In-seam diverting agent for deep coal bed gas fracturing transformation

Abstract

The invention discloses an in-seam diverting agent for deep coal bed gas fracturing transformation. The in-seam diverting agent is selected from one or a mixture of more of polycaprolactone type polyurethane, polylactic acid, polyglycolic acid, poly (butylene succinate), thermoplastic starch, poly (terephthalic acid)-adipic acid-butylene glycol copolyester and a polyethylene-vinyl acetate copolymer. Through reasonable proportioning and shape design, the diverting agent can realize crack plugging and diversion optimization in a deep coal seam environment. The method can effectively improve the complexity of the fracture network, increases the contact area of the fractures and the coal seam matrix, and improves the recovery rate of the coal seam gas. Particularly, a normal-temperature series (20-40 DEG C) and a high-temperature series (40-60 DEG C) are designed according to different geological conditions and can be completely degraded into harmless substances within 2-36 hours and 1-24 hours respectively, and secondary pollution is avoided. In addition, the diverting agent can realize multi-stage cluster fracturing transformation without a special downhole tool, so that the construction complexity and the development cost are remarkably reduced.

Description

Technical Field

[0001] The invention relates to the field of deep coalbed methane transformation, and in particular to an in-fracture diverter for deep coalbed methane fracturing transformation. Background Art

[0002] With the development of deep coalbed methane resources, horizontal wells and large-scale volume fracturing technology have gradually become the core technical means for deep coalbed methane development. The permeability of deep coal seams is usually very low, and the flow of coalbed methane mainly depends on the seepage channels provided by the fracture system. Therefore, increasing the density of fractures, enhancing the complexity of the fracture network, and increasing the contact area between fractures and the matrix are the keys to improving the efficiency of deep coalbed methane development.

[0003] However, the existing deep coalbed methane fracturing technology has many limitations in practical application. Specifically:

[0004] 1. Insufficient complexity of the fracture network: In the deep high-stress environment, the traditional fracturing technology forms mainly main fractures with few branch fractures. The fracture system is single and has poor connectivity, making it difficult to form an effective complex fracture network.

[0005] 2. The contact area between the fractures and the coal seam matrix is ​​limited: Due to the small number of fractures and their insufficient extension, the seepage path of coalbed methane from the matrix to the fracture system is long, the seepage resistance is large, and the gas escape is difficult, which directly affects the recovery rate of coalbed methane.

[0006] 3. Low single-well production: Due to the above problems, the single-well production of coalbed methane after fracturing transformation is generally low, failing to fully tap the potential of deep coalbed methane resources.

[0007] 4. The effect of fracturing transformation is not ideal: the existing technology lacks effective means in temporary plugging of fractures, diversion optimization, and efficient extension and distribution control of fractures, resulting in the reservoir transformation effect after fracturing not meeting expectations.

[0008] In addition, the high formation pressure and high temperature environment of deep coal seams also put forward higher requirements for fracturing construction and materials in the fractures. Traditional fracturing processes and materials may experience performance degradation in deep environments, further limiting the formation and expansion of fracture networks.

[0009] Therefore, there is an urgent need for a new type of material that can effectively increase the density of fractures, improve the complexity of fracture networks, and expand the contact area between fractures and coal seam matrix in deep coal seam environments. This will significantly improve the extraction efficiency of deep coalbed methane, increase the production of single wells, and promote the further upgrading of deep coalbed methane resource development technology. Summary of the invention

[0010] The present invention aims to provide a fracture diverter for deep coalbed methane fracturing transformation in order to solve the technical problems such as low complexity of fracture network, small contact area between fracture and coalbed matrix, low single well production, and unsatisfactory transformation effect after fracturing in the existing deep coalbed methane fracturing transformation process. The present invention can effectively improve the distribution of fractures and the complexity of fracture network through unique material design and function optimization, thereby improving the recovery rate of coalbed methane and fracturing transformation efficiency, while reducing development costs.

[0011] The present invention is achieved by adopting the following technical solutions.

[0012] A diverter for deep coalbed methane fracturing transformation, which is selected from one or a mixture of polycaprolactone (PCL) type polyurethane, polylactic acid (PLA), polyglycolic acid (PGA), polybutylene succinate (PBS), thermoplastic starch (TPS), polyterephthalate-adipate-butylene glycol copolyester (PBAT) and polyethylene-vinyl acetate copolymer (EVA). The diverter used in this application can be obtained from the following table:

[0013] Information table of materials used for diverting agents

[0014]

[0015] The above materials are selected in this application because they have good biodegradability, environmental friendliness, and excellent mechanical and rheological properties, and can play an efficient temporary blocking and diversion role in the complex deep coalbed methane fracturing environment. During fracturing construction, this intra-fracture diversion agent can flexibly adapt to the complex geometric structure of the cracks by injecting it into the coal seam cracks, and play a role in temporarily blocking some cracks, thereby guiding the construction pressure to the uncracked or insufficiently cracked coal seam areas. This process not only helps to optimize the expansion of the fracture network, but also improves the uniformity and effectiveness of fracturing construction, and maximizes the release of coalbed methane resources.

[0016] In addition, by combining and applying a variety of polymer materials, the physical and chemical properties of the diverter in the fracture, such as degradation rate, strength and toughness, can be further adjusted to adapt to the geological conditions and construction requirements of different coal seams. This flexible material selection and ratio scheme provides an innovative solution for the efficient exploitation of deep coalbed methane.

[0017] Furthermore, polylactic acid is selected as the diverting agent in the fracture. Polylactic acid has excellent biodegradability, mechanical properties and cost-effectiveness. In the coalbed methane fracturing transformation that takes into account temporary plugging performance and environmental protection requirements, polylactic acid is an ideal choice for high efficiency and economy. When polylactic acid is used as a diverting agent, it can enter the coal seam cracks with the flow of the fracturing fluid, and achieve rapid deposition and temporary plugging in the cracks. Through a reasonably designed degradation rate, it can be naturally degraded into harmless substances such as carbon dioxide and water within a certain period of time, which not only avoids secondary pollution, but also effectively improves the conductivity of coal seam fracturing transformation and the efficiency of coalbed methane extraction.

[0018] Furthermore, the shape of the diverter in the seam is granular, and it is divided into coarse particles, medium particles and fine particles according to the particle size; the coarse particle size is 10 / 20 mesh, the medium particle size is 16 / 30 mesh, and the fine particle size is 20 / 40 mesh. The width of the cracks in the coal seam varies greatly. Through the design of overlapping particle size ranges, it is ensured that more particles are involved in filling and temporary plugging in the junction area, which can adapt to the complex and changeable crack environment, improve the coverage rate of temporary plugging agents, and improve the use efficiency and application scope of the diverter in the seam.

[0019] Furthermore, the in-fracture diverter includes a normal temperature series of 20-40°C and a high temperature series of 40-60°C; the normal temperature series in-fracture diverter has a dissolution time of 2-36h, which is suitable for low-temperature geological conditions. By controlling the degradation rate and chemical stability of the material, the sustainability of the temporary plugging effect is ensured; the high temperature series in-fracture diverter has a dissolution time of 1-24h, which is suitable for high-temperature geological conditions. It can maintain good mechanical properties and degrade quickly in a high temperature environment, thereby meeting the temporary plugging and diversion needs of cracks.

[0020] The room temperature series seam diverter includes the following components in mass percentage: 60-80% polylactic acid, 10-20% polybutylene succinate, 5-15% thermoplastic starch, 5-10% polyglycolic acid, 5-15% polyethylene-vinyl acetate copolymer. The molecular weight of polylactic acid is 50,000-80,000 Da; the molecular weight of polybutylene succinate is 70,000-120,000 Da; the molecular weight of polyglycolic acid is 10,000-50,000 Da; the molecular weight of polyethylene-vinyl acetate copolymer is 40,000-80,000 Da.

[0021] The high temperature series seam diverter includes the following components in mass percentage: 20-40% polylactic acid, 10-30% polyglycolic acid, 40-60% polycaprolactone polyurethane, 5-15% polyterephthalic acid-adipate-butylene glycol copolyester, 10-20% polyethylene-vinyl acetate copolymer. The molecular weight of polylactic acid is 100,000-200,000 Da; the molecular weight of polyglycolic acid is 70,000-150,000 Da; the molecular weight of polycaprolactone polyurethane is 80,000-200,000 Da; the molecular weight of polyterephthalic acid-adipate-butylene glycol copolyester is 120,000-200,000 Da; the molecular weight of polyethylene-vinyl acetate copolymer is 60,000-100,000 Da.

[0022] The normal temperature series and high temperature series of seam diverters of the present invention achieve performance differences by selecting different material components. Among them, the main components of the normal temperature series are polylactic acid (PLA), polybutylene succinate (PBS), thermoplastic starch (TPS), polyglycolic acid (PGA) and polyethylene-vinyl acetate copolymer (EVA), focusing on moderate degradation rate and lasting temporary plugging effect; the main components of the high temperature series are polycaprolactone (PCL) type polyurethane, polylactic acid (PLA), polyglycolic acid (PGA), polyterephthalate-adipate-butylene glycol copolyester (PBAT) and polyethylene-vinyl acetate copolymer (EVA), focusing on rapid degradation and high temperature stability. Through the selection of targeted materials, the needs of different geological conditions in the process of deep coalbed methane development can be effectively met.

[0023] Comparison of components between normal temperature and high temperature systems

[0024]

[0025] During the fracturing transformation process, the deep coalbed methane fracturing transformation diverter is introduced into the fracture through a sand mixing truck using a low-displacement pumping method. During the pumping process, close attention is paid to the changes in the ground construction pressure, especially after the deep coalbed methane fracturing transformation diverter enters the fracture. If the construction pressure shows signs of increasing while the displacement remains unchanged, it indicates that the deep coalbed methane fracturing transformation diverter has bridged in the fracture. With continued pumping, the blockage and compaction will further reduce the permeability of the original channel, and the pressure will further increase, opening new branch fractures and forcing the fracturing fluid to enter the new fractures. Subsequently, the construction displacement is quickly increased, and close attention is paid to the changes in the construction pressure. When the construction pressure permits, it is increased to the designed construction displacement to enter the next construction stage.

[0026] This application has the following beneficial effects.

[0027] (1) The fracture diversion agent of the present invention can realize multi-stage and cluster fracturing transformation measures without using downhole completion tools;

[0028] (2) The in-fracture diverter of the present invention helps to produce a more complex and uniform fracture network;

[0029] (3) The intra-fracture diverting agent of the present invention improves the recovery rate of oil and gas reservoirs, improves the fracturing efficiency, and reduces the cost;

[0030] (4) The diverter in the fracture of the present invention improves the effect of repeated fracturing

[0031] (5) The seam diversion agent of the present invention does not require the use of additional special pumping equipment

[0032] (6) The in-fracture diverter of the present invention can still dissolve in a low-temperature environment, ensuring the communication between the wellbore and the oil reservoir, and will not affect the post-compression flowback and production of the coalbed methane well. It is suitable for various cased wells, open hole wells, vertical wells, horizontal wells, and wells where downhole tools cannot be lowered due to casing deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of plugging new seams with a seam diverter for deep coalbed methane fracturing reformation according to the present invention;

[0034] Figure 2 It is the construction procedure of diverter joint control technology;

[0035] Figure 3 This is a diagram showing the plugging effect of the normal temperature series of in-seam diverting agents used for deep coalbed methane fracturing transformation of the present invention;

[0036] Figure 4 This is a diagram showing the plugging effect of the high-temperature series of in-fracture diverting agents used for deep coalbed methane fracturing transformation of the present invention.

[0037] Among them, 1. Main crack; 2. Secondary crack; 3. Diverter. DETAILED DESCRIPTION

[0038] The present patent application is further described below in conjunction with embodiments.

[0039] like Figure 1 As shown, Figure 1 The process of using diverters in fractures to plug and guide the direction of new fractures during deep coalbed methane fracturing transformation is shown. In the figure, the main fracture 1 is the main fracturing fracture, which is the main path for liquid to enter the coalbed methane reservoir. The small fractures next to the main fracture 1 are secondary fractures 2, and the fracturing fluid is further spread through these fractures to enhance the transformation effect. The granular material is the diverter 3, which forms an artificial barrier by filling the end of the main fracture, thereby changing the expansion direction of the fracture. At the end of the main fracture 1, the accumulation of the diverter blocks the further extension of the fracture and forces the fracturing fluid to turn to a new path, forming a new secondary fracture 2. Figure 1The role of diverter 3 in CBM fracturing transformation is intuitively described, namely, by plugging the end of the main fracture and inducing the formation of new fractures, thereby more effectively expanding the fracture network and improving the recovery rate of CBM.

[0040] Example 1

[0041] In the Shanxi Linxing deep coalbed methane mining demonstration area, the target coal seam is buried at a depth of 1500m, the reservoir temperature is 38℃, a deep coal seam directional well, the coal seam thickness is 5m, the perforation section length is 5m, the perforation density is 12 holes / meter, and there are 60 holes in total. In order to increase the complexity of the fractures and fully transform the target reservoir, a large-scale temporary plugging volume fracturing process is adopted. The designed sand volume is 250 cubic meters, the liquid volume is 1800 cubic meters, and the normal temperature series of fracture diverter for coalbed methane fracturing transformation is 180kg, of which polylactic acid accounts for 65%, polybutylene succinate accounts for 15%, thermoplastic starch accounts for 10%, polyglycolic acid accounts for 5%, and polyethylene-vinyl acetate copolymer accounts for 5%, and the displacement is 16m 3 / min.

[0042] After fracturing begins, the designed displacement is increased to 16 cubic meters, and sand is added. When the amount of sand added reaches 120 cubic meters, the sand is stopped to replace the wellbore, and the construction displacement is reduced to 2m 3 / min, 180kg of high-temperature seam diverting agent for coalbed methane fracturing transformation was added to the sand mixer truck and quickly poured into the mixing tank of the sand mixer truck within 1 minute. When the temporary plugging agent reached the bottom of the well, attention was paid to the changes in the construction pressure. It can be seen that when the construction displacement is 2m 3 / min constant, the construction pressure slowly increased from 28MPa to 31MPa, the pressure stopped increasing and remained basically stable, and then the construction displacement continued to increase to the designed construction displacement of 16m 3 / min, enter the next stage of fracturing construction (temporary plugging and turning construction curve as shown in Figure 3 shown).

[0043] This example demonstrates the actual application effect of the normal temperature series of seam diversion agents under the condition that the burial depth is close to the deep coal seam depth but the temperature is still within the normal temperature range. By optimizing the construction displacement, pressure monitoring and material ratio, the efficient transformation of the reservoir is successfully achieved, and the recovery rate of coalbed methane is improved.

[0044] Example 2

[0045] In the Shanxi Linxing Deep Coalbed Methane Exploitation Demonstration Area, the target coal seam is buried at a depth of 1950m, the reservoir temperature is 50℃, a deep coal seam directional well, the coal seam thickness is 6m, the perforation section length is 6m, the perforation density is 16 holes / meter, and there are 96 holes in total. In order to increase the complexity of the fractures and fully transform the target reservoir, a large-scale temporary plugging volume fracturing process is adopted. The designed sand volume is 300 cubic meters, the liquid volume is 2100 cubic meters, and the high-temperature series of fracture diverter for coalbed methane fracturing transformation is 200kg, of which polylactic acid accounts for 30%, polyglycolic acid accounts for 20%, polycaprolactone polyurethane accounts for 40%, polyterephthalic acid-adipate-butylene glycol copolymer accounts for 5%, and polyethylene-vinyl acetate copolymer accounts for 5%, and the displacement is 18m 3 / min.

[0046] After fracturing begins, the designed displacement is increased to 18 cubic meters, and sand is added. When the amount of sand added reaches 150 cubic meters, the sand is stopped and replaced in one wellbore, and the construction displacement is reduced to 2m 3 / min, 200kg of high-temperature seam diverting agent for coalbed methane fracturing transformation was added to the sand mixer, and quickly poured into the mixing tank of the sand mixer within 1 minute. When the temporary plugging agent reached the bottom of the well, attention was paid to the changes in the construction pressure. It can be seen that when the construction displacement is 2m 3 / min constant, the construction pressure slowly increased from 30MPa to 33MPa, the pressure stopped increasing and remained basically stable, and then the construction displacement continued to increase to the designed construction displacement of 18m 3 / min, enter the next stage of fracturing construction (temporary plugging and turning construction curve as shown in Figure 4 shown).

[0047] This embodiment fully utilizes the advantages of high-temperature diverting agents, effectively forms complex fractures during the construction process, improves reservoir permeability and transformation effects, and provides technical support for the efficient development of deep coalbed methane. This construction mode has good reference significance for the development of similar deep coalbed methane fields.

[0048] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A seam diverter for deep coalbed methane fracturing, characterized in that: One or a mixture of polycaprolactone polyurethane, polylactic acid, polyglycolic acid, polybutylene succinate, thermoplastic starch, polyterephthalic acid-adipate-butylene glycol copolyester and polyethylene-vinyl acetate copolymer is selected.

2. The in-seam diverting agent for deep coalbed methane fracturing reformation according to claim 1, characterized in that: Polylactic acid is used as the in-seam diverting agent.

3. The in-fracture diversion agent for deep coalbed methane fracturing according to claim 1, characterized in that: The shape of the seam diverter is granular, and is divided into coarse particles, medium particles and fine particles according to the particle size; the coarse particle size is 10 / 20 mesh, the medium particle size is 16 / 30 mesh, and the fine particle size is 20 / 40 mesh.

4. The in-fracture diversion agent for deep coalbed methane fracturing according to claim 1, characterized in that: The seam diverter includes a normal temperature series of 20-40°C and a high temperature series of 40-60°C. The dissolution time of the normal temperature series seam diverter is 2-36h, and the dissolution time of the high temperature series seam diverter is 1-24h.

5. The in-fracture diversion agent for deep coalbed methane fracturing according to claim 4, characterized in that: The room temperature series seam diverting agent comprises the following components in percentage by mass: 60-80% of polylactic acid, 10-20% of polybutylene succinate, 5-15% of thermoplastic starch, 5-10% of polyglycolic acid, and 5-15% of polyethylene-vinyl acetate copolymer.

6. The in-fracture diversion agent for deep coalbed methane fracturing according to claim 5, characterized in that: The molecular weight of polylactic acid is 50,000 to 80,000 Da; the molecular weight of polybutylene succinate is 70,000 to 120,000 Da; the molecular weight of polyglycolic acid is 10,000 to 50,000 Da; and the molecular weight of polyethylene-vinyl acetate copolymer is 40,000 to 80,000 Da.

7. The in-fracture diversion agent for deep coalbed methane fracturing according to claim 4, characterized in that: The high-temperature series seam diverter includes the following components in percentage by mass: 20-40% of polylactic acid, 10-30% of polyglycolic acid, 40-60% of polycaprolactone polyurethane, 5-15% of polyterephthalic acid-adipate-butylene glycol copolyester, and 10-20% of polyethylene-vinyl acetate copolymer.

8. The in-fracture diversion agent for deep coalbed methane fracturing according to claim 7, characterized in that: The molecular weight of polylactic acid is 100,000 to 200,000 Da; the molecular weight of polyglycolic acid is 70,000 to 150,000 Da; the molecular weight of polycaprolactone polyurethane is 80,000 to 200,000 Da; the molecular weight of poly(terephthalic acid-adipate-butylene glycol) copolyester is 120,000 to 200,000 Da; and the molecular weight of polyethylene-vinyl acetate copolymer is 60,000 to 100,000 Da.

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