CN113445978B - Method for optimizing hydraulic fracturing of shale gas reservoir through heat treatment - Google Patents

Abstract

The invention belongs to the field of oil and gas field development, and discloses a method for optimizing hydraulic fracturing of shale gas reservoirs by heat treatment. Hydration state The reservoir rock is made into a sample with the same degree of hydration as the reservoir rock after fracturing; the hydration sample is heated, and the highest temperature when the rock is thermally broken or obviously severely damaged is set as the highest heat treatment temperature ; Heating the hydration samples and maintaining the constant temperature for different durations; measuring the permeability of each sample, selecting the corresponding threshold constant temperature duration when the permeability changes abruptly, and setting the heat treatment constant temperature duration slightly higher than the threshold duration; according to the heat treatment heating temperature and constant temperature The setting of the time length selects the heating equipment that can meet the conditions for heating; the heat treatment of the reservoir is completed according to the setting. This method can optimize the effect of hydraulic fracturing to enhance the efficiency of subsequent shale gas production.

Description

A method of heat treatment to optimize hydraulic fracturing of shale gas reservoirs

technical field

The invention belongs to the field of oil and gas field development, in particular to a method for optimizing hydraulic fracturing of shale gas reservoirs by heat treatment.

Background technique

Shale gas is an emerging energy that changes the world's energy pattern. The reservoir rock of shale gas is usually tight, and it is often necessary to carry out reservoir stimulation before exploitation. Among many reservoir stimulation methods, hydraulic fracturing is relatively environmentally friendly and inexpensive. And effective, it is currently the most widely used method of reservoir reconstruction. The effect of hydraulic fracturing directly determines the efficiency of shale gas production. Therefore, improving and optimizing hydraulic fracturing is very important for the shale gas industry.

While hydraulic fracturing enhances the reservoir conductivity, it will also cause certain damage to the reservoir. The main component of the fracturing fluid used in hydraulic fracturing is water, and the flowback rate after fracturing is low, and most of the fracturing fluid stays in the reservoir. In the reservoir, the shale gas reservoir has a high clay content and has the property of swelling with water. The fracturing fluid and the reservoir rock are hydrated, forcing the reservoir rock to expand. On the one hand, the expansion force will force the fractures in the reservoir to continue to develop, further enhancing the conductivity of the reservoir. Engineers use this phenomenon to create a "stuffed well" method to enhance the hydraulic fracturing effect. On the other hand, the hydration and expansion of the reservoir rock will squeeze the original fracture, and the hydration will also reduce the strength of the reservoir rock, so that the proppant is embedded in the rock fracture wall, reducing the opening of the reservoir diversion channel, and when the channel is When it is squeezed to a certain extent, water lock will occur on site, causing secondary damage to the reservoir.

The rock hydration phenomenon after hydraulic fracturing in shale gas reservoirs has both advantages and disadvantages in practical engineering, and the advantages are used in engineering, but there are few ways to deal with its disadvantages. Therefore, there is an urgent need for a method that preserves the beneficial effects of reservoir rock hydration after hydraulic fracturing of shale gas reservoirs and removes its deleterious effects. The present invention mainly solves the above problems, eliminates the influence of hydration of shale gas reservoirs through a heat treatment method, and optimizes and enhances hydration fracturing.

SUMMARY OF THE INVENTION

In order to solve the above problems, the present invention proposes a method for optimizing hydraulic fracturing of shale gas reservoirs by heat treatment, which can optimize the effect of hydraulic fracturing and maximize the effect, so as to enhance the efficiency of subsequent shale gas exploitation.

For achieving the above object, the technical scheme adopted in the present invention is:

A method for optimizing hydraulic fracturing of shale gas reservoirs by heat treatment, comprising the following steps:

Step 1. Obtain hydraulic fracturing information, boring well information and reservoir rock, and analyze the hydration state of the reservoir rock according to the field information;

Step 2. According to the hydration state, the reservoir rock is made into a sample with the same degree of hydration as the reservoir rock after fracturing;

Step 3. Heating the hydration sample, and selecting the highest temperature when the rock is thermally broken or obviously severely damaged to be set as the highest heat treatment temperature;

Step 4. Heat the hydration sample to the maximum temperature set in step 3, and keep the temperature constant for different time periods; measure the permeability of each sample, select the corresponding threshold constant temperature duration when the permeability changes abruptly, and set the heat treatment constant temperature duration to slightly higher than the threshold duration;

Step 5, according to the setting of the heat treatment heating temperature and the constant temperature duration, select a heating device that can meet the conditions for heating;

Step 6. Complete the heat treatment of the reservoir according to the settings in Step 5, and then take out the heating equipment to start production.

Preferably, in step 1, the hydraulic fracturing information includes the fracturing fluid type and hydration time of the hydraulic fracturing, and the reservoir rock selects the core rock during the drilling process.

Preferably, in step 2, the rock obtained in step 1 is made into a cylindrical rock sample with a height of 50 mm and a diameter of 25 mm, and the sample is hydrated with a fracturing fluid. The hydration treatment is the same as the hydration of the reservoir after fracturing in the project. the same time;

If the hydration time of the reservoir is too long after fracturing, the samples are hydrated for different lengths of time, and the relationship between the hydration time and the change of the quality of the sample before and after hydration is analyzed. When the quality does not change with the change of the hydration time, it can be regarded as Hydration saturation, take the hydration time corresponding to the hydration saturation to hydrate the sample.

Preferably, in step 3, when the hydrated shale is heated, in order to ensure that the heating tool is not damaged during heating, the fracture and collapse phenomenon cannot occur during the heat treatment of the reservoir, that is, when the heat treatment temperature is set, use Heating in a heating furnace that can display the temperature, heat the hydration sample until thermal fracture occurs, record the fracture temperature, and set the reservoir heat treatment temperature to be slightly lower than the thermal fracture temperature to ensure that the hydrated shale remains intact when heated to the highest temperature .

Preferably, in step 4, a heating furnace with a controllable temperature is selected to heat the hydrated shale, heated to the set temperature in step 3, maintained at a constant temperature when the set temperature is reached, and different constant temperature times are set, After the heat treatment, the permeability experiment was carried out on the sample to seek the relationship between the permeability and the constant temperature duration. When the permeability changes abruptly, the constant constant temperature duration corresponding to the sudden change in permeability is the threshold value. The heat treatment duration of the reservoir is set to be slightly higher than the threshold constant temperature duration. .

Preferably, in step 5, according to the heat treatment temperature set in step 3 and the heat treatment duration set in step 4, a reservoir heating device that meets the conditions is selected and used to optimize the heat treatment of the sample.

Preferably, in step 6, according to the settings in step 5, heat treatment is performed on the hydrated shale gas reservoir after hydration fracturing in the actual project, and after completion, the heating equipment is taken out, and the page can be officially entered. Rock gas mining.

Preferably, the reservoir heating device is an electric heating device or a microwave radiation heating device.

The beneficial effects of using the present invention are:

The heat treatment of the shale gas reservoir after hydraulic fracturing in the present invention can not only retain the benefits brought by the expansion and capacity expansion, but also remove the damage caused by the hydration to the reservoir. For secondary reconstruction, multiple expansion mechanisms work together to increase reservoir fractures, optimize and improve hydraulic fracturing, and maximize its effect to enhance subsequent shale gas production efficiency.

Description of drawings

FIG. 1 is a flow chart of a method for optimizing hydraulic fracturing of a shale gas reservoir by heat treatment according to the present invention.

FIG. 2 is a graph showing the relationship between mass change and hydration time in the method for optimizing hydraulic fracturing of shale gas reservoirs by heat treatment according to the present invention.

FIG. 3 is a graph showing the relationship between permeability and constant temperature duration in the method for optimizing hydraulic fracturing of shale gas reservoirs by heat treatment according to the present invention.

FIG. 4 is a schematic diagram showing the effect of the method for optimizing hydraulic fracturing of shale gas reservoirs by heat treatment according to the present invention.

Detailed ways

In order to make the purpose, technical solution and advantages of the technical solution more clear, the technical solution will be further described in detail below with reference to the specific embodiments. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the technical solution.

As shown in FIG. 1, the present invention proposes a method for optimizing hydraulic fracturing of shale gas reservoirs by heat treatment, including the following steps:

Step 1. Obtain hydraulic fracturing information, boring well information and reservoir rock, and analyze the hydration state of the reservoir rock according to the field information; Step 2, prepare the reservoir rock and hydrate the reservoir rock after fracturing according to the hydration state Samples with the same degree; step 3, heat the hydrated sample, and select the highest temperature when the rock is thermally broken or obviously severely damaged to be set as the maximum heat treatment temperature; step 4, heat the hydration sample to step 3. Set the highest temperature, and keep constant temperature for different time periods; measure the permeability of each sample, select the threshold constant temperature time period corresponding to the sudden change of permeability, and set the heat treatment constant temperature time period to be slightly higher than the threshold value time period; step 5, according to the heat treatment heating temperature and the setting of the constant temperature duration, select the heating equipment that can meet the conditions for heating; step 6, complete the heat treatment of the reservoir according to the setting of step 5, and then take out the heating equipment to start production.

The above method will be described in detail below.

In step 1, the hydraulic fracturing information includes the type of fracturing fluid and the hydration time of the hydraulic fracturing, and the reservoir rock selects the core rock during the drilling process.

In step 2, the rock obtained in step 1 is made into a cylindrical rock sample with a height of 50 mm and a diameter of 25 mm, and the sample is hydrated with a fracturing fluid. The hydration treatment is the same as the hydration time of the reservoir after fracturing in the project; if The reservoir hydration time after fracturing is too long, the samples are hydrated for different time periods, and the relationship between the hydration time and the quality change of the samples before and after hydration is analyzed. When the quality does not change with the hydration time, it can be regarded as a water hydration saturation, take the hydration time corresponding to the hydration saturation, and hydrate the sample.

In step 3, when heating the hydrated shale, in order to ensure that the heating tool is not damaged during heating, the fracture and collapse phenomenon cannot occur during the heat treatment of the reservoir, that is, when the heat treatment temperature is set, use a heating device that can display the temperature. The furnace is heated to heat the hydration sample until thermal fracture occurs, record the fracture temperature, and set the heat treatment temperature of the reservoir to be slightly lower than the thermal fracture temperature to ensure that the hydrated shale remains intact when heated to the highest temperature.

In step 4, a heating furnace with a controllable temperature is selected to heat the hydrated shale to the set temperature in step 3. When the set temperature is reached, the heating is maintained at a constant temperature, and different constant temperature times are set. The sample was subjected to permeability experiments to find the relationship between permeability and constant temperature duration. When the permeability changed abruptly, the constant constant temperature duration corresponding to the sudden change of permeability was the threshold value, and the reservoir heat treatment duration was set to be slightly higher than the threshold constant temperature duration.

In step 5, according to the heat treatment temperature set in step 3 and the heat treatment duration set in step 4, a reservoir heating device that meets the conditions is selected and used to optimize the heat treatment of the sample. Reservoir heating equipment such as electric heating equipment, microwave radiation heating equipment, etc.

In step 6, according to the settings in step 5, heat treatment is performed on the hydrated shale gas reservoir after hydration fracturing in the actual project, and after completion, the heating equipment is taken out, and shale gas production can be officially started.

Example 1

Specific embodiments of the present invention are as follows:

Obtain mud shale rocks from Longmaxi Formation in Sichuan. Hydraulic fracturing generally uses fracturing fluid with a content of 99.5% water and quartz, so water is used instead of fracturing fluid. The mud shale was cut into cylindrical samples with a height of 50mm and a diameter of 25mm, and the samples were infiltrated into water for hydration, respectively, for 1, 2, 3, 4 and 5 hours. The mass changes of the samples before and after hydration were measured, as shown in Figure 1 , it can be seen from Fig. 2 that the rock tends to be saturated when it is hydrated for 3h-5h, so the hydration sample with 5h hydration is selected as the sample in the subsequent step. The permeability of the sample hydrated for 5 h was measured to be 0.01361×10 ^-3 μm ² .

The shale hydrated for 5 hours was heated. When heated to 360 °C, the rock was thermally broken. In order to ensure the safety of the downhole heating tool, the heat treatment temperature was set to 300 °C. The hydrated sample was heated to 300 °C for 5 h, and the temperature was kept constant for 5, 10, 15, 20, 25 and 30 minutes. After the heat treatment, the permeability was measured. The results are shown in Figure 3. It can be seen from Fig. 3 that the permeability changes abruptly when the constant temperature duration is 25min-30min. Therefore, the reservoir heat treatment duration can be set to 40min.

According to the above steps, the permeability of hydrated shale is only 0.01361×10 ^-3 μm ² , while the permeability of hydrated shale is heated to 300°C for 30 minutes, and the permeability reaches 2.21150×10 ^-3 μm ² , and the permeability increases. Up to 162.4 times, the diversion capacity is greatly improved, and the effect is excellent.

Hydraulic fracturing fluid stagnant in shale gas reservoirs will cause hydration of the reservoir rocks, which will cause damage to the reservoir and weaken the fracturing effect while hydration expansion and expansion. Aiming at the above phenomenon, the present invention proposes a method for optimizing hydration fracturing to eliminate the damage caused by hydration to the reservoir. After this method is applied to the hydraulic fracturing of shale gas reservoirs, if the project needs to block the well, it should be applied after the blocked well, and the heat treatment will be performed after the hydration expansion is completed. The heat treatment hydration mud shale mainly changes as follows:

1 After heat treatment of hydrated shale, the water dissipates, the hydration expansion is released, the opening of the squeezed cracks increases, and it returns to the unhydrated state.

2 During the heat treatment of hydrated shale, the water in it is heated and expanded, which expands the cracks in the rock, so that the cracks continue to develop to enhance its conductivity.

3 When the rock temperature reaches a certain level, thermal cracking occurs in the rock, and further new cracks are generated.

4 Reservoir shale is rich in kerogen, which decomposes under the action of high temperature, thereby increasing the pore volume.

As shown in Fig. 4, after drilling, the reservoir rock is tight, and hydraulic fracturing is needed to reform the reservoir. After hydraulic fracturing, the reservoir rock is fractured, and the fracture fluid has a low flowback rate and stays in the reservoir. After the hydration of the reservoir rock, the fractures continue to develop and new fractures are generated, but the opening of the fractures decreases. After heat treatment, the cracks continue to develop, the original crack opening increases, and new cracks are formed again.

To sum up, the heat treatment of shale gas reservoirs after hydraulic fracturing can not only retain the benefits of expansion and capacity expansion, but also remove the damage caused by hydration to the reservoir, and can also be used for thermal cracking, kerogen decomposition and other phenomena. For the secondary reconstruction of the reservoir, multiple expansion mechanisms work together to increase reservoir fractures, optimize and improve hydraulic fracturing, and maximize its effect to enhance the efficiency of subsequent shale gas production.

The above content is only a preferred embodiment of the present invention. For those of ordinary skill in the art, according to the idea of the technical content, many changes can be made in the specific implementation and application scope, as long as these changes do not depart from the concept of the present invention, All belong to the protection scope of this patent.

Claims (8)

1. a method for heat treatment optimization shale gas reservoir hydraulic fracturing, is characterized in that: comprise the steps, Step 1. Obtain hydraulic fracturing information, boring well information and reservoir rock, and analyze the hydration state of the reservoir rock according to the field information; Step 2. According to the hydration state, the reservoir rock is made into a sample with the same degree of hydration as the reservoir rock after fracturing; Step 3. Heating the hydration sample, and selecting the highest temperature when the rock is thermally broken or obviously severely damaged to be set as the highest heat treatment temperature; Step 4. Heat the hydration sample to the maximum temperature set in step 3, and keep the temperature constant for different time periods; measure the permeability of each sample, select the corresponding threshold constant temperature duration when the permeability changes abruptly, and set the heat treatment constant temperature duration to slightly higher than the threshold duration; Step 5, according to the setting of the heat treatment heating temperature and the constant temperature duration, select a heating device that can meet the conditions for heating; Step 6. Complete the heat treatment of the reservoir according to the settings in Step 5, and then take out the heating equipment to start production. 2. The method for optimizing hydraulic fracturing of shale gas reservoirs by heat treatment according to claim 1, wherein in step 1, the hydraulic fracturing information includes the fracturing fluid type and hydration time of hydraulic fracturing, and the Layer rock is selected to be cored during drilling. 3. The method for optimizing shale gas reservoir hydraulic fracturing by heat treatment according to claim 2, characterized in that: in step 2, the rock obtained in step 1 is made into a cylindrical rock sample with a height of 50mm and a diameter of 25mm, and the fracturing method is used. The sample is hydrated with liquid, and the hydration treatment is the same as the hydration time of the reservoir after fracturing in the project; If the hydration time of the reservoir is too long after fracturing, the samples are hydrated for different lengths of time, and the relationship between the hydration time and the change of the quality of the sample before and after hydration is analyzed. When the quality does not change with the change of the hydration time, it can be regarded as Hydration saturation, take the hydration time corresponding to the hydration saturation to hydrate the sample. 4. The method for optimizing hydraulic fracturing of shale gas reservoirs by heat treatment according to claim 3, characterized in that: in step 3, when the hydrated shale is heated, in order to ensure that the heating tool is not affected by the heating during heating Damage, breakage and collapse should not occur during heat treatment of the reservoir, that is, when the heat treatment temperature is set, use a heating furnace that can display the temperature to heat, heat the hydrated sample until thermal breakage occurs, record the breakage temperature, and set the heat treatment temperature of the reservoir Slightly lower than the thermal fracture temperature to ensure that the hydrated shale remains intact when heated to the highest temperature. 5. The method for optimizing hydraulic fracturing of shale gas reservoirs by heat treatment according to claim 4, characterized in that: in step 4, a heating furnace with a controllable temperature is selected to be used to heat the hydrated mud shale, and the heating To the set temperature in step 3, keep the constant temperature heating when the set temperature is reached, set different constant temperature times, and conduct permeability experiments on the samples after the heat treatment to seek the relationship between the permeability and the constant temperature time. When the permeability changes abruptly, the permeability The constant temperature duration corresponding to the mutation is the threshold value, and the heat treatment duration of the reservoir is set to be slightly higher than the threshold constant temperature duration. 6. The method for optimizing hydraulic fracturing of shale gas reservoirs by heat treatment according to claim 5, characterized in that: in step 5, through the heat treatment temperature set in step 3 and the heat treatment duration set in step 4, Select the reservoir heating equipment that meets the conditions to optimize the heat treatment of the sample. 7. The method for optimizing hydraulic fracturing of shale gas reservoirs by heat treatment according to claim 6, characterized in that: in step 6, according to the setting in step 5, the hydration fracturing in actual engineering The hydration shale gas reservoir is subjected to heat treatment, and after completion, the heating equipment is taken out, and the shale gas production can be officially started. 8 . The method for optimizing hydraulic fracturing of a shale gas reservoir by heat treatment according to claim 6 , wherein the reservoir heating device is an electric heating device or a microwave radiation heating device. 9 .

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