CN111663930B - Fracturing method for horizontal seam of shallow tight oil reservoir - Google Patents
Fracturing method for horizontal seam of shallow tight oil reservoir Download PDFInfo
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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
Abstract
The invention relates to a fracturing method for a horizontal seam of a shallow tight oil reservoir, belonging to the technical field of fracturing production increase of oil and gas wells. The fracturing method comprises the following steps: opening and expanding the main seam; opening and expanding the micro-seam; filling micro-cracks; plugging the seam end; when the net pressure is larger than the maximum and minimum stress difference, opening and expanding the branch seam; filling branch seams; filling the main seam; and performing displacement operation to finish fracturing of the horizontal seam. The invention completes the fracturing of the horizontal seam by forming the micro-seam in the main seam of the horizontal seam, expanding and filling the micro-seam, blocking the seam end to form the branch seam, and further filling the branch seam and the main seam. The invention forms complex seams such as vertical seams or T-shaped seams and the like on the basis of the horizontal seams by fracturing the horizontal seams, increases the effective reconstruction volume, fully reconstructs a reservoir stratum, improves the longitudinal and plane reserve utilization degree of a shallow tight reservoir oil layer and improves the oil production of an oil well.
Description
Technical Field
The invention relates to a fracturing method for a horizontal seam of a shallow tight oil reservoir, belonging to the technical field of fracturing production increase of oil and gas wells.
Background
The fracturing process is an important technology for increasing the yield and injection of an oil field and maintaining the stable yield of the oil field, and the conventional fracturing method generally adopts three stages for fracturing: a pad fluid stage, a sand carrying fluid stage and a displacement stage. In the pre-liquid stage, the performance of liquid pressure conduction is utilized, a high-pressure pump set is utilized on the ground, liquid with certain viscosity is pumped into a well at the discharge capacity larger than the stratum absorption capacity, high pressure is suppressed at the bottom of the well, the pressure exceeds the ground stress of an oil layer and the tensile strength of rocks, and cracks are generated in the stratum; in the sand carrying liquid stage, sand carrying liquid with propping agent is injected into the crack, and the crack is supported while being extended; in the displacement stage, active water or linear glue is generally adopted to completely displace the sand-carrying liquid in the fracturing pipe column and the ground manifold into the crack, so that sand blocking and sand blockage of the fracturing pipe column are avoided. After the pump is stopped, a high-permeability sand filling crack with a certain width is formed in the oil layer, and the high-permeability sand filling crack comprises two cracks: the research shows that the buried depth of the stratum generating the fracturing horizontal seam is generally less than 1000m, and the vertical fracture is formed when the buried depth of the oil reservoir is more than 1000 m. And the high-permeability sand filling crack enlarges an oil-gas flow channel, changes the flow mode and reduces the seepage resistance, thereby playing the roles of increasing the yield and increasing the injection.
The reservoir with the buried depth of less than 1000m comprises a shallow compact reservoir, and through research, most of the residual oil remains in the compact reservoir, and the reservoirs have the characteristics of low permeability, low oil yield under natural conditions, most of rocks, compact sandstone, more natural fractures and the like, and the air permeability is basically less than 0.1 multiplied by 10 -3 μm 2 . Unconventional reservoirs such as compact oil reservoirs and the like are paid more and more attention at home and abroad, along with the deepening of oil exploration and development, the exploration and development of the compact oil reservoirs are gradually increased, the difficulty of the exploration and development is also increased, and the fracturing technology is necessary for the transformation of the reservoirs in order to economically and effectively exploit oil and gas resources in the oil and gas resources.
However, for shallow tight oil reservoirs, because the reservoir is buried shallowly (less than 650 m), horizontal seams are formed by fracturing, although the recovery ratio of the oil reservoir is improved to a certain extent by adopting the existing fracturing method, the horizontal seams after fracturing are low in longitudinal and plane exploitation degrees, the reservoir is not fully reformed, the development effect is poor, and the recovery ratio is influenced, so that a scheme for fracturing the horizontal seams of the shallow tight oil reservoirs needs to be provided.
Disclosure of Invention
The application aims to provide a fracturing method for the horizontal seams of the shallow tight oil reservoir, and an effective scheme is added for fracturing the horizontal seams of the shallow tight oil reservoir.
In order to achieve the purpose, the application provides a technical scheme of a fracturing method of a shallow tight reservoir horizontal seam, which comprises the following steps:
1) Opening and expanding the main seam;
2) Opening and expanding the micro-seam;
3) Filling the micro-cracks;
4) Plugging the seam end;
5) When the net pressure is larger than the stress difference, opening and expanding the branch seams;
6) Filling branch seams;
7) Filling the main seam;
8) And performing displacement operation to finish fracturing of the horizontal seam.
The fracturing method of the shallow compact reservoir horizontal seam has the beneficial effects that: the invention increases the net pressure when plugging the seam end by forming the micro-seam in the main seam of the horizontal seam and expanding and filling the micro-seam, and opens and expands the branch seam when the net pressure is larger than the stress difference, thereby filling the branch seam and the main seam and completing the fracturing of the horizontal seam. According to the invention, through fracturing the horizontal seam, a vertical seam or a T-shaped seam and other complex seams are formed on the basis of the horizontal seam, so that the effective reconstruction volume is increased, the reservoir is fully reconstructed, the longitudinal and plane reserve utilization degree of the oil layer of the shallow tight oil reservoir is improved, and the oil yield of the oil well is improved.
Further, in order to improve the effect after fracturing and form a larger effective volume, the fracturing fluid is injected in a first discharge amount in the steps 1) to 4); and in the steps 5) to 8), injecting the fracturing fluid at a second displacement, wherein the second displacement is larger than the first displacement.
Further, in order to ensure the formation of the complex fracture, the fracturing fluid injected in the steps 1), 6) and 7) is medium-viscosity fracturing fluid; the fracturing fluid injected in the steps 2) -5) is low-viscosity fracturing fluid; the fracturing fluid injected in the step 8) is a primary glue solution; the viscosity of the medium viscosity fracturing fluid is greater than that of the low viscosity fracturing fluid.
Further, in order to reduce the fluid loss of the fracturing fluid, in the step 3), the micro-cracks are filled with a propping agent with a small particle size and a low sand ratio to reduce the fluid loss of the fracturing fluid, wherein the low sand ratio is 6-10%.
Further, in order to improve the net pressure, opening the branch seams, and plugging seam ends by using a propping agent with medium particle size and low sand ratio in the step 4) to improve the net pressure; the low sand ratio is 6-10%.
Furthermore, in order to support the branch seams, in the step 6), a proppant with a medium-grain size and a small-grain size which are mixed in an equal ratio and a medium-sand ratio is used for filling the branch seams, wherein the medium-sand ratio is 10% -20%.
Further, in order to support the main seam, the branch seams are filled with a proppant with large grain size and high sand ratio in the step 7); the high sand ratio is 20-40%.
Furthermore, in order to support the branch seams more stably, when the branch seams are filled, the filling mode is a mode of gradually increasing the sand ratio.
Furthermore, in order to support the main joint more stably, when the main joint is filled, the filling mode is a mode of gradually increasing the sand ratio.
Drawings
FIG. 1 is a flow chart of the fracturing method of the horizontal fractures of the shallow tight reservoir of the invention.
Detailed Description
The first embodiment of the fracturing method of the shallow tight oil reservoir horizontal seam is as follows:
the fracturing method of the shallow tight oil reservoir horizontal seam has the main concept that because the horizontal seam is the main fracture formed by fracturing the shallow tight oil reservoir, more vertical seams or T-shaped seams and the like are produced on the basis of fracturing the main fracture when the horizontal seam is fractured, so that the horizontal seam forms a complex seam network, the reservoir is fully reformed, the reforming volume is enlarged, and the oil yield is improved.
In this embodiment, a new well is fractured, a layer of main fractures are generally fractured first for the fracturing of the new well, the fracturing can be continued if necessary subsequently, bedding fractures are avoided when the new well is perforated, and specifically, the fracturing method of the horizontal fractures of the shallow tight oil reservoir includes the following steps as shown in fig. 1:
1) Selected fracturing interval
Firstly, potential analysis is carried out on a fracturing layer section, the fracturing layer section needs to meet the conditions that the oil saturation of the fracturing layer is more than 35%, the reserve utilization rate is less than 15%, a water well corresponds to the fracturing layer section, the connectivity is good, and no horizontal layer seam exists in the fracturing layer section.
And secondly, analyzing the ground stress and the reservoir physical properties, including calculating and analyzing a ground stress profile, wherein the vertical stress is smaller than or close to the horizontal minimum main stress, a horizontal seam is formed by fracturing, the difference between the maximum stress and the minimum stress is smaller than 3MPa, and the reservoir physical properties are relatively good.
Finally, the shaft condition is analyzed, including no casing damage, and the well cementation quality is qualified.
2) Running fracturing string, installing well mouth, and testing pressure of ground pipeline
3) And (3) pump injection construction: pre-liquid stage
The fracturing of a pad fluid stage is realized by injecting fracturing fluid through a pump, and the pad fluid stage comprises opening and expanding of a main seam; opening and expanding the micro-seam; filling the micro-cracks; blocking and sealing; if the net pressure is greater than the difference between the maximum stress and the minimum stress, the branch seam is opened and expanded.
The specific process is as follows:
a. pumping medium-viscosity fracturing fluid with first displacement, and opening and expanding the main crack (because the medium-viscosity fracturing fluid is adopted, the viscosity is higher, the medium-viscosity fracturing fluid is not easy to enter a micro-crack in a near-wellbore zone, and the main crack can be ensured to extend to the deep part);
b. pumping the low-viscosity fracturing fluid with the first discharge capacity, opening and expanding the micro-cracks, and opening the micro-cracks (the low-viscosity fracturing fluid can easily enter the micro-cracks)
c. Then adding (namely carrying) propping agent with small particle size and low sand ratio into the low-viscosity fracturing fluid with the first displacement injected by the pump to fill the micro-cracks, reducing the fluid loss of the fracturing fluid, and then continuing the injection by the pump to expand the cracks;
d. when the formation of the crack is steadily increased, adding a propping agent with medium particle size and low sand ratio into low-viscosity fracturing fluid with first displacement injected by a pump, pushing a propping agent slug with medium particle size and low sand ratio to the deep part of the crack and even the end part area, achieving the effect of blocking the crack end (the crack end refers to a main crack end), and improving the net pressure in the crack; in order to make the pressure-holding effect of the fracture end plugging more obvious, 2-3 slugs (increasing the fracturing fluid amount among the slugs) are adopted for the fracture end plugging; of course, a slug may also be used, while ensuring the filling effect.
e. When the net pressure is larger than the stress difference, the net pressure is increased, the branch seams are opened (the branch seams are new seams which are forcibly opened due to the fact that the net pressure is too large, the stress difference is the difference value between the horizontal minimum main stress and the vertical stress, the net pressure is increased, the probability of forming the vertical seams is improved, and therefore the branch seams are vertical seams), and the pump is used for injecting the low-viscosity fracturing fluid with the second displacement to expand the branch seams.
In the pad fluid stage, the second displacement is larger than the first displacement, and the first displacement is determined according to the thickness of an oil layer, the well pattern and the well distance and the experience of a person in the field; the second displacement may also be determined based on reservoir thickness, and pattern hole spacing, and experience of one skilled in the art, or the displacement may be increased empirically.
Meanwhile, the net pressure is obtained by analyzing construction pressure data, the stress difference is obtained by calculating logging data (obtained by calculation during fracturing design), and then whether the branch joint is opened or not can be judged, and the discharge capacity during fracturing can be changed.
4) And (3) pump injection construction: sand-carrying fluid stage
In the stage, the branch seams and the main seams are mainly filled with saturated sand, so that the effective support of the complex net is improved, and efficient communication is achieved. The method is mainly realized by continuously pumping the fracturing fluid and adding the proppant into the fracturing fluid. For the propping agent, the propping agent matched with the size of the crack is selected, so that better propping can be realized.
Therefore, after the branch seams are expanded, the branch seams are formed, the branch seams are filled by adding a propping agent with a medium particle size and a small particle size which are mixed in an equal ratio and a medium sand ratio into the medium-viscosity fracturing fluid with the second discharge capacity through a pump (because the micro-seams are continuously opened on the branch seams when the branch seams are expanded, the propping agent with the medium particle size and the small particle size which are mixed in the equal ratio is adopted when the branch seams are filled, the medium-particle-size propping agent is used for filling the branch seams, and the small-particle-size propping agent is used for filling new micro-seams, so that the branch seams can be fully filled, high-efficiency communication is achieved, and effective reconstruction volume is improved), and then the main seams are filled by adding a propping agent with a large particle size and a high sand ratio into the medium-viscosity fracturing fluid with the second discharge capacity through a pump.
In the steps 3) and 4), the viscosity of the low-viscosity fracturing fluid is 24-27mPa.s, and the low-viscosity fracturing fluid comprises the following components in percentage by weight: 0.2% of thickening agent, 0.1% of cleanup additive, 1% of clay stabilizer, 0.2% of low-temperature gel breaking activator, 0.12% of cross-linking agent, 0.01-0.1% of gel breaker and the balance of water; the viscosity of the medium-viscosity fracturing fluid is 48-51mPa.s, and the medium-viscosity fracturing fluid comprises the following components in percentage by weight: 0.3% of thickening agent, 0.1% of cleanup additive, 1% of clay stabilizer, 0.2% of low-temperature gel breaking activator, 0.16% of cross-linking agent, 0.01-0.1% of gel breaker and the balance of water. Wherein the thickening agent is acrylamide and acrylic acid polymer, and the molecular weight of the thickening agent is about 50 ten thousand; the cross-linking agent is sodium dodecyl benzene sulfonate; the clay stabilizer is one or two of potassium chloride and polyquaternary amine; the cleanup additive is a cleanup additive for fracturing of a fluorocarbon surfactant; the low-temperature gel breaking activating agent is one or two of sodium sulfite and dodecyl diethylamine; the gel breaker is ammonium persulfate;
small particle size proppant: the density was 1.60g/cm 3 Quartz sand for fracturing, which has a particle size of 70 to 140 meshes (212 to 106 μm); medium particle size proppant: the density is 1.60g/cm 3 Quartz sand for fracturing, having a particle size of 40 to 70 mesh (425 to 212 μm); large particle size proppant: the density was 1.60g/cm 3 Quartz sand for fracturing, having a particle size of 20 to 40 mesh (850 to 425 μm);
the low sand ratio is 6-10%, the medium sand ratio is 10-20%, and the high sand ratio is 20-40%, wherein 10% and 20% are critical sand ratios, generally, the critical sand ratio can be any one range, and during actual construction, the critical sand ratio is not clear, that is, the 10% sand ratio can be low sand ratio, or medium sand ratio, and the 20% sand ratio can be medium sand ratio, or high sand ratio.
Because the low sand ratio, the medium sand ratio and the high sand ratio are all in a range, in order to improve the filling effect, the filling mode is a mode of gradually increasing the sand ratio when filling the branch seams, and the filling mode is a mode of gradually increasing the sand ratio when filling the main seams, and certainly, the fixed sand ratio can be adopted for filling, and the invention is not limited.
5) And (3) pump injection construction: and in the displacement stage, injecting the original glue solution through a pump to finish the displacement stage.
And after the complex fracture network fracturing is finished, closing the well and reacting for 4 hours, controlling open flow, and pumping down and pumping for production.
The method of the present invention for fracturing a new well will be described in detail below with reference to a certain oil field as an example.
The oil field belongs to a shallow low-temperature low-pressure tight sandstone oil reservoir, the reservoir has multiple thicknesses, is thin and poor in grade, the artificial fracture form formed by fracturing is mainly horizontal fracture, the longitudinal exploitation degree of the reservoir is low, the reserve capacity and the mobility rate are only 14%, and the development potential is large. The buried depth of certain oil Tian Chuceng is 300-650 m, the average buried depth is 550m, the main oil reservoir is a long 3 reservoir, 3 developed oil reservoirs are provided, the average porosity is 12.2%, the average permeability is 0.76mD, and the reservoir is a low-pore ultralow-permeability reservoir; the formation pressure coefficient is 0.65, and the low-pressure oil reservoir is formed; the ground temperature gradient is 3.53-4.51 ℃/100m, and the formation temperature is about 30 ℃; the oil saturation is low, and the average is about 38 percent.
Wherein, the fracturing operation is carried out on one directional well in the long 3 reservoir of the oil field, the maximum well deviation of the well is 57.7 degrees, the fracturing interval is 717 to 720m, the vertical depth is 537.2 to 540.1m, the average porosity of a target layer is 4.26 percent, the permeability is 0.14mD, the oil saturation is 34.5 percent, and the temperature is 32 ℃.
Through the calculation of the ground stress profile, the average vertical stress of a target layer is 14.4MPa, the minimum horizontal main stress is 15.9MPa, the maximum horizontal main stress is 18MPa, and a horizontal seam is formed by fracturing, wherein the fracturing is carried out by adopting the method disclosed by the invention, and the method comprises the following steps:
1) D, setting an oil pipe (a fracturing pipe column) with the diameter of 88.9mm, a bell mouth and 10m from the upper part of an oil layer (a well mouth is installed), and carrying out pressure test on a ground pipeline;
2) And (3) pump injection construction: the method comprises a pad fluid stage, a sand carrying fluid stage and a displacement stage, and is specifically characterized in that the fracturing construction pumping procedure is shown in the table I.
3) And (5) closing the well, reacting for 4 hours, open-blowing, and performing pump production according to geological requirements.
Pumping program for surface fracturing construction
After the well is constructed according to the design, the oil production per day is 2.2t and the water content is 64 percent in the initial stage after the well is pressed, the oil production per day is 1.7t and the water content is 58 percent at present, the oil production per day is 2.5 months after the oil production per year 3 in 2020, and the oil production per phase is 132.7t, and the effect is continued.
On the basis of forming horizontal seams, the invention strives to form vertical seams or T-shaped complex seams, increases the complexity of the whole fracture, effectively supports the formed complex fracture, improves the fracture flow conductivity, improves the planar utilization degree of a reservoir stratum and improves the yield.
The fracturing method of the shallow tight reservoir horizontal seam comprises the following steps:
the fracturing method of the embodiment has the same main concept as that of the first embodiment, and is different from the first embodiment in that the fracturing method of the embodiment is used for performing repeated fracturing on an old well, namely performing fracturing reformation on a multi-layer reservoir. And fracturing each layer comprises a pad fluid stage, a sand carrying fluid stage and a displacement stage, after fracturing each layer is completed, plugging the fractured reservoir and then fracturing other reservoirs.
Specifically, the fracturing method of the shallow tight oil reservoir horizontal seam comprises the following steps:
1) Selecting a fracturing interval section;
2) A fracturing pipe column is put in, a well mouth is installed, and a ground pipeline is subjected to pressure test;
3) And (3) fracturing pump grouting construction of the first layer of seam net: a pre-liquid stage;
4) And (3) fracturing pump injection construction of the first layer of seam net: carrying a sand carrying liquid;
5) And (3) fracturing pump injection construction of the first layer of seam net: a displacement stage, namely injecting the primary glue solution through a pump to finish the displacement stage;
the fracturing process of the first layer of seam network in the steps 1) to 5) is the same as that in the first embodiment, and is not described herein again. The fracturing construction of the first layer of slotted net is not directed to one layer of slotted net, but to a plurality of layers of slotted nets with good physical properties (the permeability corresponding to good physical properties is large) and small permeability difference, the first layer of slotted net is generally fractured simultaneously when fractured.
6) Plugging perforation holes of the first layer of seam net;
stopping the pump, and throwing a shot hole for temporarily blocking the ball from the high-pressure pipeline by using a ball injector; and then starting a pump, and conveying the low-viscosity fracturing fluid to the blasthole for temporarily plugging the ball to realize plugging of the perforation hole with the pressed crack. When plugging is carried out, the selection of temporary plugging balls of the blastholes is very important, the diameter and the number of the temporary plugging balls of the blastholes need to be designed, the diameter of the temporary plugging balls of the blastholes is at least 2-3 mm larger than that of the perforation holes generally, and the number of the temporary plugging balls of the blastholes is 1.2-1.25 times of the number of the perforation holes.
In general, the temporary plugging ball of the blast hole is one of plastic balls or water-soluble composite material balls, the diameter of the temporary plugging ball is 18-20 mm, and the density of the temporary plugging ball is 1.3-1.4 g/cm 3 And the compressive strength is not less than 20MPa.
7) And (3) fracturing pump injection construction of the second layer of seam net: a pre-liquid stage;
the difference between the pad fluid stage in this step and the pad fluid stage in step 3) is that, because the first layer with bedding seams and natural cracks is opened first, compared with the first layer, the second layer has no bedding seams and natural cracks do not develop, the steps of opening and expanding main seams and micro seams and filling the micro seams are not needed in step 3), the step of plugging the seam ends is directly carried out, and the fracturing processes of the rest pad fluid stages are the same as that in step 3), and are not repeated here.
8) And (3) fracturing pump injection construction of the second layer of seam net: carrying a sand carrying liquid;
9) And (3) fracturing pump injection construction of the second layer of seam net: a displacement stage, namely injecting the primary glue solution through a pump to finish the displacement stage;
steps 8) to 9) are the same as steps 4) to 5), and are not described herein.
Similarly, the fracturing of the second layer of seam net is not only for one layer of seam net, but also for a plurality of layers of seam nets with poor physical properties (the permeability corresponding to the poor physical properties is lower) and small permeability difference.
10 Plugging perforation holes of the second layer of slotted net;
the number of the temporary plugging balls of the blastholes in the step is calculated according to the number of the perforation holes of the fractured first layer and the fractured second layer, and the rest is the same as that in the step 6), and the detailed description is omitted.
11 Fracturing pump injection construction of the third layer of seam net;
the step is the same as the step 7) to the step 9), and the description is omitted; the third layer of seamed net refers to an interval which is not fractured by pressure when the second layer of seamed net is fractured, and the fracturing of the third layer of seamed net can be carried out if necessary.
And (5) closing the well for reaction for 4 hours until fracturing is finished, controlling open flow, and pumping down to produce.
The following describes a multilayer fracturing method for an old well, taking a certain oil field as an example.
The repeated fracturing of one directional well of a long 3 reservoirs of a certain oil field, the well deviation is 41.74 degrees, 8 perforation intervals are provided, the interval 1: 463.5-465 m, 11% porosity, 0.43mD permeability and 35% oil saturation; layer section 2: 471.5-473 m, 12% porosity, 0.46mD permeability and 37.1% oil saturation; layer section 3: 495-497 m, 12 percent of porosity, 0.53mD of permeability and 39.5 percent of oil saturation; layer section 4: 501-507 m, the porosity is 17.8%, the permeability is 1.53mD, and the oil saturation is 39.8%; layer segment 5:510.5 to 512.5m, 11 percent of porosity, 0.48mD of permeability and 37.8 percent of oil saturation; layer section 6: 514-516.5 m, the porosity is 15.5%, the permeability is 1.37mD, and the oil saturation is 35.3%; interval 7:524.5 to 526.5m, 14.3 percent of porosity, 1.23mD of permeability and 39 percent of oil saturation; interval 8: 528.5-530.5 m, 11.1% porosity, 0.33mD permeability and 35% oil saturation; the temperature of a target layer is 34.5 ℃, the viscosity of the crude oil in a stratum is 6.64mPa & s, the crude oil belongs to light crude oil, the total mineralization is 33447.89mg/L, the chlorine content is 18540.8mg/L, and the water type is CaCl 2 。
According to the results of the explanation of the ground stress, interval 1: 436.5-465 m, vertical depth 408.28-409.42 m, vertical stress 10.4MPa, horizontal minimum main stress 10.53MPa and horizontal maximum main stress 11.98MPa; layer section 2: 471.5-473 m, vertical depth 414.36-415.5 m, vertical stress 10.6MPa, horizontal minimum main stress 10.73MPa and horizontal maximum main stress 12.18MPa; layer section 3: 495-497 m, vertical depth 432.22-433.74 m, vertical stress 11MPa, horizontal minimum principal stress 11.05MPa, and horizontal maximum principal stress 12.58MPa; layer section 4: 501-507 m, vertical depth 436.78-441.34 m, vertical stress 11.17MPa, horizontal minimum main stress 11.24MPa, and horizontal maximum main stress 12.78MPa; layer section 5:510.5 to 512.5m, 444 to 445.52m vertical stress, 11.3MPa vertical stress, 11.37MPa horizontal minimum main stress and 12.95MPa horizontal maximum main stress; layer section 6: 514-516.5 m, vertical depth 446.66-448.56 m, vertical stress 11.4MPa, horizontal minimum main stress 11.58MPa and horizontal maximum main stress 13.15MPa; layer section 7:524.5 to 526.5m, the vertical depth 454.64 to 465.16m, the vertical stress is 11.6MPa, the horizontal minimum main stress is 11.59MPa, and the horizontal maximum main stress is 13.19MPa; layer section 8: 528.5-530.5 m, vertical depth 457.68-459.2 m, vertical stress: 11.68MPa, horizontal minimum principal stress: 11.64MPa, horizontal maximum principal stress: 13.24MPa. The vertical stress is less than or equal to the minimum horizontal main stress, and the horizontal seam is formed by fracturing.
The fracturing operation initial stage has certain productivity, the production condition is better, and the water injection quantity of the corresponding water injection well is high; because the horizontal layer reason seam is developed in the used layer section, when the primary transformation is carried out, the fracturing fluid easily enters the horizontal layer reason seam section, the fracturing yield-increasing effect is influenced, and meanwhile, the comprehensive analysis considers that the artificial fracturing form of the well is a horizontal seam, and the longitudinal oil layer use degree is low. Thus increasing the extent of longitudinal and planar reserve utilization by performing multiple stages of repeated fracturing while avoiding horizontal bedding seams. Analyzing the primary fracturing used of the interval 1 and the interval 2 of the well (the primary fracturing is performed by adopting a packer for layered fracturing), wherein the primary fracturing dynamic degree of the intervals 3 to 8 is low, comprehensively analyzing the fractured well fracture form and distribution condition according to the well logging interpretation result and the reservoir characteristics, judging that the fracturing possibility of 3 layers of the perforated intervals 4, 6 and 7 is high (the 3 layers have good physical properties and small permeability difference) during the primary fracturing construction of the well, and the fracturing possibility of 3 layers of the rest perforated intervals 3, 5 and 8 is low (the 3 layers have poor physical properties and the small permeability difference). Therefore, the horizontal seam multi-fracture fracturing process for the shallow tight reservoir carries out the layered fracturing on the intervals 3-8, firstly, the intervals 4, 6 and 7 are repeatedly fractured, then, phi 20mm plastic blastholes are thrown to temporarily plug the blastholes and then the intervals 3, 5 and 8 are pressed open, and the process comprises the following steps:
1) The lower packer seals two fractured well sections of the upper interval 1 and the interval 2;
2) Firstly, according to a fracturing construction pumping procedure I (corresponding to the fracturing of a first layer fracture net in the method, as shown in a table II), repeating 3 fracturing layer sections 4, 6 and 7;
3) Stopping the pump, and feeding 200 blasthole temporary plugging balls for temporarily plugging the layer sections 4, 6 and 7; 5m for pumping 3 Conveying the low-viscosity fracturing fluid into a blast hole for temporarily plugging a ball to realize plugging of a perforation hole;
4) A fracturing construction pumping-injection program II (corresponding to the second layer of seam network fracturing in the method as shown in the third table) is performed, the fracturing layer sections 3, 5 and 8 are subjected to pumping stop and pressure measurement for 30min after the displacement is finished;
5) And (5) closing the well, reacting for 4 hours, open-blowing, and performing pump production according to geological requirements.
Pumping procedure for secondary fracturing construction
Pumping and injecting program II for top-three fracturing construction
2.8t of initial daily oil production after fracturing is 7 times of the daily oil production before the measures, 1.8 times of the conventional fracturing, 1.9t of current daily oil production and 16.5 percent of water, and the oil production is continued to be effective after 12 months of normal production until 3 months in 2020, 560.7t of stage oil production and 416.7t of oil increment.
The fracturing method of the shallow tight reservoir horizontal seam comprises the following steps:
the fracturing method of the embodiment has the same main concept as that of the first embodiment, and is different in that when the branch cracks are filled, the medium-viscosity fracturing fluid with the second displacement is added with the proppant with medium particle size and medium sand ratio, and newly generated micro cracks are ignored in the situation, but the effect of filling the branch cracks can also be achieved.
The rest of the fracturing method is the same as the first embodiment, and is not described herein.
The fracturing method of the shallow tight reservoir horizontal seam comprises the following four steps:
the fracturing method of the embodiment has the same main concept as that of the second embodiment, and is directed to fracturing of a multi-layer slotted net, except that the step of opening, expanding main slots, micro slots and filling the micro slots is not performed in the step 7) of the second embodiment, and the step of not opening, expanding the main slots, the micro slots and filling the micro slots is obtained through empirical judgment.
The fracturing process of each layer of seam net is the same as the steps 3) to 5), and the description is omitted here.
Claims (8)
1. A fracturing method for horizontal fractures of a shallow tight oil reservoir is characterized by comprising the following steps:
1) Opening and expanding the main seam of the horizontal seam;
2) Opening and expanding the micro-seam;
3) Filling micro-cracks;
4) Plugging the main seam end;
5) When the net pressure is larger than the stress difference, opening and expanding the branch seams, wherein the stress difference is the difference value between the horizontal minimum main stress and the vertical stress, and the branch seams are vertical seams;
6) Filling branch seams;
7) Filling the main seam;
8) Performing displacement operation to complete fracturing of the horizontal seam;
injecting fracturing fluid in a first displacement in the steps 1) to 4); in the steps 5) to 8), injecting fracturing fluid at a second displacement, wherein the second displacement is larger than the first displacement;
in the step 4), low-viscosity fracturing fluid of 24-27mPa.s and 3.5m are adopted 3 The medicine has a volume of 2-3 pieces per minute and a density of 1.60g/cm 3 And the medium-grain-size quartz sand proppant slug has a grain size of 40-70 meshes.
2. The fracturing method of the shallow tight oil reservoir horizontal seam according to claim 1, characterized in that the fracturing fluid injected in step 1), step 6) and step 7) is a medium viscosity fracturing fluid; the fracturing fluid injected in the steps 2) -5) is low-viscosity fracturing fluid; the fracturing fluid injected in the step 8) is a virgin cement solution; the viscosity of the medium viscosity fracturing fluid is greater than that of the low viscosity fracturing fluid.
3. The fracturing method of the horizontal joints of the shallow tight oil reservoir according to claim 1, wherein in the step 3), the micro-joints are filled with proppant with small particle size and low sand ratio to reduce the fluid loss of the fracturing fluid, and the low sand ratio is 6-10%.
4. The fracturing method of the horizontal joints of the shallow tight oil reservoir according to claim 1, wherein in the step 4), the joints are plugged by using a medium-particle-size and low-sand-ratio proppant so as to improve the net pressure; the low sand ratio is 6-10%.
5. The fracturing method of the horizontal seam of the shallow tight oil reservoir as claimed in claim 1, wherein the step 6) is to fill the branch seams with proppant with medium grain size and small grain size which are mixed in equal ratio and medium sand ratio, wherein the medium sand ratio is 10-20%.
6. The fracturing method of the shallow tight reservoir horizontal joints according to claim 1, wherein in the step 7), the main joints are filled with proppant with large grain size and high sand ratio; the high sand ratio is 20-40%.
7. The fracturing method of the horizontal seam of the shallow tight reservoir as claimed in claim 5, wherein the filling mode is a mode of increasing the sand ratio step by step when filling the branch seam.
8. The fracturing method of the horizontal joints of the shallow tight reservoir as claimed in claim 6, wherein the filling mode is a mode of gradually increasing the sand ratio when filling the main joints.
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