A carbon dioxide gas energized fracturing method

Abstract

The application provides a carbon dioxide gas energized fracturing method, and relates to the technical field of oil and gas field development, and comprises the following steps: S1, injecting supercritical state carbon dioxide gas into a tight sandstone reservoir; S2, adjusting the pressure of the injected carbon dioxide, improving the pressure of the formation, and promoting the expansion of the original fracture and the formation of a new fracture; S3, adjusting the pressure of the injected carbon dioxide, and after the formation of the new fracture, pressure recovery is carried out, and the carbon dioxide gas is replaced out of the tight sandstone gas in the expanded original fracture and the new fracture; S4, after the tight sandstone gas energized fracturing and recovery, the injection of the carbon dioxide gas into the tight sandstone reservoir is stopped, and the carbon dioxide gas is partially sealed in the pores and fractures of the tight sandstone gas reservoir. The application has the beneficial effects that the release and flow of the tight sandstone gas are promoted, the natural gas production cycle is prolonged, the production capacity of the natural gas reservoir is maintained, and the recovery rate of the sandstone gas is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas field development, and particularly relates to a carbon dioxide gas energy-increasing fracturing method. BACKGROUND

[0002] Tight sandstone gas is a main type of unconventional natural gas. Due to poor physical properties of the tight sandstone gas reservoir, the overall characteristics are "four lows, two highs and one strong", that is, low porosity, low permeability, low reserve abundance, low single-well natural production, high water saturation, high development cost and strong reservoir heterogeneity. These characteristics make the recovery rate of the tight sandstone gas much lower than that of conventional gas reservoirs, and the recovery rate technology needs to be urgently improved. The traditional water-based fracturing fluid has problems of incomplete gel breaking, incomplete flowback and large amount of retention in the formation, and causes serious damage to the formation. Therefore, the traditional fracturing technology cannot effectively improve the recovery rate, and the existing technology needs to be improved.

[0003] Meanwhile, as a greenhouse gas, the emission of carbon dioxide is increasingly valued. Carbon dioxide geological storage is an important technical means for reducing carbon dioxide emission. The technology refers to capturing carbon dioxide that is originally discharged into the atmosphere, injecting the treated carbon dioxide into underground geological structures, and storing the carbon dioxide in the geological body through a series of rock physical binding, dissolution and mineralization. The technology can realize the increase of oil and gas resources while storing carbon dioxide, and can realize the unity of economic benefits and environmental benefits. SUMMARY

[0004] Therefore, in order to solve the problems of incomplete gel breaking, incomplete flowback and large amount of retention in the formation of the traditional water-based fracturing fluid, the embodiments of the present application provide a carbon dioxide gas energy-increasing fracturing method.

[0005] The embodiments of the present application provide a carbon dioxide gas energy-increasing fracturing method, which comprises the following steps:

[0006] S1, injecting supercritical state carbon dioxide gas into a tight sandstone reservoir;

[0007] S2, adjusting the pressure of the injected carbon dioxide to improve the pressure of the formation, and promoting the expansion of the original fracture and the formation of a new fracture;

[0008] S3, adjusting the pressure of the injected carbon dioxide, using the expansion characteristics of the carbon dioxide gas to restore the pressure after the formation of the new fracture, enhancing the effective pressure of the tight sandstone reservoir, and displacing the tight sandstone gas in the expanded original fracture and the new fracture by the carbon dioxide gas;

[0009] S4, stopping injecting carbon dioxide gas into the tight sandstone reservoir after the enhanced fracture and recovery of the tight sandstone gas, so that the carbon dioxide gas is partially sealed in the pores and fractures of the tight sandstone gas reservoir.

[0010] Further, the step S3 further comprises reducing the influence of residual water in the tight sandstone reservoir by the flushing and displacement of the carbon dioxide gas, and reducing the water resistance effect.

[0011] Further, the pressure of the supercritical state carbon dioxide gas is greater than 7.38 MPa, and the temperature is greater than 31.1℃.

[0012] Further, in the step S2, the pressure of the supercritical state carbon dioxide gas injected when the original fractures are expanded and the new fractures are formed is greater than the formation pressure.

[0013] Further, in the step S3, the tight sandstone gas is CH4.

[0014] Further, in the steps S1, S2 and S3, the injection amount and pressure of the supercritical state carbon dioxide gas are obtained under laboratory conditions.

[0015] Further, in the steps S1, S2 and S3, the injection amount and pressure of the supercritical state carbon dioxide gas are obtained according to the following method:

[0016] S100, preparing a representative tight sandstone sample, the tight sandstone sample being consistent with the physical properties of the tight sandstone reservoir;

[0017] S200, placing the tight sandstone sample into a container that can simulate the underground conditions of the tight sandstone reservoir;

[0018] S300, respectively controlling the pressure and water content in the tight sandstone sample, gradually injecting different amounts of supercritical state carbon dioxide into the tight sandstone sample, and monitoring the changes in carbon dioxide pressure and fluid flow;

[0019] S400, evaluating the gas recovery rate: by measuring the change in gas volume before and after injecting carbon dioxide into the tight sandstone sample to evaluate the recovery rate of the gas;

[0020] S400, evaluating the gas recovery rate: by measuring the change in gas volume before and after injecting carbon dioxide into the tight sandstone sample to evaluate the recovery rate of the gas;

[0021] S500, evaluating the carbon dioxide storage efficiency: by monitoring the difference between the amount of injected carbon dioxide and the original amount of carbon dioxide in the tight sandstone sample to evaluate the storage efficiency;

[0022] S600, analyzing the monitoring experimental data to determine the relationship between the carbon dioxide injection amount, pressure, and gas recovery rate and storage efficiency under different conditions.

[0023] Further, the physical properties include porosity and permeability.

[0024] Further, the container is an autoclave.

[0025] The technical scheme provided by the embodiment of the present application has the following beneficial effects:

[0026] 1. The carbon dioxide gas energy-increasing fracturing method of the present application first injects supercritical carbon dioxide gas into the tight sandstone reservoir, uses the physical properties of low viscosity and high diffusivity of the supercritical carbon dioxide gas to make it permeate into the micro cracks, expand the original cracks, form new cracks, and thus form a complex fracture network, increase the channel for gas flow, and thus improve the gas recovery rate; then uses the expansion property of the carbon dioxide gas to enhance the effective pressure of the tight sandstone reservoir after the formation of the fracture network, further promote the release and flow of the tight sandstone gas, prolong the natural gas production cycle, maintain the production capacity of the natural gas reservoir, and thus improve the recovery rate of the sandstone gas.

[0027] 2. The carbon dioxide gas energy-increasing fracturing method of the present application, after the injection of carbon dioxide, adsorbs on the rock surface or dissolves in the formation water due to the adsorption and dissolution effect, helps long-term geological storage of carbon dioxide, can improve the gas reservoir sealing property, prevent gas leakage, and prolong the production cycle; at the same time, the stored carbon dioxide can reduce the emission of greenhouse gases and has good environmental benefits.

[0028] 3. The carbon dioxide gas energy-increasing fracturing method of the present application, the viscosity of carbon dioxide is lower than that of water, so it can flow more easily in the pores, and under the same conditions, it is not easy to form water lock at the pore throat, compared with the traditional water-based fracturing fluid, carbon dioxide gas reduces the damage to the reservoir and avoids the water lock effect, and further improves the gas recovery rate. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a working schematic diagram of the carbon dioxide gas energy-increasing fracturing method of the present application;

[0030] Figure 2 is a working principle diagram of the carbon dioxide gas energy-increasing fracturing method of the present application. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the present application clearer, the following will further describe the embodiments of the present application in combination with the drawings. The following introduces a relatively preferred one of the multiple possible embodiments of the present application, which is intended to provide a basic understanding of the present application, but is not intended to identify the key or decisive elements or limit the scope of protection.

[0032] In all of the examples shown and discussed herein, any specific values should be interpreted as merely exemplary, and not as a limitation. Thus, other examples of the exemplary embodiments can have different values.

[0033] Techniques, methods, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail herein. However, where appropriate, such techniques, methods, and apparatus should be considered as part of the present disclosure.

[0034] It should be noted that like reference numerals and letters refer to like items throughout the attached drawings, and once an item is defined in one drawing, it should not require further discussion in subsequent drawings. It is to be understood that the drawings are shown by way of example and are not to be construed as limiting the application.

[0035] It should be noted that, unless otherwise explicitly specified and limited, the terms "mounting", "connecting" should be interpreted broadly, for example, can be fixed connection, can also be detachable connection, or integral connection; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through intermediate medium, can be internal communication of two elements. For those of ordinary skill in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0036] Please refer to Figure 1 and 2 The embodiments of the present application provide a carbon dioxide gas energized fracturing method, which can improve the recovery of low-pressure water-containing compact sandstone gas and effectively store carbon dioxide, and specifically comprises the following steps:

[0037] S1. Injecting supercritical state carbon dioxide gas into the compact sandstone reservoir.

[0038] The supercritical state carbon dioxide gas generally has a pressure greater than 7.38 MPa and a temperature greater than 31.1℃. The supercritical state carbon dioxide gas is injected into the compact sandstone gas reservoir, and its physical and chemical properties are used to penetrate into the microcracks in the reservoir under high pressure. The supercritical state carbon dioxide gas has special physical properties such as low viscosity and high diffusivity, and can penetrate into the cracks in the compact sandstone reservoir.

[0039] S2. Adjusting the pressure of the injected carbon dioxide to increase the pressure of the formation, and promoting the expansion of the original cracks and the formation of new cracks.

[0040] The pressure of the injected carbon dioxide is adjusted to be greater than the formation pressure when the primary fractures are expanded and new fractures are formed. The injected carbon dioxide gas increases the pressure of the formation, and the expansion effect of the carbon dioxide gas promotes the expansion of the fractures, not only permeating into the primary fractures to expand the primary fractures, but also forming new fractures in the tight sandstone reservoir to form a complex fracture network, thereby increasing the flow path of the gas and the recovery rate.

[0041] S3, adjusting the pressure of the injected carbon dioxide, using the expansion characteristics of the carbon dioxide gas to restore the pressure after the formation of the new fractures, enhancing the effective pressure of the tight sandstone reservoir, and the carbon dioxide gas displacing the tight sandstone gas in the expanded primary fractures and the new fractures.

[0042] Using the expansion characteristics of the carbon dioxide gas, the pressure is restored after the fractures are expanded to form a complex fracture network, the effective pressure of the reservoir is enhanced, and the release and flow of the tight sandstone gas are further promoted.

[0043] The tight sandstone gas is CH4. In the tight sandstone gas reservoir, the percolation of the fluid in the sandstone micropores is different from that in the conventional reservoir. When CO2 is injected into the tight pores of the sandstone, the interaction between CO2 and CH4 makes the percolation mechanism more complex. Studies have shown that when CO2 is present, CO2 can displace about half of the CH4, and after competitive adsorption, the total adsorption amount of CO2 is greater than that of CH4, so the injection of CO2 can promote the desorption of CH4, thereby improving the recovery rate of the sandstone gas.

[0044] And the flushing and displacement effect of the carbon dioxide gas can also reduce the influence of residual water in the tight sandstone reservoir and reduce the water resistance effect. The viscosity of carbon dioxide is lower than that of water, so it can flow more easily in the pores. Under the same conditions, it is not easy to form water lock at the pore throat, compared with the traditional water-based fracturing fluid, the carbon dioxide gas reduces the damage to the reservoir and avoids the water lock effect, further improving the gas recovery rate.

[0045] S4, stopping the injection of carbon dioxide gas into the tight sandstone reservoir after the enhanced fracturing and recovery of the tight sandstone gas, so that part of the carbon dioxide gas is sealed in the pores and fractures of the tight sandstone gas reservoir.

[0046] After the gas enhanced fracturing and recovery, part of the injected carbon dioxide is sealed in the pores and fractures of the tight sandstone gas reservoir, forming a long-term stable carbon sequestration effect. Part of the carbon dioxide is adsorbed on the surface of the rock, and part of the carbon dioxide is dissolved in the formation water. These effects can improve the sealing of the gas reservoir and achieve long-term carbon sequestration. At the same time, the sequestration of carbon dioxide can reduce the emission of greenhouse gases and has good environmental benefits.

[0047] It should be noted that the injection conditions of the supercritical state carbon dioxide gas in the steps S1, S2 and S3 need to be adjusted according to the actual situation of the tight sandstone reservoir to achieve the effect of promoting the diffusion and gas replacement of carbon dioxide, and to achieve the purpose of high yield of natural gas.

[0048] The injection amount and pressure of the supercritical state carbon dioxide gas in the steps S1, S2 and S3 can be obtained under laboratory conditions, and the specific method is as follows:

[0049] S100, a representative tight sandstone sample is prepared, which is consistent with the physical properties of the tight sandstone reservoir. The physical properties include porosity and permeability.

[0050] S200, the tight sandstone sample is placed in a container that can simulate the underground conditions of the tight sandstone reservoir. The container can be selected as an autoclave to simulate the underground conditions, including temperature, pressure and fluid flow.

[0051] S300, the pressure and water content in the tight sandstone sample are controlled respectively, different amounts of supercritical state carbon dioxide are injected into the tight sandstone sample, and the changes of carbon dioxide pressure and fluid flow are monitored;

[0052] S400, evaluate the gas recovery rate: by measuring the volume of carbon dioxide injected into the tight sandstone sample

[0053] The change of the volume of the gas before and after the gas is evaluated. The tight sandstone sample is subjected to decompression treatment to release the adsorbed gas, and the amount of released gas is measured, so that the gas recovery rate can be calculated.

[0054] S500, evaluate the carbon dioxide storage efficiency: by monitoring the difference between the amount of injected carbon dioxide and the original amount of carbon dioxide in the tight sandstone sample to evaluate the storage efficiency. Gas analysis technology is used to determine the amount of carbon dioxide that is not stored, so that the carbon dioxide storage efficiency can be calculated.

[0055] S600, analyze the monitoring experimental data to determine the relationship between the carbon dioxide injection amount, pressure and gas recovery rate and storage efficiency under different conditions. Statistical and mathematical models are used to analyze the experimental data to determine the relationship between the carbon dioxide injection amount and the gas recovery rate and storage efficiency under different conditions, so that the injection conditions of the supercritical state carbon dioxide gas for the actual tight sandstone reservoir stimulation fracturing can be selected.

[0056] Under the conditions of proper pressure and water content, the injection amount of carbon dioxide gas has certain relationship with the gas recovery and the storage efficiency, and the control of the pressure, the water content, the injection amount of carbon dioxide gas and the like can improve the gas recovery and the storage efficiency of carbon dioxide gas to a certain extent.

[0057] The carbon dioxide gas energy increasing fracturing method has been applied to a gas field, and the physical properties of a tight sandstone reservoir of the gas field are as follows: the depth of the gas layer is 3370m, the thickness of the producing gas layer+the gas containing layer is 8.4m, the average porosity is 9.5%, the average permeability is 2.7mD, the average gas saturation is 67.7%, the average movable water saturation is 14.1%, the argillaceous content is 9.2%, the predicted formation pressure is 28.6MPa, and the reservoir temperature is 110.4℃. The specific implementation steps are as follows: (1) through high temperature and high pressure experiments, the influence law of different temperature confining pressures and pore pressures on the elastic modulus, the compressive strength, the Poisson's ratio and the brittleness index of the tight sandstone is tested, and the key coefficients such as the fracturing pressure of the area (the fracturing pressure of the area is 24MPa) are determined; (2) supercritical state carbon dioxide gas (the pressure is greater than 7.38MPa, and the temperature is greater than 31.1℃) is injected into the reservoir; (3) the pressure is adjusted to be greater than the tested cracking pressure (that is, greater than 24MPa), so that the crack expansion and the new crack formation are realized; (4) after the formation pressure state is restored to be stable (at this time, the pressure is 35MPa), the injection of the carbon dioxide is stopped, at this time, the replacement of the tight sandstone gas and the partial storage of the carbon dioxide can be realized. The highest gas production after the field pressure is 2.4x104m 3 / d, and the gas production at the end of the first year still maintains about 1.0x104m 3 / d, and good yield increasing and stable production effects are obtained.

[0058] The field test shows that the method reduces the water consumption by 80% compared with the water-based fracturing, and the reverse flow rate after fracturing is 50~70%, and the application results show that the method greatly reduces the water consumption, realizes the environmental protection benefit, and saves the water resources; at the same time, the reverse flow rate is 10 percentage points higher, and the effect is remarkable.

[0059] In addition, the embodiments of the present application also verify the carbon dioxide gas energy increasing fracturing method by indoor experimental devices, and the specific steps are as follows:

[0060] The highest temperature of the fracturing experiment currently used is 300 DEG C, and the maximum applied stress is 52.5 MPa. Through certain indoor experimental devices, the role of the technology in realizing gas recovery and carbon dioxide geological storage can be felt. The indoor experiment is carried out under the condition that the confining pressure is 38 MPa and the temperature is 85 DEG C. The experiment selects the tight sandstone core of Sugeli gas field. The experiment uses rock triaxial testing device and carbon dioxide pressure increasing device to realize monitoring of carbon dioxide injection pressure and stress of rock after carbon dioxide injection in the experiment. The specific experimental steps are as follows: (1) adjust the confining pressure and temperature to the condition value (confining pressure 38 MPa, temperature 85 DEG C) through the experimental device; (2) liquid carbon dioxide is converted into supercritical state (pressure greater than 7.38 MPa, temperature greater than 31.1 DEG C) through the pressure increasing device, and is injected into the core; (3) continuously increase the injection pressure to reach the set pore pressure value; (4) stop injection until the core is damaged; (5) in this stage, collect stress-strain data and obtain stress-strain curve through detection software. Through the experiment, it is found that the brittleness index of the tight sandstone increases first and then decreases with the increase of the injection pressure, which shows that after the early carbon dioxide fully contacts with the tight sandstone, the brittleness of the tight sandstone can be strengthened, the rock brittleness is strengthened, the rock is prone to breakage, the original pore expansion and new fracture formation are realized, new channels for the flow of tight sandstone gas are established, and space for carbon dioxide storage is provided, which shows that the method is feasible in the application of the tight sandstone reservoir, and the expected effect can be achieved.

[0061] In this article, the front, back, up, down and other orientation words are defined by the position of the parts in the drawing and the position of the parts relative to each other in the drawing, just to express the technical solution clearly and conveniently. It should be understood that they are relative concepts, which can be changed accordingly according to different ways of use and placement, and the use of the orientation words should not limit the scope of the application.

[0062] In the case of no conflict, the above-mentioned embodiments and features in the embodiments can be combined with each other. The above-mentioned only for the preferred embodiments of the present application, and does not limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application, should be included in the protection scope of the present application.

Claims

1. A carbon dioxide gas-enhanced fracturing method, characterized in that, Includes the following steps: S1. Injecting supercritical carbon dioxide gas into tight sandstone reservoirs; S2. Adjust the pressure of the injected carbon dioxide to increase the formation pressure, promote the expansion of primary fractures and the formation of new fractures; S3. Adjust the pressure of the injected carbon dioxide and utilize the expansion characteristics of carbon dioxide gas to restore the pressure after the formation of new fractures, thereby enhancing the effective pressure of the tight sandstone reservoir. The carbon dioxide gas displaces the tight sandstone gas in the expanded primary fractures and new fractures. S4. After the tight sandstone gas is enhanced by fracturing and harvesting, stop injecting carbon dioxide gas into the tight sandstone reservoir so that part of the carbon dioxide gas is sealed in the pores and fractures of the tight sandstone gas reservoir. The injection volume and pressure of supercritical carbon dioxide gas in steps S1, S2 and S3 were obtained by simulation under laboratory conditions. The injection volume and pressure of supercritical carbon dioxide gas in steps S1, S2, and S3 are obtained as follows: S100. Prepare representative tight sandstone samples with physical properties consistent with tight sandstone reservoirs. S200. Place the tight sandstone sample into a container that can simulate the underground conditions of a tight sandstone reservoir. S300: Control the pressure and water content inside the dense sandstone sample respectively, and gradually inject different amounts of supercritical carbon dioxide into the dense sandstone sample, while monitoring the changes in carbon dioxide pressure and fluid flow. S400, Assessing Gas Recovery: Measuring the Injection of Carbon Dioxide into Tight Sandstone Samples The gas recovery rate is assessed by the change in gas volume before and after the process. S500. Evaluate carbon dioxide sequestration efficiency: Efficiency is evaluated by monitoring the difference between the amount of carbon dioxide injected and the amount of carbon dioxide originally present in the dense sandstone sample. S600: Analyze the monitoring experimental data to determine the relationship between carbon dioxide injection volume, pressure, gas recovery rate, and storage efficiency under different conditions.

2. The carbon dioxide gas-enhanced fracturing method as described in claim 1, characterized in that: Step S3 further includes reducing the influence of residual water in tight sandstone reservoirs and reducing the water resistance effect through the flushing and displacement effect of carbon dioxide gas.

3. The carbon dioxide gas-enhanced fracturing method as described in claim 1, characterized in that: The pressure of supercritical carbon dioxide gas is greater than 7.38 MPa and the temperature is greater than 31.1 °C.

4. The carbon dioxide gas-enhanced fracturing method as described in claim 1, characterized in that: In step S2, the pressure of the supercritical carbon dioxide gas injected during the expansion of the primary fracture and the formation of new fractures is greater than the formation pressure.

5. The carbon dioxide gas-enhanced fracturing method as described in claim 1, characterized in that: In step S3, the tight sandstone gas is CH4.

6. The carbon dioxide gas-enhanced fracturing method as described in claim 1, characterized in that: The physical properties include porosity and permeability.

7. The carbon dioxide gas-enhanced fracturing method as described in claim 1, characterized in that: The container is a high-pressure autoclave.

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