A method for realizing low-permeability oil reservoir old well lateral opening new cracks

Abstract

The present application provides a kind of method for realizing low permeability reservoir old well lateral opening new fracture, specific steps are as follows: step one, first, using small displacement injection preflush, make the original fracture open;Step two, using small displacement injection the required amount of sand slurry, make sand slurry form sand plug in the original fracture and block;Step three, improve the displacement, inject sand carrying fluid with large displacement, open new lateral fracture;Step four, continue to inject sand carrying fluid, make the newly opened lateral fracture continue to extend the remaining oil enrichment area on both sides and bring in proppant, realize the support of lateral fracture;Step five, finally, inject displacement fluid, displace the proppant in wellbore to lateral fracture, complete the whole fracturing operation.The present application forms sand plug in the original fracture, thereby reducing the through capacity of fracturing fluid.By injecting sand carrying fluid, make the new lateral fracture extend, and establish the fracture channel between remaining oil enrichment area and wellbore, realize the fracturing of remaining oil enrichment area.

Description

Technical Field

[0001] This invention pertains to a technology used in petroleum fracturing operations, applicable to repeated fracturing of old wells in oil fields, and specifically relates to a method for laterally opening new fractures in old wells in low-permeability reservoirs. Background Technology

[0002] In low-permeability reservoirs, repeated fracturing is an important technical means to increase production in old wells. However, because these wells have already undergone fracturing when they were put into production, the formation near the fractures has a relatively high recovery rate, while the remaining oil is relatively concentrated in the formation on both sides of the fractures and away from the fractures.

[0003] Due to the influence of the existing fractures, when repeated fracturing is carried out, the fracturing fluid will preferentially enter the existing fractures. Therefore, the existing fracturing technology mainly restores the conductivity of the fractures or changes the fracture length. The fractures will not extend to both sides and reach the remaining oil-rich areas.

[0004] Chinese patent CN109236259A discloses a fracturing method for adjusting the contradiction of planar water drive in injection wells, including the following steps: displacing the fluid in the wellbore and then setting the packer; injecting pre-fluid to open natural fractures; injecting a mixed solution into the depth of the natural fractures opened in step 2, filtering it along the direction of the natural fractures and removing sand at the ends of the natural fractures; the mixed solution contains at least proppant and the fluid from step 2; sequentially injecting liquid rubber plugging agent, isolation fluid, and temporary plugging agent into the opened natural fractures; if there are multiple natural fractures, repeating steps 2-4 for each natural fracture; injecting liquid rubber plugging agent into the natural fractures, raising the tubing string and shutting in the well to allow it to solidify, thus sealing the natural fractures; performing temporary plugging fracturing in the injection well to form artificial fractures along the direction of the maximum horizontal principal stress. This shortens the water drive radius, thereby improving the planar water drive effect and enhancing the overall reservoir development effect.

[0005] Although the above patents have made some improvements, there is still a problem that the cracks do not extend to both sides and reach the area where the remaining oil is concentrated. Summary of the Invention

[0006] To overcome the problem that existing fractures do not extend to both sides and reach the area where residual oil is enriched, this invention provides a method for opening new fractures laterally in old wells in low-permeability reservoirs. This invention enables the opening of new lateral fractures during repeated fracturing, which is beneficial for the extraction of residual oil on both sides of the original fractures after fracturing, thereby increasing the production of oil wells after repeated fracturing.

[0007] The technical solution adopted in this invention is as follows: A method for laterally opening new fractures in old wells in low-permeability reservoirs, comprising the following steps: Step 1: First, inject pre-fluid at a small flow rate to open the existing cracks; Step 2: Inject the required amount of sand-mixing liquid using a small flow rate, so that the sand-mixing liquid forms a sand plug in the original crack to seal it. Step 3: Increase the displacement and inject the sand-carrying fluid with a large displacement to open new lateral cracks; Step 4: Continue injecting the proppant-carrying fluid to extend the newly opened lateral cracks into the areas on both sides where the remaining oil is concentrated and to bring in the proppant, thereby supporting the lateral cracks. Step 5: Finally, inject displacement fluid to replace the proppant in the wellbore with the lateral fractures, completing the entire fracturing operation.

[0008] In step two, the sand-mixing fluid includes fracturing fluid, quartz sand, and a breaker. The volume ratio of the fracturing fluid to the quartz sand is 10:(3-4), and the mass of the breaker accounts for 0.5-2.0‰ of the mass of the fracturing fluid.

[0009] In step two, the process of forming a sand plug in the original crack by the sand-mixing liquid is as follows: the sand-mixing liquid is broken in the original crack by the use of a de-gelling agent, and the quartz sand in the sand-mixing liquid sinks and accumulates in the original crack to form a sand plug.

[0010] The quartz sand mentioned is 20 / 40 mesh quartz sand, or a mixture of 20 / 40 mesh and 40 / 70 mesh quartz sand, wherein the 40 / 70 mesh accounts for 20-40% of the mixture.

[0011] The de-gelling agent is potassium persulfate or ammonium persulfate.

[0012] In step three, the specific process of opening a new lateral fracture is as follows: increase the injection rate of the sand-carrying fluid so that the amount of sand-carrying fluid entering the original fracture is higher than the amount of fracturing fluid that has permeated through the sand plug. The pressure inside the fracture between the sand plug and the wellbore will continue to rise. When the pressure inside the fracture is higher than the opening pressure of a natural fracture, or when the pressure inside the fracture exceeds the strength limit of the formation rock, a new lateral fracture can be opened on both sides of the original fracture.

[0013] The determination of the opening of a new lateral fracture is as follows: pressure is measured at the wellhead, and when the pressure drops, a new fracture is opened.

[0014] In step four, the volume ratio of proppant to fracturing fluid in the mixed sand is (1-4:10).

[0015] In step one, the displacement does not exceed 2 m³ / min.

[0016] In step three, the maximum displacement is 6-18 m³ / min.

[0017] The beneficial effects of this invention are as follows: This invention provides a method for laterally opening new fractures in old wells in low-permeability oil reservoirs. By artificially adding a breaker and quartz sand to the fracturing fluid, sand plugs are formed in the original fractures, thereby reducing the flow capacity of the fracturing fluid.

[0018] In this invention, the breaker can break the gel quickly. Potassium persulfate or ammonium persulfate is preferred as the breaker, which is economical and effective, and can make the fracturing fluid break the gel quickly in the original fracture.

[0019] In this invention, quartz sand, after settling and accumulating, can form a sand plug. The formed sand plug has good stability and effectively seals the original cracks.

[0020] In this invention, after the sand plug is formed, sand-carrying fluid is injected by increasing the construction flow rate, which forces the pressure inside the crack between the sand plug and the wellbore to rise continuously until a new lateral crack is opened.

[0021] In this invention, by injecting sand-carrying fluid, new lateral fractures are extended, thereby achieving fracturing of the remaining enriched areas on both sides and establishing a fracture channel between the remaining oil-rich area and the wellbore, thus achieving fracturing of the remaining oil-rich area.

[0022] The following will provide further explanation in conjunction with the accompanying drawings. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the opening of a lateral crack. Detailed Implementation

[0024] The following description, with reference to the accompanying drawings and embodiments, further illustrates a method for laterally opening new fractures in old wells in low-permeability reservoirs according to the present invention. The drawings and embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are provided.

[0025] Example 1: To overcome the problem that existing fractures do not extend to both sides and reach the area where residual oil is enriched, this invention provides a method for opening new fractures laterally in old wells in low-permeability reservoirs. This invention enables the opening of new lateral fractures during repeated fracturing, which is beneficial for the extraction of residual oil on both sides of the original fractures after fracturing, thereby increasing the production of oil wells after repeated fracturing.

[0026] A method for laterally opening new fractures in old wells in low-permeability reservoirs, comprising the following steps: Step 1: First, inject pre-fluid at a small flow rate to open the existing cracks; Step 2: Inject the required amount of sand-mixing liquid using a small flow rate, so that the sand-mixing liquid forms a sand plug in the original crack to seal it. Step 3: Increase the displacement and inject the sand-carrying fluid with a large displacement to open new lateral cracks; Step 4: Continue injecting the proppant-carrying fluid to extend the newly opened lateral cracks into the areas on both sides where the remaining oil is concentrated and to bring in the proppant, thereby supporting the lateral cracks. Step 5: Finally, inject displacement fluid to replace the proppant in the wellbore with the lateral fractures, completing the entire fracturing operation.

[0027] In this invention, the existing fractures are the hydraulic fracturing fractures that already existed in the formation of the oil well before the implementation of this invention, that is, the fractures formed during the previous hydraulic fracturing.

[0028] The lateral new seam in this invention is a new crack formed during the implementation of this invention.

[0029] This invention provides a method for laterally opening new fractures in old wells in low-permeability oil reservoirs. By artificially adding a breaker and quartz sand to the fracturing fluid, sand plugs are formed within the existing fractures, thereby reducing the fracturing fluid's permeability. The fracturing fluid used in this invention is a plant-based gum fracturing fluid, including guar gum, sesame gum, and coumarin gum. This is a newly developed type of natural plant gum in my country. Plant-based gum fracturing fluids are a mature existing technology and will not be further described in this invention.

[0030] After the sand plug is formed, the flow rate is increased to inject sand-carrying fluid, forcing the pressure within the fracture between the sand plug and the wellbore to rise continuously until a new lateral fracture is opened. Continued injection of sand-carrying fluid extends the new lateral fracture, thereby achieving fracturing of the remaining enriched areas on both sides and establishing a fracture channel between the remaining oil-rich area and the wellbore, thus achieving fracturing of the remaining oil-rich area.

[0031] In this invention, the newly opened lateral fractures extend along both sides of the original fractures to reach the remaining oil-rich area, and then open a stable fracturing channel to carry out subsequent fracturing of the remaining oil-rich area, thereby improving the oil well production after repeated fracturing.

[0032] Example 2: Based on Example 1, in this embodiment, preferably, in step two, the sand mixing fluid includes fracturing fluid, quartz sand and a breaker, the volume ratio of the fracturing fluid to the quartz sand is 10:(3-4), and the mass of the breaker accounts for 0.5-2.0‰ of the mass of the fracturing fluid.

[0033] In this invention, the amount of the breaker is selected according to the requirements. The preferred mass of the breaker is 0.6‰, 0.8‰, 0.9‰, 1.0‰, 1.2‰, 1.4‰, 1.6‰, or 1.8‰ of the fracturing fluid mass.

[0034] In conventional fracturing, the amount of breaker is usually a few parts per ten thousand, not exceeding 10 parts per ten thousand. However, in this invention, the amount is basically between 0.5 and 2 parts per thousand. The purpose of choosing such a large dose of breaker is to break the rupture more quickly.

[0035] Preferably, in step two, the process of forming a sand plug in the original crack using the sand-mixing liquid is as follows: the sand-mixing liquid is broken open in the original crack using a de-gelling agent, and the quartz sand in the sand-mixing liquid sinks and accumulates in the original crack to form a sand plug.

[0036] Preferably, the quartz sand is 20 / 40 mesh quartz sand, or a mixture of 20 / 40 mesh and 40 / 70 mesh quartz sand, wherein the 40 / 70 mesh accounts for 20-40% of the mixture.

[0037] In this invention, the quartz sand in the sand-mixing solution settles and accumulates within the existing cracks, forming a sand plug. Quartz sand is inexpensive and has good sealing performance. While expanded clay can also be used to form the sand plug, it is more expensive. Therefore, quartz sand is generally chosen for forming the sand plug, ensuring effective sealing.

[0038] In this invention, based on the original production data and the condition of the existing cracks, appropriate quartz sand is selected as the final sand plug. The formation of the sand plug effectively seals the original cracks, ensuring that subsequent injection of sand-carrying fluid will not reopen the sealed cracks.

[0039] In this invention, the content of quartz sand is selected according to requirements to ensure that the final sand plug will not be crushed.

[0040] In this invention, quartz sand, after settling and accumulating, can form a sand plug. The formed sand plug has good stability, is highly resistant to being crushed, and effectively seals existing cracks.

[0041] Preferably, the desiccant is potassium persulfate or ammonium persulfate.

[0042] In this invention, potassium persulfate or ammonium persulfate is preferred as the breaker, which is economical and effective. It enables the fracturing fluid to rapidly break up the existing fracture.

[0043] In this invention, the mixing of the sand-mixing fluid is carried out using existing sand-mixing equipment. The quartz sand and breaker added to the fracturing fluid are added and mixed evenly using appropriate equipment, and then injected from the wellhead into the existing fracture.

[0044] The sand-mixing solution in this invention can be prepared on-site or pre-prepared and injected directly. This ensures that the injection volume is sufficient at one time, preventing insufficient sand-mixing solution from causing the sand plug to fail to form.

[0045] In this invention, the proportion of quartz sand is relatively large, accounting for 30-40% of the volume of the fracturing fluid. This high content of quartz sand can form a stable plug, effectively sealing the original fractures. A breaker is added to the fracturing fluid in this invention to accelerate the breaking of the gel, ensuring that the subsequent quartz sand can seal quickly and firmly.

[0046] In this invention, the preferred content of the breaker is 5‰ of the fracturing fluid volume, which is sufficient to rapidly break up the fracturing fluid.

[0047] Preferably, in step three, the specific process of opening a new lateral fracture is as follows: increase the injection rate of the sand-carrying fluid so that the amount of sand-carrying fluid entering the original fracture is higher than the amount of fracturing fluid that has permeated through the sand plug. The pressure inside the fracture between the sand plug and the wellbore will continue to rise. When the pressure inside the fracture is higher than the opening pressure of a natural fracture, or when the pressure inside the fracture exceeds the strength limit of the formation rock, a new lateral fracture can be opened on both sides of the original fracture based on the original fracture.

[0048] Preferably, the determination of the opening of a new lateral fracture is as follows: pressure is measured at the wellhead, and when the pressure drops, a new fracture opens.

[0049] Preferably, in step three, the displacement is 6-18 m³ / min.

[0050] In this invention, the sand-carrying liquid is injected through a corresponding device, and the injection volume is much greater than the volume of the pre-treatment liquid and the sand-mixing liquid.

[0051] In this invention, the injection rate of the sand-carrying fluid is selected according to requirements and can be adjusted at any time based on on-site construction. This ensures rapid and safe injection of the sand-carrying fluid. The preferred injection rates of the sand-carrying fluid in this invention are 8 m³ / min, 9 m³ / min, 10 m³ / min, 12 m³ / min, 14 m³ / min, 15 m³ / min, and 16 m³ / min.

[0052] Preferably, in step four, the volume ratio of proppant to fracturing fluid in the sand mixing fluid is (1-4:10).

[0053] In this invention, when the sand-carrying fluid is injected subsequently, a proppant is added to the sand-carrying fluid, and then the proppant is mixed evenly with the sand-carrying fluid at that location before being injected, thereby effectively supporting the newly opened lateral cracks.

[0054] In this invention, the preferred volume ratio of proppant to fracturing fluid is 2:10, 2.5:10, 3:10, or 3.5:10. The amount of proppant used is determined according to requirements. During injection, the proppant is mixed in the subsequent proppant-carrying fluid, providing support for the newly opened lateral fractures.

[0055] In this invention, the storage, transportation, and injection of proppant and proppant-carrying fluid are all carried out systematically using appropriate equipment. The injection volumes of fracturing fluid and proppant-carrying fluid are calculated and determined in detail before construction to ensure that there is no waste or insufficiency during the injection process.

[0056] Preferably, in step one, the displacement does not exceed 2 m³ / min.

[0057] In this invention, the injection rates of the pretreatment liquid and the sand mixing liquid are basically the same, preferably 1.5 m³ / min and 2 m³ / min respectively.

[0058] like Figure 1 As shown, there were existing fractures on both sides of the oil well. The distal ends of the existing fractures were sealed with sand plugs. Lateral fractures were then opened on both the upper and lower sides of the existing fractures. The number and angle of the lateral fractures were variable. Based on the newly opened lateral fractures, subsequent fracturing channels were established, and finally, subsequent fracturing operations were carried out.

[0059] The specific construction process of this invention is as follows: First, pre-fracturing fluid is injected to open the existing fractures. The existing fractures were created during the initial fracturing of the oil well. During repeated fracturing, this is the area with the weakest stress, so pre-fracturing fluid will preferentially enter and open it during repeated fracturing.

[0060] Then, 20 / 40 mesh quartz sand, or a combination of 20 / 40 mesh and 40 / 70 mesh quartz sand, is added to the fracturing fluid, along with APS (ammonium persulfate). This causes the fracturing fluid to break up the gel in the existing fracture, allowing the quartz sand to sink and accumulate within the fracture, forming a sand plug.

[0061] Increasing the injection rate of the sand-carrying fluid makes the amount of sand-carrying fluid entering the original fracture higher than the amount of fracturing fluid that has permeated through the sand plug. The pressure inside the fracture between the sand plug and the wellbore will continue to rise. When the pressure inside the fracture is higher than the opening pressure of the natural fracture, or when the pressure inside the fracture exceeds the strength limit of the formation rock, a new lateral fracture can be opened on the basis of the original fracture.

[0062] Then, the proppant-carrying fluid is injected to allow the new lateral cracks to extend into the areas on both sides where the remaining oil is concentrated and to introduce proppant, thus supporting the new cracks.

[0063] Finally, the displacement fluid is injected to replace the proppant in the wellbore with the new lateral fracture, completing the entire fracturing operation.

[0064] In this invention, the amount of fracturing fluid used is determined according to requirements, and is preferably 100 cubic meters.

[0065] In this invention, the amount of sand-carrying liquid used is large, at least 200 cubic meters, and then the amount is calculated and selected according to the requirements and finally determined.

[0066] In this invention, the amount of sand-carrying liquid used is 200-1000 cubic meters. Preferably, it is 300 cubic meters, 400 cubic meters, 500 cubic meters, 600 cubic meters, 700 cubic meters, 800 cubic meters, or 900 cubic meters.

[0067] In this invention, the displacement fluid ensures complete displacement of the proppant into the lateral fractures, with the proppant acting as a lateral fracture, establishing a safe and stable fracturing channel. The displacement fluid in this invention does not contain sand. It also does not contain other substances that affect fracturing and will not interfere with subsequent fracturing production in the remaining oil-rich areas.

[0068] In this invention, such as Figure 1 As shown, the angle of the newly opened lateral fracture is uncontrollable. Its angle is related to the direction of the instantaneous force agent crushing when the pressure exceeds the strength limit of the formation rock. The resulting lateral fractures are irregular. These irregular lateral fractures can continue to extend to the remaining oil-rich areas on both sides and bring in proppant, thus supporting the new lateral fractures.

[0069] Unless otherwise specified, all embodiments in this invention are existing technologies or can be implemented using existing technologies. Furthermore, the embodiments described in this invention are merely preferred embodiments and are not intended to limit the scope of this invention. That is, all equivalent changes and modifications made to the content of the claims of this invention should be considered within the technical scope of this invention. Devices, equipment, and method steps not described in detail in this invention are all existing technologies and will not be further described in this invention.

Claims

1. A method for laterally opening new fractures in old wells in low-permeability oil reservoirs, characterized in that: The specific steps are as follows: Step 1, firstly, inject pre-fluid with a small flow rate to open the original cracks; Step two: Inject the required amount of fracturing fluid at a small flow rate to form a sand plug within the existing fractures for sealing. The fracturing fluid includes fracturing fluid, quartz sand, and a breaker. The volume ratio of the fracturing fluid to the quartz sand is 10:(3-4), and the mass of the breaker accounts for 0.5-2.0‰ of the mass of the fracturing fluid. The quartz sand is 20 / 40 mesh quartz sand, or a mixture of 20 / 40 mesh and 40 / 70 mesh quartz sand, with the 40 / 70 mesh comprising 20-40% of the mixture. Step 3: Increase the displacement and inject the sand-carrying fluid with a large displacement to open new lateral cracks; Step 4: Continue injecting the proppant-carrying fluid to extend the newly opened lateral cracks into the areas on both sides where the remaining oil is concentrated and to bring in the proppant, thereby supporting the lateral cracks. Step 5: Finally, inject displacement fluid to replace the proppant in the wellbore with the lateral fractures, completing the entire fracturing operation.

2. The method for laterally opening new fractures in old wells of low-permeability reservoirs according to claim 1, characterized in that: In step two, the process of forming a sand plug in the original crack by the sand-mixing liquid is as follows: the sand-mixing liquid is broken in the original crack by the use of a de-gelling agent, and the quartz sand in the sand-mixing liquid sinks and accumulates in the original crack to form a sand plug.

3. The method for laterally opening new fractures in old wells of low-permeability reservoirs according to claim 1, characterized in that: The de-gelling agent is potassium persulfate or ammonium persulfate.

4. The method for laterally opening new fractures in old wells of low-permeability reservoirs according to claim 1, characterized in that: In step three, the specific process of opening a new lateral fracture is as follows: increase the injection rate of the sand-carrying fluid so that the amount of sand-carrying fluid entering the original fracture is higher than the amount of fracturing fluid that has permeated through the sand plug. The pressure inside the fracture between the sand plug and the wellbore will continue to rise. When the pressure inside the fracture is higher than the opening pressure of a natural fracture, or when the pressure inside the fracture exceeds the strength limit of the formation rock, a new lateral fracture can be opened on both sides of the original fracture.

5. The method for laterally opening new fractures in old wells of low-permeability reservoirs according to claim 4, characterized in that: The determination of the opening of a new lateral fracture is as follows: pressure is measured at the wellhead, and when the pressure drops, a new fracture is opened.

6. The method for laterally opening new fractures in old wells of low-permeability reservoirs according to claim 1, characterized in that: In step four, the volume ratio of proppant to fracturing fluid in the mixed sand is (1-4):

10.

7. The method for laterally opening new fractures in old wells of low-permeability reservoirs according to claim 1, characterized in that: In step one, the displacement does not exceed 2 m³ / min.

8. The method for laterally opening new fractures in old wells of low-permeability reservoirs according to claim 1, characterized in that: In step three, the maximum displacement is 6-18 m³ / min.

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