CN103195402B - A kind of system and method for staged fracturing of coal bed gas well - Google Patents

Abstract

The invention discloses a segmented fracturing system and method for a coalbed gas well. The system includes: a casing nipple, a fracturing device, a ball thrower and a packing ball. Between the fracturing sections of the fracturing section, the production casing installed with the casing nipple is lowered into the well for cementing after the drilling is completed; the ball feeder is connected to the upper part of the Christmas tree in the coalbed methane well, and the ball feeder is arranged from near to far according to the distance Sequentially, the inner diameter of each casing pup joint decreases in turn; the fracturing device is used to fracturing each fracturing section in the order from far to near to the ball launcher, and after the fracturing of one fracturing section is completed, and After the next fracturing section to be fractured is perforated, the fracturing fluid is injected, and the packing ball dropped by the ball feeder is sent to the casing nipple near the ball feeder side of the completed fracturing section , to seal off the casing sub-section, and the packing ball matches the casing sub-section. The invention can achieve the beneficial effects of shortening the construction period and reducing the cost.

Description

A system and method for staged fracturing of a coalbed methane well

technical field

The invention relates to the field of fracturing of coalbed gas wells, in particular to a system and method for staged fracturing of coalbed gas wells.

Background technique

Coalbed methane reservoirs are characterized by low porosity and low permeability, and generally require fracturing to obtain better gas production. Among them, coalbed methane mining can use various development methods such as coalbed methane vertical wells, coalbed methane directional wells, and coalbed methane horizontal wells.

In the existing technology, the drilling and completion technology of coalbed methane horizontal wells completed with casing is basically mature. If there is a mature fracturing stimulation technology matching it, the method of casing completion and fracturing can greatly promote CBM development, but there are still some technical problems in its staged fracturing. Among them, fracturing is a commonly used stimulation method for conventional oil and gas fields or unconventional oil and gas layers, the purpose of which is to improve the permeability of the near-wellbore area and thus increase the productivity.

In the prior art, hydraulic jet perforation and fracturing technology are adopted. Although the fracturing construction progress is fast, the risk of the pipe string being stuck by sand is high, which easily delays the construction progress, resulting in high workover costs. The cost is also higher.

In the prior art, using the rapid drilling bridge plug staged fracturing technology, staged ignition is required to complete the two processes of plug sealing and perforation of the operation seat. After fracturing all layers, special tools are required to repair the bridge plug Drilling and grinding make the construction process complicated and the period is long, and the staged fracturing technology of rapid drilling bridge plug is adopted, the process is complicated and the construction cost is high.

Contents of the invention

The invention provides a system and method for staged fracturing of a coal bed gas well to solve the problems of high construction risk, complex process and high construction cost.

The invention discloses a staged fracturing system for a coalbed methane well. The system includes: a casing nipple, a fracturing device, a ball thrower and a packing ball.

Each casing nipple is connected to the production casing of the coalbed methane well, and is respectively located between the two fracturing sections or fracturing layers. The production casing installed with the casing nipple is lowered into the well for cementing after the drilling is completed;

The ball launcher is connected to the upper part of the Christmas tree in the coalbed methane well, and the lower part of the Christmas tree is connected to the production casing. The inner diameter of each casing nipple decreases in order from the closest to the farthest from the ball launcher;

The fracturing device is used to fracturing each fracturing section or fracturing layer in the order from farthest to the ball launcher. After a fracturing section or fracturing layer is perforated, the fracturing fluid is injected into the production casing, and the packing ball dropped by the ball feeder is sent to the completed fracturing section or fracturing layer near the ball feeder. At the short joint of the casing on the side, the short joint of the casing is blocked, and the packing ball is matched with the short joint of the casing.

Wherein, the casing nipple includes: an outer sleeve and an inner sleeve,

The jacket specifications of each casing pup joint are the same, and the strength of the jacket is greater than that of the production casing;

The outer diameters of the inner sleeves of each casing pup joint are the same, and the inner sleeves are connected and fixed with the outer sleeve with threads;

The inner diameters of the inner sleeves of the pup joints of the bushings decrease in order from the closest to the farthest from the pitcher.

Wherein, the material used in the inner sleeve is a composite material.

Wherein, the inner diameters of the inner sleeves of the two adjacent casing pup joints differ by any value between 7mm and 8mm.

Wherein, the diameter of the packing ball is any value between 3.5 mm and 4 mm larger than the inner diameter of the matched casing sub-section.

Wherein, the material used for the packing ball is a composite rubber material, and the pressure difference strength is greater than 40MPa.

Among them, when the production casing is a 5.5-inch casing, the number of fracturing sections or fracturing layers is any value from 2 to 7;

and / or,

When the production casing is a 7.5-inch casing, the number of fracturing stages or layers is any value from 2 to 10.

The invention also discloses a segmented fracturing method for a coalbed methane well, said method comprising:

Connect each casing nipple with the production casing of the coalbed methane well. Each casing nipple is located between the two fracturing sections or fracturing layers. After the drilling is completed, the production casing is lowered into the well for cementing. The lower part of the Christmas tree in the coalbed methane well is connected with the production casing, and the ball feeder is connected with the upper part of the Christmas tree; the inner diameters of each casing pup joint decrease in order from the closest to the farthest from the ball feeder;

Use the fracturing device to fracturing each fracturing section or fracturing layer in order from far to near to the ball launcher. After fracturing one fracturing section or fracturing layer, the next stage to be fractured will be fractured. After perforating the fracture section or fracturing layer, the ball feeder puts the packing ball into the production casing, injects the fracturing fluid, and sends the packing ball to the completed fracturing section or fracturing layer close to the ball feeder At the short joint of the casing on one side, the short joint of the casing is blocked, and the packing ball is matched with the short joint of the casing.

Wherein, the casing nipple includes: an outer sleeve and an inner sleeve,

The jacket specifications of each casing pup joint are the same, and the strength of the jacket is greater than that of the production casing;

The outer diameters of the inner sleeves of each casing pup joint are the same, and the inner sleeves are connected and fixed with the outer sleeve with threads;

The inner diameters of the inner sleeves of the pup joints of the bushings decrease in order from the closest to the farthest from the pitcher.

Among them, the difference between the inner diameters of the inner sleeves of two adjacent casing pup joints is any value between 7mm and 8mm,

and / or,

The diameter of the packing ball is any value between 3.5 mm and 4 mm larger than the inner diameter of the matched casing nipple.

The beneficial effect of the present invention is: by using a plurality of matched casing nipples and packing balls, after a fracturing segment or fracturing layer is fractured, the next segment of fracturing segment or fracturing layer to be fractured is completed. After the layer is perforated, the fracturing fluid for fracturing the next fracturing stage or layer is injected, and the packing ball dropped by the ball feeder is sent to the fracturing stage or layer that has completed fracturing through the fracturing fluid. At the casing nipple of the fracturing layer, plug the casing nipple; it is only necessary to install the casing nipple in the production casing of the coalbed methane well. After completing one section of fracturing, when fracturing the next section, Using the fracturing fluid for fracturing, the packing ball is sent into the casing sub-joint for plugging, and segmental fracturing can be realized to meet the needs of large displacement in coalbed gas fracturing construction. Moreover, the adoption of this technical solution does not need to add complicated construction operations, safely, reliably, and quickly realizes staged fracturing, and at the same time avoids unnecessary workover, and achieves the beneficial effects of shortening the construction period and reducing costs.

Description of drawings

Fig. 1 is the structural diagram of the staged fracturing system of the coalbed methane horizontal well of an embodiment of the present invention;

Fig. 2 is a cross-sectional view of a casing nipple according to an embodiment of the present invention;

Fig. 3 is a structural diagram of the staged fracturing system of a coalbed methane vertical well according to an embodiment of the present invention;

Fig. 4 is a structural diagram of the staged fracturing system of the coalbed methane directional well according to an embodiment of the present invention;

Fig. 5 is a flow chart of a method for staged fracturing of a coalbed methane well according to an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the implementation manner of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Referring to Fig. 1 , it is a structural diagram of a system for staged fracturing of a coalbed methane horizontal well according to an embodiment.

The system includes: a casing sub 200, a fracturing device, a ball launcher 100, and a packing ball. In order to make the structural diagram concise and easy to explain, the fracturing device and the packing ball are not shown in Fig. 1 . Wherein, the fracturing device is a commonly used device in the field. In this embodiment, it can be any device for fracturing the coal seam with fracturing fluid, and there is no special limitation here.

In this embodiment, there are six casing nipples 200, namely, the first-level casing nipple 200a, the second-level casing nipple 200b, the third-level casing nipple 200c, and the fourth-level casing nipple. Section 200d, the fifth-level casing pup joint 200e, and the sixth-level casing pup joint 200f. The number of fracturing stages in this embodiment is 7. Here, it is only an example in this embodiment. When the production casing is a 5.5-inch casing, the number of fracturing sections is any value from 2 to 7; when the production casing is a 7.5-inch casing, The number of fracturing stages can be anywhere from 2 to 10.

Each casing nipple 200 is connected with the production casing 300 of the coalbed methane well, and is respectively located between two fracturing stages or fracturing layers. In a horizontal well, as shown in Figure 1, each stage of staged fracturing corresponds to a fracturing stage; in a vertical or directional well, as shown in Figure 3 or 4, each stage of staged fracturing corresponds to a fracturing stage layer. The length of each fracturing section or the height of the fracturing layer depends on the requirements of the staged fracturing.

The production casing 300 installed with the casing nipple 200 is lowered into the well for cementing after the drilling is completed. The ball feeder 100 is connected to the upper part of the christmas tree 400 in the coalbed methane well, and the lower part of the oil tree 400 is connected to the production casing 300. The inner diameters of the casing nipples 200 decrease in order from the closest to the farthest from the ball feeder 100.

Referring to FIG. 2 , it is a structural diagram of a casing nipple according to an embodiment of the present invention. The casing nipple 200 includes an outer sleeve 210 and an inner sleeve 220 . The casing 210 of each casing pup joint 200 has the same specification, and the strength of the casing 210 is greater than that of the production casing 300 . The outer diameters of the inner sleeves 220 of each casing pup joint 200 are the same, and the inner sleeves 220 are connected and fixed to the outer sleeves 210 with screws. The inner diameters of the inner casings 220 of the casing pup joints 200 decrease in order from the closest to the farthest from the ball launcher 100 . The inner diameters of the inner sleeves 220 of two adjacent casing nipples 200 differ by 8mm, that is, from the sixth casing nipple 200f to the first casing nipple 200a, the inner diameters of the inner casings decrease by 8mm sequentially. The material used for the inner sleeve 220 is a composite material, so as to realize drilling and grinding.

In this embodiment, the casing nipple as shown in Fig. 2 is adopted. The casing nipple 200 is connected with the casing thread, the part 2001 circled on the left in Fig. It is connected with the production casing 300 at the lower part.

The fracturing device is used to perform fracturing on each fracturing section in the order of distance from the ball launcher 100 from far to near. After the hole is drilled, a small amount of fracturing fluid is injected, and the packing ball dropped by the ball feeder 100 is sent to the casing nipple 200 of the fracturing section that has been fractured, so as to seal the casing nipple 200, and the packing The ball fits the casing nipple 200 . Wherein, the diameter of the packing ball is 4 mm larger than the inner diameter of the matched casing nipple 200 . The material used for the isolation ball is a composite rubber material, and the pressure difference strength is greater than 40MPa.

In this embodiment, the fracturing device may be any device for fracturing the coal seam through fracturing fluid. For example, a fracturing device includes: a fracturing train unit, a surface high-pressure pipeline, a wellhead device, and an equipped perforating gun. The fracturing vehicle group includes: main fracturing vehicle, sand mixing vehicle, and instrument vehicle.

In the system shown in Fig. 1, after the production casing 300 is lowered into the well for cementing, the perforation is transported by tubing, such as coiled tubing or cable plus crawler, to transport the perforating gun to the first fracturing area. The first fracturing section is perforated, and the perforating gun is raised to perform fracturing on the first fracturing section. The specific fracturing process is that the fracturing crew injects fracturing fluid into the formation at a displacement higher than the absorption capacity of the formation to break the formation rocks and form fractures, and then use the sand-carrying fluid to carry proppant into the fractures, and the fractures after fracturing When closed, the proppant stays in the fractures to play a supporting role, thus forming fractures with high conductivity, which is conducive to the flow of oil and gas.

After fracturing the first fracturing stage, the perforating gun is sent to the second fracturing stage for perforation by means of cable pumping, and the perforating gun is lifted out. Inject the fracturing fluid to pump the packing ball put in by the ball feeder 100 to the first-stage casing nipple 200a, and then seal the first fracturing section of the fracturing, and continue to inject fracturing fluid to the second fracturing section. Perform fracking. Wherein, the packing ball thrown by the ball thrower 100 is a packing ball matched with the first-stage casing sub-joint 200a, and the diameter of the packing-off ball is 4mm larger than the inner diameter of the first-stage casing sub-joint 200a. After the fracturing hydraulic fracturing is completed, the proppant is carried into the fracture with the sand-carrying fluid, and the fracture is closed after fracturing, and the proppant stays in the fracture to play a supporting role.

The perforating gun is sent to the third fracturing section for perforation by means of cable pumping, and the perforating gun is lifted out. Inject the fracturing fluid, pump the packing ball put in by the ball feeder 100 to the second-stage casing nipple 200b, and then seal the second fracturing stage of fracturing, and continue to inject fracturing fluid to the third stage of fracturing section undergoes fracturing. Wherein, the packing ball thrown by the ball thrower 100 is a packing ball matched with the second-stage casing sub-joint 200b, and the diameter of the packing ball is 4mm larger than the inner diameter of the second-stage casing sub-joint 200b. After the fracturing hydraulic fracturing is completed, the proppant is carried into the fracture with the sand-carrying fluid, and the fracture is closed after fracturing, and the proppant stays in the fracture to play a supporting role.

The above operations are repeated until the casing sub-joint 200f of the sixth stage is blocked by the packing ball, and the fracturing stage of the seventh stage is fractured.

The system in the present invention can be used in coalbed methane vertical wells and coalbed methane directional wells in addition to coalbed methane horizontal wells.

Referring to FIG. 3 , it is a structural diagram of a system for staged fracturing of vertical coalbed methane wells according to an embodiment of the present invention. In this embodiment, there are two casing sub-joints 200, namely, the first-level casing sub-joint 200a and the second-level casing sub-joint 200b. In this embodiment, the coalbed methane well is a vertical well, and the number of fractured layers is three. The devices included in the system and the connections between the devices are the same as those of the above-mentioned horizontal well embodiment. In order to make the structural diagram concise and easy to explain, the fracturing device and packing ball are not shown in Fig. 3, and the black square part in the figure represents the coal seam.

Referring to FIG. 4 , it is a structural diagram of a staged fracturing system for a coalbed methane directional well according to an embodiment of the present invention. In this embodiment, there are two casing sub-joints 200, namely, the first-level casing sub-joint 200a and the second-level casing sub-joint 200b. In this example, the coalbed methane well is a directional well, and the number of fractured layers is three. The devices included in the system and the connections among the devices are not different from the above-mentioned horizontal well embodiment. In order to make the structural diagram concise and easy to explain, the fracturing device and packing ball are not shown in Fig. 4, and the black square part in the figure represents the coal seam.

The present invention also provides a staged fracturing method for a coalbed gas well, and the method includes the following steps.

Step S510, connecting each casing nipple with the production casing of the coalbed methane well, each casing nipple is respectively located between the two fracturing stages or fracturing layers, and after the drilling is completed, the production casing is lowered into the well for solidification. Well, connect the lower part of the Christmas tree in the coalbed methane well with the production casing, and connect the ball launcher with the upper part of the Christmas tree. Wherein, according to the sequence from near to far away from the pitcher, the inner diameters of the casing nipples decrease successively.

Step S520, use the fracturing device to perform fracturing on each fracturing segment or fracturing layer in the order from far to near to the ball launcher, and after fracturing a fracturing segment or fracturing layer is completed, and After the next fracturing stage or fracturing layer is perforated, the ball feeder puts the packing ball into the production casing, injects the fracturing fluid, and sends the packing ball to the fracturing stage or fracturing layer that has been fractured. Plug the casing nipple near the side of the pitcher.

The packing ball is matched with the casing nipple.

The method is applicable to coalbed methane horizontal wells, coalbed methane vertical wells, and coalbed methane directional wells. In a horizontal well, as shown in Figure 1, each stage of staged fracturing corresponds to a fracturing stage; in a vertical or directional well, as shown in Figure 3 or 4, each stage of staged fracturing corresponds to a fracturing stage layer. The length of each fracturing section or the height of the fracturing layer depends on the requirements of the staged fracturing.

Further, the sleeve sub-joint includes: an outer sleeve and an inner sleeve,

The jacket specifications of each casing pup joint are the same, and the strength of the jacket is greater than that of the production casing;

The outer diameters of the inner sleeves of each casing pup joint are the same, and the inner sleeves are connected and fixed with the outer sleeve with threads;

The inner diameters of the inner sleeves of the pup joints of the bushings decrease in order from the closest to the farthest from the pitcher.

Further, the inner diameters of the inner sleeves of two adjacent casing sub-joints differ by any value between 7mm and 8mm.

Further, the diameter of the packing ball is larger than the inner diameter of the matched casing sub-section by any value between 3.5mm and 4mm.

Further, the material used for the inner sleeve is a composite material.

Further, the material used for the packing ball is a composite rubber material, and the pressure difference strength is greater than 40MPa.

Further, when the production casing is a 5.5-inch casing, the number of fracturing sections or fracturing layers is any value from 2 to 7;

Further, when the production casing is a 7.5-inch casing, the number of fracturing sections or fracturing layers is any value from 2 to 10.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims (10)

1. A staged fracturing system for a coalbed methane well, characterized in that the system comprises: a casing nipple, a fracturing device, a ball thrower and a packing ball, Each casing nipple is connected to the production casing of the coalbed methane well, and is respectively located between the two fracturing sections or fracturing layers. The production casing installed with the casing nipple is lowered into the well for cementing after the drilling is completed; The ball launcher is connected to the upper part of the Christmas tree in the coalbed methane well, and the lower part of the Christmas tree is connected to the production casing. The inner diameter of each casing nipple decreases in order from the closest to the farthest from the ball launcher; The fracturing device is used for fracturing each fracturing section or fracturing layer in the order from farthest to the ball launcher, including: fracturing each fracturing section or fracturing layer with fracturing fluid, Then use the sand-carrying fluid to carry the proppant into the fracturing fracture; after the fracturing of a fracturing section or fracturing layer is completed, and the next fracturing section or fracturing layer to be fractured is perforated , inject fracturing fluid into the production casing, and send the packing ball dropped by the ball feeder to the casing sub-joint of the completed fracturing section or fracturing layer near the ball feeder to seal the casing A short joint, the packing ball is matched with the casing short joint. 2. The system of claim 1, wherein: The casing nipple includes: an outer sleeve and an inner sleeve, The jacket specifications of each casing pup joint are the same, and the strength of the jacket is greater than that of the production casing; The outer diameters of the inner sleeves of each casing pup joint are the same, and the inner sleeves are connected and fixed with the outer sleeve with threads; The inner diameters of the inner sleeves of the pup joints of the bushings decrease in order from the closest to the farthest from the pitcher. 3. The system of claim 2, wherein: The material used for the inner sleeve is a composite material. 4. The system according to claim 2 or 3, characterized in that, The difference between the inner diameters of the inner sleeves of two adjacent casing pup joints is any value between 7mm and 8mm. 5. The system of claim 1, wherein: The diameter of the packing ball is any value between 3.5 mm and 4 mm larger than the inner diameter of the matched casing nipple. 6. The system of claim 1, wherein: The material used for the packing ball is a composite rubber material, and the pressure difference resistance strength is greater than 40MPa. 7. The system of claim 1, wherein: When the production casing is a 5.5-inch casing, the number of fracturing sections or fracturing layers is any value from 2 to 7; and / or, When the production casing is a 7.5-inch casing, the number of fracturing stages or layers is any value from 2 to 10. 8. A staged fracturing method for a coalbed methane well, characterized in that the method comprises: Connect each casing nipple with the production casing of the coalbed methane well. Each casing nipple is located between the two fracturing sections or fracturing layers. After the drilling is completed, the production casing is lowered into the well for cementing. The lower part of the Christmas tree in the coalbed methane well is connected with the production casing, and the ball feeder is connected with the upper part of the Christmas tree; the inner diameters of each casing pup joint decrease in order from the closest to the farthest from the ball feeder; The fracturing device is used to fracturing each fracturing section or fracturing layer in the order from far to near to the ball launcher, including: fracturing each fracturing section or fracturing layer with fracturing fluid, and then using The sand-carrying fluid carries proppant into the fracturing fractures; after fracturing a fracturing section or fracturing layer, and perforating the next fracturing section or fracturing layer to be fractured, the ball is thrown Put the packing ball into the production casing, inject fracturing fluid into the production casing, and send the packing ball to the casing nipple near the side of the ball feeder for the completed fracturing section or fracturing layer, and seal the casing The pipe sub-joint, the packing ball is matched with the casing sub-joint. 9. The method of claim 8, wherein The casing nipple includes: an outer sleeve and an inner sleeve, The jacket specifications of each casing pup joint are the same, and the strength of the jacket is greater than that of the production casing; The outer diameters of the inner sleeves of each casing pup joint are the same, and the inner sleeves are connected and fixed with the outer sleeve with threads; The inner diameters of the inner sleeves of the pup joints of the bushings decrease in order from the closest to the farthest from the pitcher. 10. The method of claim 9, wherein, The difference between the inner diameters of the inner sleeves of two adjacent casing pup joints is any value between 7mm and 8mm, and / or, The diameter of the packing ball is any value between 3.5 mm and 4 mm larger than the inner diameter of the matched casing nipple.