CN114856521A - Method for improving repeated reconstruction effect of shale oil and gas reservoir by thermal shock - Google Patents

Abstract

The invention provides a method for improving repeated reconstruction effect of a shale oil and gas reservoir by using thermal shock, which comprises the following steps of S1: closing the shale oil-gas well after hydraulic fracturing modification, and gathering residual shale oil-gas in a hydraulic fracture; s2: injecting an oxygen source into the hydraulic fracture, and setting a packer to seal off the hydraulic fracturing well section; s3: igniting the mixture in the hydraulic fracture in the underground manner, closing an underground packer to form thermal shock, and inducing the wall surface of the hydraulic fracture to be micro-fractured by high-temperature shock; s4: and opening the packer, injecting cooling water into the hydraulic fracture, and rapidly cooling the shale in a high-temperature state when the shale meets the cooling water to form thermal shock again, so that the wall surface of the hydraulic fracture is induced to be micro-fractured again to form more dense micro-fractures. The method fully crushes and reforms the shale matrix blocks among the hydraulic fractures, so as to greatly improve the fracture density of the shale oil-gas reservoir and enhance the oil-gas supply capacity of the shale matrix blocks to the hydraulic fractures and the mineshaft.

Description

A method for improving the effect of repeated stimulation of shale oil and gas reservoirs by thermal shock

technical field

The invention relates to the technical field of tight oil and gas development, in particular to a method for improving the effect of repeated stimulation of shale oil and gas reservoirs by utilizing thermal shock.

Background technique

After the shale oil and gas wells are drilled, they usually have to go through hydraulic fracturing technology before they can be exploited. Therefore, the first hydraulic fracturing of a new well is also called the primary stimulation (relative to repeated stimulation). Hydraulic fracturing is an effective way to develop shale oil and gas reservoirs. key means. The cross-scale fractures (hydraulic fractures, micro-fractures) formed by hydraulic fracturing make the dense shale matrix cut and broken, shorten the diffusion path of oil and gas in the shale matrix, and facilitate the rapid entry of oil and gas into hydraulic fractures and wellbore Therefore, hydraulic fracturing can greatly increase the production of shale oil and gas wells.

Shale oil and gas wells usually have high initial production, but the production declines rapidly. For example, the initial single-well production in the Eagle Ford shale gas field in the United States can be as high as 3×10 ⁴ m ³ /d, but it decays to less than 0.8×10 within a year. ⁴ m ³ /d. The reason is not that the reserves are exhausted, but that the density of hydraulic fractures generated by hydraulic fracturing (initial reconstruction) is not high enough, and only the oil and gas near the area connected by the hydraulic fractures are recovered. Oil and gas well production dropped sharply. It can be seen that it is difficult to fully reform shale oil and gas reservoirs by one fracturing, resulting in a limited number of micro-fractures, large fracture spacing, and insufficient fragmentation of the shale matrix, resulting in rapid production decline and low recovery.

Therefore, in the later stage of production of shale oil and gas wells, hydraulic fracturing technology is usually used for secondary stimulation (ie, repeated stimulation) to further increase the number of micro-fractures in oil and gas reservoirs. In the process of repeated stimulation, hydraulic fractures extend quickly, easily communicate, interfere with the fracture network of adjacent wells, and cause pressure channeling, resulting in high risk of repeated stimulation and unpredictable stimulation effects.

Thermal shock is an important method for increasing the permeability of underground dense rocks. When the rock is rapidly heated or cooled, a large amount of heat exchange will occur in a short period of time, and a large temperature difference will be generated on the surface and inside of the rock. Due to the thermal expansion, a large thermal stress will be generated in the material, which is called thermal shock. Fracture of rock under thermal shock can greatly increase its permeability. Existing thermal shock methods include electric heating, microwave heating, high-temperature gas injection, and dry-hot rock injection of liquid nitrogen, etc. Electric heating is difficult to achieve rapid temperature rise (>10°C/min) due to the limitation of power, and thermal shock cannot be formed; microwave heating It can heat up quickly, but its heating range is limited to the surrounding of the wellbore; the heating efficiency of high-temperature gas injection is not high; and the liquid nitrogen injection method is usually only suitable for hot dry rock reservoirs with formation temperature higher than 180 °C, without artificial heating, only A thermal shock can occur when a sharp cooling is required. All of the above methods have certain disadvantages.

Therefore, based on the in-situ heating technology, the present invention proposes to use the thermal shock effect of rapid heating and rapid cooling of rocks to form dense micro-fractures in shale oil and gas reservoirs, improve the effect of repeated stimulation, and further increase the production and production of shale oil and gas reservoirs. recovery rate.

SUMMARY OF THE INVENTION

In order to solve the defects existing in the prior art, the present invention provides a method for improving the effect of repeated reformation of shale oil and gas reservoirs by using thermal shock. After heating, a significant temperature gradient is formed on the fracture wall to generate thermal shock, and then a large amount of cooling water is rapidly injected, and the fracture wall is rapidly cooled to form thermal shock again. Significantly increase the density of micro-fractures, shorten the oil and gas diffusion path, and enhance the oil and gas supply capacity of shale blocks to hydraulic fractures and wellbores.

In order to achieve the above-mentioned purpose, the technical scheme provided by the present invention is: utilize thermal shock to improve the method for the repeated reformation effect of shale oil and gas reservoirs, which comprises the following steps, S1: shutting in the shale oil and gas well after hydraulic fracturing reformation, residual Shale oil and gas accumulate in hydraulic fractures; S2: inject oxygen source into hydraulic fractures, run a packer to seal the hydraulic fracturing well section; S3: conduct downhole ignition to ignite the mixture in hydraulic fractures, and at the same time close downhole to seal S4: Open the packer and inject cooling water into the hydraulic fractures, the shale under high temperature is rapidly cooled by the cooling water, and thermal shock is formed again, which induces micro-fractures again. Forms denser micro-cracks.

Preferably, in step S1, the fracturing fluid used in the hydraulic fracturing stimulation is a water-based fracturing fluid commonly used in shale oil and gas reservoirs.

Preferably, in step S2, the oxygen source includes oxygen and/or an oxygen supply agent; the oxygen supply agent includes one or more of hydrogen peroxide, sodium peroxide, potassium peroxide, and peracetic acid.

Preferably, the oxygen supply agent can be used together with a catalyst, and the catalyst includes one or more of catalase, manganese dioxide, and alkaline solution.

Preferably, the cooling medium is water.

Preferably, in the step S1, the shale oil and gas well after hydraulic fracturing is formed by the following steps: (1) Drilling at least one horizontal well in the shale oil and gas reservoir, and drilling the horizontal well The first hydraulic fracturing is carried out in the interval to form hydraulic fractures; (2) After the hydraulic fracturing is completed, wells are opened to produce shale oil and gas, until the daily oil and gas production continues to decline to no commercial value.

The present invention utilizes thermal shock to improve the mechanism of the method for the repeated stimulation effect of shale oil and gas reservoirs as follows:

The invention is a new technology of repeated reconstruction, which utilizes the thermal expansion and cold contraction properties and hard and brittle properties of rocks to form dense micro-fractures with a smaller size in the vicinity of the hydraulic fracture wall, and accelerates the shale gas in the nearby area. Convergence within hydraulic fractures to restore and increase production from shale oil and gas wells. When shale is heated by in-situ combustion, its surface is heated first and the temperature rises sharply. Affected by the low thermal conductivity and thermal conductivity of shale, its internal temperature rises with a hysteresis, and the hysteresis occurs when the heating rate is faster. When the shale is cooled by water, if the cooling rate is fast, a considerable and opposite temperature gradient will be established between the surface and the interior of the shale. . Significant thermal stress is generated due to the difference in the amount of thermal expansion (contraction) at different temperatures, resulting in thermal shock. Combustion is an unstable dynamic process, so shale is heated unevenly during oil and gas combustion, which can also generate uneven temperature gradients in the lateral direction. Intensive thermal fracture occurs on the wall of hydraulic fracture due to thermal shock, resulting in dense micro-fractures.

The beneficial effects of the present invention are as follows:

(1) The material is obtained locally, and the cost is low. The method uses the residual or unproduced oil and gas in the shale oil and gas reservoir in the later stage of production as the fuel for heating shale, which is convenient for large-scale implementation in the field; according to the actual situation and economic conditions of the shale oil and gas reservoir, the injection of oxygen or oxygen supply can be controlled by controlling Compared with the secondary fracturing, the amount of repeated reformation works is small, the cost is low, and the best technical and economic reformation effect can be obtained;

(2) The repeated stimulation process can avoid the interference to the offset well to the greatest extent. The repeated reformation scheme provided by the present invention, the reformation scope is in the shale rock layer near the hydraulic fracture wall surface, does not greatly extend the original hydraulic fracture length, and avoids the pressure channeling caused by the secondary fracturing technology which is easy to connect the hydraulic fractures of adjacent wells. Disadvantages, no interference between wells;

(3) Increase the density and width of micro-cracks and establish more efficient multi-scale mass transfer channels. On the basis of hydraulic fracturing, the invention forms micro-fractures on the walls of hydraulic fractures, and fully breaks and reforms the shale base blocks between hydraulic fractures, so as to greatly increase the fracture density of shale oil and gas reservoirs and establish multi-scale oil and gas mass transfer. channel, shorten the oil and gas diffusion path, and enhance the gas supply capacity of shale matrix to hydraulic fractures and wellbore.

Description of drawings

Fig. 1 is the flow chart that utilizes thermal shock to improve shale oil and gas reservoir repeated reforming effect of the present invention;

Fig. 2 is a schematic diagram of hydraulic fractures formed by staged fracturing of horizontal wells in shale oil and gas reservoirs according to an embodiment of the present invention; Fig. 3 is a schematic diagram of dense micro-fractures formed on the fracture wall surface by combustion and heating of a mixture of oil and gas according to an embodiment of the present invention, showing that thermal expansion stress causes The micro-fractures in the figure; the red glow (shaded area) in the figure represents the high-temperature rock after combustion, 1- the mixture of oil and gas and oxygen is burned; 2- the temperature gradient from the fracture wall to the interior of the rock layer produced by the combustion; 3- the heated page near the hydraulic fracture 4- Micro-fractures generated under the action of thermal shock; 5- Running a packer to prevent combustion products and heat from escaping to areas outside the production interval; Figure 4 is an embodiment of the present invention that injects a large amount of cooling into the reservoir Schematic diagram of thermal shock after rapid cooling of water; blue glow (shaded area) in the figure represents low-temperature water, 6-cooling water in hydraulic fractures; 7-temperature gradient from the inside of the rock formation to the fracture wall caused by rapid cooling; 8-sharp More dense micro-fractures are formed under cooling thermal shock; Fig. 5 is the acoustic emission signal of shale rupture under rapid heating; Fig. 6 is the acoustic emission signal of shale rupture under rapid cooling; Fig. 7 is the original shale SEM image; Fig. 8 Fig. 9 is the SEM image of shale after rapid heating and thermal shock; Fig. 9 is the SEM image of shale after rapid cooling and thermal shock.

Detailed ways

In order to make the above objects, features and advantages of the present invention more clearly understood, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Example 1

As shown in Figure 1, at least one horizontal well is drilled in the shale oil and gas reservoir, and the first staged hydraulic fracturing is performed on the production interval of the horizontal well to form hydraulic fractures, as shown in Figure 2. Then wells were opened to produce shale oil and gas, and oil and gas near the walls of hydraulic fractures were gradually recovered, while oil and gas far from the walls of the fractures were difficult to be recovered quickly due to the large seepage resistance of the shale matrix, resulting in a continuous decline in daily oil and gas production. Shut in the well after it has commercial value. During the shut-in process, the oil and gas far away from the fracture wall will converge into the hydraulic fracture under the action of pressure difference and concentration difference; wait for several months to a year, and inject oxygen or oxygen supply agent and its catalyst into the hydraulic fracture, under the action of the concentration difference. Then, the oxygen, oxygen supply agent, and its catalyst are fully mixed with the oil and gas in the hydraulic fracture through diffusion; the packer is installed to seal the hydraulic fracturing well section, and the downhole ignition device is used to ignite the oil and gas and oxygen mixture in the hydraulic fracture. , so that it can be fully burned in the hydraulic fracture, as shown in Figure 3, and the downhole packer is closed at the same time to prevent the combustion products and heat from escaping to the area outside the production interval; the heat generated by the combustion causes the shale temperature on the wall of the hydraulic fracture to rise sharply Thermal shock is formed, and shale produces dense micro-fractures under the action of thermal shock; after the micro-fractures induced by high-temperature thermal shock are stopped, the packer is opened, and a large displacement of cooling water not higher than 20 °C is injected into the hydraulic fractures of the production interval. Water, the shale under high temperature is rapidly cooled by cooling water, and thermal shock is formed again, as shown in Figure 4. A large range of tensile stress is generated in the shale on the fracture wall, which again induces shale micro-fractures and forms more dense micro-fractures.

Example 2

This embodiment is used as an experimental verification for using thermal shock to generate micro-fractures to reform shale oil and gas reservoirs. In order to prove the effect of thermal shock, the acoustic emission monitoring experiment of shale thermal fracture process and the scanning electron microscope observation experiment before and after shale thermal fracture were carried out.

When a rock breaks, it produces vibrations (sound waves) that travel outward from the location where the breakup occurred at the speed of sound waves within the solid. When the sound wave reaches the acoustic emission probe, it is received by the sensor and displayed on the acoustic emission waveform, and each wave peak (or trough) corresponds to a rupture event. Figures 5 and 6 are the AE waveform diagrams of the shale samples in the rapid heating stage and the rapid cooling stage, respectively. The AE signal in Figure 5 mainly appears in the first half of the waveform, that is, the rapid heating stage of the rock in the heating experiment. The acoustic emission signal mainly appears in the second half of the waveform, that is, the sharp cooling stage of the rock in the heating experiment. From the comparison of the two figures, it can be seen that the thermal fracture signals in the sharp cooling stage of the rock are more dense, which means that the internal fracture frequency of the rock is higher, and the average amplitude of the rock sharp cooling stage is also larger, which means that a single fracture releases more energy. That is, the rupture amplitude is larger, and the difference is very obvious.

Rock is a material that is compressive but not tensile. During the rapid heating process, the mineral particles in the rock expand and squeeze each other, resulting in compressive stress. During the rapid cooling process, the mineral particles in the rock shrink and generate tensile stress. Rocks fracture with greater frequency and magnitude under tensile stress. Cracks are formed after the rock is cracked by thermal shock. Using scanning electron microscope to observe in situ before and after thermal shock can analyze and determine the effect of thermal cracking. Fig. 7, Fig. 8 and Fig. 9 are scanning electron microscope observation images of the same position of the shale sample under different conditions, among which, Fig. 7 is the original shale sample; Fig. 8 is the sheet after the sharp heating and thermal shock obtained by the ignition treatment It can be seen from the figure that many micro-fractures (indicated by the arrow in the figure) along the edge of the mineral grains or passing through the mineral grains are produced after the rapid heating and thermal shock. Although most of these micro-fractures are isolated fractures, they are not connected to each other or Connected to the natural fractures in the shale, new mass transfer paths can still be generated, which shortens the oil and gas diffusion paths and enhances the oil and gas seepage capacity of the shale. The shale in Figure 8 is cooled with cooling water, and the results are shown in Figure 9 . Figure 9 shows the shale sample after rapid cooling and thermal shock. After the rapid cooling and thermal shock, the shale further produces more dense micro-fractures (indicated by the arrow in the figure), and the original micro-fractures are extended in length and greatly increased in width. The isolated fractures gradually connect to form a complex fracture network, which greatly shortens the oil and gas mass transfer paths in the shale, greatly improves the seepage capacity of the shale, and enhances the oil and gas production capacity.

It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be Modifications or equivalent substitutions without departing from the spirit and scope of the technical solutions of the present invention should be included in the scope of the claims of the present invention.

Claims (6)

1. utilize thermal shock to improve the method for shale oil and gas reservoir repeated transformation effect, it is characterized in that: comprise the following steps, S1: shut down the shale oil and gas well after hydraulic fracturing, and the residual shale oil and gas will accumulate in the hydraulic fracture; S2: inject an oxygen source into the hydraulic fracture, and run a packer to seal the hydraulic fracturing well section; S3: Perform downhole ignition to ignite the mixture in the hydraulic fracture, and at the same time close the downhole packer to form thermal shock, and perform high temperature shock to induce micro-fractures on the hydraulic fracture wall; S4: Open the packer and inject cooling medium into the hydraulic fractures. The shale in the high temperature state is rapidly cooled by the cooling water, and thermal shock is formed again, which induces micro-fractures on the walls of the hydraulic fractures to form more dense micro-fractures. Repeated reconstruction of shale oil and gas reservoirs. 2. The method according to claim 1, characterized in that: in step S1, the fracturing fluid used in the hydraulic fracturing stimulation is a water-based fracturing commonly used in shale oil and gas reservoirs liquid. 3. The method according to claim 1, characterized in that: in step S2, the oxygen source comprises oxygen and/or an oxygen-supplying agent; The oxygen supply agent includes one or more of hydrogen peroxide, sodium peroxide, potassium peroxide and peracetic acid. 4. The method for improving the effect of repeated transformation of shale oil and gas reservoirs by thermal shock according to claim 3, wherein the oxygen supply agent can be used in combination with a catalyst, and the catalyst comprises catalase, manganese dioxide, One or more of alkaline solutions. 5 . The method for improving the effect of repeated stimulation of shale oil and gas reservoirs by thermal shock according to claim 1 , wherein the cooling medium is water. 6 . 6. The method for improving the effect of repeated stimulation of shale oil and gas reservoirs by thermal shock according to any one of claims 1-5, wherein in the step S1, the shale oil and gas after hydraulic fracturing stimulation well, which is formed by the following steps, (1) Drill at least one horizontal well in the shale oil and gas reservoir, and carry out the first hydraulic fracturing on the production interval of the horizontal well to form hydraulic fractures; (2) After the completion of hydraulic fracturing, wells are opened to produce shale oil and gas, until the daily oil and gas production continues to decline to the point of no commercial value.

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