A method of performing a liquid energy fracturing

Abstract

The application discloses a kind of liquid energy storage deflagration fracturing implementation methods, steps are as follows: first, target reservoir is pumped potassium bicarbonate solution;Then, the reservoir after injecting potassium bicarbonate solution is implemented deflagration fracturing, and the high temperature of thousands of degrees Celsius generated by deflagration makes the potassium bicarbonate solution of near wellbore zone instantaneous gasification decomposition, generates CO2 and steam to form secondary pressure superposition, while the huge pressure wave generated by deflagration drives the remaining solution that is not decomposed to flow into deep along the newly generated fracture, and continues thermal decomposition at the position away from wellbore by formation temperature;Finally, acid liquid is injected into the reservoir, and the acid liquid reacts with the alkaline substance and rock mineral remaining after deflagration, to realize deep secondary gas production and hole expansion, and generate potassium chloride to stabilize clay.The application converts the instantaneous work of deflagration into long-acting potential energy through chemical, mechanical and thermodynamic triple coupling, so that the effective length of fracture and conductivity are improved, and the application has the multiple effects of simultaneous fracture creation and collapse prevention, wettability improvement and acid-base synergy.

Description

Technical Field

[0001] This invention relates to the field of oilfield reservoir stimulation technology, and in particular to a method for implementing liquid energy storage and explosive combustion fracturing. Background Technology

[0002] The efficient development of low-permeability and ultra-low-permeability reservoirs is a key research direction for enhancing oil and gas production. Explosive fracturing technology (also known as high-energy gas fracturing technology) has become an effective reservoir stimulation method due to its low cost, simple construction, rapid effectiveness, low platform resource requirements, and lack of in-situ stress limitations. However, conventional explosive fracturing has inherent drawbacks such as short action time (milliseconds), rapid shock wave decay, and inability to generate sustained tension at the fracture tip, resulting in limited stimulation scale (fracture length typically 1-15 meters). Furthermore, the deeper the well conditions and the higher the peak pressure, the shorter the resulting fracture length and the worse the effect, making it difficult to meet the stimulation needs of deep and tight reservoirs.

[0003] To further improve the fracturing effect, the industry has developed liquid explosive combustion fracturing technology, which extends the fracture to 25-50 meters by generating a large amount of high-pressure gas (peak pressure 50-80 MPa) and prolonging the action time (up to 40-50 seconds). However, in practical applications, this technology still faces problems such as cumbersome operation procedures (requiring at least two tubing runs), easy leakage of liquid explosives or mixing with well fluid leading to reduced concentration, the risk of high-pressure falling objects during prolonged periods of time with the ignition tubing, and the transportation and storage of hazardous chemicals.

[0004] Furthermore, while conventional acidizing techniques can dissolve minerals and increase permeability, they suffer from problems such as acid inrush, limited treatment depth, and difficulty in targeting the ends of microfractures formed by deflagration. Traditional fluid-assisted fracturing, on the other hand, typically relies on continuous high-volume injection from hydraulic fracturing, failing to effectively utilize the instantaneous high energy generated by deflagration to activate chemical energy.

[0005] Domestically, a process combining deflagration fracturing and acidizing has been developed, which mainly improves the effectiveness of deflagration fracturing operations through physical fracturing and chemical erosion, but has not yet been able to further enhance the physical fracturing function of deflagration fracturing.

[0006] Therefore, there is currently a lack of reservoir stimulation technology, both domestically and internationally, that can deeply integrate the instantaneous mechanical energy and chemical energy of deflagration, and achieve the construction of deep complex fracture networks without the need for large-scale hydraulic equipment, and that is convenient, safe and reliable for construction. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a liquid-storage deflagration fracturing method. This method follows a sequence of first injecting liquid for energy storage, then deflagration to create fractures, followed by acidizing to enlarge the borehole. A specific potassium bicarbonate (KHCO3) solution is injected as the energy storage medium. The high temperature of the deflagration triggers its decomposition, converting the instantaneous energy of the deflagration into long-term potential energy. This energy is then used in subsequent acidizing to achieve acid-base synergy and fracture stabilization, ultimately achieving the goal of constructing a deep, complex fracture network and efficiently enhancing the reservoir. This method is suitable for unconventional oil and gas reservoirs, especially for enhancing production in high-temperature, water-sensitive reservoirs.

[0008] The present invention is achieved by the following technical solution.

[0009] A method for implementing liquid-storage explosive combustion fracturing includes the following steps: S1. Pre-storage fluid injection stage: Pump KHCO3 solution into the target reservoir as a pre-storage fluid; S2. Explosive fracturing stage: Explosive fracturing is carried out on the reservoir after KHCO3 solution is injected, and the high temperature generated by the explosion causes some of the KHCO3 to decompose into CO2, H2O and K2CO3. S3. Post-acidizing stage: After deflagration fracturing, acid is injected into the reservoir. The acid reacts with the K2CO3 generated in step S2 and the reservoir rock to achieve secondary pore enlargement and generate KCl.

[0010] Furthermore, in step S1, the mass concentration of the KHCO3 solution is 10% to 30%, and the injection radius into the reservoir is not less than 2 meters.

[0011] Furthermore, in step S1, before pumping the KHCO3 solution, clean water or anti-swelling fluid is injected into the target reservoir as a separator, with a separator volume of not less than 5m³. 3 This is to prevent the potassium bicarbonate solution from causing scaling damage to the formation fluids.

[0012] Furthermore, in step S2, deflagration fracturing technology is a mature reservoir stimulation technology that uses the combustion of gunpowder or propellant to generate high-temperature and high-pressure gas to fracture formations (e.g., Huang Yulin and Dai Zufeng, "Deflagration Fracturing Technology and Application" published in Volume 16, Issue 1, 1994). At the same time, oilfields combine deflagration fracturing technology with acidizing technology, which can be used for dissolution and fracture widening and deep unblocking, such as the deflagration fracturing and acidizing combined operation method disclosed in Chinese invention patent with publication number CN106246156A.

[0013] The peak pressure generated by deflagration fracturing can reach 60-120 MPa, and the instantaneous temperature can reach over 2000 degrees Celsius. The high temperature generated by deflagration not only causes the KHCO3 solution in the near-wellbore zone to vaporize and decompose instantly, but the huge pressure wave generated also pushes the undecomposed remaining solution along the newly formed fractures to the depths, where it undergoes thermal decomposition far from the wellbore, continuing to generate gas.

[0014] Furthermore, in step S3, the acid solution is one or more of hydrochloric acid, oxalic acid, formic acid, and acetic acid; the total amount of acid solution is not less than the amount of KHCO3 solution used, i.e., the treatment radius is not less than 2 meters. Simultaneously, the effective content of the acid solution can completely eliminate the influence of the alkaline salts produced by the KHCO3 solution.

[0015] Furthermore, the reservoir temperature suitable for the liquid energy storage and explosive combustion fracturing process is 100~200℃.

[0016] This application has the following beneficial effects: 1) In-situ high-temperature deflagration-induced energy enhancement and long-term conductivity improvement (energy enhancement): Utilizing the high temperature of deflagration to trigger the staged decomposition of potassium bicarbonate solution (potassium bicarbonate has a suitable decomposition temperature of 100-200℃ for reservoirs, high gas production efficiency, and does not produce other toxic gases; compared to gas-producing agents such as sodium bicarbonate, urea, and ammonium carbamate, it has advantages such as being more suitable for high-temperature reservoirs, having high gas production efficiency, being safe and controllable, and being green and non-toxic), energy is converted into energy in space and time. In the first stage, the near-wellbore solution instantly vaporizes, increasing the total amount of gas driving fracture expansion; in the second stage, pressure waves drive the remaining solution deeper into the fracture; in the third stage, the deep solution undergoes thermal decomposition due to formation temperature, continuously generating CO2. This mechanism converts the instantaneous work of deflagration into long-term potential energy, generating in-situ high-pressure gas in the formation pores, which dissolves the fracture surface, improves conductivity, and the gas pressure opens the fracture, preventing closure. The increase in peak pressure is not significant, but the effective fracture length and fracture conductivity are increased.

[0017] 2) Synergistic effect of fracture formation and chemical anti-collapse (fracture stabilization): The rapid temperature and pressure rise caused by deflagration induces microfractures in the reservoir, while potassium ions (K+) in the potassium bicarbonate solution also contribute to the formation of microfractures. + As an excellent clay anti-swelling agent, it can immediately adsorb onto clay minerals on the surface of fresh cracks, preventing their hydration and dispersion, and consolidating the crack channels formed by deflagration fracturing.

[0018] 3) Alkaline solutions alter rock wettability: The high temperature of the deflagration causes the potassium bicarbonate solution near the well to vaporize rapidly, forming an alkaline vapor cloud (containing K). + CO3 2- / HCO3 - It is easier for it to enter micropores. In addition, for oil-wet reservoirs, alkaline solutions can react with organic acids in crude oil to generate surfactants, causing the rock surface to change from oil-wet to water-wet, thereby stripping away the oil film and improving the final recovery rate.

[0019] 4) Synergistic effect of acid and alkali treatment: The post-acidification step plays two key roles on the basis of existing dissolution and fracture widening: First, it activates deep "secondary vapor generation," where the acid reacts with the residual alkali (K2CO3) after deflagration to continuously generate CO2 in the deep formation, transmitting pressure to the fracture tip; second, it eliminates alkali sensitivity and calcium scale hazards, dissolving any CaCO3 precipitates that may form and restoring permeability. Combined with existing synergistic effects, this further enhances the overall effect of deflagration fracturing. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process of the present invention; In the diagram: 1. Wellbore; 2. Reservoir section; 3. Explosive fracturing string; 4. Potassium bicarbonate injection zone; 5. Explosive fracturing fracture propagation zone; 6. Explosive fracturing fracture; 7. Acid injection zone. Detailed Implementation

[0021] The present patent application will be further described below with reference to the embodiments.

[0022] Example 1:

[0023] The liquid energy storage and explosive combustion fracturing process of this invention was implemented on a typical high-temperature (140℃), water-sensitive sandstone oil reservoir well.

[0024] Step 1: Wellbore pretreatment and pre-fluid injection All tubing and tools were retrieved from the wellbore for well cleaning and flushing. Then, the injection tubing was lowered, and 5m³ of fluid was pumped into the target reservoir. 3 Seawater was used as the isolation fluid, and then a 25% potassium bicarbonate (KHCO3) solution was pumped in at a stable flow rate of 20m³. 3 Ensure the solution treatment radius is 2 meters. After pumping is complete, remove the injection tubing.

[0025] Step 2: Deflagration Fracturing Run the deflagration fracturing string 3 and position the deflagration fracturing tool string in the perforated section. Ignite to initiate deflagration fracturing, which instantly generates a peak pressure of approximately 100 MPa and a temperature of 2000°C. At this high temperature, some of the KHCO3 solution in the near-wellbore zone (within approximately 2 meters) undergoes instantaneous thermal decomposition, generating a large amount of CO2 and water vapor, which are added to the deflagration gas, enhancing the initial impact energy. Simultaneously, the enormous pressure wave drives the remaining undecomposed KHCO3 solution in the wellbore and near-wellbore zone to surge deeper along the multiple radial fractures newly formed by the deflagration at extremely high speed.

[0026] Step 3: Post-acidification After the deflagration fracturing was completed, 15m³ each of hydrochloric acid (12% HCl) and terrine (12% HCl + 3% HF) were injected into the reservoir using deflagration fracturing string 3. 3The acid first neutralizes the residual alkaline solution (K₂CO₃) remaining in the pore throat after the deflagration, generating a large amount of CO₂ and achieving deep "secondary vaporization," which transmits pressure to the fracture tip. Simultaneously, the acid dissolves any CaCO₃ precipitate that might form under alkaline conditions and non-uniformly etches the fracture wall, creating highly conductive acid-etched channels. The KCl generated in the reaction adsorbs onto clay minerals on the surface of the new fracture, providing long-term anti-swelling protection.

[0027] Step 4: Production After the acidizing operation is completed, the residual fluid should be drained back in a timely manner. After the wellhead pressure drops to zero, the production tubing should be run in to start production.

[0028] Example 2:

[0029] The liquid energy storage and explosive combustion fracturing process of this invention was implemented on a high-temperature (160°C) carbonate oil reservoir well.

[0030] Unlike Example 1, due to the strong heterogeneity of the carbonate reservoir and the absence of water-sensitive clay, the concentration of the potassium bicarbonate solution pumped in step 1 was adjusted to 15%, solely to enhance its energy storage and wettability alteration capabilities. In step 3, a slow-moving gelling acid of 20m³ was selected as the acid solution. 3 This increases the acid etching distance. The other steps are the same as in Example 1.

[0031] The concentration of the potassium bicarbonate solution in this invention can be adjusted according to the specific reservoir temperature, mineral composition, and porosity; the deflagration fracturing method can be solid propellant delivered by cable or liquid propellant delivered by tubing; the type and formulation of acid for post-acidification should be optimized according to the reservoir lithology.

[0032] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for implementing liquid-storage explosive combustion fracturing, characterized in that, Includes the following steps: S1. Pre-storage fluid injection stage: Pump KHCO3 solution into the target reservoir as a pre-storage fluid; S2. Explosive fracturing stage: Explosive fracturing is carried out on the reservoir after KHCO3 solution is injected, and the high temperature generated by the explosion causes some of the KHCO3 to decompose into CO2, H2O and K2CO3. S3. Post-acidizing stage: After deflagration fracturing, acid is injected into the reservoir. The acid reacts with the K2CO3 generated in step S2 and the reservoir rock to achieve secondary pore enlargement and generate KCl.

2. The method for implementing liquid energy storage and explosive combustion fracturing according to claim 1, characterized in that, In step S1, the mass concentration of the KHCO3 solution is 10% to 30%, and the injection radius into the reservoir is not less than 2 meters.

3. The method for implementing liquid energy storage deflagration fracturing according to claim 1, characterized in that, In step S1, before pumping the KHCO3 solution, clean water or anti-swelling fluid is injected into the target reservoir as a separating fluid.

4. The method for implementing liquid energy storage deflagration fracturing according to claim 1, characterized in that, In step S2, the peak pressure generated by the deflagration fracturing reaches 60~120MPa, and the instantaneous temperature reaches over 2000 degrees Celsius.

5. The method for implementing liquid energy storage deflagration fracturing according to claim 1, characterized in that, In step S3, the acid solution is one or more of hydrochloric acid, oxalic acid, formic acid, and acetic acid.

6. The method for implementing liquid energy storage deflagration fracturing according to claim 1, characterized in that, The liquid energy storage and explosive combustion fracturing process is suitable for reservoir temperatures of 100~200℃.

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