoustic waves in the borehole is gradual rather than abrupt. One particularly preferred shape for the body comprises one in which the diameter is greatest towards the center of the body, for example the shape formed by two cones placed base to base, or a cylinder having conically tapered ends. A number of bodies can be used where appropriate.

Abstract: A method for determining the approximately length and the azimuth of a hydraulic fracture after it has been formed in a subterranean formation without requiring the use of dedicated monitor wells or the need for positioning sensors at subsurface locations. Basically, the present method involves the comparison of routine, seismic surveys carried out at the surface before and after the fracture is formed to thereby determine the approximate length and azimuth of the fracture.

Abstract: A multivibrator waveform monitoring system uses a plurality of seismic energy sources for giving vibrations to strata and a prospector, connected to a geophone, for measuring reflected vibrations. Each of the plurality of seismic energy sources includes a vibrator, a communication unit and a control unit for controlling the starting of the vibrator based on phase difference cancellation information and an operation starting instruction from the prospector. The prospector includes a communication unit and a synchronization control unit for controlling the synchronization of each of the seismic energy sources.

Abstract: A method for obtaining seismic data in frigid regions without interference from flexural ice waves. In an exemplary embodiment, seismic data is produced by using an energy source to generate a seismic wave in a floating ice sheet. Seismic disturbances caused by the energy source are detected by one or more hydrophones and geophones, which produce hydrophone and geophone response signals, respectively. In a first embodiment, the hydrophone response signal is integrated. The integrated signal and/or the geophone response signal are scaled, and the two signals are then added. Alternatively, instead of integrating the hydrophone response signal, the geophone response signal may be differentiated prior to scaling and summing. A method is also disclosed for overcoming phase errors that might be introduced, for example, by the use of a transformer-coupled hydrophone.

Abstract: In the exploration for petroleum or natural gas, drilling targets are identified by locating local maxima of horizontal gradient in the top-of-geopressure surface of a region of exploration. The probability of finding hydrocarbon deposits is significantly improved where the drilling targets are local maxima of the horizontal gradient in the top-of-geopressure surface which coincide with local maxima of subsurface heat flow in the region of exploration, particularly where the local maxima in the horizontal gradient of the top-of-geopressured surface is concentrated across major fault offsets and are parallel to the predominant strike directions of the faults. The top-of-geopressure surface may be remotely sensed by performing complex trace analysis on reflection seismic traces gathered for the region of exploration to derive corresponding reflection strength attribute traces.

Abstract: Methods are provided for making use of an apparatus for generating vibrational energy in a borehole, the apparatus utilizes a mass and a rotary source for suspending the mass in a borehole or in casing in a borehole or in an instrument housing that may be positioned in an opened or cased borehole arranged to cause frictional contact with the surface of the rotating mass, the mass being rotatable about is rotational axis in one direction to cause it to backward whirl in the opposite direction, the centrifugal force of the whirling mass serving to generate vibrational energy that is used to obtain geophysical information as to the structure of the earth surrounding and adjacent to the borehole and for enhancing cementing and production enhancing techniques in oil or gas wells.

Abstract: The invention comprises a seismic recording apparatus and method. A multichannel recorder is connected to a cable formed from a plurality of signal conductors. Each of the signal conductors is connected to a different channel of the recorder via a multiplexer. The cable has a plurality of takeouts located at spaced distances along its length. Each of the takeouts is connected to a different signal conductor of the cable. A switch means is operably connected to one of the takeouts for selectively interconnecting the takeout and any one or more of several seismic detector connections upon receipt of a remotely generated signal. The invention also includes a number of detector conduits, each of which has one end operably connected to a different one of the seismic detector connections of the switch means. Each detector conduit has at least one geophone located along its length and operably connected thereto. A control means is provided for transmitting a signal to the switch means.

Abstract: The invention comprises a seismic recording apparatus and method. A multichannel recorder is connected to a cable formed from a plurality of signal conductors. Each of the signal conductors is connected to a different channel of the recorder via a multiplexer. The cable has a plurality of takeouts located at spaced distances along its length. Each of the takeouts is connected to a different signal conductor of the cable. A switch means is operably connected to one of the takeouts for selectively interconnecting the takeout and any one or more of several seismic detector connections upon receipt of a remotely generated signal. The invention also includes a number of detector conduits, each of which has one end operably connected to a different one of the seismic detector connections of the switch means. Each detector conduit has at least one geophone located along its length and operably connected thereto. A control means is provided for transmitting a signal to the switch means.

Abstract: A method and system for geophysical exploration including obtaining, processing, displaying and interpreting seismic data. Seismic energy is imparted into the earth's subterranean formation along at least two linear independent lines of action in a seismic survey. At least two linearly independent components of the seismic wave energy imparted along each line of action are detected within the seismic survey. A concord of seismic signals is produced from the seismic wave energy detected for selected combinations of receiver and source locations. An orientation module operates on the concord of the seismic signals so as to generate synthetic concords of seismic signals so as to focus on a particular component of the seismic wave energy in order to infer the geologic characteristics of the earth's subterranean formations.

Abstract: A method for determining the location of steeply dipping subsurfaces includes acquiring seismic reflection data, identifying select data which has characteristics indicating that the acoustic pulses which it represents have been reflected from a substantially horizontal interface and a steeply dipping interface, analyzing the select data to locate the steeply dipping interface and displaying the analyzed data.

Abstract: A system of monitoring the fluid contents of a petroleum reservoir, wherein a reservoir model is employed to predict the fluid flow in the reservoir, includes a check on the reservoir model by comparison of synthetic seismograms with the observed seismic data. If the synthetic output predicted by the model agrees with the observed seismic data, then it is assumed that the reservoir is being properly worked. If not then the reservoir model, in particular its reservoir description, is updated until it predicts the observed seismic response. The seismic survey may be periodically repeated during the productive life of the reservoir and the technique used to update the reservoir model so as to ensure that the revised reservoir description predicts the observed changes in the seismic data and hence reflects the current status of fluid saturations. Implementation of this invention results in more efficient reservoir management.

Abstract: A seismic method for determining the thickness of a subterranean layer of interest and the velocity of seimic in the layer. Seismic waves are transmitted into the layer, and a plurality of waves are detected wherein each detected wave is reflected from a different point along the lower boundary of the layer. Two parameters, .DELTA.x and .DELTA.T, are determined for each reflected wave. .DELTA.x is defined as the horizontal distance a wave travels between the upper boundary and the lower boundary of the layer, and .DELTA.T is defined as the one way travel time of a wave between the upper boundary and the lower boundary of the layer. A set of data pairs are obtained, wherein each data pair includes a (.DELTA.x).sup.2 value and a (.DELTA.T).sup.2 value. These pairs are fitted to a linear function so as to yield slope value and intercept values. These values may be utilized to calculate the wave velocity and thickness of the layer.

Abstract: A blast recorder and method for monitoring and processing vibrations from blasts, and for displaying the results in a nearly real time basis and in a manner which is easily interpreted by a relatively unskilled field worker and corresponds to a form which closely correspond to the real damage causing aspect of the blast than heretofore.

Abstract: A method of processing seismic data involves the input of common depth point data for determination of obliquity of downward propagating energy. Data having known surface offset and travel time is then processed with interval velocities along the depth of survey to solve by matrix inversion for the earth elastic parameters at selected depths.

Abstract: Polarized shear wave surveys are performed to determine azimuthal variations in the earth's subsurface caused by fracture orientation and density. The surveys may be done by using the same polarization (either horizontal or vertical) shear waves along two different seismic lines of profile, or by using different polarization shear waves along one common line of profile. The survey data are then processed and compared; any differences constitute a measure of fracture orientation and density. Subsurface zones of high fracture density, once identified, have been found to afford a higher likelihood of successful well completion.

Abstract: The invention permits the measurement of the propagation anisotropy of a transverse wave between two given reference points of a non-isotropic medium (M), particularly a shear wave in a stratified or fissured rock.According to the invention: a source (S) and two detectors (G.sub.1, G.sub.2) are arranged along a single ray vector, the detectors being positioned at the location of respective reference points; the source is excited by an excitation signal producing a transverse wave in the medium; the respective resultant measurement signals produced by each of the detectors are received; from the excitation signal and the measurement signals the transfer function of the medium along each of the respective source-detector paths is determined; the differential transfer function of the medium between the two reference points is deduced.

Abstract: A method of seismic exploration including processing and displaying shear wave seismic data for identifying gaseous hydrocarbon-containing formations and for inferring changes in the geological character of subterranean formations. A measure of the shear wave reflection coefficient is obtained for selected seismic events in the shear wave seismic data. Measures of formation property contrasts represented by the selected seismic event are obtained from the shear wave reflection coefficients.

Abstract: The present invention is a downhole seismic source capable of generating seismic forces in excess of 1000 newtons. The source produces seismic waves for seismic applications, particularly cross borehole measurements and vertical seismic profiling. Coupled with motion sensing devices, the present invention also performs as a seismic logging tool. The source is comprised of an outer housing, a means for clamping the source securely to the wellbore, and a linear electromagnetic actuator which utilizes permanent magnetic material having remanent magnetic field exceeding about 0.9 T such as rare earth permanent magnetics. The source has a diameter of about 12.5 cm to fit within a typical wellbore and the acuator has a length of about 1 meter.

Abstract: A method for determining the position of a subterranean plane reflector relative to a known location on the earth surface from unprocessed seismic data received at a number of colinear acoustic receiver locations. A traveltime curve associated with the reflector is identified from the seismic data. From two points on the traveltime curve, a signal indicative of the reflector's dip angle is generated. Using the dip angle signal, signals indicative of the position of each imaged point of the reflector are generated. The inventive method assumes knowledge of the average velocity of seismic waves in the subterranean formation above the reflector, and that such formation region can adequately be considered to have constant velocity equal to such average velocity. The method may be applied to process raw data generated during a vertical seismic profiling operation.

Abstract: The present invention relates to a ground position controller utilizing a microcomputer system interconnected to a digital field system (DFS) via a system bus, for generating, formatting and displaying information (for insuring integrity of field operations) under a variety of shooting and collecting conditions.

Abstract: A seismic exploration system where a plurality of geophone locations are employed in one spread along a survey line. The recording procedure uses a roll-along switch for successively connecting a lesser number of recording channels to the geophone locations as separate records are taken without changing the spread. A signal is superimposed at one of the geophone locations. The signal is outside the useful range of seismic energy so that the particular geophone location may be identified on successive records without interfering with the recording of the seismic energy.

Abstract: The present invention indicates that in exploration of permafrost regions of the world for oil and gas accumulations, flexure noise can be attenuated by careful placement of the vibratory source vis-a-vis the receiver array during collection of the Vibroseis.RTM.-type data. If the explorationist adopts a survey strategy in which the vibratory source is separated from the receiver array by a pressure ridge or its equivalent over the ice formation of the region under survey, then - surprisingly - the seismic reflection signals can be easily collected and displayed. Result: continuity of events from onshore reflectors can be easily followed offshore through the transition zone into deeper sea ice regions. He is aided in formulating his exploration strategy by the use of aerial and/or radar photographs or LANDSAT unmanned satellite data for mapping the pressure ridges of the area under survey.

Abstract: The present invention indicates that in exploration of permafrost regions of the world for oil and gas accumulations, flexure noise can be attenuated by careful placement of the vibratory source vis-a-vis the receiver array during collection of the Vibroseis.RTM.-type data. It has been surprisingly found that if the explorationist adopts a survey strategy in which the vibratory source is separated from the receiver array by a pressure ridge or its equivalent over the ice formation of the region under survey, then the seismic reflection signals can be easily collected and displayed. Result: continuity of events from onshore reflectors can be easily followed offshore through the transition zone into deeper sea ice regions.

Abstract: In the hydraulic fracturing of deep geologic formations for the production of fluid hydrocarbons, and where vertical fractures are formed, a method is described, using seismic geophysical techniques, for determining the azimuth and length of the fractures. This is accomplished by injecting into the formation through the fracture a selected fluid, or producing the fluid hydrocarbons from the formation into the fracture, until the formation, over a selected distance from the walls of the fracture, has a different gas saturation from the condition in the formation farther from the fracture. This condition is mapped by seismic methods.