RU2822231C2 - Method of searching for coal bed of coal methane deposit - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to seismic exploration and can be used to search for a coal bed of a coal-methane deposit. Method comprises performing field passive seismic monitoring during hydraulic fracturing. Seismic data are recorded from surface seismic profiles in the vicinity of the well under study. As a result of recording, sets of seismograms are obtained, the duration of which corresponds to the time of the hydraulic fracturing process. Navigation files and files of field seismic material are formed. Obtained seismic material is processed with extraction of a low-frequency highly dispersed Krauklis wave, which is a search feature of a coal bed.

EFFECT: increased information content of coal bed search at methane-coal deposit.

1 cl, 4 dwg

Description

The invention relates to specific methods for studying hydrocarbon systems using passive seismic monitoring (PSM) of events during the process of hydraulic fracturing of a coal seam (hydraulic fracturing) in methane-coal deposits, with the isolation of a low-frequency, highly dispersed wave (Kraukliks wave) from the observed seismic field.

Coal seams are unconventional reservoirs of sorbed methane. Their capacitive characteristics are predetermined by the micropore structure (up to 80% are pores ranging in size from 4 to 80 Angstroms). The coal matrix is practically impenetrable, therefore the filtration characteristics of the layers are determined by the fracturing of the coal. Naturally, identifying areas with increased open fracturing is one of the tasks of exploration of methane-coal deposits.

This method is intended for differentiation of coal seams, as unconventional reservoirs of coalbed methane, according to the degree of their prospects. The proposed method of searching for a coal seam of a methane-coal deposit, which consists in conducting field passive seismic monitoring during hydraulic fracturing, characterized in that seismic data is recorded using ground seismic profiles in the vicinity of the well being studied, obtaining at the output sets of seismograms with a duration corresponding to the time of the hydraulic fracturing process , navigation files and files of field seismic material are generated, the resulting seismic material is processed with the selection of a low-frequency highly dispersed Krauklis wave, which is a search feature of a coal seam. P.

Currently, in Russia, to obtain information on the spread of artificial fracturing during hydraulic fracturing in traditional hydrocarbon fields, surface seismic monitoring using standard seismic equipment with observation at several azimuths located in the vicinity of the well being studied is widely used. However, the information content of the results of ground-based PSM in traditional fields is not always satisfactory for a number of reasons.

The increased information content of the method in methane-coal deposits is due to a number of the following reasons.

1. Relatively shallow (up to 1 km) occurrence of the studied formation. In this regard, due to the large attenuation of the original signal with depth, obtaining an unreliable result is minimized.

2. Features of the physical and mechanical characteristics of the coal seam. The coal seam is a typical fractured reservoir.

3. Small thickness of industrial objects (coal seams) contrasting in quality with the seismic properties of 1-10 meters.

4. The gas in the studied reservoirs is in a sorbed state. The cleat cracks are filled with water.

The difference between the proposed method and “standard” solutions for monitoring the production of hydraulic fracturing is the identification and mapping of the geometry of artificial cracking with the identification of a slow, highly dispersed wave, the occurrence of which in a coal seam is a search sign for assessing the prospects of the studied object, with the aim of involving it in further development. Figure 1 shows a diagram of azimuths for monitoring the production of hydraulic fracturing in the RN-15 well in the Naryk area of Kuzbass.

The problem of elastic wave propagation in layered media has been intensively studied in seismic exploration, acoustics, physiology and physics of materials over the past century and a half. A separate story has a question about the propagation of waves in a three-layer elastic model in the case when a layer filled with fluid is enclosed between two elastic half-spaces. For the first time in 1962, P.V. Krauklis showed that in such a model a slow dispersive wave arises, the speed of which tends to zero as the frequency tends to zero. Krauklis obtained his results in analytical form in the general case of two half-spaces with different elastic parameters. After Krauklis's work, the slow wave was independently discovered by numerical calculations in acoustics for a model with elastic layers of finite thickness and in seismology in a model with two identical half-spaces.

In 1998, F. Kolovrat et al. obtained an analytical expression for the slow wave velocity for a symmetrical model with two elastic plates. Based on the variational approach and the assumption of the thickness of the plates, it was called a modular wave. V. A. Korneev in 2008 studied the propagation of a slow wave in a viscous layer of liquid located between elastic half-spaces and described low-frequency approximations for the phase velocity of a slow wave.

For the first time, the practical application of the method using a slow, highly dispersed wave in field conditions took place in the Naryk-Ostashkinskaya area of Kuzbass in 2015. At various wells in the study area, specialists from OJSC Gazprom Promgaz carried out passive seismic monitoring (PSM) of the process of hydraulic fracturing of a coal seam (HFR).

The implementation of the method is carried out in stages.

At the first stage, field seismic work of PSM was carried out during hydraulic fracturing:

1. Observation and recording of seismic material. The location of observation azimuths is shown in Fig. 1.

2. Generation of navigation files, files of field seismic material with transmission for subsequent processing.

At the second stage, the received field material was processed and interpreted:

1. Assigning geometry to seismic traces from navigation files

2. Calculation and application of static corrections.

3. Substage of processing the initial seismic field.

A coherent seismic signal of two types was extracted from the observed seismic field, corresponding to different stages of hydraulic fracturing from coal seams with different geological and physical-mechanical characteristics. The wave field presented in Fig. 3 corresponds to 91 "dense" coal seams. The selected coherent wave is approximated by a hyperbola, develops along all channels of the receiving arrangement, has a commensurate amplitude for all channels, and is confined to a point diffractor at a depth corresponding to the hydraulic fracturing operation. The spectrum of the seismic record is quite high-frequency. The resonant frequency tends to 30 Hz. The observed seismic field characterizes a dense isotropic formation. The main crack is not formed

The wave field shown in Fig. 4, corresponds to 89 fractured coal seam. The identified coherent wave has a fragmented development along the channels of the receiving arrangement, the amplitude for each channel is different, and corresponds to a source at depth, which slowly moves in a certain direction along the formation. The spectrum of the seismic record is clearly low-frequency. The resonant frequency tends to 0 Hz. The observed seismic field is characteristic of a fractured formation with pronounced anisotropic properties. The interpretation of the seismic field characterizes the formation of a main fracture in a certain direction during hydraulic fracturing. For formation 89, the hydraulic fracturing procedure was quite successful.

4. Interpretive substage. Construction of the geometry of artificial cracking using a selected wave. In fig. Figure 2 shows the selected slow highly dispersed wave and the corresponding construction of the geometry of artificial cracking.

In fig. Figure 1 shows the nature of the seismic field for 91 coal seams and the amplitude spectrum. In fig. Figure 2 shows the nature of the observed seismic field for the 89th coal seam and the amplitude spectrum.

Based on the rational use of various methods of exploration and development of methane-coal deposits in Kuzbass, a method is proposed to directly search for promising objects using a slow dispersive wave for selective involvement in the development of the studied coal seams, as well as assessing the effectiveness of the expensive hydraulic fracturing procedure. The application of the method is expected in the mining and geological conditions of the Kuznetsk and other methane-coal basins of the Russian Federation, in intervals of occurrence of coal seams up to 1000 m, with different geological and commercial characteristics.

Claims (1)

A method for searching for a coal seam in a methane-coal deposit, which consists in conducting field passive seismic monitoring during hydraulic fracturing, characterized in that seismic data is recorded using ground seismic profiles in the vicinity of the well being studied, obtaining at the output sets of seismograms with a duration corresponding to the time of the hydraulic fracturing process, navigation files and files of field seismic material are generated, the resulting seismic material is processed with the selection of a low-frequency highly dispersed Krauklis wave, which is a search feature of a coal seam.