Fracturing method to increase coalbed methane production
The fracturing method using exothermic gas-producing fluid to increase coal seam temperature and enhance permeability addresses the inefficiencies of conventional methods, promoting desorption and stable production of coalbed methane by adhering to isothermal and isobaric adsorption principles.
Patent Information
- Application Number
- CN202411288590.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-14
- Publication Date
- 2024-12-13
- Estimated Expiration
- 2044-09-14
AI Technical Summary
Conventional methods for coalbed methane production face challenges such as low single well production, low recovery rate, high construction cost, poor economic benefits, rapid decline in production, and short stable production period due to difficulties in efficiently desorbing and diffusing adsorbed gas, poor permeability, and rapid decompression leading to fracture blockage and permeability reduction.
A fracturing method that utilizes exothermic gas-producing fracturing fluid to increase coal seam temperature, destroy hydrogen bonds, and enhance permeability by incorporating resistance reducing, foam stabilizing, and penetrant agents to promote desorption and drainage, adhering to isothermal and isobaric adsorption principles.
Enhances coalbed methane production by increasing desorption rate and amount, improving permeability, and extending stable production through controlled temperature and pressure, thereby optimizing gas diffusion and migration.
Smart Images
Figure CN118793422B_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of coalbed methane development, and in particular relates to a fracturing method for increasing coalbed methane production. Background Art
[0002] Conventional oil and gas production can no longer meet demand, and the supply and demand situation of oil and gas resources is becoming increasingly severe. Strengthening the exploration and development of coalbed methane resources can make up for the shortage of existing conventional oil and gas resources. Compared with conventional reservoirs, the content of free gas in coal seams is very small, and most of them are stored in the micropores of coal seams in the form of adsorption. Most of the micropores are closed and unconnected, and their pore throat structure is poor. At the same time, compared with tight sandstone gas and shale gas, the buried depth of coalbed methane is shallower, basically concentrated at around 1000-1500 meters, so the original formation temperature is very low, generally at 30-40℃, and there are characteristics of low gas pressure, low saturation and low permeability, which makes it very difficult to exploit efficiently. At present, coalbed methane development has problems such as low single well production, low recovery rate, high construction cost, poor economic benefits, rapid decline in production after production, and short stable production period.
[0003] The transformation of coalbed methane in existing mining areas is mainly focused on the seepage field and stress field. Through hydraulic fracturing, only the stress field is changed to form artificial fractures, the seepage capacity of the reservoir is improved, and the decompression and desorption are adopted after fracturing. The adsorbed gas in the fracture is difficult to desorb and has a slow diffusion rate, which makes it difficult to be efficiently utilized. At the same time, due to the low original pressure of the formation and the rapid decompression and exploitation method after fracturing, the formation energy is quickly emptied, the liquid accumulated in the fracture is difficult to be discharged, and the reservoir is easily locked by water, and finally the gas is difficult to produce. In addition, the rapid decompression and drainage of this process will erode the coal seam and transport the original coal powder, causing the effective fracture blockage of the coal seam in the near-wellbore area, the reduction of the permeability of the coal reservoir, or the jamming of the pump, the leakage of the oil pump and other underground faults; the coal seam is a multi-pore-fracture system, and the conventional fracturing method is difficult to achieve ultra-high connectivity of the fractures and improve the seepage capacity in the matrix, making it difficult for the in-situ free gas and the desorbed adsorbed gas to diffuse and migrate efficiently, so it is difficult to increase the production of a single well and ensure long-term stable production. Currently, chemical methods are used to change the seepage field and increase the desorption rate of adsorbed gas in order to improve the coalbed methane infiltration and displacement effect. However, it cannot be effectively implemented due to the large amount of chemical agents used, poor compatibility with formation media, great damage to the reservoir, large amount of filtration loss after the displacement fluid enters the formation, and short duration of the drug effect. Summary of the invention
[0004] In order to solve the above technical problems, the present invention provides a fracturing method for increasing coalbed methane production, comprising:
[0005] The expression of the maximum adsorption capacity of coalbed methane is established based on the Langmuir equation, and the calculation expression of the desorption efficiency is determined according to the maximum adsorption capacity of coalbed methane.
[0006] According to the set desorption efficiency and the total adsorbed gas volume, the desorption heat required to achieve the desorption efficiency is determined to obtain the maximum adsorption amount of coalbed methane;
[0007] The relationship model between temperature change and maximum adsorption of coalbed methane is derived using Weibull function.
[0008] Determine the temperature change according to the maximum adsorption amount of coalbed methane;
[0009] According to the expression of the heat required to break the bond energy, input the temperature change and determine the heat released by breaking the bond energy;
[0010] According to the heat released by breaking the bond energy, exothermic gas-producing fracturing fluid is prepared, and the fracturing fluid formula and concentration are adjusted according to the coal seam composition to regulate the intensity and rate of gas production and heat release.
[0011] Based on the above technical solution, the present invention can also be improved as follows.
[0012] Furthermore, assuming that the maximum adsorption capacity of coalbed methane is The saturated adsorption capacity is , the adsorption constant is , the formation pressure is ,but:
[0013] .
[0014] Furthermore, assuming that the maximum adsorption capacity of coalbed methane is The actual adsorption amount is , is the desorption efficiency, then:
[0015] .
[0016] Furthermore, let the adsorption amount of coalbed methane be , the maximum adsorption capacity of coalbed methane is , the adsorption constant is The adsorption temperature is The apparent temperature of the coal seam is ,but:
[0017] .
[0018] Further, according to the expression of the heat required for breaking the bond energy, the temperature change is input to determine the heat released by breaking the bond energy, including: assuming that the heat required for breaking the bond energy is The specific heat capacity of the coal seam is The mass of the reservoir is , the temperature change is ,but:
[0019] .
[0020] Furthermore, the fracturing fluid formula includes a resistance reducing and foam stabilizing agent, an exothermic gas generating agent and a penetrant.
[0021] Furthermore, the fracturing fluid formula includes 0.05-0.1% resistance reducing and foam stabilizing agent, 1-6% exothermic gas generating agent and 0.1-0.3% penetrant.
[0022] Furthermore, the resistance reducing and foam stabilizing agent is at least one of polyacrylamide, xanthan gum, hydroxypropyl guar gum and diutan gum.
[0023] Furthermore, the exothermic gas generating agent is at least one of hydrogen peroxide, sodium hypochlorite, potassium permanganate and sodium persulfate.
[0024] Furthermore, the penetrant is at least one of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, sodium hexadecyl sulfonate and polyoxyethylene octylphenol ether.
[0025] The beneficial effects of the present invention are as follows: the present invention can solve the problems in the prior art that it is difficult to increase the single-well production of coalbed methane and cannot maintain stable production for a long time due to fracturing mainly relying on seepage fields and stress fields. Based on the physical adsorption mechanism of hydrogen bonds, when the energy in the environment is greater than the adsorption bond energy, the hydrogen bonds can be forcibly destroyed to achieve physical desorption. Therefore, the amount of coalbed methane adsorption is subject to the dual control of pressure and temperature, and obeys the isothermal adsorption theorem and the isobaric adsorption theorem. Increasing the temperature of the coal seam is conducive to promoting coalbed methane desorption, increasing the desorption rate and desorption amount of the adsorbed gas, thereby increasing the coalbed methane production. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Figure 1 A schematic diagram of a fracturing method for increasing coalbed methane production provided in Example 1 of the present invention;
[0027] Figure 2 The exothermic curve of the fracturing fluid formula at different addition amounts;
[0028] Figure 3 This is the gas production curve of the fracturing fluid formula at different addition amounts. DETAILED DESCRIPTION
[0029] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.
[0030] As an example, Figure 1As shown, in order to solve the above technical problems, this embodiment provides a fracturing method for increasing the production of coalbed methane, specifically a fracturing method for promoting complete desorption of adsorbed gas and promoting hydraulic fracturing energy enhancement and drainage by changing the temperature field of coal rock, including:
[0031] The expression of the maximum adsorption capacity of coalbed methane is established based on the Langmuir equation, and the calculation expression of the desorption efficiency is determined according to the maximum adsorption capacity of coalbed methane.
[0032] According to the set desorption efficiency and the total adsorbed gas volume, the desorption heat required to achieve the desorption efficiency is determined to obtain the maximum adsorption amount of coalbed methane;
[0033] The relationship model between temperature change and maximum adsorption of coalbed methane is derived using Weibull function.
[0034] Determine the temperature change according to the maximum adsorption amount of coalbed methane;
[0035] According to the expression of the heat required to break the bond energy, input the temperature change and determine the heat released by breaking the bond energy;
[0036] According to the heat released by breaking the bond energy, exothermic gas-producing fracturing fluid is prepared, and the fracturing fluid formula and concentration are adjusted according to the coal seam composition to regulate the intensity and rate of gas production and heat release.
[0037] The present invention can solve the problem that it is difficult to increase the production of a single coalbed methane well and cannot maintain stable production for a long time due to the existing technology mainly relying on the seepage field and the stress field for fracturing.
[0038] The coalbed gas adsorbed is mainly adsorbed on the surface of coal rock organic matter in the form of hydrogen bonds. The present invention is based on the physical adsorption mechanism of hydrogen bonds. When the energy in the environment is greater than the adsorption bond energy, the hydrogen bonds can be forcibly destroyed to achieve physical desorption. Therefore, the amount of coalbed methane adsorption is subject to the dual control of pressure and temperature, and obeys the isothermal adsorption theorem and the isobaric adsorption theorem. Increasing the coal seam temperature is conducive to promoting coalbed methane desorption, increasing the desorption rate and desorption amount of adsorbed gas, thereby increasing coalbed methane production.
[0039] The temperature field distribution of coal rock heating was simulated and analyzed by finite element software. The results show that heat injection can significantly increase the temperature of coal seams, and the temperature increase can effectively destroy the hydrogen bond adsorption of coalbed methane, increase the free gas content, and high-energy hot steam can improve the permeability of coal seams. At the same time, the organic matter in coal rocks will also undergo thermal cracking or thermal cracking, further increasing the permeability and porosity of coal rocks. Therefore, heating and gasification can promote the pressure holding, energy increase and permeability increase of coal seams, and randomly open closed and semi-closed pores, greatly improving the permeability of coal seams.
[0040] Optionally, the maximum adsorption capacity of coalbed methane is The saturated adsorption capacity is , the adsorption constant is , the formation pressure is ,but:
[0041] .
[0042] Optionally, the maximum adsorption capacity of coalbed methane is The actual adsorption amount is , is the desorption efficiency, then:
[0043] .
[0044] Optionally, the adsorption capacity of coalbed methane is , the maximum adsorption capacity of coalbed methane is , the adsorption constant is The adsorption temperature is The apparent temperature of the coal seam is ,but:
[0045] .
[0046] Optionally, according to the expression of the heat required to break the bond energy, the temperature change is input to determine the heat released by breaking the bond energy, including: assuming that the heat required to break the bond energy is The specific heat capacity of the coal seam is The mass of the reservoir is , the temperature change is ,but:
[0047] .
[0048] According to the temperature increase required for the reservoir, exothermic gas-producing fracturing fluid is prepared. In actual application, the fracturing fluid formula and concentration can be optimized and adjusted according to the different coal rock components to regulate the intensity and rate of gas production and heat release.
[0049] Assume A is an exothermic gas generating agent, and the exothermic gas generating reaction mechanism is:
[0050] FeS2+A Fe 3+ +SO4 2- +H + +H2O;
[0051] CaMg(CO3)2+4H + Ca 2+ +Mg 2+ +2H2O+2CO2↑;
[0052] CaCO3+2H + Ca 2++H2O+CO2↑.
[0053] Optionally, the fracturing fluid formula includes a resistance reducing and foam stabilizing agent, an exothermic gas generating agent and a penetrant.
[0054] Optionally, the fracturing fluid formula includes 0.05~0.1% resistance reducing and foam stabilizing agent, 1~6% exothermic gas generating agent and 0.1~0.3% penetrant.
[0055] In actual application, the resistance reducing and foam stabilizing agent in the fracturing fluid formula stabilizes the gas generated by the reaction to form foam; the permeating agent has ultra-high permeability, which can ensure that the fracturing fluid can penetrate into the fracture system. The fracturing fluid formula reacts with pyrite (FeS2) and calcite (CaMg(CO3)2) in the coal seam, generating heat and producing carbon dioxide. The high heat can promote the desorption of coal seam adsorbed gas, and the generated CO2 can also replace coal seam methane. The CO2 foam can also disperse coal powder, increase energy and promote drainage, and extend the fracture network through communication.
[0056] Optionally, the resistance reducing and foam stabilizing agent is at least one of polyacrylamide, xanthan gum, hydroxypropyl guar gum and diutan gum.
[0057] Optionally, the exothermic gas generating agent is at least one of hydrogen peroxide, sodium hypochlorite, potassium permanganate and sodium persulfate.
[0058] Optionally, the penetrant is at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium hexadecyl sulfate and polyoxyethylene octylphenol ether.
[0059] Attached Figure 2 The exothermic curves of the fracturing fluid formula at different dosages are shown in Figure 2. The horizontal axis is time t, unit: min, and the vertical axis is temperature, unit: Celsius. L21 is the exothermic curve when the dosage of the agent is 1 mol / L, L22 is the exothermic curve when the dosage of the agent is 2 mol / L, and L23 is the exothermic curve when the dosage of the agent is 3 mol / L. Figure 3 The gas production curve of the fracturing fluid formula at different dosages, the horizontal axis is time t, unit: min, the vertical axis is: volume, unit: ml, L31 is the gas production curve when the dosage of the agent is 1 mol / L, L32 is the gas production curve when the dosage of the agent is 2 mol / L, and L33 is the gas production curve when the dosage of the agent is 3 mol / L. At normal temperature and pressure, the fracturing fluid produces gas in situ and releases a lot of heat. In 10-15 minutes, the liquid temperature increases from normal temperature to 95°C; in a closed environment, the fracturing fluid produces gas in situ and releases a lot of heat. In 20-30 minutes, the liquid temperature increases from normal temperature to a peak of 140°C, and the pressure is increased by 10Mpa. Through experiments, the coal rock core in the open container reacts and heats up in the exothermic gas-producing fracturing fluid, and the temperature rises to 95°C, and boiling is achieved at normal temperature and pressure.
[0060] The common hydrogen bond energy in coalbed methane is concentrated in the range of 5.44-29.31 kJ·mol-1. The burial depth of coalbed methane is relatively shallow, and the coal seam temperature is generally 20-30°C. The formation temperature can rise to 140°C during the exothermic reaction. Therefore, the heat released by this fracturing method meets the energy conditions required for high-temperature desorption of hydrogen bonds.
[0061] During the entire fracturing construction process from the pre-fluid joint creation to the replacement of the sand-carrying fluid in the on-site fracturing construction process, the resistance reducing and foam stabilizing agent, the exothermic gas generating agent A, and the penetrant are sucked out through the fracturing vehicle fluid adding pump and injected into the formation together with the fracturing fluid. The injection can be carried out throughout the process or intermittently. The construction is convenient and fast, and it is efficient and highly adaptable.
[0062] After the temperature of the coal seam increases, the hydrophobic multi-chain polymers such as PAM polyacrylamide in the fracturing fluid can also break the chain and degrade at high temperature, realizing a self-cleaning reservoir and protecting the reservoir from pollution; high-temperature pyrolysis can also increase the desorption rate and amount of adsorbed gas, so that the adsorbed gas and dissolved gas in the matrix can quickly seep into the diffusion pores and thus separate from the original filled adsorption pores, avoiding reverse adsorption after fracturing.
[0063] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.
Claims
1. A fracturing method for increasing coalbed methane production, characterized in that: include: The expression of the maximum adsorption capacity of coalbed methane is established based on the Langmuir equation, and the calculation expression of the desorption efficiency is determined according to the maximum adsorption capacity of coalbed methane. According to the set desorption efficiency and the total adsorbed gas volume, the desorption heat required to achieve the desorption efficiency is determined to obtain the maximum adsorption amount of coalbed methane; The relationship model between temperature change and maximum adsorption of coalbed methane is derived using Weibull function, including: assuming the adsorption of coalbed methane is , the maximum adsorption capacity of coalbed methane is , the adsorption constant is The adsorption temperature is The apparent temperature of the coal seam is ,but: ； Determine the temperature change according to the maximum adsorption amount of coalbed methane; According to the expression of the heat required to break the bond energy, input the temperature change and determine the heat released by breaking the bond energy, including: assuming that the heat required to break the bond energy is The specific heat capacity of the coal seam is The mass of the reservoir is , the temperature change is ,but: ； According to the heat released by breaking the bond energy, exothermic gas-producing fracturing fluid is prepared, and the fracturing fluid formula and concentration are adjusted according to the coal seam composition to regulate the intensity and rate of gas production and heat release.
2. The fracturing method for increasing coalbed methane production according to claim 1, characterized in that: Assume that the maximum adsorption capacity of coalbed methane is The saturated adsorption capacity is , the adsorption constant is , the formation pressure is ,but: 。 3. The fracturing method for increasing coalbed methane production according to claim 1, characterized in that: Assume that the maximum adsorption capacity of coalbed methane is The actual adsorption amount is , is the desorption efficiency, then: 。 4. The fracturing method for increasing coalbed methane production according to claim 1, characterized in that: The fracturing fluid formula includes resistance reducing and foam stabilizing agent, exothermic gas generating agent and penetrant.
5. The fracturing method for increasing coalbed methane production according to claim 1, characterized in that: The fracturing fluid formula includes 0.05~0.1% resistance reducing and foam stabilizing agent, 1~6% exothermic gas generating agent and 0.1~0.3% penetrant.
6. The fracturing method for increasing coalbed methane production according to claim 5, characterized in that: The resistance reducing and foam stabilizing agent is at least one of polyacrylamide, xanthan gum, hydroxypropyl guar gum and diutan gum.
7. The fracturing method for increasing coalbed methane production according to claim 5, characterized in that: The exothermic gas generating agent is at least one of hydrogen peroxide, sodium hypochlorite, potassium permanganate and sodium persulfate.
8. The fracturing method for increasing coalbed methane production according to claim 5, characterized in that: The penetrant is at least one of sodium dodecyl sulfonate, sodium dodecylbenzene sulfonate, sodium hexadecyl sulfonate and polyoxyethylene octylphenol ether.