RU2393353C1 - Method for extracting methane on fields of abandoned coal mines - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: invention involves determination, according to mining-and-geological and mining-and-technical conditions of the mine, of technogenic methane reservoirs formed with disintegration of rocks during extraction of coal beds. There chosen are location places of wells on the basis of extracting maximum amount of methane from one or several technogenic reservoirs through each well at its depth providing optimum unit costs for methane extraction from those reservoirs. Invention allows increasing methane content in the extracted gas mixture owing to limited air inflow to the well due to high aerodynamic resistance of the deformed massif in the section of unextinguished mine workings to well perforation channels. Invention allows extracting conditioned methane-air mixtures in conditions of occasional disturbance of tightness of mine workings with atmosphere or absence of tightness in widely used mine abandonment technologies.

EFFECT: increasing productivity of degassing wells owing to degassing of several technogenic reservoirs opened with one well.

1 dwg, 1 tbl, 1 ex

Description

The invention relates to the mining industry and can be used to extract methane from liquidated coal mines.

A known method for the extraction of methane in the fields of operating coal mines, based on drilling from the surface of degassing wells into the zone of disintegration of rocks under the influence of rock pressure as the moving face [1]. This zone is characterized by a high methane influx due to the development of a network of main cracks providing aerodynamic connection of the well with unloaded coal seams and host rocks.

The disadvantage of this method is that when developing the underlying layers in the formation, it is necessary to drill additional degassing wells.

There is a method of extracting methane from abandoned coal mines, based on drilling from the surface of degassing wells into the methane inflow zone, while aerodynamic isolation of underground mine workings is carried out before the mine is liquidated [2]. The zones of methane inflow and accumulation are underground mine workings, which serve as a gas collector, into which methane comes from the surrounding carbonaceous massif. This method is taken by us as a prototype.

This method of extracting methane from abandoned mines with timely aerodynamic isolation of underground mines with access to the day surface allows the extraction of conditioned methane-air mixtures.

The disadvantage of the prototype is the difficulty of accurately getting the wells into production, which requires the use of expensive high-precision means of controlling the drilling process to reduce production risks.

The objective of this invention is to increase the productivity of degassing wells and the concentration of methane in the gas mixture extracted from the rock mass in the fields of liquidated mines in the absence of aerodynamic isolation of underground mine workings with the atmosphere, as well as reducing the cost of drilling degassing wells.

This is achieved by the fact that in the method for extracting methane from the fields of abandoned coal mines, based on drilling from the surface of degassing wells into the methane inflow zone, technogenic methane collectors formed by the disintegration of rocks during the extraction of coal seams are determined in the rock mass, then the location is chosen degassing wells based on the condition for extracting the maximum amount of methane from one or more technogenic reservoirs through each well at its depth, which provides optical cial unit cost of extraction of methane from these reservoirs.

The drawing schematically in section shows options for the mutual arrangement of technogenic collectors in the mountain range.

The method of methane extraction in the fields of liquidated coal mines is carried out in the following way.

Before liquidation, a coal mine developed coal seams 1, 2, 3, 4, 5, 6, 7, and 8, between which substandard seams lie. After completion of mining operations on the mined-out spaces, zones of collapse and disintegration of the rock mass formed — technogenic reservoirs into which methane from cracks and substandard coal seams and the adjacent rock mass flow through cracks. According to geological and mining data, information is analyzed on the relative position of the worked out mine field spaces on vertical sections of sections A, B, C, D and technogenic methane collectors are determined: collectors A1, A2 and A4 on section A, collectors B1 on section B , B2 and B3, in section C - collectors C4 and C5, in section D - collectors D1, D3, D6, D7 and D8. The area of each technogenic reservoir in plan is equal to the area of the corresponding worked out space, and the height depends on geological and technological factors and is in the range (20 ... 40) m, where m is the taken-out thickness of the formation. Man-made reservoirs are in undisturbed rock mass. After determining the dimensions of the technogenic methane collectors, the locations of the degassing wells are selected based on the condition for extracting the maximum amount of methane through each well at its depth, which ensures the optimal unit costs for the extraction of methane from these technogenic collectors. Degassing of technogenic reservoirs in sections A, B, C, D can be done using wells 9, 10, 11, 12, respectively. Well drilling is carried out with the intersection of man-made reservoirs or opening the collector in the presence of aerodynamic communication between it and the underlying reservoirs. With the same total amount of methane in the reservoirs A1, A2, A4 and B1, B2, B3, the second option is preferred, since the depth of the well 10 is less than the well 9, and therefore, the specific cost of extracting methane from the well 10 is less than the specific cost of extracting methane from the well 9. The extraction of methane in section C will be less efficient compared to section A by the criterion of a lower amount of methane in the reservoirs, and compared to section B, according to the criteria of less methane and a greater depth of the well. Extraction of methane in sections D and A can have the same efficiency at the same specific costs for the extraction of methane. In cases where the specific costs for the extraction of methane correspond to the optimal values, well drilling is advisable. If the specific costs of methane extraction from all technogenic reservoirs opened by one well in one section exceed the optimal values, then it is advisable to consider the option in which the optimal specific costs of methane extraction will be ensured by reducing the depth of the well. In this case, the optimal unit costs are determined by the necessary profitability of the enterprise and the market environment. In each of these wells, casing is perforated at the intervals of intersection and opening of technogenic reservoirs. The productivity of degassing wells is increased due to the degassing of several technogenic reservoirs in one well. The high quality of the extracted gas is ensured by a limited suction of air into the borehole due to the high aerodynamic resistance of the deformed massif in the area from the outstanding mine workings to the borehole perforation channels. In conditions of accidental violation of the tightness of mine workings with the atmosphere or lack of tightness in widely used technologies for the elimination of mines, this method also allows the extraction of conditioned methane-air mixtures due to the high aerodynamic resistance of the deformed massif.

Implementation example. The liquidated mine “Capital” is located in the Kuznetsk coal basin, in the south of the Kemerovo region (Osinniki). Productive stratum with a total thickness of 680 m includes 34 seams and a layer of coal. Of the 21 layers of industrial importance, 19 layers were developed.

From the analysis of geological and mining information, the predicted mass methane inflows during the design period of 10 years of operation of degassing wells and the cost of drilling and development of the corresponding wells are determined. The results are presented in the table.

Technical and economic indicators of options for the development of degassing wells Option Number, i The cost of drilling and development of a degassing well, Z _i , million rubles Mass flow of methane over 10 years of well operation, Q _i , mln kg

, руб./кгUnit costs of the option,

RUB / kg one 10 52 0.192 2 12 69 0.174 3 fifteen 34 0.441 four 6 25 0.40 5 eighteen 78 0.231 6 13 55 0.236 7 fourteen 41 0.341

Costs Z _i for drilling wells are determined by market conditions and depend on the depth of the wells and rock strength. The mass influx of methane during the life of degassing wells drilled into one or more technogenic methane reservoirs is calculated based on the solution of the known equations for filtering methane from a coal seam and a rock mass adjacent to the reservoir with the following initial physical properties:

- reservoir pressure of methane - 2.0 ... 2.5 MPa;

- gas content of coal - 10 ... 25 m ³ / t;

- coal permeability - 0.3 ... 0.5 mD;

- permeability of the rock mass - 0.1 ... 0.3 mD;

- porosity of coal - 0.02 ... 0.03;

- porosity of the rock mass - 0.01 ... 0.02.

Computer simulation of the non-stationary problem of methane filtration in a fractured-porous medium with the indicated initial physical properties allows us to determine the desired mass flow of methane into a degassing well during its operation. Computer simulation data are confirmed by the current monitoring of the gas content in the liquidated mine. The predicted results of methane inflows are presented in the table above.

The calculation of the unit costs of the considered options according to the table allows us to consider optimal the priority drilling and development of degassing wells according to option i = 2 with an indicator of Z ₂ / Q ₂ = 0.174 rubles / kg. The second most important option is i = 1 with the next ascending indicator Z ₁ / Q ₁ = 0.191 rubles / kg. Thus, in accordance with the claimed method for methane extraction, the optimal location of degassing wells is chosen according to options 2 and 1. The subsequent optimal sequence of implementation of development options for wells is chosen in a similar way depending on the needs of methane consumers.

The developed methane extraction method provides maximum technical and economic efficiency with minimal production risks at the stage of well drilling, regardless of the tightness of the mine workings, with a high concentration of methane in the mixture of recoverable gases and optimal unit costs for practical implementation.

Information sources

1. Auth. certificate No. 1011865 by class E21F 7/00 from 08/04/81, bull. 14 from 04/15/83.

2. V.A. Bezpflyug, J. Mayer. Assessment of the status of JI / PSO and CDM / CDM mine gas projects. // Gluckauf. - 2006. December, No. 4. - S.36-40 (prototype).

Claims (1)

The method of methane extraction in the fields of abandoned coal mines, based on drilling from the surface of degassing wells into the methane inflow zone, characterized in that technogenic methane collectors formed by the disintegration of rocks during the extraction of coal seams are determined in the rock mass, then the locations of the degassing wells are selected based on the condition for extracting the maximum amount of methane from one or more technogenic reservoirs through each well at its depth, which provides optimal The specific unit costs of extracting methane from these reservoirs.