CN110344801A - Fracturing work method, recovery method and mining system for combustible ice exploitation - Google Patents

Abstract

The invention discloses a fracturing operation method applied in a single well and a double well, a corresponding method of exploiting natural gas, and a system device used in exploitation. The fracturing operation is performed in pairs by means of pressurization and decompression. Guided by the field, most of the fracturing fractures finally point to the production branch wellbore, which greatly reduces the damage to the overlying strata caused by fracturing operations, and protects the overlying layer on the combustible ice, which is one of the guarantees for the safe mining of combustible ice; Wells control the exploitation of combustible ice resources, increase single well production, and reduce well density. During mining, pressurization and decompression paired push-pull operation is also used between the injection branch wellbore and the production branch wellbore, which is conducive to keeping the seepage flow channel from injection to production unblocked, preventing secondary freezing and filling of fracturing fractures, and maintaining long-term Stable gas extraction of combustible ice.

Description

Fracturing operation method, mining method and mining system for combustible ice mining

technical field

The invention relates to energy mining technology, in particular to a method for fracturing strata by applying pressurized and depressurized paired pressure fields, and a method and system for exploiting natural gas in combustible ice formations using the fracturing method.

Background technique

Decompression (negative pressure) mining is to reduce the pressure in the wellbore, partially break the temperature and pressure environment where the combustible ice is stored, and melt the combustible ice. There are several factors to consider in this mining process. With the melting of combustible ice, gas is formed, and the local pressure will increase; the melting of combustible ice absorbs heat and reduces the local temperature; the local temperature and pressure environment will soon return to the range of freezing temperature and pressure conditions, causing the mining process to stop. In order to make the mining of combustible ice more sustainable, fracturing has naturally become an important means. However, the fracturing method used in the mining of combustible ice has the following two problems:

First, because the pressure recovers within a very short distance in the radial direction, the spatial range that satisfies the pressure condition for combustible ice melting is very small. Taking a uniform and infinitely thick formation as an example, the melting area is from the borehole wall to tens of centimeters in the radial direction. The range of cylindrical space. If the perforation channel is also regarded as the extension of the wellbore, the control radius of a well is only approximately equal to the perforation radius plus tens of centimeters.

Second, the fracturing operation has become an effective means to expand the production range of a single well. After the fracturing operation, the control radius of a well is approximately larger than the area covered by the fracture. However, because the stratum overlying the combustible ice is thin and soft, in order to protect the strata overlying the combustible ice from damage, high-intensity fracturing operations such as shale gas exploitation cannot be used. In addition, due to the secondary freezing of combustible ice, the cracks generated by the fracturing operation are quickly filled, so that the effect of the fracturing operation cannot be continuously retained.

Contents of the invention

In order to solve the above-mentioned problems, the present invention provides a method for fracturing the strata by using pressurized and decompressed pairs of pressure fields, and a method and system for exploiting natural gas in combustible ice formations by using the fracturing method.

The fracturing operation method applied in a single well includes the following steps:

1) At least one production branch wellbore is drilled in the production layer of the formation, and at least one injection branch wellbore is drilled in the injection layer; several jets are arranged in the pipelines of the production branch wellbore and the injection branch wellbore. Pores for fracturing fluid to flow in or out;

2) After finishing the casing operation, cementing operation, perforation operation and installation of inlet devices, etc., lower the booster pipeline and the plug for fracturing isolation along the casing to the production branch wellbore and the injection branch well in the cannula between the eyes;

3) The booster pipe communicates with the injection branch wellbore through the plug on the path; the booster pipe is connected with a booster pump, so that the booster pump communicates with the injection branch wellbore; The annular space between them is a decompression channel; one end of the decompression pipe is connected to the decompression pump, and the other end is connected to the production branch wellbore through the decompression channel;

4) Start the booster pump and decompression pump to perform fracturing operations: the booster pump injects fracturing fluid into the formation through injecting the branch wellbore, and forms a positive pressure gradient field in the formation around the injected branch wellbore; the decompression pump passes through The decompression channel extracts liquid from the production branch wellbore, forming a negative pressure gradient field in the formation around the production branch wellbore; on the path between the injection branch wellbore and the production branch wellbore, positive and negative pressure gradients The push-pull fields strengthen each other, resulting in larger fracturing fractures; in other formation regions, the positive and negative pressure gradient fields cancel each other, resulting in smaller fracturing fractures or no fracturing fractures.

A method for exploiting natural gas in combustible ice formations by applying the above-mentioned fracturing operation method: after the fracturing operation is completed, the pressurized pipe is replaced with a warm water pipe, and the decompression pipe is replaced with a gas-water channel, and the warm water pipe is connected to a warm water control system, the air-water channel is connected to the separation and lifting system;

The warm water control system delivers the injection fluid to the injection branch wellbore through the warm water pipe, and the injection fluid percolates to the production well through large fractures. The channels flow into the separation lift system.

The fracturing operation method applied in two wells, including the following steps:

1) Two left and right wells are drilled, the left well is used for production, and the right well is used for injection;

At least one production branch wellbore is drilled in the left well, and at least one injection branch wellbore is drilled in the right well. Several perforation tunnels are opened in the pipelines of the production branch wellbore and the injection branch wellbore for the fracturing fluid to flow in or out ;

2) Complete casing operation, cementing operation, perforation operation and installation of inlet device;

3) Install plugs in the wells respectively. In the production well on the left, the output end of the decompression pipe passes through the plugs on the path in turn to connect to the production branch wellbore; in the well on the right, the output end of the booster pipe sequentially After passing through the plug on the path, it communicates with the injection branch wellbore;

4) Start the booster pump and decompression pump to carry out fracturing operations; the booster pump injects fracturing fluid into the formation through injection of the branch wellbore, forming a positive pressure gradient field in the surrounding formation; the decompression pump passes through the production branch wellbore The liquid is extracted from the decompression channel to form a negative pressure gradient field in the surrounding formation; on the path from the injection branch wellbore to the production branch wellbore, the positive and negative pressure gradient fields push and pull each other to strengthen each other to generate larger fractures; In other formation regions, the positive and negative pressure gradient fields cancel each other to produce smaller fractures or no fractures.

The method of exploiting flammable ice natural gas by applying the fracturing operation method of the above two wells: replace the pressurized pipe with a warm water pipe, replace the decompression pipe with a gas-water channel, and connect the upper end of the warm water pipe to a warm water control system. The upper end of the gas-water channel is connected to the separation and lifting system; the warm water control system sends the injection fluid to the injection branch wellbore through the warm water pipe, the injection fluid seeps into the production well through the large fracture, and the combustible ice melting fluid in the formation flows into it under the pressure difference drive. In the production branch wellbore, natural gas flows to the separation and lifting system through the gas-water channel.

A mining system for mining flammable ice natural gas by applying the above-mentioned fracturing operation method. The mining system is applied in a vertical well, and includes a casing, a warm water control system and a separation and lifting system. The casing is equipped with a warm water pipe and a downhole control device. The upper end of the warm water pipe is connected to the warm water control system, and the lower end is connected to the downhole control device; the space between the casing and the warm water pipe forms an air-water channel, and the air-water channel is connected to the separation and lifting system;

The formation at the extraction branch wellbore is a combustible ice reservoir, and the formation at the injection branch wellbore is a pore reservoir;

Sand control screens are respectively installed in the casings at the combustible ice reservoir and the pore reservoir, and the upper and lower ends of each sand control screen are equipped with isolation devices, and a number of liquid A through hole for flow; the downhole control device is set on the casing at the porous reservoir.

Beneficial effects of the present invention:

(1) The fracturing operation is carried out in pairs by pressurization and decompression. Guided by the negative pressure gradient field, most of the fracturing fractures are finally directed to the production branch wellbore, which greatly reduces the damage to the overlying formation caused by the fracturing operation. Protecting the overburden of combustible ice is one of the guarantees for the safe mining of combustible ice;

(2) Fracturing operations are carried out in pairs by pressurization and decompression, which greatly increases the control range of single wells for the exploitation of combustible ice resources, increases the output of single wells, and reduces the density of well layout;

(3) During mining, pressurization and decompression paired push-pull work is also used between the injection branch wellbore and the production branch wellbore, which is conducive to keeping the seepage flow channel from injection to production unblocked and preventing secondary icing and filling of fracturing fractures , to maintain long-term and stable exploitation of combustible ice natural gas.

(4) When recovering after shutdown, secondary fracturing operations along old fractures can also be carried out to reduce the cost of secondary fracturing operations.

(5) During the production process, if the production rate drops seriously due to blockage, the injection branch wellbore and the production branch wellbore can be exchanged, that is, the original injection branch wellbore is regarded as the production branch wellbore, and the original production branch wellbore is replaced. The wellbore is treated as an injection branch wellbore, and the positive and negative push-pull pressurization causes the fluid to flow in reverse in the formation to achieve the effect of clearing the blockage.

Description of drawings

Figure 1 is a diagram of the range of temperature and pressure conditions for the formation and preservation of combustible ice (common knowledge in the professional field);

Fig. 2 is a graph of estimation results of radial variation of downhole pressure;

Fig. 3 is the estimation result diagram of radial variation of downhole pressure gradient;

Fig. 4 is a schematic diagram of pressurization and decompression paired fracturing operation method;

Fig. 5 is a schematic diagram of the effects of pressurization and decompression paired fracturing operations;

Fig. 6 is a schematic diagram of a system for exploiting natural gas from combustible ice formations by applying pressurization and decompression in paired fracturing operations;

Fig. 7 is a schematic diagram of the system structure for exploiting natural gas in combustible ice formations by applying pressurization and decompression paired fracturing operations in vertical wells;

Fig. 8 is a schematic diagram of a paired fracturing operation method for pressurization and decompression between two wells;

Fig. 9 is a schematic diagram of the fracturing effect of the paired fracturing operation method of boosting and depressurizing between two wells.

In the figure: 11 is a booster pump, 12 is a decompression pump, 13 is a booster pipe, 14 is a negative pressure pipe, 15 is a casing, 16 is a production branch wellbore, 17 is an injection branch wellbore, and 18 is a injection tunnel, 19 is a plug, 21 is a warm water control system, 22 is a separation and lifting system, 23 is a warm water pipe, 24 is a gas-water channel, 25 is a sand control screen, 26 is a packing device, 27 is a downhole control device,

3 is casing, 4 is combustible ice storage layer, 5 is pore storage layer, and 6 is hot water layer.

Detailed ways

The present invention will be further explained below in conjunction with the accompanying drawings.

Figure 1 shows the temperature and pressure conditions for the formation and storage of combustible ice. Negative pressure mining is to reduce the pressure in the wellbore, partially break the temperature and pressure environment where the combustible ice is stored, and melt the combustible ice. There are several factors to consider in this mining process. With the melting of combustible ice to form methane gas, the pressure will increase, and the melting of combustible ice will absorb heat and reduce the local temperature, and the local temperature and pressure environment will soon return to the freezing area; therefore, it is necessary to continuously increase the wellbore fluid to maintain negative pressure Poor environment, while supplementing heat energy and substances. Under the action of negative pressure difference, when the pressure difference gradient is greater than the critical value of fracture pressure difference, the formation ruptures. Under the joint action of sand production and fracture, the formation will collapse locally. The size of the negative pressure difference control area directly determines the output of a single well, directly determines the density of the well pattern, and directly determines whether to use horizontal wells, etc.

After a negative pressure differential is applied to the formation, the reaction of the formation is the same as the fracturing process. It's just that conventional fracturing is a positive pressure difference. For a wellbore passing through an infinitely thick formation, under the condition of ignoring the fluid transmission pressure in pores and fractures, the pressure distribution is a radial one-dimensional problem, and the pressure at point r in the radial radius can be roughly written as:

(I)

in, is the original formation pressure, for the unconsolidated formation hundreds of meters below the seabed, It is approximately equal to the static pressure of sea water here; is the wellbore pressure; is the borehole radius.

Figure 2 shows the simple estimation results of the radial variation of pressure. Among them, the undisturbed formation pressure is 10Mpa (equivalent to the pressure at a water depth of 1000m), the borehole pressure is 6MPa (equivalent to the pressure at a water depth of 600m), the borehole radius is 0.1m, and the model used is radial one-dimensional. The solid line shown in the figure is the radial variation of pressure calculated according to formula (I). After considering the pressure transmission of fluid in pore channels and fractures, as shown by the dotted line in Fig. 2, the calculation formula is much more complicated and related to many other formation parameters. It can be seen from the figure that due to the radial recovery of the pressure, the range where the pressure meets the melting pressure conditions of combustible ice is not very large. Taking Figure 2 as an example, if the critical pressure is 9MPa, the melting area is from the well wall to the diameter of 25cm to the range. If the perforation channel is also regarded as the extension of the wellbore, the control radius of a well is approximately equal to the perforation radius plus 25cm. If fractures are also taken into consideration, the control radius of a well is approximately equal to the area covered by fractures. However, due to the thin and soft strata overlying combustible ice, large-scale fracturing like shale gas exploitation cannot be used. In addition, due to the secondary freezing of combustible ice, the cracks created by fracturing are quickly filled.

During the decompression mining of combustible ice in the formation, the formation may be broken under the action of negative pressure difference. The pressure gradient in the formation can be simulated and calculated. For the case where the wellbore passes through the infinitely thick formation and the fluid transmission pressure in the pores and fractures is ignored, the pressure distribution is a radial one-dimensional problem. The pressure gradient at point r in the radial radius can be roughly written as:

. (II)

Figure 3 shows the simple estimation results of the radial variation of the pressure gradient. In the figure, the undisturbed formation pressure is 10Mpa (equivalent to the pressure at a water depth of 1000m), the borehole pressure is 6MPa (equivalent to the pressure at a water depth of 600m), and the borehole radius is 0.1m. The model used is radial one-dimensional. The solid line in Fig. 3 is calculated according to formula (II). When pores and fractures are considered, the pressure gradient is shown as the dotted line. If the pressure gradient is greater than the fracture critical value of the formation, the formation will rupture and produce fractures. The formation generally has a critical pressure gradient for sand production and a critical pressure gradient for fractures. Controlling the pressure gradient in the formation is one of the important contents of the control of the combustible ice mining process. Pressure difference control can be achieved by injecting liquid into the formation to supplement the deficient material.

Example 1

The present invention has the best effect in horizontal branch wells. The fracturing method shown in Figures 4 and 5, its fracturing steps are:

1) Horizontally drill the production branch wellbore 16 at the position of the combustible ice reservoir 4, and horizontally drill the injection branch wellbore 17 in the pore reservoir 5 below the combustible ice reservoir 4; the production branch wellbore 16 and the injection branch A number of perforation tunnels 18 are opened in the pipeline of the wellbore 17 to release the pressure;

2) Put the casing in the well 3, do well cementing, perforating and install the inlet device;

3) Put the plug 19 and the booster pipe 13 down along the casing 3, and the booster tube 13 passes through the plug 19 on the path in turn and communicates with the injection branch wellbore 17; the booster tube 13 is connected to the booster pump 11 ;

The annular space between the booster pipe 13 and the casing 3 is a negative pressure channel; one end of the negative pressure pipe 14 is connected to the decompression pump, and the other end is connected to the negative pressure channel, so as to communicate with the production branch wellbore 16;

4) Start booster pump 11 and decompression pump 12 . Combined with Fig. 5, the schematic diagram of positive and negative pressure on fracturing effect: the production branch wellbore 16 is connected to the decompression pump 12, and the injection branch wellbore 17 is connected to the booster pump 11; In the formation, the positive and negative pressure fields push and pull each other to strengthen each other, resulting in larger fracturing fractures; in other areas, the positive and negative pressure fields cancel each other out, resulting in smaller fracturing fractures or even no fracturing fractures. Since the positive pressure range is generally greater than the negative pressure range, the fractures below the injection branch wellbore 17 are moderate, and the fractures above the production branch wellbore 16 are relatively small.

So far, after the above-mentioned fracturing operations, corresponding large, medium and small fractures appear in the formation. The large fractures appear in the formation between the production branch wellbore 16 and the injection branch wellbore 17. The middle fractures Occurring in the formation below the injection lateral borehole 17 , the small fractures occur in the formation above the production lateral borehole 16 .

Fig. 6 is a schematic diagram of positive and negative pressure on post-fracturing production system: the positive pressure pipe 13 in the fracturing operation is replaced with a warm water pipe 23, and the negative pressure pipe 14 is replaced with a gas-water channel 24 to produce branch wells 16 connected and separated The lifting system 22 is connected to the warm water control system 21 for injection into the branch wellbore 17 to realize warm water suction, heating and pressurization. The injection fluid seeps through the large fractures to the production branch wellbore 16, and transfers heat energy and activator to the combustible ice reservoir 4, and at the same time, the warm water injection fluid can replenish the lack of formation materials.

Fig. 7 is a schematic diagram of the system structure for exploiting natural gas in combustible ice formations in vertical wells using pressurized and decompressed paired fracturing operations: sand control devices are installed in casings 3 in combustible ice reservoirs 4 and pore reservoirs 5 respectively. As for the screen pipes 25, the upper and lower ends of each sand control screen pipe 25 are equipped with isolation devices 26, and the sand control screen pipes 25 are provided with a number of through holes for liquid flow. A downhole control device 27 is installed in the casing 3 at the porous reservoir 5 , and the downhole control device 27 adjusts the injection rate and injection volume of the warm water liquid into the porous reservoir 5 . When the hot water in the deep formation is available, the hot water in the deep formation flows into the pore reservoir 5 from below at the same time.

Example 2

The fracturing method shown in Figure 8 is implemented in multiple wells, taking two wells as an example. Implemented between two wells, the fracturing steps are:

1) Two left and right wells are drilled, wherein the left well is drilled to the extraction position of the combustible ice reservoir 4, and the right well is drilled to the injection position of the pore reservoir 5.

Drill a horizontal production branch wellbore 16 at the position of the combustible ice reservoir 4, and drill a horizontal injection branch wellbore 17 in the pore reservoir 5 below the combustible ice reservoir 4; the production branch wellbore 16 and the injection branch wellbore 17 pipelines are provided with a number of perforation tunnels 18 to penetrate the pressure;

2) Place casings in the left and right wells respectively. 3. Do well cementing, perforating and installing inlet devices;

3) Install plugs 19 respectively in the left and right wells, as shown in Figure 8, in the well on the left, the output end of the negative pressure pipe 14 passes through the plugs 19 on the path successively and communicates with the production branch wellbore 16; In the well on the right, the output end of the pressurized pipe 13 passes through the plug 19 on the path in turn, and then connects to inject into the branch wellbore 17;

4) Start booster pump 11 and decompression pump 12 . The production branch wellbore 16 is connected to the decompression pump 12, and the injection branch wellbore 17 is connected to the booster pump 11; Larger fracturing fractures; in other areas, the positive and negative pressure fields cancel each other, resulting in smaller fracturing fractures or even no fracturing fractures. Since the positive pressure range is generally greater than the negative pressure range, the fracturing fractures below the injection branch wellbore 17 are moderate, and the fractures above the production branch wellbore 16 are relatively small.

Fig. 9 shows the application of the positive and negative pressure fracturing production method in two wells: the positive pressure pipe 13 in the fracturing operation is replaced with a warm water pipe 23, and the negative pressure pipe 14 is replaced with a gas-water channel 24. The production branch wellbore 16 is connected to the separation and lifting system 22 through the gas-water channel 24 , and the injection branch wellbore 17 is connected to the warm water control system 21 through the warm water pipe 23 . The warm water injection fluid seeps into the production branch wellbore 16 through the large fracturing fractures, and transfers heat energy and activator to the combustible ice reservoir 4, and at the same time, the warm water injection fluid can replenish the formation material deficit.

Claims (5)

1. A method of fracturing operations, comprising the steps of:

1) drilling at least one production branch borehole at a production layer of the formation and at least one injection branch borehole at an injection layer; a plurality of injection pore canals are formed in pipelines of the production branch well hole and the injection branch well hole so that fracturing fluid can flow in or out;

2) after casing running operation, well cementation operation, perforation operation, inlet device installation and the like are finished, a plug for pressurizing pipelines and fracturing packing is lowered into a casing between a production branch well hole and an injection branch well hole along the casing;

3) the pressure increasing pipe penetrates through the plug and is communicated with the injection branch well hole; the booster pipe is connected with a booster pump, so that the booster pump is communicated with the injection branch well hole; the annular space between the pressure increasing pipe and the sleeve is a pressure reducing channel; one end of the pressure reducing pipe is connected with the pressure reducing pump, and the other end of the pressure reducing pipe is communicated with the production branch well hole through the pressure reducing channel;

4) starting a booster pump and a pressure reducing pump to perform fracturing operation: the booster pump injects fracturing fluid into the stratum through the injection branch well hole, and a positive pressure gradient field is formed in the stratum around the injection branch well hole; the pressure reducing pump extracts liquid from the production branch well hole through the pressure reducing channel, and a negative pressure gradient field is formed in the stratum around the production branch well hole; on a path from the injection branch well hole to the extraction branch well hole, the positive and negative pressure gradient fields are mutually pushed and pulled to be strengthened to generate a larger fracture; in other formation zones, the positive and negative pressure gradient fields cancel each other, producing smaller or no fracture fractures.

2. A method of fracturing operations, comprising the steps of:

1) drilling a left well and a right well, wherein the left well is used for production, and the right well is used for injection;

drilling at least one extraction branch well hole in the left well, drilling at least one injection branch well hole in the right well, and opening a plurality of injection pore canals in pipelines of the extraction branch well hole and the injection branch well hole so that fracturing fluid can flow in or out;

2) completing casing running operation, well cementation operation, perforation operation and inlet device installation operation;

3) installing plugs in the wells respectively, and communicating the output ends of the pressure reducing pipes with the production branch well bores after sequentially penetrating the plugs on the paths in the production wells on the left; in the right well, the output end of the booster pipe sequentially penetrates through the plugs on the path and then is communicated with the injection branch well hole;

4) starting a booster pump and a pressure reducing pump to perform fracturing operation; the booster pump injects fracturing fluid into the stratum through the injection branch well hole to form a positive pressure gradient field in the surrounding stratum; the pressure reducing pump extracts liquid from the pressure reducing channel through the extraction branch well hole to form a negative pressure gradient field in the surrounding stratum; on the path from the injection branch well hole to the extraction branch well hole, the positive and negative pressure gradient fields push and pull each other to strengthen and generate a larger fracture; in other formation zones, the positive and negative pressure gradient fields cancel each other to create smaller or no fracture fractures.

3. A method for exploiting natural gas from a combustible ice formation by applying the fracturing operation method of claim 1, wherein: after the fracturing operation is finished, the pressure increasing pipe is replaced by a warm water pipe, the pressure reducing pipe is replaced by an air-water channel, the warm water pipe is connected with a warm water regulation and control system, and the air-water channel is connected with a separation lifting system;

the warm water regulation and control system conveys injection liquid into the injection branch well through a warm water pipe, the injection liquid seeps into the production well through a large crack, combustible ice melting liquid in the stratum flows into the production branch well under the driving of pressure difference, and natural gas flows into the separation lifting system through a gas-water channel.

4. A method for exploiting combustible ice natural gas by applying the fracturing operation method of claim 2, wherein:

the pressure increasing pipe is replaced by a warm water pipe, the pressure reducing pipe is replaced by an air-water channel, the upper end of the warm water pipe is connected with a warm water regulation and control system, and the upper end of the air-water channel is connected with a separation lifting system;

the warm water regulation and control system conveys injection liquid into the injection branch well bore through a warm water pipe, the injection liquid seeps into the production well through a large crack, combustible ice melting liquid in the stratum flows into the production branch well bore under the driving of pressure difference, and natural gas flows into the separation lifting system through a gas-water channel.

5. A production system for producing combustible ice natural gas by applying the fracturing operation method according to claim 1, wherein: the mining system is applied to a vertical well and comprises a sleeve, a warm water regulating and controlling system and a separation and lifting system, wherein a warm water pipe and an underground regulating and controlling device are arranged in the sleeve, the upper end of the warm water pipe is connected with the warm water regulating and controlling system, and the lower end of the warm water pipe is connected with the underground regulating and controlling device; a gas-water channel is formed in the space between the sleeve and the warm water pipe and is connected with the separation and lifting system;

the stratum at the extraction branch well hole is a combustible ice reservoir, and the stratum at the injection branch well hole is a pore reservoir;

the method comprises the following steps that sand control screen pipes are respectively arranged in sleeves at a combustible ice reservoir stratum and a pore reservoir stratum, packing devices are respectively arranged at the upper end and the lower end of each sand control screen pipe, and a plurality of through holes for liquid to flow are formed in the sand control screen pipes; the downhole conditioning device is disposed in a casing at a pore reservoir.