EP0002877B1 - Method for the removal of methane - Google Patents

Method for the removal of methane Download PDF

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Publication number
EP0002877B1
EP0002877B1 EP78200398A EP78200398A EP0002877B1 EP 0002877 B1 EP0002877 B1 EP 0002877B1 EP 78200398 A EP78200398 A EP 78200398A EP 78200398 A EP78200398 A EP 78200398A EP 0002877 B1 EP0002877 B1 EP 0002877B1
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Prior art keywords
coal
pressure
cavities
borehole
process according
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German (de)
French (fr)
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EP0002877A2 (en
EP0002877A3 (en
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Johannes Wilhelmus Maria Steeman
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Stamicarbon BV
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Stamicarbon BV
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    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21F—SAFETY DEVICES, TRANSPORT, FILLING-UP, RESCUE, VENTILATION, OR DRAINING IN OR OF MINES OR TUNNELS
    • E21F7/00—Methods or devices for drawing- off gases with or without subsequent use of the gas for any purpose
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/25—Methods for stimulating production
    • E21B43/26—Methods for stimulating production by forming crevices or fractures
    • E21B43/2605—Methods for stimulating production by forming crevices or fractures using gas or liquefied gas
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/30—Specific pattern of wells, e.g. optimising the spacing of wells
    • E21B43/305—Specific pattern of wells, e.g. optimising the spacing of wells comprising at least one inclined or horizontal well

Definitions

  • the invention relates to a method for the production of methane simultaneously from a plurality of coal seams forming a seam bundle, in that a column system is formed in the rock layers lying between the seam layers above and below a specific seam lying within the seam bundle and from the specific seam with the aid of at least one at least one partially cased borehole methane is discharged.
  • the amount of methane that is released in this way and can be partially recovered is usually a multiple of the amount of methane that will come from the mined seam itself. This is possible because there are other seams and coal corrugations in the cracked rock package above and below, each of which releases a certain amount of methane via the column system. If the geological structure of the seam bundle is known, a number of parameters - mostly changing for each field - can be used to calculate exactly how much methane is expected to be released via the column system (see, among others, Geologie en Mijnbouw, 41, 1962, pp. 55 to 57 ).
  • An advantage of the recovery of methane present in seams is that it is released in almost pure form and can be recovered as such; this is in contrast to the gas that is generated when coal is burned in situ.
  • page 104-106 describes how to drill several holes in the seam plane to free the methane from the seam, which methods are useful for degassing a single seam, but if there are many seams, these methods are used the frequent repetition of the same procedure is very time-consuming.
  • the object of the present invention is to extract methane simultaneously from a plurality of seams and coal reefs which form a seam package, without the need for a conventional extraction method, in that the rock package in which they are located is based on one from the classic underground coal mining known manner forms a column system through which the seams can degas and the gas released finally discharges through at least one borehole.
  • this can be accomplished by drilling at least one well from above the surface into the previously determined seam, after which in the seam concerned by means of the borehole or the boreholes or with the aid of through the borehole or the boreholes into the seam introduced means for loosening the coal a number of cavities separated by coal peaks is generated until the coal piles remaining between the cavities and the hanging area suddenly collapse under the influence of the static rock pressure, after which from the cavities and crevices in which a pressure which is below the original methane pressure in the seams is maintained, the released methane is obtained through the borehole (s). “ suddenly” is understood to mean that the hanging part collapses within a few minutes to about a day.
  • the cavities are preferably under a pressure which forms a counterpressure to the static rock pressure, in such a way that the coal bursts do not collapse at a specific ratio of the cavity width and the coal pile width.
  • the pressure is reduced to such an extent that the coal piles collapse and the hanging part collapses.
  • the coal puffs remaining between the cavities are destroyed by means of explosives.
  • the cavities are caused by partial combustion of the coal, dissolution (see, for example, US Pat. No. 4,032,193) and the like. Like. Can form, these methods are less suitable because of the conditions to be met for it. So you need quite a lot of boreholes, and the required dimensions of the cavities and coal piles are less easy to control. It is preferable to work in such a way that the cavities are generated under hydraulic back pressure.
  • a mining device according to DE-A-2 434 408 or the corresponding US-A-3 961 824 or embodiments derived therefrom is very well suited for this.
  • the device consists of a scraper system with shots that are inserted into the borehole when stretched and arranged in a zigzag shape.
  • the shots arranged in this way are moved back and forth hydraulically or mechanically so that the scratches (or other means for releasing the coal) located on the joints of the shots can detach the wall of the borehole and thus the coal.
  • the coal thus released is discharged through the same borehole with the help of flushing liquid.
  • the length and width of the part of the room whose coal is mined in this way can be adjusted.
  • the lifting of the hydrostatic (counter) pressure can be done in a very simple manner by one or more of the chambers filled with the liquid with a gas, for. B. air, methane or nitrogen, emptied through a separate line through the borehole under pressure. It is necessary that the collapse area that forms is drained as well as possible so that the pressure is so low that the seams can release the adsorbed gas as completely as possible. Of course, it is also possible to pump out the existing water in a different way using means known from the oil industry, if necessary through a separate borehole. It is also necessary to keep the collapse area water-free continuously or discontinuously if it is connected to a natural water inflow.
  • a gas for. B. air, methane or nitrogen
  • the methane adsorbed in the seams and coal reefs will emerge with a slight overpressure and look for a way to the bottom of one or more of the boreholes via the crevice system and the collapse area, and it can then be obtained in almost pure form at the mouth .
  • the invention takes advantage of the fact that a large number of seams and coals corrugation can form methane through the formation of a column system, and essentially consists in suddenly forming such a column system by e.g. B. under (hydrostatic) pressure first forms a cavity system made up of chambers and pillars and this suddenly collapses when the pillars collapse.
  • a borehole 3 is drilled from the earth's surface 1 using a drilling rig 2. This borehole is deflected to a certain height above a seam 4 in such a way that a part 5a of the borehole 3 strikes the seam 4 at a small angle at a point 6a, after which drilling continues in the plane of the seam 4. The part that was drilled in the level of seam 4 becomes.
  • a chamber 7a using the system already described or another system.
  • the length of this chamber 7a of which the front surface shows a cross section in the drawing, can be several 100 m long.
  • a second borehole 5b is then drilled in a known manner from the borehole 3 and expanded into a chamber 7b in the plane of the seam 4.
  • a third part 5c is drilled in a deflected manner and a chamber 7c is created.
  • a lot of chambers can be formed around the borehole 3. All of this happens under possibly increased hydrostatic pressure to prevent premature collapse.
  • collars 8a and 8b there are collars 8a and 8b and possibly other collisions and chambers, not shown.
  • the width of the chambers and the width of the intermediate coal bursts 8a, 8b etc. are calculated in advance taking into account the factors already described, including the hydrostatic pressure used.
  • this collapse area which can have a length and a width of several 100 m, the column system already described forms, through which a seam 9 can release methane into the collapse area A, B, C, D, which from there on at least one of the holes 5a, 5b and 5c and can be extracted over the hole 3 for days.
  • the coal puffs can spontaneously decay even under the influence of the methane adsorbed in the coal and release the gas, in analogy to the sudden outbursts of firedamp (see Geologie en Mijnbouw, 41, 1962, p. 79 ff).
  • the borehole 3 can be arranged in such a way that, owing to the possible deflectability, it lies outside the fracture area of the cavity (s) formed and is not impaired thereby.

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  • Engineering & Computer Science (AREA)
  • Mining & Mineral Resources (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Geology (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Physics & Mathematics (AREA)
  • Environmental & Geological Engineering (AREA)
  • Fluid Mechanics (AREA)
  • Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)
  • Piles And Underground Anchors (AREA)
  • Solid Fuels And Fuel-Associated Substances (AREA)

Description

Die Erfindung betrifft ein Verfahren zur Gewinnung von Methan gleichzeitig aus mehreren ein Flözpaket bildenden Kohlenflözen, indem oberhalb und unterhalb eines bestimmten, innerhalb des Flözpakets liegenden Flözes in den zwischen den Flözen liegenden Gebirgsschichten ein Spaltensystem gebildet und aus dem bestimmten Flöz mit Hilfe von zumindest einem wenigstens teilweise verrohrten Bohrloch Methan abgeführt wird.The invention relates to a method for the production of methane simultaneously from a plurality of coal seams forming a seam bundle, in that a column system is formed in the rock layers lying between the seam layers above and below a specific seam lying within the seam bundle and from the specific seam with the aid of at least one at least one partially cased borehole methane is discharged.

Es ist bekannt, dass beim Einstürzen eines Hohlraums, der durch Abbau eines Flözes gebildet wurde, in dem oberhalb aber auch unterhalb des eingestürzten Hohlraums befindlichen Gestein ein mehr oder weniger senkrechtes Spaltensystem gebildet wird und die Gesteinsschichten sich durch Senkung etwas voneinander trennen («bedseparation»). Auf diese Weise entsteht ein ausgedehntes System von Spalten, durch die unabgebauten Flöze und Kohlenriffel (nicht abbauwürdige Flöze), die sich im Bereich des Spaltensystems befinden, das in ihnen adsorbierte Methan mindestens teilweise in den gebildeten Hohlraum abgeben können, sofern im Hohlraum ein Druck herrscht, der niedriger ist als der Druck des in den betreffenden Flözen adsorbierten Methans. Das Spaltensystem erstreckt sich normalerweise bis etwa 120 m über etwa 100 m unter dem abgebauten Flöz (siehe Geologie en Mijnbouw, 41, 1962, S. 41 bis 44 und S.53).It is known that when a cavity collapses, which was formed by mining a seam, a more or less vertical column system is formed in the rock above but also below the collapsed cavity, and the rock layers separate somewhat from one another by lowering ("bed separation") ). In this way, an extensive system of crevices is created, through the undeveloped seams and coal corrugations (seams not worthy of degradation), which are located in the area of the crevice system, which can at least partially release the methane adsorbed in them into the cavity formed, provided there is pressure in the cavity , which is lower than the pressure of the methane adsorbed in the affected seams. The crevice system normally extends up to about 120 m over about 100 m below the excavated seam (see Geologie en Mijnbouw, 41, 1962, pp. 41 to 44 and p.53).

Es ist möglich und bekannt, das auf diese Weise freiwerdende Methan zumindest teilweise zu gewinnen, indem man in das gespaltene Gestein von dem in Abbau befindliche Flöz aus mindestens ein Bohrloch in das Hangende und/ oder Liegende bis zu anderen Flözen einbringt und das Methan, das sich im Spaltensystem befindet, über das wenigstens teilweise verrohrte Bohrloch abführt (siehe u. a. Geologie en Mijnbouw, 41, 1962, S. 59 bis 61).It is possible and known to at least partially recover the methane released in this way by introducing at least one borehole into the hanging and / or lying area to other seams in the split rock from the seam being mined and the methane that is located in the crevice system through which at least partially cased borehole leads (see, among others, Geologie en Mijnbouw, 41, 1962, pp. 59 to 61).

Die Methanmenge, die auf diese Weise frei wird und teilweise gewonnen werden kann, beträgt meistens ein Vielfaches der Methanmenge, die aus dem abgebauten Flöz selbst stammen wird. Dies ist möglich, weil in dem rissigen Gesteinspaket oberhalb und unterhalb andere Flöze und Kohlenriffel vorhanden sind, die je für sich über das Spaltensystem eine gewisse Menge Methan abgeben. Wenn der geologische Aufbau des Flözpakets bekannt ist, lässt sich anhand einer Anzahl von - für jedes Feld meistens wechselnden - Parametern genau berechnen, wieviel Methan erwartungsgemäss über das Spaltensystem freiwerden wird (siehe u. a. Geologie en Mijnbouw, 41, 1962, S. 55 bis 57).The amount of methane that is released in this way and can be partially recovered is usually a multiple of the amount of methane that will come from the mined seam itself. This is possible because there are other seams and coal corrugations in the cracked rock package above and below, each of which releases a certain amount of methane via the column system. If the geological structure of the seam bundle is known, a number of parameters - mostly changing for each field - can be used to calculate exactly how much methane is expected to be released via the column system (see, among others, Geologie en Mijnbouw, 41, 1962, pp. 55 to 57 ).

Es ist bekannt, dass sich unter fast dem ganzen niederländischen Gebiet und grossen Teilen der Nordsee in Teufen von 1000 m bis 5000 m ein Kohlenpaket mit einer Mächtigkeit von mindestens 20 m befindet, gemessen als die Gesamtmächtigkeit aller dort vorhandenen Flöze und Kohlenriffel. Auf einer Fläche von z. B. 100 x 100 km = 1010 m2 befindet sich dann eine Steinkohlenmenge von 2 x 1011 m3 = 200 Milliarden m3. Wenn man annimmt, dass im Durchschnitt 10 m3 CH4 je M 3 Kohle absorbiert sind (für das Peel-Gebiet wurden ca. 10 m3 CH4 je m3 Kohle ermittelt, in Südlimburg ca. 17 m3 CH4 je m3 Kohle, siehe den Bericht der Peelcommissie, Verhandelingen van het K. N. G. M. B. Mijnbouwkundige serie, Band 5, S. 83), so sind auf dieser Fläche 2 x 1012 m3 CH4 = 2000 Milliarden m3 CH4 in der Kohle absorbiert.It is known that there is a coal packet with a thickness of at least 20 m beneath almost the entire Dutch area and large parts of the North Sea at depths of 1000 m to 5000 m, measured as the total thickness of all seams and coal reefs there. On an area of z. B. 100 x 100 km = 10 10 m 2 then there is a hard coal quantity of 2 x 10 11 m3 = 200 billion m 3 . If one assumes that on average 10 m 3 CH 4 per M 3 coal are absorbed (approx. 10 m 3 CH 4 per m 3 coal were determined for the peel area, in South Limburg approx. 17 m 3 CH 4 per m 3 Coal, see the report of the Peelcommissie, Verhandelingen van het KNGMB Mijnbouwkundige serie, volume 5, p. 83), 2 x 10 12 m 3 CH 4 = 2000 billion m 3 CH 4 are absorbed in the coal on this surface.

Dies ist eine Menge, die derjenigen des Gasvorkommens in Groningen entspricht, welches eines der grössten Vorkommen darstellt. Das Methanvorkommen unter dem gesamten Gebiet der Niederlande und Teilen der Nordsee beträgt somit ein Vielfaches des Vorkommens in Groningen. Sollte es möglich sein, wenigstens einen Teil dieses Methans zu gewinnen, so wird in den Niederlanden auf lange Sicht kein Mangel an Erdgas auftreten. Ähnliche Verhältnisse findet man auch in einigen anderen europäischen Ländern vor.This is an amount that corresponds to that of the gas deposits in Groningen, which is one of the largest deposits. The methane deposit under the entire area of the Netherlands and parts of the North Sea is therefore a multiple of the deposit in Groningen. If it is possible to recover at least part of this methane, there will be no shortage of natural gas in the Netherlands in the long run. Similar conditions can also be found in some other European countries.

Ein Vorteil der Gewinnung von in situ in Flözen vorhandenem Methan ist, dass es in nahezu reiner Form frei wird und als solches gewonnen werden kann; dies im Gegensatz zu dem Gas, das bei der Verbrennung von Steinkohle in situ entsteht.An advantage of the recovery of methane present in seams is that it is released in almost pure form and can be recovered as such; this is in contrast to the gas that is generated when coal is burned in situ.

Es ist bereits bekannt, in Steinkohle absorbiertes Gas durch Steigerung der Permeabilität eines Flözes oder des unmittelbar oberhalb eines Flözes befindlichen Gebirges über Bohrlöcher zu gewinnen. Methoden hierfür sind aus der Erdölindustrie bekannt. Beispiele hierfür sind die sog. hydraulische Frac-Behandlung oder das hydraulische Heben des Deckgebirges eines Flözes und Versetzen des Raums mit Sand, wie diese u. a. in der Schachtanlage Klarenthal im Saarland geschehen ist (siehe u. a. Annales des Mines de Belgique, 1, 1976, S. 25 und weiterhin die US-A-3 814 480. In «Coal Age» 80, Nr. 8 von Juli 1975, Seite 104-106 ist beschrieben, wie man durch das Bohren von mehreren Löchern in der Flözebene, das Methan aus dem betreffenden Flöz befreien kann. Diese Methoden sind für die Entgasung eines einzigen Flözes zweckmässig. Handelt es sich um viele Flöze, sind diese Methoden jedoch durch die häufige Wiederholung des gleichen Verfahrens sehr aufwendig.It is already known to extract gas absorbed in hard coal by increasing the permeability of a seam or the mountains located directly above a seam via boreholes. Methods for this are known from the petroleum industry. Examples of this are the so-called hydraulic frac treatment or the hydraulic lifting of the overburden of a seam and covering the room with sand, such as this. a. in the Klarenthal mine in Saarland (see, inter alia, Annales des Mines de Belgique, 1, 1976, p. 25 and also US-A-3 814 480. In "Coal Age" 80, No. 8 from July 1975, page 104-106 describes how to drill several holes in the seam plane to free the methane from the seam, which methods are useful for degassing a single seam, but if there are many seams, these methods are used the frequent repetition of the same procedure is very time-consuming.

Der vorliegenden Erfindung liegt die Aufgabe zugrunde, Methan gleichzeitig aus mehreren, ein Flözpaket bildenden Flözen und Kohlenriffeln zu gewinnen, ohne dass ein konventionelles Gewinnungsverfahren notwendig ist, indem man in dem Gesteinpaket, in dem sich diese befinden, auf eine aus dem klassischen Steinkohlenbergbau unter Tage an sich bekannte Weise ein Spaltensystem bildet, über welches sich die Flöze entgasen können, und das freiwerdende Gas anschliessend durch zumindest ein Bohrloch abführt.The object of the present invention is to extract methane simultaneously from a plurality of seams and coal reefs which form a seam package, without the need for a conventional extraction method, in that the rock package in which they are located is based on one from the classic underground coal mining known manner forms a column system through which the seams can degas and the gas released finally discharges through at least one borehole.

Nach der Erfindung kann dies bewerkstelligt werden, indem mindestens ein Bohrloch von über Tage aus bis in das vorher dazu bestimmte Flöz niedergebracht wird, wonach in dem betreffenden Flöz mittels des Bohrlochs oder der Bohrlöcher oder mit Hilfe von durch das Bohrloch oder die Bohrlöcher in das Flöz eingebrachten Mitteln zum Lösen der Kohle so lange eine Anzahl durch Kohlenstösse getrennter Hohlräume erzeugt wird, bis die zwischen den Hohlräumen verbliebenen Kohlenstösse und das Hangende unter dem Einfluss des statischen Gebirgsdrucks plötzlich zusammenstürzen, wonach aus den Hohlräumen und Spalten, in denen ein Druck, der unter dem ursprünglichen Methandruck in den Flözen liegt, aufrechterhalten wird, das freiwerdende Methan über das oder die Bohrlöcher gewonnen wird. Unter «plötzlich» wird verstanden, dass das Hangende innerhalb einiger Minuten bis etwa einem Tag hereinbricht.According to the invention, this can be accomplished by drilling at least one well from above the surface into the previously determined seam, after which in the seam concerned by means of the borehole or the boreholes or with the aid of through the borehole or the boreholes into the seam introduced means for loosening the coal a number of cavities separated by coal peaks is generated until the coal piles remaining between the cavities and the hanging area suddenly collapse under the influence of the static rock pressure, after which from the cavities and crevices in which a pressure which is below the original methane pressure in the seams is maintained, the released methane is obtained through the borehole (s). “Suddenly” is understood to mean that the hanging part collapses within a few minutes to about a day.

Vorzugsweise stehen die Hohlräume unter einem Druck, der einen Gegendruck zum statischen Gebirgsdruck bildet, und zwar derart, dass die Kohlenstösse bei einem bestimmten Verhältnis von Hohlraumbreite und Kohlenstossbreite nicht zusammenstürzen.The cavities are preferably under a pressure which forms a counterpressure to the static rock pressure, in such a way that the coal bursts do not collapse at a specific ratio of the cavity width and the coal pile width.

Schliesslich wird der Druck so weit herabgesetzt, dass die Kohlenstösse zusammenstürzen und das Hangende hereinbricht. Gemäss einer Ausführungsform der Erfindung werden die zwischen den Hohlräumen verbleibenden Kohlenstösse mittels Sprengstoff zerstört.Finally, the pressure is reduced to such an extent that the coal piles collapse and the hanging part collapses. According to one embodiment of the invention, the coal puffs remaining between the cavities are destroyed by means of explosives.

Aus den Diagrammen in «Geologie en Mijnbouw», 41, S. 41 bis 44 geht hervor, dass der Überdruck in den Hohlräumen nach dem Zusammenbruch vorzugsweise unter 0,1 MPa liegen soll.The diagrams in "Geologie en Mijnbouw", 41, pp. 41 to 44 show that the overpressure in the cavities should preferably be below 0.1 MPa after the collapse.

Obwohl man bei der Ausübung des erfindungsgemässen Verfahrens die Hohlräume durch partielle Verbrennung der Kohle, Auflösen (siehe z. B. die US-A-4 032 193) u. dgl. bilden kann, sind diese Methoden wegen der dafür zu erfüllenden Bedingungen weniger gut geeignet. So benötigt man ziemlich viele Bohrlöcher, und es lassen sich die erforderlichen Abmessungen der Hohlräume und Kohlenstösse weniger gut unter Kontrolle halten. Vorzugsweise wird so gearbeitet, dass die Hohlräume unter hydraulischem Gegendruck erzeugt werden.Although in the practice of the method according to the invention the cavities are caused by partial combustion of the coal, dissolution (see, for example, US Pat. No. 4,032,193) and the like. Like. Can form, these methods are less suitable because of the conditions to be met for it. So you need quite a lot of boreholes, and the required dimensions of the cavities and coal piles are less easy to control. It is preferable to work in such a way that the cavities are generated under hydraulic back pressure.

Es ist vorteilhaft, die Hohlräume mit mechanischen Mitteln zu erzeugen. Sehr gut geeignet hierfür ist ein Abbaugerät nach der DE-A-2 434 408 bzw. der entsprechenden US-A-3 961 824 oder davon abgeleitete Ausführungsformen. Das Gerät besteht aus einer Kratzeranlage mit Schüssen, die in gestrecktem Zustand in das Bohrloch eingebracht und darin zickzackförmig angeordnet werden. Die auf diese Weise angeordneten Schüsse werden hydraulisch oder mechanisch hin und her bewegt, so dass die Kratzer (oder andere Mittel zum Lösen der Kohle), die sich auf den Gelenken der Schüsse befinden, die Wand des Bohrlochs und somit die Kohle loslösen können. Die so gelöste Kohle wird mit Hilfe von Spülflüssigkeit durch das gleiche Bohrloch abgeführt. Die Länge und die Breite des Raumteiles, dessen Kohle auf diese Weise abgebaut wird, ist einstellbar. Durch die Wahl eines geeigneten Hohlraumsystems, wie z. B. in Abb. 1 der DE-A-2 434 408 bzw. der US-A-3 961 824 dargestellt, kann man die gestellten Bedingungen erfüllen. Die zwischen den Hohlräumen stehengebliebenen Kohlenstösse (Pfeiler) stützen zusammen mit dem Druck der Spülflüssigkeit das Hangende ab.It is advantageous to create the cavities by mechanical means. A mining device according to DE-A-2 434 408 or the corresponding US-A-3 961 824 or embodiments derived therefrom is very well suited for this. The device consists of a scraper system with shots that are inserted into the borehole when stretched and arranged in a zigzag shape. The shots arranged in this way are moved back and forth hydraulically or mechanically so that the scratches (or other means for releasing the coal) located on the joints of the shots can detach the wall of the borehole and thus the coal. The coal thus released is discharged through the same borehole with the help of flushing liquid. The length and width of the part of the room whose coal is mined in this way can be adjusted. By choosing a suitable cavity system, such as. B. in Fig. 1 of DE-A-2 434 408 and US-A-3 961 824, one can meet the conditions. The piles of coal (pillars) that remain between the cavities, together with the pressure of the flushing liquid, support the hanging area.

Für die anzuwendende Breite des Hohlraums und der zwischenliegenden Kohlenstösse lassen sich keine allgemein gültigen Werte angeben. Diese hängen u. a. von der Zusammensetzung und den mechanisch-physikalischen Eigenschaften des Deckgebirges bis einige 10 m über dem Hohlraum, von den mechanisch-physikalischen Eigenschaften der Kohle, von der natürlichen Rissbildung sowie von dem benutzten (hydrostatischen) (Gegen-)Druck ab. Die Eigenschaften von Gestein und Kohle kann man aus Kernen der betreffenden Bohrung ermitteln. Anschliessend kann man, unter Berücksichtigung der Teufe und des damit zusammenhängenden statischen Gebirgsdrucks und des zu benutzenden (hydrostatischen) (Gegen-)Drucks, die zu benutzenden Abmessungen berechnen. Diese Werte können auch empirisch bestimmt bzw. kontrolliert werden. Aus der DE-A-2 434 408 ist es in diesem Zusammenhang bekannt, das Zusammendrücken der zwischen den Kohlenstössen befindlichen Hohlräume durch das Hangend- oder Liegendgestein durch eine Flüssigkeit zu erreichen, deren spezifisches Gewicht höher ist als das der Kohle. Die schwere Flüssigkeit erzeugt einen erhöhten hydrostatischen (Gegen-)Druck.No generally applicable values can be given for the width of the cavity to be used and the coal piles in between. These hang u. a. on the composition and the mechanical-physical properties of the overburden up to a few 10 m above the cavity, on the mechanical-physical properties of the coal, on the natural formation of cracks and on the (hydrostatic) (counter) pressure used. The properties of rock and coal can be determined from the cores of the hole concerned. Then, taking into account the depth and the associated static rock pressure and the (hydrostatic) (counter) pressure to be used, the dimensions to be used can be calculated. These values can also be determined or controlled empirically. In this connection, it is known from DE-A-2 434 408 to compress the cavities between the coals by means of the hanging or lying rock by means of a liquid whose specific weight is higher than that of the coal. The heavy liquid creates an increased hydrostatic (counter) pressure.

Die Aufhebung des hydrostatischen (Gegen-) Drucks kann auf sehr einfache Weise erfolgen, indem man eine oder mehrere der mit der Flüssigkeit gefüllten Kammern mit einem Gas, z. B. Luft, Methan oder Stickstoff, über eine separate Leitung durch das Bohrloch unter Druck entleert. Es ist erforderlich, dass das sich dabei bildende Einsturzgebiet so gut wie möglich entwässert wird, damit der Druck so niedrig ist, dass die Flöze das adsorbierte Gas möglichst ganz abgeben können. Selbstverständlich ist es auch möglich, das vorhandene Wasser auf anderem Wege mit aus der Ölindustrie bekannten Mitteln, erforderlichenfalls durch ein separates Bohrloch, abzupumpen. Auch ist es nötig, das Einsturzgebiet kontinuierlich oder diskontinuierlich wasserfrei zu halten, wenn es mit einem natürlichen Wasserzufluss in Verbindung steht.The lifting of the hydrostatic (counter) pressure can be done in a very simple manner by one or more of the chambers filled with the liquid with a gas, for. B. air, methane or nitrogen, emptied through a separate line through the borehole under pressure. It is necessary that the collapse area that forms is drained as well as possible so that the pressure is so low that the seams can release the adsorbed gas as completely as possible. Of course, it is also possible to pump out the existing water in a different way using means known from the oil industry, if necessary through a separate borehole. It is also necessary to keep the collapse area water-free continuously or discontinuously if it is connected to a natural water inflow.

Gleich nach dem Einsturz wird das in den Flözen und Kohlenriffeln adsorbierte Methan mit einem geringen Überdruck austreten und sich über das Spaltensystem sowie das Einsturzgebiet einen Weg zur Sohle von einem oder mehreren der Bohrlöcher suchen, und es kann anschliessend in nahezu reiner Form an der Mündüng gewonnenwerden.Immediately after the collapse, the methane adsorbed in the seams and coal reefs will emerge with a slight overpressure and look for a way to the bottom of one or more of the boreholes via the crevice system and the collapse area, and it can then be obtained in almost pure form at the mouth .

Die Erfindung macht sich die Tatsache zunutze, dass eine grosse Anzahl von Flözen und Kohlenriffeln durch Bildung eines Spaltensystems Methan abgeben kann, und besteht im wesentlichen darin, ein solches Spaltensystem plötzlich zu bilden, indem man z. B. unter (hydrostatischem) Druck zunächst ein aus Kammern und Pfeilern aufgebautes Hohlraumsystem bildet und dies durch zusammenbrechen der Pfeiler plötzlich einstürzen lässt.The invention takes advantage of the fact that a large number of seams and coals corrugation can form methane through the formation of a column system, and essentially consists in suddenly forming such a column system by e.g. B. under (hydrostatic) pressure first forms a cavity system made up of chambers and pillars and this suddenly collapses when the pillars collapse.

Die Erfindung wird anhand einer Zeichnung näher erläutert. Von der Erdoberfläche 1 aus wird mit Hilfe einer Bohranlage 2 ein Bohrloch 3 gebohrt. Dieses Bohrloch wird in gewisser Höhe über einem Flöz 4 derart abgelenkt, dass ein Teil 5a des Bohrlochs 3 unter einem kleinen Winkel bei einem Punkt 6a auf das Flöz 4 auftrifft, wonach in der Ebene des Flözes 4 weiter gebohrt wird. Der Teil, der in der Ebene des Flözes 4 gebohrt wurde, wird. nun mit Hilfe der bereits beschriebenen Anlage oder einer anderen Anlage zu einer Kammer 7a erweitert. Die Länge dieser Kammer 7a, von der die Vorderfläche in der Zeichnung einen Querschnitt zeigt, kann mehrere 100 m lang sein.The invention is explained in more detail with reference to a drawing. A borehole 3 is drilled from the earth's surface 1 using a drilling rig 2. This borehole is deflected to a certain height above a seam 4 in such a way that a part 5a of the borehole 3 strikes the seam 4 at a small angle at a point 6a, after which drilling continues in the plane of the seam 4. The part that was drilled in the level of seam 4 becomes. now expanded to a chamber 7a using the system already described or another system. The length of this chamber 7a, of which the front surface shows a cross section in the drawing, can be several 100 m long.

Anschliessend wird vom Bohrloch 3 aus auf bekannte Weise ein zweites Bohrloch 5b abgelenkt gebohrt und in der Ebene des Flözes 4 zu einer Kammer 7b erweitert. Auf gleiche Weise wird auch ein dritter Teil 5c abgelenkt gebohrt und eine Kammer 7c erzeugt. Auf dieselbe Weise kann um das Bohrloch 3 noch eine Menge Kammern gebildet werden. Dies alles geschieht unter evtl. erhöhtem hydrostatischem Druck, um ein vorzeitiges Hereinbrechen zu verhindern. Zwischen den Kammern 7a, 7b und 7c befinden sich Kohlenstösse 8a und 8b und evtl. weitere nichtdargestellte Stösse und Kammern. Die Breite der Kammern und die Breite der zwischenliegenden Kohlenstösse 8a, 8b usw. wird unter Berücksichtigung der bereits beschriebenen Faktoren, darunter auch dem benutzten hydrostatischen Druck, vorher berechnet. Nach Fertigstellung der Kammern wird der hydrostatische Druck weggenommen, evtl. mit Hilfe von Gasdruck über ein hier nichtgezeichnetes Rohr durch das Bohrloch 3, bis in eine oder mehrere der Kammern 7. Die zu erwartende Folge ist, dass die Kohlenstösse 8a und 8b unter dem Einfluss des statischen Gebirgsdrucks hereinbrechen und das Hangende der Kammern 7a, 7b und 7c plötzlich einstürzt. Auf diese Weise bildet sich ein Einsturzgebiet, das in der Zeichnung durch Punkte A, B, C und D begrenzt wird. Oberhalb und unterhalb dieses Einsturzgebiets, das eine Länge und eine Breite von mehreren 100 m haben kann, bildet sich das bereits beschriebene Spaltensystem, durch das ein Flöz 9 Methan in den Einsturzraum A, B, C, D abgeben kann, das von dort aus über mindestens eines der Löcher 5a, 5b und 5c und über das Bohrloch 3 über Tage gewonnen werden kann. Bemerkt wird, dass die Kohlenstösse dank der ptötzttchan Druckentspannung selbst unter dem Einfluss des in der Kohle adsorbierten Methans spontan zerfallen können und das Gas abgeben, in Analogie zu den plötzlichen Schlagwetterausbrüchen (siehe Geologie en Mijnbouw, 41, 1962, S. 79 ff).A second borehole 5b is then drilled in a known manner from the borehole 3 and expanded into a chamber 7b in the plane of the seam 4. In the same way, a third part 5c is drilled in a deflected manner and a chamber 7c is created. In the same way, a lot of chambers can be formed around the borehole 3. All of this happens under possibly increased hydrostatic pressure to prevent premature collapse. Between the chambers 7a, 7b and 7c there are collars 8a and 8b and possibly other collisions and chambers, not shown. The width of the chambers and the width of the intermediate coal bursts 8a, 8b etc. are calculated in advance taking into account the factors already described, including the hydrostatic pressure used. After the completion of the chambers, the hydrostatic pressure is removed, possibly with the help of gas pressure through a pipe not shown here, through borehole 3, into one or more of the chambers 7. The expected consequence is that the coal strikes 8a and 8b are influenced of the static rock pressure and suddenly the slopes of the chambers 7a, 7b and 7c collapse. In this way, a collapse area is formed, which is delimited in the drawing by points A, B, C and D. Above and below this collapse area, which can have a length and a width of several 100 m, the column system already described forms, through which a seam 9 can release methane into the collapse area A, B, C, D, which from there on at least one of the holes 5a, 5b and 5c and can be extracted over the hole 3 for days. It is noted that thanks to the ptötzttchan pressure relief, the coal puffs can spontaneously decay even under the influence of the methane adsorbed in the coal and release the gas, in analogy to the sudden outbursts of firedamp (see Geologie en Mijnbouw, 41, 1962, p. 79 ff).

Bei Anwendung eines hohen hydrostatischen Drucks wird man die mit der Spülung mitgerissene Kohle durchschleusen müssen, um den Druck an Ort und Stelle aufrechtzuerhalten. Derartige Schleusen sind aus dem Bereich des hydraulischen Kohlentransports in vielen Varianten bekannt.If a high hydrostatic pressure is used, the coal carried along with the flushing will have to be passed through in order to maintain the pressure in place. Such locks are known in many variants from the field of hydraulic coal transport.

Das folgende Rechenbeispiel gibt einen Eindruck, wie gross in einem bestimmten Fall die zu erwartenden Methanmengen sein können. Es wird angenommen, dass von einem Flözpaket, dessen Flöze je m3 Kohle 15 m3 adsorbiertes CH4 enthalten, ein Flöz 4 von 1 m Mächtigkeit grösstenteils abgebaut wird und das bearbeitete Gebiet einstürzt. Oberhalb dieses Flözes 4 sollen sich in 10, 20, 30, 40 bzw. 80 m Entfernung fünf weitere Flöze mit einer Mächtigkeit von 0,8, 1,5, 1,0, 0,5 bzw. 1,5 m befinden. Unter demselben Flöz 4 sollen sich in 10, 20, 40, 60 bzw. 80 m Entfernung ebenfalls fünf Flöze mit einer Mächtigkeit von 0,8, 1,5, 1,0, 0,5 bzw. 1,5 m befinden. Nach der u. a. in Geologie en Mijnbouw, 41, 1962 angegebenen Methode kann berechnet werden, dass gut 70 m3 CH4 je m2 Einsturzgebiet freiwerden. Auf ein so geschaffenes Einsturzgebiet von 200 x 300 m fallen somit 4 x 106 m3 CH4 an. Da auch noch Kohle abgebaut wird (angenommen von den vorhandenen 6 x 104 m3 eine Menge von 3 x 104 m3; der Rest bleibt als Kohlenstösse und Verluste zurück), so stellt sich heraus, dass nach Abzug der Ausbeute dieser abgebauten ca. 3 x 104 m3 Kohle die restlichen Kosten zur Gewinnung des Methans gering sind.The following calculation example gives an impression of how large the expected amounts of methane can be in a particular case. It is assumed that a seam package, the seams of which contain 15 m 3 adsorbed CH4 per m 3 coal, will largely mine a seam 4 of 1 m thickness and collapse the processed area. Above this seam 4, five further seams with a thickness of 0.8, 1.5, 1.0, 0.5 or 1.5 m should be located at a distance of 10, 20, 30, 40 or 80 m. Under the same seam 4 there should also be five seams with a thickness of 0.8, 1.5, 1.0, 0.5 and 1.5 m at a distance of 10, 20, 40, 60 and 80 m. According to the method given, inter alia, in Geologie en Mijnbouw, 41, 1962, it can be calculated that a good 70 m 3 CH 4 per m 2 collapse area is released. In a collapse area of 200 x 300 m created in this way, 4 x 10 6 m 3 CH 4 occur . Since coal is also mined (assuming a quantity of 3 x 10 4 m 3 of the existing 6 x 10 4 m 3 ; the rest remains as coal piles and losses), it turns out that after deducting the yield of these mines approx 3 x 10 4 m 3 coal the remaining costs for the production of methane are low.

Bemerkt wird, dass vom Bohrloch 3 aus das gleiche Verfahren für mehrere Flözpakete verwendet werden kann. Wenn das ganze stratigrafische Profil mit den Abständen und Mächtigkeiten der Flöze und Kohlenriffel und die zu erwartenden Methaninhalte bekannt sind, so lassen sich mit Hilfe des Computers die am besten geeigneten Flözpakete und die abzubauenden Flöze ziemlich einfach und genau bestimmen.It is noted that the same procedure can be used for several seam bundles from borehole 3. If the entire stratigraphic profile with the spacing and thickness of the seams and coal reefs and the expected methane contents are known, then the most suitable seam packs and the seams to be mined can be determined quite simply and precisely with the aid of the computer.

Schliesslich wird darauf hingewiesen, dass das Bohrloch 3 so angeordnet werden kann, dass es aufgrund der möglichen Ablenkbarkeit ausserhalb des Bruchgebiets des (der) gebildeten Hohlraums (räume) liegt und dadurch nicht beeinträchtigt wird.Finally, it is pointed out that the borehole 3 can be arranged in such a way that, owing to the possible deflectability, it lies outside the fracture area of the cavity (s) formed and is not impaired thereby.

Claims (13)

1. Process of recovering methane from several coal seams in a pack of seams at the same time, by forming a fissure system over and under a seam of the pack, in the rock strata between the coal seams, and withdrawing methane from the seam through an at least partly tube-lined borehole, this process being characterized in that at least one borehole (3, 5) is drilled from the surface into the previously selected coal seam (4), after which a number of cavities (7a, b, c) separated by coal walls are formed in the said seam (4) along the borehole (5) or boreholes (5a, b, c) or with the use of coal-loosening means introduced into the seam through the borehole (3, 5) or boreholes (5a, b, c), to the point where the coal walls that had remained between the cavities, as well as the overlying rock, suddenly collapse under the influence of the static rock pressure, whereupon the released methane is recovered, along the borehole(s) (3), from the cavities and fissures, in which a pressure lower than the original methane pressure in the coal is maintained.
2. Process according to claim 1, characterized in that in the cavities formed a pressure is maintained which constitutes a counter-pressure to the static rock pressure so that, with a given width of the cavities and a given width of the coal walls between them, the coal will not collapse, and in that after the cavities have been completed the counter-pressure is so decreased that the coal walls collapse and the overlying rock crashes into the cavities.
3. Process according to claim 1 or 2, characterized in that after the collapse the excess pressure in the cavities is lower than 0.1 MPa.
4. Process according to claims 1-3, characterized in that the counter-pressure is a hydrostatic pressure.
5. Process according to claims 1-3, characterized in that the cavities are formed by partial combustion or dissolution of the coal.
6. Process according to claims 1-5, characterized in that the cavities are formed with the use of mechanically driven scrapers of a knowr type, introduced into the borehole.
7. Process according to claims 1-6, characterized in that the width of the cavities and the width of the coal walls remaining between them are determined with reference to the composition and the mechanico-physical properties of the rock up to some tens of metres over the cavities, to the mechanico-physical properties of the coal, to the natural cleavage, and to the (counter-) pressure applied.
8. Process according to claims 1-7, characterized in that the properties of the rock and the coal are determined from cores extracted from the borehole, and the dimensions to be applied are calculated with due allowance being made for the depth and the related static pressure, as well as for the (counter-)pressure to be used.
9. Process according to claims 1-8, characterized in that the hydrostatic pressure is first replaced by a gas pressure, by introduction of a gas through a separate conduit in the borehole, and this gas pressure is eventually decreased.
10. Process according to claims 1-9, characterized in that the collapse area formed is kept free of water.
11. Process according to claims 1-9, characterized in that an additional borehole is used for keeping the area free of water.
12. Process according to claims 1-11, characterized in that the process according to one or more of the preceding claims is carried out in several packs of coal seams, with use being made of the same borehole.
13. Process according to claims 1-12, characterized in that the coal walls remaining between the cavities are destroyed by means of an explosive.
EP78200398A 1978-01-02 1978-12-30 Method for the removal of methane Expired EP0002877B1 (en)

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NL7800005A NL7800005A (en) 1978-01-02 1978-01-02 PROCEDURE FOR GETTING METHANE IN SITU FROM GREAT DEPTH CARBON LAYERS.
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