CN108240209B - Method for secondary fracturing of coal-bed gas well - Google Patents
Method for secondary fracturing of coal-bed gas well Download PDFInfo
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- CN108240209B CN108240209B CN201611219769.8A CN201611219769A CN108240209B CN 108240209 B CN108240209 B CN 108240209B CN 201611219769 A CN201611219769 A CN 201611219769A CN 108240209 B CN108240209 B CN 108240209B
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
Abstract
The invention discloses a secondary fracturing method for a coal-bed gas well, and belongs to the technical field of coal-bed gas well fracturing. The method comprises the following steps: and starting the fracturing truck group, pumping and injecting fracturing fluid into the target coal bed gas well through the fracturing truck group, and performing small-scale fracturing to dredge the original cracks in the reservoir. And a plurality of plugging balls with the number less than that of the perforation holes are thrown into the target coal-bed gas well, and meanwhile, the fracturing truck group is used for pumping active water fracturing fluid into the target coal-bed gas well, and the plugging balls plug the perforation holes of the original fracturing cracks under the action of the active water fracturing fluid pressure. And (4) continuing pumping and injecting fracturing fluid into the target coal-bed gas well by adopting a fracturing truck group to perform medium-scale fracturing, and forming a new fracturing in the reservoir. And closing the fracturing truck group, and after the plugging ball leaves the perforation hole and falls into the well bottom, returning the plugging ball to the ground to complete secondary fracturing. By adopting the method, the problem of low gas production rate of the coal-bed gas well caused by small primary fracturing modification range is effectively solved, and the exploitation efficiency of the coal-bed gas is improved.
Description
Technical Field
The invention relates to the technical field of coal-bed gas well fracturing, in particular to a secondary fracturing method for a coal-bed gas well.
Background
The coal bed gas is mainly stored in coal rocks, and a coal bed gas reservoir is reformed through a fracturing technology, so that the exploitation efficiency of the coal bed gas can be improved. At present, a coal bed gas reservoir is mainly reformed through a hydraulic fracturing technology, so that one or more fracturing cracks communicated with a coal bed gas well appear in the reservoir, and further, the exploitation amount of the coal bed gas well is improved. The coal bed gas well after hydraulic fracturing has a small first fracturing transformation range, so that the yield of part of single wells is low; in the process of drainage and production, the yield of a part of single wells is reduced due to the closure of cracks, the blockage of coal dust and the like. At present, an effective yield increase measure for a coal-bed gas well is a blockage removal secondary fracturing process, and the process achieves the purpose of recovering the yield of a single well by dredging the original cracks.
Patent document CN104251131A provides a secondary fracturing method for plugging removal of a coal-bed gas well, which comprises five steps of circulation, pressure testing, fracturing, sand adding, pressure drop testing and pressure relief. The secondary fracturing method comprises the following specific steps: (1) and pumping the fracturing fluid to the fracturing pump truck from the tank truck by using the fracturing pump truck and then returning the fracturing fluid to the tank truck, and checking the working conditions of the fracturing pump and the pipeline. (2) And then closing the well head gate, and carrying out pressure building on the ground high-pressure pipeline for 5 minutes, wherein the pressure building is stable, no puncture and no leakage exist, and the pressure test is qualified. (3) And pumping the fracturing fluid into the coal bed gas well by using a fracturing pump truck, and forming a fracturing fracture in the reservoir when the pressure born by the reservoir is exceeded. (4) And injecting sand carrying liquid into the coal-bed gas well by a pump to form a sand filling crack. (5) And measuring the pressure drop in the coal bed gas well by using a pressure gauge. (6) And then closing the well and open-blowing. Wherein the dosage of the fracturing fluid is 600-800m3The fracturing fluid is prepared into a solution with the concentration of 1 percent by water and an anti-swelling agent KCl, and the pumping capacity of a fracturing pump is 6-8m3Min, the sand content of the quartz sand is 40-60m3Coarse sand with particle size of 0.85-1.15mm 10m320 percent of the sand, and 80 percent of the medium sand with the grain diameter of 0.425-0.85 mm. The method can effectively solve the problem of yield reduction caused by the closure of the fracturing crack in the production process of the coal bed gas well, the blockage of the crack by the coal dust output in the production process of the gas well and the like.
The inventor finds that the prior art has at least the following problems:
although the method for secondary fracturing of the coal-bed gas well provided by the prior art can achieve the purpose of recovering the yield of a single well by dredging the original cracks, the problem of low yield caused by small range of primary fracturing modification cannot be solved, and the exploitation efficiency of the coal-bed gas well cannot be greatly improved.
Disclosure of Invention
The technical problem to be solved by the embodiment of the invention is to provide a method for secondary fracturing of a coal bed gas well, which can solve the problem of low gas production rate of the coal bed gas production well due to small range of primary fracturing modification and can greatly improve the exploitation efficiency of coal bed gas. The specific technical scheme is as follows:
the embodiment of the invention provides a secondary fracturing method for a coal-bed gas well, which comprises the following steps:
step a, starting a fracturing truck group, pumping and injecting fracturing fluid into a target coal bed gas well through the fracturing truck group, and performing small-scale fracturing to dredge original pressure fractures in a reservoir stratum.
And b, putting a plurality of plugging balls with the number less than that of the perforation holes into the target coal-bed gas well, and simultaneously pumping active water fracturing fluid into the target coal-bed gas well by using the fracturing truck group, wherein the plugging balls plug the perforation holes of the original fracturing cracks under the action of the active water fracturing fluid pressure.
And c, continuing pumping and injecting fracturing fluid into the target coal-bed gas well by adopting the fracturing truck group, performing medium-scale fracturing, and forming a new fracturing in the reservoir.
And d, closing the fracturing truck group, and discharging the blocking ball back to the ground after the blocking ball leaves the perforation hole and falls into the bottom of the well, so as to finish secondary fracturing on the target coal-bed gas well.
Specifically, preferably, the pumping and injecting the fracturing fluid into the target coal-bed gas well in the step a and the continuing pumping and injecting the fracturing fluid into the target coal-bed gas well both include: sequentially pumping and injecting a pad fluid, a sand carrying fluid and a displacement fluid into the target coal-bed gas well; in the step b, the active water fracturing fluid is an aqueous solution with the concentration of 0.5-1.5% prepared by clear water and KCl.
Specifically, in the step a, the pad fluid is preferably 50-60m when the small-scale fracturing is carried out3The active water fracturing fluid, the sand carrying fluid is 140-150m3Active water fracturing fluid and 10-15m3The displacement fluid is active water fracturing fluid, and the discharge capacity of the displacement fluid is 1m3Stepwise increasing min to 5m3/min。
In particular, as excellentOptionally, the pad fluid is 50-60m when the medium-scale fracturing is carried out3The active water fracturing fluid comprises 180-200m sand carrier fluid3Active water fracturing fluid and 20-25m3The displacement fluid is active water fracturing fluid, and the discharge capacity of the displacement fluid is 1m3Stepwise increasing min to 6m3/min。
Specifically, preferably, when the sand-carrying liquid is pumped into the target coal-bed gas well, the sand grains are quartz sand, the sand-carrying liquid containing fine sand grains with the grain size of 40-70 meshes is pumped firstly, and then the sand-carrying liquid containing medium sand grains with the grain size of 20-40 meshes is pumped.
Specifically, preferably, when the small-scale fracturing is carried out, the volume of the medium sand grains accounts for 60 to 70 percent of the total volume of the sand grains; in the middle-scale fracturing, the volume of the middle sand grains accounts for 75-80% of the total volume of the sand grains.
Specifically, the diameter of the plugging ball is preferably 1-2 times of the diameter of the perforation hole, and the density of the plugging ball is preferably 1.1-1.2g/cm3。
Specifically, the number of plugging balls thrown into the target coal-bed gas well may be preferably obtained according to the following formula:
wherein n is a second predetermined amount; k is any value between 1.1 and 1.2; m is the number of perforations.
Particularly, in the step b, the volume of the active water fracturing fluid is preferably 10-12m3The discharge capacity is 1m3The/min gradually increases to 2m3/min。
Specifically, as an optimization, after the plugging ball leaves the perforation hole and falls into the bottom of the well, the operations of blowout and sand washing are sequentially performed, and then the plugging ball is discharged back to the ground, so that the secondary fracturing of the target coal-bed gas well is completed.
The technical scheme provided by the embodiment of the invention has the following beneficial effects:
according to the method for secondary fracturing of the coal-bed gas well, provided by the embodiment of the invention, the original pressure fractures in the reservoir can be dredged by pumping and injecting the fracturing fluid into the target coal-bed gas well to perform small-scale fracturing. After dredging the original fracturing, a plurality of plugging balls with the number smaller than that of the perforation holes are thrown into the target coal bed gas well and matched with the active water fracturing fluid pumped by the fracturing truck set, the perforation holes of the original fracturing can be plugged, the fracturing fluid pumped continuously is convenient to fracture to form new fracturing at the perforation holes which are not plugged, the transformation area of a reservoir is increased, and the exploitation efficiency of the coal bed gas can be greatly improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a flow chart of a method for secondary fracturing of a coal bed gas well provided by an embodiment of the invention;
FIG. 2-1 is a schematic structural diagram of a reservoir before secondary fracturing of a target coal-bed gas well provided by an embodiment of the invention;
2-2 are schematic diagrams of a plugging ball provided by an embodiment of the invention in plugging perforations in a reservoir;
2-3 are schematic diagrams of new fractures in a reservoir during secondary fracturing of a target coal-bed gas well provided by embodiments of the invention.
Wherein the reference numerals denote:
1 the target of a coal-bed gas well,
2 the number of the reservoirs is 2,
3, pressing the crack in the original shape,
4, sealing the ball, wherein the ball is sealed,
5 the perforation holes are arranged on the inner wall of the casing,
6 new fracturing.
Detailed Description
Unless defined otherwise, all technical terms used in the examples of the present invention have the same meaning as commonly understood by one of ordinary skill in the art. In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The embodiment of the invention provides a secondary fracturing method for a coal-bed gas well, which comprises the following steps of:
102, putting a plurality of plugging balls with the number less than that of the perforation holes into the target coal-bed gas well, and simultaneously, pumping active water fracturing fluid into the target coal-bed gas well by using a fracturing truck group, wherein the plugging balls plug the perforation holes of the original fracturing cracks under the action of the active water fracturing fluid pressure.
And 103, adopting a fracturing truck group to continuously pump and inject fracturing fluid into the target coal-bed gas well, performing medium-scale fracturing, and forming a new fracturing in the reservoir.
And step 104, closing the fracturing truck group, and discharging the blocking ball back to the ground after the blocking ball leaves the perforation hole and falls into the bottom of the well, so as to finish secondary fracturing on the target coal-bed gas well.
The following description is given of a method for secondary fracturing of a coal-bed gas well provided by the embodiment of the invention:
as shown in fig. 2-1, 2-2 and 2-3, when the target coal-bed gas well 1 is not subjected to secondary fracturing, the original fracturing fractures 3 and the perforation holes 5 exist in the reservoir 2, part of the perforation holes 5 are located on the original fracturing fractures 3, and the original fracturing fractures 3 do not exist in part of the perforation holes 5. Before secondary fracturing, the fracturing truck group is started to prepare corresponding fracturing fluid, and the fracturing fluid is pumped into the target coal-bed gas well 1 to perform small-scale fracturing so as to dredge the original fracturing crack 3 in the reservoir 2, and a later-stage plugging ball 4 is convenient to plug the perforation hole 5 in the original fracturing crack 3. Then a plurality of plugging balls 4 are put into the target coal-bed gas well 1, the number of the put plugging balls 4 is smaller than the number of perforation holes 5 in the target coal-bed gas well 1, meanwhile, a fracturing truck group is used for pumping active water fracturing fluid into the target coal-bed gas well 1, the plugging balls 4 are carried into the well by the active water fracturing fluid, and due to the fact that the stress of the original fracturing crack 3 is low, the plugging balls 4 migrate to the perforation holes 5 of the original fracturing crack 3 under the action of the active water fracturing fluid, and the perforation holes 5 are plugged under the action of the active water fracturing fluid. And further pumping and injecting fracturing fluid into the target coal-bed gas well 1 by using a fracturing truck group to perform medium-scale fracturing, wherein in the process, the fracturing fluid gives pressure to the plugging ball 4, the plugging ball 4 continues to plug the perforation holes 5, and meanwhile, the fracturing fluid performs fracturing at the non-plugged perforation holes 5 to form new fracturing cracks 6. And then closing the fracturing truck group, no longer injecting the fracturing fluid into the target coal-bed gas well 1 by a fracturing fluid pump, enabling the plugging ball 4 to leave the perforation 5 due to the action of gravity and fall into the bottom of the well, and then discharging the plugging ball 4 back to the ground through open flow and sand washing operation to complete secondary fracturing on the target coal-bed gas well 1. In addition, for the target coal-bed gas well 1, the number of the perforation holes 5 contained in the reservoir 2 is the number of the original perforation holes obtained by perforating the reservoir by a perforation method (such as shaped perforation) before the target coal-bed gas well 1 is fractured once, and the number is recorded in the data obtained in the early-stage gas well reconstruction process and is obtained by consulting.
It should be noted that, as shown in fig. 2-1, the perforation 5 is located on the original fracturing 3 and also on the reservoir 2 without fracturing, and the secondary fracturing can fracture the perforation 5 without fracturing or the perforation 5 which is not blocked by the blocking ball 4. The target coal-bed gas well 1 is a coal-bed gas well of which the modification area of the reservoir 2 is small after the first fracturing, the exploitation efficiency is low after the target coal-bed gas well is used for a period of time, and the reservoir 2 is to be further modified. It will be understood that "small scale fracturing" is where less fracturing fluid is pumped into the target coal bed methane well than "medium scale fracturing," which is primarily to open the original fractures in the reservoir, and "medium scale fracturing" is primarily where fracturing causes new fractures to form in the reservoir.
Based on the above, the method for secondary fracturing of the coal-bed gas well provided by the embodiment of the invention can dredge the original pressure fractures in the reservoir by pumping and injecting the fracturing fluid into the target coal-bed gas well to perform small-scale fracturing. After dredging the original fracturing, a plurality of plugging balls with the number smaller than that of the perforation holes are thrown into the target coal bed gas well and matched with the active water fracturing fluid pumped by the fracturing truck set, the perforation holes of the original fracturing can be plugged, the fracturing fluid pumped continuously is convenient to fracture to form new fracturing at the perforation holes which are not plugged, the transformation area of a reservoir is increased, and the exploitation efficiency of the coal bed gas can be greatly improved.
Specifically, in the embodiment of the invention, the fracturing truck group comprises a fracturing pump truck, a sand mixer truck, a tank truck, a fracturing manifold truck and an instrument truck, and under the control action of the instrument truck, fracturing fluid is pressurized by the fracturing pump truck and pumped into the target coal bed gas well by the fracturing manifold truck so as to perform fracturing. The fracturing pump truck can pressurize fracturing fluid to a pressure higher than that of a reservoir of the coal-bed gas well so as to facilitate fracturing of the reservoir, the sand blender truck can fully mix the proppant and the liquid, and the tank truck can provide sufficient liquid for the pump truck. The specific structure and operation of a fracturing truck set is well known to those skilled in the art and will not be described in detail herein.
Specifically, in step 101, before pumping the fracturing fluid into the target coal-bed gas well, the target coal-bed gas well needs to be shut down, and whether the fracturing truck set can operate normally is checked. And then, pumping fracturing fluid into the target coal bed gas well by adopting a fracturing truck group to perform small-scale fracturing, mainly dredging original fracturing cracks in the reservoir, and possibly forming a few new fracturing cracks or not forming new fracturing cracks.
The method comprises the steps of pumping and injecting fracturing fluid into a target coal-bed gas well, wherein the pumping and injecting of the fracturing fluid into the target coal-bed gas well comprises the steps of sequentially pumping and injecting of pad fluid, sand carrying fluid and displacing fluid into the target coal-bed gas well. The pre-fluid is convenient for crack formation and cooling, the sand-carrying fluid is convenient for carrying a propping agent into a crack to form a sand-filled crack so as to prevent the fracturing crack from being closed, and the replacing fluid can replace the sand-carrying fluid to a preset position so that the propping agent in the sand-carrying fluid can better support the fracturing crack. When small-scale fracturing is carried out, the pad fluid is 50-60m3The active water fracturing fluid with sand carrying fluid of 140-3Active water fracturing fluid and 10-15m3The mixed liquid of sand grains and the displacing liquid are active water fracturing fluid with the discharge capacity of 1m3Stepwise increasing min to 5m3Permin, e.g. the pad may be 50m3、52m3、54m3、56m3、58m3、60m3The active water fracturing fluid and the sand carrying fluid can be 140m3Active water fracturing fluid and 10m3Mixed solution of sand grains 144m3Active water fracturing fluid and 12m3Mixed solution of sand grains, 148m3Active water fracturing fluid and 14m3Mixture of sand grains, 150m3Active water fracturing fluid and 15m3The mixed liquid of sand grains and the like can play a role in excellently dredging the original pressure cracks by adopting the pre-solution, the sand carrying solution and the displacement solution with the variable displacement. The displacement of the displacement liquid is stepped, namely the displacement is increased in gradient, such as 1m3/min、2m3/min、3m3/min、4m3/min、5m3The displacement fluid pumping rate, which may be based on wellbore volume and displacement, may be determined empirically by one skilled in the art and will not be described in detail herein. When the sand carrying liquid is pumped and injected into a target coal-bed gas well, the sand carrying liquid containing fine sand grains with the grain size of 40-70 meshes is pumped and injected firstly, for example, the grain size of the fine sand grains can be 40 meshes, 50 meshes, 60 meshes, 70 meshes and the like, then the sand carrying liquid containing medium sand grains with the grain size of 20-40 meshes is pumped and injected, for example, the grain size of the medium sand grains can be 20 meshes, 25 meshes, 30 meshes, 35 meshes, 40 meshes and the like, and the volume of the medium sand grains accounts for 60% -70% of the total volume of the sand grains, for example, 60%, 62%, 64%, 66%, 68%, 70% and the like. The granularity and the proportion of the sand grains in the sand carrying liquid are set in such a way, so that the fine sand grains and the medium sand grains can cooperate to support the original fracturing crack to efficiently dredge the original fracturing crack, the sand carrying liquid containing the fine sand grains is pumped firstly to support the remote fine crack in the reservoir, and then the sand carrying liquid containing the medium sand grains is pumped to support the large crack at the closer position so as to dredge the original fracturing crack. Wherein, the sand grains are quartz sand which is cheap and easy to obtain. The active water fracturing fluid is prepared from clear water and KClThe active water fracturing fluid can prevent clay from swelling, has small damage to a coal reservoir, ensures the stability of the coal reservoir and is beneficial to the exploitation of coal bed gas.
Specifically, in step 102, a plurality of plugging balls with the number less than that of perforation holes are thrown into the target coal-bed gas well, and meanwhile, an active water fracturing fluid is pumped into the target coal-bed gas well by using a fracturing truck group, wherein the volume of the active water fracturing fluid is 10-12m3The discharge capacity is 1m3The/min gradually increases to 2m3And/min, so that the plugging ball can conveniently carry to reach the well, and the plugging ball migrates to the perforation of the original fracturing crack to be plugged under the action of the hydraulic pressure of the active hydraulic fracturing because the stress at the original fracturing crack is low.
Wherein the diameter of the blocking ball is 1-2 times of the diameter of the perforation hole so as to block the perforation hole, and the density is 1.1-1.2g/cm3The plugging ball under the density can be mixed with active water fracturing fluid, and can plug perforation holes, especially perforation holes of the original fracturing cracks, under the action of the active water fracturing fluid pressure; in addition, the blocking ball is favorable for being carried by water or other liquid to be discharged back to the ground. For example, the blocking ball can be a nylon ball, a rubber ball or a steel core rubber ball, and the blocking balls are low in price, easy to obtain and recyclable.
Specifically, the blocking balls can be thrown into the well through a ball injector arranged at the wellhead of the target coal-bed gas well, and the number of the blocking balls thrown into the target coal-bed gas well can be obtained according to the following formula:
wherein n is a second predetermined amount; k is any value between 1.1 and 1.2; m is the number of perforations.
The number of the plugging balls which are put in is set in such a way, the perforation holes at the positions of large cracks and partial small cracks in the original fracturing cracks can be plugged, and the perforation holes without the original fracturing cracks in the reservoir are not plugged or plugged in a small number, so that the medium-scale fracturing can be conveniently carried out in the step 103.
Specifically, in step 103, pumping fracturing fluid into the target coal-bed gas well by using a fracturing truck group to perform medium-scale fracturing, wherein the fracturing fluid is fractured into the reservoir from the non-blocked perforation holes to form new fractures, namely new fractures. The fracturing fluid continuously pumped and injected into the target coal-bed gas well comprises pad fluid, sand carrying fluid and displacing fluid which are sequentially pumped and injected into the target coal-bed gas well. When the scale fracturing is underway, the pad fluid is 50-60m3The active water fracturing fluid with sand carrying fluid of 180-200m3Active water fracturing fluid and 20-25m3The mixed liquid of sand grains and the displacing liquid are active water fracturing fluid with the discharge capacity of 1m3Stepwise increasing min to 6m3Permin, e.g. the pad may be 50m3、51m3、53m3、55m3、57m3、59m3、60m3The active water fracturing fluid and the sand carrying fluid can be 180m3Active water fracturing fluid and 20m3Mixture of sand grains 185m3Water active water fracturing fluid and 21m3Mixed solution of sand grains, 190m3Active water fracturing fluid and 23m3Mixture of sand grains, 195m3Active water fracturing fluid and 24m3Mixture of sand grains, 200m3Active water fracturing fluid and 25m3And the mixed liquid of sand grains and the like are adopted, and the pre-posed liquid, the sand carrying liquid and the displacement liquid with the volumes are adopted, so that a new fracturing gap can be formed, and the reconstruction area of the target coal-bed gas well reservoir is increased. The displacement of the displacement liquid is stepped, namely the displacement is increased in gradient, such as 1m3/min、2m3/min、3m3/min、4m3/min、5m3The displacement fluid pumping rate, which may be based on wellbore volume and displacement, may be determined empirically by one skilled in the art and will not be described in detail herein. When the sand carrying liquid is pumped into the target coal-bed gas well, the sand carrying liquid containing fine sand grains with the granularity of 40-70 meshes is pumped firstly, then the sand carrying liquid containing medium sand grains with the granularity of 20-40 meshes is pumped, and the volume of the medium sand grains accounts for the total volume of the sand grains75% -80% of the total amount of the sand grains in the sand carrying liquid can be 75%, 76%, 77%, 78%, 79%, 80% and the like, and the granularity and the proportion of the sand grains in the sand carrying liquid are set, so that the fine sand grains and the medium sand grains can cooperate to support new fracturing, and a good sand filling diversion fracture can be formed to increase the reconstruction area of the target coal bed gas well reservoir, wherein the sand carrying liquid containing the fine sand grains is pumped firstly, so that the fine sand grains can support the remote fine fractures in the reservoir, and then the sand carrying liquid containing the medium sand grains is pumped to support the large fractures at the closer position so as to support the new fracturing. Wherein, the sand grains are quartz sand which is cheap and easy to obtain. The active water fracturing fluid is an aqueous solution with the concentration of 0.5-1.5% prepared from clear water and KCl, the concentration represents the mass concentration of the KCl, the active water fracturing fluid can prevent clay from swelling, has small harm to a coal reservoir, ensures the stability of the coal reservoir and is beneficial to the exploitation of coal bed gas.
Specifically, in step 104, the fracturing truck group is closed, the pumping of the fracturing fluid into the target coal-bed gas well is stopped, the plugging ball does not bear the pressure action of the active water fracturing fluid pumped in step 102 or the pressure action of the fracturing fluid pumped in step 103, so that the plugging ball falls to the bottom of the well from the perforation hole, after leaving the perforation hole and falling to the bottom of the well, the blowout and sand washing operations are sequentially performed, and then the plugging ball is discharged back to the ground, so that the secondary fracturing of the target coal-bed gas well is completed. The specific open flow, sand washing and flowback are realized by the following modes:
the discharge nozzle is arranged on a discharge pipe line of a wellhead of a target coal-bed gas well, and the valve is opened, so that the mixed liquid of the fracturing fluid, the active water fracturing fluid and other substances in the target coal-bed gas well is discharged to the ground. And then, pumping a proper amount of water into the target coal-bed gas well by using a fracturing truck group, carrying the washed sand to the ground by using high-speed upward-returning liquid, and simultaneously carrying the plugging ball to the ground.
The present invention will be further described below by way of specific examples.
In the following examples, those whose operations are not subject to the conditions indicated, are carried out according to the conventional conditions or conditions recommended by the manufacturer. The raw materials are conventional products which can be obtained commercially by manufacturers and specifications.
Example 1
In this example 1, the yield increasing effect of the method for secondary fracturing of a coal-bed gas well provided by the invention is evaluated. The coal bed gas well is targeted by an X well, and the highest daily gas production rate of the well is 600m3The daily output of the coal bed gas wells adjacent to the periphery is 1000m3The average value of the recent daily gas production of the well is 144m3And the daily gas yield of the target coal-bed gas well is low, the modification area of the first fracturing on the reservoir is small, and part of the original fracturing cracks are blocked, so that the target coal-bed gas well is selected. As shown in fig. 2-1, an original fracturing crack 3 and perforation holes 5 exist in a reservoir stratum 2 in a target coal-bed gas well 1 (an X well), a part of the perforation holes 5 are located on the original fracturing crack 3, and the original fracturing crack 3 does not exist in the part of the perforation holes 5. And then performing secondary fracturing on the target coal-bed gas well 1 by adopting the following method:
firstly, starting a fracturing truck group, and sequentially pumping 60m into an X well through the fracturing truck group3Active water fracturing fluid (pad fluid) 150m3Active water fracturing fluid and fine sand particles of 5m3And medium sand grain 10m3Mixed liquor (sand carrying liquid) of (9.3 m)3Active water fracturing fluid (displacement fluid, displacement is from 1m3The/min gradually increases to 5m3Min) to dredge the original pressure crack 3 in the reservoir 2, wherein the sand-carrying liquid is pumped and injected with the sand-carrying liquid containing fine sand grains firstly, and then the sand-carrying liquid containing medium sand grains is pumped and injected. Then a ball injector is adopted to inject 45 nylon balls 4 into the X well, and a fracturing truck group pumps 10m into the X well3The active water fracturing fluid has the discharge capacity of 1m3The/min gradually increases to 2m3And/min, enabling the nylon ball 4 to block the perforation 5 of the original fracturing crack 3, and referring to the attached figure 2-2. Then a fracturing truck group is adopted to pump 60m into the X well in sequence3Active water fracturing fluid (pad fluid) 200m3Active water fracturing fluid and fine sand particles of 5m3And medium sand grain 15m3Mixed liquor (sand carrying liquid) of (9.3 m)3Active water fracturing fluid (displacement fluid, displacement is from 1m3The/min gradually increases to 6m3/min) to form new fractures 6, see figures 2-3. And finally, closing the fracturing truck group, and after the nylon balls 4 fall into the well bottom, performing open flow and sand washing to discharge the nylon balls 4 to the ground to complete secondary fracturing. Wherein the active water fracturing fluid is a 1% aqueous solution prepared from clear water and KCl.
Then the X well is operated again, and after one-year drainage and production period, the daily gas production of the X well is 1806m3. Therefore, the secondary fracturing method for the coal-bed gas well can greatly improve the reservoir area of the coal-bed gas well and can greatly improve the gas production efficiency of the coal-bed gas well.
The above description is only exemplary of the present invention and should not be taken as limiting the scope of the present invention, as any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (9)
1. A method for secondary fracturing of a coal-bed gas well is characterized by comprising the following steps:
step a, starting a fracturing truck set, pumping fracturing fluid into a target coal bed gas well through the fracturing truck set, and performing small-scale fracturing to dredge original pressure fractures in a reservoir;
b, putting a plurality of plugging balls with the number less than that of the perforation holes into the target coal-bed gas well, simultaneously pumping active water fracturing fluid into the target coal-bed gas well by using the fracturing truck group, plugging the perforation holes of the original fracturing crack by using the plugging balls under the action of the active water fracturing hydraulic pressure, wherein the plugging balls are nylon balls, rubber balls or steel core rubber balls, the diameter of each plugging ball is 1-2 times of the diameter of each perforation hole, and the density of each plugging ball is 1.1-1.2g/cm3；
C, continuing pumping and injecting fracturing fluid into the target coal-bed gas well by adopting the fracturing truck group, performing medium-scale fracturing, and forming a new fracturing in the reservoir;
and d, closing the fracturing truck group, and discharging the blocking ball back to the ground after the blocking ball leaves the perforation hole and falls into the bottom of the well, so as to finish secondary fracturing on the target coal-bed gas well.
2. The method of claim 1, wherein the pumping of the fracturing fluid into the target coalbed methane well in step a and the continuing of the pumping of the fracturing fluid into the target coalbed methane well in step c each comprise: sequentially pumping and injecting a pad fluid, a sand carrying fluid and a displacement fluid into the target coal-bed gas well;
in the step b, the active water fracturing fluid is an aqueous solution with the concentration of 0.5-1.5% prepared by clear water and KCl.
3. The method of claim 2, wherein in step a, the pad fluid is 50-60m when the small-scale fracturing is performed3The active water fracturing fluid, the sand carrying fluid is 140-150m3Active water fracturing fluid and 10-15m3The displacement fluid is active water fracturing fluid, and the discharge capacity of the displacement fluid is 1m3Stepwise increasing min to 5m3/min。
4. The method of claim 2, wherein the pad is 50-60m when performing the medium scale fracturing3The active water fracturing fluid comprises 180-200m sand carrier fluid3Active water fracturing fluid and 20-25m3The displacement fluid is active water fracturing fluid, and the discharge capacity of the displacement fluid is 1m3Stepwise increasing min to 6m3/min。
5. The method of claim 3 or 4, wherein the sand particles are quartz sand when the sand-carrying fluid is pumped into the target coal-bed gas well, the sand-carrying fluid containing fine sand particles with a particle size of 40-70 mesh is pumped first, and then the sand-carrying fluid containing medium sand particles with a particle size of 20-40 mesh is pumped.
6. The method according to claim 5, wherein the volume of the medium sand grains is 60-70% of the total volume of the sand grains when the small scale fracturing is performed;
in the middle-scale fracturing, the volume of the middle sand grains accounts for 75-80% of the total volume of the sand grains.
7. The method of claim 1, wherein the number of plugging balls thrown into the target coal-bed gas well is obtained according to the following formula:
wherein n is a second predetermined amount; k is any value between 1.1 and 1.2; m is the number of perforations.
8. The method according to claim 1, wherein in the step b, the volume of the active water fracturing fluid is 10-12m3The discharge capacity is 1m3The/min gradually increases to 2m3/min。
9. The method of claim 1, wherein after the plugging ball leaves the perforation hole and falls to the bottom of the well, the operations of blowout and sand washing are sequentially carried out, and then the plugging ball is drained back to the ground, so that secondary fracturing of the target coal-bed gas well is completed.
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| CN110318674B (en) * | 2019-06-13 | 2020-10-23 | 太原理工大学 | Method for preventing outburst caused by cracking of roadway roof |
| CN111075419A (en) * | 2019-12-18 | 2020-04-28 | 山西蓝焰煤层气集团有限责任公司 | Squeezing permeability-increasing blockage removing process for low-yield coal bed gas vertical well |
| CN112963136A (en) * | 2021-03-10 | 2021-06-15 | 四川省煤田地质工程勘察设计研究院 | Multi-time sand fracturing method for low-permeability coal-based gas reservoir |
| CN114622886A (en) * | 2022-02-10 | 2022-06-14 | 中国石油化工集团有限公司 | Cross fracturing gas testing construction method for well factory |
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