CN113356822A - Fracturing method - Google Patents
Fracturing method Download PDFInfo
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- CN113356822A CN113356822A CN202010153056.6A CN202010153056A CN113356822A CN 113356822 A CN113356822 A CN 113356822A CN 202010153056 A CN202010153056 A CN 202010153056A CN 113356822 A CN113356822 A CN 113356822A
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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
- E21B43/11—Perforators; Permeators
Abstract
The invention provides a fracturing method for a horizontal well, which comprises the following steps of perforating a horizontal section of the horizontal well; improving the stress gradient of a near well zone, and opening micro cracks in the stratum; and step three, performing hydraulic fracturing operation to generate a main crack, wherein before the fracturing operation, the fracturing method firstly performs operation of improving the stratum so as to form a new stress field near a near well zone and open micro cracks, so that a reservoir which is not suitable for volume fracturing originally can achieve the transformation effect of the volume fracturing, and has good practicability and popularization value.
Description
Technical Field
The invention relates to the field of oil and gas field development engineering, in particular to a fracturing method for a horizontal well.
Background
The volume fracturing refers to that in the hydraulic fracturing process, natural fractures are continuously expanded and brittle rocks generate shearing slippage to form a fracture network in which the natural fractures and artificial fractures are staggered, so that the modification volume is increased, and the initial yield and the final recovery rate are improved.
Volume fracturing techniques are typically used in horizontal wells in order to achieve large scale reservoir reconstruction. For example, in a patent "compact oil-water horizontal well three-dimensional fracture network clustering fracturing optimization method (CN 201811146295.8)" applied by zhuyiyao (2018), a fracture network optimization evaluation method based on seepage flow energy is provided, so that a fracturing form is optimized. In a patent of 'an atmospheric shale gas sieve tube well completion hydraulic jet volume fracturing method (CN 201710350835.1)' applied in Jiangting science (2017), the atmospheric shale gas sieve tube well completion hydraulic jet volume fracturing method is formed through construction procedures of pre-pressing evaluation, sand blasting perforation, low-viscosity slickwater crack formation, high-viscose liquid sand carrying and the like. In the patent of 'temporary plugging volume fracturing technology (CN201810120615.6) applying closely cutting high sand content temporary plugging' (2018), a temporary plugging agent is used for plugging dominant cracks in the fracturing process, so that liquid enters cracks which are not fully expanded in the early stage, and the volume fracturing effect is improved.
However, successful construction of volume fracturing has extremely severe requirements on reservoir conditions, such as strong brittleness, natural fracture development, small ground stress difference and the like, and most reservoir layers are difficult to reach the construction standard of volume fracturing. The research in the prior art is to improve and optimize the prior art and improve the volume fracturing effect, and the structural stress field is not involved to improve the applicability of the volume fracturing under different reservoir conditions. Therefore, a new fracturing method needs to be invented to improve the adaptability of volume fracturing in different reservoirs and further promote the application of the volume fracturing technology.
Disclosure of Invention
Aiming at part or all of the technical problems in the prior art, the invention provides a fracturing method for a horizontal well. The fracturing method is characterized in that before fracturing operation, operation for improving stratum is carried out to form a new stress field near a near well zone and open micro cracks, so that a reservoir which is not suitable for volume fracturing originally can achieve the transformation effect of volume fracturing, and the method has good practicability and popularization value.
According to the invention, a fracturing method for a horizontal well is provided, which comprises the following steps:
step one, perforating at the horizontal section of the horizontal well,
step two, improving the stress gradient of the near-wellbore zone, opening micro-cracks in the stratum,
and step three, performing hydraulic fracturing operation to generate main cracks.
In one embodiment, in step two, the working fluid is injected into the formation at an injection pressure lower than the fracture pressure by low displacement to perform a hydraulic expansion operation to open the micro fractures without creating primary fractures.
In one embodiment, step two includes:
a first sub-step of injecting a first amount of working fluid at a first injection pressure,
a second step of increasing the injection pressure in turn until it is equal to the extension pressure, the injection displacement being actively increased with the increase in the injection pressure,
and the third step, increasing the injection pressure in turn until the rupture sign appears, and determining the maximum injection displacement,
and fourthly, injecting at the maximum injection displacement until reaching the expansion limit.
In one embodiment, the first injection pressure is P in the first substepi，PiFrom Pi＝r*PeCalculating, wherein r ═ Pe/Pf，PfBurst pressure, PeIn order to extend the pressure, the pressure is,
or/and in the first step, the first amount of the injected working fluid is 15-60 m3。
In one embodiment, in the third substep, the injection pressure is increased in steps of equal magnitude, with each increase being of equal magnitude from one fifth to one tenth of the difference between extension pressure and burst pressure, and the duration of the interval between adjacent step injections is gradually increased.
In one embodiment, in the third step, as the injection pressure increases, when the injection pressure decreases by at least an equal amount, it may be judged that the rupture sign appears.
In one embodiment, the maximum injection displacement is set to the injection pressure of the first step above the injection pressure corresponding to the occurrence of the sign of rupture in the third step.
In one embodiment, in the fourth step, during the maximum displacement injection, the injection pressure is gradually decreased, the change of the injection pressure is recorded, one node is recorded every time the injection pressure is decreased by a certain percentage, when the time interval of the node is gradually decreased, the node is in the expansion validity period, and when the time interval of the node is gradually increased, the node can be judged to reach the expansion limit.
In one embodiment, the difference in the corresponding percentages between the nodes is different according to the formation, and the difference in the corresponding percentages between the nodes is smaller when the formation is denser.
In one embodiment, the working fluid may be clear water or slick water diluted 8-12 times with clear water.
Compared with the prior art, the fracturing method has the advantages that the stratum is improved before fracturing operation, so that a new stress field is formed in a near well zone, and the microcracks are opened, so that the method has the capability of generating a plurality of branch cracks in the extension process of the main cracks during the fracturing operation, and further, a reservoir which is not suitable for volume fracturing originally can achieve the transformation effect of volume fracturing, and the effect of volume fracturing is achieved. Meanwhile, the fracturing method can effectively improve the number of cracks and the oil drainage area during fracturing, and further improve the transformation degree of a reservoir stratum. In addition, the influence of physical properties of partial reservoirs is reduced through stratum improvement, such as large ground stress difference, insufficient natural fractures and the like, and the application range of the volume fracturing technology is expanded.
Drawings
Preferred embodiments of the present invention will be described in detail below with reference to the attached drawing figures, wherein:
FIG. 1 shows a process flow diagram of a fracturing method according to an embodiment of the invention;
FIG. 2a shows the original stress field around a perforation of a near zone in accordance with an embodiment of the present invention;
FIG. 2b illustrates an expanded geostress field around a near-wellbore strip perforation according to one embodiment of the invention;
FIG. 3 shows a schematic representation of a formation after a perforating operation according to an embodiment of the present invention;
FIG. 4 illustrates a formation schematic diagram of a hydraulically expanded formation stress field according to one embodiment of the present disclosure;
FIG. 5 shows a schematic illustration of a formation with hydraulically expanded formation microfractures according to one embodiment of the invention;
FIG. 6 shows a schematic of a formation producing a primary fracture according to one embodiment of the invention.
In the drawings, like parts are provided with like reference numerals. The figures are not drawn to scale.
Detailed Description
The invention will be further explained with reference to the drawings.
Figure 1 shows a process flow diagram of a fracturing method according to the invention. The fracturing method is used for a horizontal well. Specifically, as step one of S1, a perforating operation is first performed in the horizontal wellbore section 1 to form perforations 3 extending into the formation 2 in the horizontal wellbore section 1, as shown in fig. 3. Step two of S2, then, a formation improvement operation is performed to create a new stress field in the near zone in the formation 2 (as shown in fig. 2a, 2b and 4) and to open the microfractures 4 (as shown in fig. 5). In step three of S3, finally, a hydraulic fracturing operation is performed based on step two to form the primary fracture 5, as shown in fig. 6.
The fracturing method is characterized in that before hydraulic fracturing operation, stratum improvement operation is firstly carried out, a new stress field is formed in a near well zone, and existing micro fractures are opened, so that the fracturing method has the capability of generating a plurality of branch fractures in the extending process of a main fracture in subsequent fracturing operation, and the effect of volume fracturing is achieved. Furthermore, the fracturing method enables the reservoir which is not suitable for volume fracturing originally to achieve the transformation effect of the volume fracturing, and improves the effect of the volume fracturing. In addition, the fracturing method can effectively improve the number of cracks and the oil drainage area during fracturing, thereby improving the transformation degree of a reservoir stratum. In addition, the influence of physical properties of partial reservoirs is reduced through stratum improvement, such as large ground stress difference, insufficient natural fractures and the like, and the application range of the volume fracturing technology is expanded.
According to the invention, after perforation operation and before fracturing, only working fluid needs to be injected into a target well to carry out hydraulic expansion transformation. During hydraulic expansion, the working fluid is injected into the stratum in a manner of following low discharge and being lower than fracture pressure. At the initial stage of expansion, the liquid of the working fluid enters the formation gap along the perforation holes and starts to form support. Along with the increase of the injection quantity, the expansion range is gradually increased, meanwhile, the pore pressure of the stratum is gradually increased, the rock framework is displaced, the effective stress of the rock body is changed, and then a new stress field is formed. With the further increase of the injection amount, the rock mass in the expansion range has self-defects or reaches the stretching limit, and the micro-cracks with tensile property or shearing property are gradually generated. Therefore, the hydraulic expansion achieves the aim of improving the stratum.
More specifically, first, at the time of the preliminary injection, the injection pressure is limited to the first injection pressure and a certain amount is injected. Wherein the first injection pressure may be PiAnd is formed by Pi＝r*PeCalculating, wherein r ═ Pe/Pf，PfBurst pressure, PeIs the extension pressure. The injection amount may be preferably 15 to 60m3E.g. 40m3. Due to PeLess than PfThen the injection pressure does not reach the extension pressure at this point, but is less close to the burst pressure. This operation causes the working fluid to enter the formation void along the perforations and initiate the formation of proppants。
It should be noted that P in the formulafAnd PeReference can be made to the value of the pressure P of the fracture of the same layer of the adjacent well, if anyfExtension pressure PeThe data can be used directly. However, absent this data, a small fracture of the well of interest in the field is required to obtain parameter PfAnd Pe. For example, 10 to 30m is used3Performing small-scale fracturing on the liquid, wherein the fracturing depth is not less than 1m3Injecting at a displacement of/min, increasing the displacement further if the formation has not fractured, until the formation fractures, at which point the fracture pressure P is recordedf. Then, the injection is continued while maintaining the displacement at rupture, and the extension pressure P is recordede。
Then, the injection pressure is sequentially increased until it is equal to the extension pressure. For example, the injection pressure is increased stepwise and by an equal amount. For example, according to different construction conditions, 1-2MPa is added each time. During this process, the displacement naturally increases as the injection pressure increases.
Then, when the injection pressure is increased to the extension pressure, the difference between the extension pressure and the burst pressure is uniformly divided into 5 to 10 steps, and the injection pressure is increased by one step at intervals (for example, 1 hour). In this process, the displacement increases with increasing pressure. As the injection pressure approaches the burst pressure gradually, the time between increasing steps increases, for example, by increasing the injection pressure one step every 2 hours instead. Until the injection pressure at a step shows signs of rupture (i.e. a significant drop in pressure, e.g. the value of the pressure drop is not less than the value corresponding to a step). And reducing the injection pressure to the upper step value, and setting the corresponding injection displacement as the maximum injection displacement. The aforesaid improves injection pressure's injection mode in proper order, along with the increase of injection quantity, the dilatation scope progressively increases, and the pore pressure in stratum increases gradually simultaneously, and the rock skeleton takes place the displacement, and the effective stress of rock mass changes, and then has formed new stress field.
And finally, performing injection operation by adopting the maximum displacement until the expansion is finished. Specifically, under maximum displacement injection conditions, long term injection causes the micro-fractures to open. With the gradual reduction of the injection pressure, the change of the injection pressure is recorded, and when the injection pressure is reduced by x%, the change is recorded as a node (for example, x can take a value of 1-2, and if the stratum is denser, the value of x is reduced, for example, 0.1-0.5). When the time interval of the node is gradually reduced, the node can be determined to be in the expansion validity period. When the time interval of the node is gradually increased, the expansion limit is considered to be reached, the marginal benefit of the expansion is rapidly reduced, and the expansion can be finished at the moment.
Before the expansion operation, the stress field in the field is relatively uniform, as shown in fig. 2 a. And the stress in the field changes by the expansion operation, as shown in fig. 2b and 4, wherein the value of the stress field gradually decreases in the direction from the perforation 3 to the far end until the original ground stress field is restored. Especially, when the horizontal well has a plurality of perforation points, the stress fields constructed by the perforations are mutually communicated to form a continuous stress field with a larger range, and the effective action range of capacity expansion is improved.
Preferably, the injected working fluid can be clear water or slick water diluted by the clear water. For example, the slickwater may be diluted 8-12 times, preferably 10 times, with clear water.
In the fracturing method, before the fracturing operation, a fracturing truck can be assigned to a well site for capacity expansion operation. Due to factors such as low injection displacement of the capacity expansion operation, the requirement on equipment is low. And other fracturing equipment can gradually enter the field in the later stage of hydraulic expansion, and the other fracturing equipment and the fracturing construction form seamless butt joint as much as possible when the hydraulic expansion is finished. During fracturing construction, a main crack along the direction of the horizontal maximum main stress is generated firstly, and a new stress field formed by combining micro cracks formed during hydraulic expansion is beneficial to opening multi-directional complex cracks, and the complex cracks are further expanded to communicate a plurality of main cracks to form a reservoir stratum transformation effect of the complex multi-cracks similar to volume fracturing.
It should be noted that the fracturing method can be applied to both new wells and old wells, but hydraulic expansion can be directly performed on the new wells, and formation reinjection is performed on the developed old wells to recover formation energy.
The above is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily make changes or variations within the technical scope of the present invention disclosed, and such changes or variations should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. A fracturing method for a horizontal well, comprising:
step one, perforating at the horizontal section of the horizontal well,
step two, improving the stress gradient of the near-wellbore zone, opening micro-cracks in the stratum,
and step three, performing hydraulic fracturing operation to generate main cracks.
2. The method of fracturing of claim 1 wherein in step two, a hydraulic expansion operation is performed by injecting a working fluid into the formation at an injection pressure below the fracture pressure with low displacement to open the microfractures without creating primary fractures.
3. The fracturing method of claim 2, comprising in step two:
a first sub-step of injecting a first amount of working fluid at a first injection pressure,
a second step of increasing the injection pressure in turn until it is equal to the extension pressure, the injection displacement being actively increased with the increase in the injection pressure,
and the third step, increasing the injection pressure in turn until the rupture sign appears, and determining the maximum injection displacement,
and fourthly, injecting at the maximum injection displacement until reaching the expansion limit.
4. A fracturing method according to claim 3, wherein in the first fraction the first injection pressure is Pi，PiFrom Pi＝r*PeCalculating, wherein r ═ Pe/Pf，PfBurst pressure, PeIn order to extend the pressure, the pressure is,
or/and in the first step, the first amount of the injected working fluid is 15-60 m3。
5. The fracturing method according to claim 3 or 4, wherein in the third substep, the injection pressure is increased stepwise by the same amount, and each increase is by the same amount of one fifth to one tenth of the difference between the extension pressure and the burst pressure, and the time interval between adjacent stepwise injections is gradually increased.
6. The fracturing method according to claim 5, wherein in the third step, as the injection pressure increases, when the injection pressure decreases by at least an equal amount, it is judged that the fracture sign appears.
7. The fracturing method according to claim 6, wherein in the third step, the maximum injection displacement is set to the injection pressure of the first step above the injection pressure corresponding to the occurrence of the sign of fracture.
8. The fracturing method according to any one of claims 3 to 7, wherein in the fourth sub-step, during the maximum displacement injection, the injection pressure is gradually decreased, the change of the injection pressure is recorded, one node is recorded for each decrease of the injection pressure by a certain percentage, and when the time interval of the node is gradually decreased, the node is in the expansion validity period, and when the time interval of the node is gradually increased, the node is judged to reach the expansion limit.
9. The fracturing method of claim 8, wherein the difference in percentage between nodes is different according to the formation, and the difference in percentage between nodes is smaller for denser formations.
10. The fracturing method according to any one of claims 2 to 9, wherein the working fluid is clear water or slickwater diluted 8-12 times by clear water.
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| CN108121844A (en) * | 2016-11-30 | 2018-06-05 | 中国石油天然气股份有限公司 | Waterpower involves the preparation method of radius |
| CN110242266A (en) * | 2019-07-08 | 2019-09-17 | 新疆中凌工程技术有限公司 | A kind of horizontal well group of SAGD is temporarily stifled to be segmented dilatation reservoir reconstruction method |
| CN110439521A (en) * | 2019-08-05 | 2019-11-12 | 中国石油天然气股份有限公司 | A kind of advanced accumulation of energy fracturing process |
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2020
- 2020-03-06 CN CN202010153056.6A patent/CN113356822A/en active Pending
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20170284181A1 (en) * | 2014-08-26 | 2017-10-05 | Gas Technology Institute | Hydraulic fracturing system and method |
| CN104847315A (en) * | 2015-03-25 | 2015-08-19 | 大庆红祥寓科技有限公司 | Expansion composite perforating gun |
| CN105201468A (en) * | 2015-09-06 | 2015-12-30 | 中国石油天然气股份有限公司 | Method for assisting in communication of horizontal wells |
| CN108121844A (en) * | 2016-11-30 | 2018-06-05 | 中国石油天然气股份有限公司 | Waterpower involves the preparation method of radius |
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Application publication date: 20210907 |