Fracturing method for shallow bottom water reservoir by using clean water carrying air suspension proppant

Abstract

The invention discloses a clean water carrying air suspension proppant fracturing method for a shallow bottom water reservoir. The clean water carrying air suspension proppant fracturing method comprises the following steps: preparing an air suspension proppant; optimizing an underground fluid system, and selecting clear water as prepad fluid, sand-carrying fluid and displacing fluid; according to the reservoir geologic characteristics and the oil-bearing property, in combination with software, the fracture expansion condition is simulated, the sand amount, the construction displacement, the sand ratio and the prepad fluid proportion parameters are optimized, a construction pump injection program is designed according to the optimized parameters, the fracturing construction process is determined, and a clear water gas suspension sand fracturing technical mode is formed. The surface of the quartz sand is modified, the fracturing propping agent which can generate a large number of bubbles on the surface when encountering water and is fully suspended or flocculent semi-suspended in water is obtained, the fracturing method that clear water carries the air suspension propping agent is adopted, on one hand, the net pressure in a crack can be reduced, the crack height can be controlled, bottom water channeling due to pressure is avoided, and the fracturing propping agent can be recycled; and on the other hand, the sanding profile can be improved to realize effective support of the middle-upper oil layer, so that benefit development of the shallow bottom water reservoir is realized.

Description

Technical Field

[0001] This invention belongs to the technical field of fracturing methods in oilfield development, specifically relating to a water-carrying air-suspended proppant fracturing method for shallow bottom water reservoirs. Background Technology

[0002] Shallow reservoirs are typically characterized by shallow burial (200–1500 m), widespread distribution, small reservoir size, multiple strata (Triassic, Jurassic, etc.), and localized bottom water development with poor bottom water shielding. Stimulation of shallow bottom water reservoirs requires both controlling fracture height to prevent water channeling and effectively laying fractures longitudinally to improve fracture conductivity, thereby enhancing fracturing and oil production. Conventional fracturing techniques such as low-volume, low-spar, low-displacement, low-spar-ratio water-controlled fracturing and hydraulic jet fracturing aim to control fracture height and prevent water channeling that would result in water production without oil output. However, excessively small-scale fracturing can lead to insufficient stimulation and low test fluid volume. Therefore, it is urgent to explore new water-controlled fracturing technologies to effectively control fracture height to prevent water channeling while simultaneously increasing production. Summary of the Invention

[0003] The purpose of this invention is to provide a water-carrying air-suspended proppant fracturing method for shallow bottom-water reservoirs, which solves the problem of low oil production in conventional small-scale hydraulic fracturing tests.

[0004] The technical solution adopted in this invention is: a water-carrying air-suspended proppant fracturing method for shallow bottom-water reservoirs, as detailed below:

[0005] Step 1: By modifying the surface of quartz sand, a gas suspension proppant is obtained that can generate a large number of bubbles when it comes into contact with water, thus forming a fully suspended or flocculent semi-suspended state in water.

[0006] Step 2: Optimize the infiltration system by selecting clean water as the pretreatment fluid, sand-carrying fluid, and displacement fluid;

[0007] Step 3: Based on the reservoir geological characteristics and oil-bearing properties, and combined with software simulation of fracture propagation, optimize parameters such as sand volume, construction discharge rate, sand ratio, and pre-flush fluid ratio. Based on the optimized parameters, design the construction pumping program and determine the fracturing construction process to form a clear water air suspension sand fracturing technology model.

[0008] The present invention is further characterized in that,

[0009] The proppant comprises a quartz sand matrix and a surface spray coating. The surface spray coating is formed by mechanically mixing a silane coupling agent, a surfactant, a diluent, and additives to prepare a treatment solution, which is then sprayed onto the quartz sand surface in a high-speed disperser and stirred for a certain period. The mass ratio of the treatment solution to the matrix is ​​(0.5–1.0):100. The treatment solution comprises, by mass percentage: 10–25% silane coupling agent, 5–15% surfactant, 0.5–1.0% additives, with the balance being a diluent, and the sum of the mass percentages of the above components is 100%.

[0010] The quartz sand matrix is ​​one or more of 30 / 50 mesh, 40 / 70 mesh and 70 / 140 mesh quartz sand;

[0011] The silane coupling agent is one or a mixture of two or more of vinyltrimethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, γ-chloropropyltrimethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane.

[0012] The surfactant is one or a mixture of two or more of the following: dodecyl dimethylamine hydantoin, hexadecyl trimethylammonium bromide, sodium dodecyl sulfate, and octadecyl trimethylammonium chloride;

[0013] The diluent is a mixture of one or more organic solvents, such as toluene, ethanol, and methanol, with water (volume ratio of organic solvent:water = 9:1).

[0014] The additive is one or a mixture of two or more of glacial acetic acid, formic acid, and acetic acid.

[0015] Furthermore, the preference for using clean water as the pre-flush fluid, proppant carrier fluid, and displacement fluid in step 2 is because selecting a low thickener concentration is actually controlling the viscosity of the fracturing fluid. The higher the viscosity, the easier it is for the fracture height to become uncontrollable. Clean water fracturing maximizes the use of a low thickener concentration. Conventional quartz sand proppant can only maintain its suspension effect in clean water by relying on a high flow rate. The air-suspended proppant in this invention can be suspended in clean water by relying on low density and air bubbles, thus maintaining its suspension effect even at a low flow rate. Therefore, clean water is selected as the pre-flush fluid, proppant carrier fluid, and displacement fluid to maximize control over fracture height expansion.

[0016] Furthermore, the optimization of construction parameters mentioned in step 3 is because the stress difference between the reservoir layers in shallow bottom-water reservoirs is generally very small (<3MPa), and many of them are oil-water connected reservoirs. On the one hand, for reservoirs with poor bottom-water shielding, the construction scale should be as small as possible to avoid excessive extension of artificial fractures to the bottom-water layer, resulting in high water production during oil testing. On the other hand, the improvement of single-well production largely depends on the reasonable increase of the reservoir stimulation scale. Therefore, it is necessary to reasonably optimize the stimulation scale to balance the dual needs of increasing single-well production and controlling fracture height expansion.

[0017] Furthermore, the software mentioned in step 3 is FracproPT fracturing simulation software;

[0018] Furthermore, step 3 optimized and determined the fracturing operation parameters as follows: sand volume 2.0-10.0 m³. 3 / min, construction discharge rate 0.8-1.0m 3 / min, the sand ratio is 10.0%-11.5%, and the pre-liquid ratio (=pre-liquid volume / (pre-liquid volume+sand-carrying liquid volume)×100%) is 20%-21%.

[0019] Furthermore, the fracturing process determined in step 3 is as follows:

[0020] ① Low-pressure and sealing stage: 0.0-0.8m 3 The construction flow rate is reduced by injecting clean water at a rate of / min (the fluid volume is designed to be 1.5m less than the tubing volume from the wellhead to the perforation section). 3 Then the discharge rate is increased to the design discharge rate of the pre-fluidization stage, and clean water is used to seal the packer.

[0021] ② Pre-flushing stage: with a solution of 0.7-0.9m 3 Pump clean water at a construction flow rate of / min (control the pre-fluid ratio to 20%);

[0022] ③ Sand-carrying slurry stage: Discharge 0.8-1.0m³ according to the designed construction flow rate. 3 / min, add air suspension proppant in a wedge-shaped sand addition manner, gradually increase the construction sand ratio from small to large, and inject air suspension proppant in the order of first increasing and then decreasing.

[0023] ④ Displacement fluid stage: 0.0-0.2m lower than the sand addition stage. 3 Pump clean water at a construction flow rate of / min (the fluid volume is designed to be equal to the tubing volume from the wellhead to the perforation section).

[0024] The beneficial effects of this invention are:

[0025] 1. The present invention proposes an additive for surface modification of quartz sand using an additive composed of silane coupling agent, surfactant, diluent and auxiliary agent, resulting in an air suspension proppant that can generate bubbles in water. This proppant can be carried by clean water under low construction flow rate, with good suspension effect and minimizes the viscosity of fracturing fluid.

[0026] 2. The present invention uses an air-suspended proppant for fracturing, which on the one hand can reduce the net pressure inside the fracture and control the fracture height to avoid pressure-induced water leakage into the bottom layer, and on the other hand can improve the sand-laying profile to achieve effective support for the middle and upper oil layers, thereby realizing the efficient development of shallow bottom water reservoirs.

[0027] 3. The air-suspension proppant fracturing method of the present invention has been field-tested in more than 50 wells in Changqing Oilfield. Compared with conventional small-scale fracturing, the success rate of oil testing and the proportion of high-yield wells have been significantly improved. The proportion of high-yield wells in oil testing has increased by 26.1% compared with conventional small-scale hydraulic fracturing. In the initial stage of production, the daily oil production increased by 0.8t / d, and the production improvement effect was significant. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the fracturing construction curve of well A in Embodiment 1 of the present invention. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0030] Example 1

[0031] Taking well A as an example, such as Figure 1 The method of the present invention will be further explained as shown below:

[0032] Well A is located in the western exploration area of ​​Huanxian County, at the Yan 10 layer, with an oil layer thickness of 0.6m. The layer to be fractured is adjacent to a water layer. If conventional hydraulic fracturing or other stimulation techniques are used, it is easy to cause channeling and connect the water layer. Therefore, the well is fracturing using water-carrying air-suspended proppant. The specific steps are as follows:

[0033] Step 1: Prepare a preferred air suspension proppant, including a quartz sand matrix and a surface spray coating. The surface spray coating is formed by forcibly mixing a silane coupling agent, a surfactant, and appropriate diluents and additives to prepare a treatment liquid. The treatment liquid is then sprayed onto the surface of the quartz sand in a high-speed disperser and stirred for a certain period of time.

[0034] The aforementioned quartz sand matrix is ​​30 / 50 mesh quartz sand;

[0035] The mass ratio of the treatment solution to the quartz sand matrix is ​​0.5:100;

[0036] The above-mentioned treatment solution is composed of the following components by mass percentage: 10% silane coupling agent, 5% surfactant, 0.5% auxiliary agent, and the balance being diluent solvent. The sum of the mass percentages of the above components is 100%.

[0037] The silane coupling agent mentioned above is γ-(methacryloyloxy)propyltrimethoxysilane, the surfactant is octadecyltrimethylammonium chloride, the diluent is a mixture of toluene and water (volume ratio of 9:1), and the auxiliary agent is glacial acetic acid;

[0038] Step 2: Optimize the infiltration system, prioritizing clean water as the pretreatment fluid, sand-carrying fluid, and displacement fluid;

[0039] Step 3: (1) Based on the geological and logging data of the target shallow bottom water-oil layer, and considering the stimulation technology, stimulation parameters, and stimulation effects of adjacent wells, combined with the simulation results of fracturing fractures using FracproPT software, the fracturing stimulation parameters for the shallow bottom water-oil layer are optimized and determined, as shown in Table 1. The designed fracturing parameters are 30 / 50 mesh air suspension proppant 3.0m 3 The fracturing fluid volume was 43.9 m³. 3 Fracturing displacement: 0.8-1.0 m³ 3 / min, average sand ratio 10.0%, pre-fluid ratio 20.0%.

[0040] (2) Based on the proppant addition amount, sand ratio, construction discharge rate and other parameters determined in (1), the construction pumping procedure is designed. The specific construction pumping procedure is shown in Table 1:

[0041] Table 1 shows the pumping procedure for gas-suspended proppant fracturing construction in Well A.

[0042]

[0043] (3) The fracturing operation is carried out according to the design and construction pumping procedure in (2). The fracturing operation process is as follows:

[0044] ① Low-pressure and sealing stage: 0.0-0.5m 3 The construction discharge rate is 7.5m³ / min, replacing the injection of clean water. 3 (The fluid volume is designed to be 1.5m less than the tubing volume from the wellhead to the perforation section) 3 Subsequently, the displacement was increased to 0.8m³, as designed for the pre-fluidization stage. 3 / min, using 2.0m 3 Clean water is used to seal the packer seat;

[0045] ② Pre-fluidization stage: with 0.8m 3 Pumping capacity of 2.0 m³ / min. 3 Clean water (control the pre-fluid ratio to 20%)

[0046] ③ Sand-carrying fluid stage: Well A uses water to carry air-suspended proppant for fracturing. According to the designed construction pumping procedure, 30 / 50 mesh air-suspended proppant is used for sand addition throughout the process. The sand ratio is gradually increased from small to large in a wedge-shaped sand addition method, and the air-suspended proppant is injected in the order of first increasing and then decreasing.

[0047] With 0.8m 3 A construction flow rate of / min is used to add 0.3m of 30 / 50 mesh air-suspended proppant. 3 , sand ratio 5.3%, clean water volume 5.6m 3 Subsequently, the displacement was increased to 1.0m. 3 / min;

[0048] At 1.0m 3 A construction flow rate of / min is used to add 0.7m of 30 / 50 mesh air-suspended proppant. 3 , sand ratio 8.4%, clean water volume 8.3m 3 ;

[0049] With 1.0m 3 A construction flow rate of / min is used to add 1.2m of 30 / 50 mesh air suspension proppant. 3 , sand ratio 12.0%, clean water volume 10.0m 3 ;

[0050] With 1.0m 3 / min of construction flow rate plus 0.8m of 30 / 50 mesh air suspension proppant 3 , sand ratio 13.3%, clean water volume 6.0m 3 ;

[0051] ④ Displacement fluid stage: with 1.0m 3 The construction flow rate of the pump is 6.0 m³ / min. 3 Clean water (the volume of which is designed to be equal to the tubing volume from the wellhead to the perforation section).

[0052] The air-suspension proppant provided in Example 1 of this invention was tested in a field sample suspension state test. The quartz sand matrix was 30 / 50 mesh quartz sand, and the sand-to-liquid ratio (the volume ratio of the air-suspension proppant to the water) was 10% (the average sand-to-liquid ratio designed for the field test was 10.0%). When the air-suspension proppant was added to water and vigorously shaken and fully agitated, it was observed that some of the air-suspension proppant was fully suspended in the water, while some was in a flocculent semi-suspended state.

[0053] like Figure 1 As shown, the fracturing operation of Well A, extending through 10 layers, proceeded smoothly and successfully, with an operating pressure of 26.0 MPa and good proppant carrying capacity. After fracturing, the well underwent a total of 20 pumping operations, reaching a depth of 1050 m and a dynamic fluid level of 850 m, producing 31.03 t / d of oil per day, setting a new record for oil production in the area. This well employed tubing injection. After pressure breaking (after 18 minutes of curve time), as the discharge rate (blue curve) increased from 0.8 m³ to 1.0 m³ / d... 3 / min, sand concentration (black curve) increases from 100 to 200 kg / m³ 3 When water was used as the pre-fluid, sand-carrying fluid and displacement fluid throughout the process, the construction pressure (oil pressure, red curve) remained stable and the sand-addition process was relatively smooth, indicating that the air suspension proppant was well carried by water.

[0054] Example 2

[0055] The Ba B well, in its 6th formation, achieved a high oil production of 21.42 t / d during testing using this air-suspended proppant. The target formation has a depth of 1615 m and a reservoir thickness of 5.9 m. The proppant matrix is ​​40 / 70 mesh quartz sand. The surface coating consists of a treatment solution prepared by mechanical mixing of 15% silane coupling agent, 8% surfactant, 0.7% additives, and the balance being a diluent. This solution is then sprayed onto the quartz sand surface using a high-speed disperser, with the total mass percentage of the above components being 100%. In this embodiment, the mass ratio of the treatment solution to the matrix is ​​0.6:100. The silane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane, the surfactant is sodium dodecyl sulfate, the diluent is a mixture of ethanol and water (volume ratio 9:1), and the additive is formic acid. The fracturing parameters are 2.0 m of 40 / 70 mesh air-suspended proppant. 3 The fracturing fluid volume was 28.4 m³. 3 Fracturing displacement 1.0 m³ 3 The well operated smoothly and steadily, with an average sand ratio of 11.5% and a pre-flush fluid ratio of 21.0%. After fracturing, the well was pumped 20 times, reaching a depth of 1250m and a dynamic fluid level of 1100m, achieving a high daily oil production of 21.42t / d.

[0056] Example 3

[0057] The Yue C well, in its Yan 9 formation, achieved a high oil production of 11.48 t / d during the initial testing by using this air-suspended proppant. The target formation has a depth of 1595 m and a reservoir thickness of 9.2 m. The proppant matrix consists of 30 / 50 mesh and 40 / 70 mesh quartz sand. The surface coating is prepared by mechanically mixing 20% ​​silane coupling agent, 12% surfactant, 0.8% additives, and the balance being a diluent. This mixture is then sprayed onto the quartz sand surface using a high-speed disperser, with the total mass percentage of the above components being 100%. In this embodiment, the mass ratio of the treatment solution to the matrix is ​​0.8:100. The silane coupling agent is γ-chloropropyltrimethoxysilane, the surfactant is hexadecyltrimethylammonium bromide, the diluent is a mixture of methanol and water (volume ratio 9:1), and the additive is acetic acid. The fracturing parameters are 5.0 m of 40 / 70 mesh air-suspended proppant. 3 Fracturing fluid volume 60.0 m³ 3 Fracturing displacement 0.8m³ 3 The fracturing rate was 10.1% per minute, the average sand ratio was 10.1%, and the pre-flush fluid ratio was 20.1%. The fracturing operation proceeded smoothly and successfully. After fracturing, the well was pumped for a total of 24 shifts, with a pumping depth of 1500m and a dynamic fluid level of 1400m, achieving a high production of 11.48t / d of oil per day.

[0058] Example 4

[0059] The Huang D well, in its Yan 10 layer, achieved a high oil production of 10.46 t / d during the initial testing by using this air-suspended proppant. The target layer has a burial depth of 2385 m and a reservoir thickness of 7.1 m. The proppant matrix is ​​70 / 140 mesh quartz sand. The surface coating consists of a treatment fluid prepared by mechanical mixing of 25% silane coupling agent, 15% surfactant, 1.0% additive, and the balance being a diluent. This fluid is then sprayed onto the quartz sand surface in a high-speed disperser, with the total mass percentage of the components being 100%. In this embodiment, the mass ratio of the treatment fluid to the matrix is ​​1.0:100. The silane coupling agent is vinyltrimethoxysilane, the surfactant is dodecyl dimethylamine hydantoin, the diluent is a mixed solvent of methanol, ethanol, and water (volume ratio 5:4:1), and the additive is a mixed solvent of formic acid and acetic acid. The fracturing parameters are: 3.0 m³ of 70 / 140 mesh air-suspended proppant. 3 The fracturing fluid volume was 46.4 m³. 3 Fracturing displacement: 0.8-1.0 m³ 3 The fracturing rate was 10.3% per minute, the average sand ratio was 10.3%, and the pre-flush fluid ratio was 20.3%. The fracturing operation proceeded smoothly and successfully. After fracturing, the well was pumped for a total of 21 shifts, with a pumping depth of 1290m and a dynamic fluid level of 1170m, achieving a high production of 10.46t / d of oil per day.

[0060] The above examples are merely illustrative of the present invention and do not constitute a limitation on the scope of protection of the present invention. All designs that are the same as or similar to the present invention are within the scope of protection of the present invention.

Claims

1. A method for fracturing shallow bottom-water reservoirs using water-carrying air-suspended proppant, characterized in that, The specific operating steps are as follows: Step 1: Preparation of air suspension proppant; Step 2: Optimize the infiltration system by selecting clean water as the pretreatment fluid, sand-carrying fluid, and displacement fluid; Step 3: Based on the reservoir geological characteristics and oil-bearing properties, and combined with software simulation of fracture propagation, optimize parameters such as sand volume, construction discharge rate, sand ratio, and pre-flush fluid ratio. Based on the optimized parameters, design the construction pumping program and determine the fracturing construction process to form a clear water air suspension sand fracturing technology model.

2. The water-carrying air-suspended proppant fracturing method for shallow bottom-water reservoirs according to claim 1, characterized in that, The proppant in step 1 includes a quartz sand matrix and a surface spray coating; wherein the surface spray coating is formed by mechanically mixing a silane coupling agent, a surfactant, a diluent, and an additive to prepare a treatment liquid, spraying the treatment liquid onto the surface of the quartz sand in a high-speed disperser, and stirring for a certain period of time; wherein the mass ratio of the treatment liquid to the matrix is ​​0.5 to 1.0:

100. The treatment solution is composed of the following components by mass percentage: 10-25% silane coupling agent, 5-15% surfactant, 0.5-1.0% additive, and the balance being a diluent. The sum of the mass percentages of the above components is 100%.

3. The water-carrying air-suspended proppant fracturing method for shallow bottom-water reservoirs according to claim 2, characterized in that, The quartz sand matrix is ​​one or more of 30 / 50 mesh, 40 / 70 mesh, and 70 / 140 mesh quartz sand.

4. The water-carrying air-suspended proppant fracturing method for shallow bottom-water reservoirs according to claim 2, characterized in that, The silane coupling agent is one or a mixture of two or more of vinyltrimethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, γ-chloropropyltrimethoxysilane, and γ-(methacryloyloxy)propyltrimethoxysilane. The surfactant is one or a mixture of two or more of the following: dodecyl dimethylamine hydantoin, hexadecyl trimethylammonium bromide, sodium dodecyl sulfate, and octadecyl trimethylammonium chloride. The diluting solvent is one or more organic solvents such as toluene, ethanol, and methanol, mixed with water, and the volume ratio of the organic solvent to water is 9:

1. The additive is one or a mixture of two or more of glacial acetic acid, formic acid, and acetic acid.

5. The water-carrying air-suspended proppant fracturing method for shallow bottom-water reservoirs according to claim 1, characterized in that, The software mentioned in step 3 is FracproPT fracturing simulation software.

6. The water-carrying air-suspended proppant fracturing method for shallow bottom-water reservoirs according to claim 2, characterized in that, Step 3 determines the optimized parameters for fracturing operations as follows: sand volume 2.0-10.0 m³. 3 / min, construction discharge rate 0.8-1.0m 3 / min, sand ratio 10.0%-11.5%, pre-flue volume is 20%-21% of the following ratio A, the specific calculation is as follows: Proportion A=pre-liquid volume / (pre-liquid volume+sand-carrying liquid volume)×100%.

7. The water-carrying air-suspended proppant fracturing method for shallow bottom-water reservoirs according to claim 6, characterized in that, The fracturing process determined in step 3 is as follows: ① Low-pressure and sealing stage: 0.0-0.8m 3 The construction flow rate is reduced by injecting clean water at a rate of / min, and the fluid volume is designed to be 1.5m less than the tubing volume from the wellhead to the perforation section. 3 Then the discharge rate was increased to the design discharge rate of the pre-fluidization stage, and clean water was used to seal the packer. ② Pre-flushing stage: with a solution of 0.7-0.9m 3 Pump clean water at a construction flow rate of / min, and control the pre-fluid ratio at 20%; ③ Sand-carrying slurry stage: Discharge 0.8-1.0m³ according to the designed construction flow rate. 3 / min, add air suspension proppant in a wedge-shaped sand addition manner, gradually increase the construction sand ratio from small to large, and inject air suspension proppant in the order of first increasing and then decreasing; ④ Displacement fluid stage: 0.0-0.2m lower than the sand addition stage. 3 The pump injects clean water at a flow rate of / min; the fluid volume is designed to be equal to the tubing volume from the wellhead to the perforation section.

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