Method for realizing lateral communication acid fracturing of ultra-deep carbonate reservoir

Abstract

The invention relates to the technical field of oil exploitation, and discloses a method for achieving lateral communication acid fracturing of an ultra-deep carbonate reservoir. The method comprises the steps that (1) high-viscosity fracturing fluid is injected for fracture forming; (2) sand-carrying fluid is injected to plug the ends of the fractures; (3) sequentially injecting a low-viscosity acid solution, a medium-viscosity acid solution and a high-viscosity acid solution in a manner of first constant displacement and then cyclic variable displacement, and carrying out acid etching on the lateral crack; (4) injecting an ultralow-viscosity acid solution for closed acidification; and (5) slickwater is injected for displacement operation. According to the method, firstly, acid liquid is rapidly injected in a constant-displacement mode, and at the moment, the acid liquid can reach the end of the crack at the fastest speed. The acid liquor injected in a circulating variable displacement mode cannot continue to extend forwards, and can only move, remain and be distributed in the side wing direction of the acid liquor fingering channel which the acid liquor enters previously, so that a turbulent flow effect can be generated at a plurality of points in the side wing direction of the main fingering channel, and the non-uniform etching effect of an acid liquor turbulent flow area is greatly improved.

Description

Technical Field

[0001] The invention relates to the technical field of oil extraction, and in particular to a method for realizing lateral communication and acid fracturing in ultra-deep carbonate reservoirs. Background Art

[0002] At present, with the deepening of exploration and development, more and more ultra-deep carbonate reservoirs above 6,000 meters have been discovered. For example, in the Shunbei Oil and Gas Field in the Tarim Basin, most wells have a vertical depth of more than 7,300 meters, and some wells have a vertical depth of even close to 9,000 meters. The extreme increase in vertical depth has brought the following technical challenges to acid fracturing oil production:

[0003] (1) The temperature is extremely high. The temperature of some wells exceeds 200°C. Under high temperature environment, the reaction speed of acid rock is extremely fast, making it difficult to increase the effective length of acid-etched fractures. (2) The well depth causes large friction along the wellbore, limiting the injection displacement. (3) The closure stress is high. The closure stress of most wells exceeds 100 MPa, resulting in low conductivity and fast decline rate of acid-etched fractures in conventional acid fracturing, which easily produces flow retardation effect in the flow of fractures.

[0004] Conductivity is closely related to the length of the acid-etched fracture. In order to achieve a truly deep penetration effect, it is crucial to maintain the conductivity of the acid-etched fracture. In the previous deep penetration acid fracturing of ultra-deep carbonate reservoirs, the non-uniform etching technology based on variable viscosity acid was generally used, that is, high viscosity acid was injected first, and then low viscosity acid was injected, and the viscosity difference was used to increase the non-uniformity of etching. Although this operation has a certain effect, the conductivity of the acid-etched fracture has not been improved much, and the trend of rapid decrease in conductivity has not been fundamentally reversed.

[0005] Therefore, for ultra-deep carbonate reservoirs, there is an urgent need to provide an acid fracturing method that can increase fracture length, improve conductivity, and delay the trend of conductivity decline. Summary of the invention

[0006] The purpose of the present invention is to solve the problems of poor conductivity and rapid decline of acid fracturing fractures in the prior art, and to provide a method for realizing lateral communication acid fracturing in deep carbonate reservoirs.

[0007] In order to achieve the above object, the present invention provides a method for realizing lateral communication acid fracturing in ultra-deep carbonate reservoirs, wherein the method comprises the following steps:

[0008] (1) Injecting high-viscosity fracturing fluid to create fractures;

[0009] (2) Injecting sand-carrying fluid to seal the ends of the cracks;

[0010] (3) Using a method of first constant displacement and then cyclic variable displacement, low-viscosity acid, medium-viscosity acid, and high-viscosity acid are injected in sequence to acid-etch the lateral cracks;

[0011] (4) Injecting ultra-low viscosity acid for closed acidification;

[0012] (5) Inject slippery water for displacement.

[0013] Through the above technical solution, the beneficial technical effects achieved by the present invention are as follows:

[0014] 1) The present invention provides a method for realizing lateral channel acid fracturing in ultra-deep carbonate reservoirs. After the main fracture is formed by acid fracturing in the deep carbonate reservoir, the end screen-out effect is utilized to ensure that the end of the main fracture does not continue to extend.

[0015] 2) The present invention provides a method for implementing lateral channel acid fracturing in a deep carbonate reservoir, wherein the density of the proppant used is 1.7-1.8 g / cm 3 Compared with the extension speed of the fracture end, the proppant within this density range is more likely to migrate toward the fracture end in the fracture length direction, so that most of the proppant can be mainly plugged at the fracture end.

[0016] 3) The present invention provides a method for realizing lateral communication acid fracturing in deep carbonate reservoirs, which adopts a cyclic variable displacement injection method, and can greatly improve the turbulence effect of the acid in the fracture. After the high-viscosity fracturing fluid is used to form the expected fracture area, the acid is first injected rapidly at a constant displacement, and the acid at this time can reach the end of the fracture at the fastest speed. The acid subsequently injected in a cyclic variable displacement manner cannot continue to extend forward, and can only migrate and retain in the flank direction of the acid finger channel that entered previously, thereby generating a turbulence effect at multiple points in the flank direction of the main finger channel, greatly improving the non-uniform etching effect of the acid turbulence zone;

[0017] 4) The present invention provides a method for realizing lateral acid fracturing in deep carbonate reservoirs, which uses a constant displacement followed by a cyclic variable displacement method to sequentially inject low-viscosity acid, medium-viscosity acid and high-viscosity acid into the wellhead, thereby increasing the connectivity of the acid etching channel and between different etching channels.

[0018] 5) The present invention provides a method for realizing lateral communication acid fracturing in deep carbonate reservoirs. In the process of cyclic alternating displacement, since the viscosity of the acid liquid is different each time, the acid liquid fingering channels will not overlap with each other, and the acid liquid channels in the flank direction are also different. The ideal situation is that each time the acid liquid is fingered along a different channel, and the acid liquid channel finally formed is on the fracture area formed by the fracturing fluid, and the acid liquid etching channels are staggered in each fracture area area. The acid etched fracture channel formed in this way is relatively stable, the acid etched fracture conductivity is relatively high, and it can provide a relatively high long-term fracture conductivity and stable production effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the structure of the main fracture after the sand-carrying fluid is injected;

[0020] Figure 2 It is a schematic diagram of the structure of the lateral cracks generated after the injection of low-viscosity acid;

[0021] Figure 3 It is a schematic diagram of the structure of the lateral cracks generated after the injection of medium-viscosity acid solution;

[0022] Figure 4 It is a schematic diagram of the structure of lateral cracks generated after the injection of high-viscosity acid. DETAILED DESCRIPTION

[0023] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0024] Among them, in the present invention, high viscosity fracturing fluid, low viscosity fracturing fluid, low viscosity acid fluid, medium viscosity acid fluid, high viscosity acid fluid, ultra-low viscosity acid fluid and slick water have the meanings well known in the art, and the present invention will not elaborate on them one by one.

[0025] The present invention provides a method for realizing lateral channel acid fracturing in ultra-deep carbonate reservoirs, wherein the method comprises the following steps:

[0026] (1) Injecting high-viscosity fracturing fluid to create fractures;

[0027] (2) Injecting sand-carrying fluid to seal the ends of the cracks;

[0028] (3) Using a method of first constant displacement and then cyclic variable displacement, low-viscosity acid, medium-viscosity acid, and high-viscosity acid are injected in sequence to acid-etch the lateral cracks;

[0029] (4) Injecting ultra-low viscosity acid for closed acidification;

[0030] (5) Inject slippery water for displacement.

[0031] Among them, the present invention provides a method for realizing lateral acid fracturing in ultra-deep carbonate reservoirs. After the main fracture is formed by acid fracturing in the deep carbonate reservoir, a plurality of lateral acid-etched fractures are formed on the flanks of the main fracture by utilizing the end screen-out effect, and low-viscosity acid, medium-viscosity acid and high-viscosity acid are injected in sequence by first constant displacement and then cyclic variable displacement to improve the conductivity of each lateral acid-etched fracture, slow down the decline rate, and thus improve the production capacity of a single well.

[0032] The process of acid etching lateral cracks in the present invention is as follows Figure 1-Figure 4 As shown. Figure 1 It can be seen that the proppant enters the upper end of the main fracture and prevents the fracture from closing. Figure 2 It can be seen that after the low-viscosity acid is injected, the low-viscosity acid can reach the upper end of the main fracture. However, due to the presence of the proppant, the low-viscosity acid cannot continue to flow toward the end, and can only spread to the side of the main fracture, forming lateral acid-etched cracks at the weakest surface of the reservoir or the most developed natural fractures (as shown in the figure, lateral acid-etched cracks 1 and lateral acid-etched cracks 2, where the lateral cracks are randomly cracked according to the characteristics of the reservoir. The figure is only a schematic diagram, and the lateral cracks can be parallel or cross). Figure 3 It can be seen that after the medium-viscosity acid is injected, since the low-viscosity acid has already dissolved and filled the cracks that are easy to crack, the medium-viscosity acid can only spread to the side of the main crack, thereby activating the secondary weak surface or natural crack development that is easy to open, and continue to form lateral acid-etched cracks (as shown in lateral acid-etched cracks 3 and lateral acid-etched cracks 4 in the figure). Figure 4 It can be seen that after the high-viscosity acid solution is injected, there is already a large resistance at the low-viscosity acid solution and the medium-viscosity acid solution in front, and the high-viscosity acid solution continues to form lateral acid-etched cracks at other locations (as shown in lateral acid-etched cracks 5 and lateral acid-etched cracks 6 in the figure). Finally, under the action of low-viscosity acid solution, medium-viscosity acid solution and high-viscosity acid solution, multiple lateral cracks can be formed at different heights on the side of the main crack, thereby significantly improving the conductivity of the acid-etched crack and slowing down the decline rate.

[0033] In step (1):

[0034] In some embodiments of the present invention, before fracture creation, conventional means such as well logging, core analysis and well test analysis can be used to conduct a detailed evaluation of the lithology, rock mechanics, geostress, natural fractures and caves of the target layer. If necessary, the inversion analysis results of the acid fracturing construction data of adjacent wells can be used.

[0035] In some embodiments of the present invention, the viscosity of the high viscosity fracturing fluid is 60-200 mPa·s, preferably 80-120 mPa·s.

[0036] In some embodiments of the present invention, the injection volume of the high viscosity fracturing fluid is 10-50% by volume, preferably 10-30% by volume, of the total fracturing scale. In the present invention, the total fracturing scale refers to the total volume of the sand-carrying fluid, the high viscosity fracturing fluid, the low viscosity acid solution, the medium viscosity acid solution, the high viscosity acid solution and the ultra-low viscosity acid solution.

[0037] In some embodiments of the present invention, the injection rate of the high viscosity fracturing fluid is 80-100% of the maximum injection rate under wellhead pressure limitation, preferably 90-100%.

[0038] In step (2):

[0039] In some embodiments of the present invention, the sand-carrying fluid comprises a proppant and a low-viscosity fracturing fluid; wherein the particle size of the proppant is 140-210 mesh and the density is 1.7-1.8 g / cm 3 , selected from one or more of ceramsite, coated sand, and self-suspending proppant, preferably ceramsite, and more preferably ceramsite with a pressure resistance exceeding 69 MPa. The viscosity of the low-viscosity fracturing fluid is 30-50 mPa.s.

[0040] Among them, in the present invention, through the seam end screen-out effect of the sand-carrying fluid, different numbers of lateral acid-etched fractures can be effectively formed around the main fracture, thereby increasing the penetration range of the deep carbonate reservoir.

[0041] In some embodiments of the present invention, step (2) is carried out in a continuous sand adding mode, and the sand-carrying liquid is divided into N levels according to the trend of increasing sand-liquid ratio, and the injection amount of each level of sand-carrying liquid is 5-20m 3 Wherein, N is any integer between 2 and 10, the initial sand-liquid ratio is 1-5%, the increase in the sand-liquid ratio at each stage is independently selected from 1-5%, and the rising speed of the wellhead pressure after the sand-carrying liquid injection is completed is ≥1mPa / min.

[0042] In the present invention, the increase in each level of sand-liquid ratio refers to the difference between adjacent sand-liquid ratios. By adjusting the displacement of the sand-carrying liquid and the sand-liquid ratio, the rising speed of the wellhead pressure after the sand-carrying liquid injection can meet the requirement of ≥1mPa / min.

[0043] In some embodiments of the present invention, the sand-carrying liquid is divided into five levels according to the increasing trend of the sand-to-liquid ratio, and the sand-to-liquid ratio of each level of the sand-carrying liquid is (3-5)%, (5-7%), (7-9%), (9-11%), (11-13%), preferably (3.5-4.5)%, (5.5-6.5%), (7.5-8.5%), (9.5-10%), (11.5-12.5%).

[0044] In some embodiments of the present invention, the sand-carrying liquid is divided into three levels according to the trend of increasing sand-to-liquid ratio, and the sand-to-liquid ratio of each level of the sand-carrying liquid is (2-4)%, (4-6%) and (6-8%), preferably (2.5-3.5)%, (4.5-5.5%) and (6.5-7.5%).

[0045] In some embodiments of the present invention, the injection displacement of the sand-carrying fluid is 70-100% of the maximum displacement under wellhead pressure limitation, preferably 80-100%.

[0046] In step (3):

[0047] In some embodiments of the present invention, the constant displacement is 8-15m 3 / min, preferably 10-12m 3 / min.

[0048] In some embodiments of the present invention, the operation of circulating variable displacement includes: the maximum circulating displacement is 0.5-3.5m 3 / min, the reduction rate is gradually reduced to the minimum circulation displacement and then increased to 0.5-3.5m 3 / min increase step by step to the maximum cycle displacement.

[0049] Preferably, the maximum circulation displacement is 1.5-2.5m 3 / min, the reduction rate is gradually reduced to the minimum circulation displacement and then increased to 1.5-2.5m 3 / min increase step by step to the maximum cycle displacement.

[0050] Among them, in the present invention, the maximum circulation displacement is 95-100% of the maximum displacement under wellhead pressure limitation, and the minimum circulation displacement is 15-25% of the maximum displacement under wellhead pressure limitation.

[0051] In some embodiments of the present invention, the cyclic variable displacement operation includes: cycling 1-5 times in a manner of first decreasing step by step the maximum cyclic displacement to the minimum cyclic displacement and then increasing step by step to the maximum cyclic displacement.

[0052] In the present invention, one cycle is defined as the change from the maximum cycle displacement to the minimum cycle displacement to the maximum cycle displacement. The injection amount corresponding to each cycle is preferably evenly divided according to the number of cycles, and the injection amount corresponding to each cycle displacement in each cycle is preferably evenly divided according to the number of cycle stages.

[0053] In some embodiments of the present invention, the cyclic variable displacement operation includes: 12-10-7-5-2.5-5-7-10-12-10-7-5-2.5-5-7-10-12-10-7-5-2.5-5-7-10-12-10-7-5-2.5-5-7-10-12m 3 / min in a cyclic variable displacement manner to inject low-viscosity acid liquid, medium-viscosity acid liquid and high-viscosity acid liquid respectively; among which, the injection amount corresponding to each cyclic displacement is thirty-third of the cyclic variable displacement injection amount of the low-viscosity acid liquid, medium-viscosity acid liquid and high-viscosity acid liquid respectively.

[0054] In some embodiments of the present invention, the cyclic variable displacement operation includes: 10-8-6-4-2-4-6-8-10-8-6-4-2-4-6-8-10-8-6-4-2-4-6-8-10m 3 / min, low-viscosity acid liquid, medium-viscosity acid liquid and high-viscosity acid liquid are injected respectively; wherein, the injection amount corresponding to each circulating displacement is one twenty-fifth of the circulating variable displacement injection amount of the low-viscosity acid liquid, medium-viscosity acid liquid and high-viscosity acid liquid respectively.

[0055] In some embodiments of the present invention, the volume ratio of the constant displacement injection amount to the cyclic variable displacement injection amount is 1:1-3.5, preferably 1:1.5-2.8.

[0056] In some embodiments of the present invention, the viscosity of the low-viscosity acid fluid is 12-20 mPa·s, and the injection amount of the low-viscosity acid fluid is 5-25v% of the total fracturing scale.

[0057] In some embodiments of the present invention, the viscosity of the medium-viscosity acid fluid is 25-35 mPa·s, and the injection amount of the medium-viscosity acid fluid is 10-30v% of the total fracturing scale.

[0058] In some embodiments of the present invention, the viscosity of the high-viscosity acid fluid is 40-50 mPa·s, and the injection amount of the high-viscosity acid fluid is 15-35v% of the total fracturing scale.

[0059] Among them, in the present invention, when the low-viscosity acid liquid, medium-viscosity acid liquid and high-viscosity acid liquid are respectively injected in a manner of first constant displacement and then cyclic variable displacement, the constant displacement, constant displacement injection amount, cyclic variable displacement and cyclic variable displacement injection amount corresponding to the low-viscosity acid liquid, medium-viscosity acid liquid and high-viscosity acid liquid respectively may be the same or different, and the present invention does not make any special limitation on it.

[0060] In step (4):

[0061] In some embodiments of the present invention, before injecting ultra-low viscosity acid solution for closed acidification, the mixture is allowed to stand for 20-40 minutes.

[0062] In the present invention, static means shutting down the injection pump. The pump is stopped at this stage mainly to seek the closure or near-closure of the crack. For acid fracturing of ultra-deep carbonate reservoirs, factors such as high closure stress and large filtration caused by the development of natural fractures all lead to a small dynamic width of the cracks during acid fracturing. Therefore, the crack closure time is short, and 20-40 minutes is enough to ensure that the cracks are closed or near-closed.

[0063] In some embodiments of the present invention, the viscosity of the ultra-low viscosity acid is 1-10 mPa·s, the injection displacement is 60-80% of the maximum displacement under the wellhead pressure limit, and the injection volume is 80-100 m 3 .

[0064] Among them, in the present invention, after the crack is closed or nearly closed, the ultra-low viscosity acid solution is immediately injected to further deepen the depth of the groove and increase the conductivity of the acid-etched crack.

[0065] In step (5):

[0066] In some embodiments of the present invention, the viscosity of the slippery water is 1-3 mPa·s.

[0067] In some embodiments of the present invention, the injection amount of the slick water is 100-150% of the wellbore volume.

[0068] In some embodiments of the present invention, the injection rate of the slick water is 75-100% of the maximum injection rate under wellhead pressure limitation.

[0069] Among them, in the present invention, by injecting slick water for displacement operation, the pore structure collapse effect caused by excessive dissolution of acid rock near the wellbore fracture can be avoided, which will lead to a significant loss of conductivity. The flowback, testing and normal production after acid fracturing are carried out according to the conventional process and parameters.

[0070] The present invention will be described in detail below through examples.

[0071] Example 1

[0072] A deep carbonate reservoir in the Tarim Basin has a well depth of 8137 meters and a reservoir temperature of 178°C. A 140MPa pressure-resistant wellhead is used. The maximum injection displacement of the well is calculated to be 12m 3 / min, the total fracturing scale is 1633m 3 .

[0073] (1) 12m 3 / min displacement injection 250m 3 , high-viscosity fracturing fluid with a viscosity of 100 mPa·s, which presses the formation to create fractures;

[0074] (2) Using continuous sand adding mode, 10m 3 / min, the sand-carrying fluid with a sand-liquid ratio of 4%, 6%, 8%, 10%, and 12% was injected in sequence. After the injection of the sand-carrying fluid, the wellhead pressure rose at a rate of 1.4MPa / min; the sand-carrying fluid included 140-210 mesh and a density of 1.7g / cm 3 The pressure-resistant ceramsite of more than 69 MPa and the low-viscosity fracturing fluid with a viscosity of 40 mPa·s are used. The sand-carrying fluid is divided into 5 levels according to the increasing trend of the sand-liquid ratio. The injection volume of each level of sand-carrying fluid is 15m 3 ;

[0075] (3) First, 12m 3 / min displacement injection 96m 3 , a low viscosity acid with a viscosity of 12mPa·s, and then a low viscosity acid with a viscosity of 12-10-7-5-2.5-5-7-10-12-10-7-5-2.5-5-7-10-12-10-7-5-2.5-5-7-10-12-10-7-5-2.5-5-7-10-12m 3 / min cyclic variable displacement mode injects 198m 3 The injection volume of low-viscosity acid corresponding to each displacement is 6m 3 ;

[0076] Then 10m 3 / min displacement injection 120m 3 , medium viscosity acid with a viscosity of 27mPa·s, and then at 12-10-7-5-2.5-5-7-10-12-10-7-5-2.5-5-7-10-12-10-7-5-2.5-5-7-10-12-10-7-5-2.5-5-7-10-12-10-7-5-2.5-5-7 3 / min cyclic variable displacement mode injects 297m 3 The injection volume of medium viscosity acid corresponding to each displacement is 9m 3 ;

[0077] Then 10m 3 / min displacement injection 144m 3 , a high viscosity acid with a viscosity of 42mPa·s, followed by 12-10-7-5-2.5-5-7-10-12-10-7-5-2.5-5-7-10-12-10-7-5-2.5-5-7-10-12-10-7-5-2.5-5-7-10-12m 3 / min cyclic variable displacement mode injects 363m 3 The injection volume of high-viscosity acid corresponding to each displacement is 11m 3 ;

[0078] (4) Stop the pump for 30 minutes and then 3 / min displacement injection 90m 3 , 10mPa·s ultra-low viscosity acid solution for closed acidification;

[0079] (5) The shaft volume is 72.4m 3 , with 10m 3 / min displacement injection 95m 3 , 2mPa·s slippery water for replacement operation.

[0080] By using the method in Example 1 of the present invention, the production of the well after pressure testing was 427 t / d, and the production after one month was 150 t / d.

[0081] Example 2

[0082] A deep carbonate reservoir in the Sichuan Basin has a well depth of 7880 meters and a reservoir temperature of 182°C. A 140MPa pressure-resistant wellhead is used. The maximum displacement of the well is calculated to be 10m 3 / min, the total fracturing scale is 1536m 3 .

[0083] (1) 9m 3 / min displacement injection 400m 3 , high-viscosity fracturing fluid with a viscosity of 100 mPa·s, which presses the formation to create fractures;

[0084] (2) Using continuous sand adding mode, 10m 3 / min displacement, the sand-carrying fluid with sand-liquid ratio of 3%, 5%, and 7% was injected in turn. After the injection of the sand-carrying fluid, the wellhead pressure rose at a rate of 1.4MPa / min; the sand-carrying fluid included 140-210 mesh and a density of 1.7g / cm 3The pressure-resistant ceramsite of more than 69 MPa and the low-viscosity fracturing fluid with a viscosity of 40 mPa·s are used. The sand-carrying fluid is divided into three levels according to the increasing trend of the sand-liquid ratio. The injection volume of each level of sand-carrying fluid is 15m 3 ;

[0085] (3) 10m 3 / min displacement injection 72m 3 , a low viscosity acid with a viscosity of 12mPa·s, followed by 10-8-6-4-2-4-6-8-10-8-6-4-2-4-6-8-10-8-6-4-2-4-6-8-10m 3 / min cyclic variable displacement mode injects 175m 3 The injection volume of low-viscosity acid corresponding to each displacement is 7m 3 ;

[0086] Then 10m 3 / min displacement injection 90m 3 , medium viscosity acid with a viscosity of 27mPa·s, followed by 10-8-6-4-2-4-6-8-10-8-6-4-2-4-6-8-10-8-6-4-2-4-6-8-10m 3 / min cyclic variable displacement mode injects 225m 3 The injection volume of medium viscosity acid corresponding to each displacement is 9m 3 ;

[0087] Then 10m 3 / min displacement injection 164m 3 , high viscosity acid with a viscosity of 45mPa·s, followed by 10-8-6-4-2-4-6-8-10-8-6-4-2-4-6-8-10-8-6-4-2-4-6-8-10m 3 / min cyclic variable displacement mode injects 275m 3 The injection volume of high-viscosity acid corresponding to each displacement is 11m 3 ;

[0088] (4) Stop the pump for 30 minutes and then 3 / min displacement injection 90m 3 , 5mPa·s ultra-low viscosity acid solution for closed acidification;

[0089] (5) The shaft volume is 67.8m 3 , with 10m 3 / min displacement injection 80m 3 , 2mPa·s slippery water for replacement operation.

[0090] Using the method in Example 2 of the present invention, the well production after pressure testing was 113.6×10 4 m 3 / d.

[0091] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for realizing lateral channel acid fracturing in ultra-deep carbonate reservoirs, characterized in that: The method comprises the following steps: (1) Injecting high-viscosity fracturing fluid to create fractures; (2) Injecting sand-carrying fluid to seal the ends of the cracks; (3) Using a method of first constant displacement and then cyclic variable displacement, low-viscosity acid, medium-viscosity acid, and high-viscosity acid are injected in sequence to acid-etch the lateral cracks; (4) Injecting ultra-low viscosity acid for closed acidification; (5) Inject slippery water for displacement.

2. The method according to claim 1, wherein: The viscosity of the high viscosity fracturing fluid is 60-200 mPa·s, preferably 80-120 mPa·s; Preferably, the injection amount of the high viscosity fracturing fluid is 10-50v%, preferably 10-30v% of the total fracturing scale; Preferably, the displacement of the high viscosity fracturing fluid is 80-100% of the maximum value under the wellhead limit pressure, preferably 90-100%.

3. The method according to claim 1 or 2, wherein: The sand-carrying fluid includes a proppant and a low-viscosity fracturing fluid; wherein the particle size of the proppant is 140-210 mesh and the density is 1.7-1.8 g / cm 3 , selected from one or more of ceramsite, coated sand, and self-suspending proppant; the viscosity of the low-viscosity fracturing fluid is 30-50mPa.s.

4. The method according to any one of claims 1 to 3, wherein: Step (2) is carried out in a continuous sand adding mode. The sand-carrying liquid is divided into N levels according to the increasing trend of the sand-liquid ratio. The injection amount of the sand-carrying liquid in each level is 5-20m3. 3 ; wherein N is any integer between 2 and 10, the initial sand-to-liquid ratio is 1-5%, and the increase in the sand-to-liquid ratio at each stage is independently selected from 1-5%.

5. The method according to any one of claims 1 to 4, wherein: The operation of the cycle variable displacement includes: the maximum cycle displacement is 0.5-3.5m 3 / min, the reduction rate is gradually reduced to the minimum circulation displacement and then increased to 0.5-3.5m 3 / min increases step by step to the maximum cycle displacement; Preferably, the operation of circulating variable displacement includes: the maximum circulating displacement is 1.5-2.5m 3 / min, the reduction rate is gradually reduced to the minimum circulation displacement and then increased to 1.5-2.5m 3 / min increases step by step to the maximum cycle displacement; Preferably, the maximum circulation displacement is 95-100% of the maximum displacement under wellhead pressure limitation, and the minimum circulation displacement is 15-25% of the maximum displacement under wellhead pressure limitation.

6. The method according to any one of claims 1 to 5, wherein: The volume ratio of the constant displacement injection volume to the cyclic variable displacement injection volume is 1:1-3.5, preferably 1:1.5-2.

8.

7. The method according to claim 1, wherein: The viscosity of the low-viscosity acid liquid is 12-20 mPa·s, and the injection amount of the low-viscosity acid liquid is 5-25v% of the total fracturing scale.

8. The method according to claim 1, wherein: The viscosity of the medium-viscosity acid solution is 25-35 mPa·s, and the injection amount of the medium-viscosity acid solution is 10-30v% of the total fracturing scale.

9. The method according to claim 1, wherein: The viscosity of the high-viscosity acid liquid is 40-50 mPa·s, and the injection amount of the high-viscosity acid liquid is 15-35v% of the total fracturing scale.

10. The method according to claim 1, wherein: The viscosity of ultra-low viscosity acid is 1-10mPa·s, the displacement is 60-80% of the maximum displacement under wellhead pressure limit, and the injection volume is 80-100m 3 ; Preferably, the viscosity of the slick water is 1-3 mPa·s, the injection amount of the slick water is 100-150% of the wellbore volume, and the injection displacement of the slick water is 75-100% of the maximum displacement under wellhead pressure limitation.

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