RU2343275C2 - Method of intensification of natural gas extraction from coal beds - Google Patents

Method of intensification of natural gas extraction from coal beds Download PDF

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RU2343275C2
RU2343275C2 RU2006105514/03A RU2006105514A RU2343275C2 RU 2343275 C2 RU2343275 C2 RU 2343275C2 RU 2006105514/03 A RU2006105514/03 A RU 2006105514/03A RU 2006105514 A RU2006105514 A RU 2006105514A RU 2343275 C2 RU2343275 C2 RU 2343275C2
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pressure
well
pressure pulses
fluid
coal
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RU2006105514/03A
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Russian (ru)
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RU2006105514A (en
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Мэттью МИЛЛЕР (RU)
Мэттью Миллер
Алексей Евгеньевич Барыкин (RU)
Алексей Евгеньевич Барыкин
Эрни БРАУН (US)
Эрни БРАУН
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Шлюмбергер Текнолоджи Б.В.
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    • EFIXED CONSTRUCTIONS
    • E21EARTH DRILLING; MINING
    • E21BEARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B28/00Vibration generating arrangements for boreholes or wells, e.g. for stimulating production
    • EFIXED CONSTRUCTIONS
    • E21EARTH DRILLING; MINING
    • E21BEARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/003Vibrating earth formations
    • EFIXED CONSTRUCTIONS
    • E21EARTH DRILLING; MINING
    • E21BEARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/006Production of coal-bed methane
    • EFIXED CONSTRUCTIONS
    • E21EARTH DRILLING; MINING
    • E21BEARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/25Methods for stimulating production
    • E21B43/26Methods for stimulating production by forming crevices or fractures
    • E21B43/267Methods for stimulating production by forming crevices or fractures reinforcing fractures by propping

Abstract

FIELD: oil and gas industry.
SUBSTANCE: invention refers to methods of intensification of natural gas extraction from coal beds. Method consists in exposure of the bed to pressure pulses and in forming a cavity in the coal bed by means of cyclic increase and decrease of pressure of liquid in borehole. Also, as pressure pulses low frequency pressure pulses of high amplitude are employed. Exposure of the bed to low frequency pressure pulses of high amplitude is performed at increase of pressure of liquid in the borehole.
EFFECT: increased efficiency of natural gas extraction from coal beds due to exposure of bed to pressure pulses.
4 cl, 4 ex

Description

The present invention relates to a method for intensifying the production of natural gas from coal seams.

The world's reserves of natural gas associated with coal deposits occupy a volume of 8,000 trillion cubic feet. This gas is adsorbed on the surface of coal and is released when pressure decreases. The evolved gas may pass to production wells through a network of coal seam fractures. Due to the low effective permeability of coal seams, various methods of intensifying natural gas production are used. In addition, some coal seams are moistened, and their drainage is required to reduce pressure in the pores, so that the gas evolution process begins. Water is much more difficult to remove than gas, due to the fact that its viscosity is more than two orders of magnitude higher than the viscosity of the gas, which leads to an increase in hydraulic resistance in a low-permeable porous network of coal seam cracks. Moreover, water must be pumped out of the well using any mechanical device. Water also reduces the effective permeability of the coal seam crack network, creating obstructions at the entrances to the narrowing portions of the conductive cracks, occupying most of the pore space.

The most common existing methane recovery methods include creating cavities in a coal seam (cavity formation), hydraulic fracturing and directional drilling parallel to the formation.

The creation of cavities in the coal seam reduces the negative consequences of drilling, which are manifested in clogging of the pores of the bottomhole zone, and also increases the area from which methane can be extracted. Typically, the creation of a cavity is performed by cyclic pressure loads in wells with a trunk that is uncased in the area of the production interval. This processing is usually called cyclic cavity creation.

The usual method of hydraulic fracturing is used in cased holes with perforation mainly in cases where the permeability of coal is less than 20 millidars. A variation of this method is hydraulic drilling, which includes drilling an initial cased well and an additional well at a distance from the original well to collect fragments of coal material and drain water from the formation.

Directional drilling involves tilting the drill string so that drilling does not occur in the vertical direction, but parallel to the coal seam.

As soon as the corresponding well is completed using one of these methods, it is drained to reduce the pressure in the reservoir. The pressure drop in the formation contributes to the release of methane from the thickness of the coal into cracks oriented along the layers. If these cracks have a sufficiently high permeability, that is, interconnectedness, methane can flow from the coal seam into the well and will be available for extraction.

In the cyclical creation of a cavity, the most commonly used method for producing methane, various of the following mechanisms are used to connect the wellbore to a network of coal seam fractures: creating a physical cavity in the coal seam in an uncased area (up to 10 feet in diameter); creating a self-developing vertical crack that extends up to 200 feet from the wellbore parallel to the direction of minimum stress; creation of a fracture zone due to shear stresses, which increases permeability in a direction perpendicular to the direction of minimum stresses, as described, for example, in the book by I. Palmer, S. Lambert and Spitler Lj.L. “Completion and stimulation of methane coal seam wells. Chapter 14 in lectures on geology 38, pp. 303-341, 1993 and the article by M. Khodavsryan and McLennan “Formation of cavities: study of mechanisms and applications. Papers of the International Symposium on Coal Bed Methane Extraction 1993 (University of Alabama / Tuscaloosa), 1993, pp. 89-97.

The creation of cavities is carried out by increasing the pressure in the well with compressed air or foam, after which the pressure is sharply relieved. Stresses arising in the formation lead to cracking of the coal rock, and a sharp outflow of fluid leads to the removal of fragments of coal into the well. These cycles of pressure increase and depressurization are repeated many times over several hours or days, and the periodic destruction of the coal seam by shear stresses propagates laterally from the wellbore, as described, for example, in the article by Kakhail A. and Masszy D. “Method of cavity formation by loading unloading for intensification of methane emission from wells ”. Issue SPE 12843. Reports of the SPE Symposium on Non-Standard Methods of Gas Production, 1984.

The usual method of hydraulic fracturing is described in many publications, including in relation to coal seams, for example, in the article by S. Holdich. 1990 "Methods of completion in coal deposits." SPE 20670 / Reports of the 65th SPE Annual Technical Conference (New Orleans), p. 533.

Directional drilling cannot be considered as a way only to intensify the production of natural gas. It should be noted that both fracture (conventional hydraulic fracturing or cavity creation) and directional drilling simply increase the total area of contact with the coal seam, but do not provide an increase in the initial porosity of the coal.

A known tool for forming a cavity in the formation, which produces a mechanical cutting action using nozzles to create a cavity in the formation and its cleaning, is disclosed in US patent 6609668, 08/26/2003. This tool contains many nozzles for the release of jets carrying air, water and / or foam drilling fluid, and injected through each nozzle as the tool rotates. The tool is designed to clean and flush old decommissioned coal wells.

The advantages of this tool include the simultaneous washing of the well and increasing its diameter, performed in one run of the tool. However, pressure pulses are not created with this tool.

The following documents disclose methods that use the action of pressure pulses on oil reservoirs to increase oil production. However, none of the documents aimed at increasing methane production from coal seams.

The principle of simultaneous pumping and vibration is disclosed in US patent 4164978 (1978), Russian patent 16074 (1962), in the book "Scientific Research", M., MGI, 1975, p.61: "The use of vibration in oil production", M .: Nedra , 1977, in European patent 0512331 (1992), US patent 41644978 (1978), Russian patents 1165801 (1985), 2084705 (1993), 2085721 (1997), 2100571 (1992), 2085721 (1994), 2175718 (1997), 2,193,649 (2002).

Simultaneous pumping and vibration with a specially selected frequency (calculated resonant frequencies) are disclosed in US patents 4702315 (1987), 3863717 (1975), 3744017 (1973), Russian patents 1143150 (1994), 2231631 (2002). Simultaneous pumping and vibration, pulsed pumping mode are disclosed in US patent 4456068 (1984), Russian patents 2221141 (2004), 2176728 (2000), 2200832 (2001).

Simultaneous pumping and vibration, vibration at a special frequency, burning mixtures of solid / liquid fuels and an oxidizing agent are disclosed in US patents 3520362 (1970), 3768520 (1973), Russian patents 2128770 (1994), 2191896 (2002), 2003111855 (2004), 1434831 (1999), 1639127 (1987), 2087756 (1994).

Injection and vibration during depressurization, cyclic injection, vibrations with a special frequency are disclosed in US patent 3520362 (1970), Russian patents 2128770 (1994), 219896 (2002), 2003111855 (2004), 1434831 (1999), 1639127 (1987 ), 2087756 (1994), 2066746 (1996), 94023110 (1994).

Simultaneous injection and vibration, pulse mode of injection, vibration with a special frequency, injection of chemical agents, proppants are disclosed in US patents 5197543 (1993), 5662165 (1997), Russian patents 2193649 (2002), 2186953 (2000), 2243364 (2002) , 2003111855 (2004), 2066746 (1996), 94023110 (1994).

Simultaneous pumping and vibration, vibrations with special frequencies, and the injection of chemical agents are disclosed in US patents 5718289 (1998), Russian patents 2175058 (1999), 2186953 (2000), 2111348 (1994), 2078200 (1994).

Injection, vibration, injection of foamy agents, simultaneous vibration with special frequencies, injection of foamy agents are disclosed in US patents 6467542 (2000), 6015010 (2000), 6405797 (2000), 6241019 (2000).

The aim of the present invention is to increase the efficiency of the method of intensifying the production of natural gas from coal seams using pressure pulses on the formation.

This goal is achieved in that the method of intensifying the production of natural gas from coal seams involves creating a cavity in the coal seam by cyclically increasing and decreasing the pressure of the liquid in the well and exposing the formation to low-frequency high-pressure pressure pulses with increasing pressure in the well.

When carrying out the method, it is possible to further clean the well using an effective foamy cleaning medium.

To create pressure pulses, you can use a liquid-driven generator, and pump the foamy cleaning medium into the well through this generator.

In another embodiment of the method, a generator located in an adjacent well can be used to create pressure pulses and simultaneously apply pressure pulses to the formation and inject a foamy cleaning medium into the well being treated.

When processing only pressure pulses, the application of high-frequency low-frequency pressure pulses to the coal seam leads to the destruction of the seam and the formation of cracks as a result of the action of tensile and shear stresses on it. These cracks can form mainly along the network of cracks in the coal seam or along new fracture planes. Cracks tend to occupy a chaotic position due to the relaxation of anisotropic stresses that previously existed in coal seams. In addition, chipping, chipping, or shearing of the formation material may occur, which prevents the complete closure of these cracks. In all cases, the permeability of the rock increases, which increases the evolution of gas and the rate of drainage of coal seams, if water is present.

Pressure pulse treatment can be used to enhance the cavity formation process, which is limited by the stresses in the coal seam and the possibility of creating deep gaps around the well as a result of tensile and shear stresses applied to the formation during each pressure increase and release cycle. The application of low-frequency high-pressure pressure pulses during the process of increasing and depressurizing leads to an expansion of the fracture zone during each cavity formation cycle. As a result of this, fewer cycles are required to achieve the required increase in the effective diameter of the wellbore, or the resulting diameter of the effective wellbore can be significantly larger than with the standard cavity formation process.

Pressure pulse treatment can be used to improve the well cleaning process. After a cavity formation cycle in which water or another medium was used to transmit pressure pulses, the water or other medium is replaced with an effective foamy cleaning medium. This cleaning cycle will lead to the removal of small fragments of coal by the flow of fluid from the well and thereby to ensure unhindered gas evolution from the coal seam. The use of pressure pulses has an advantage over a conventional process with a constant pressure due to the fact that pressure pulses provide periodic compression and expansion of foam bubbles with gas. During compression, a gas bubble penetrates into the pores of fragments of a coal seam. During expansion, the bubbles dilute fragments of coal, facilitating their removal by a fluid stream. This particle removal process is necessary for effective well cleaning and is intensified by pressure pulsations.

Pressure pulse treatment can be used to improve hydraulic fracturing. Hydraulic fracturing is carried out by forcing a fracture fluid into a wellbore at high speeds and pressure to create a fracturing and then introducing a proppant, such as sand, into the fluid. The resulting gap is filled with proppant, which prevents the gap from closing. This channel with high conductivity allows both water and gas to flow at high speed from the coal seam to the wellbore. The main parameters of hydraulic fracturing include hydraulic conductivity of the fracture and fracture geometry. Artificial fractures are capable of conducting produced fluids or gases. Gaps with regular geometric shapes connect a large number of natural cracks, permeating the reservoir and combining it with the well. The impact of pressure pulses on the formation before creating a fracture in the formation, at the stage of pumping the fracture fluid without proppant into the reservoir, at the stage of pumping the fracture fluid with proppant, or during all fracturing operations, leads to the following results.

Coal seam cracks located along layers that intersect with a fracture expand and become uneven, thereby increasing their permeability and ability to nourish the fracture.

The coal seam along the fracture surface undergoes fracture as a result of tension and shear. Coal is colored, and the resulting gap becomes wider than the gap formed in the usual process. A wider gap has greater hydraulic conductivity than a narrower gap. Such a gap does not require the use of proppant to prevent closure of the gap. The exclusion of proppant in breaks leads to an increase in the porosity of the channel (if the channel does not overlap under the action of the crack closing voltage), which in turn increases the hydraulic conductivity of the fracture. The gap is easier to propagate due to the fact that pressure pulses cause the effect of fatigue fracture of the rock.

The creation of pressure pulses for the above methods of intensifying the production of natural gas from coal seams can be carried out, for example, by the following pressure pulse generators. A downhole hydrodynamic generator can be used, which creates pressure fluctuations when fluid is pumped through it. A special mechanism for temporarily blocking and discharging fluid flow creates oscillations. Such a mechanism can be mechanical valves, vortex type inertial valves, rotating nozzles, from which liquid is discharged when nozzles are aligned, and is blocked when nozzles are not aligned. In a fully mechanical pressure pulse generator, compression pulses in a liquid are created when two bodies collide with each other. An electrodynamic pulse generator uses an electric discharge to create a strong shock wave. Generators using water hammer and pulse generators based on the combustion of combustible oxidizing compounds can also be used.

For the methods according to the present invention, pressure pulse generators can be used, disclosed, for example, in the following patents: US Pat. Nos. 4,164,978 (1978), 4,164,478 (1978), 4,704,315 (1987), 3,863,717 (1975), 4,456,068 (1984), 3,520,362 (1970), 3768520 (1973), 5197543 (1993), 5662165 (1997), 5718289 (1998), 6467542 (2000), 6015010 (2000), 6405797 (2000), 6241019 (2000); Patent Documents of Russia No. 16074 91962), 1165801 (1985), 2084705 (1993), 2085721 (1997), 2100571 (1992), 2085721 (1994), 2175718 (1997), 2193649 (2002), 1143150 (1994), 2231631 (2002), 2221141 (2004), 2176728 (2000), 2200832 (2001), 2128770 (1994), 2191896 (2002), 2003111855 (2004), 1434831 (1999), 1639127 (1987), 2087756 (1994), 2066746 (1996), 94023110 (1994), 2193649 (2002), 2186953 (2000), 2243364 (2002), 2003111855 (2004), 2175058 (1999), 2186953 (2000), 2111348 (1994), 2078200 (1994), 2175058 (1999), 2186953 (2000), 2111348 (1994), 2078200 (1994) and in the above publication “Scientific Research” 1975, p. 61.

The most preferred, but not necessary option for the claimed methods is the use of downhole pressure pulses generating pulses in the well being treated. Well generators that can be used in the methods of the invention include, for example, the generator disclosed in US Pat. No. 6,015,010, for generating compression waves in a wellbore and comprising a pumping unit installed at the wellhead, a tubing string running down into casing production casing of a well, a block of hollow cylinders connected to the lower part of the tubing string, and a pair of plungers installed in the cylinder block and connected to the pumping unit with pumping and polishing units paid-rods which serve to compress the liquid contained in the cylinder block, and for supplying compressed fluid in the well casing, thus creating a shock wave. The cylinder block includes a hollow upper cylinder, a hollow lower cylinder mounted under the upper cylinder, a transition cylinder installed between the upper and lower cylinders, and a compressor cylinder with a compression chamber installed between the transition and upper cylinders. The inner diameter of the lower cylinder is larger than the upper, and the diameter of the lower plunger is larger than the diameter of the upper. In addition, the lower cylinder corresponds to the size of the lower plunger, and the upper cylinder corresponds to the size of the upper plunger. When the plungers move up the cylinder block, the lower plunger enters the compression chamber, and the upper plunger leaves it. Due to the fact that the diameter of the lower plunger is larger than the diameter of the upper one, the volume of the compression chamber is reduced, thus, the liquid in it is compressed. When the pump unit reaches its upper position, the lower plunger releases the compressed fluid located in the compression chamber into the well. At this point, rapid pressure release occurs and an extensive impact is created in the wellbore with an amplitude of 200-250 bar.

A method of intensifying natural gas production from coal seams by treating the seam with pressure pulses can be implemented by applying low-frequency high-pressure pressure pulses to the coal seam, leading to gaps in the formation structure. This method is as follows.

The wellbore is prepared by placing the pressure pulse generator in the wellbore approximately in the treatment zone and, if necessary, filling the well with incompressible fluid to ensure effective communication of the pressure pulse generator with the coal seam and transmitting pressure pulses to the formation. Next, adjust the pressure pulse generator so that it creates pressure pulses of the required frequency and amplitude. To ensure processing by pressure pulses at a penetration depth of several meters, low-frequency waves should be used that are closest to the resonant frequency of the coal seam. Information on the correct determination of the frequency and amplitude of pressure pulses for a particular type of formation is contained, for example, in European patent 0512331 (1992), US patent 41644978 (1978), Russian patents 1165801 (1985), 2084705 (1993), 2085721 (1997), 2100571 (1992), 2085721 (1994), 2175718 (1997), 2193649 (2002).

Processing time is determined empirically depending on the properties of the coal seam treatment mode. Recommendations for the duration of the operation can also be found in the above patents.

After stopping the supply of pressure pulses, if necessary, carry out the drainage of the coal seam using a pump to remove excess water or completely remove water from the well. Further, if necessary, it is possible to carry out a procedure for cleaning a well from coal fragments by any known method, for example, by injecting a cleaning foamy medium, for example nitrogen, foam or aerated liquid.

The above steps may be repeated as many times as necessary. Then, if necessary, the generator is removed, the operational equipment is installed and gas production begins.

A method of intensifying natural gas production from coal seams can be carried out by treating the formation with pressure pulses to improve the formation of cavities in the coal seam.

When carrying out this method, a wellbore is prepared, in which a pulse generator, for example, a fluid-driven generator, is placed in the wellbore, having it located approximately in the processing zone, if necessary, the wellbore is filled with incompressible fluid to ensure the connection of the pressure pulse generator with the coal seam and transmission pressure pulses to the reservoir. At the same time, the pressure pulse generator is regulated so that it creates pressure pulses of the required frequency and amplitude. The choice of mode and duration of processing is carried out as described above. When implementing this method, you can use the pressure pulse generator with the release of fluid without a resonator so that the pulsating jet produces a cutting effect on the reservoir. Further, the pressure in the well is increased above the pressure in the pores by injecting a liquid, for example nitrogen, foam or aerated liquid, which can be carried out through the specified generator. A quick pressure relief is carried out in the borehole, at which fragments of coal are formed. On the surface, open the valve on the "flow well". Then, if necessary, the well is cleaned by passing aerated liquid or foam through the processed interval of the well to thin and carry coal fragments to the surface.

To carry out the next cycle of cavity formation, the well is filled with an incompressible fluid and the above steps are repeated until the removal of coal fragments during depressurization ceases. If necessary, the generator is removed and installed operational equipment and start gas production.

Pressure pulse treatment can be used to improve the cleaning of the well from fragments of coal. For this, after conducting a cycle of formation of a cavity in a coal seam, a liquid intended to transmit pressure impulses, for example water or another effective medium, is replaced by an effective cleaning foam medium. When compressed, the foamy medium penetrates into the pores of the coal fragments and dilutes them, facilitating the entrainment of the coal fragments by the flow. This process of removal of fragments of coal is required for effective cleaning of the well and can be intensified using pressure pulses.

When implementing this method combine the supply of pressure pulses and injection of cleaning fluid. In this case, when using generators with a liquid drive, the cleaning fluid is pumped through this generator. When using a pressure pulse generator installed in a neighboring well, simultaneously supply pulses to the formation and supply cleaning fluid to the well being treated. The circulation of the cleaning fluid in the well is completed in the absence of removal of coal fragments to the surface.

Pressure pulse treatment can be used to improve hydraulic fracturing.

In the implementation of this method, the wellbore is prepared by placing a pulse generator in the well approximately in the processing zone and filling the well with an incompressible fluid, if necessary, to ensure the connection of the pressure pulse generator with the coal seam.

Prepare for injection of hydraulic fracturing fluid into the reservoir, adjust the pressure pulse generator in such a way as to create pressure pulses of the required frequency and amplitude. The choice of mode and duration of processing is carried out, for example, according to the above patents.

Hydraulic fracturing of a coal seam is carried out by the stages of pumping a fracture fluid into a wellbore at high speeds and pressures to create a fracture, then introducing a proppant into the fracture fluid to prevent closure of the created fracture and finally injecting the fracture fluid without proppant to flush the well. In this case, pressure pulses are applied to the coal seam until a hydraulic fracture is created or when a fracture fluid is injected into the wellbore to create a fracture, or when a proppant is introduced into the fracture fluid, or during the final injection of the fracture fluid to flush the well, or when several or all these stages. The selected mode of exposure to pressure pulses at various stages of hydraulic fracturing affects the resulting fracture geometry.

In one embodiment of the method, hydraulic fracturing operations are carried out without the use of proppant. The possibility of implementing such a method has been explained above.

After completion of the hydraulic fracturing stages, if necessary, the generator is removed, production equipment is installed and gas production is started.

The following are specific examples of the implementation of the above methods.

To determine the required frequency of the generation of pressure pulses for various application modes in the above methods, the following algorithms are used, which are further called the "Algorithm".

Algorithm 1 is the use of experimental data indicating that the effective formation of cracks as a result of extension and shear of the formation occurs in the range of pulse repetition frequencies (number of pulses per second) from 0.1 to 500 hertz.

Algorithm 2 involves the installation of a measuring system before processing the formation in an observation well to measure the characteristics of the vibration of the formation. The measuring system must be connected with the studied productive interval. Then, a pressure pulse generator is installed in a neighboring well, it is turned on to create pressure pulses, the generator frequency is increased stepwise, formation oscillations are recorded in the observation well and the most effective frequency is selected by evaluating the formation vibrations in the observation well corresponding to certain generator operating frequencies.

Algorithm 3 involves writing down a system of equations of a linearly elastic porous medium representing the formation around the wellbore, solving equations for the conditions under which the formation is exposed to periodic pressure pulses or a single pressure impulse, calculating the formation destruction zone from the action of tensile and shear forces in the formation around the wellbore and the selection of the frequency and amplitude of the pressure pulses that provide the maximum dimensions of the fracture zone.

Algorithm 4 involves writing down a system of equations of a linearly elastic porous medium representing a formation around a wellbore, solving an equation for the conditions under which a formation is exposed to periodic pressure pulses or a single pressure impulse, and calculating the formation destruction zone from the action of tensile and shear forces in the formation around the fracture in formation and the choice of frequency and amplitude, which provide the maximum size of the fracture zone.

In the examples below, the pressure pulse generator disclosed in U.S. Pat. No. 6,015,010, which is mechanical, uses pressure pulses when the sucker rods move up and down when the rocking pump operates on the surface and is capable of providing a water hammer in the wellbore with an amplitude of 200-250 bar.

Example 1

The use of pressure pulses on a coal seam to increase the efficiency of creating a cavity in a coal seam

a) The well passes into a coal seam containing adsorbed methane to a depth of approximately 800 meters. The production interval has a length of 10 meters, porosity of 2%, permeability of 25 millidarsi, temperature of 25 ° C, reservoir pressure of 50 bar, elastic modulus of 0.5 million pounds per square. inch and Poisson's ratio of 0.34.

Use the "Algorithm" to determine the possibility of processing this well with a generator that generates pressure pulses of 50 bar with a frequency of 60 hertz.

The well is filled with saline with a KCl concentration of 4% by weight to control pressure. Using a well overhaul installation, a downhole sucker rod pump, sucker rods and tubing production string with a packer are removed. The pressure pulse generator is installed on the tubing production string, and this string is again lowered into the well. The injection of fluid for processing the borehole zone begins after the descent of the generator to a depth corresponding to the roof of the productive interval. A filtered solution (with a weight concentration of KCl of 4%) is pumped through the generator. The injected fluid, passing through the generator, periodically creates pressure in the accumulator. During pressure increase, some part of the injected fluid enters the accumulator, and therefore the total injection rate into the reservoir is less than the average injection rate, and therefore the injection pressure at the bottom decreases. When the accumulator is completely filled, the pressure increase initiates a rapid discharge of the accumulated liquid. This discharge increases the total flow rate of injection into the reservoir, which exceeds the average flow rate of injection, and therefore the injection pressure at the bottom increases. Using this mechanism of periodic pulsations, the necessary amplitudes and frequencies of pressure pulses are created. The injection is continued until the fracture pressure is reached. Here, the hydraulic fracturing pressure is the pressure at which the hydrostatic pressure of the fluid initiates the development of a fracture from the wellbore. The pressure pulses created by the generator periodically exceed the hydraulic fracture pressure. When the injected fluid enters the rock, a pressure gradient is created in the borehole zone. The pressure gradient in combination with periodic pressure pulses causes the destruction of the rock in the near-wellbore zone of the reservoir due to tensile deformations. Pressure pulses destroy the blocks of the matrix of the coal seam, crushing the coal seam along the network of cracks. Such treatment with pressure pulses is performed over a period of time from 15 minutes to several hours.

At the end of the treatment with pressure pulses, the specified saline solution is displaced into the formation using foam nitrogen (0.7 / 0.3 volume mixture of nitrogen and water with a thickener and a surfactant) to stabilize the structure of the foam, specific volume fractions are determined for the bottomhole data conditions). The nitrogen injection is continued to create pressure in the near-wellbore zone to a value much higher than the reservoir pressure. Foam can easily penetrate a weakened and destroyed coal seam. After pumping the entire volume of foam (the volume should ensure that the productive interval is filled to a depth of up to 3 meters), the pressure in the wellbore rapidly drops. When the pressure is released, the coal weakened and destroyed to the state of crushed stone is carried through the borehole to the surface into the receiving tank. The removal of fragments of coal and nitrogen from the well continues until the pressure is completely released. During processing, the radius of the wellbore increases, and the pores of the coal are cleaned directly around the wellbore. Over a period of time from several hours to one or several days, from 2 to 10 treatment cycles can be performed, including the generation of pressure pulses, the creation of excess bottomhole pressure using foam and a quick pressure relief in the well. The process of creating pressure pulses significantly increases the efficiency of the destruction of the coal seam and the creation of the cavity.

Then, the well is cleaned by pumping foam liquid and its subsequent circulation through the wellbore to dilute and remove the sludge from the wellbore. Such circulation is carried out by pumping fluid through flexible tubing (tubing), lowered to the roof level of the productive interval and gradually advanced to the bottom at small intervals. Periodically, the immersion depth of the flexible tubing is kept constant to ensure thorough cleaning of this interval from collapsed material. Flexible wellbore cleaning is continued until the bottom hole is reached. Flexible tubing is then removed from the well while continuing to circulate. After the flexible tubing has been lifted into the well, the tubing string, pump rods and pump are again lowered. The well is once again being exploited.

b) The method according to this example is carried out analogously to example a), but the well cleaning process is modified.

As in the above example, the well is cleaned at the end of pressure boost and pressure relief cycles. The circulation is performed by pumping fluid through flexible tubing (tubing), lowered to the roof level of the productive interval and gradually lowered to the bottom at small intervals in the accumulation of collapsed material. Periodically, the immersion depth of the flexible tubing is kept constant for more thorough cleaning of this interval of the wellbore before further advancement to the bottom. The wellbore cleaning using flexible tubing is continued until the well is cleaned up to the bottom. In this example, the well cleaning efficiency is improved by using a pulse pressure generator during the circulation of the foam. During operation of the pressure pulse generator, the foam bubbles begin to pulsate, increasing and decreasing in turn. During compression pulses, the foam penetrates into the pores between the coal fragments located in the wellbore. During the expansion of the bubbles, the foam loosens the layer of coal debris, facilitating their capture by a circulating stream. A pressure pulse generator is installed at the end of the flexible tubing. It has the same mechanism for generating pressure pulses and pulse characteristics as the generator used to create the cavity. The main difference is that the pressure in the wellbore during cleaning operations is lower than the pressure of the hydraulic fracturing, and has a value low enough for the outflow of fluids from the formation for subsequent removal through the well. At the end of well cleaning, the flexible tubing is removed from the well while continuing to circulate. After the flexible tubing is lifted into the well, the production casing, sucker rods and pump are again lowered, and the well is re-launched.

Example 2

The use of pressure pulses on a coal seam to increase the efficiency of hydraulic fracturing of a coal seam, carried out without the use of proppants

a) The well passes into a coal seam containing adsorbed methane to a depth of approximately 800 meters. The production interval has a length of 10 meters, porosity of 2%, effective permeability of 25 millidarsi, temperature of 25 ° C, reservoir pressure is 50 bar, elastic modulus is 0.5 million pounds per square. inch and Poisson's ratio of 0.34.

Use the "Algorithm" to determine the possibility of processing this well with a generator that generates pressure pulses of 75 bar with a frequency of 20 hertz.

The well is filled with saline with a mass concentration of KCl of 4% to control the pressure, a pressure pulse generator is installed and the fracture fluid is pumped after the generator is lowered to a depth corresponding to the roof of the productive interval.

During hydraulic fracturing, fracturing fluids are pumped through tubing and also through the annulus between the tubing and the casing. The rupture fluid contains additives that increase its viscosity. In this example, this liquid contains a polymer thickener - guar in a volume of 0.4% by weight, boric acid in a volume of 0.014% by weight, the required amount of caustic soda to increase the pH in the fluid to 9.6, a biocide in a volume of 0.003% by weight A surfactant in a volume of 0.2% to impart hydrophobic characteristics to the coal surface (ethoxylated butoxylated alcohol) and an oxidizing agent in capsules in a volume of 0.25% by weight for hydration of the fluid. Such a liquid is called a crosslinked gel.

The crosslinked gel begins to be pumped simultaneously through the annulus and through the tubing. The injection rate is increased slowly until the hydraulic fracturing pressure is reached. The injection rate is increased from approximately a flow rate of 0.5 m 3 / min to a constant flow rate of 3 to 4 m 3 / min for the development of a fracture over a large distance from the wellbore. The flow rate of the crosslinked gel pumped through the annulus is constant, while the flow rate of the crosslinked gel exiting the end of the tubing is pulsating due to the operation of the downhole pressure pulse generator. A cross-linked gel flowing through the generator periodically increases the pressure in the battery. During pressure increase, some part of the injected fluid enters the accumulator, and therefore the total injection rate into the reservoir is less than the average injection rate, and therefore the injection pressure at the bottom decreases. When the accumulator is completely filled, the pressure increase initiates a rapid discharge of the accumulated liquid. This discharge increases the total flow rate of injection into the reservoir, which exceeds the average flow rate of injection, and therefore the injection pressure at the bottom increases. Using this mechanism of periodic pulsations, the necessary amplitudes and frequencies of pressure pulses are created. During this treatment, only the fracturing fluid is pumped: only about 200 m 3 . The pressure pulse generator operates during the entire injection time. Injection of the fracturing fluid creates and develops a crack away from the wellbore from 300 to 400 feet apart, while pressure pulses contribute to fracture of the formation, creating compressive-tensile and shear stresses on the surface of the fracture and in planes parallel to the surface of the fracture. In contrast to the main hydraulic fractures, the cracks created by pressure pulses propagate along the network of cracks in the coal seam: along and perpendicular to the coal interlayers. Pressure pulses destroy the structure of the matrix of the coal seam, effectively crushing the seam through a network of cracks. This treatment, combining hydraulic fracturing and the action of pressure pulses on the formation, is performed for approximately 1 hour during the injection of the entire volume of fluid into the formation.

At the end of the injection of the crosslinked gel, the latter is displaced from the casing using KCl saline with a concentration of 4%, containing guar with a concentration of 0.2% by weight. Then the displacement is carried out using a foam solution containing guar with a concentration of 0.2% and KCl brine, which is injected in order to weaken the hydrostatic pressure in the wellbore (downhole foam characteristics: 70% nitrogen by volume, 30% water containing 0.2 % guar by weight and from 0.1 to 1.0% by volume of surfactant). Injection into the annulus is terminated after the crosslinked gel is finally displaced into the formation (when the foamless crosslinked guar solution fills the entire annulus and tubing). Foam injection is continued through tubing. A valve in the annulus is opened, allowing the wellbore fluid to flow through the wellbore and through the valve into the receiving reservoir. During the outflow of fluid from the well, the bottomhole pressure in the wellbore drops to a level of about 5 to 10 bar, and the injected fracturing fluid exits the well. During the exit of the borehole fluid from the crack, the fragments of coal acquire an orientation in which the prevention of complete closure of the main and additional cracks occurs. The resulting cracks are characterized by high hydraulic conductivity.

The well is cleaned at the end of the downhole fluid exit process, as in Example 1.

b) The well passes into a coal seam containing adsorbed methane to a depth of approximately 800 meters. The production interval is 10 meters long, porosity 2%, effective permeability 25 millidarsi, temperature 25 ° C, reservoir pressure equal to 800 psi. inch, the modulus of elasticity is 0.5 million pounds per square. inch and Poisson's ratio of 0.34.

Use the "Algorithm" to determine the possibility of processing this well with a generator that generates pressure pulses of 200 bar with a frequency of 0.1 hertz.

In this example, the method is carried out similarly to the method of example a), but the pressure pulse generator is set to a depth of 5 meters above the roof of the productive interval, and as a fracture fluid in this example, a fracture fluid containing KCl with a concentration of 4% by weight, viscoelastic Surfactants with a concentration of from 0.5 to 3% by volume, an organic surfactant with a concentration of from 0.2 to 0.4 by volume in the form of ethoxylated-butoxylated glycols having from 1 to 5 ethylene oxide groups and from 5 to 10 bottles Flax-oxide groups. This composition is a non-damaging viscoelastic surfactant solution. Well cleaning is carried out without using a pulse generator.

c) The well passes into a coal seam containing adsorbed methane to a depth of approximately 800 meters. The production interval has a length of 10 meters, its porosity is 2%, effective permeability is 25 millidarsi, temperature is 25 ° C, reservoir pressure is 50 bar, elastic modulus is 0.5 million pounds per square meter. inch and Poisson's ratio of 0.34.

Apply the "Algorithm" to determine the possibility of processing this well with a generator that can create pressure pulses with an amplitude of 70 bar and a frequency of 300 hertz.

The method is carried out similarly to the method of example a), but using a generator to create pressure pulses with a built-in venturi. When a crosslinked gel passes through a venturi, cavitation occurs. The source of pressure pulses is the collapse of gas bubbles in the expanding part of the venturi. Using this pulsation mechanism, the necessary amplitude and frequency of pressure pulses are provided. During this treatment, only crosslinked gel is pumped. In total, its volume is 200 m 3 . The pressure pulse generator runs all the time. The pressure pulses created by this generator focus downward and along the crack and create a stress concentration as the bubbles collapse near the walls of the crack. A gel injection creates and expands a crack extending from the wellbore to a distance of 300-400 feet, and pressure pulses contribute to the destruction of the formation, creating compressive-tensile and shear stresses on the surface of the fracture and in planes parallel to the surface of the fracture. These pressure pulses, as mentioned earlier, effectively destroy the coal seam along the network of cracks in the coal seam. The entire process of hydraulic fracturing, together with processing by pressure pulses, takes about 1 hour, while the entire volume of fluid is pumped into the reservoir.

Example 3

Application of pressure pulses to a coal seam only during injection of the fracturing fluid into the reservoir to increase the efficiency of hydraulic fracturing using a proppant The well passes into a productive coal seam containing adsorbed methane to a depth of approximately 800 meters. The production interval has a length of 10 meters, its porosity is 2%, effective permeability is 25 millidarsi, temperature is 25 ° C, reservoir pressure is 50 bar, elastic modulus is 0.5 million pounds per square meter. inch and Poisson's ratio of 0.34.

Apply the "Algorithm" to determine the possibility of processing this well using a generator capable of creating pressure pulses with an amplitude of 75 bar and a frequency of 20 hertz.

The well is filled with a saline solution with a KCl concentration of 4% by weight to control the pressure, the pressure pulse generator is installed in the well and the fracture fluid is injected to treat the near-barrel zone after the generator is lowered to a depth corresponding to the roof of the production interval.

During the hydraulic fracturing operation, fluid is pumped both into the tubing string and into the annulus. As the fracturing fluid, the above-described crosslinked gel or a solution of a viscoelastic surfactant is used. The process of hydraulic fracturing is carried out as described in other examples above, while the injected fluid, passing through the generator, periodically causes an increase in pressure in the accumulator. During pressure increase, some part of the injected fluid enters the accumulator, and therefore the total injection rate into the reservoir is less than the average injection rate, and therefore the injection pressure at the bottom decreases. When the accumulator is completely filled, the pressure increase initiates a rapid discharge of the accumulated liquid. This discharge increases the total flow rate of injection into the reservoir, which exceeds the average flow rate of injection, and therefore the injection pressure at the bottom increases. Using this mechanism of periodic pulsations, the necessary amplitudes and frequencies of pressure pulses are created. During this treatment, 70 m 3 of fracturing fluid is pumped without proppant — the stage of pumping fracturing fluid into the formation without proppant. The pressure pulse generator works only at this stage. By injecting the fracturing fluid, a crack extending from the wellbore to a distance of 300-400 feet is created and expanded, and pressure pulses contribute to the fracture of the formation, creating compressive-tensile and shear stresses on the surface of the fracture and in planes parallel to the surface of the fracture. The entire process of hydraulic fracturing, together with processing by pressure pulses, takes about 1 hour, while the entire volume of fluid is pumped into the reservoir.

After completing this injection step, a proppant is added to the remaining fracture fluid. At the initial stage, the proppant concentration is low, but gradually increase. At the beginning of the treatment, the proppant concentration is 1% by weight of the fracturing fluid and by the end, 50% by weight of the fracturing fluid. Rupture fluid with proppant is pumped only into the annulus. The total volume of injected fluid is 140 m 3 . In the process of pumping a fracturing fluid with a proppant, the pressure pulse generator does not work. Further stages of the process are carried out as in example 2.

4. An example of the use of continuous exposure to pressure pulses on a coal seam during hydraulic fracturing during the stage of injection of the fracturing fluid and at the stage of pumping proppant.

a) The well passes into a productive coal seam containing adsorbed methane to a depth of about 800 meters. The production interval is 10 meters long, its porosity is 2%, permeability is 25 millidarsi, temperature is 25 ° C, reservoir pressure is 50 bar, elastic modulus is 0.5 million pounds per square inch, Poisson's ratio is 0.34.

Apply the "Algorithm" to determine the possibility of processing this well with a generator that can create pressure pulses of 75 bar at a frequency of 20 hertz.

The well is filled with saline with a KCl concentration of 4% by weight to control the pressure, the pressure pulse generator is lowered into the well. They begin to pump the fracture fluid to treat the near-barrel zone after the generator is lowered to a depth corresponding to the roof of the productive interval.

The fluid is pumped into the annulus between the tubing and the casing. As the fracturing fluid, the above-described crosslinked gel or solution of a viscoelastic surfactant is used.

The injection of fracturing fluid without proppant when exposed to pressure pulses created by the generator, is carried out analogously to example 3. Hydraulic fracturing and exposure to pressure pulses lasts about 1 hour, until the entire volume of fluid is pumped into the reservoir.

After the first injection step, a proppant is added to the remainder of the fracture fluid. At the beginning of the treatment, the concentration of the proppant is 1% of the weight of the gel, and by the end it increases to 50%. The rupture fluid with proppant is pumped only through the annulus. In total, about 140 m 3 of liquid solution is pumped. The pressure pulse generator also works during this stage - the stage of pumping the fracturing fluid with proppant. The remaining stages of the process are carried out similarly to the previous examples.

Claims (4)

1. A method of intensifying natural gas production from coal seams, including creating a cavity in the coal seam by cyclically increasing and decreasing the pressure of the liquid in the well and exposing the formation to low-frequency high-pressure pressure pulses with increasing pressure of the liquid in the well.
2. The method according to claim 1, wherein the well is further cleaned using a foamy cleaning medium.
3. The method according to claim 2, in which a liquid-driven generator is used to create pressure pulses and the foamy cleaning medium is injected into the well through this generator.
4. The method according to claim 2, in which to create pressure pulses, use a generator located in an adjacent well, and simultaneously apply pressure pulses to the formation and inject the cleaning foam medium into the treatment well.
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