RU2121062C1 - Method of withdrawal of methane from coal bed - Google Patents

Abstract

FIELD: mining industry; may be used in methane withdrawal from cold beds. SUBSTANCE: method includes drilling-in coal bed, well casing, grouting of annular space, perforation of casing and hydraulic fracturing of formation to form system of fractures. Then provision is made of conditions of self-emission of methane from coal bed and its withdrawal. After ceasing of methane self-emission, injected into coal bed is substance with sorption ability higher than that of methane, for instance, carbon dioxide gas in volume determined by mathematical expression taking into account of lengths of fractures formed by hydraulic fracturing, coal bed thickness, coal bed filtering porosity, temperature of injected substance and its pressure, and initial temperature of bed; holding of this substance up to ceasing of methane desorption from coal and then methane is withdrawn from one of wells. EFFECT: fuller withdrawal of methane from coal beds. 2 cl, 1 dwg

Description

 The present invention relates to the mining industry and can be used to extract methane from a coal seam.

 A known method of degassing a coal seam, including opening a coal deposit and cyclic exposure to it with a liquid and a refrigerant [1].

 The disadvantage of this method is the low efficiency of methane extraction over time.

 The closest to the proposed technical essence and the achieved result is a well-known method of degassing a coal seam, including drilling wells from the surface, injecting the working fluid into the reservoir in the mode of hydraulic separation, holding it in the reservoir and forcing it out of filter cracks by injecting air into the reservoir, followed by methane extraction with its self-flow [2].

 The main disadvantage of this method is the disadvantage indicated above.

 The task of the invention is to enable more complete extraction of methane from the coal seam. Currently, known technologies make it possible to extract from the bowels of up to 70% of the gas of the total amount, and this invention up to 98%.

где
l - длина раскрытых при гидрорасчленении трещин, м;
h - мощность пласта или свиты пластов, м;
m_ф - фильтрующая пористость пласта (на момент закачивания десорбирующего метан вещества);
K₁ - коэффициент, учитывающий потери вещества из угольного массива (1,2-1,8);
T_в - температура закачиваемого вещества, град;
Z - коэффициент сверхсжимаемости вещества (0,9-0,95);
P_σ - барометрическое давление, МПа;
T₀ - начальная температура пласта, ^oC;
P_зак - давление закачиваемого вещества, МПа,
затем выдерживают это вещество в пласте до прекращения процесса десорбции метана из угля, после чего метан выводят через одну из скважин. В качестве закачиваемого вещества может быть применен углекислый газ.This is achieved by the fact that in the method, including drilling wells from the surface, injecting the working fluid into the reservoir in the mode of hydraulic separation, holding it in the reservoir and releasing it from the filter cracks by injecting air into the reservoir, followed by methane extraction during its self-discharge, after completion of the methane self-discharge process a substance with a sorption capacity greater than that of methane in the volume determined from the following expression is pumped from the coal seam into the last one:

Where
l is the length of the cracks uncovered during hydrodividing, m;
h is the thickness of the formation or formation, m;
m _f - filtering porosity of the formation (at the time of injection of the desorbing methane substance);
K ₁ - coefficient taking into account the loss of substance from the coal mass (1.2-1.8);
T _in - temperature of the injected substance, degrees;
Z is the coefficient of supercompressibility of the substance (0.9-0.95);
P _σ - barometric pressure, MPa;
T ₀ - the initial temperature of the reservoir, ^o C;
P _Zack - pressure of the injected substance, MPa,
then this substance is kept in the formation until the process of desorption of methane from coal ceases, after which methane is removed through one of the wells. Carbon dioxide can be used as the injected material.

 This ensures that the previously lost part of methane is recovered by exchange desorption of methane with an injected substance having a higher sorption capacity.

 The drawing shows a variant of the scheme for the extraction of methane from a coal seam according to the proposed method.

 The method is as follows.

где
l - длина раскрытых при гидрорасчленении трещин, м;
h - мощность пласта или свиты пластов, м;
m_ф - фильтрующая пористость пласта (на момент закачивания десорбирующего метан вещества);
K₁ - коэффициент, учитывающий потери вещества из угольного массива (1,2-1,8);
T_в - температура закачиваемого вещества, град;
Z - коэффициент сверхсжимаемости вещества (0,9-0,95);
P_σ - барометрическое давление, МПа;
T₀ - начальная температура пласта, ^oC;
P_зак - давление закачиваемого вещества, МПа.The methane-containing coal seam 1 is opened with boreholes or one well 2 from the surface, casing it with tubes 3, plug the annulus 4, perforate the casing at the level of the coal seam. Next, injection into the reservoir of the working fluid in the mode of hydraulic separation. After the opening of cracks 5 and exposure of the working fluid in the reservoir 1, it is pushed out by forcing air into the reservoir. As a result, methane self-discharge from coal seam 1 occurs. Methane self-discharge continues for several years. After that, 25-30% of methane from its initial amount remains in the coal seam. To ensure the extraction of the remaining methane into the coal seam, a substance is injected with a sorption capacity greater than that of methane in a volume determined from the following expression:

Where
l is the length of the cracks uncovered during hydrodividing, m;
h is the thickness of the formation or formation, m;
m _f - filtering porosity of the formation (at the time of injection of the desorbing methane substance);
K ₁ - coefficient taking into account the loss of substance from the coal mass (1.2-1.8);
T _in - temperature of the injected substance, degrees;
Z is the coefficient of supercompressibility of the substance (0.9-0.95);
P _σ - barometric pressure, MPa;
T ₀ - the initial temperature of the reservoir, ^o C;
P _Zack - pressure of the injected substance, MPa.

 Carbon dioxide can be used as the injected material. Such an amount of injected substance provides filling the filtering volume of the coal seam, which allows the process of desorption of methane from coal. This substance is kept in the reservoir until the methane desorption from coal ceases. The end of the methane desorption process in the reservoir is established by well-known methods of gas-dynamic testing of the well. After that, the methane self-discharge process of their well is resumed and methane residues are recovered.

 Example.

The methane-containing coal seam 1 is opened by the well 2 and work is carried out on its equipment, followed by hydraulic segregation of the formation by the SIN-31 pump unit. The pressure of injection of the working fluid into the formation (P _discharge ), volume (V) and its injection rate (q) are determined by a known method depending on the depth of the formation (H), its power (h), the filtering porosity of the formation (m _f ) and radius of a given exposure zone (R).

When H = 1000 m, h = 1 m, m _f = 6.0, R = 100 m, then
P _load = 15 MPa, V = 450 thousand m ³ , q = 50 l / s.

After the opening of cracks 5 and holding for 2-3 months of the working fluid in the reservoir 1, it is displaced by forcing air into the reservoir. For this, a compressor KPU-16/250 is connected to well 2. The volume of injected air is determined by a known method, depending on the volume of open cracks after hydraulic fracturing. In this example, the volume of air injection is equal to 500 thousand m ³ .

As a result of this, methane self-discharge from coal seam 1 occurs. Methane self-discharge continues over 5 years. To extract residual free methane, which does not flow out as a result of a decrease in gas pressure in the reservoir, it is possible to connect a vacuum pump station. After that, 25-30% of methane from its initial amount remains in the coal seam. To ensure the extraction of the remaining methane, a substance, for example carbon dioxide, is pumped into the coal seam with a sorption capacity greater than that of methane in a volume determined from the above expression. When l = 100 m, h = 1 m, m _f = 6.0, K ₁ = 1.2, T _in = 20 ^o C, Z = 0.9, P _σ = 1 MPa, T ₀ = 10 ^o C , P _Zak = 12 MPa, the volume of injected carbon dioxide is 500 thousand m ³ . This amount of injected substance provides filling the filtering volume of the coal seam. Since carbon dioxide has a high sorption capacity, it actively desorbs methane from the coal seam. This substance is kept in the reservoir until the methane desorption from coal ceases. The end of the methane desorption process in the formation is established by the well-known method of gas-dynamic testing of the well. After that, the process of methane self-discharge from the reservoir is resumed and it is further extracted from the coal seam through the well 2.

 The positive effect of the proposed technical solution is to increase the efficiency of methane extraction from the coal seam by recovering the remaining 25% of the sorbed methane gas by a substance with increased sorption ability.

Sources of information
1. Copyright certificate N 1511435, cl. E 21 F 7/00.

 2. Copyright certificate N 1375839, cl. E 21 F 7 / 00.1

Claims (2)

1. The method of extracting methane from a coal seam, including drilling wells from the surface, injecting the working fluid into the reservoir in the mode of hydraulic separation, keeping it in the reservoir and pushing it out of the filter cracks by injecting air into the reservoir, followed by methane extraction during its self-discharge, characterized in that after completion of the process of methane self-discharge from a coal seam, a substance with a higher sorption capacity than that of methane is pumped into the latter in a volume determined from the following expression:

where l is the length of the cracks uncovered during hydrodividing, m;
h is the thickness of the formation or formation, m;
m _f - filtering porosity of the formation (at the time of injection of the desorbing methane substance);
K ₁ - coefficient taking into account the loss of substance from the coal mass (1.2 - 1.8);
T _in - temperature of the injected substance, degrees;
Z is the coefficient of supercompressibility of the substance (0.9 - 0.95);
P _σ - is the barometric pressure, MPa;
T ₀ - the initial temperature of the reservoir, ^o C;
P _Zack - pressure of the injected substance, MPa,
then this substance is kept in the formation until the process of desorption of methane from coal ceases, after which methane is removed through one of the wells.  2. The method according to p. 1, characterized in that carbon dioxide is pumped into the coal seam.