Unconventional oil and gas development and carbon sequestration method

Abstract

The invention discloses an unconventional oil and gas development and carbon sequestration method, which comprises the following steps of: constructing a vertical slotted well and a horizontal drill hole in a delineated carbon sequestration area, then performing hydraulic fracturing and forming a compact solid with extremely low permeability in a hydraulic fracture to surround an unconventional oil and gas reservoir, and then horizontal well staged fracturing and unconventional oil and gas exploitation are conducted on the reservoir, supercritical or liquid CO2 fracturing is conducted again after exploitation is completed, and finally supercritical or liquid CO2 is continuously injected into the reservoir to achieve carbon sequestration. By means of the method, large-range permeability increasing and oil and gas resource development can be conducted on the reservoir, secondary reinforcement can be conducted on the carbon sequestration area, and the risk of carbon sequestration leakage is effectively reduced.

Description

Technical Field

[0001] The invention relates to an unconventional oil and gas development and carbon sequestration method, belonging to the technical field of unconventional oil and gas development. Background Art

[0002] Oil and gas resources will remain the main energy source in the world for a long time. The combustion of oil and gas resources increases carbon dioxide emissions, resulting in an increase in the concentration of carbon dioxide in the atmosphere, leading to an increasingly serious greenhouse effect. In order to slow down the growth trend of the greenhouse effect, storing carbon dioxide underground has become a more feasible option. Among them, oil and gas reservoirs and abandoned mines are the storage sites that many scholars currently recognize. The storage state is generally supercritical or liquid carbon dioxide. However, there is a certain risk of leakage in the current underground carbon dioxide storage, which will bring potential threats to terrestrial ecosystems, especially near-surface terrestrial ecosystems. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a method for unconventional oil and gas development and carbon sequestration.

[0004] The present invention is achieved through the following technical solutions.

[0005] The present invention provides a method for unconventional oil and gas development and carbon sequestration, comprising the following steps:

[0006] An unconventional oil and gas development and carbon sequestration method comprises the following steps:

[0007] (1) Exploring the stratigraphic lithology and geological conditions of the target unconventional oil and gas reservoirs, identifying the geological structures in the geological reservoirs, calculating and analyzing the carbon storage capacity, and delineating the carbon storage areas;

[0008] (2) Construct a vertical slotted well from the ground at the designed position downward to the designated layer and start to turn to horizontal drilling. After reaching the set position, withdraw the drill bit to the turning position, and then drill horizontally in another direction. After drilling is completed, withdraw the drill bit;

[0009] (3) Continue to drill downward in the vertical slotted well, and then turn to horizontal drilling after reaching the designated layer, and then turn to continue horizontal drilling after retreating;

[0010] (4) After completing the drilling of multiple horizontal boreholes according to the design requirements, the horizontal boreholes are directionally slotted, and after the slotting is completed, the slotted wells and horizontal boreholes are flushed;

[0011] (5) After the drilling construction at the designed location is completed, the process of slotting wells, horizontal drilling, ultra-high pressure slotting, well washing, etc. will continue at the new location;

[0012] (6) Conducting guided fracturing on all slotted wells. The fracture network formed after fracturing can cover the entire carbon storage area. The fracturing fluid used in fracturing is divided into pre-flush fluid, mid-flush fluid and post-flush fluid. The pre-flush fluid has a high-efficiency fracture-forming effect, and the mid-flush and post-flush fluids have the property of chemically reacting to generate solids.

[0013] (7) After the reaction is completed, a vertical production well is constructed from the center of the carbon storage area to a specified depth, and then radial horizontal wells are constructed and fracturing is performed. After the fracturing is completed, drainage is performed to develop unconventional oil and gas resources;

[0014] (8) After mining is completed, supercritical or liquid CO is injected into the mining well. 2 , carbon storage is carried out in the designated carbon storage area.

[0015] The delineated carbon storage area is generally rectangular, with no major geological structures in the area. There are generally two slotted wells, which are arranged diagonally at the boundary vertices of the storage area.

[0016] When turning and drilling horizontally along the slotted well to the designated layer, the first turning position is generally the soft rock above the reservoir closest to the unconventional oil and gas reservoir. The judgment criteria are that the rock mechanical parameters decrease by more than 40% or the permeability increases by more than 1 times. The last turning position is generally about 20m below the unconventional oil and gas reservoir.

[0017] The drilling length of horizontal boreholes is generally enough to cover the designated storage area. The vertical spacing of horizontal boreholes is related to the cutting depth, which is generally 8 times the cutting depth. If there is no specific data, 10m can be used.

[0018] The fracturing fluid used in the fracturing process of slotted wells is divided into pre-fracture fluid, which has the characteristics of small filtration loss and low viscosity, and can make the hydraulic fractures expand rapidly forward. The middle and post-fracture fluids have the characteristics of chemical reaction to generate solids. The generated solids are extremely dense, with extremely low permeability, can withstand weak acids, and do not produce physical and chemical reactions with carbonic acid.

[0019] After fracturing the slotted well, an outer layer with extremely low permeability can be formed in the carbon storage area, surrounding the unconventional oil and gas reservoir.

[0020] The production wells are generally located in the middle of the carbon storage area. The horizontal wells formed by drilling are located in unconventional oil and gas reservoirs. The fracturing layer is an unconventional oil and gas reservoir. The fracturing technology used is the horizontal well staged fracturing technology, and then oil and gas resources are exploited.

[0021] After the oil and gas resources are extracted, the reservoir is fractured again, and the fracturing medium is supercritical or liquid CO 2 During the fracturing process, proppant is added, and supercritical or liquid CO is continuously injected into the reservoir after the fracturing is completed. 2 The injection volume is determined based on the delineated carbon storage area.

[0022] The calculation of carbon storage capacity is divided into two parts. One part is to calculate the storage capacity by analyzing the porosity of the reservoir, and the other part is to calculate the storage capacity by the spatial volume of the gaps formed by fracturing.

[0023] The slotting device used has positioning, orientation and adjustment devices such as a horizontal compass, which can realize the adjustment of the azimuth angle, and the slotting technology used is ultra-high pressure hydraulic slotting technology or ultra-high pressure abrasive jet slotting technology or laser slotting technology. The slotting technology used is not unique, but it can cut a slot of a certain depth in the set direction.

[0024] The beneficial effects of the present invention are as follows: the permeability of unconventional oil and gas reservoirs can be increased and exploited, and the carbon storage area can be effectively trapped, thereby reducing or even eliminating the risk of carbon dioxide leakage. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic plan view of a slotted well constructed by the unconventional oil and gas development and carbon sequestration method of the present invention;

[0026] Figure 2 AA cross-sectional schematic diagram of a slotted well constructed by the unconventional oil and gas development and carbon sequestration method of the present invention;

[0027] Figure 3 It is a schematic plan view of a slotted well after fracturing in the unconventional oil and gas development and carbon sequestration method of the present invention;

[0028] Figure 4 It is a schematic diagram of the AA cross section of a slotted well after fracturing in the unconventional oil and gas development and carbon sequestration method of the present invention;

[0029] Figure 5 It is a schematic plan view of a completed production well of the unconventional oil and gas development and carbon sequestration method of the present invention;

[0030] Figure 6 It is a schematic diagram of the BB cross section of a production well constructed by the unconventional oil and gas development and carbon sequestration method of the present invention;

[0031] Figure 7 It is a schematic diagram of horizontal drilling of slotted wells according to the present invention;

[0032] In the figure: 1- slotted well; 2- horizontal slotted borehole a; 3- horizontal slotted borehole b; 4- boundary line of carbon storage area; 5- horizontal slotted borehole c; 6- horizontal slotted borehole d; 7- horizontal slotted borehole e; 8- horizontal slotted borehole f; 9- horizontal slotted borehole g; 10- horizontal slotted borehole h; 11- horizontal slotted borehole i; 12- rock formation a; 13- rock formation b; 14- rock formation c; 15- unconventional oil and gas reservoir; 16- rock formation d; 17- hydraulic fracture; 18- hydraulic slotted groove; 19- production well; 20- horizontal well of production well. DETAILED DESCRIPTION

[0033] The present invention will be further described below by way of embodiments and in conjunction with the accompanying drawings:

[0034] Combination Figure 1 As shown, firstly, the stratigraphic lithology and geological conditions of the target unconventional oil and gas reservoir are explored, the geological structure in the geological reservoir is explored, and the area without large geological structure is delineated (so that the fault drop in the area is less than 5m). The carbon storage area is generally rectangular, and the boundary line is the carbon storage area delineation line 4.

[0035] Determine the porosity of the soft rock 13, rock layer 14, and unconventional oil and gas reservoir 15 above the unconventional oil and gas reservoir 15, and calculate the carbon dioxide space V that can be stored in the formation pores. 1 , the calculation formula is:

[0036] V 1 =S∑h i θ i

[0037] Where: V 1 is the carbon dioxide storage space in the formation pores; S is the carbon storage area; h i is the thickness of rock layer i; θ i is the porosity of rock layer i.

[0038] Through simulation, it is determined that the reasonable fracture height of the unconventional oil and gas reservoir after fracturing is h f , the fracturing area is S f , then the diameter of the proppant used in the fracturing process is h f , the amount of proppant injected during the fracturing process is V z , then the volume of the space formed by the fracture is V 2 for:

[0039] V 2 =S z h f -V z

[0040] Where: V 2S is the spatial volume of the gap formed by fracturing; f is the fracturing area; h f is the reasonable fracture height after fracturing; V z The amount of proppant injected during the fracturing process.

[0041] Then the total carbon storage space is V=V1+V2.

[0042] Then, a slit well 1 is constructed from a boundary vertex selected from the delineated carbon storage area, and a vertical slit well is constructed from the ground downward to the soft rock 13 above the unconventional oil and gas reservoir 15 and closest to the unconventional oil and gas reservoir 15, and then the horizontal slit borehole a2 is turned horizontally, and the turning direction is along the delineated boundary line 4 of the carbon storage area, and the drill is withdrawn to the initial turning position after drilling to another intersection of the delineated boundary line 4 of the carbon storage area, and then the horizontal slit borehole b3 is drilled horizontally in another direction, and the drill is withdrawn again to the initial turning position after drilling to the delineated boundary line 4 close to the carbon storage area, and then the horizontal slit borehole c4 is drilled horizontally in another direction, and the drill is withdrawn to the initial turning position after drilling to another intersection of the delineated boundary line 4 of the carbon storage area. The criterion for determining the soft rock closest to the unconventional oil and gas reservoir 15 is that the rock mechanical parameters are reduced by more than 40% or the permeability is increased by more than 1 time.

[0043] The vertical slotted well 1 is further drilled downward to a depth of 10 m, and then the previous step is repeated to drill multiple horizontal slotted boreholes at the same level. This step is repeated until the lower part of the unconventional oil and gas reservoir 15 is about 20 m.

[0044] After that, the drill bit is replaced with a slotting device. Here, laser slotting technology is used. The slotting device moves along each horizontal slot drilling hole. The slotting direction of the horizontal slot drilling holes (including horizontal slot drilling holes a2, horizontal slot drilling holes b3, and horizontal slot drilling holes c4) of the first layer is vertically downward. The slotting directions of the horizontal slot drilling holes of the remaining layers are as follows: Figure 7 As shown, the slots 18 are cut vertically in the upward and downward directions respectively. After the slotting is completed, the slotted well 1 and each horizontal slotted borehole are flushed.

[0045] Then, another diagonal boundary vertex is selected in the demarcated carbon storage area to repeat the above steps, that is, constructing the vertical slotted well 1, horizontal slotted drilling, slotting and flushing the horizontal slotted drilling, etc.

[0046] Two slotted wells were plugged and fractured. The distribution of fractures after fracturing is as follows: Figure 3 , Figure 4As shown, the hydraulic fractures 17 formed after fracturing can cover the entire carbon storage area, forming an outer layer with extremely low permeability in the carbon storage area, surrounding the unconventional oil and gas reservoir. The fracturing fluid used in fracturing is divided into pre-fluid, mid-stage fluid and post-fluid. The pre-fluid has the characteristics of low filtration loss and low viscosity, which can make the hydraulic fractures expand forward quickly. The mid-stage and post-fluid have the characteristics of chemical reaction to generate solids. The generated solids are extremely dense, extremely low in permeability, resistant to weak acids, and do not produce physical and chemical reactions with carbonic acid.

[0047] After the reaction of the middle section and the post-fluid is completed (generally one month after the fracturing of the slotted well is completed), a vertical production well 19 is constructed from the center of the carbon storage area to the unconventional oil and gas reservoir 15, and then a radial horizontal well 20 is constructed in the middle of the unconventional oil and gas reservoir 15 and staged fracturing of the horizontal well is carried out. After the fracturing is completed, drainage is carried out to develop unconventional oil and gas resources;

[0048] After the oil and gas resources are extracted, the reservoir is fractured again, and the fracturing medium is supercritical or liquid CO 2 , proppant is added during fracturing, and the diameter of the proppant is h f After fracturing is completed, supercritical or liquid CO is continuously injected into the reservoir. 2 The injection amount is determined according to the carbon sequestration space V of the enclosed carbon sequestration area.

Claims

1. A method for unconventional oil and gas development and carbon sequestration, comprising the following steps: (1) Exploring the stratigraphic lithology and geological conditions of the target unconventional oil and gas reservoirs, identifying the geological structures in the geological reservoirs, calculating and analyzing the carbon storage capacity, and delineating the carbon storage areas; (2) Construct a vertical slotted well from the ground at the designed position downward to the designated layer and start to turn to horizontal drilling. After reaching the set position, withdraw the drill bit to the turning position, and then drill horizontally in another direction. After drilling is completed, withdraw the drill bit; (3) Continue to drill downward in the vertical slotted well, and then turn to horizontal drilling after reaching the designated layer, and then turn to continue horizontal drilling after retreating; (4) After completing the drilling of multiple horizontal boreholes according to the design requirements, the horizontal boreholes are directionally slotted, and after the slotting is completed, the slotted wells and horizontal boreholes are flushed; (5) After the drilling construction at the designed location is completed, the process of slotting wells, horizontal drilling, ultra-high pressure slotting, well washing, etc. will continue at the new location; (6) Conducting guided fracturing on all slotted wells. The fracture network formed after fracturing can cover the entire carbon storage area. The fracturing fluid used in fracturing is divided into pre-flush fluid, mid-flush fluid and post-flush fluid. The pre-flush fluid has a high-efficiency fracture-forming effect, and the mid-flush and post-flush fluids have the property of chemically reacting to generate solids. (7) After the reaction is completed, a vertical production well is constructed from the center of the carbon storage area to a specified depth, and then radial horizontal wells are constructed and fracturing is performed. After the fracturing is completed, drainage is performed to develop unconventional oil and gas resources; (8) After mining is completed, supercritical or liquid CO2 is injected into the mining well to store carbon in the designated carbon storage area.

2. The unconventional oil and gas development and carbon sequestration method according to claim 1, characterized in that: The delineated carbon storage area is generally rectangular, with no major geological structures in the area. There are generally two slotted wells, which are arranged diagonally at the boundary vertices of the storage area.

3. The unconventional oil and gas development and carbon sequestration method according to claim 1, characterized in that: When turning and drilling horizontally along the slotted well to the designated layer, the first turning position is generally the soft rock above the reservoir closest to the unconventional oil and gas reservoir. The judgment criteria are that the rock mechanical parameters decrease by more than 40% or the permeability increases by more than 1 times. The last turning position is generally about 20m below the unconventional oil and gas reservoir.

4. The unconventional oil and gas development and carbon sequestration method according to claim 1, characterized in that: The drilling length of horizontal boreholes is generally enough to cover the designated storage area. The vertical spacing of horizontal boreholes is related to the cutting depth, which is generally 8 times the cutting depth. If there is no specific data, 10m can be used.

5. The unconventional oil and gas development and carbon sequestration method according to claim 1, characterized in that: The fracturing fluid used in the fracturing process of slotted wells is divided into pre-fracture fluid, which has the characteristics of small filtration loss and low viscosity, and can make the hydraulic fractures expand rapidly forward. The middle and post-fracture fluids have the characteristics of chemical reaction to generate solids. The generated solids are extremely dense, with extremely low permeability, can withstand weak acids, and do not produce physical and chemical reactions with carbonic acid.

6. The unconventional oil and gas development and carbon sequestration method according to claim 1, characterized in that: After fracturing the slotted well, an outer layer with extremely low permeability can be formed in the carbon storage area, surrounding the unconventional oil and gas reservoir.

7. The unconventional oil and gas development and carbon sequestration method according to claim 1, characterized in that: The production wells are generally located in the middle of the carbon storage area. The horizontal wells formed by drilling are located in unconventional oil and gas reservoirs. The fracturing layer is an unconventional oil and gas reservoir. The fracturing technology used is the horizontal well staged fracturing technology, and then oil and gas resources are exploited.

8. The unconventional oil and gas development and carbon sequestration method according to claim 1, characterized in that: After the oil and gas resources are extracted, the reservoir is fractured again. Supercritical or liquid CO2 is used as the fracturing medium. Proppant is added during the fracturing process. After the fracturing is completed, supercritical or liquid CO2 is continuously injected into the reservoir. The injection amount is determined according to the designated carbon storage area.

9. The method for calculating carbon sequestration capacity according to claim 1, wherein: The calculation of carbon storage capacity is divided into two parts. One part is to calculate the storage capacity by analyzing the porosity of the reservoir, and the other part is to calculate the storage capacity by the spatial volume of the gaps formed by fracturing.

10. The slitting technique according to claim 4, characterized in that: The slotting device used has positioning, orientation and adjustment devices such as a horizontal compass, which can realize the adjustment of the azimuth angle, and the slotting technology used is ultra-high pressure hydraulic slotting technology or ultra-high pressure abrasive jet slotting technology or laser slotting technology. The slotting technology used is not unique, but it can cut a slot of a certain depth in the set direction.

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