Drilling filling type multi-scale thermal fracturing method used in shale reservoir

Abstract

The invention relates to a drilling filling type multi-scale thermal fracturing method used in a shale reservoir, belongs to the technical field of oil and gas field fracturing, and aims to improve the complexity and permeability of a fracture network of the shale reservoir. Drilling holes in the wall of the casing pipe in the radial direction in the layer, mixing sand-carrying fluid and a self-heat-generating agent, and filling the sand-carrying fluid and the self-heat-generating agent into radial holes; the initiation medium is injected to excite the heat generation particles to generate an exothermic reaction; the exothermic reaction enables rocks around reservoir holes to generate heat shock damage, cold fluid is pumped in at high pressure, a temperature field drastically changes, and a hydraulic-thermal-stress-chemical effect composite transformation effect is formed; according to the technology, deep penetration drilling-in-layer self-heat-generation-hydraulic fracturing synergy can be achieved, and the main action mechanism comprises thermal damage permeability increasing rock, high-temperature and high-pressure weak acid gas seam expanding, plug removing and permeability increasing, hydraulic-thermal alternating synergy transformation and the like; and finally, excitation is carried out within the range of 200 m around the well to form a transformation area of the fracture net and the permeability-increasing matrix.

Description

Technical Field

[0001] The invention relates to a multi-scale thermal fracturing method for drilling and filling in a shale reservoir, belonging to the technical field of oil and gas field fracturing. Background Art

[0002] As the exploitation of medium- and high-permeability oil and gas fields enters the later stage and the demand for oil and gas resources continues to increase, the proportion of low-permeability and unconventional oil and gas reservoirs in oil and gas reserve increase has gradually increased, among which tight gas, shale gas, coalbed methane, etc. have become the main components of oil and gas reserve increase. The degree of improvement in the fracture network cutting density and matrix permeability of shale reservoirs has become a key factor restricting the efficiency of shale reservoir volume transformation and capacity release. Due to the common geological problems of domestic shale reservoirs, such as dense reservoirs, low porosity, low permeability, and small pore throats that cannot be effectively used, technological innovation is urgently needed to break through the existing mining restrictions.

[0003] At present, the combination of horizontal well drilling technology and large-volume fracturing technology has become the mainstream development strategy for optimizing the permeability of tight reservoirs and improving oil and gas recovery. Traditional hydraulic fracturing technology faces limitations in improving fracture efficiency, and the existence of high energy consumption has resulted in the development efficiency and economic returns of shale oil resources not reaching the expected goals. Fracturing technologies such as acid fracturing and explosive fracturing have good effects in improving reservoir transformation, but the cost is high and there are many uncertain factors in the construction process, which increases the technical risk and economic burden of development. To this end, based on the previous work, we proposed a hydraulic-thermal-stress-chemical (HTMC) composite transformation technology, which can achieve multi-scale coordinated transformation and is an effective way to efficiently develop shale reservoirs. How to achieve deep and efficient thermal energy excitation has become the key to this composite transformation technology. Summary of the invention

[0004] In view of the limitations of current hydraulic fracturing technology in reservoir transformation, especially the problems related to the formation and utilization of hydraulic fractures, the present invention proposes a multi-scale thermal fracturing technology for drilling and filling in shale reservoirs. This technology can achieve the synergy of deep penetration drilling-self-heating in the layer-hydraulic fracturing. The main mechanism of action includes thermal damage to increase the permeability of rocks, high temperature and high pressure weak acid gas expansion and unblocking and permeability enhancement, hydraulic-thermal alternating synergistic transformation, etc., and finally stimulates the formation of a transformation zone of fracture network + permeability matrix within 200m around the well.

[0005] The technical solution of the present invention is as follows:

[0006] A multi-scale thermal fracturing method for drilling and filling in shale reservoirs, the specific steps are as follows:

[0007] (1) Drilling radial holes into the layer on the casing wall to drill a series of deep radial holes;

[0008] (2) mixing the sand-carrying liquid with the self-heating agent and filling the mixture into the radial holes;

[0009] (3) by injecting an initiating medium, the self-heating agent is stimulated to produce an exothermic reaction;

[0010] (4) The exothermic reaction causes thermal damage to the rocks around the reservoir pores, and the thermal fluid further expands the existing fracture network;

[0011] (5) High-pressure pumping of cold fluid causes a dramatic change in the temperature field, forming a composite transformation effect of hydraulic-thermal-stress-chemical effects;

[0012] (6) Cycle steps (2) to (5) to repeat the rock thermal activation and cooling process to achieve thermal fatigue transformation, increase fracture complexity and matrix permeability, and stimulate the formation of a fracture network + permeability-enhancing matrix transformation zone within 200 m around the well.

[0013] Preferably, the directional drilling technology in step (1) adopts the intra-layer multi-branch reverse drilling and completion technology, which uses flexible reverse drilling tools, wellbore trajectory guidance control systems and flexible reverse screens to perform horizontal drilling and completion; windows are opened in multiple directions in the existing wellbore to drill multiple branch wells, the branch wellbore diameter is generally smaller than the main wellbore, the curvature radius is controlled within the range of 1.5 to 3.5 meters, and the wellbore turns 90 degrees to drill horizontally for 50 to 200 meters. The layout and depth of the radial holes are determined by comprehensive analysis of rock mechanical properties and reservoir geological structures to ensure maximum fracture propagation efficiency.

[0014] Preferably, in step (2), the self-heating agent is a NaNO2 / NH4Cl system, which is mixed with the sand-carrying liquid and filled into the radial holes; the system is based on the chemical reaction of sodium nitrite (NaNO2) and ammonium chloride (NH4Cl) in an aqueous solution:

[0015] NaNO2+NH4Cl=N2↑+NaCl+2H2O+Q (1)

[0016] Q represents the heat generated by the reaction. The reaction can release a large amount of heat and nitrogen in a short period of time, causing the reservoir temperature to rise rapidly, resulting in thermal expansion and thermal cracking of the rock, thereby forming new cracks or expanding existing cracks; the nitrogen generated can form high pressure in the cracks, further promoting the extension and expansion of the cracks and increasing the permeability of the reservoir.

[0017] Further preferably, in step (2), when the mass ratio of NaNO2 and NH4Cl is (1.2-1.3):1, the molar ratio of the two substances can make the reaction proceed more efficiently according to the stoichiometric relationship, and can stably release a large amount of heat within a certain period of time, which is conducive to maintaining a continuous high temperature environment in the reservoir and effectively transferring heat to the surrounding rocks.

[0018] Further preferably, in step (2), the amount of NaNO2 and NH4Cl is calculated based on reservoir characteristics and fracture geometry parameters according to the formula Determine the amount of self-heating agent, where: m is the mass of the self-heating agent, in kg; L is the crack length, in m; W is the crack width, in m; H is the crack height, in m; is the fracture porosity, in %; ρ is the density of the autogenous heat generating agent, in g / cm 3 .

[0019] Preferably, the initiating medium in step (3) is water, and its injection amount is determined according to the amount of the self-heating agent NaNO2 and NH4Cl, and the liquid-solid volume ratio is (2-3):1.

[0020] Preferably, in step (5), after the exothermic reaction has been carried out for 15 to 30 minutes, a cold fluid with a ground temperature of 20°C is injected, and the formation temperature change is detected in real time using a temperature sensor line. When the formation temperature difference reaches 80°C to 120°C, a fracturing effect is produced inside the formation.

[0021] Preferably, the volume of the cold fluid injected in step (5) is 1.0 to 1.2 times the pore volume of the formation.

[0022] Preferably, the hot-cold alternating reaction in the formation in step (6) is repeated 2 to 3 times.

[0023] The present invention can realize the synergy of deep penetration drilling, self-generated heat within the layer and hydraulic fracturing during the transformation process. The main action mechanisms include thermal damage to increase the permeability of rocks, high-temperature and high-pressure weak acid gas expansion and unblocking and permeability enhancement, hydraulic-thermal alternating synergistic transformation, etc., and finally stimulate the formation of a transformation zone of fracture network + permeability-enhancing matrix within 200m around the well, realizing hydraulic-thermal-stress-chemical multi-scale composite transformation.

[0024] The beneficial effects of the present invention are:

[0025] 1. The present invention is a method for realizing the thermal shock effect of alternating hot and cold reservoirs by controlling the formation temperature. It is mainly aimed at actual formation problems such as dense reservoirs, low porosity, low permeability, and small pore throats that cannot be effectively utilized. It conducts multi-level composite reservoir transformation to make the oil and gas layer fracture network more complex and improve the reservoir permeability.

[0026] 2. Through the precise control of directional drilling technology, a more rationally arranged fracture network is created in the reservoir, which helps to maximize the propagation efficiency of the fractures. The deep concentrated transmission of thermal energy is realized, providing a new way for hydraulic-thermal-stress-chemical composite transformation, which can directly act on shale reservoirs, improve oil and gas extraction efficiency, and bring direct benefits to production.

[0027] 3. The chemical reaction of the injected heat-generating particles leads to local thermal cracking of the reservoir rock and changes in the pore structure, which in turn expands the fracture network of the entire reservoir as a whole. The injection of cold fluid rapidly cools the reservoir rock, causing the fracture extension to continue to expand. Through the periodic cooling and thermal activation process, a composite transformation mechanism of hydraulic, thermal, stress and chemical effects is achieved, which helps to increase the complexity and connectivity of the fractures and improve the permeability of the reservoir matrix through repeated thermal stress.

[0028] 4. Compared with traditional hydraulic fracturing technology, the present invention has better fracturing effect, broader prospects and wider application range. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a construction process flowchart of the present invention;

[0030] Figure 2 It is a schematic diagram of the above-ground equipment and underground equipment of the present invention;

[0031] Figure 3 It is a schematic diagram of the reaction process of the solid heat-generating particles of the present invention;

[0032] Among them, 1. a mixture of sand-carrying fluid and self-heating agent; 2. an initiating medium; 3. a cold fluid; 4. a pump truck; 5. a wellhead; 6. a production casing; 7. a wellbore casing; 8. a packer; 9. a mixture of sand-carrying fluid and self-heating agent; 10. a radial hole; 11. a formation; 12. a fracture. DETAILED DESCRIPTION

[0033] The present invention will be further described below by way of embodiments in conjunction with the accompanying drawings, but is not limited thereto.

[0034] Embodiment 1:

[0035] A multi-scale thermal fracturing method for drilling and filling in shale reservoirs, the specific steps are as follows:

[0036] (1) Drilling radial holes into the layer on the casing wall to drill a series of deep radial holes; Directional drilling technology uses multiple reverse drilling and completion technology in the layer, which uses flexible reverse drilling tools, wellbore trajectory guidance control systems and flexible reverse screens for horizontal drilling and completion; Opening windows in multiple directions in the existing wellbore to drill multiple branch wells. The diameter of the branch wellbore is generally smaller than that of the main wellbore, and the curvature radius is controlled within the range of 1.5 to 3.5 meters. The wellbore turns 90 degrees and drills horizontally for 50 to 200 meters. The layout and depth of the radial holes are determined by comprehensive analysis of rock mechanical properties and reservoir geological structures to ensure maximum fracture propagation efficiency.

[0037] (2) Mixing the sand-carrying liquid with a self-heating agent and filling the mixture into the radial holes; the self-heating agent is a NaNO2 / NH4Cl system, which is mixed with the sand-carrying liquid and filled into the radial holes; the system is based on the chemical reaction of sodium nitrite (NaNO2) and ammonium chloride (NH4Cl) in an aqueous solution:

[0038] NaNO2+NH4Cl=N2↑+NaCl+2H2O+Q (1)

[0039] Q represents the heat generated by the reaction. The reaction can release a large amount of heat and nitrogen in a short period of time, causing the reservoir temperature to rise rapidly, causing thermal expansion and thermal cracking of the rock, thereby forming new cracks or expanding existing cracks; the nitrogen generated can form high pressure in the cracks, further promoting the extension and expansion of the cracks and increasing the permeability of the reservoir. The mass ratio of NaNO2 and NH4Cl is (1.2-1.3):1.

[0040] The calculation of the amount of NaNO2 and NH4Cl is based on the reservoir characteristics and fracture geometry parameters, according to the formula Determine the amount of self-heating agent, where: m is the mass of the self-heating agent, in kg; L is the crack length, in m; W is the crack width, in m; H is the crack height, in m; is the fracture porosity, in %; ρ is the density of the autogenous heat generating agent, in g / cm 3 .

[0041] (3) By injecting an initiating medium, the self-heating agent is stimulated to produce an exothermic reaction; the initiating medium is water, and its injection amount is determined according to the amount of the self-heating agent NaNO2 and NH4Cl, and the liquid-solid volume ratio is (2-3):1.

[0042] (4) The exothermic reaction causes thermal damage to the rocks around the reservoir pores, and the hot fluid further expands the existing fracture network.

[0043] (5) After the exothermic reaction has been going on for 15 to 30 minutes, a cold fluid with a ground temperature of 20°C is injected to cause a dramatic change in the temperature field, forming a composite transformation effect of hydraulic, thermal, stress and chemical effects; the temperature sensor line is used to detect the change in formation temperature in real time. When the formation temperature difference reaches 80°C to 120°C, a fracture effect occurs inside the formation. The injection volume of the cold fluid is 1.0 to 1.2 times the pore volume of the formation.

[0044] (6) Steps (2) to (5) are cycled 2 to 3 times to repeat the rock thermal activation and cooling process to achieve thermal fatigue transformation, increase fracture complexity and matrix permeability, and stimulate the formation of a fracture network + permeability-enhancing matrix transformation zone within 200 m around the well.

[0045] In this embodiment, the basic parameters of the target well are shown in Table 1:

[0046] Table 1 Basic data of target wells

[0047]

[0048]

[0049] According to the fracture geometry parameters of the fractured layer, the total fracture volume is calculated to be 50×6.1×0.007=2.14m 3 , the fracture porosity is set to 30%.

[0050] In this embodiment, the density of the self-heating particles is 1.8 g / m 3 The estimated amount of self-heating particles is m=50*0.007*6.1*30%*1.8*1000t=1.15t, among which the mass ratio of NaNO2 and NH4Cl is 1.25:1, then the mass of NaNO2 is 630.32kg, and the mass of NH4Cl is 525.27kg.

[0051] In this embodiment, the liquid-to-solid ratio of the initiating medium water to the self-heating agent is 2:1, so the injection volume of the initiating medium water is V = 2.14 × 0.3 × 2 = 1.28 m 3 .

[0052] In this embodiment, the volume of the wellbore (also called casing) in the target well 1 is

[0053]

[0054] In this embodiment, the injection amount of the cold fluid in step 5 is V 水 =2.14×1.2=2.604m 3 In actual use, the injection amounts of the isolation fluid and the displacement fluid can be adjusted accordingly according to specific needs.

[0055] Assume that the target fracturing layer is a shale layer, the elastic modulus of shale is E = 4.1 GPa, and the thermal expansion coefficient of shale is α = 8×10 -6 / ℃, the temperature of ammonium perchlorate after reaction with aluminum powder can reach 150℃, the temperature of the cold fluid injected into the formation is 50℃, then the temperature difference ΔT=100℃, the half length of the crack is 0.01m, the applied stress σ=50MPa, the fracture toughness K of shale IC =(0.8~1.2)MPa·m 1 / 2 .

[0056] Thermal stress σ caused by a dramatic change in temperature field 热 =4.1×10 9 ×8×10-6 ×100=32.8MPa,

[0057] Total stress σ 总 =σ 热 +σ=50+32.8=82.8MPa,

[0058] Stress Intensity Factor

[0059] Comparing K and K IC :14.66>(0.8~1.2),

[0060] Therefore, the stress intensity factor that can be achieved by the present invention is greater than the fracture toughness of the shale formation, which indicates that the shale formation can be fully expanded and extended under the change of this temperature field to form a transformation zone of fracture network + permeability-enhancing matrix.

[0061] Example 2

[0062] A multi-scale thermal fracturing method for drilling and filling in shale reservoirs, wherein the steps are as described in Example 1, except that the mass ratio of NaNO2 to NH4Cl in step (2) is 1.2:1.

[0063] Example 3

[0064] A multi-scale thermal fracturing method for drilling and filling in shale reservoirs, wherein the steps are as described in Example 1, except that the mass ratio of NaNO2 to NH4Cl in step (2) is 1.3:1.

[0065] Example 4

[0066] A multi-scale thermal fracturing method for drilling and filling in shale reservoirs, wherein the steps are as described in Example 1, except that in step (3), the liquid-to-solid ratio of the initiating medium water and the self-heating agent is controlled to be 3:1.

[0067] Example 5

[0068] A multi-scale thermal fracturing method for drilling and filling in shale reservoirs, wherein the steps are as described in Example 1, except that the injection volume of the cold fluid in step (5) is 1 times the pore volume of the formation.

Claims

1. A multi-scale thermal fracturing method for drilling and filling in shale reservoirs, characterized in that: The specific steps are as follows: (1) Drilling radial holes into the layer on the casing wall to drill a series of deep radial holes; (2) mixing the sand-carrying liquid with the self-heating agent and filling the mixture into the radial holes; (3) by injecting an initiating medium, the self-heating agent is stimulated to produce an exothermic reaction; (4) The exothermic reaction causes thermal damage to the rocks around the reservoir pores, and the thermal fluid further expands the existing fracture network; (5) High-pressure pumping of cold fluid causes a dramatic change in the temperature field, forming a composite transformation effect of hydraulic-thermal-stress-chemical effects; (6) Cycle steps (2) to (5) to repeat the rock thermal activation and cooling process to achieve thermal fatigue transformation and stimulate the formation of a fracture network + permeability matrix transformation zone within 200 m around the well.

2. The multi-scale thermal fracturing method for drilling and filling in shale reservoirs according to claim 1, characterized in that: In step (1), a flexible reverse drilling tool and a flexible reverse screen are used to perform horizontal drilling and completion; windows are opened in multiple directions in the existing wellbore to drill multiple branch wells. The diameter of the branch wellbore is smaller than that of the main wellbore, and the curvature radius is controlled within the range of 1.5 to 3.5 meters. The wellbore is turned 90 degrees and drilled horizontally for 50 to 200 meters.

3. The multi-scale thermal fracturing method for drilling and filling in shale reservoirs according to claim 1, characterized in that: In step (2), the self-heating agent is a NaNO2 / NH4Cl system, which is mixed with the sand-carrying liquid and filled into the radial holes; the system is based on the chemical reaction of sodium nitrite (NaNO2) and ammonium chloride (NH4Cl) in aqueous solution: NaNO2+NH4Cl=N2↑+NaCl+2H2O+Q (1) Q represents the heat generated by the reaction. The reaction releases a large amount of heat and nitrogen in a short period of time, which increases the reservoir temperature and causes thermal expansion and thermal cracking of the rock, thereby forming new cracks or expanding existing cracks.

4. The multi-scale thermal fracturing method for drilling and filling in shale reservoirs according to claim 3, characterized in that: In step (2), the mass ratio of NaNO2 and NH4Cl is (1.2-1.3):

1.

5. The multi-scale thermal fracturing method for drilling and filling in shale reservoirs according to claim 1, characterized in that: In step (2), according to the formula Determine the amount of self-heating agent, where: m is the mass of the self-heating agent, in kg; L is the crack length, in m; W is the crack width, in m; H is the crack height, in m; is the fracture porosity, in %; ρ is the density of the autogenous heat generating agent, in g / cm 3 .

6. The multi-scale thermal fracturing method for drilling and filling in shale reservoirs according to claim 1, characterized in that: The initiating medium in step (3) is water, and its injection amount is determined according to the amount of the self-heating agent used, and the liquid-to-solid volume ratio is (2-3):

1.

7. The multi-scale thermal fracturing method for drilling and filling in shale reservoirs according to claim 1, characterized in that: In step (5), after the exothermic reaction has been carried out for 15 to 30 minutes, a cold fluid with a ground temperature of 20°C is injected, and the temperature change of the formation is detected in real time using a temperature sensor line. When the temperature difference of the formation reaches 80°C to 120°C, a fracturing effect occurs inside the formation.

8. The multi-scale thermal fracturing method for drilling and filling in shale reservoirs according to claim 1, characterized in that: In step (5), the injection volume of the cold fluid is 1.0 to 1.2 times the pore volume of the formation.

9. The multi-scale thermal fracturing method for drilling and filling in shale reservoirs according to claim 1, characterized in that: The hot and cold alternating reaction in the formation in step (6) is repeated 2 to 3 times.

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