RU2339978C1 - Method of borehole sesmic exploration works - Google Patents

Abstract

FIELD: mining engineering.

SUBSTANCE: vibration source installed in the near-surface region excites elastic oscillations. The vibrations are recorded by a probe in the receiving points located in the well. The vibrations are recorded when the instrument is in a specified position in relation to the vibration source. Moreover, the vibration source is successively induced in several points whose coordinates are determined so that valuable waves are reflected in the points with defined coordinates.

EFFECT: enhanced accuracy of determination of a structural form of specific geological objects.

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Description

The method of borehole seismic exploration relates to the field of earth subsurface research in the search and exploration of minerals by geophysical methods and, in particular, by the seismic method. The main objective of the seismic exploration method is to study the geological structure and composition of rocks.

The well-known "Method of vertical seismic profiling" [1]. In this method, the excitation of oscillations is produced on the surface at some point lying on a straight line passing through the receiving point in a deep well and perpendicular to the plane boundaries of the layers.

This method is intended to more accurately determine the elastic characteristics of the geological section in studies in deviated wells. However, when moving away from the well in the general case, the speed characteristic can change significantly and the use of data on velocities obtained near the well to solve structural problems can also lead to large errors. In addition, for the implementation of the method requires information on the angles of inclination of geological formations, which researchers do not always have.

The above disadvantages of the method create significant limitations on its scope.

The well-known "Method of vertical seismic profiling" [2]. Here, in order to expand the scope of the method due to its use in the conditions of azimuthal disagreement of obliquely occurring borders. For this, a reflection line orthogonal to the contour of the reconnaissed anomaly is set. The excitation point is calculated from the condition of ray tracing through the receiving point in the well and a given point on the reflection line. In this case, it is necessary to ensure the equality of the angles of incidence of the wave from each source to the corresponding reflection point.

The main disadvantages of this method are elusive conditions that must be met before the next work.

1. Ensuring the equality of angles of incidence at different points of reflection.

2. To specify the line of reflection points orthogonal to the contour, information is needed on the position of the contour of the anomalous section, the receipt of which is not an easy task.

3. The simultaneous change in the coordinates of the points of reception and excitation increases the instability of the conditions for recording oscillations and, accordingly, reduces the accuracy of determining the signal parameters.

The aim of the invention is to improve the accuracy of determining the structural form of specific geological objects.

This goal is achieved by the fact that according to the proposed method, the oscillations are recorded at one or more points by the device in the well and at each fixed position of the device, the oscillation source is sequentially excited at several points, the coordinates of which are determined so that the reflection of useful waves occurs at points with specified coordinates.

Thus, the proposed method, which consists in the excitation of elastic oscillations by an oscillation source installed in the near-surface zone, registration of oscillations by a probe at the receiving points located in the well, according to the invention, the oscillations are recorded at a fixed position of the device from the oscillation source, sequentially excited at several points, the coordinates of which are determined so that the reflections of useful waves occur at points with given coordinates.

The method is illustrated in the drawing, which shows: surface 1, wellhead 2, well 3, receiving points of vibrations 4 and 5 in well 3; on the studied boundary 7, there are many reflection points 6 located in the area where it is necessary to clarify the boundary 7, then on the surface 1 the points of excitation 8-9 are shown, and the coordinates of the points of excitation 8 are designed so that the waves propagating from them to the border 7 are reflected at given points 6, respectively, and recorded at the same reception point - 4, and the coordinates of the excitation points 9 are set so that the waves propagating from them to border 7 are reflected at the same points 6 and respectively 5 at the same but different reception point.

The method is implemented as follows.

Before making observations in the well, the geologist, based on a priori data, determines the coordinates of the set of reflection points 6 on plane 7, which is the first approximation to the surface shape of the studied boundary. Then, using a priori information about the geological structure of the section above the studied boundary 7 and the known coordinates of one of the reception points, for example, 4, the corresponding coordinates of the excitation points 8 are calculated for each of the intended reflection points.

After the coordinates of the excitation points 8 for one receiving point, for example, 4, and, accordingly, for all the intended reflection points 6, are determined, the oscillations in each point 8 are sequentially excited and the oscillations are recorded when the device is in the same position in the well. According to the data obtained, waves are reflected that are reflected from the studied boundary at the designated points and on this basis, the refined coordinates of the reflection points are determined and, accordingly, new information about the shape and behavior of the boundary is obtained.

The accuracy of determining the shape of the reflecting boundary depends on the accuracy of the selection of useful waves. To increase the accuracy of the selection of useful waves reflected from the studied boundary at the same designated points 6, it is possible to register oscillations at one or more reception points, for example, 5. Moreover, for each reception point, it is necessary to determine the new coordinates of the excitation points 9.

Performing further the summation of the vibration records related to one reflecting point, but to different points of receiving vibrations, we obtain an averaged signal with a higher signal / noise ratio, which ensures an increase in the accuracy of the extracted signals and, accordingly, their parameters, which are used in further calculations to refine the coordinates of the reflection points .

The number of reflection points and reception points for one studied boundary is determined only by the geological and economic feasibility and physical capabilities of the method.

Information sources

1. Kozlov EA, Shekhtman G.A. The method of vertical seismic profiling. A.S. 1002997 USSR, MKI 01V 1/40.

2. Shekhtman G.A., Zernov A.E. The method of vertical seismic profiling. A.S. SU 1345849 G01V 1/40.

Claims (1)

The method of downhole seismic exploration, which consists in the excitation of elastic oscillations by an oscillation source installed in the near-surface zone, registering oscillations with a probe at the receiving points located in the well, characterized in that the oscillations are recorded at a fixed position of the device from the oscillation source, sequentially excited at several points, the coordinates which are determined so that the reflection of the useful waves occurs at points with given coordinates.