RU2644442C1 - Method of vibration seismic survey - Google Patents

Abstract

FIELD: geophysics.

SUBSTANCE: invention relates to geophysics and can be used during seismic surveys. Disclosed is method for vibration seismic survey, which includes the excitation and recording of seismic oscillations when the sources are located in the near-surface zone, and the receivers in the near-surface zone or in the well. Oscillations are excited by means of continuous sweep signals in a wide frequency band or at a fixed frequency. Method is characterized by that the oscillations are excited many times, alternating oscillations in a wide frequency band and monochromatic oscillations. Thus, whenever oscillations are emitted in a wide frequency band, it is proposed to isolate associated with fluctuations in the oil reservoir resonance oscillations from the seismic record. Since the frequency of resonance oscillations can vary with time, then multiple excitations of oscillations in a wide frequency band allow essentially to carry out monitoring at the deposit, in a timely manner correcting the monochromatic oscillations excited by the vibration source, contributing to increase in oil recovery from the deposit. In those cases, where one or more oil deposits generate different resonant oscillations, it is proposed to simultaneously initiate monochromatic oscillations with different vibration sources, each of which is tuned to the excitation of the corresponding monochromatic oscillations. Duration of monochromatic oscillations is taken by at least three orders of magnitude greater than the duration of the vibrations adopted in standard vibroseismic survey in a wide frequency band.

EFFECT: increase in oil recovery of hard-to-recover reserves.

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Description

The invention relates to geophysical methods for the study of the geological environment and is intended mainly for the search and exploration of oil fields, as well as to increase the oil recovery of oil deposits at the stage of field operation.

Vibrational seismic exploration (vibro-seismic exploration) is based on the long-time excitation of oscillations, which can be implemented in the form of quasi-harmonic variables in the frequency of the loads, at which points of the medium perform forced oscillations in accordance with the frequency of the external load.

The method of controlled vibro-acoustic impact on productive oil-saturated formations has been developed since the 1970s. Currently, it has been widely tested in various seismic and geological conditions for the intensification of downhole hydrocarbon production. There are many experimental studies that indicate that exposure to an oil-saturated formation with frequencies close to the resonant frequencies of the oil reservoir increases oil inflow to the well under study and reduces its water cut (Alelyukhin et al., 2004; Zhukov et al., 2011; Barabanov , 2013). The intensity of the low-frequency vibroseismic effect on oil deposits from the earth's surface is less than 10 W / cm, which is several orders of magnitude less than the specific acoustic power required by laboratory experiments to influence physical processes in porous fluid-saturated media. The discrepancy between the results of full-scale and laboratory tests, as well as the qualitative nature of the ideas about the mechanism of interaction of low-intensity vibroseismic vibrations with an oil deposit, predetermined the experimental nature of the work on creating an effective method of vibration processing of oil productive formations from the earth's surface.

Initially, oil from the reservoir is produced due to the fact that the primary pressure in it is higher than the action of the complex forces of fluid adhesion to the porous medium. When the pressure decreases during production, an equilibrium point is reached at which the adhesive forces are more significant than the residual pressure in the reservoir. However, most of the oil is still in the reservoir. It is believed that on average it can reach 85% of the oil that was in the reservoir initially. Therefore, the goal of all the developed methods is to increase oil production associated with overcoming the adhesion forces in the reservoir.

One of the main reasons for these adhesion forces is the wettability of the reservoir. It affects its capillary pressure, its relative permeability and other properties. In the case when the rock does not show any strong affinity for any fluid, it is believed that its wettability should be neutral or intermediate.

The experience gained with vibration sources gained as a result of many studies has led to the conclusion that they should be reliable, inexpensive, durable and synchronized with the natural frequency of geological formations. It was found that the effective intrinsic frequency of reservoir oscillations is usually in the range from 0.5 to 5 Hz and can provide sound pressure of the order of 2 to 20 MPa, depending on the pressure prevailing in the reservoir (Yanturin et al., 1986). At the same time, it turned out that the frequency of intrinsic (dominant) oscillations can reach 100 Hz, and the Brazilian oil field, where at a given frequency the pressure was 1.67 MPa, was cited as an example. The literature provides data on dominant frequencies located in almost the entire operating frequency range used in vibrational seismic exploration (Barabanov, 2013).

It has been confirmed that vibrations provide various effects in the fluids contained in the formations. Vibrations release cohesive and adhesive bonds, as well as most of the capillary forces, thereby allowing hydrocarbons to flow through the formation. Vibrations that propagate inside the oil reservoir in the form of elastic waves will change the contact angle between the formation and the fluids and reduce the coefficient of hydraulic resistance. Thus, there will be a more free flow of fluid in the direction of the well.

The mechanism of the effect of seismic effects on the natural reservoir of oil fields is a complex chain of interconnected processes (Alelyukhin et al., 2004). Seismic action leads to the excitation of weak electromagnetic fields in saturated porous media. The most intense fields are generated in the field of shear waves by periodic displacements of the double electric layer along the surface of the mineral skeleton - liquid. This is manifested in the form of a change in the effective contact angle. Under favorable circumstances, electromagnetic disturbances can change the wettability of the natural collector in the direction of its greater neutrality.

A known method of increasing oil production from an oil reservoir and a device for its implementation (RF patent No. 2097544). In this method, the geological formation is simultaneously affected by elastic sound waves and electric heating. For this purpose, an insulating bridge is preliminarily created in the well above the oil reservoir by performing a cavity by cutting out part of the casing string and filling this cavity with insulating material. Electric current is supplied to the oil manifold along the part of the casing located below the insulation bridge through mechanical or hydraulic actuators connected to the vibrator from the vibrator or through an electrical conductor connecting the vibrator to the hydraulic conductors located above the insulation bridge. Electric current to the vibrator or to the hydraulic connectors located above the insulating bridge is supplied through an electric cable, production string or insulated casing. Use different types of vibrators. This method creates vibrations of the formations in the oil reservoir with a frequency closest to the natural frequency of the formations in order to reduce the adhesion forces between the formations and the oil. The disadvantage of this method is the complexity of the devices used in it and the technology itself, which involves the invasion of standard types of equipment into the operation of wells.

Closest to the proposed invention (prototype) is a method of developing an irrigated oil field (RF patent No. 2197603), which includes opening a layer of at least one injection and one production well, locating one or more irrigated sections of the field with a fixed oil phase and seismic effect on formation from at least one source of oscillation. The differences of this method are that it constructs a radiation pattern of the radiation source of the oscillations along the transverse waves, determines the areas of maximum amplitudes of the transverse waves from it, and sets the oscillation source so that the boundary of the flooded section of the field with a fixed oil phase and the perforated production interval the wells were simultaneously in the region of the maximum amplitudes of the transverse waves, while the seismic effect is carried out until irreversible changes natural electric potential or pore pressure or sudden changes in its relative permeability.

The disadvantages of the prototype are as follows:

1. It completely does not take into account the intrinsic (dominant) oscillation frequency of the oil reservoir.

2. The spatial radiation pattern of the vibration source requires spatial observations in the vicinity of the source, which inevitably complicates the technology of work.

3. It is practically impossible to determine the region of maximum amplitudes of shear waves so that it coincides with the boundary of the flooded area in difficult-to-build environments, since it is necessary to conduct detailed multiwave studies using the VSP method in the vicinity of the well, which complicates and increases the cost of the proposed method.

4. Vibration sources of shear waves are extremely unstable during their continuous operation, necessary for vibration exposure to the formation. There is a backlash between the teeth (lugs) of the platform and the ground in the process of exciting vibrations. It is dangerous when its value is greater than the amplitude of free movement of the base plate of the vibrator, as a result of which the plate begins to touch the ground. Since for a given force the movement of the base plate depends on the frequency, the effect of backlash has a different effect at the beginning and at the end of the source vibration session. Sliding the base plate shifts the frequency spectrum of the shear waves downward and thereby degrades the parameters of the vibration source, which is initially tuned to some fixed frequency.

The purpose of the proposed method of vibrational seismic exploration is the expansion of its functionality.

This goal is achieved by the fact that in the method of vibrational seismic exploration, including the excitation of seismic vibrations by vibration sources located in the near-surface zone using a continuous or monochromatic sweep signal and recording vibrations by seismic receivers installed in the near-surface zone or in the well, vibrations are repeatedly excited by alternating broadband and monochromatic sweep signals, and after recording signals from a broadband sweep signal, resonant ysmic oscillations formed by the oil reservoir, after which they excite monochromatic oscillations at the selected resonant frequency. The duration of the excitation of signals at the resonant frequency is taken no less than three orders of magnitude longer than the duration of the signals during excitation of oscillations in a wide frequency band, and the removal of vibration sources from the projection onto the earth's surface of the center of the oil reservoir is taken commensurate with the depth of the reservoir.

Compared with the prototype of the proposed method of vibrational seismic exploration in accordance with the invention is characterized by such significant differences:

- a method of obtaining input information that purposefully includes alternating the excitation of oscillations using broadband and monochromatic sweep signals;

- monitoring changes in the resonant frequency excited by the oil reservoir in the process of vibration exposure to it;

- excitation of longitudinal vibrations on inclined seismic rays with the possibility of the formation of transverse waves as a result of exchange at sharp boundaries located above the reservoir.

The essence of the proposed method is as follows.

When exciting seismic oscillations in a wide frequency band on a seismic record obtained in the near-surface zone and inside the medium, resonance oscillations caused by noise and useful signals are distinguished by known processing methods. After identifying the resonant vibrations on the recording with the resonant vibrations emitted by the oil reservoir, monochromatic vibrations are excited at this resonant frequency, which affect the oil reservoir, amplifying its own (dominant) vibrations. Since the removal of the source of oscillations from the projection of the oil reservoir onto the earth's surface is significant (it is commensurate with the depth of the reservoir), seismic rays propagate to the depth at significant angles of inclination. The act of exchanging longitudinal waves for transverse waves does not lead to a change in frequency, therefore, the transverse waves arising from the exchange will have the same frequency as the longitudinal waves, the excitation of which does not cause the above-mentioned problems associated with the excitation of transverse waves directly in the source. The duration of monochromatic oscillations is hours or more. During this time, the parameters of the oil deposit can change significantly, and with their change, the resonant frequency excited in them can also change. With prolonged vibroseismic impact on the oil reservoir, a shift in the reaction maximum of seismic rock emission is observed towards higher dominant frequencies (Barabanov, 2013). What this dominant frequency has become can be judged by processing the re-recorded record, which is excited using a sweep signal in a wide frequency band. The spectrum of the target signal, which will be used to configure the excited monochromatic signals, can be obtained directly by registering signals inside the medium during vertical seismic profiling.

The method is as follows.

In the near-surface zone, geophones are installed at a point that coincides with the projection of the center of the oil reservoir onto the earth's surface, as well as at distances from this point that are comparable with the depth of the reservoir. At distances commensurate with the depth of the reservoir, vibration sources are installed in different azimuths. At first, at least one vibration source excites oscillations using a sweep signal in a wide frequency band. Vibration signals recorded by different geophones, by means of mutual correlation with a sweep signal or deconvolution using a reference sweep signal, are converted into a pulsed form and interpreted to detect resonance oscillations generated by the oil reservoir on the obtained records. There can be several such resonant oscillations, depending on the partial resonant frequencies excited in the oil reservoir. After identifying these resonant frequencies, at least one vibration source is tuned to each of them, and monochromatic oscillations are excited, the task of which is to increase the oil recovery of the reservoir.

The introduction of the invention into the practice of vibrational seismic exploration does not require the creation of new technical means and can be started already at present. Its use will allow more reasonable control of monochromatic oscillations, thereby achieving an increase in the efficiency of vibration exposure to the oil reservoir. EFFECT: enhanced oil recovery of hard-to-recover reserves.

INFORMATION SOURCES

Asan-Jalalov A.G., Barabanov V.L., Zvezdov A.V., Martos V.N., Lavrov B.C., Nikolaev A.V., Sevalnev A.V. A method of developing a waterlogged oil field // RF Patent No. 2197603, publ. 01/27/2003. Olav Ellingsen, Carlos Roberto Corvalho De Olleven, Carlo Alberto De Castro Goncalves, Euclides Jose Bonet, Paulo Jose Villani De Andrade, Roberto Francisco Messomo // Method of increasing oil production from the oil reservoir and device for its implementation. RF patent No. 2097544, publ. 11/27/1997.

Alelyukhin N.P., Asan-Jalalov A.G., Barabanov V.L., Lavrov B.C., Nikolaev A.V. Enhanced oil recovery by seismic impact on the reservoir // Instruments and systems for exploration geophysics, No. 3, 2004. P. 39-41.

Barabanov V.L. Seismic effects on oil deposits: problems and prospects // Nefteservis, No. 3 (23), 2013. P. 26-27.

Barabanov V.L. On the selectivity of the dynamic response of permeable porous media to seismic effects // Trigger effects in systems. Materials of the second All-Russian seminar-meeting, Moscow, June 18-21, 2013, pp. 94-101.

Zhukov A.P., Kolesov S.V., Shekhtman G.A., Schneerson M.B. Seismic exploration with vibration sources. Tver, 2011.412 s.

Yanturin A.Sh., Rakhimkulov R.Sh., Kagarmanov N.F. The choice of frequencies with vibrational impact on the bottomhole formation zone // Oil industry. No. 12, 1986. S. 40-42.

Claims (4)

1. The method of vibrational seismic exploration, including the excitation of seismic vibrations by vibration sources located in the near-surface zone using a continuous or monochromatic sweep signal and registration of vibrations by seismic receivers installed in the near-surface zone or in the well, characterized in that, in order to expand the functionality, many times excite oscillations by alternating broadband and monochromatic sweep signals, while after recording signals from broadband sweep c The ignals emit resonant seismic vibrations formed by an oil reservoir, after which they excite monochromatic oscillations at the selected resonant frequency. 2. The method according to p. 1, characterized in that the duration of the excitation of signals at a resonant frequency is taken no less than three orders of magnitude greater than the duration of the signals upon excitation of oscillations in a wide frequency band. 3. The method according to p. 1, characterized in that when the oil reservoir is excited by resonance oscillations at different frequencies, monochromatic oscillations are simultaneously excited by different vibration sources, each of which excites monochromatic oscillations tuned to one of the resonant frequencies. 4. The method according to p. 1, characterized in that the removal of vibration sources from the projection onto the earth's surface of the center of the oil reservoir is taken commensurate with the depth of the reservoir.