An acidizing process based on hierarchical pore creation forming fishbone branches

Abstract

The application discloses an acidification process based on hierarchical pore forming and fishbone branch forming, and relates to the technical field of oil and gas field development engineering; the process comprises the following steps: lowering a jetting tool group carried by an oil pipe to a target transformation position, jetting acid liquid to a stratum, and forming a guide hole at the transformation position; switching the pump injection liquid to a fluid loss reduction liquid, performing fixed-point jetting on the same transformation position, and forming a high flow conductivity channel; pumping sand-carrying liquid to the stratum, sand-blasting and perforating the transformation position, and forming a fishbone-shaped branch hole; switching the pump injection liquid to acid liquid, performing fixed-point injection on the same transformation position, and making the acid liquid rapidly advance along the fishbone-shaped branch hole to erode the stratum rock and form an earthworm hole, meanwhile, the acid liquid pushes sand particles to the deep part of the stratum; when the acid liquid injection amount reaches a preset equivalent value, the oil pipe is dragged to the next designated target transformation position to repeat the operation; the application forms an oil and gas flow channel with high flow conductivity, improves the segmented transformation effect, is beneficial to increasing the production capacity of an oil well, and is simple in operation and high in safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field development engineering, and particularly relates to an acidification process based on hierarchical pore forming fishbone branch. BACKGROUND

[0002] The carbonate reservoir has complex reservoir characteristics and strong heterogeneity, and especially, horizontal well development faces many challenges, which promotes a series of reconstruction technologies to develop and evolve. At present, three commonly used carbonate horizontal well segmented acid fracturing reconstruction technologies in the petroleum industry include perforation + packer segmented acid fracturing technology, tubing external seal + ball sliding sleeve segmented acid fracturing technology and coiled tubing drag segmented acid fracturing technology.

[0003] The perforation + packer segmented acid fracturing technology is to divide the horizontal well section into several independent fracturing sections by using a packer, and then to perform acid fracturing construction on each fracturing section through a pipe string. The limitation of this technology is that the packer and other tools need to be lowered into the wellbore, which requires high wellbore conditions, increases the complexity and cost of construction, and has high requirements for the performance of the packer. If the packer is not sealed tightly, it may cause acid liquid channeling and affect the acid fracturing effect. When the horizontal well section is long, the packer is difficult to lower and set, and the construction risk is also increased accordingly.

[0004] The tubing external seal + ball sliding sleeve segmented acid fracturing technology is to install an external packer outside the casing in advance, cooperate with a completion pipe string with a sliding sleeve, activate the sliding sleeve by ball launching, and sequentially open the acid fracturing channel to realize segmented reconstruction. The limitation of this technology is that the reliability of the sliding sleeve tool needs to be guaranteed. If the sliding sleeve fails, it may not be able to be normally opened or closed, which affects the smooth progress of acid fracturing construction. The sliding sleeve has high requirements for pressure resistance and acid resistance. Under the action of high pressure and high concentration acid liquid, the sliding sleeve may be damaged or corroded. The sliding sleeve driven by ball launching and pressure holding may have problems in ball lowering and setting when multiple sections are reconstructed, which affects the reconstruction of subsequent sections.

[0005] The coiled tubing drag segmented acid fracturing technology is to use a coiled tubing to carry a drillable bridge plug or a retrievable packer into the well, to seal and implement acid fracturing by a drag tool section by section, and to drill the bridge plug or retrieve the packer after construction to restore the full well bore diameter. The limitation of this technology is that the operation efficiency is low, the coiled tubing needs to be frequently raised and lowered, the construction period is long, the coiled tubing is easily worn and corroded in the well, and needs to be regularly inspected and replaced, which increases the construction cost and maintenance workload. When segmented acid fracturing is performed on a long horizontal well section, the well depth is limited and the coiled tubing with the packer is difficult to lower and operate, which requires high technical level and construction experience.

[0006] Therefore, the existing conventional acid fracturing reconstruction process technology has defects such as complex construction process, high operation difficulty, high requirement for downhole tool performance, and easy problems in setting and sealing, which further increases the construction risk and operation cost, and greatly limits the efficient application and popularization of the staged acid fracturing technology in the complex well conditions of carbonate rocks, long horizontal well sections and large-scale reconstruction scenarios. SUMMARY

[0007] The present application is to solve the technical problems that the conventional acid fracturing reconstruction process technology has complex construction process, high operation difficulty, high requirement for downhole tool performance, and easy problems in setting and sealing, which leads to increased construction risk and construction cost, and aims to provide an acidification process based on hierarchical pore formation of fishbone branches, which forms a guide hole by the first acid injection, forms a high conductivity channel by injecting a fluid loss reducing fluid, forms a fishbone-shaped branch hole by sandblasting, and further dissolves the four-stage pore formation in stages by the second acid injection, finally forming an oil and gas flow channel with high conductivity, improving the staged reconstruction effect, which is beneficial to improve the oil well productivity, and the operation is simple, does not require complex tools and cumbersome construction process, and will not cause sand sticking and other accidents to affect the operation safety.

[0008] The present application is realized by the following technical solutions.

[0009] An acidification process based on hierarchical pore formation of fishbone branches, comprising the following steps:

[0010] S1, the oil tube carries the injection tool group to the toe end of the open hole horizontal section or the preset target reconstruction position, and sprays acid liquid to the stratum through the ground pump injection system to form a guide hole at the reconstruction position;

[0011] S2, switch the pump injection liquid to a fluid loss reducing fluid, and implement point injection at the same reconstruction position to form a high conductivity channel;

[0012] S3, pump sand-carrying liquid to the stratum, and perform sandblasting perforation on the reconstruction position based on the high conductivity channel to form a fishbone-shaped branch hole;

[0013] S4, switch the pump injection liquid to acid liquid, and implement point injection at the same reconstruction position, the acid liquid rapidly advances along the fishbone-shaped branch hole to dissolve the stratum rock to form a wormhole, and the acid liquid pushes the sand particles to the deep part of the stratum;

[0014] S5, when the acid injection amount reaches the preset equivalent value, drag the oil tube to the next designated target reconstruction position;

[0015] S6, repeat steps S1-S4 until the reconstruction of all preset target points of the open hole horizontal section is completed.

[0016] The acidizing process of the method first forms a guide hole with a depth of 50-80 cm by spraying acid, and then sprays filtrate-reducing liquid to reduce the filtration property of the guide hole, forms a high flow channel, and creates conditions for subsequent liquid breakthrough.

[0017] To sum up, the method forms a guide hole by first spraying acid, forms a high flow channel by spraying filtrate-reducing liquid, forms a fishbone-shaped branch hole by spraying sand, and further dissolves by secondly spraying acid, thereby forming an oil and gas flow channel with high flow capacity through a four-stage pore-forming method, improving the effect of staged reconstruction, being beneficial to increasing the productivity of oil wells, and being simple in operation, not requiring complex tools and cumbersome construction procedures, and not causing sand sticking and other accidents to affect operation safety.

[0018] Further, the sand-carrying liquid is linear glue with a sand ratio of 7-20%, and the proppant in the linear glue is abrasive or quartz sand.

[0019] Further, the particle size of the abrasive is selected according to the following principles: the diameter of the nozzle in the jetting tool group should be greater than 3 times the maximum particle size of the abrasive.

[0020] Further, the particle size specification of the quartz sand is 40-70 mesh.

[0021] Further, the sand ratio of the sand-carrying liquid is adjusted according to the formation permeability:

[0022] When the formation permeability is less than 5 mD, linear glue with a sand ratio of 7% is used;

[0023] When the formation permeability is 5-10 mD, linear glue with a sand ratio of 10% is used;

[0024] When the formation permeability is 10-20 mD, linear glue with a sand ratio of 15% is used;

[0025] When the formation permeability is greater than 20 mD, linear glue with a sand ratio of 20% is used.

[0026] Further, steps S1-S4 are all carried out under high pressure, and the pump pressure is greater than or equal to 55 MPa.

[0027] Further, the acid liquid used in steps S1 and S4 is hydrochloric acid with a mass concentration of 15% to 28%.

[0028] Further, the mass concentration of the acid liquid is adjusted according to the formation permeability:

[0029] Formation permeability < 5 mD, mass concentration of hydrochloric acid >= 28%;

[0030] Formation permeability 5-10 mD, mass concentration of hydrochloric acid 25-28%;

[0031] Formation permeability 10-20 mD, mass concentration of hydrochloric acid 20-25%;

[0032] Formation permeability > 20 mD, mass concentration of hydrochloric acid 15-20%.

[0033] Further, in step S5, when the acid liquid injection amount reaches the preset equivalent value, the ground pump injection system is switched to a low pressure mode, and the pump pressure is 25 MPa to 35 MPa.

[0034] Further, it further comprises step S7:

[0035] After the modification of all the preset target points is completed, the tubing is pulled out of the wellhead by flushing the tubing with water after stopping the pump, and the well is opened for flowback.

[0036] Compared with the prior art, the present application has the following advantages and beneficial effects.

[0037] 1. The gravel acidizing process of the method first sprays acid to form a 50-80 cm guide hole, then sprays a fluid with reduced filtration loss to reduce the filtration loss of the guide hole, forms a high conductivity channel, and creates conditions for subsequent liquid breakthrough. After the above two steps, a sand-carrying liquid is used to spray sand at a fixed point to form a fishbone-shaped branch, forming a penetration hole with a depth of 1-3 meters. Subsequently, on the basis of the bone-shaped branch hole, acid is continuously sprayed, the acid liquid rapidly advances along the high permeability channel to dissolve the formation rock to form 5-20 cm of wormholes. At the same time, the acid liquid carries sand particles to the deep part of the formation. With the decrease of formation pressure, the sand particles form effective support during the closure of the formation, ensuring the continuous effectiveness of the high conductivity three-dimensional channel in the entire process, strengthening the reservoir modification effect, expanding the horizontal well drainage area, and improving the productivity of the oil well. It has strong adaptability for segmented modification of open hole horizontal wells in low permeability carbonate reservoirs.

[0038] 2. The acidification process of the present application uses the first acid spraying to form a guide hole, the spraying of a fluid loss reducing liquid to form a high conductivity channel, the sand spraying to form a fishbone-shaped branched hole, and the second acid spraying to further dissolve, thereby forming an oil and gas flow channel with high conductivity, improving the effect of staged reconstruction, and eliminating the problems of complex tools and cumbersome construction process in the prior art, achieving reservoir reconstruction of all horizontal segment preset targets by one trip of the pipe column, and achieving the purpose of improving construction efficiency.

[0039] 3. The acidification process of the present application can achieve staged reconstruction by relying on water power isolation for carbonate bare hole horizontal wells, without the need for additional downhole isolation tools, and the effect of staged reconstruction is proved by actual cases, and accidents such as sand sticking will not affect the safety of the operation. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present application clearer and more apparent, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments. Obviously, the illustrative embodiments of the present application and the description thereof are only used to explain the present application, and are not intended to limit the present application.

[0041] The following detailed description of an embodiment of the acidification process based on hierarchical pore forming fishbone branching of the present application. However, there may be cases of omitting unnecessary detailed description. For example, there are cases of omitting detailed description and repeated description of matters well known. This is to avoid the following description from becoming unnecessarily lengthy, facilitating understanding by those skilled in the art.

[0042] The "range" disclosed in the present application is limited in the form of lower limit and upper limit, and the given range is limited by selecting a lower limit and an upper limit. The selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can include or not include the end value, and can be arbitrarily combined, i.e. any lower limit can be combined with any upper limit to form a range.

[0043] If not specifically stated, all embodiments and optional embodiments of the present application can be combined to form new technical solutions.

[0044] If not specifically stated, all technical features and optional technical features of the present application can be combined to form new technical solutions.

[0045] If not specifically stated, the "includes" and "contains" mentioned in the present application mean open-ended, and can also be closed. For example, the "includes" and "contains" can mean that other substances not listed can also be included or contained, or only the listed substances can be included or contained.

[0046] If not otherwise specified, all steps of the present application can be carried out in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c), which means that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0047] The technical solutions of the present application are further described in detail below in combination with examples.

[0048] It should be noted that the experimental methods used in the examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained by commercial channels by those skilled in the art.

[0049] Example 1

[0050] An acidizing process based on hierarchical pore forming to form fishbone branches, comprising the following steps:

[0051] S1, the injection tool group carried by the tubing is lowered to the toe end of the open hole horizontal section or a preset target modification position, acid liquid is injected into the formation through the ground pump injection system, and a pilot hole is formed at the modification position;

[0052] S2, switch the pump injection liquid to a fluid loss reduction liquid, and implement point injection at the same modification position to form a high conductivity channel;

[0053] S3, pump sand-carrying liquid into the formation, and perform sand-blasting perforation at the modification position based on the high conductivity channel to form a fishbone-shaped branch hole;

[0054] S4, switch the pump injection liquid to acid liquid, and implement point injection at the same modification position, the acid liquid rapidly advances along the fishbone-shaped branch hole to dissolve the formation rock to form a wormhole, and the acid liquid pushes the sand particles to the deep part of the formation;

[0055] S5, when the acid injection amount reaches a preset equivalent value, the ground pump injection system switches to a low pressure mode, the pump pressure is 25MPa~35MPa, and the tubing is dragged at a low speed until the next designated target modification position;

[0056] S6, repeat steps S1~S4 until the modification of all preset target points of the open hole horizontal section is completed;

[0057] S7, after the completion of all the preset target modification, by the water to replace the liquid in the tubing, pump after dragging out of the wellhead tubing, open well flowback, with the decrease of formation pressure, the channel and micro crack formed by the modification, sand particles produce supporting effect, to ensure the completion of the entire process of high flow channel.

[0058] The acidizing process of the method first forms a 50-80 cm guide hole by spraying acid, then sprays a fluid loss reducing liquid to reduce the fluid loss of the guide hole, forms a high flow channel, and creates conditions for subsequent liquid breakthrough.

[0059] In summary, the application adopts the first acid spraying to form a guide hole, sprays a fluid loss reducing liquid to form a high flow channel, sprays sand to form a fishbone-shaped branch hole, and the second acid spraying further dissolves, through the four-stage pore-forming method in stages, finally forms an oil and gas flow channel with high flow capacity, improves the effect of segmented modification, is beneficial to increase the productivity of oil wells, and is simple in operation, does not require complex tools and cumbersome construction process, and will not cause sand sticking and other accidents to affect the safety of operation.

[0060] The injection tool group used in the application comprises a guide shoe, a centralizer, a shear type safety trip, a hydraulic safety trip device and a spray gun.

[0061] Table 1, selection standard of tubing and nozzle parameters

[0062]

[0063] In the application, steps S1-S4 are all carried out under high pressure, and the pump pressure is greater than or equal to 55 MPa.

[0064] Table 2, selection standard of pump pressure and displacement of sand-carrying liquid

[0065]

[0066] In the present application, the sand-carrying liquid refers to linear glue with a sand ratio of 7-20%, and the proppant in the linear glue is abrasive or quartz sand.

[0067] The particle size of the abrasive is selected according to the following principle: the nozzle diameter in the jet tool set should be greater than 3 times the maximum particle size of the abrasive. For example, the abrasive particle size is 2 mm, and the nozzle diameter should be ≥6 mm to prevent the flow channel from being blocked. In addition, for formations with high hardness, the abrasive hardness is large, and a wear-resistant nozzle needs to be matched, such as a diamond abrasive that needs to be matched with a wear-resistant tungsten carbide nozzle.

[0068] The particle size specification of the quartz sand is 40-70 mesh.

[0069] The sand ratio of the sand-carrying liquid is adjusted according to the formation permeability:

[0070] When the formation permeability is <5 mD, the sand ratio of the linear glue is 7%;

[0071] When the formation permeability is 5-10 mD, the sand ratio of the linear glue is 10%;

[0072] When the formation permeability is 10-20 mD, the sand ratio of the linear glue is 15%;

[0073] When the formation permeability is >20 mD, the sand ratio of the linear glue is 20%.

[0074] The selection of the sand ratio of the sand-carrying liquid specifically follows the specification standard of Table 3.

[0075] Table 3, sand ratio selection standard of sand-carrying liquid

[0076]

[0077] The selection of the viscosity of the sand-carrying liquid specifically follows the specification standard of Table 4.

[0078] Table 4, viscosity selection standard of sand-carrying liquid

[0079]

[0080] In the present application, the acid liquid used in steps S1 and S4 is hydrochloric acid with a mass concentration of 15%-28%.

[0081] The mass concentration of the acid liquid is adjusted according to the formation permeability:

[0082] When the formation permeability is <5 mD, the mass concentration of hydrochloric acid is ≥28%;

[0083] When the formation permeability is 5-10 mD, the mass concentration of hydrochloric acid is 25-28%;

[0084] When the formation permeability is 10-20 mD, the mass concentration of hydrochloric acid is 20-25%;

[0085] Formation permeability > 20 mD, hydrochloric acid mass concentration 15-20%.

[0086] The acid amount and concentration of the acid liquid are selected according to the specification standard of Table 5.

[0087] Table 5, acid amount and concentration selection standard of acid liquid

[0088]

[0089] Application example

[0090] A development well with a drilled well depth of 3700 meters and a bare hole horizontal section length of 1190 meters is taken as an example to illustrate the gravel packing fishbone branch acidification process of the present application. The reservoir lithology is limestone, the average formation permeability is less than 5 mD, and the main construction fluid includes 28% hydrochloric acid, linear glue with a viscosity of 15 cp, 40-70 mesh quartz sand and water. A total of 25 fixed-point modifications are performed. Except for the first three targets, the remaining 22 targets are deep modified by using the gravel packing fishbone branch acidification process. The downhole tool uses a coiled tubing with a pipe length of 5000 meters and an outer diameter of 60.3 mm, and the jet tool combination is shown in Table 6.

[0091] Table 6, jet tool combination parameters

[0092]

[0093] The method of Example 1 is used for construction, and the construction process is as follows:

[0094] (1) The coiled tubing and the jet tool combination are connected on the ground;

[0095] (2) The coiled tubing carrying the jet tool is lowered to the position of the bare hole horizontal section 3700 meters, and high-pressure pump acid modification is performed at three target points of 3700 meters, 3650 meters and 3600 meters, respectively;

[0096] (3) The coiled tubing carrying the jet tool is dragged to the target position of the bare hole horizontal section 3550 meters, and the acidification construction of forming fishbone branches by staged hole making is started, and the construction process is shown in Table 7.

[0097] (4) After the modification at the target position of 3550 meters is completed, the acidification construction steps are repeated, the coiled tubing jet tool combination is dragged to 3500 meters, and the remaining 21 target reservoir modifications of the bare hole horizontal section are completed in turn.

[0098] (5) After all the modification targets of the bare hole horizontal section are completed, the coiled tubing is pulled up to a depth of 2510 meters, and 11 m 3 The coiled tubing is replaced with water, and the displacement is 1 m 3Pump rate 0.5-1.0 L / min, pump pressure 59-60 MPa, pump off, coiled tubing up to wellhead.

[0099] Table 7, acidizing process of grading pore forming fishbone branch

[0100]

[0101] Finally, it should be noted that the above specific examples are only used to explain the purpose, technical solutions and beneficial effects of the present application in detail. It should be understood that the above description is only a specific embodiment of the present application and does not limit the protection scope of the present application; although the present application has been described in detail with reference to the foregoing specific embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement, improvement, etc. to part or all of the technical features; and these modifications, equivalent replacement, improvement do not make the essence of the corresponding technical solution deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and description of the present application.

Claims

1. A fishbone branching acidizing process based on hierarchical pore creation, characterized by, It comprises the following steps: S1, lowering the oil pipe carrying the injection tool group to the toe end of the open hole horizontal section or the preset target modification position, injecting acid liquid into the formation through the ground pumping system, and forming a guide hole at the modification position; S2, switching the pumped liquid to a fluid loss reducer, and performing point injection at the same modification position to form a high conductivity channel; S3, pumping sand-carrying liquid into the formation, and performing sand-blasting perforation at the modification position based on the high conductivity channel to form a fishbone-shaped branch hole; S4, switching the pumped liquid to acid liquid, and performing point injection at the same modification position, the acid liquid rapidly advances along the fishbone-shaped branch hole to form a wormhole by dissolving the formation rock, and the acid liquid pushes the sand particles to the deep part of the formation; S5, when the acid liquid injection amount reaches the preset equivalent value, the oil pipe is dragged to the next designated target modification position; S6, repeating steps S1-S4 until the modification of all preset target points in the open hole horizontal section is completed.

2. The fishbone branching acidizing process based on hierarchical pore creation according to claim 1, wherein, The sand-carrying liquid refers to linear gel with a sand ratio of 7-20%, and the proppant in the linear gel uses abrasive or quartz sand.

3. The fishbone branching acidizing process based on hierarchical pore creation according to claim 2, characterized in that, The particle size of the abrasive is selected according to the following principles: the nozzle diameter in the injection tool group should be greater than 3 times the maximum particle size of the abrasive.

4. The fishbone branching acidizing process based on hierarchical pore creation according to claim 2, wherein, The particle size specification of the quartz sand is 40-70 mesh.

5. The fishbone branching acidizing process based on hierarchical pore creation according to claim 2, wherein, The sand ratio of the sand-carrying liquid is adjusted according to the formation permeability: When the formation permeability is <5 mD, linear gel with a sand ratio of 7% is used; When the formation permeability is 5-10 mD, linear gel with a sand ratio of 10% is used; When the formation permeability is 10-20 mD, linear gel with a sand ratio of 15% is used; When the formation permeability is >20 mD, linear gel with a sand ratio of 20% is used.

6. The fishbone branching acidizing process based on hierarchical pore creation according to claim 1, wherein, Steps S1-S4 are all carried out under high pressure, and the pump pressure is ≥55 MPa.

7. The fishbone branching acidizing process based on hierarchical pore creation according to claim 1, wherein, The acid liquid used in steps S1 and S4 is hydrochloric acid with a mass concentration of 15%-28%.

8. The fishbone branching acidizing process based on hierarchical pore creation according to claim 7, wherein, The mass concentration of the acid liquid is adjusted according to the formation permeability: When the formation permeability is <5 mD, the mass concentration of hydrochloric acid is ≥28%; When the formation permeability is 5-10 mD, the mass concentration of hydrochloric acid is 25-28%; When the formation permeability is 10-20 mD, the mass concentration of hydrochloric acid is 20-25%; When the formation permeability is >20 mD, the mass concentration of hydrochloric acid is 15-20%.

9. The fishbone branching acidizing process based on hierarchical pore creation according to claim 1, wherein, In step S5, when the acid liquid injection amount reaches the preset equivalent value, the ground pumping system is switched to a low-pressure mode, and the pump pressure is 25-35 MPa.

10. The fishbone branching acidizing process based on hierarchical pore creation according to any one of claims 1-9, characterized in that, It also comprises step S7: After the modification of all preset target points is completed, the liquid in the oil pipe is replaced with clean water, the oil pipe is dragged out of the wellhead after the pump is stopped, and the well is opened for flowback.

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