Carbonate reservoir fine acid fracturing process determination method

Abstract

The invention discloses a method for determining a fine acid fracturing process of a carbonate reservoir, and solves the problems in the background art that the acid fracturing effect is affected as the acid fracturing of the common carbonate reservoir cannot be selected according to the characteristics of the reservoir and the acid fracturing process. The method comprises the following steps: S1, preparing a carbonate reservoir core to be detected into a rock plate, and optimizing an acid liquid system; s11, performing comparison and optimization on etching performance parameters of the rock plate by using the acid liquor; s12, optimizing the flow guide performance of the acid liquor based on the optimized acid liquor; s2, optimizing an acid fracturing process based on the selected optimal acid liquid system; s21, determining an acidic fracturing fluid suitable for the target reservoir and a working fluid composed of an acid fluid system with determined optimal flow conductivity; and S22, based on the determined working fluid, selecting an optimal working fluid combination according to the diversion performance comparison. According to the method, the acid liquid system and the acid fracturing process can be optimized in a targeted manner, the acid fracturing success rate is effectively increased, and the acid fracturing effect is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of reservoir fracturing technology, and in particular to a method for determining the fine acid fracturing process of carbonate reservoirs. Background Technology

[0002] Carbonate reservoirs are one of the major oil and gas reservoir types, with great resource potential and broad prospects. These reservoirs are characterized by deep burial, high formation temperatures (>100℃), and numerous vertically developed strata, exhibiting various fracture-cavity systems such as solution-porosity, solution-fracture, and fracture-solution-porosity. Acid fracturing is an important measure for enhancing production in carbonate reservoirs and has been widely applied in the field. However, due to the diverse reservoir types, the rapid acid-rock reaction rate, and the difficulty in optimizing targeted acid systems and fracturing processes, a suitable approach remains. Summary of the Invention

[0003] This invention addresses the problem in the prior art where commonly used acid fracturing techniques for carbonate reservoirs cannot fully consider reservoir characteristics when selecting acid types and fracturing processes, thus affecting fracturing effectiveness. Instead, it provides a method for precisely determining the acid fracturing process for carbonate reservoirs. This method enables targeted optimization of the acid system and fracturing process, effectively improving the fracturing success rate and ensuring optimal fracturing results.

[0004] The present invention solves its problems through the following technical solution: the method for determining the fine acid fracturing process of carbonate reservoirs includes the following steps:

[0005] S1: Prepare rock plates from the core of the carbonate reservoir to be tested, and optimize the acid solution system; including the following steps:

[0006] S11: Comparison and optimization of acid etching performance parameters on rock slabs;

[0007] S12: Based on the selected acid solution, optimize the acid solution's flow conductivity;

[0008] S2: Based on the selected optimal acid solution system, the acid fracturing process is optimized; including the following steps:

[0009] S21: Determine the working fluid consisting of an acidic fracturing fluid suitable for the target reservoir and an acidic fluid system with optimal conductivity.

[0010] S22: Based on the determined working fluid, select the optimal working fluid combination according to the comparison of flow-conducting performance.

[0011] Preferably, the method for comparing and optimizing the etching performance parameters of the acid solution on the rock slab in step S11 includes the following steps:

[0012] The full-diameter core was processed into a rock slab. The processed rock slab was placed in a standard brine solution, evacuated, and saturated with standard brine. Adhesive was evenly applied to both sides to ensure that the acid solution only contacted the upper and lower surfaces of the rock slab, simulating the etching of the crack surface by the acid solution during the acid pressure process.

[0013] The rock slab was placed in an acid etching apparatus and heated to the experimental design temperature.

[0014] Different types of acid solutions are pumped in to form acid etching marks on the surface of the rock slab;

[0015] The parameters of the acid etching degree of the rock slab were determined by scanning with a 3D laser scanner.

[0016] By comparing the etching parameters formed by different types of acid solutions, 2-3 acid solutions with higher parameter values ​​are selected as preferred acid solutions for acid conductivity testing.

[0017] Preferably, the acid etching parameters of the rock slab are the maximum profile height (Ry), the average height of microscopic unevenness of the profile (Re), and the arithmetic mean deviation of the profile (Ra).

[0018] Preferably, the acid solution is a gelling acid, a crosslinking acid, or an autogenous acid.

[0019] Preferably, the rock slab is 160mm in length, 30-38mm in width, 15-20mm in thickness, and has rounded ends with a radius of 19mm.

[0020] Preferably, step S12, based on the selected acid solution, is a method for optimizing the acid solution's conductivity, comprising the following steps:

[0021] The rock core was made into a rock slab, which was then placed into a fracture conductivity tester, heated to the experimental design temperature, and the selected acid solution was injected into the flow chamber. The pressure was gradually increased, and the flow rate under different closure pressures was tested.

[0022] The flow guiding performance was calculated using the flow guiding formula, and the relationship curve between the flow guiding performance and the closing pressure was plotted.

[0023] The optimal acid solution system is selected based on the highest conductivity value.

[0024] Preferably, the acid fracturing fluid suitable for the target reservoir in step S21 is an acid fracturing fluid that is suitable for the target reservoir, can withstand high temperatures of 120 degrees Celsius, is acid-resistant, and has anti-swelling, demulsification, and drainage-aiding properties.

[0025] Preferably, the method for selecting the optimal working fluid combination in step S22 includes the following steps:

[0026] The rock slabs of the target layer are prepared, and then the rock slabs are put into the fracture conductivity tester, heated to the experimental design temperature, and different combinations of working fluids are injected into the conductivity chamber. The pressure is gradually increased, and the conductivity under different closure pressures is tested.

[0027] Plot the relationship between flow-guiding performance and closing pressure;

[0028] The optimal working fluid combination is selected based on a comparison of fluid conductivity.

[0029] Preferably, the working fluid combination is a two-stage alternation of working fluid, a three-stage alternation of working fluid, or a three-stage alternation of working fluid.

[0030] The working fluid is alternated in two stages: acidic fracturing fluid + acid + acidic fracturing fluid + acid.

[0031] The working fluid is alternated in three stages: acidic fracturing fluid + acid + acidic fracturing fluid + acid + acidic fracturing fluid + acid.

[0032] The working fluid is alternated in four stages: acidic fracturing fluid + acid + acidic fracturing fluid + acid + acidic fracturing fluid + acid + acidic fracturing fluid + acid.

[0033] Preferably, the expression for the relationship between the flow guiding performance and the closing pressure is as follows:

[0034] kW f =5.555μQ / ΔP

[0035] In the formula:

[0036] kW f —Flow capacity, unit: μm 2 ·cm;

[0037] μ—Fluid viscosity at the test temperature, unit: cP;

[0038] Q—Test displacement, unit: cm 3 / min;

[0039] ΔP—Closed pressure difference (upstream closed pressure minus downstream closed pressure), unit: kPa;

[0040] And / or,

[0041] The pressure boost range is 0-60 MPa.

[0042] Compared with the above-mentioned background technology, the present invention has the following beneficial effects:

[0043] 1. The method for determining the fine acid fracturing process of carbonate reservoirs in this invention can optimize the acid system and acid fracturing process in a targeted manner, effectively improve the success rate of acid fracturing, and ensure the acid fracturing effect.

[0044] 2. The present invention can select a suitable and targeted acid system for the target layer, so as to achieve "one layer, one solution", that is, each layer has a corresponding acid system.

[0045] 3. This invention optimizes the acid fracturing process and construction parameters to adapt to the acid fracturing process of each target layer, effectively improving the construction results. In the field application of this invention in the Mao Er Member limestone reservoir of the Sichuan-Chongqing exploration area, the acid system and the use of a three-stage alternating acid fracturing process of acidic fracturing fluid + gelling acid were optimized, resulting in a daily gas production of up to 2 million cubic meters after construction. Attached Figure Description

[0046] Figure 1 These are surface morphology characterization images of the cemented acid rock slab before and after etching, according to an embodiment of the present invention; (where: a represents before etching; b represents after etching)

[0047] Figure 2 This is a curve showing the relationship between the conductivity of the acid-etched crack and the closing pressure in an embodiment of the present invention.

[0048] Figure 3 This invention illustrates the relationship between the conductivity of a fracture etched by alternating gelling acid and fracturing fluid in a two-stage process and the closing pressure.

[0049] Figure 4 This invention illustrates the relationship between the conductivity of a fracture etched by fracturing fluid and gelling acid in a three-stage alternating process and the closing pressure.

[0050] Figure 5 This is a flowchart illustrating the method for determining the fine acid fracturing process of carbonate reservoirs according to the present invention. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0052] like Figure 5 As shown, a method for determining the fine acid fracturing process of carbonate reservoirs includes the following steps:

[0053] Step 1: Optimization of acid solution system

[0054] (11) Comparison and optimization of acid etching performance parameters on rock slabs

[0055] The full-diameter core was processed into a rock slab with a length of 160mm, a width of 30-38mm, a thickness of 15-20mm, and 19mm radius arcs at both ends. The core was then placed in a standard brine solution, evacuated, and saturated with standard brine. Adhesive was evenly applied to both sides to ensure that the acid solution only came into contact with the upper and lower surfaces of the rock slab, simulating the etching of the crack surface by the acid solution during the acid pressing process.

[0056] The rock slab was placed in an acid etching apparatus and heated to the experimental design temperature.

[0057] Different types of gelling acid, cross-linking acid, and self-generated acid are pumped in to form acid etching marks on the surface of the rock slab.

[0058] The values ​​of Ry (maximum profile height) / mm, Re (average profile unevenness height / mm), and Ra (arithmetic mean profile deviation) / mm were determined by scanning with a 3D laser scanner.

[0059] By comparing the etching parameters of different types of gelling acid, crosslinking acid, and self-generated acid, 2-3 acid systems with higher parameter values ​​are selected as preferred acid systems, and then the acid conductivity is tested.

[0060] (12) Optimization of acid conductivity: The core is made into a rock plate (the method is the same as step (11)). The rock plate is placed into the fracture conductivity tester, heated to the experimental design temperature, and the optimized acid is injected into the conductivity chamber. The pressure is gradually increased (0-60 MPa). The flow rate under different closing pressures is tested. The conductivity is calculated by the conductivity formula, and the relationship curve between conductivity and closing pressure is plotted.

[0061] The expression for the relationship between the flow guiding performance and the closing pressure is as follows:

[0062] kW f =5.555μQ / ΔP

[0063] In the formula:

[0064] kW f —Flow capacity, unit: μm 2 ·cm;

[0065] μ—Fluid viscosity at the test temperature, unit: cP;

[0066] Q—Test displacement, unit: cm 3 / min;

[0067] ΔP—Closed pressure difference (upstream closed pressure minus downstream closed pressure), unit: kPa.

[0068] The optimal acid solution system is selected based on the highest conductivity value.

[0069] Step 2, Optimization of acid frosting process

[0070] (21) Select a working fluid suitable for the target reservoir

[0071] The selected working fluids include acidic fracturing fluids suitable for the target reservoir and acid systems with optimal conductivity. The acidic fracturing fluids suitable for the target reservoir are acidic fracturing fluids that are suitable for the target layer, can withstand high temperatures of 120 degrees Celsius, are acid-resistant, and have properties such as anti-swelling, demulsification, and drainage assistance.

[0072] (22) Select the optimal working fluid combination

[0073] Prepare a rock slab for the target layer, load the rock slab into a fracture conductivity tester, heat it to the experimental design temperature, and inject two-stage (acidic fracturing fluid + acid + acidic fracturing fluid + acid), three-stage alternating, and four-stage alternating working fluid combinations into the conductivity chamber. Gradually increase the pressure (0-60 MPa) and test the conductivity under different closure pressures. Plot the conductivity performance versus closure pressure curve.

[0074] The expression for the relationship between the flow guiding performance and the closing pressure is as follows:

[0075] kW f =5.555μQ / ΔP

[0076] In the formula:

[0077] kW f —Flow capacity, unit: μm 2 ·cm;

[0078] μ—Fluid viscosity at the test temperature, unit: cP;

[0079] Q—Test displacement, unit: cm 3 / min;

[0080] ΔP—Closed pressure difference (upstream closed pressure minus downstream closed pressure), unit: kPa.

[0081] Based on the comparison of flow conductivity, the combination with the highest flow conductivity value is selected as the optimal working fluid combination.

[0082] Example 1

[0083] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings, taking the Mao Er Member limestone reservoir in the Sichuan-Chongqing exploration area as an example.

[0084] A method for determining the fine acid fracturing process of carbonate reservoirs includes the following steps:

[0085] Step 1: Optimization of acid solution system

[0086] (1) Comparison and optimization of acid etching performance parameters on rock slabs

[0087] The full-diameter core was processed into a rock slab with a length of 160mm, a width of 30mm, a thickness of 15mm, and 19mm radius arcs at both ends. It was placed in a standard brine solution, evacuated, and saturated with standard brine solution. Adhesive was evenly applied to both sides to ensure that the acid solution only came into contact with the upper and lower surfaces of the rock slab, simulating the etching of the crack surface by the acid solution during the acid pressure process.

[0088] The rock slab was placed in an acid etching instrument and heated to the formation temperature of 120°C.

[0089] Different types of gelling acids are pumped in to form acid etching marks on the surface of the rock slab;

[0090] Using a 3D laser scanner, a gelling acid system formulation with high etching parameters such as Ry2.68 / mm, Re0.7609 / mm, and Ra0.2603 / mm was selected from various gelling acid systems, including solid gelling agents, low-concentration liquid gelling agents, and high-concentration gelling acid agents. The acid system consisted of 3% liquid gelling agent + 3% high-temperature corrosion inhibitor + 1.2% composite additive.

[0091] The surface morphology characterization of the cementitious rock slab before and after etching is shown in the figure. Figure 1 .

[0092] (2) Optimal acid flow conductivity

[0093] The core was made into a rock slab (the method is the same as step (1)). The rock slab was put into a fracture conductivity tester, heated to 120 degrees, and the selected acid solution was injected into the conductivity chamber. The pressure was gradually increased (0-60 MPa). The flow rate under different closing pressures was tested, and the relationship curve between conductivity performance and closing pressure was plotted. The system has high conductivity performance.

[0094] The relationship between the conductivity of the acid-etched crack and the closing pressure is shown in the figure. Figure 2 .

[0095] Step 2: Optimization of acid frosting process

[0096] (1) Select a working fluid suitable for the target reservoir

[0097] The selected working fluids include acidic fracturing fluids suitable for the target reservoir and acid systems with optimal conductivity.

[0098] The acidic fracturing fluid suitable for the target reservoir is an acidic fracturing fluid that is suitable for the target reservoir, can withstand high temperatures of 120°C, is acid-resistant, and has properties such as anti-swelling, demulsification, and drainage assistance.

[0099] (2) Select the optimal working fluid combination

[0100] A rock slab was prepared for the target layer. The slab was then placed in a fracture conductivity tester and heated to the experimental design temperature. Alternating combinations of two-stage (acidic fracturing fluid + acid + acidic fracturing fluid + acid) and three-stage (acidic fracturing fluid + acid + acidic fracturing fluid + acid + acidic fracturing fluid + acid) working fluids were injected into the conductivity chamber. The pressure was gradually increased (0-60 MPa), and the conductivity under different closure pressures was tested. The relationship curve between conductivity and closure pressure was plotted.

[0101] (3) Alternating use of acidic fracturing fluid and gelling acid in two stages

[0102] Using a two-stage alternating process of acidic fracturing fluid and gelling acid, the initial conductivity of the rock slab was 140 D·cm, and the conductivity was 1.04 D·cm at a closure pressure of 60 MPa. The relationship between the conductivity of the acidic fracturing fluid + gelling acid alternating process and the closure pressure is shown in the figure. Figure 3 .

[0103] (4) Alternating use of acidic fracturing fluid and gelling acid in three stages.

[0104] Using a three-stage alternating process of acidic fracturing fluid and gelling acid, the initial conductivity of the rock slab was 235.61 D·cm, and the conductivity was 4.81 D·cm when the conductivity closure pressure was 60 MPa.

[0105] The relationship between the conductivity of the fracture etched by the three alternating stages of acid fracturing fluid and gelling acid and the closure pressure is shown in the figure. Figure 4 .

[0106] (5) Determine the optimal working fluid combination

[0107] By comparing the conductivity of two-stage alternating acid fracturing fluid + gelling acid and three-stage alternating acid fracturing fluid + gelling acid, the acid fracturing process was determined to be three-stage alternating acid fracturing fluid + gelling acid.

[0108] Step 3, Construction Results

[0109] After the three-stage alternating acid fracturing operation using acidic fracturing fluid and gelling acid was carried out, the daily gas production of this section reached 2 million cubic meters.

[0110] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the implementation methods of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of the present invention.

Claims

1. A method for determining a fine acid fracturing process of a carbonate reservoir, characterized in that: The method comprises the following steps: S1: making a carbonate reservoir core to be tested into a rock plate to optimize an acid liquid system; The method comprises the following steps: S11: comparing and optimizing acid liquid etching performance parameters of the rock plate; S12: optimizing acid liquid conductivity performance based on the optimized acid liquid; S2: optimizing acid fracturing technology based on the selected optimal acid liquid system; The method comprises the following steps: S21: determining an acid fracturing fluid suitable for the target reservoir and an optimal working fluid system composed of the acid liquid with optimal conductivity performance; S22: selecting an optimal working fluid combination based on the determined working fluid and the comparison of conductivity performance.

2. The method according to claim 1, wherein: The method for comparing and optimizing acid liquid etching performance parameters of the rock plate in step S11 comprises the following steps: The full-diameter core is processed into a rock plate, the processed rock plate is placed into standard brine, vacuumed and saturated with standard brine, and uniformly glued on both sides to ensure that the acid liquid only contacts the upper and lower surfaces of the rock plate, simulating the etching of the acid liquid to the surface of the fracture in the acid fracturing process; The rock plate is loaded into an acid etching instrument and heated to the designed temperature of the experiment; Different types of acid liquids are pumped to form acid etching traces on the surface of the rock plate; The acid etching degree parameters of the rock plate are determined by scanning with a three-dimensional laser scanner; The etching parameters of different types of acid liquids are compared, and 2-3 acid liquid systems with higher parameter values are selected as the optimized acid liquids for acid liquid conductivity performance testing. The acid etching degree parameters of the rock plate are the maximum profile height (Ry), the average height of the micro-unsmoothness of the profile (Re) and the profile arithmetic average deviation (Ra).

3. The method according to claim 2, wherein: The acid liquid is gelled acid, cross-linked acid and self-generating acid.

4. The method according to claim 2, wherein: The rock plate has a length of 160 mm, a width of 30-38 mm, a thickness of 15-20 mm and a radius of 19 mm at both ends.

5. The method of claim 2, wherein: The method for optimizing acid liquid conductivity performance based on the optimized acid liquid in step S12 comprises the following steps:

6. The method of claim 1, wherein: The core is processed into a rock plate, the rock plate is loaded into a fracture conductivity testing instrument, heated to the designed temperature of the experiment, the optimized acid liquid is injected into the conductivity chamber, the pressure is gradually increased, and the flow rate under different closure pressures is tested; The conductivity performance is calculated by a conductivity formula, and a conductivity performance-closure pressure relationship curve is drawn; The optimal acid liquid system is selected according to the highest value of the conductivity performance. The acid fracturing fluid suitable for the target reservoir in step S21 is an acid fracturing fluid suitable for the target layer, which is resistant to 120-degree high temperature, acid-resistant and has the properties of anti-swelling, demulsification and cleanup assistance.

7. The method of claim 1, wherein: The method for selecting the optimal working fluid combination in step S22 comprises the following steps:

8. The method of claim 1, wherein: The rock plate of the target layer is made, the rock plate is loaded into a fracture conductivity testing instrument, heated to the designed temperature of the experiment, different working fluid combinations are injected into the conductivity chamber, the pressure is gradually increased, and the conductivity under different closure pressures is tested; A conductivity performance-closure pressure relationship curve is drawn; The optimal working fluid combination is selected according to the comparison of the conductivity performance.

9. The method for determining the fine acid fracturing process of the carbonate reservoir according to claim 8, characterized in that: The working fluid combination is two-stage alternation of the working fluid, three-stage alternation of the working fluid and three-stage alternation of the working fluid; The two-stage alternation of the working fluid is acid fracturing fluid+acid liquid+acid fracturing fluid+acid liquid; ​ The working fluid three-stage alternation is acid fracturing fluid + acid + acid fracturing fluid + acid + acid fracturing fluid + acid. The working fluid four-stage alternation is acid fracturing fluid + acid + acid fracturing fluid + acid + acid fracturing fluid + acid + acid fracturing fluid + acid.

10. The method according to claim 6 or 8, characterized in that: The expression of the flow conductivity and the closure pressure relationship curve is: kW f = 5.555 μQ / ΔP In the formula, kW f Conductivity, unit: μm 2 · cm; μ is the fluid viscosity at the test temperature, in cP; Q - test volume, in cm 3 / min; ΔP is the closure pressure difference (the upstream closure pressure minus the downstream closure pressure), in KPa; And / or, The pressure boosting range is 0-60 Mpa.

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