Shale oil carbon dioxide huff and puff development method and system based on underground nuclear radiation
By generating carbon dioxide in an underground nuclear radiation device, the problems of small storage space and poor fluidity of shale oil have been solved, achieving a high recovery rate without the need for external carbon dioxide injection and reducing costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- PETROCHINA CO LTD
- Filing Date
- 2022-06-30
- Publication Date
- 2026-06-30
AI Technical Summary
In existing technologies, shale oil has small storage space, poor crude oil liquidity, and low recovery rate. Traditional development methods are inefficient, and gas injection huff and puff methods have the problem of high gas source costs.
By generating carbon dioxide in situ under the action of an underground nuclear radiation device, and controlling the pressure using a downhole pressure monitoring device, shale oil can be cracked in situ to generate carbon dioxide, thereby reducing crude oil viscosity and increasing recovery rate.
It achieves an economical and effective increase in shale oil recovery rate, a reduction in crude oil viscosity, and an increase in reservoir development momentum without the need for external carbon dioxide injection.
Smart Images
Figure CN117365410B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of petroleum exploration technology, and in particular to a method and system for developing carbon dioxide huff and puff of shale oil based on underground nuclear radiation. Background Technology
[0002] Unconventional shale oil resources are abundant and will become an important type of unconventional petroleum. Organic-rich mudstone and shale strata are widely developed in Mesozoic and Cenozoic sedimentary basins, but the exploration and development of shale oil is relatively low. One important reason is that shale oil has small reservoir space, poor crude oil mobility, and low recovery rate. Traditional development methods, such as depletion-based quasi-natural production development, only achieve a recovery rate of 5-8%. Overall, shale oil development faces the challenge of low effective exploitability and urgently needs to develop technologies to improve recovery rates in the mid-to-late stage of supplemental energy development.
[0003] Currently, enhanced oil recovery (EOR) technologies in the mid-to-late stage of supplemental energy development include two main methods: water injection and gas injection displacement, and water injection / gas injection huff and puff. In shale and tight reservoirs, gas injection is the preferred extraction method due to the ultra-low permeability and high injection rate of gas; displacement or huff and puff methods can also be used. However, due to the ultra-low permeability of the matrix, pressure drops mostly occur near the injection well, and it generally takes a long time for injected gas to displace oil into the production well. Therefore, the displacement method loses its previous advantages. Conversely, in the huff and puff method, injection and production occur in the same well. During injection, the pressure near the well increases rapidly, and fluids (gas, oil, and water) can be produced quickly after the well enters production mode. The advantage of injection is that it yields quick returns, and the injection-well-production process can be repeated (multiple rounds). This advantage can last for a long time, making the huff and puff method the preferred method, which can employ various media such as water injection huff and puff, and gas injection huff and puff.
[0004] The traditional gas injection huff and puff extraction mechanism mainly involves two aspects: replenishing formation energy and, because the injected gas can dissolve in crude oil, reducing its viscosity and increasing its oil saturation. Pressure changes can be clearly observed in large-scale physical model experiments of CO2 injection huff and puff. The gas injection process is called "huffing," where the injected gas first enters the large fractures, causing a rapid increase in pressure within the fractures, while the matrix pressure changes slowly. When gas injection stops, the well enters a shut-in phase, where the pressure in the fractures slowly diffuses outwards, albeit at a slow rate. After shut-in, production begins, and the fluid in the fractures is extracted first, causing a rapid decrease in pressure and fracture closure. Then, the pressure in the matrix gradually decreases. The CO2 huff and puff backflow process requires control of the pressure drop rate. Currently, CO2 is the primary injection medium in field tests conducted both domestically and internationally. The Bakken Formation in the Burning Tree-State oil field in the Montana region is a tight oil-type shale oil. In early 2009, Hoffman and Evans conducted CO2 injection and huff-and-puff operations on well 36-2H. This horizontal well employed a one-stage hydraulic fracturing method to enhance production, injecting approximately 45 million cubic feet (2,570 tons) of CO2 into the well over 45 days, followed by a 64-day shutdown period. From January to March 2010, oil production gradually increased, reaching a peak of 44 barrels per day in March 2010 (higher than the previous 14 months before the injection and huff-and-puff test). In the An83 well area of the Ordos Basin, a tight oil-type shale oil field in China, CO2 injection and huff-and-puff were also implemented. In 2016, one directional well and two horizontal wells in the Chang 7 reservoir of the An83 area of the Xin'anbian Oilfield were deployed for CO2 huff-and-puff testing. Currently, the first round of huff-and-puff testing has been completed for one directional well and one horizontal well in the An83 area. Among them, the directional well (An237-25) test showed significant effects in adjacent wells, with 9 wells showing effectiveness, representing a 47% effectiveness rate. The effectiveness period was 14-35 days, with an average daily oil increase of 0.7t per well and a cumulative increase of 290.8t. The water cut reduction effect in medium-to-high water-cut wells was particularly outstanding, with an overall water cut reduction of 20% in the effective wells. The salinity of the effective wells increased, expanding the swept volume. Overall, carbon dioxide huff and puff can effectively replenish energy and reduce viscosity in shale oil, significantly increasing production.
[0005] In current domestic and international indoor theoretical and field experimental research, gas injection huff and puff is a promising method for enhancing the recovery rate of shale oil reservoirs. Commonly used injection gases include CO2, natural gas, and nitrogen. Among these, CO2 has advantages over other gases, such as better solubility in crude oil, a larger expansion coefficient, better viscosity reduction effect, and lower miscibility pressure. Traditional CO2 huff and puff for enhanced oil recovery mainly includes three steps: injection, well shut-in, and oil production. Figures 1a-1c ):
[0006] ① Injection Stage: Production wells cease oil production, and gas is injected into the huff and puff wells. In the initial stage of gas injection, the injected gas flows into the formation through artificial and natural fractures, causing a rapid increase in fracture pressure. Under the pressure difference between the fractures and the matrix system, the injected gas gradually enters the matrix. (e.g.) Figure 1a (As shown)
[0007] ② Well Shutdown Stage: After stopping gas injection, the well is shut in for a period of time. After shutting in, the injected gas gradually seeps into the matrix crude oil from the fractures under the influence of pressure differential, and continues to expand its reach to distant areas through diffusion. The dissolution of the gas increases pressure and replenishes formation energy, while simultaneously promoting crude oil volume expansion and reducing viscosity, making the crude oil more flowable. (e.g.) Figure 1b (As shown)
[0008] ③ Oil Production Stage: The huff and puff well is opened, and oil production begins. Crude oil flows from the matrix into the fractures and from the fractures into the wellbore through pressure differential; the pressure reduction also causes dissolved gases in the oil to expand, forming dissolved gas drive, effectively increasing production. (e.g.) Figure 1c (As shown)
[0009] On the other hand, the main sources of gas for conventional CO2 injection huff and puff are purchasing CO2 gas and exploiting CO2 gas reservoirs. The cost of purchasing / exploiting, transporting, and storing CO2 gas is relatively high compared to other gases, which has become a major challenge for achieving profitable development of shale oil reservoirs through CO2 injection huff and puff. Summary of the Invention
[0010] The purpose of this invention is to provide a method and system for the carbon dioxide huff and puff development of shale oil based on underground nuclear radiation, which induces the direct generation of CO2 inside the reservoir without the need for external CO2 injection, thereby achieving the goal of "injecting" gas to replenish energy in shale oil reservoirs, improving recovery rate, and realizing efficient development.
[0011] To achieve the above objectives, the present invention provides the following technical solution:
[0012] A method for developing shale oil using carbon dioxide huff and puff based on underground nuclear radiation, the method comprising:
[0013] The nuclear radiation device and downhole pressure monitoring device were connected and fixed to the coiled tubing and lowered into the horizontal wellbore.
[0014] The nuclear radiation device is activated, and a predetermined time and radiation intensity are set to cause the shale oil to crack in situ and generate carbon dioxide.
[0015] After the shale oil is cracked in situ to generate carbon dioxide, the nuclear radiation device is shut down. The downhole pressure monitoring device is used to determine whether the fluid pressure after carbon dioxide energy enhancement and viscosity reduction has risen to the predetermined pressure. After the nuclear radiation device and coiled tubing are pulled out of the horizontal wellbore, tubing and oil pump are run into the horizontal wellbore and the well is shut in and left to simmer.
[0016] After the well is shut down, oil production begins.
[0017] Preferably, the nuclear radiation device includes a radiation layer, a heating rod, and a downhole fluid pressure monitor, wherein the radiation layer is wrapped around the heating rod; the downhole fluid pressure monitor is configured at the coiled tubing connection; and the radiation layer includes a radioactive agent.
[0018] Preferably, the horizontal well is a horizontal well that has undergone fracturing.
[0019] Preferably, the step of activating the nuclear radiation device to cause in-situ pyrolysis and upgrading of shale oil to generate carbon dioxide includes,
[0020] The electric heating rod is turned on, and the radiation intensity of the nuclear radiation device is adjusted to promote in-situ cracking and upgrading of crude oil underground, generating carbon dioxide in the reservoir; the downhole pressure monitoring device monitors the increase in downhole fluid pressure and increases the downhole flowing pressure.
[0021] The regulation of radiation intensity of the nuclear radiation device includes controlling the radiation time and dose of the radiation source in the radiation layer.
[0022] Preferably, the method further includes,
[0023] Conduct on-site simulation experiments of nuclear radiation;
[0024] Based on the results of the nuclear radiation field simulation experiment, a parameter system was established for the amount of carbon dioxide generated by the cracking of different shale oils and the intensity of nuclear radiation.
[0025] The parameter system for nuclear radiation intensity is determined based on the differences in shale with varying organic matter abundance; the specific parameters of nuclear radiation include the duration of nuclear radiation, radiation dose, radiation intensity, radiation mode, and radiation source parameters.
[0026] Preferably, the carbon dioxide dissolves in the crude oil and diffuses beyond the wellbore.
[0027] Preferably, the in-situ pyrolysis of shale oil to generate carbon dioxide includes,
[0028] After the nuclear radiation device is lowered into the well along with the oil pipe, the intensity and duration of underground nuclear radiation are controlled, and the shale oil is cracked in situ to generate carbon dioxide.
[0029] The carbon dioxide injection increases the driving force for reservoir development and reduces crude oil viscosity.
[0030] A shale oil carbon dioxide huff and puff development system based on underground nuclear radiation, the system comprising a nuclear radiation device, a downhole pressure monitoring device, coiled tubing, oil tubing, and a pumping unit, wherein...
[0031] The nuclear radiation device is connected and fixed to the downhole pressure monitoring device and coiled tubing. It is used to be lowered into the horizontal wellbore and the nuclear radiation device is turned on to cause the shale oil to be cracked and upgraded in situ to generate carbon dioxide.
[0032] The oil pump is installed inside the tubing and is used to shut down the nuclear radiation device after the in-situ cracking and upgrading of shale oil is completed. After the nuclear radiation device and coiled tubing are pulled out of the horizontal wellbore, the tubing and the oil pump are lowered into the horizontal wellbore to shut down and stagnate the well. After the stagnation is completed, the well is opened to produce oil.
[0033] Preferably, the nuclear radiation device includes a radiation layer and a heating rod, with the radiation layer covering the outside of the heating rod; the radiation layer includes radioactive material.
[0034] Preferably, the horizontal well is a horizontal well that has undergone fracturing.
[0035] Preferably, the step of activating the nuclear radiation device to cause in-situ pyrolysis of shale oil to generate carbon dioxide includes,
[0036] The electric heating rod is turned on, and the radiation intensity of the nuclear radiation device is adjusted to promote in-situ cracking and upgrading of crude oil underground, generating carbon dioxide in the reservoir; the downhole pressure monitoring device monitors the increase in downhole fluid pressure and increases the downhole flowing pressure.
[0037] The regulation of radiation intensity of the nuclear radiation device includes controlling the radiation time and dose of radioactive material in the radiation layer.
[0038] The technical effects and advantages of this invention are as follows:
[0039] 1. Current methods for enhancing oil recovery by injecting CO2 into shale oil reservoirs all involve injecting CO2 from the wellbore into the reservoir from the outside, and there is no research on generating CO2 from within the reservoir.
[0040] 2. The methods of enhancing oil recovery in conventional oil reservoirs, such as burning oil layers and injecting flue gas, both rely on the idea of generating CO2 inside the reservoir using heat, and no experimental research has been conducted in shale oil reservoirs.
[0041] In view of the above factors, this invention proposes an economical, effective, and feasible CO2 injection method and system that induces the direct generation of CO2 inside the reservoir without the need for external CO2 injection, thereby achieving the goal of "injecting" gas to replenish energy in shale oil reservoirs, improving recovery rate, and realizing efficient development.
[0042] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description
[0043] Figure 1a This is a schematic diagram of the injection stage in the gas injection and puffing process in the prior art;
[0044] Figure 1b This is a schematic diagram of the well-closing stage in the gas injection and huff-and-puff process in existing technology.
[0045] Figure 1c A schematic diagram of the production stages in the gas injection and puffing process in the existing technology;
[0046] Figure 2 This is a schematic diagram of the underground nuclear radiation CO2 generation device of the present invention;
[0047] Figure 3 This is a partial schematic diagram of the heating rod being turned on in the underground nuclear radiation CO2 generation device of the present invention;
[0048] Figure 4 This is a partial schematic diagram of the CO2 generation process in the underground nuclear radiation CO2 generation device of the present invention;
[0049] Figure 5 This is a schematic diagram of the oil inlet tubing and oil pump inside the wellbore of the present invention;
[0050] Figure 6 This is a partial schematic diagram of the well-sealing process of running tubing into the wellbore according to the present invention;
[0051] Figure 7 This is a partial schematic diagram of crude oil flow after well opening and production according to the present invention.
[0052] In the diagram: 1. Pumping unit; 2. Casing; 3. Coiled tubing; 4. Hydraulic fracturing fracture; 5. Radioactive material; 6. Electric heating rod; 7. Tubing; 8. Pump; 9. Carbon dioxide. Detailed Implementation
[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0054] To address the shortcomings of existing technologies, this invention discloses a method for developing carbon dioxide huff and puff in shale oil based on underground nuclear radiation. By selecting specific parameters such as the nuclear radiation dose and duration, the method promotes in-situ carbon dioxide generation from shale oil, achieving a novel and economical method for energy replenishment. The method includes: conducting on-site nuclear radiation simulation experiments; and establishing the relationship between shale carbon dioxide generation and nuclear radiation parameter settings using Matlab software based on the results of the simulation experiments. The specific nuclear radiation parameters are determined based on the differences in shale with varying organic matter abundance. These parameters include the nuclear radiation duration, radiation dose, radiation intensity, radiation mode, and radiation source parameters. Connect and fix the nuclear radiation device, downhole pressure monitoring device, and coiled tubing 3 to the horizontal wellbore, and lower them into the horizontal wellbore after fracturing. Turn on the nuclear radiation device, set the predetermined time and radiation intensity, and cause the shale oil to undergo in-situ cracking and upgrading to generate carbon dioxide 9. After the shale oil has undergone in-situ cracking and generated carbon dioxide 9, turn off the nuclear radiation device. Use the downhole pressure monitoring device to determine whether the fluid pressure after the carbon dioxide 9 has increased energy and reduced viscosity has risen to the predetermined pressure. After the nuclear radiation device and coiled tubing 3 are pulled out of the horizontal wellbore, tubing 7 and pump 8 are lowered into the horizontal wellbore, and the well is shut in and shut off. After the well is shut off, the well is opened for oil production.
[0055] Furthermore, the in-situ cracking of shale oil generates carbon dioxide 9, which is then activated by the electric heating rod 6. The radiation intensity of the nuclear radiation device is adjusted to promote in-situ cracking and upgrading of the shale oil underground, generating carbon dioxide 9 in the reservoir. The carbon dioxide 9 dissolves in the shale oil and diffuses to areas outside the wellbore. The downhole pressure monitoring device monitors the increase in downhole fluid pressure and increases the downhole flowing pressure.
[0056] Furthermore, the radiation intensity of the nuclear radiation device includes controlling the radiation time of the radiation source in the radiation layer and the dose of the radiation source. Adjusting the radiation intensity of the nuclear radiation device includes controlling the radiation time of the radioactive material 5 in the radiation layer and the dose of the radioactive material 5.
[0057] Furthermore, the in-situ pyrolysis of shale oil to generate carbon dioxide 9 includes controlling the radiation intensity and time of underground nuclear radiation after the nuclear radiation device is lowered into the well along with the oil pipe 7, so that the shale oil is pyrolyzed in situ to generate carbon dioxide 9; the carbon dioxide 9 injection and discharge increases the driving force for reservoir development and reduces the viscosity of shale oil.
[0058] This invention also provides a shale oil carbon dioxide huff and puff development system based on underground nuclear radiation. The system includes a nuclear radiation device, a downhole pressure monitoring device, coiled tubing 3, tubing 7, and a pump 8. The nuclear radiation device is connected and fixed to the downhole pressure monitoring device and the coiled tubing 3, and is used to be lowered into the horizontal wellbore. The nuclear radiation device is activated to cause in-situ cracking and upgrading of the shale oil, generating carbon dioxide 9. The pump 8 is located inside the tubing 7 and is used to shut down the nuclear radiation device after the in-situ cracking and upgrading of the shale oil is completed. After the nuclear radiation device and the coiled tubing 3 are pulled out of the horizontal wellbore, the tubing 7 and the pump 8 are lowered into the horizontal wellbore for well shut-off and well stagnation. After the well stagnation is completed, the well is opened for oil production.
[0059] Furthermore, the nuclear radiation device includes a radiation layer, an electric heating rod 6, and a downhole fluid pressure monitor. The radiation layer is wrapped around the outside of the heating rod; the downhole fluid pressure monitor is located at the connection position of the coiled tubing 3; and the radiation layer includes radioactive material 5.
[0060] Furthermore, in a specific embodiment of the present invention, nuclear radiation field experiments were conducted on shale oil development zones. Based on the differences in shale with different organic matter abundances, parameters such as the time, radiation dose, radiation intensity, radiation mode, and radiation source of nuclear radiation were determined to ensure the fastest and largest amount of shale oil generation. Using Matlab professional software and with the help of relevant neural network clustering analysis, the relationship between shale carbon dioxide generation and nuclear radiation intensity and time parameters was established.
[0061] The nuclear radiation-related parameters include parameters such as the time, radiation dose, radiation intensity, radiation mode, and radiation source of nuclear radiation, which are determined based on the differences in shale with different organic matter abundances, to ensure the fastest and largest amount of shale oil generation.
[0062] Furthermore, based on the radiation dose calculated from the model, an appropriate amount of radioactive material is wrapped around the electric heating rod 6, and the electric heating device is connected and fixed to the coiled tubing 3, then lowered into the horizontal wellbore that has been fracturing (e.g., Figure 2 (as shown); combined with Figure 2 As can be seen, the specific embodiment of the present invention employs an underground nuclear radiation CO2 generation device comprising a pumping unit 1, casing 2, coiled tubing 3, hydraulic fracturing fractures 4, radioactive material 5, and an electric heating rod 6. The pumping unit 1 is located outside the wellhead. The radioactive material 5 and the electric heating rod 6 constitute the nuclear radiation device, which is connected and fixed to the coiled tubing 3 for use in lowering into the horizontal wellbore. Activating the nuclear radiation device allows for in-situ cracking and upgrading of shale oil, generating carbon dioxide 9. The casing 2 is located outside the coiled tubing 3, and the horizontal portion of the coiled tubing 3 includes multiple hydraulic fracturing fractures 4. The radiation layer surrounds the heating rod; the radiation layer includes the radioactive material 5.
[0063] Furthermore, by activating the electric heating rod 6 in the nuclear radiation device and adjusting parameters such as radiation time, radiation dose, radiation intensity, and radiation source, in-situ underground cracking and upgrading of shale oil is induced, generating a large amount of carbon dioxide (CO2) in the reservoir (e.g., Figure 3 (as shown); combined with Figure 3 It can be seen that by turning on the electric heating rod 6 in the nuclear radiation device and adjusting the parameters such as the radiation time, radiation dose, radiation intensity and radiation source of the radioactive material 5, nuclear radiation is emitted in all directions, and the nuclear radiation enters the shale through the casing 2.
[0064] Furthermore, such as Figure 4 As shown, after the in-situ cracking and modification of shale oil is completed (after reaching the designed radiation concentration and time), a large amount of carbon dioxide 9 is generated in the shale and near the hydraulic fracturing fracture 4. The electric heating rod 6 is turned off, and the nuclear radiation device and coiled tubing 3 are pulled out of the wellbore.
[0065] Furthermore, after the nuclear radiation device and coiled tubing 3 are removed from the wellbore, as... Figure 5 As shown, the production tubing 7 and the pump 8 are lowered into the horizontal wellbore. The pump 8 is located inside the tubing 7. The tubing 7 and the pump 8 are then lowered into the wellbore. Figure 6 It is known that when a well is shut in and left to simmer for a period of time (20-40 days), the generated carbon dioxide 9 gradually dissolves in the crude oil and is transferred to a larger area near the wellbore through diffusion.
[0066] Furthermore, such as Figure 7 As shown, after the well is shut down, the oil pumping unit 1 is used to produce oil. The carbon dioxide 9 generated in the crude oil can promote more crude oil to flow into the wellbore through mechanisms such as expansion, viscosity reduction, and pressurization.
[0067] Furthermore, in a specific embodiment of this application, the samples used in this simulation experiment were taken from low-maturity shale samples from terrestrial freshwater and saline lacustrine basins. Shale samples from the Chang 7 Member of the Ordos Basin and the Lucao Gou Formation of the Santanghu Basin were selected for in-situ carbon dioxide 9 generation simulation experiments simulating nuclear radiation. The freshwater lacustrine basin shale was the Chang 7 low-maturity shale from well ZK1 in the Ordos Basin, with a core depth of 652m, an organic carbon abundance of 6.45-11.8%, and an Ro of 0.5-0.65. The saline lacustrine basin shale was the Lucao Gou Formation low-maturity shale from well Ma 804 in the Santanghu Basin, with a core depth of 1876.9-1927m, an organic carbon abundance of 2.06-7.48%, and an Ro of 0.74-0.81.
[0068] Furthermore, among the aforementioned low-maturity shale samples from terrestrial freshwater and saline lacustrine basins, a total of five shale samples were collected: M1, M2, M3, ZK1, and ZK2. M1 exhibits horizontal lamination, with poorly rounded quartz. Its mineral composition is dominated by dolomite, illite, albite, and quartz, with a TOC (total organic carbon) of 6.56 and an Ro of 0.74. M2 also exhibits horizontal lamination, with dolomite, calcite, illite, albite, and quartz as the main components, a TOC of 2.06, and an Ro of 0.81. M3 further exhibits horizontal lamination, with illite, quartz, calcite, and albite as the main components, a TOC of 7.48, and an Ro of 0.74. ZK-1 shows weak lamination, with illite, albite, and quartz as the main components, a TOC of 11.80, and an Ro of 0.55. ZK-2 exhibits organic lamellar formation, with illite, albite, and quartz as the main components, a TOC of 6.45, and a Ro of 0.65. Five shale samples were pulverized to 200 mesh, thoroughly mixed, and divided into several equal portions to ensure the homogeneity and consistency of samples used for different irradiation doses.
[0069] Samples M1, M2, M3, ZK1, and ZK2 were irradiated with gamma rays and high-energy electrons generated by a radioactive isotope (60Co) at doses of 0.5, 1, 10, 50, 100, and 1000 kGy, respectively. The changes in organic carbon content before and after irradiation at different doses were analyzed using rock thin sections, X-ray diffraction analysis, TOC content analysis, scanning electron microscopy, infrared spectroscopy, and pyrolysis testing. The experimental results showed that after irradiation with doses of 0.5, 1, 10, 50, 100, and 1000 kGy, the organic carbon content of the five samples decreased significantly with increasing radiation intensity. For sample M1, the organic carbon content decreased by 0.02% after 1 kGy radiation, 0.43% after 10 kGy radiation, 0.6% after 100 kGy radiation, and 1.11% after 1000 kGy radiation. This shows that the higher the dose, the greater the reduction in organic carbon. The carbon dioxide production was also the highest. Based on this, we can explore the effect of in-situ carbon dioxide huff and puff experiments in shale oil, which has important scientific and theoretical significance for realizing an economical and effective way to supplement the energy development of shale oil.
[0070] ICP-MS (Inductively Coupled Plasma Mass Spectrometry) measurements showed that the background of samples M1, M2, M3, ZK1, and ZK2 was 0.1 × 10⁻⁶. - 6The radiation dose was measured in Gy / hour. The samples tested were from the Permian and Triassic periods. The samples received a dose of approximately 150-200 kGy in the strata. Therefore, the radiation doses used in this study were 1000 kGy, 10 kGy, 100 kGy, and 1000 kGy, respectively. The sample irradiation was carried out at the 97892 Curie 60Co source device and the high-energy electron linear accelerator. The dose was monitored using a potassium dichromate dosimeter. The experiment was conducted at the China Institute of Atomic Energy. The dose of the 60Co source device was 10 Gy / h. The irradiation of 500 Gy and 1000 Gy samples was carried out using the 60Co source device, with the test environment temperature below 30 degrees Celsius and the sample irradiation time being 2-5 days. Considering the time cost, the irradiation of 10 kGy, 50 kGy, 100 kGy and 1000 kGy samples was carried out using high-energy electron irradiation, with the test environment temperature below 70 degrees Celsius. Then, the differences in mineral composition, organic matter content, and pyrolysis components between the original samples and the irradiated samples were tested. It was found that the dolomite content decreased and the illite content increased after irradiation of the five samples, while the changes in other minerals were not obvious. The samples showed a decrease in organic carbon and an increase in light hydrocarbons.
[0071] 2. Effects of irradiation on the molecular structure of organic matter
[0072] Gas chromatographic analysis of the original and irradiated samples showed that after irradiation, the content of high-carbon alkanes in shale organic matter decreased while the content of low-carbon alkanes increased. With increasing irradiation dose, the overall alkane content shifted towards lower carbon numbers, and C6-C hydrocarbons, not present in the original sample, were also produced. 10 The presence of alkanes indicates that the bonds of organic macromolecules break during irradiation, the molecular structure of organic matter is destroyed, and smaller molecules are formed. At the same time, gaseous substances are produced, mainly carbon dioxide.
[0073] Infrared spectral analysis of the original and irradiated samples showed that the functional groups of shale organic matter also changed after irradiation. The original M1 sample showed changes at 1700 cm⁻¹. -1 A ketone group (C=O) is present at the site. Samples were irradiated at 1700 cm⁻¹ with 500 Gy, 1000 Gy, and 1000 kGy. -1 The ketone group disappeared; M2 original sample 2946cm -1 The methine (CH2) functional group is present; the methine disappears in samples irradiated with 500 Gy and 1000 kGy, and at 1700 cm⁻¹ in the 1000 Gy irradiated sample. -1 The ketone group disappears at 2926 cm⁻¹. -1 and 2856cm -1 New methines are produced at this site; compared with other samples, the M3500Gy irradiated sample at 1712 cm⁻¹ produces a higher concentration of methines. -1 New ketone groups are generated at 1700 cm⁻¹; the original ZK1 sample and the 500 Gy irradiated sample were subjected to 1700 cm⁻¹ irradiation. -1 There is no ketone group (C=O) present at this location, and irradiation at 1000 Gy and 1000 kGy results in the same effect at 1700 cm⁻¹.-1 Ketone groups (C=O) appeared nearby, and the sample with the highest irradiation dose of 1000 kGy was observed at 1625 cm⁻¹. -1 C=C aromatic hydrocarbon functional groups were found at the location; the original ZK2 sample was at 1700 cm⁻¹. -1 The ketone group (C=O) is absent at this location. Irradiation samples at 1700 cm⁻¹ were subjected to 500 Gy, 1000 Gy, and 1000 kGy. -1 A ketone group (C=O) was observed; the sample irradiated at 1000 kGy reached 2946 cm⁻¹. -1 The methyl group (CH2) disappears.
[0074] Overall, the ketone groups disappeared after irradiation of sample M1; the methine group disappeared after irradiation of sample M2, while a new methine group was generated; and new ketone groups were generated after irradiation of samples M3 and ZK1. Irradiation at a dose of 1000 kGy may cause the organic matter to polymerize and form C=C aromatic hydrocarbon functional groups.
[0075] 3. Evaluation of the effectiveness of CO2 huff and puff supplementary energy development method for shale oil under nuclear radiation mode
[0076] Gases generated from irradiated organic matter in shale can be considered as a gas source for huff-and-puff energy replenishment development. Gas injection displacement is a common development mode used in oil extraction to replenish energy. Because gas molecules are small and easily flowable, they can improve oil recovery after forming a miscible phase with underground crude oil. In shale oil extraction, due to the extremely low permeability of the matrix, it takes a long time for injected gas to displace oil into the production well during gas injection displacement. However, in the gas injection huff-and-puff energy replenishment development mode, the pressure near the well increases rapidly during injection, allowing for the rapid generation of gas, oil, and water after entering production mode. The role of gas injection huff-and-puff is to replenish formation energy, reduce crude oil viscosity, and increase oil saturation. Nuclear irradiation experiments on Alum shale in existing technology show that when the radiation dose is between 82-285 mrad (820-2850 KGy), the carbon-containing gases produced during the dehydrogenation polymerization of hydrocarbon compounds include CO2, CO, CH4, and C2H6, with CO2 accounting for over 90% and CH4 accounting for about 5%. Furthermore, as the radiation dose increases, the proportion of CO2 decreases while the proportion of CH4 increases. Therefore, calculations based on the correlation between radiation dose and different product quantities show that after 1000 kGy irradiation, approximately 1% of the organic carbon in M1 is converted to CO2, compared to 0.1% for M2, 0.2% for M3, 0.5% for ZK-1, and 0.1% for ZK-2. After irradiation, samples with relatively high TOC (such as ZK-1) show a greater reduction in organic carbon and higher gas production than samples with low TOC (such as M2). Therefore, irradiating shale not only produces low-to-medium carbon chain hydrocarbons, increasing oil liquidity, but the associated gases can also be used in huff and puff recovery. Additionally, the aromatic hydrocarbons generated by irradiation can also improve oil liquidity; therefore, nuclear radiation is of great significance for improving shale oil recovery.
[0077] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for developing shale oil carbon dioxide huff and puff based on underground nuclear radiation, characterized in that, The method includes: The nuclear radiation device and downhole pressure monitoring device are connected and fixed to the coiled tubing (3) and lowered into the horizontal wellbore; The process of activating a nuclear radiation device and setting a predetermined time and radiation intensity to induce in-situ cracking of shale oil to generate carbon dioxide (9) includes: activating an electric heating rod (6); adjusting the radiation intensity of the nuclear radiation device to induce in-situ cracking and regeneration of shale oil underground, thereby generating carbon dioxide (9) in the reservoir; and using a downhole pressure monitoring device to monitor the increase in downhole fluid pressure and increase the downhole flowing pressure. The adjustment of the radiation intensity of the nuclear radiation device includes controlling the radiation time and dose of radioactive material (5) in the radiation layer. After the shale oil is cracked in situ to generate carbon dioxide (9), the nuclear radiation device is shut down. The downhole pressure monitoring device is used to determine whether the fluid pressure after the carbon dioxide (9) increases energy and reduces viscosity has risen to the predetermined pressure. After the nuclear radiation device and the coiled tubing (3) are pulled out of the horizontal wellbore, the tubing (7) and the oil pump (8) are lowered into the horizontal wellbore and the well is shut off and left to simmer. After the well is shut down, oil production begins. The method also includes, Before connecting and fixing the nuclear radiation device, downhole pressure monitoring device and coiled tubing (3) and lowering them into the horizontal wellbore, a nuclear radiation field simulation experiment was conducted. Based on the results of the nuclear radiation field simulation experiment, a parameter system was established for the amount of carbon dioxide (9) generated by the cracking of different shale oils and the intensity of nuclear radiation. The parameter system for nuclear radiation intensity is determined based on the differences in shale with varying organic matter abundance; the specific parameters of nuclear radiation include the duration of nuclear radiation, radiation dose, radiation intensity, radiation mode, and radiation source parameters.
2. The shale oil carbon dioxide huff and puff development method based on underground nuclear radiation according to claim 1, characterized in that, The nuclear radiation device includes a radiation layer, an electric heating rod (6), and a downhole fluid pressure monitor. The radiation layer is wrapped around the heating rod. The downhole fluid pressure monitor is located at the connection point of the coiled tubing (3). The radiation layer includes radioactive material (5).
3. The shale oil carbon dioxide huff and puff development method based on underground nuclear radiation according to claim 1, characterized in that, The horizontal well is a horizontal well that has been fractured.
4. The shale oil carbon dioxide huff and puff development method based on underground nuclear radiation according to claim 1, characterized in that, The carbon dioxide (9) dissolves in the shale oil and diffuses beyond the wellbore.
5. The shale oil carbon dioxide huff and puff development method based on underground nuclear radiation according to claim 1, characterized in that, The in-situ pyrolysis of the shale oil produces carbon dioxide (9), including, After the nuclear radiation device is lowered into the well along with the oil pipe (7), the radiation intensity and time of the underground nuclear radiation are controlled so that the shale oil is cracked in situ to generate carbon dioxide (9); The carbon dioxide (9) injection and discharge increases the driving force for reservoir development and reduces the viscosity of shale oil.
6. A shale oil carbon dioxide huff and puff development system based on underground nuclear radiation, characterized in that, The system includes a nuclear radiation device, a downhole pressure monitoring device, coiled tubing (3), tubing (7), and a pumping unit (8), wherein, The nuclear radiation device is connected and fixed to the downhole pressure monitoring device and the coiled tubing (3) for use in the horizontal wellbore. The nuclear radiation device is turned on to cause the shale oil to be cracked and reformed in situ to generate carbon dioxide (9). The oil pump (8) is installed inside the tubing (7) and is used to shut down the nuclear radiation device after the in-situ cracking and upgrading of shale oil is completed. After the nuclear radiation device and the coiled tubing (3) are pulled out of the horizontal wellbore, the tubing (7) and the oil pump (8) are lowered into the horizontal wellbore for shut-off and well stagnation. After the well stagnation is completed, the well is opened for oil production. The nuclear radiation device is used to cause in-situ cracking of shale oil to generate carbon dioxide (9), including, Turn on the electric heating rod (6) to adjust the radiation intensity of the nuclear radiation device, promote the in-situ cracking and upgrading of crude oil underground, and generate carbon dioxide (9) in the reservoir; the downhole monitoring pressure device monitors the increase of downhole fluid pressure and increases downhole flowing pressure; The regulation of the radiation intensity of the nuclear radiation device includes controlling the radiation time and the dose of the radioactive material (5) in the radiation layer; before connecting and fixing the nuclear radiation device, the downhole monitoring pressure device and the coiled tubing (3) and lowering them into the horizontal wellbore, a nuclear radiation field simulation experiment is carried out. Based on the results of the nuclear radiation field simulation experiment, a parameter system was established for the amount of carbon dioxide (9) generated by the cracking of different shale oils and the intensity of nuclear radiation. The parameter system for nuclear radiation intensity is determined based on the differences in shale with varying organic matter abundance; the specific parameters of nuclear radiation include the duration of nuclear radiation, radiation dose, radiation intensity, radiation mode, and radiation source parameters.
7. The shale oil carbon dioxide huff and puff development system based on underground nuclear radiation according to claim 6, characterized in that, The nuclear radiation device includes a radiation layer, an electric heating rod (6), and a downhole fluid pressure monitor. The radiation layer is wrapped around the electric heating rod (6); the radiation layer includes radioactive material (5).
8. The shale oil carbon dioxide huff and puff development system based on underground nuclear radiation according to claim 6, characterized in that, The horizontal well is a horizontal well that has been fractured.