A method for in-situ upgrading of low to medium mature shale oil

Abstract

The present application provides a kind of middle-low mature shale oil in-situ modification mining method, which comprises: sequentially carrying out hydraulic fracturing and explosive fracturing on the target layer of middle-low mature shale oil, forming a fracture system;Combustion and air are injected into the target layer of middle-low mature shale oil, and fire heating is carried out;High-temperature completion method is used for oil production well, and gas well separation and recovery are carried out.The method can effectively improve the oil shale reservoir, generate a large number of fine cracks in the shale oil reservoir, greatly increase the porosity and permeability of shale;At the same time, the recovery rate of oil shale can be greatly improved, and the cost of in-situ conversion of middle-low mature shale oil can be significantly reduced, so that the development of middle-low mature shale oil has economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of in-situ oil shale extraction simulation technology, and relates to a method for in-situ upgrading and extraction of medium- and low-maturity shale oil. Background Technology

[0002] Shale oil refers to the collective term for residual oil and unconverted organic matter in shale. Based on the difference in organic matter maturity (vitrinite reflectance Ro), shale oil is divided into two categories: medium-high maturity shale oil (Ro≥0.95%) and medium-low maturity shale oil (Ro<0.95%).

[0003] Preliminary research estimates that in-situ petroleum conversion technology for medium-to-low maturity, organic-rich shale oil is feasible worldwide.

[0004] my country's shale oil reserves are estimated at approximately 1.4 trillion tons, with technically recoverable natural gas resources of about 1100 trillion cubic meters. The technically recoverable resources from in-situ conversion of shale oil into petroleum are estimated at 70-90 billion tons, and technically recoverable natural gas resources at 57-65 trillion cubic meters. These are more than three times the technically recoverable resources of conventional petroleum and natural gas, indicating enormous potential. Shale oil pyrolysis can be divided into above-ground and underground pyrolysis methods. Surface pyrolysis refers to the process where oil shale, after being extracted through open-pit or underground mining, is brought to the surface, crushed and screened to the required particle size or block size, and then pyrolyzed in a retort furnace to obtain shale oil, gas, and residue. While surface retort technology for oil shale is mature, it suffers from low utilization rates, high pollution, small scale, high costs, and the generation of large amounts of waste residue in the retort furnace, which occupies land and is difficult to treat.

[0005] Against this backdrop, in-situ pyrolysis technology has been proposed. In-situ pyrolysis refers to a new technology that directly heats the underground oil shale, collects the produced oil and gas, transports it to the surface, and condenses it to obtain shale oil and non-condensable gas. In-situ pyrolysis eliminates the need for mining operations and large-scale exhaust gas treatment facilities for shale oil extraction. It allows for the development of deep, thick oil shale resources and offers advantages such as high product quality, high oil recovery rate, small land footprint, and environmental friendliness. Extensive research has been conducted both domestically and internationally, and it is currently in the industrial pilot stage.

[0006] The in-situ pyrolysis technology for oil shale needs to address the following three issues:

[0007] ① Kerogen must be converted into flowable liquid oil and gas, petroleum, and pyrolysis gas. That is, sufficient heat is provided in a certain area underground to ensure that high-temperature decomposition occurs at a reasonable temperature and time to complete the conversion process; according to the heating method, in-situ oil shale mining technology can be divided into more than ten technologies such as conduction heating, convection heating, and radiation heating.

[0008] Of the three technologies mentioned above, conductive heating is slow, prone to heat loss, and costly. Furthermore, the thermal expansion of oil shale causes some fractures to close, reducing permeability and thus the recovery rate of oil and gas. In contrast, convection heating of oil shale is faster but difficult to control. Due to fluid pressure, fractures generally do not close, resulting in faster oil and gas extraction, but it is prone to creating fluid short circuits. Radio frequency heating has strong penetration and a fast heating rate, but it is costly and technically challenging. Due to the low permeability of oil shale formations, fracturing is necessary to increase porosity and permeability for successful extraction of distillation gases, thereby improving shale oil recovery.

[0009] Meanwhile, the in-situ conversion costs of the three technologies are very high, and they are not economically viable under current technological conditions, which greatly restricts the development and utilization of medium and low maturity shale oil. Therefore, there is an urgent need for a method that can reduce costs and increase sufficient heat to ensure the in-situ conversion temperature of oil shale kerogen.

[0010] ② Fracturing is performed on the dense, low-permeability oil shale layer surrounding kerogen to increase permeability. Fracturing of the dense, low-permeability oil shale layer surrounding kerogen usually uses hydraulic fracturing. However, when hydraulic fracturing is conventionally used to modify shale oil reservoirs, it mainly generates two main fractures in the stress direction, while fewer fractures are generated in other locations of the shale oil reservoir. As a result, the oil and gas generated after the medium-grade modification of the oil shale cannot be effectively connected with the fractures, resulting in the phenomenon of ineffective in-situ modification of medium- and low-maturity shale oil that is not effectively extracted after modification.

[0011] ③ Oil shale residues remaining underground after dry distillation pollute the environment. After in-situ regeneration of kerogen from oil shale, approximately 40% of the kerogen produces residual carbon, which pollutes the formation environment and also generates significant amounts of waste heat. How to rationally utilize the waste heat and energy from this residual carbon is crucial for reducing the cost of in-situ shale oil conversion. Summary of the Invention

[0012] To address the aforementioned technical problems, this application provides a method for in-situ upgrading and extraction of medium- and low-maturity shale oil. This method can effectively improve oil shale reservoirs by generating numerous micro-fractures in the shale oil reservoir, significantly increasing the porosity and permeability of the shale. At the same time, it can significantly improve the recovery rate of oil shale and substantially reduce the cost of in-situ conversion of medium- and low-maturity shale oil, making the development of medium- and low-maturity shale oil economically viable.

[0013] To achieve the above-mentioned technical effects, the present invention adopts the following technical solution:

[0014] This invention provides a method for in-situ upgrading and extraction of medium- and low-maturity shale oil, the method comprising:

[0015] Hydraulic fracturing and explosive fracturing were sequentially performed on the target layer of medium- and low-maturity shale oil to form a fracture system;

[0016] Inject combustion aids and air into the target layer of medium- to low-maturity shale oil for combustion heating;

[0017] High-temperature well completion is used in oil production wells, and produced gas is separated and recovered from wells.

[0018] As a preferred technical solution of the present invention, a first high-temperature resistant proppant is injected into the fracturing fracture after hydraulic fracturing.

[0019] As a preferred technical solution of the present invention, explosive fracturing includes injecting explosive agents.

[0020] As a preferred embodiment of the present invention, the explosive agent includes nitroglycerin.

[0021] As a preferred technical solution of the present invention, explosive fracturing includes injecting water slugs to push away explosives from the steam injection well.

[0022] As a preferred technical solution of the present invention, the ignition method for explosive fracturing is electrochemical ignition.

[0023] As a preferred technical solution of the present invention, a second high-temperature resistant proppant is injected into the fracture system after explosive fracturing.

[0024] As a preferred embodiment of the present invention, the particle size of the second high-temperature resistant proppant is smaller than that of the first high-temperature resistant proppant.

[0025] As a preferred embodiment of the present invention, the combustion aid includes ammonium nitrate and / or ammonium perchlorate.

[0026] As a preferred technical solution of the present invention, the air flow rate of the injection well is regulated to control the degree of combustion of oil shale and the speed of fire line advancement.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects:

[0028] (1) This invention provides a method for in-situ upgrading and exploitation of medium- and low-maturity shale oil. This method uses hydraulic and explosive methods as reservoir fracturing means, which can effectively modify the oil shale reservoir by creating fractures and greatly improve the permeability of shale oil in the reservoir.

[0029] (2) This invention provides a method for in-situ upgrading and extraction of medium- and low-maturity shale oil. This method involves injecting air into the oil shale to heat it and pyrolyze the kerogen, thereby producing crude oil. This method can significantly improve the recovery rate of oil shale and significantly reduce the cost of in-situ conversion of medium- and low-maturity shale oil, making the development of medium- and low-maturity shale oil economically beneficial. Detailed Implementation

[0030] The technical solution of the present invention will be further described below through specific embodiments.

[0031] This invention provides a method for in-situ upgrading and extraction of medium- and low-maturity shale oil, the method comprising:

[0032] Hydraulic fracturing and explosive fracturing were sequentially performed on the target layer of medium- and low-maturity shale oil to form a fracture system;

[0033] Inject combustion-enhancing agents and air into the target layer of medium- and low-maturity shale oil for combustion heating;

[0034] High-temperature well completion is used in oil production wells, and produced gas is separated and recovered from wells.

[0035] This invention comprehensively utilizes development mechanisms such as combustion heat energy, dissolved gas drive, high-temperature pyrolysis, and improved conductivity. Employing hydraulic and explosive methods as reservoir fracturing techniques effectively modifies oil shale reservoirs, significantly enhancing the permeability of shale oil within the reservoir. Simultaneously, air, as the combustion medium in the well, is readily available, inexpensive, and easy to implement, facilitating underground combustion. High-temperature combustion greatly reduces crude oil viscosity, improves its fluidity, and ultimately enhances shale oil recovery.

[0036] In one specific embodiment of the present invention, the target layer of medium- and low-maturity shale oil is screened before mining, and high-enriched oil shale with an organic matter abundance greater than 6% is selected.

[0037] In one specific embodiment of the present invention, hydraulic fracturing is performed directly on the injection well and the horizontal well.

[0038] In one specific embodiment of the present invention, hydraulic fracturing can be performed in layers, consisting of two hydraulic fracturing fractures (upper and lower), based on the thickness of the shale oil reservoir, to establish a main oil drainage channel.

[0039] In one specific embodiment of the present invention, the specific parameters of hydraulic fracturing can be selected according to the specific environment and extraction needs of the target layer of medium- and low-maturity shale oil, and are not further limited here.

[0040] In one specific embodiment of the present invention, the parameters for hydraulic fracturing may be as follows: fracturing fluid flow rate of 50–120 bpm, requiring a high flow rate to ensure rapid fracture formation and propagation; proppant concentration of 2.5–8 ppg, a high proppant concentration helps maintain fracture openness during combustion; number of fracturing stages of 15–40, multi-stage fracturing helps to distribute fractures more evenly, thereby promoting more efficient airflow and heat transfer; single-stage fracturing fluid volume of 25,000–100,000 gallons, increasing the single-stage fracturing fluid volume to ensure sufficient fracturing fluid participates in fracture formation and proppant delivery; and downhole pressure of 6,000–15,000 psi to ensure sufficient downhole pressure to overcome formation pressure and achieve effective fracture propagation. The fracturing fluid used is a low-residue, high-volatility fracturing fluid to reduce the negative impact of the fracturing fluid on subsequent ignition and combustion.

[0041] In one specific embodiment of the present invention, the first high-temperature proppant may include ceramsite proppant, quartz sand proppant, resin-coated sand, or synthetic proppant, etc.

[0042] In one specific embodiment of the present invention, the particle size of the first high-temperature proppant can be selected according to the specific width of the hydraulic fracturing fracture, and is not further limited here.

[0043] In one specific embodiment of the present invention, the amount of the first high-temperature proppant can be 1000-3000t, increasing the total amount of proppant to improve the stability and high-temperature resistance of the crack.

[0044] In one specific embodiment of the present invention, the explosive agent is injected along the crack surface.

[0045] In one specific embodiment of the present invention, parameters such as the injection volume of explosive agents in explosive fracturing can be selected according to the specific environment and extraction needs of the target layer of medium- and low-maturity shale oil, and are not further limited here. In one specific embodiment of the present invention, as an example, the parameters for explosive fracturing may be: a total nitroglycerin dosage of 5–30 kg per meter of well depth, the specific dosage needing to be adjusted according to formation characteristics, well depth, and well diameter; the calculation method is: total dosage = dosage (kg / m) × target well section length (m); fracturing fluid discharge rate of 30–70 bpm, since the formation has been partially fractured after the explosion, a relatively low discharge rate can be used; and proppant concentration of 2.5–5 ppg, maintaining a suitable concentration to provide sufficient support in the formed fractures.

[0046] In one specific embodiment of the present invention, the second high-temperature proppant may include quartz sand proppant, resin-coated sand, or synthetic proppant, etc.

[0047] In one specific embodiment of the present invention, the particle size of the second high-temperature proppant can be selected according to the specific width of the explosive fracturing crack, and is not further limited here, but it must be satisfied that the particle size of the second high-temperature proppant is smaller than the particle size of the first high-temperature proppant.

[0048] In one specific embodiment of the present invention, the amount of the second high-temperature proppant can be 500 to 1500 tons, and the total amount of proppant is adjusted based on the initial formation of the crack and the crack length that needs to be maintained.

[0049] In this invention, air is injected into the oil shale for combustion, making reasonable use of the residual heat and heat from the residual carbon after shale oil cracking to heat the oil shale. The high-temperature range generated by the combustion of oil shale can improve the efficiency of kerogen conversion into oil and gas and shorten the conversion time.

[0050] In one specific embodiment of the present invention, the combustion accelerant can release oxygen during combustion, thereby enhancing combustion.

[0051] In one specific embodiment of the present invention, the injection amount of the combustion accelerator can be selected based on conditions such as the expected combustion temperature, combustion rate, and formation characteristics, and is not further limited herein. For example, the injection amount of the combustion accelerator can be 100–1000 kg / 100 m well depth.

[0052] In one specific embodiment of the present invention, the degree of burning of oil shale and the speed of fire line advance are controlled by reducing the air injection volume in stages in the steam injection well.

[0053] In one specific embodiment of the invention, the air injection rate is calculated based on the amount of oxygen required per cubic meter of rock, generally ranging from 10,000 to 100,000 cubic meters per day, depending on the volume of the fractures and the amount of oxygen required for combustion. The composition, porosity, permeability, and other geological parameters of the oil shale are assessed to estimate the required combustion-supporting agent dosage and air injection rate.

[0054] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0055] Example 1

[0056] This embodiment provides a method for in-situ upgrading and extraction of medium- and low-maturity shale oil. The medium- and low-maturity shale oil belongs to a certain oil field, with Ro < 0.95% and organic matter abundance greater than 6%. The method includes:

[0057] (1) Hydraulic fracturing is carried out directly in injection wells and horizontal wells. According to the thickness of shale oil reservoir, the fracturing is carried out in layers into two hydraulic fracturing fractures, upper and lower, to establish the main oil drainage channel and fill the first high temperature resistant proppant 1000-3000t.

[0058] In hydraulic fracturing, the fracturing fluid discharge rate is 50–120 bpm, the proppant concentration is 2.5–8 ppg, the number of fracturing stages is 15–40, the fracturing fluid consumption per stage is 25,000–100,000 gallons, and the downhole pressure is 6,000–15,000 psi.

[0059] (2) Nitroglycerin is injected along the fracture surface, and the water slug drives the nitroglycerin away from the steam injection well. After being detonated by electrochemical method, a fracture system is formed. Water is injected and carries 500-1500t of the second high-temperature proppant.

[0060] In explosive fracturing, the total amount of nitroglycerin used is 5-30 kg per meter of well depth, the fracturing fluid discharge rate is 30-70 bpm, and the proppant concentration is 2.5-5 ppg.

[0061] (3) Inject ammonium nitrate, a combustion accelerant, into the fracture system and use nitrogen to drive the combustion accelerant away from the wellbore; inject air, and the air reacts chemically with the combustion accelerant to achieve chemical ignition; in the steam injection well, the degree of burning of the oil shale and the speed of the fire line advance are controlled by reducing the amount of air injected in stages.

[0062] (4) High-temperature well completion method is used for oil production wells, and gas produced is separated and recovered.

[0063] Comparative Example 1

[0064] The conditions in this comparative example are the same as those in Example 1, except that hydraulic fracturing is not performed.

[0065] Comparative Example 2

[0066] Except for the absence of explosive fracturing, the conditions in this comparative example are the same as those in Example 1.

[0067] Comparative Example 3

[0068] This comparative example is identical to Example 1 except that the air burning treatment is replaced with conductive heating in the prior art.

[0069] Comparative Example 4

[0070] This comparative example is identical to Example 1 except that the air burning treatment is replaced with convection heating in the prior art.

[0071] Comparative Example 5

[0072] This comparative example is identical to Example 1 except that the air burning treatment is replaced with radio frequency heating in the prior art.

[0073] The in-situ upgrading and extraction method for medium- and low-maturity shale oil provided in this invention can significantly improve the recovery rate of oil shale and significantly reduce the cost of in-situ conversion of medium- and low-maturity shale oil, making the development of medium- and low-maturity shale oil economically viable. In Comparative Examples 1-5, Comparative Examples 1 and 2 did not undergo hydraulic fracturing and explosive fracturing, respectively, resulting in a significant decrease in oil shale recovery rates. Comparative Examples 3-5 employed existing technologies for formation heating, significantly increasing extraction costs.

[0074] The applicant declares that the detailed process equipment and process flow of this invention are illustrated through the above embodiments, but this invention is not limited to the above detailed process equipment and process flow, that is, it does not mean that this invention must rely on the above detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the products of this invention, additions of auxiliary components, and selection of specific methods, all fall within the protection scope and disclosure scope of this invention.

Claims

1. A method for in-situ upgrading and extraction of medium- and low-maturity shale oil, characterized in that, The method includes: Hydraulic fracturing and explosive fracturing were sequentially performed on the target layer of medium- and low-maturity shale oil to form a fracture system; Inject combustion-supporting agents and air into the target layer of medium- and low-maturity shale oil for combustion heating; High-temperature well completion is used in oil production wells, and produced gas is separated and recovered from wells.

2. The method according to claim 1, characterized in that, After hydraulic fracturing, a first high-temperature resistant proppant is injected into the fracturing fracture.

3. The method according to claim 1, characterized in that, The explosive fracturing includes injecting explosives.

4. The method according to claim 3, characterized in that, The explosive agent includes nitroglycerin.

5. The method according to claim 3, characterized in that, The explosive fracturing involves injecting explosives into a water slug to drive the steam injection well away.

6. The method according to claim 1, characterized in that, The ignition method for the explosive fracturing is electrochemical ignition.

7. The method according to claim 1, characterized in that, Following the explosive fracturing, a second high-temperature resistant proppant is injected into the fracture system.

8. The method according to claim 1, characterized in that, The particle size of the second high-temperature resistant proppant is smaller than that of the first high-temperature resistant proppant.

9. The method according to claim 1, characterized in that, The combustion aid includes ammonium nitrate and / or ammonium perchlorate.

10. The method according to claim 1, characterized in that, By regulating the air flow rate in the injection well, the degree of combustion of oil shale and the speed of fire line advancement can be controlled.