A method of fracturing process for thin interbed longitudinal reformation

Abstract

The present application relates to the technical field of oil and gas field development, and more particularly to a fracturing process method for longitudinal reconstruction of thin interbeds, which comprises the steps of preliminary planning, fracturing operation, simulation experiment, temporary plugging by ball injection, repeated operation and completion. The quantitative evaluation of temporary plugging holes reduces the risk and uncertainty of field operation. Since the degree of utilization of low-permeability thin interbed reservoirs in the vertical direction is directly proportional to the post-pressing effect, the full pressure opening of each layer in the vertical direction is ensured as much as possible, so that all small layers in the vertical direction of the thin interbeds are fully reconstructed, and the fracturing reconstruction effect of the thin interbeds is improved.

Description

Technical Field

[0001] This invention relates to the field of oil and gas field development technology, and in particular to a fracturing process method for vertical stimulation of thin interbedded layers. Background Technology

[0002] Thin interbedded reservoirs refer to a geological phenomenon characterized by the alternation of thin layers of different lithologies, featuring relatively thin individual oil-bearing reservoirs and the recurrence of thin interlayers of the same lithology. In these thin interbedded reservoirs, adjacent layers differ in lithology, and thin interlayers of the same lithology appear repeatedly, resulting in significant differences in permeability and low reserve abundance. Early stimulation of low-permeability thin interbedded reservoirs primarily involved stratified stimulation with sliding sleeve packers, with the horizontal direction being lateral and the vertical direction being longitudinal. However, due to the low displacement and small scale of stratified stimulation with sliding sleeve packers, it was difficult to achieve uniform vertical stimulation of the thin interbedded reservoirs, failing to fully utilize the production capacity of each oil and gas layer, leading to poor post-pressure effects and an inability to maximize production capacity.

[0003] Existing methods for longitudinal layering modification of thin interlayered structures mainly fall into two categories: mechanical and non-mechanical. Mechanical methods utilize various mechanical tools to achieve layering modification, offering relatively high efficiency in thin interlayered structures. However, for sliding sleeve packers, this method suffers from low displacement and small-scale modification requirements. Furthermore, packers frequently experience packer failures such as seal loss and jamming during unsealing, leading to extended operation cycles, increased construction risks, and poor applicability. Non-mechanical methods typically use various chemical stoppers for layering modification, but both the reliability and efficiency of achieving fine layering are low. In summary, existing technologies result in low longitudinal opening depth, hindering capacity improvement. Summary of the Invention

[0004] Based on this, the present invention provides a fracturing process method for longitudinal modification of thin interlayers that can achieve a higher degree of pressure opening in the longitudinal direction.

[0005] The technical solution of this invention is: a fracturing process method for longitudinal modification of thin interbedded layers, comprising the following steps:

[0006] Preliminary planning: Divide the reservoir into stratified sections, select the perforated sections to be modified in each stratified section, and stratify the perforated sections to be modified from bottom to top. Then, use bridge plugs to divide each perforated section to be modified into multiple multi-perforated sections to be modified according to the stratification results.

[0007] Fracturing operation: After determining the perforation density, perforation is carried out on the multi-hole section to be modified according to the perforation density, so that the perforated section to be modified is formed.

[0008] Simulation experiment: Combining the physical simulation experiment of perforation erosion, a prediction model for the change of perforation diameter based on the amount of sand added is formed, and the diameter of the temporary plugging ball is adjusted according to the amount of sand added;

[0009] Temporary blocking of pitches: Conduct a reduced displacement friction test, and carry out temporary blocking of pitches based on the results of the reduced displacement friction test;

[0010] Repeated construction until completion: After the first layer of perforated sections to be modified has completed the step-by-step fracturing construction, step-by-step simulation experiment and step-by-step ball-dropping temporary plugging, the remaining layers of perforated sections to be modified are sequentially subjected to step-by-step fracturing construction, step-by-step simulation experiment and step-by-step ball-dropping temporary plugging, so that the perforated sections to be modified are formed into perforated sections.

[0011] Optionally, each perforation to be modified may undergo sequential fracturing, simulation experiments, and temporary plugging with ball-dropping from bottom to top.

[0012] Optionally, in the fracturing process, the formula for calculating the perforation density is:

[0013]

[0014] Where, p perf Where is the orifice friction (MPa), and Q is the construction displacement (m³). 3 / min); ρ is the density of fracturing fluid (g / cm³) 3 );d p N is the diameter of the aperture (cm). p denoted as the number of orifices; c is the orifice flow coefficient, where 0.8 <c<0.9。

[0015] Optionally, during the temporary blocking of the ball-throwing process, if the construction displacement is reduced by 1m each time... 3 If the construction pressure decreases by more than 3 MPa per minute, then the number of temporary plugging operations must be at least two.

[0016] Optionally, in the temporary blocking injection mode, the number of temporary blocking balls is a, (1 / 3)*N p <a<(1 / 2)*N p Construction displacement 3m 3 / min <Q<4m 3 / min.

[0017] Optionally, during the temporary blocking of the ball-throwing process, if the construction displacement is reduced by 1m each time... 3 If the construction pressure decreases by less than 3 MPa per minute, then the number of temporary plugging operations is counted as one.

[0018] Optionally, in the temporary blocking injection mode, the number of temporary blocking balls is a, (1.2)*N p <a<(1.5)*N p Construction discharge volume 8m 3 / min <Q<12m 3 / min.

[0019] Optionally, in the step simulation experiment, the formula for the prediction model of the aperture diameter change is:

[0020] H = H0 + 2.4 * 10 -4 *M,

[0021] Where H0 is the initial perforation diameter (mm); H is the perforation diameter after abrasion (mm); and M is the mass of proppant added in a single stage (kg).

[0022] Compared with the prior art, implementing the embodiments of the present invention has the following beneficial effects:

[0023] The fracturing process method for vertical stimulation of thin interbedded layers of the present invention reduces the risks and uncertainties of on-site temporary plugging by quantitatively evaluating the temporary plugging hole. At the same time, since the degree of vertical activation of low-permeability thin interbedded layer reservoirs is directly proportional to the post-fracturing effect, it ensures that each layer in the vertical direction is fully activated, so that all the small layers in the vertical direction of the thin interbedded layer are fully stimulated, thereby improving the fracturing stimulation effect of thin interbedded layers. Attached Figure Description

[0024] Figure 1 This is a flowchart of the fracturing process method for longitudinal modification of thin interlayers as described in an embodiment of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] In the description of this invention, it should be noted that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0027] Furthermore, the terms "first," "second," etc., are used in this invention to describe various types of information, but these terms should not be limited to them; they are only used to distinguish information of the same type from one another. For example, without departing from the scope of this invention, "first" information can also be referred to as "second" information, and similarly, "second" information can also be referred to as "first" information.

[0028] Reference Figure 1 This embodiment provides a fracturing process method 100 for longitudinal modification of thin interbedded layers, including the following steps: preliminary planning, fracturing construction, simulation experiment, ball-dropping for temporary plugging, and repeated construction until completion.

[0029] The preliminary plan includes dividing the reservoir into stratified sections, selecting perforated sections to be modified within each stratified section, and stratifying the perforated sections from bottom to top. Based on the stratification results, each perforated section to be modified is divided into multiple multi-perforated sections to be modified using bridge plugs.

[0030] The fracturing operation includes determining the perforation density, and then performing perforation construction on the multi-hole section to be modified according to the perforation density, so that the perforated section to be modified is formed into a perforated section.

[0031] The simulation experiments include combining physical simulation experiments of perforation erosion to form a prediction model of perforation diameter change based on sand content, and adjusting the diameter of the temporary plugging ball according to the amount of sand added.

[0032] Temporary blocking of pitches includes conducting a reduced displacement friction test and carrying out temporary blocking of pitches based on the results of the reduced displacement friction test.

[0033] The repeated construction process includes, after completing the step-by-step fracturing construction, step-by-step simulation experiment, and step-by-step ball-dropping temporary plugging of the first layer of porous section to be modified, the remaining layers of porous sections to be modified are sequentially subjected to step-by-step fracturing construction, step-by-step simulation experiment, and step-by-step ball-dropping temporary plugging, so that the perforated sections to be modified are formed into perforated sections.

[0034] By quantitatively evaluating the temporary plugging hole, the risks and uncertainties of on-site temporary plugging construction are reduced. At the same time, since the degree of vertical activation of low-permeability thin interbedded reservoirs is proportional to the post-fracturing effect, it is possible to ensure that each layer in the vertical direction is fully fractured, so that all the small layers in the vertical direction of the thin interbedded reservoirs can be fully stimulated, thereby improving the fracturing effect of thin interbedded reservoirs.

[0035] Preferably, in this embodiment, each perforation to be modified is subjected to step-by-step fracturing construction, step-by-step simulation experiment, and step-by-step ball-dropping temporary plugging in sequence from bottom to top. This can avoid accidentally touching the modified perforations in the upper layer during the construction of the lower perforation section to be modified, thus preventing deformation.

[0036] Preferably, in this embodiment, the formula for calculating the perforation density during the fracturing operation is:

[0037]

[0038] Where, p perf Where is the orifice friction (MPa), and Q is the construction displacement (m³). 3 / min); ρ is the density of the fracturing fluid (g / cm 3 ); d p is the hole diameter (cm); N p is the number of holes; c is the hole flow coefficient, where 0.8 < c < 0.9. After determining the maximum stress difference between the perforation sections within a large section, through this formula, the number of holes that can be set under the hole friction conditions meeting the construction requirements can be obtained, thereby obtaining the optimal perforation density, so that each layer along the longitudinal direction can be fully stimulated.

[0039] Preferably, in this embodiment, in the step of ball plugging, if the construction displacement is reduced by 1 m 3 / min each time, and the construction pressure reduction is greater than 3 Mpa, then the number of plugging times is at least two. Specifically, in this embodiment, in the injection mode of plugging, the number of plugging balls is a, (1 / 3)*N p < a < (1 / 2)*N p , the construction displacement is 3 m 3 / min < Q < 4 m 3 / min. If the construction displacement is reduced by 1 m 3 / min each time, and the construction pressure reduction is greater than 3 MPa, it indicates that the hole friction is relatively large, the number of holes for the first liquid injection is small, the number of opened fractures is small, the difficulty of plugging diversion is relatively small, but it is easy to overpressure. At this time, 2 plugging operations can be implemented to ensure the construction efficiency and success rate.

[0040] Preferably, in this embodiment, in the step of ball plugging, if the construction displacement is reduced by 1 m 3 / min each time, and the construction pressure reduction is less than 3 Mpa, then the number of plugging times is one. Preferably, in this embodiment, in the injection mode of plugging, the number of plugging balls is a, (1.2)*N p < a < (1.5)*N p , the construction displacement is 8 m 3 / min < Q < 12 m 3 / min. If the construction displacement is reduced by 1 m 3 / min each time, and the construction pressure reduction is less than 3 MPa, it indicates that the hole friction is relatively small, the number of holes for the first liquid injection is large, the number of opened fractures is large, the difficulty of plugging diversion is relatively large. At this time, 1 plugging operation can be implemented to ensure the construction safety and stability.

[0041] Preferably, in this embodiment, in the step of simulation experiment, the formula of the predicted model of the hole diameter change formed is: H = H0 + 2.4*10 -4*M, where H0 is the initial perforation diameter (mm); H is the perforation diameter after abrasion (mm); and M is the mass of proppant added in a single section (kg). Under simulated actual construction conditions of discharge rate, sand concentration, and proppant particle size, the initial perforation diameter is the actual perforation diameter on site. After 2 hours of abrasion, the change pattern of the perforation diameter is studied, and the diameter of the temporary plugging ball is adjusted in real time based on the perforation diameter change prediction model.

[0042] Specifically, taking a well with a completed drilling depth of 3530m, a completed formation of the first flow section, a section to be irrigated of 3335-3417m with a large span of 82m, and a total of 19 perforations as an example, the following steps will be used for construction:

[0043] The preliminary plan includes selecting the best perforation intervals based on the values ​​of matrix porosity, permeability, saturation and geostress in the vertical direction of the well. Reservoirs with high matrix porosity, permeability and saturation and low geostress are selected as the perforation intervals to be improved, with a total of 18 high-quality perforation intervals selected. Based on the longitudinal span relationship of the 18 perforation sections, and according to the stratification principle, the longitudinal span of each perforation section to be modified is 10-30m. Bridge plugs are set between two large sections, maintaining a distance of more than 5m between the upper and lower sections. Two bridge plugs are installed, resulting in three perforation sections to be modified. The bridge plug setting positions are 3390m and 3355m, respectively. Each layer in the perforation section to be modified is labeled and tested. The first large section contains layers 277, 279, 280, 281, and 283; the second large section contains layers 264, 26, 267, 268, 269, 271, 273, and 274; and the third large section contains layers 253, 254, 255, 256, and 258. Specific parameters for each layer are shown in Table 1.

[0044]

[0045]

[0046] Table 1

[0047] The fracturing operation includes, first, fracturing the lowest section. The layers with the greatest stress difference within this section are layers 277 and 280, with a stress difference P of 4.0 MPa. According to the formula for calculating the perforation friction, when the designed flow rate is 10 m³ / min, the fracturing fluid density is taken as 1.0, the perforation diameter as 1 cm, and the perforation flow coefficient as 0.8. When the perforation friction is greater than 4.0 MPa, the formula is used to calculate the number of perforations that meet this condition, which is 29. The total perforation thickness of the 6 sub-layers within the section is 3.5 m. Dividing the number of perforations by the total perforation thickness yields the optimal perforation density of approximately 8.2 perforations / m, which facilitates on-site perforation operations. The perforation density is rounded to an integer, and is set at 8 perforations / m. The perforated section is then formed according to this perforation density value.

[0048] The simulation experiments included a model predicting the change in perforation diameter under actual construction conditions of perforation discharge rate, sand concentration, and proppant particle size, based on a physical simulation experiment of perforation erosion. The designed sand addition rate before the first major section of temporary plugging was 23m³. 3 The proppant density is 1700 kg / m³. 3 The initial perforation diameter is 10mm. According to the above calculation formula, the diameter of the perforation after abrasion is 19.3mm. Therefore, the diameter of the added temporary plugging ball is adjusted to 19mm.

[0049] Temporary plugging with ball-throwing includes conducting a reduced displacement friction test before the temporary plugging operation, testing the friction of the perforation orifice, and determining the ball-throwing method. The construction displacement starts from 10m³ / h. 3 The discharge rate gradually decreases from 0.00 to 1m³ / min, decreasing each time. 3 / min, observe the changes in construction pressure, and obtain the changes from 10m 3 / min dropped to 1m 3 During the process, the pressure drop ranged from 0.7 to 2.1 MPa, with all drops less than 3 MPa, indicating low orifice friction. This resulted in a large number of orifices being opened during the initial fluid injection, leading to more cracks being created. The optimization strategy was to use 1.2 times the number of perforation orifices as the temporary plugging balls, with 35 balls designed, each with a diameter of 19 mm. Due to the relatively high construction pressure, a low discharge rate (3-4 m³ / min) was used throughout the process. 3 The injection mode was set at ( / min). After the temporary plugging ball was inserted, the changes in construction pressure before and after temporary plugging were compared. Under the same displacement, the construction pressure of the pre-fluidization stage before temporary plugging was 42.5MPa, and the construction pressure of the pre-fluidization stage after temporary plugging was 46.2MPa. The pressure increase after temporary plugging was 3.7MPa, and the temporary plugging effect was good. The construction after temporary plugging was continued.

[0050] The repeated construction process includes, after the first major section of work is completed, repeating the steps of fracturing construction, simulation experiment, and ball-dropping temporary plugging for the second and third major sections in sequence until the overall operation is completed.

[0051] Based on the above construction layout, actual measurements confirmed that the 0.6m differential oil layer was effectively utilized, significantly reducing the lower limit of thin interlayer utilization. Fiber optic monitoring confirmed that all small layers were opened. The liquid entry section before temporary plugging mainly consisted of clusters 1, 2, and 5. After temporary plugging, the liquid entry of clusters 3 and 4 increased. Temporary plugging improved the uniformity of liquid entry and greatly increased production capacity.

[0052] The fracturing process method 100 for longitudinal modification of thin interlayers in this embodiment has the following beneficial effects:

[0053] First, by quantitatively evaluating the temporary plugging hole, the risks and uncertainties of on-site construction of the temporary plugging are reduced. At the same time, since the degree of vertical activation of low-permeability thin interbedded reservoirs is proportional to the post-fracturing effect, it is possible to ensure that each layer in the vertical direction is fully fractured, so that all the small layers in the vertical direction of the thin interbedded reservoirs can be fully transformed, thereby improving the fracturing effect of the thin interbedded reservoirs.

[0054] Second, after determining the maximum stress difference between the perforation sections within a large segment, the number of smoke control measures that can be set under the perforation density calculation formula to meet the construction requirements and friction conditions can be obtained, thus obtaining the optimal perforation density, so that each layer along the longitudinal direction can be fully modified.

[0055] 3. If the construction discharge volume is reduced by 1m each time 3 If the construction pressure drops by more than 3 MPa per minute, it indicates that the orifice friction is large, the number of orifices for the first liquid injection is small, the number of cracks opened is small, and the difficulty of temporary plugging and turning is small, but it is easy to overpressure. In this case, two temporary pluggings can be implemented to ensure the efficiency and success rate of construction.

[0056] IV. If the construction discharge volume is reduced by 1m each time 3 If the construction pressure drops by less than 3 MPa per minute, it indicates that the orifice friction is small, the number of orifices for the first liquid injection is large, the number of cracks opened is large, and the difficulty of temporary plugging and turning is large. In this case, one temporary plugging can be implemented to ensure the safety and stability of the construction.

[0057] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A fracturing process method for longitudinal modification of thin interbedded layers, characterized in that, Includes the following steps: Preliminary planning: Divide the reservoir into stratified sections, select the perforated sections to be modified in each stratified section, and stratify the perforated sections to be modified from bottom to top. Then, use bridge plugs to divide each perforated section to be modified into multiple multi-perforated sections to be modified according to the stratification results. Fracturing operation: After determining the perforation density, perforation is carried out on the multi-hole section to be modified according to the perforation density, so that the perforated section to be modified is formed. Simulation experiment: Combining the physical simulation experiment of perforation erosion, a prediction model for the change of perforation diameter based on the amount of sand added is formed, and the diameter of the temporary plugging ball is adjusted according to the amount of sand added; Temporary ball-throwing blockade: Conduct a reduction in displacement friction test, and implement temporary ball-throwing blockade based on the test results. If the construction displacement is reduced by 1m each time... 3 If the construction pressure decreases by more than 3 MPa per minute, then the number of temporary plugging operations must be at least two. If the construction discharge rate is reduced by 1 m³ / min each time... 3 If the construction pressure decreases by less than 3 MPa per minute, then the number of temporary plugging operations is counted as one. Repeated construction until completion: After the first layer of perforated sections to be modified has completed step fracturing construction, step simulation experiment and step ball-dropping temporary plugging, the remaining layers of perforated sections to be modified are sequentially subjected to step fracturing construction, step simulation experiment and step ball-dropping temporary plugging, so that the perforated sections to be modified are formed into perforated sections. Each perforated section to be modified is sequentially subjected to step fracturing construction, step simulation experiment and step ball-dropping temporary plugging from bottom to top.

2. The fracturing process method for longitudinal modification of thin interbedded layers according to claim 1, characterized in that, In the step-by-step fracturing operation, the formula for calculating the perforation density is: Where, p perf Where is the orifice friction (MPa), and Q is the construction displacement (m³). 3 / min); fracturing fluid density (g / cm³) 3 ); d p N is the diameter of the aperture (cm). p denoted as the number of orifices; c is the orifice flow coefficient, where 0.8 <c<0.9。 3. The fracturing process method for longitudinal modification of thin interbedded layers according to claim 1, characterized in that, In the temporary blocking injection mode, the number of temporary blocking balls is a, (1 / 3)*N p <a<(1 / 2)*N p Construction displacement 3m 3 / min <Q<4m 3 / min.

4. The fracturing process method for longitudinal modification of thin interbedded layers according to claim 1, characterized in that, In the temporary blocking injection mode, the number of temporary blocking balls is a, (1.2)*N p <a<(1.5)*N p Construction discharge volume 8m 3 / min <Q<12m 3 / min.

5. The fracturing process method for longitudinal modification of thin interbedded layers according to claim 1, characterized in that, In the step-by-step simulation experiment, the formula for predicting the change in aperture diameter is: H = H0 + 2.4 * 10 -4 *M, Where H0 is the initial perforation diameter (mm); H is the perforation diameter after abrasion (mm); and M is the mass of proppant added in a single stage (kg).

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