CN111911122B - Fracturing method for unswept area of shale gas encrypted well - Google Patents
Fracturing method for unswept area of shale gas encrypted well Download PDFInfo
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- CN111911122B CN111911122B CN201910375839.6A CN201910375839A CN111911122B CN 111911122 B CN111911122 B CN 111911122B CN 201910375839 A CN201910375839 A CN 201910375839A CN 111911122 B CN111911122 B CN 111911122B
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- slickwater
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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
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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
- E21B43/267—Methods for stimulating production by forming crevices or fractures reinforcing fractures by propping
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21C—MINING OR QUARRYING
- E21C41/00—Methods of underground or surface mining; Layouts therefor
- E21C41/16—Methods of underground mining; Layouts therefor
- E21C41/24—Methods of underground mining; Layouts therefor for oil-bearing deposits
Abstract
The invention provides a fracturing method for unswept areas of shale gas encrypted wells, which comprises the following steps of: s1, pretreating a reservoir by using acid liquor; s2, carrying out seam forming on the reservoir subjected to acid liquor pretreatment by using foam slickwater to generate a crack; s3, injecting foam slickwater carrying micro proppant into the crack; s4, injecting foam slickwater carrying small-particle-size propping agent into the crack; s5, injecting foamed slickwater carrying medium-particle-size propping agent into the crack; s6, injecting foam slickwater carrying large-particle-size propping agent into the cracks; and S7, replacing by using fracturing fluid. The method provided by the invention can transform unswept areas among wells in a large range and improve the staged fracturing effect of the shale gas encrypted well.
Description
Technical Field
The invention relates to a fracturing method for unswept areas of shale gas encrypted wells.
Background
After the shale gas horizontal well is subjected to staged fracturing and put into operation, along with the reduction of yield and wellhead pressure, sometimes the wellhead pressure is even close to the gas transmission pressure of a ground gathering and transportation station, so that in order to further improve the utilization rate of the recoverable reserves of the shale gas, a packed horizontal well needs to be drilled, and staged fracturing transformation is carried out. In recent years, the number of drilling and fracturing shale gas encrypted wells is greatly increased by constructing a demonstration area Fuling shale gas field in the first national-grade shale gas production energy which enters into commercial development in China.
Due to the relatively long production time after the adjacent well of the infill well is fractured, a large pressure deficit area is formed. In other words, compared with the original situation, the gas content of the area through which the encrypted well passes is greatly reduced, and the formation pressure is also greatly reduced, which is equivalent to the normal pressure shale gas which is not completely broken through at present, and even is lower than the gas content and the formation pressure of the normal pressure shale gas. Therefore, the fracturing of the encrypted well is difficult to break through. The main reason is that, firstly, the adjacent well is pressed and then produced, a large amount of shale gas is produced, and large-area depletion of formation pressure is caused. The reduction of the formation pressure, which leads to the reduction of the ground stress and the effective permeability, requires more complex seam networks to achieve the expected effect; secondly, due to the existence of the first fracturing fracture of the adjacent well, the induced stress is increased more in the direction of the minimum horizontal main stress, and even if the conductivity of the first fracture is reduced or even disappears, the induced stress cannot be correspondingly lost along with the complete closing of the fracture due to the shaping characteristic of the shale. And after long-term production after pressing, the induced stress is just opposite to that of the first crack, the induced stress is reduced but not increased, and the direction of the maximum main stress is also the direction of the maximum permeability, so that the reduction range of the induced stress caused by production in the crack direction is maximum, and the reduction of the induced stress in the direction vertical to the crack is minimum. In other words, due to the long-term presence of induced stress effects in the first fractures of adjacent wells and induced stress reduction effects from production, there is an inherent mechanism that contributes to the reduction of the bi-directional horizontal stress difference, i.e., towards the stress isotropic effect. Therefore, the conventional shale gas fracturing technology is adopted for the encrypted well, and the fracture initiation direction and the subsequent extension process of the fracture have the risk of having no dominant extension direction. The risk easily induces the extension of the crack to a low-pressure area affected by an adjacent well, on one hand, the gas content of the low-pressure area is greatly reduced, the crack does not have a good gas production effect when extended to the low-pressure area, and on the other hand, the sand blocking risk of the fracturing construction of the encrypted well can be caused due to the greatly increased filtration loss.
Therefore, a new fracturing technology is needed to be researched and provided, which can plug small micro-fracture systems with different dimensions, improve the flow conductivity of the fracture, promote the fracture steering, improve the fracture-forming efficiency, transform unswept areas among wells in a large range and improve the staged fracturing effect of the shale gas-filled wells.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a novel fracturing sand-adding technology for unswept areas of shale gas-tight wells, which adopts an injection mode of carbon dioxide foam slickwater crack formation and carrying a fine propping agent to furthest block small micro-crack systems with different scales, reduce the using amount of fracturing fluid when a main crack extends to an unswept area of an adjacent well, inhibit the expansion of clay to a certain extent, further improve the flow conductivity of cracks with different scales, promote the crack diversion, improve the crack formation efficiency, transform unswept areas among wells in a large range and improve the staged fracturing effect of the shale gas-tight wells.
According to a first aspect of the invention, a method for fracturing an unswept zone of a shale gas encrypted well is provided, which comprises the following steps carried out in sequence:
s1, pretreating a reservoir by using acid liquor;
s2, carrying out seam forming on the reservoir subjected to acid liquor pretreatment by using foam slickwater to generate a crack;
s3, injecting foam slickwater carrying micro proppant into the crack;
s4, injecting foam slick water carrying small-particle-size propping agents into the cracks;
s5, injecting foamed slickwater carrying medium-particle-size propping agent into the crack;
s6, injecting foam slickwater carrying large-particle-size propping agent into the cracks;
and S7, replacing by using fracturing fluid.
And S3, injecting foam slickwater carrying the micro proppant into the cracks, wherein the micro proppant can be filled in the cracks with different sizes, so that the crack forming efficiency is improved, the steering effect of the cracks is better, and the full suspension and complete plugging and steering effects of the proppant on the height of the cracks can be ensured.
According to a preferred embodiment of the invention, the froth slick is a carbon dioxide froth slick. The carbon dioxide foam slickwater is weakly acidic and can greatly reduce filtration loss, so that the extending distance of an early crack to a low-pressure area of an adjacent well is reduced, the using amount of a fracturing fluid when a main crack extends to an unswept area of the adjacent well fracturing can be reduced to the maximum extent, the using amount of a water phase can also be reduced, the expansion of clay is inhibited to a certain extent, and the flow conductivity of cracks with different scales is improved.
Preferably, the foam mass is 30-50% in the foam slick water. "froth quality" as used herein refers to the ratio of the volume of gas in the froth slick to the total volume of the froth slick.
According to a preferred embodiment of the present invention, the particle size of the fine proppant is 140 to 210 mesh, preferably the apparent density of the fine proppant is 1.05 to 1.25g/cm 3 。
According to a preferred embodiment of the present invention, the small particle size proppant has a particle size of 70 to 140 mesh, preferably 80 to 120 mesh.
According to a preferred embodiment of the present invention, the medium particle size proppant has a particle size of 40 to 70 mesh.
According to a preferred embodiment of the present invention, the large particle size proppant has a particle size of 30 to 50 mesh.
According to the preferred embodiment of the invention, before the step S1, the method further comprises evaluating parameters of a reservoir before fracturing, optimizing fracture parameters and fracturing construction parameters according to the obtained reservoir parameters, and lowering the staged fracturing string.
According to a preferred embodiment of the invention, the reservoir parameters comprise one or more of pore pressure, minimum stress and integrated fluid loss parameters.
According to a preferred embodiment of the invention, ECLIPSE is used for fracture parameter optimization.
In accordance with a preferred embodiment of the present invention, MEYER is used for fracture construction parameter optimization.
According to a preferred embodiment of the invention, the fracture parameters comprise fracture length, conductivity and fracture spacing.
According to the preferred embodiment of the invention, the fracturing construction parameters comprise fracturing fluid volume, viscosity, displacement, proppant volume, sand-to-fluid ratio and the like.
According to a preferred embodiment of the present invention, the amount of the foamed slickwater used in step S2 is 80-100m 3 And/or a displacement of 12-16m 3 Min, preferably, the mass of carbon dioxide in the froth slick water is gradually increased from 30% to 50%. In the construction process of the foam slick water seam making, the lower discharge capacity is used in the initial stage, preferably 50-70% of the highest discharge capacity, more preferably 60% of the highest discharge capacity, and gradually increased to the highest value in the middle and later stages.
According to a preferred embodiment of the invention, in step S3, the sand-fluid ratio of the foamed slickwater carrying the fine proppant is increased stepwise from 3% to 18% with an increase of 2-4%.
According to a preferred embodiment of the present invention, in step S3, the fracturing fluid carrying the fine proppant is injected in a slug type, preferably in a long slug type. Preferably, the sand-liquid ratio of the foamed slickwater carrying the fine proppant is increased stepwise from 3% to 18% with an increase of 2-4%, and preferably, the sand is continuously added and injected every 3-4 sand-liquid ratios;
according to a preferred embodiment of the invention, in step S3, the injection amount of the foamed slickwater carrying the fine proppant per sand-to-fluid ratio is 30-40m 3 The spacer fluid is injected in an amount of 80-100% of the wellbore volume, preferably not more than 50m 3 。
According to a preferred embodiment of the invention, the foamed slickwater carrying the fine proppant in step S3 has a displacement of 12-16m 3 Min, preferably the mass of carbon dioxide in the froth slick water is 50%.
According to the preferred embodiment of the invention, in step S4, the foamed slickwater carrying the small-particle size proppant is injected in a slug type manner, so as to achieve the purpose of efficient plugging and steering; preferably, the first and second electrodes are formed of a metal,
the sand liquid ratio of the foamed slickwater carrying the small-particle-size propping agent is increased from 2 percent to 16 percent in a stepwise manner in an increasing manner of 1-3 percent;
preferably, the injection amount of the foamed slickwater carrying the small-particle size proppant per sand-to-fluid ratio is 40-50m 3 The injection amount of the spacer fluid is 40-50m 3 ；
The preferred foamed slickwater displacement carrying small particle size proppant per sand to fluid ratio is 12-16m 3 Min, preferably the mass of carbon dioxide in the froth slick water is 50%.
According to a preferred embodiment of the invention, in step S5, the foamed slickwater carrying the medium-sized proppant is injected in a long-stage plug-type manner; preferably, the first and second liquid crystal display panels are,
the sand liquid ratio of the foamed slickwater carrying the medium-particle-size propping agent is increased to 21 percent in a step-by-step manner from 6 percent by increasing the amplitude of 2 to 4 percent; preferably, the sand is continuously added and injected in every 3-4 sand-liquid ratios;
preferably, the injection amount of the foamed slickwater carrying the medium-particle size proppant per sand-to-fluid ratio is 40-50m 3 The injection amount of the isolation liquid is 50-60m 3 ；
Preferably, the displacement of the foamed slick water carrying the medium-particle size proppant per sand-to-fluid ratio is 12-16m 3 Min, preferably the mass of carbon dioxide in the froth slick water is 50%.
According to a preferred embodiment of the invention, in step S6, the foamed slickwater carrying the large particle size proppant is injected with continuous sand addition. Due to the stress isotropic effect around the infill well, once an effective plug is formed somewhere in the low pressure zone of an adjacent well, it will turn relatively easily at the fine proppant plug. After the shale gas is turned, the shale gas is easy to extend to a region with slightly high stress, then plugging and turning are carried out again, finally continuous plugging and turning are initiated through the natural selection action, and finally the main crack can gradually turn to the region with the highest stress, so that the expected shale gas yield and stable yield effect are obtained. Preferably, the first and second liquid crystal display panels are,
the sand-liquid ratio of the foamed slickwater carrying the large-particle-size proppant is increased to 24 percent in a step-by-step manner from 12 percent by increasing the amplitude of 2 to 4 percent;
carrying large particle size supports with preferred per grit ratioThe injection amount of the agent is 5-10m 3 ；
The preferred foamed slickwater displacement carrying large particle size proppant per sand to fluid ratio is 12-16m 3 Min, preferably the mass of carbon dioxide in the froth slick water is 50%.
According to a preferred embodiment of the invention, in step S7, the amount of the fracturing fluid is 110-130% of the volume of the well bore, and preferably, the fracturing fluid of 50-60mPa · S is used for sweeping the sand setting effect of the horizontal well bore, and then the displacement is carried out by using low-viscosity slickwater of 2-3mPa · S; preferably, the volume of the fracturing fluid of 50 to 60 mPas accounts for 30 to 40 percent of the total volume of the fracturing fluid used in the step S8 (comprising the fracturing fluid of 50 to 60 mPas and the low-viscosity slickwater of 2 to 3 mPas).
The invention is an important component of main fracturing, utilizes the advantages that the micro-fine propping agent and the foam slickwater crack making can greatly reduce filtration loss and generate crack steering effect, adopts the injection mode of the carbon dioxide foam slickwater crack making and the carrying micro-fine propping agent, furthest seals small micro-crack systems with different sizes, reduces the using amount of fracturing fluid when the main crack extends to an unswept zone of the adjacent well fracturing, inhibits the expansion of clay, further improves the flow conductivity of cracks with different sizes, simultaneously, the micro-fine propping agent can promote the crack steering, improves the crack making efficiency, reforms unswept zones among wells in a large range and improves the staged fracturing effect of the shale gas encryption well. The construction process is scientific and reasonable, has strong operability, and has wide application prospect in the staged fracturing of the shale gas encryption well.
Detailed Description
The present invention will be described in detail with reference to examples, but the present invention is not limited to the examples.
A fracturing method for large-scale reconstruction of unswept areas of shale gas encrypted wells comprises the following steps:
1) And evaluating key shale parameters of the encrypted well. Pore pressure is the most important shale parameter that causes changes in a range of parameters (e.g., permeability, rock mechanics parameters, tri-directional ground stress, etc.). The current pore pressure, permeability and the like can be obtained by adopting an encryption well pilot hole micro-injection test. And the temperature and the pressure of the pilot hole of the encryption well can be simulated based on the core of the pilot hole of the encryption well, and corresponding rock mechanical parameters can be tested. In addition, a small-scale test fracturing test is carried out on the pilot hole of the encrypted well, and parameters such as minimum ground stress, comprehensive fluid loss coefficient and the like are tested.
2) And (5) optimizing crack parameters. Based on the parameters in the step 1), commercial software ECLIPSE for shale gas fracturing well yield prediction is applied to simulate and optimize to obtain the optimal fracture length, the optimal flow conductivity, the optimal fracture spacing and the like.
3) And optimizing fracturing construction parameters. And (3) simulating and obtaining the volume, viscosity, discharge capacity, volume of propping agent, sand-liquid ratio and the like of the fracturing fluid under the optimized fracture parameters in the step 2) by using shale gas fracturing optimization design software MEYER.
4) Providing a lathering slick water. The foam slick water is preferably carbon dioxide foam, and the foam quality (the ratio of the gas volume in the foam to the total volume of the foam) ranges from 30 to 50 percent.
5) Lower bridge plug and perforation combined tool operation
The first section adopts a continuous oil pipe to carry a perforating gun, and the other sections adopt a pumping method to carry a bridge plug and the perforating gun.
6) And (4) acid pretreatment operation. The standard hydrochloric acid is generally used, and the injection process and parameters refer to the fracturing method of an adjacent well.
7) And (5) performing foam sliding water seam construction. And constructing according to the crack parameters optimized in the step 3). Using 80-100m 3 Pure slick water, the carbon dioxide foam mass was initially 30% and gradually increased to 50% in the middle and later stages, and this foam mass was maintained. The discharge capacity is 12-16m 3 And/min. The displacement can be low at the beginning (about 60 percent of the highest displacement can be taken), and the middle and later stages are gradually increased to the highest value. The foam fracturing fluid is weakly acidic, and can greatly reduce filtration loss, thereby reducing the extending distance of early cracks to a low-pressure area of an adjacent well, reducing the dosage of the fracturing fluid when main cracks extend to an unswept area of the adjacent well fracturing to the maximum extent, reducing the dosage of a water phase, inhibiting the expansion of clay to a certain extent, and further improving the flow conductivity of cracks with different scales.
8) And injecting the foam slickwater carrying the micro proppant into the construction. Using 140-210The mesh and apparent density is 1.05-1.25g/cm 3 The ultra-low density micro proppant can fill cracks with different sizes, improves the crack-making efficiency, has better steering effect, and can ensure full suspension and complete plugging and steering effect of the proppant on the height of the cracks. In the stage, the foamed slickwater carrying the fine proppant is injected by a slug type, preferably by a long-slug type, for example, the sand-liquid ratio is 3-6-9-12-15-18%, the former three sand-liquid ratios are continuously constructed, the latter three sand-liquid ratios are continuously constructed, and the volume of the foamed slickwater carrying the fine proppant of each sand-liquid ratio is 30-40m 3 The volume of the middle spacer fluid is taken as the volume of the section of the well bore, and is generally not more than 50m 3 . The discharge amount is 12-16m 3 Min, the foam mass is 50%.
9) Foam slickwater injection with 70-140 mesh proppant. The section of proppant adopts a slug type sand adding mode, 8 slugs are injected, the sand-liquid ratio is 2-4-6-8-10-12-14-16%, and the injection amount of slick water carrying the proppant in each sand-liquid ratio is 40-50m 3 Volume of the spacer fluid is 40-50m 3 . The discharge quantity is 12-16m 3 Min, the mass of carbon dioxide foam is 50 percent.
10 ) foamed slickwater injection with 40-70 mesh proppant. The section of proppant is constructed by adopting a long section plug, the sand-liquid ratio is 6-9-12-15-18-21%, sand is continuously added in the first three sand-liquid ratios, sand is continuously added in the last three sand-liquid ratios, and the injection amount of the foamed slickwater carrying the proppant in each sand-liquid ratio is 40-50m 3 The volume of the intermediate isolation liquid is 50-60m 3 . The displacement range is 12-16m 3 And/min. The mass of the carbon dioxide foam is 50 percent.
11 ) foam slickwater injection with 30-50 mesh proppant. The proppant is constructed by continuously adding sand, the sand-liquid ratio is 12-15-18-21-24%, and the volume of the foamed slickwater carrying the proppant is 5-10m 3 . The displacement range is 12-16m 3 And/min. The carbon dioxide foam content was 50%.
12 A replacement operation. Injecting 110-130% of fracturing fluid of the volume of the current section of the shaft, adopting glue solution with the viscosity of 50-60 mPa.s in the first 30-40% of the volume of the current section of the shaft to clean possible horizontal shaft sand setting effect, and then injecting by adopting low-viscosity slick water with the viscosity of 2-3 mPa.s until the displacement is completed.
13 ) repeating the steps 5) to 12) in other construction sections until all the construction sections are finished;
14 Drilling, plug-in, flow-back, testing, production and the like after pressing, and is executed according to a conventional process. In order to prevent sand discharge after ground stress is reduced, the flowback pressure difference is required to be reduced by 20-30% compared with the conventional pressure difference.
Example 1
The invention is applied to the volume fracturing modification construction of a certain encrypted well in the Fuling area, and the well is positioned at the central position of a horizontal well of four shale gas which is fractured in sections and produced for a long time, and has the vertical depth of 2732.60m, the inclined depth of 4941.00m, the well inclination of the bottom of the well of 89.40 degrees and the horizontal section length of 2000.00m. The method provided by the invention is used for carrying out optimization design, and the steps and the results are as follows:
1) Performing a small pressure test on the first section, explaining the minimum horizontal main stress of 76MPa and the near-wellbore crack bending friction resistance of 4-7 MPa; the evaluation of the key reservoir parameters of the well logging interpretation shale proves that the well has good shale development and good static indexes;
2) And (3) optimizing by adopting ECLIPSE software to obtain the optimal fracture parameters of the long-term yield after pressing: the optimal gap distance is 16-22m, the half length of the crack is 260-300m, and the flow conductivity is 20-35 mD.m; and (3) simulating by adopting GOFHER software to obtain construction parameters of the optimal crack form: the discharge capacity is 12-14m 3 Min, the dosage of the single-stage fracturing fluid is 1600-1900m 3 Single stage supported dose of 40m 3 -60m 3 Preferably 4 kinds of proppant particle sizes, which are 140-210 meshes (fine proppant), 70-140 meshes (small particle size proppant), 40-70 meshes (medium particle size proppant) and 30-50 meshes (large particle size proppant) respectively; carbon dioxide foam slick water, foam mass (ratio of gas volume in foam to total foam volume) range: 30-50%; low viscosity slickwater with viscosity of 2-3 mPas and glue solution with viscosity of 50-60 mPas.
3) Carrying out perforating operation by adopting a bridge plug perforating combination method;
4) Pretreatment adopted is 20m 3 Dilute hydrochloric acid, the acid injection displacement is 2m 3 /min；
5) Step ascending displacement (sequentially 2-4-6-8 m) 3 Min) injection of 30m 3 Sliding water, then ascending the displacement in steps (4-6-8-10-12 m in sequence) 3 Min) injection 80m 3 Glue solution;
6) The foam slippery water is used for making seams and the step rising displacement is 8-10-12-14m 3 Min) injection 100m 3 The carbon dioxide foam is slick water, and the foam quality gradually rises from 30 percent to 50 percent;
7) Adding sand into carbon dioxide foam slickwater, wherein the foam mass is 50 percent and is 12m 3 The flow rate of the fine proppant is sequentially injected into 140-210 meshes in a plug mode, the sand-liquid ratio is 3-6-9 percent (sand is continuously added in the 3 sand-liquid ratios), and the dosage of the carbon dioxide foam slickwater carrying the fine proppant in each sand-liquid ratio is 40m 3 (ii) a Middle injection 30m 3 And (3) taking carbon dioxide foam slickwater as a spacer fluid, and continuously adding sand in a slug mode when the pressure of a well head is stable, wherein the sand-liquid ratio is 12-15-18 percent (the sand-liquid ratio is continuously added for 3 sand-liquid ratios). Wherein the foam mass in the carbon dioxide foam slick water is 50 percent, and the discharge capacity is 14m 3 /min；
8) Injecting the foam slickwater carrying 70-140 meshes of propping agent in a plug manner, adding the foam slickwater in 7 plugs, sequentially adding the sand-liquid ratio of 2-4-6-9-12-14-16%, wherein the volume of the foam slickwater carrying 70-140 meshes of propping agent in each sand-liquid ratio is 40m 3 Volume of the intermediate spacer liquid is 50m 3 Displacement range of 12-16m 3 Min, the mass of carbon dioxide foam is 50 percent.
9) Injecting long section plug of foamed slickwater carrying 40-70 mesh proppant, wherein the sand-liquid ratio of the foamed slickwater carrying the proppant is 6-9-12% (3 sand-liquid ratios are continuously added with sand) and 15-17-20% (3 sand-liquid ratios are continuously added with sand), and the volume of the foamed slickwater carrying the proppant is 50m in each sand-liquid ratio 3 Volume of middle spacer liquid 50m 3 Displacement range of 12-16m 3 Min, the mass of carbon dioxide foam is 50 percent.
10 The foam slickwater carrying 30-50 meshes of propping agent is continuously injected, the sand-liquid ratio of the foam slickwater carrying the propping agent is 12-15-18-20% in sequence, and the continuous injection mode is adopted, and the specific volume of each sand-liquid is 10m 3 . The displacement range is 12-16m 3 Min, carbon dioxide foamThe amount is 50%.
11 In order of 20 m) are used 3 High viscosity glue and 40m 3 Replacing the low-viscosity slick water;
12 Repeat steps 3) -11) above, completing the remaining fracturing construction. After fracturing is finished, flowback, test production and formal operation are executed according to the conventional flow, and the flowback pressure difference is reduced by 30% compared with the conventional pressure difference.
By implementing the invention, the unimpeded flow rate after the well pressure reaches 16.2 multiplied by 10 4 m 3 The method has the advantages that a good fracturing effect is obtained, and a good idea and a good method are provided for the fracturing reformation of the Fuling shale gas encrypted well.
It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not constitute any limitation to the present invention. The present invention has been described in relation to an exemplary embodiment, and it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the claims and without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to all other methods and applications having the same functionality.
Claims (10)
1. A fracturing method for unswept areas of shale gas encrypted wells comprises the following steps which are carried out sequentially:
s1, pretreating a reservoir by using acid liquor;
s2, carrying out seam forming on the reservoir subjected to acid liquor pretreatment by using foam slickwater to generate a crack; the foam slickwater is carbon dioxide foam slickwater, and the mass of carbon dioxide in the foam slickwater is 30-50%; the dosage of the foamed slickwater is 80-100m 3 The discharge capacity is 12-16m 3 /min；
S3, injecting foam slickwater carrying micro proppant into the crack; the particle diameter of the fine proppant is 140-210 meshes, and the apparent density is 1.05-1.25g/cm 3 (ii) a Carrying fine proppantThe sand liquid ratio of the foamed slickwater is increased to 18 percent in a step-by-step manner from 3 percent by increasing the amplitude of 2 to 4 percent; the foam slickwater carrying the fine proppant adopts slug type injection which is long slug type injection, and the injection amount of the foam slickwater carrying the fine proppant with each sand-liquid ratio is 30-40m 3 The injection amount of the spacer fluid is 80-100% of the volume of the shaft and is not more than 50m 3 (ii) a The discharge capacity is 12-16m 3 /min；
S4, injecting foam slick water carrying small-particle-size propping agents into the cracks; the particle size of the small-particle size proppant is 70-140 meshes; injecting the foamed slickwater carrying the small-particle-size propping agent in a slug mode; the sand liquid ratio of the foamed slickwater carrying the small-particle-size proppant is increased to 16 percent in a step-shaped manner from 2 percent by increasing the amplitude of 1 to 3 percent; the injection amount of the foamed slickwater carrying the proppant with small particle size in each sand-liquid ratio is 40-50m 3 The injection amount of the spacer fluid is 40-50m 3 (ii) a The discharge capacity is 12-16m 3 /min；
S5, injecting foamed slickwater carrying medium-particle-size propping agent into the crack; the particle size of the medium-particle size proppant is 40-70 meshes; the foam slickwater carrying the medium-grain proppant is injected by a long-section plug; the sand liquid ratio of the foamed slickwater carrying the medium-particle-size propping agent is increased to 21 percent in a step-by-step manner from 6 percent by increasing the amplitude of 2 to 4 percent; continuously adding sand into the sand liquid in every 3-4 sand liquid ratios; the injection amount of the foam slickwater in each sand-liquid ratio is 40-50m 3 The injection amount of the isolation liquid is 50-60m 3 (ii) a The discharge capacity is 12-16m 3 /min；
S6, injecting foam slick water carrying a large-particle size propping agent into the cracks; the particle size of the large-particle size proppant is 30-50 meshes; injecting the foamed slickwater carrying the large-particle-size propping agent by adopting continuous sand adding; the sand-liquid ratio of the foamed slickwater carrying the large-particle-size proppant is increased to 24 percent in a step-by-step manner from 12 percent by increasing the amplitude of 2 to 4 percent; the injection amount of the foamed slickwater carrying the proppant with large particle size in each sand-to-liquid ratio is 5-10m 3 (ii) a The discharge capacity is 12-16m 3 /min；
And S7, replacing by using a fracturing fluid, wherein the using amount of the fracturing fluid is 110-130% of the volume of the shaft, cleaning the sand setting effect of the horizontal shaft by using the fracturing fluid of 50-60mPa & S in the replacing process, and then replacing by using low-viscosity slickwater of 2-3mPa & S.
2. The method according to claim 1, wherein before the step S1, the method further comprises evaluating reservoir parameters before fracturing, optimizing fracture parameters and fracturing construction parameters according to the obtained reservoir parameters, and lowering the staged fracturing string;
the reservoir parameters include one or more of pore pressure, minimum geostress, and integrated fluid loss parameters; and/or, using ECLIPSE for fracture parameter optimization, and/or, using MEYER for fracture construction parameter optimization.
3. The method of claim 2, wherein the fracture parameters include fracture length, conductivity, and fracture spacing; and/or the fracturing construction parameters comprise fracturing fluid volume, viscosity, displacement, proppant volume and sand-to-fluid ratio.
4. The method according to claim 1, wherein the mass of carbon dioxide in the froth slipstream is gradually increased from 30% to 50% in step S2; in the construction process of foam sliding water seam making, the low discharge capacity is used in the initial stage and is 50-70% of the highest discharge capacity, and the discharge capacity is gradually increased to the highest value in the middle and later stages.
5. The method of claim 4, wherein the lower displacement is used initially during the froth slick water seam construction, being 60% of the maximum displacement.
6. The method of claim 1 wherein in step S3 the mass of carbon dioxide in the froth slipstream is 50%.
7. The method of claim 1 wherein in step S4 the mass of carbon dioxide in the froth slipstream is 50%.
8. The method of claim 1 wherein in step S5 the mass of carbon dioxide in the froth slipstream is 50%.
9. The method of claim 1 wherein in step S6 the mass of carbon dioxide in the froth slipstream is 50%.
10. The method according to claim 1, wherein in step S7 the volume of the fracturing fluid of 50-60 mPa-S is 30-40% of the total volume of the fracturing fluid used in step S7.
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