Temporary plugging staged fracturing method for casing damage horizontal well

Abstract

The invention discloses a temporary plugging staged fracturing method for a casing damage horizontal well, which comprises the following steps of: performing fracturing layer section division on a casing deformation well, namely taking all fracturing sections before casing deformation as first sections, keeping away from the depth of a casing deformation point by more than 15m when the fracturing layer sections after casing deformation are divided, and controlling the number of the fracturing layer sections to be within 10; after the perforation shot hole of the previous layer section is plugged, perforation fracturing of the next layer section is carried out until perforation fracturing of all fracturing layer sections after casing deformation is completed; according to perforation fracturing, compared with design construction parameters before casing deformation, the number of perforation clusters is reduced by 40%-50%, and the construction displacement and the liquid amount are reduced by 10%-20% and 20%-30% respectively; the problems that when the proportion of the number of unfractured sections below the variable point of an existing horizontal well sleeve is high, and the minimum drift diameter ranges from 55 mm to 98 mm, staged fracturing transformation cannot be conducted, and only fracturing can be stopped or general fracturing can be achieved are solved.

Description

Technical Field

[0001] This disclosure relates to the field of fracturing technology in oil and gas production engineering, mainly targeting reservoir fracturing and production enhancement in horizontal wells with casing damage, and can realize segmented fracturing and enhancement of horizontal wells with large-diameter casing damage. Background Technology

[0002] Currently, the fracturing technology for damaged horizontal wells both domestically and internationally employs small-diameter bridge plug layered fracturing. This technology utilizes a small-diameter tool to penetrate the damaged area and completes the fracturing process using conventional mechanical layered fracturing. However, this technology is generally limited by tool size and is applied when the minimum diameter of the damaged well is ≥98mm. When the minimum diameter of the damaged horizontal well is <98mm, the diameter of the bridge plug tool cannot be further reduced due to factors such as strength and matching with the casing inner diameter. Therefore, under the degree of casing deformation with a minimum diameter <98mm, it is impossible to carry out segmented fracturing using segmented tools. Generally, fracturing is terminated or the entire well is fracturing indiscriminately, i.e., all unfractured sections are perforated and fractured at once without subdividing the fracturing sections. This results in insufficient segmented fracturing, affecting the overall fracturing effect of the horizontal well, restricting the implementation of segmented fracturing measures for the reservoir, preventing the reservoir from being fully stimulated, and hindering the effective utilization of well-controlled reserves. Summary of the Invention

[0003] In view of this, this disclosure provides a temporary plugging and segmented fracturing method for horizontal wells with casing damage, which solves the problem that existing horizontal wells with a high proportion of unfractured sections below the casing change point and a minimum diameter in the range of 55mm-98mm cannot be segmented fracturing and can only terminate fracturing or perform general fracturing.

[0004] To achieve the above-mentioned objective, the method for temporary plugging and staged fracturing of a damaged horizontal well includes:

[0005] The fracturing sections of the casing-transformed well are divided into the following methods: all fracturing sections before casing transformation are taken as the first section, and when dividing the fracturing sections after casing transformation, the depth of the casing transformation point should be avoided to more than 15m, and the number of fracturing sections should be controlled to be within 10.

[0006] After sealing the perforation holes of the previous section, perforation fracturing of the next section is carried out until all the perforation fracturing of the fracturing sections after the casing is completed.

[0007] Compared with the design and construction parameters before the casing was installed, the number of perforation clusters was reduced by 40% to 50%, and the discharge rate and fluid volume were reduced by 10% to 20% and 20% to 30%, respectively, during the perforation fracturing.

[0008] In this disclosure and possible embodiments, the perforation fracturing pressure of the second, third and subsequent stages shall not exceed 80% of the internal pressure resistance of the casing after the casing is modified; the perforating gun model shall be selected according to the perforating gun diameter being 15mm smaller than the minimum diameter of the casing well.

[0009] In this disclosure and possible embodiments, the method for sealing perforation holes includes:

[0010] The temporary plugging agent is subjected to pressure greater than the maximum construction pressure value, and the dissolution time of the temporary plugging agent is greater than the total time of subsequent fracturing operations, with a allowance of 12 to 24 hours.

[0011] In this disclosure and possible embodiments, the plugging agent is a plugging ball, the diameter of which is greater than or equal to 1.5 times the diameter of the perforation orifice.

[0012] In this disclosure and possible embodiments, the number of temporary blocking balls deployed is 1.1 to 1.8 times the number of perforation holes.

[0013] In this disclosure and possible embodiments, the temporary plugging agent is dispensed at a rate of 2.0 to 4.0 m³ / min.

[0014] In this disclosure and possible embodiments, the pressure test criteria for successful temporary plugging are: 3MPa ≤ ground pump pressure rise ≤ design maximum pressure limit, and the peak pressure must reach the maximum pressure value of the previous construction phase; if the plugging is unsuccessful, 10% of the temporary plugging agent is added again until the pressure test criteria are met.

[0015] In this disclosure and possible embodiments, the method for controlling the number of fracturing segments to be within 10 segments includes:

[0016] Based on the principle of merging reservoirs with similar physical properties into one segment, the number of fracturing segments will be controlled to within 10 segments.

[0017] In this disclosure and possible embodiments, the method further includes:

[0018] Determine whether the well condition conditions are met;

[0019] The well conditions are: φ55mm≤minimum diameter<φ98mm; no casing leaks; and the remaining unfractured sections below the casing change point account for more than 50% of the total construction section.

[0020] This disclosure has the following beneficial effects:

[0021] This disclosed method for temporary plugging and segmented fracturing in horizontal wells with casing damage utilizes a temporary plugging agent to seal the already fractured section instead of using downhole tools. This segmented fracturing method solves the problem that small-diameter bridge plugs cannot be used for mechanical segmented fracturing in wells with large casing variations. Based on process design and on-site construction control, this method forms a complete set of process design methods. Fracturing schemes for horizontal wells with large casing variations can be formulated according to this method, achieving maximum well-controlled reservoir stimulation and thus improving the fracturing effect of horizontal wells with casing damage. It effectively solves the problem that wells with this level of casing damage can only be fractured in one segment, rather than in several segments. Attached Figure Description

[0022] The above and other objects, features, and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0023] Figure 1 This is a curve showing the results of the second stage of temporary plugging operation in well YS137-5 (displacement rate 4m). 3 / min, with ground pump pressure up to 59MPa);

[0024] Figure 2 This is a curve showing the construction results of the second stage of well YS137-5, a publicly disclosed application example (actual total sand added: 210.14t, slickwater: 1912.3m). 3 );

[0025] Figure 3 This is a curve showing the results of the third stage temporary plugging operation in well YS137-5 (displacement rate 4m³). 3 / min, with ground pump pressure up to 59MPa);

[0026] Figure 4 This is a curve showing the construction results of the third section of well YS137-5, a publicly disclosed application example (actual total sand added: 210.15t, slickwater: 1916.62m). 3 ). Detailed Implementation

[0027] The present disclosure is described below based on embodiments; however, it is worth noting that the present disclosure is not limited to these embodiments. In the detailed description of the present disclosure below, certain specific details are described in detail. However, those skilled in the art will fully understand the present disclosure for the parts not described in detail.

[0028] Furthermore, unless the context explicitly requires it, the words "comprising," "including," and similar terms throughout the specification and claims should be interpreted as including rather than exclusive or exhaustive; that is, meaning "including but not limited to."

[0029] Before implementing this patented method, obtain data on minimum pipe diameter, casing damage level, and casing damage location to determine the well conditions under which this method can be applied: There was no leakage in the casing; the remaining unfractured section below the casing deformation point accounted for more than 50% of the total construction section.

[0030] The temporary plugging and staged fracturing method for damaged horizontal wells described in this embodiment includes the following specific steps:

[0031] 1. Re-division of subsequent fracturing sections in the casing-fracturing well:

[0032] For the remaining unfractured sections below the casing deformation point, since the casing deformation well needs to take into account the further damage to the casing deformation point caused by fracturing construction, the number of sections of the perforation temporary plugging needs to take into account the relationship between the overall construction time and the dissolution time of the temporary plugging ball, and the performance of the temporary plugging agent, the original design of the fracturing sections is no longer applicable. Therefore, based on the on-site construction conditions, it is necessary to re-divide the fracturing sections of the casing deformation well.

[0033] In this embodiment of the present disclosure, the preferred method for re-dividing the fracturing segments after casing deformation is as follows: avoiding conditions where the depth of the casing deformation point is more than 15m, compared with the original design fracturing segments, the number of fracturing segments is reduced according to the principle of merging reservoirs with similar physical properties into one segment, and the number of fracturing segments is controlled to within 10 segments.

[0034] 2. All perforations in the first stage of fracturing before the sealing sleeve:

[0035] (1) Take all the fracturing sections before the casing as the first section of the re-divided pressure layer. When carrying out the sealing construction, it is required to consider that after the temporary plugging agent is put into the hole, the pressure of the temporary plugging agent is greater than the maximum construction pressure value, the dissolution time of the temporary plugging agent is greater than the sum of the fracturing construction time of the subsequent layers, and reserve 12-24 hours to prevent emergencies.

[0036] In this embodiment of the disclosure, the diameter and quantity of the temporary clogging ball are preferably calculated according to the following formulas. The diameter of the temporary clogging ball is calculated according to formula (1), and the quantity is calculated according to formula (2).

[0037] D≥1.5D p (1)

[0038] n = (1.1 - 1.8)n p (2)

[0039] In the formula: D is the diameter of the temporary plugging ball, mm; D p n is the diameter of the perforation hole, in mm; n is the number of temporary plugging balls or temporary plugging knots, in units; n p The number of perforations.

[0040] (2) The preferred displacement of the temporary plugging agent is 2.0-4.0 m³. 3 The pressure is set at a rate of [ / min] to achieve better temporary plugging and dispersion effects, and to facilitate observation of the pressure increase during temporary plugging. Additionally, when using a temporary plugging agent, adding acid is not recommended, as acid will dissolve the temporary plugging material and affect its effectiveness.

[0041] (3) Conventional techniques indicate successful temporary plugging if the ground pump pressure rises after the temporary plugging agent is applied. Since this disclosure seals all the boreholes in the previous perforation section, a separate pressure test criterion for successful temporary plugging needs to be developed. The preferred criterion for successful temporary plugging is: 3MPa ≤ ground pump pressure rise ≤ design maximum pressure limit, and the peak pressure must reach the maximum pressure value of the previous construction phase. If plugging is unsuccessful, 10% of the temporary plugging agent is added again until the pressure criterion is met; the design maximum pressure limit is determined according to the relevant construction design documents.

[0042] 3. Second stage perforation fracturing:

[0043] (1) In order to ensure the smooth completion of the construction, compared with the perforation fracturing scheme before the change, the design of the newly divided fracturing section is based on the reduction of the number of perforation clusters by 40% to 50%, and the reduction of the construction discharge and scale by 10% to 20% and 20% to 30%, respectively.

[0044] (2) Adjust the construction pressure limit according to the reduction of the casing's internal pressure resistance after the casing is modified. The construction pressure shall not exceed 80% of the casing's internal pressure resistance after the casing is modified. The internal pressure resistance of the casing after the casing is modified shall be determined based on the well logging results.

[0045] (3) To ensure the smooth raising and lowering of the perforating gun, the perforating gun model should be selected according to the perforating gun diameter being 15mm smaller than the minimum diameter of the casing well.

[0046] (4) Before the second stage of perforation and fracturing, a temporary plugging agent is injected to seal the first stage perforation blast hole. The diameter and quantity of the temporary plugging ball are obtained according to formula (1) and formula (2) of this disclosure, respectively. The dissolution time of the temporary plugging agent is longer than the fracturing construction time of the subsequent stage, and 12-24 hours are reserved to prevent emergencies. The pressure test is carried out in accordance with the temporary plugging success test judgment criteria of this disclosure.

[0047] (5) The second stage of perforation and the second stage of fracturing were completed in accordance with the construction design.

[0048] 4. Construction of subsequent sections:

[0049] Before the third stage of perforation fracturing, seal the boreholes in the second stage. Repeat the above steps to complete the fracturing of subsequent stages.

[0050] As can be seen from the above description, the temporary plugging staged fracturing method for damaged horizontal wells disclosed herein uses temporary plugging balls to seal the perforations in non-operational well sections. By calculating the diameter and quantity of temporary plugging balls and establishing criteria for successful temporary plugging, the perforations in the already constructed sections can be accurately sealed. The perforations can then be opened again to allow for the construction of the next section. Therefore, the staged fracturing method, which uses temporary plugging agents to seal the already fractured sections instead of downhole tools, can effectively solve the problem that small-diameter bridge plugs cannot be used for mechanical staged fracturing in wells with large-diameter casing variations.

[0051] Application examples

[0052] After the first stage of fracturing was completed in well YS137-5, the pumping of the bridge plug encountered obstruction. Well logging showed that the casing deformation point was located 37.7m below the target depth (point A). Well temperature testing showed no abnormalities, and there was no casing leakage. The minimum inner diameter of the casing deformation point was 54.89mm. The remaining unfractured section below the casing deformation point accounted for 87.5% of the total number of constructed sections.

[0053] The well casing has a small diameter, the casing change point is close to the target point, and the remaining unmodified horizontal section is relatively long. Conventional small-diameter bridge plugs cannot be used for mechanical stratified fracturing. Therefore, the method disclosed in this paper is applied for stratified fracturing to ensure effective reservoir utilization, increase production capacity, and reduce construction risks. Details are as follows:

[0054] 1. The remaining unfractured sections below the casing deformation point of well YS137-5 are re-divided:

[0055] To reduce the number of fracturing sections, reservoirs with similar physical properties are divided into sections as much as possible, avoiding depths of more than 15m from casing deformation points. The number of fracturing sections has been changed from the original design of 12 sections to 6 sections through combined fracturing. The perforating gun is a 40-type (the diameter of the perforating gun is 15mm smaller than the minimum diameter of the casing deformation well) to take into account the minimum inner diameter of the casing deformation well. To ensure the smooth completion of the operation, according to the requirements of the re-divided fracturing section standard, the average number of clusters is reduced by 41.4%, the average operation flow rate is reduced by 14.2%, and the average fluid volume is reduced by 20.3% after the design change (see Table 1 below).

[0056] Table 1. Changes in design and construction parameters before and after casing modification for YS137-5 well.

[0057]

[0058]

[0059] 2. Temporarily plug the first perforation hole before the transformer:

[0060] The horizontal well is designed to use 89 perforations in the first stage, with a perforation diameter of 10.6 mm and a total of 50 perforations. Before the second stage of fracturing, the perforations will be plugged by inserting 65 temporary plugging balls (1.3 times the number of perforations) with a diameter of 16 mm (>1.5 times the perforation diameter). The subsequent construction time is expected to be 120 hours, and the dissolution time of the plugging agent is 144 hours (with an extra day allowed).

[0061] After the temporary plugging ball was inserted, the ground pump pressure reached 62 MPa, which is lower than the design maximum pressure limit of 63 MPa, and reached the maximum pressure value of 50.2 MPa in the previous construction phase. After stopping and restarting the pump, the pressure value of the previous construction phase was reached again, indicating that the temporary plugging was successful. The curve of the temporary plugging construction results is attached. Figure 1 .

[0062] 3. Second stage perforation fracturing:

[0063] The second stage of perforation was completed using a coiled tubing-delivered 40-type perforating gun, with a perforation diameter of 8.2 mm and a total of 48 perforations. The fracturing operation displacement was 9.0-12.0 m³ / h. 3 / min, construction pressure 43.5-52.3MPa, average sand ratio 170kg / m 3 The actual total amount of sand added was 210.14 tons, and the amount of slickwater was 1912.3 m³. 3 Construction was completed according to design requirements; the resulting construction curve is attached. Figure 2 .

[0064] 4. Construction of subsequent sections:

[0065] The third stage of fracturing was performed on the entire well. Before fracturing, the second stage perforations were plugged, and 62 temporary plugging balls (1.3 times the number of perforations) of 14mm diameter were inserted (>1.5 times the perforation diameter). The estimated subsequent operation time was 96 hours, and the dissolution time of the plugging agent was 120 hours (allowing for an extra day). The displacement was 4m³. 3 The ground pump pressure reached the construction limit of 59 MPa at a rate of [per minute]. After stopping the pump, restarting it resulted in overpressure again, indicating successful temporary plugging. See the attached graph for the temporary plugging construction results. Figure 3 .

[0066] The third stage of perforation was completed using a coiled tubing-delivered 40-type perforating gun, with a perforation diameter of 8.2 mm and a total of 50 perforations. The fracturing operation displacement was 9.0-12.0 m³ / h. 3 / min, construction pressure 46.2-52.5MPa, average sand ratio 168kg / m 3 The actual total amount of sand added was 210.15t, and the amount of slickwater was 1916.62m³. 3 Construction was completed according to design requirements; the resulting construction curve is attached. Figure 4 .

[0067] By doing so, the fracturing work of all subsequent layers can be completed by temporarily plugging the holes.

[0068] The embodiments described above are merely illustrative of implementation methods of this disclosure, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent disclosure. It should be noted that those skilled in the art can make various modifications, equivalent substitutions, and improvements without departing from the concept of this disclosure, and these all fall within the protection scope of this disclosure. Therefore, the protection scope of this patent disclosure should be determined by the appended claims.

Claims

1. A method for temporary plugging and staged fracturing of a horizontal well with casing damage, characterized in that, include: The fracturing sections of the casing-transformed well are divided into the following methods: all fracturing sections before casing transformation are taken as the first section, and when dividing the fracturing sections after casing transformation, the depth of the casing transformation point should be avoided to more than 15m, and the number of fracturing sections should be controlled to be within 10. After sealing the perforation holes of the previous section, perforation fracturing of the next section is carried out until all the perforation fracturing of the fracturing sections after the casing is completed. Compared with the design and construction parameters before the casing was installed, the number of perforation clusters was reduced by 40% to 50%, and the discharge rate and fluid volume were reduced by 10% to 20% and 20% to 30%, respectively, during the perforation fracturing.

2. The method for temporary plugging and staged fracturing of a damaged horizontal well according to claim 1, characterized in that: For the perforation fracturing of the second, third and subsequent stages, the construction pressure shall not exceed 80% of the internal pressure resistance of the casing after the casing is transformed; the perforating gun model shall be selected according to the perforating gun diameter being 15mm smaller than the minimum diameter of the casing well.

3. The method for temporary plugging and staged fracturing of a damaged horizontal well according to claim 1 or 2, characterized in that, Methods for sealing perforation holes include: The temporary plugging agent is subjected to pressure greater than the maximum construction pressure value, and the dissolution time of the temporary plugging agent is greater than the total time of subsequent fracturing operations, with a allowance of 12 to 24 hours.

4. The method for temporary plugging and staged fracturing of a damaged horizontal well according to claim 3, characterized in that: The temporary plugging agent is a temporary plugging ball, and the diameter of the temporary plugging ball is greater than or equal to 1.5 times the diameter of the perforation orifice.

5. The method for temporary plugging and staged fracturing of a damaged horizontal well according to claim 4, characterized in that: The number of temporary plugging balls deployed is 1.1 to 1.8 times the number of perforation holes.

6. The method for temporary plugging and staged fracturing of a damaged horizontal well according to claim 5, characterized in that: The temporary plugging agent is dispensed at a rate of 2.0–4.0 m³ / min.

7. The method for temporary plugging and staged fracturing of a damaged horizontal well according to claim 6, characterized in that: The criteria for judging the success of the temporary plugging test are: 3MPa ≤ ground pump pressure rise ≤ design maximum pressure limit, and the peak pressure must reach the maximum pressure value of the previous construction phase; if the plugging is unsuccessful, add 10% of the temporary plugging agent again until the aforementioned pressure test criteria are met.

8. The method for temporary plugging and staged fracturing of a horizontal well with casing damage according to any one of claims 1, 2, or 4-6, characterized in that, The method for controlling the number of fracturing segments to be within 10 segments includes: Based on the principle of merging reservoirs with similar physical properties into one segment, the number of fracturing segments will be controlled to within 10 segments.

9. The method for temporary plugging and staged fracturing of a damaged horizontal well according to claim 8, characterized in that, Also includes: Determine whether the well condition conditions are met; The well conditions are required to be: φ55mm ≤ minimum diameter < φ98mm; no casing leaks; The remaining unfractured sections below the deformation point account for more than 50% of the total construction sections.

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