CN109989737B - Method for realizing self-supporting fracture of rock - Google Patents
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- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK 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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Abstract
The invention discloses a method for realizing self-supporting cracks of rocks, which comprises the following steps: a fracture construction step, namely determining fracture acidizing construction parameter combinations aiming at different rock types, and performing fracture construction without adding a propping agent based on the fracture acidizing construction parameter combinations, wherein a low-friction high-viscosity fracturing fluid system is selected from fracturing fluids in the fracture acidizing construction parameter combinations, and the viscosity of the fracturing fluid and another injected fluid meet the viscous finger-feed effect in the inter-pumping process of the high-viscosity ratio fluid in mixed injection construction; and (3) a tunnel construction step, namely spraying a plurality of non-uniform tunnels on the formed cracks by utilizing a deep penetration hydraulic spraying technology to realize the rock self-supporting effect of the cracks. The method can enlarge the effective crack length of the main crack, and improve the long-term effective flow conductivity of the reservoir crack under high-depth high-closure stress, so as to increase the effective period of deep measures and further improve the economic development benefit.
Description
Technical Field
The invention relates to the technical field of oil and gas well production increase, in particular to a method for realizing self-supporting fracture of rock.
Background
At present, fracturing and acidizing operations of deep sandstone, carbonate rock, shale and the like are more and more, and the reserves of the deep layer are quite huge, so that the method has great development prospects. However, in the deep measure reconstruction, how to improve the fracture conductivity under high closure stress to the maximum extent is the focus and the focus of the design. No matter which lithology is adopted, no matter the hydraulic support fracture conductivity or the acid-etched fracture conductivity is adopted, the fracture conductivity is rapidly decreased as long as the effective closure stress exceeds 40MPa, so that the yield and the effective period after fracture acidizing are also rapidly decreased, and further the economic and effective development value is lost.
In terms of technology, the current deep fracturing acidizing design and construction generally has the following limitations:
1) fracture geometry is limited. Because of the problems of high stress, high frictional resistance and the like caused by the well depth, the discharge capacity of deep fracture acidizing is generally low, and the leakage is relatively large due to the development of a fracture hole of some carbonate rocks, so that the discharge capacity for making the fracture is quite low, and the extension degree of the fracture is limited.
2) The flow conductivity of the crack is low and the decrease is fast. Due to the high closure stress problem caused by the well depth, the fracture conductivity is decreased quickly.
3) The effective fracture length is short. Due to the fact that the geometric size of the fracture is limited, the concentration of the fracturing fluid is reduced due to the addition of the propping agent, and high temperature caused by well depth is combined, so that the fracturing fluid has high degradation speed (sand blocking is easy to occur, the sand adding amount is low), and acid rock is made to have high reaction speed (the length of the fracture joint corroded by acid liquor).
Disclosure of Invention
In order to solve the technical problem, the invention provides a method for realizing self-supporting rock fracture, which comprises the following steps: a fracture forming construction step, namely determining fracture acidizing construction parameter combinations aiming at different rock types, and performing fracture forming without adding a propping agent on the basis of the fracture acidizing construction parameter combinations, wherein a low-friction high-viscosity fracturing fluid system is selected from fracturing fluids in the fracture acidizing construction parameter combinations, and the viscosity of the fracturing fluid and another injected fluid meet the viscous finger-feeding effect in the process of pumping and injecting the fluids with high viscosity ratio in mixed injection construction; and (3) a tunnel construction step, namely spraying a plurality of non-uniform tunnels on the formed cracks by utilizing a deep penetration hydraulic spraying technology to realize the rock self-supporting effect of the cracks.
Preferably, the step of seam construction further comprises the steps of obtaining reservoir characteristic parameters influencing seam construction; selecting a perforation position parameter and an optimized fracture parameter based on the reservoir characteristic parameters; and obtaining fracture acidizing construction parameter combinations aiming at different rock types according to the optimized fracture parameters, wherein the fracture acidizing construction parameter combinations comprise different fracturing fluid and acid liquid parameters and fracture acidizing construction parameters.
Preferably, in the step of crack-making construction, further, aiming at sandstone or shale strata, a carboxymethyl hydroxypropyl fracturing fluid system with low friction resistance and high viscosity is adopted for injection construction; and performing mixed injection construction aiming at the carbonate stratum, and injecting a high-viscosity carboxymethyl hydroxypropyl guar gum fracturing fluid system and a low-viscosity acid solution system in sequence, wherein the viscosity ratio of the two systems meets the viscous fingering effect.
Preferably, the pit constructing step further comprises the steps of spraying the pit on the formed crack by using a water conservancy spraying tool string with a hose device and adopting a variable-displacement pulse spraying method, and withdrawing the hose device; and turning the hose device, and continuously spraying by using the device to form a plurality of spraying tunnels.
Preferably, in the gallery building step, the injection speed for the injection gallery is at least as high as 190 m/s.
Preferably, in the step of seam construction, a perforation position parameter is preliminarily selected based on the reservoir characteristic parameter; and simulating the crack propagation condition of the preliminarily selected perforation position by using crack propagation simulation software, and screening out the optimal perforation position.
Preferably, in the step of seam making construction, aiming at sandstone and carbonate reservoirs, establishing a geological model of an oil and gas reservoir based on the reservoir characteristic parameters, and further simulating a fracture by using a method of setting equivalent conductivity; and setting different fracture parameter types and level values including fracture length, flow conductivity and fracture spacing by applying an orthogonal calculation method, and optimizing an optimal fracture parameter system.
Preferably, in the step of fracture construction, based on the optimized fracture parameter system, the fracture propagation simulation software is applied to determine the fracture acidizing construction parameter combination, and the fracture acidizing construction parameter combination further includes viscosity, volume and injection displacement of fracturing fluid and acid fluid.
Preferably, in the step of constructing the seam, further, the viscosity ratio of the low-friction high-viscosity fracturing fluid system to the acid fluid system is at least 6: 1.
preferably, the method also comprises a flowback operation step, when the pressure of the well head is 2-3MPa away from the closing pressure of the formed cracks, the flowback speed is slowed down, so that the wall surface of the rock without the tunnel is gradually closed; and (3) closed acid treatment, namely performing secondary acid injection operation after the rock on the wall surface of the crack is completely supported and attached, wherein the pressure of a well mouth in the operation is kept to be 1-2MPa lower than the closed pressure of the crack.
Compared with the prior art, one or more embodiments in the above scheme can have the following advantages or beneficial effects:
the invention provides a novel technology capable of improving the flow conductivity of deep cracks based on the limitations and existing problems of the conventional acid fracturing technology, and the technology can improve the long-term effective flow conductivity of reservoir cracks under high-depth high-closure stress so as to increase the effective period of deep measures and further improve economic development benefits.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
fig. 1 is a diagram illustrating steps of a method for realizing self-supported fracture of rock according to an embodiment of the present application.
Fig. 2 is a specific flowchart of a method for implementing self-supported cracking of rock according to an embodiment of the present application.
Fig. 3 is a flowchart of steps for obtaining a fracture acidizing construction parameter combination in the method for realizing self-supported cracking of rock according to the embodiment of the present application.
Fig. 4 is a schematic diagram of a tunnel distribution for implementing a rock self-supporting fracture method according to an embodiment of the present application.
Detailed Description
The following detailed description of the embodiments of the present invention will be provided with reference to the drawings and examples, so that how to apply the technical means to solve the technical problems and achieve the technical effects can be fully understood and implemented. It should be noted that, as long as there is no conflict, the embodiments and the features of the embodiments of the present invention may be combined with each other, and the technical solutions formed are within the scope of the present invention.
In order to solve the problems, the embodiment of the invention obtains the crack-making injection liquid aiming at different rock types according to the fracture acidizing construction parameter combination, and further adopts a pulse type injection method to construct a plurality of uniformly-distributed non-uniform tunnels, so that the injection discharge capacity of the liquid is increased as much as possible under the condition of not adding friction resistance, and the effective flow conductivity of the crack is improved.
It should be noted that the method capable of achieving the fracture self-supporting effect according to the embodiment of the present application may be implemented for different rock types, and is particularly suitable for fracture acidizing operations of deep sandstone, carbonate rock, shale, and the like. Therefore, the following describes the implementation method in the present application in detail by taking sandstone and shale formations and carbonate formations as examples.
(example of achieving rock self-supporting Effect for sandstone and shale formations)
Fig. 1 is a diagram illustrating steps of a method for realizing self-supported fracture of rock according to an embodiment of the present application. As shown in fig. 1, the steps included in the method will be described below.
First, step S110 (seam construction step) will be described in detail. In the step of crack formation construction, fracture acidification construction parameter combinations aiming at different rock types need to be determined firstly, and fracture formation operation without adding a propping agent is carried out based on the fracture acidification construction parameter combinations. The fracturing fluid in the fracturing-acidizing construction parameter combination is a low-friction high-viscosity fracturing fluid system, and in mixed injection construction, the viscosity of the fracturing fluid and another injected fluid meet the viscous finger-feeding effect in the pumping process between the fluids with high viscosity ratio.
Fig. 2 is a specific flowchart of a method for implementing self-supported cracking of rock according to an embodiment of the present application. Fig. 3 is a flowchart of steps for obtaining a fracture acidizing construction parameter combination in the method for realizing self-supported cracking of rock according to the embodiment of the present application. The following will describe in detail the joint-making construction process for sandstone and shale formations with reference to fig. 2 and 3.
(refer to fig. 3) the seam construction step mainly comprises the following implementation steps: firstly, (step S111) acquiring reservoir characteristic parameters influencing seam construction; then, (step S112) selecting perforation position parameters and optimized fracture parameters based on the reservoir characteristic parameters; then, (step S113) based on the analyzed data of the fracture reservoir characteristic parameters, the perforation position parameters, the fracture parameters and the like for the sandstone and the shale, obtaining fracturing construction parameter combinations corresponding to the rock types, wherein the fracturing acidification construction parameter combinations comprise different fracturing fluid and acid liquid parameters and fracturing acidification construction parameters; and finally, according to the fracturing and acidizing construction parameter combination, carrying out seam construction and injection construction according to a conventional operation flow, and constructing a main crack.
Specifically, in step S111, the method of logging (element capture, FMI imaging, etc.), logging, core experiment, etc. is used to perform fine evaluation on the main reservoir characteristic parameters affecting fracture formation, such as rock mechanics, three-dimensional ground stress and longitudinal ground stress profile, natural fracture development, rock mineral composition and its sensitivity characteristics, etc. parameters related to the problems of fracture formation and fracture propagation. Wherein, logging mainly carries out primary identification on mineral components and oil-gas-containing conditions of rock debris. The logging is based on logging, and further explains porosity, permeability, oil (gas) saturation, rock mechanical parameters, ground stress and the like. However, the logging results are generally large and need to be corrected by performing corresponding indoor analysis with an actual core. Because the coring quantity is limited and the cost is high, the conversion relation between the logging parameters and the core parameters is generally required to be established. Therefore, even if a target layer (particularly a horizontal well section) is not cored, the most needed core parameter result in the subsequent fracture acidizing construction process can be deduced by improving the analogy of the logging parameters and the established conversion relation between the logging parameters and the core parameters.
Next, step S112 will be explained. After the evaluation of the key reservoir characteristic parameters is finished, initially selecting perforation position parameters based on the reservoir characteristic parameters, and selecting a place with good gas content and high brittleness as a perforation position. Generally, the positions such as high oil (gas) saturation (geological dessert index), high content of brittle minerals such as quartz, low rock mechanical parameters, and low ground stress (engineered dessert) are used as the preferential positions for perforation. Secondly, using the current mature fracture propagation simulation software such as FracPro PT, Stimplan, GOFHER, MEYER and the like, primarily selecting perforation positions based on the parameters, combining casing cementing quality, avoiding casing collar positions, fracture propagation simulation conditions and the like, and finally screening out the optimal perforation position from the primarily selected perforation positions. When the software is used for simulating the crack expansion condition at the perforation position, the expansion form and the area of the main crack can cover the range of an effective reservoir stratum to the maximum extent, and the crack height is prevented from extending upwards or downwards excessively, so that the risk that the crack communicates with a water layer nearby is avoided.
Then, further optimizing the crack parameters mainly comprising the length of the crack, the flow conductivity, the space between the cracks and the like. For the sandstone reservoir, a simple oil and gas reservoir geological model can be established on the basis of geological evaluation of the characteristic parameters of the fracture-making reservoir in the step S111, and hydraulic fractures (supporting fractures or acid-etched fractures) are simulated by a conventional method of setting the equivalent conductivity. Specifically, in order to reduce the simulation workload, the propping width of the hydraulic fracture is enlarged by a certain factor (generally, the width is enlarged to 0.1 or 0.3m at most, and the original propping seam width is only about 3 mm), and the permeability of the proppant in the fracture is proportionally reduced, so that the product of the width and the width, namely the diversion capacity of the fracture is kept unchanged. Practice proves that the method for simulating the hydraulic fracture based on the equivalent flow conductivity can improve the operation efficiency, avoid the ill condition of an equation set during numerical calculation, and basically ensure the simulation precision to be unchanged. Then, different fracture parameter types and level values are set by an orthogonal design method, the post-compression production dynamics is inspected, and the post-compression yield and the accumulated yield in a section are used as an optimized objective function, so that the optimal fracture parameter system is optimized. The software for dynamically simulating the yield of the well with the hydraulic fracture can be carried out by adopting the same ECLPSE on the international scale. In addition, for simulation of a plurality of parameters, 2-4 horizontal values can be set for each parameter, so that a fracture parameter orthogonal table is constructed, the fracture parameter simulation test times are optimized by using the orthogonal table, and finally, the results of hundreds of various parameter combinations can be represented by limited simulation.
Next, the process proceeds to step S113, where fracturing construction parameters are optimized. Then, in order to realize an optimized fracture parameter system, the fracture expansion simulation software is used for inspecting different fracturing fluid, acid liquor parameters and fracture acidizing construction parameters, and finally, the optimal fracture acidizing construction parameter combination comprising the viscosity, the volume and the injection discharge of the fracturing fluid and the acid liquor for various rocks is obtained. Common commercial software for fracture design is Frac Pro PT, stimlan, GOFHER, etc., which can simulate the fracture geometry and conductivity under different construction parameters. For example, based on the data included in the fracture parameter system obtained in step S112, if the length of the fracture is smaller than the target value, the amount of the proppant may be increased appropriately until the requirement is met, or if the current parameter value representing the conductivity is larger than the target value, the construction sand-liquid ratio parameter may be decreased appropriately until the simulated conductivity and the fracture length meet the requirement designed in step S112.
And finally, after the fracturing and acidizing construction parameter combination is obtained, injecting low-friction high-viscosity fracturing into the sandstone or shale by utilizing the optimized parameters such as viscosity (generally more than 200 mPa.s), discharge capacity, liquid quantity and the like so as to meet the requirements of the form and the geometric dimension of the main crack, thereby completing the fracturing and crack-making construction. The present application is directed to injection construction of sandstone or shale formations by using a low-friction high-viscosity carboxymethyl hydroxypropyl fracturing fluid system, wherein the carboxymethyl hydroxypropyl guar fracturing fluid system is a most preferred example of the above low-friction high-viscosity fracturing fluid system. On one hand, compared with the conventional hydroxypropyl guar fracturing fluid thickening agent, the carboxymethyl hydroxypropyl guar fracturing fluid can reduce the concentration by 30-50% at different temperatures, so that the damage rate, residues and the like are greatly reduced, and the carboxymethyl hydroxypropyl guar fracturing fluid has the characteristic of low concentration; on the other hand, due to the modification of the carboxyl functional group, under the same condition, when the well depth is about 3000m, the system has 10-20MPa lower friction resistance than the conventional hydroxypropyl guar fracturing fluid, so the field result proves that the system also has the characteristic of low friction resistance. It should be noted that the present application is not limited to low friction high viscosity fracturing fluid systems, and that synthetic polymer clean fracturing fluids with low damage may be used to perform acidizing injection operations on sandstone or shale formations.
Wherein, the low-friction high-viscosity fracturing fluid system generally means that the resistance reduction rate is more than 70 percent (less than 60 percent of the conventional rate) and the temperature of a reservoir stratum at a target layerThen, the conventional 170s-1Shear rate, viscosity after 2 hours of continuous shearing above 60mpa.s (normal 50 or less). In the practical application process, if the fracturing fluid with the low friction resistance characteristic is adopted for injection operation, under the same construction pressure, the injection discharge capacity can be properly improved, the smoothness of a crack surface is further improved, the self-supporting stability is favorably improved, and at the moment, the depth of a gallery formed by hydraulic injection is further increased under the matching of the improvement of the injection speed. If adopt the fracturing fluid that has high glutinous characteristic to pour into the operation into, mainly can improve and make seam efficiency, simultaneously, the crack face that forms is also more smooth, compares with the smooth effect that the above-mentioned high discharge capacity effect that has the low friction characteristic fracturing fluid to produce formed, and the two is synthesized, has further improved the smoothness nature of crack face, and then has improved self-supporting intensity and stability.
Referring again to fig. 1, the step S120 (tunnel construction step) is explained in detail. In the step, a plurality of non-uniform tunnels are formed on the formed cracks by spraying by using a deep penetration hydraulic spraying technology, so that the rock self-supporting effect of the cracks is realized. After injection construction is carried out according to the fracture acidizing construction parameter combination, main cracks are formed, so that strong supporting force can be provided by means of supporting of crack surfaces, and a tunnel formed by deep penetrating hydraulic jet is used for providing flow guiding capacity, and the tunnel forms a long and deep groove and is uniformly distributed in the self-supporting crack surfaces. Therefore, in order to provide higher flow conductivity of the main fracture, the hydraulic jetting operation needs to be carried out again by adopting a variable-displacement pulse jetting method, so that a plurality of uniformly-distributed non-uniform jetting tunnels on the fracture are formed, and the rock self-supporting effect of the fracture is realized. It should be noted that the water jet technology utilizes high-pressure water jet, the jet speed per second can reach more than 130m, and the casing and the rock can be penetrated. However, the general spray length is only 40-60cm, and the spray depth is limited. The deep penetration hydraulic jet technology can gradually deepen the jet depth, some can even reach more than 100m, by continuously feeding the jet hose forward, thereby improving the jet depth and the jet efficiency of the tunnel.
Specifically, in the embodiment, the tunnel construction process is to utilize a hydraulic jetting tool string with a hose device to jet and move ahead on the formed main crack until the main crack reaches the end part of the crack so as to form a jetting tunnel, complete variable-displacement pulse type jetting operation and withdraw the jetting hose device; and then the hose device is turned, the device is continuously utilized to spray to form a plurality of spraying tunnels, and the process is circulated for many times, and at least two non-uniform spraying tunnels which are uniformly distributed are sprayed on the cracks. Wherein, the preferred quantity of spouting gallery is 2 ~ 3. The conductivity of the fracture is now provided by the jet-formed excavation under the rock wall, so that the excavation is not affected by the high closure pressure and can be maintained for a relatively long time.
It should be noted that, in the practical application process, the distribution of the tunnels plays a key role in the flow conductivity of the main cracks. Fig. 4 is a schematic diagram of a tunnel distribution for implementing a rock self-supporting fracture method according to an embodiment of the present application. As shown in fig. 4, the line "1" indicates a tunnel formed by injecting a hose, the line "2" indicates the above-described fracture system formed by simulation, the well hole is shown between the lines "3", and the distribution of the tunnel is analyzed.
First, since the uniform distribution of the tunnels is directed to a plurality of tunnels, it is necessary to distribute the tunnels uniformly on the fracture surface as much as possible to improve the self-supporting stability of the tunnels. If several tunnels are concentrated at a certain position of the fracture surface, firstly, the formed flow conductivity is defective, and thus the fluidity of the whole fracture surface is not improved. Secondly, in the later production process, if the tunnels with the flow guide capacity are distributed on the local part, the local fluid scouring effect is formed, and the stable production of the whole crack surface is not facilitated.
Secondly, the nonuniformity of the tunnel mainly aims at the fact that for a single tunnel, the variation of the jetting speed is inevitably caused due to the high hydraulic jetting speed and the unstable telescopic effect of the jetting hose, so that the tunnel caused by jetting has the inevitable nonuniform characteristics such as the depth, the tunnel edge variation and the like. In this example, in order to obtain the effect of the non-uniformity of the injection pits, the discharge volume of the injection may be changed from large to small or from small to large, but the minimum discharge volume is required to ensure that the injection velocity can reach the minimum injection velocity of 190m/s, and the depth of the pits is required (generally, 3m or more).
Thirdly, the height of the fracture is usually 30-50 m, the thickness of the effective reservoir is usually 10-20m, therefore, the tunnels are best to penetrate the thickness of the effective reservoir in the longitudinal direction on the height of the fracture, namely 2-3 tunnels, the longitudinal distance of each tunnel is 5-7 m, and the 2-3 tunnels basically meet the design requirements considering that the seepage radius is 2.5-3.5 m. In addition, from the viewpoint of reducing construction costs, more hydraulic jet tunnels are generated, so that cost resources are consumed excessively.
Finally, in order to prevent the damage to the flow conductivity of the tunnel in the moment of closing the crack, a series of subsequent operations are required to be carried out after the tunnel construction is completed, so that the flow conductivity of the tunnel is continuously improved. Firstly, (the flowback operation step) carries out flowback operation when the pressure of a well head is 2-3MPa away from the closing pressure, and the flowback speed is slowed down so that the wall surface of the rock without the tunnel is slowly closed. And (2) performing closed acid treatment after ensuring that the rock on the wall surface of the crack is completely supported and attached, wherein acid injection operation needs to be performed again, the well head pressure is 1-2MPa lower than the closed pressure in the operation, the discharge capacity is determined by the well head pressure limit, the aim is to enable the tunnel formed by spraying to perform corrosion reaction again to form higher tunnel flow conductivity, and the type and formula of the acid liquid in the step are determined by comprehensively balancing the mineral components, the sensitivity and the like of a specific rock core. Finally, the conventional steps and processes are executed for other processes such as production finding, and so on, and thus are not described herein again.
(example of achieving rock self-supporting effect for carbonate formation)
Referring again to fig. 1 and 2, in step S110, first, since the method for obtaining the fracture-acidizing construction combination parameters for the carbonate reservoir is the same as the tool, method, and the like used for obtaining the fracture-acidizing construction combination parameters for the sandstone and the shale, the fracture-acidizing construction combination parameters for the carbonate reservoir are obtained according to the methods described in steps S111 to S113. Then, based on the fracturing and acidizing construction combination which is obtained in the embodiment and comprises the optimized parameters of viscosity (generally more than 200 mPa.s), discharge capacity, liquid amount and the like, mixed injection construction of a low-friction high-viscosity fracturing liquid system and an acid liquid system is carried out on the carbonate rock, so that the requirements on the form and the geometric dimension of the main crack are met, and the construction of the main crack is completed. The operation of injecting the fracturing fluid into the carbonate rock will be described in detail below.
For a carbonate reservoir, considering that the friction resistance of acid liquor is high, the construction pressure can be basically constant according to the viscous fingering effect between acid injected into a shaft and a fracture and carboxymethyl hydroxypropyl fracturing fluid. Specifically, a high-viscosity carboxymethyl hydroxypropyl guar fracturing fluid (preferably, the viscosity of the fracturing fluid can be designed to be more than 200 mpa.s) is injected firstly, wherein the carboxymethyl hydroxypropyl guar fracturing fluid is a most preferred example of the low-friction high-viscosity fracturing fluid system. And then injecting a low-viscosity acid liquid system (preferably, the viscosity of the acid liquid system can be designed to be about 30 mPa.s), and generating a viscous fingering effect in a rapid pumping process between high-viscosity-ratio liquids by utilizing the viscosity ratio of the front injected liquid and the rear injected liquid to be more than 6 times, so as to realize the function of constant construction pressure. Therefore, by utilizing the injection mode, the contact between the wall of the well bore and the fracture wall is the low-friction-resistance carboxymethyl hydroxypropyl guar gum fracturing fluid system injected in advance, the friction resistance between two liquids in the acid injection stage cannot be correspondingly increased, and the total injection displacement can be correspondingly improved due to the viscous finger advance effect.
In the fracturing and acidizing construction process for carbonate rock, carboxymethyl hydroxypropyl guar gum fracturing fluid with the viscosity of 200mPa.s can be injected firstly, when the total fluid injection amount reaches 50-60% (namely the fluid volume ratio of a carboxymethyl hydroxypropyl guar gum fracturing fluid system to an acid fluid system reaches 1: 1-3: 2), the injected fluid is converted into thickening acid or gelled acid with the viscosity of about 30mPa.s from the carboxymethyl hydroxypropyl fracturing fluid, the mixed injection construction of the carbonate rock reservoir is carried out, the high friction resistance of the acid fluid in the injection process is reduced, and the effective etching of the acid fluid on the fracture wall rock is realized by utilizing the viscous fingering effect with the viscosity difference of more than 6 times.
As the method and principle of the tunnel construction process for the carbonate reservoir is the same as those of the tunnel construction process for the sandstone and the shale (refer to fig. 1), further description is omitted here. However, it should be noted that, for carbonate rock, the effect of spraying with conventional low-viscosity hydrochloric acid may be better, but the frictional resistance may be higher, and the spraying speed is limited to a certain extent, and the properties of the spraying liquid can be determined by comprehensively balancing the results of the core acid corrosion rate of a specific target layer.
The invention relates to a novel method for realizing self-supporting cracks of rocks, which is particularly suitable for the fracture acidizing operation of deep sandstone, carbonate rock, shale and the like, and belongs to the technical field of yield increase of oil and gas fields. Based on different rock types, corresponding fracturing and acidizing construction parameter combinations are implemented during the fracture injection operation, so that the injection liquid combination has the characteristics of high viscosity and low friction resistance, and the purpose of increasing the injection displacement of the main fracture is achieved. Furthermore, a plurality of uniformly distributed non-uniform spraying tunnels are constructed by utilizing a hydraulic spraying technology with deep penetration capacity so as to realize the rock self-supporting effect of the cracks. The method can enlarge the effective crack length of the main crack, enhance the long-term effective flow conductivity of the reservoir cracks under high-depth high-closure stress, increase the effective period of deep measures, further improve economic development benefits, and facilitate the development and popularization of deep fracturing technology.
The above description is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in 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 (6)
1. A method of effecting self-supporting fracturing of rock, the method comprising the steps of:
a crack formation construction step, namely determining fracture acidification construction parameter combinations aiming at different rock types, and performing crack formation without adding a propping agent based on the fracture acidification construction parameter combinations, wherein a low-friction high-viscosity fracturing fluid system is selected from fracturing fluids in the fracture acidification construction parameter combinations, the viscosity of the fracturing fluid and another injected fluid meet the viscous finger-feeding effect in the process of pumping and injecting the fluids with high viscosity ratio in the mixed injection construction, wherein,
aiming at sandstone or shale strata, a carboxymethyl hydroxypropyl fracturing fluid system with low friction resistance and high viscosity is adopted for injection construction;
carry out the mixed injection construction to the carbonate stratum, successively pour into carboxymethyl hydroxypropyl guar gum fracturing fluid system and the acidizing fluid system of low viscosity of high viscosity into, wherein, the viscosity ratio of the two satisfies the viscous finger effect, low friction drag high viscosity fracturing fluid system with the viscosity ratio of acidizing fluid system is 6 at least: 1;
the method comprises the following steps of (1) constructing the tunnels, namely jetting a plurality of non-uniform tunnels on formed cracks by utilizing a deep penetration hydraulic jetting technology and adopting a variable-displacement pulse jetting method to realize the rock self-supporting effect of the cracks, wherein the tunnel constructing step comprises the following steps of:
spraying an underground tunnel on the formed crack by using a water conservancy spraying tool string with a hose device and adopting a variable-displacement pulse type spraying method, and withdrawing the hose device, wherein the spraying speed of the spraying underground tunnel at least meets the requirement of 190 m/s;
and turning the hose device, and continuously spraying by using the device to form a plurality of spraying tunnels.
2. The method of claim 1, wherein the seam construction step further comprises,
acquiring reservoir characteristic parameters influencing seam construction;
selecting a perforation position parameter and an optimized fracture parameter based on the reservoir characteristic parameters;
and obtaining fracture acidizing construction parameter combinations aiming at different rock types according to the optimized fracture parameters, wherein the fracture acidizing construction parameter combinations comprise different fracturing fluid and acid liquid parameters and fracture acidizing construction parameters.
3. The method of claim 2, wherein, in the seam construction step,
preliminarily selecting a perforation position parameter based on the reservoir characteristic parameter;
and simulating the crack propagation condition of the preliminarily selected perforation position by using crack propagation simulation software, and screening out the optimal perforation position.
4. The method of claim 2, wherein, in the seam construction step,
aiming at sandstone and carbonate reservoirs, establishing an oil-gas reservoir geological model based on the reservoir characteristic parameters, and further simulating fractures by using an equivalent conductivity setting method;
and setting different fracture parameter types and level values including fracture length, flow conductivity and fracture spacing by applying an orthogonal calculation method, and optimizing an optimal fracture parameter system.
5. The method according to any one of claims 2 to 4, wherein in the step of fracture construction, fracture propagation simulation software is applied to determine the fracture acidizing construction parameter combination based on the optimized fracture parameter system, and the fracture acidizing construction parameter combination further comprises viscosity, volume and injection displacement of fracturing fluid and acid fluid.
6. The method according to any one of claims 1 to 4, further comprising,
a flowback operation step, namely slowing down the flowback speed when the pressure of a well head is 2-3MPa away from the closing pressure of a formed crack so as to gradually close the rock wall surface without forming the tunnel;
and (3) closed acid treatment, namely performing secondary acid injection operation after the rock on the wall surface of the crack is completely supported and attached, wherein the pressure of a well mouth in the operation is kept to be 1-2MPa lower than the closed pressure of the crack.
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| CN112302613B (en) * | 2019-07-26 | 2023-03-24 | 中国石油化工股份有限公司 | Deep carbonate rock self-supporting acid fracturing method for improving acid-etched fracture channel depth |
| CN111797546B (en) * | 2020-07-29 | 2021-02-05 | 重庆科技学院 | Shale oil and gas reservoir mineral component model optimization inversion method |
| CN112780246A (en) * | 2021-02-28 | 2021-05-11 | 西南石油大学 | Organic acid solution treatment method for enhancing and maintaining flow conductivity of tight sandstone reservoir fracture |
| CN113218770B (en) * | 2021-03-12 | 2022-07-01 | 西南石油大学 | Multi-lithologic fracturing crack test method |
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