CN115263266B - Reverse-order acid fracturing method for carbonate reservoir - Google Patents
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- 239000002253 acid Substances 0.000 title claims abstract description 217
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- 239000007788 liquid Substances 0.000 claims abstract description 89
- 238000002347 injection Methods 0.000 claims abstract description 37
- 239000007924 injection Substances 0.000 claims abstract description 37
- 239000012530 fluid Substances 0.000 claims abstract description 32
- 238000010276 construction Methods 0.000 claims abstract description 7
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- 238000006073 displacement reaction Methods 0.000 claims description 3
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- 238000010008 shearing Methods 0.000 claims description 3
- 238000004364 calculation method Methods 0.000 claims description 2
- 239000011229 interlayer Substances 0.000 claims description 2
- 150000001875 compounds Chemical class 0.000 claims 2
- 230000035515 penetration Effects 0.000 claims 1
- BULVZWIRKLYCBC-UHFFFAOYSA-N phorate Chemical compound CCOP(=S)(OCC)SCSCC BULVZWIRKLYCBC-UHFFFAOYSA-N 0.000 claims 1
- 238000005530 etching Methods 0.000 abstract description 13
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Abstract
The invention relates to a reverse-order acid fracturing method for a carbonate reservoir, which comprises the following steps: s1: calculating the geometric size of the hydraulic fracture formed under the condition of injecting a certain amount of pad fluid and the average temperature in the hydraulic fracture based on the engineering geological characteristics of the target reservoir; s2: calculating the viscosity ratio and the acid injection amount of the high-viscosity acid liquid and the low-viscosity acid liquid required for forming stable viscosity finger advance in the hydraulic fracture; s3: carrying out an indoor acid liquid rheological property experiment, and determining an acid liquid system meeting the viscosity ratio of reverse-order acid injection based on the viscosity ratio of the high-viscosity acid liquid and the low-viscosity acid liquid determined in the step S2; s4: and (4) carrying out reverse acid fracturing construction according to the acid liquor system determined in the step (S3) and the acid injection amount determined in the step (S2), namely, alternately injecting the high-viscosity acid liquor and the low-viscosity acid liquor in multiple stages. The method has the advantages of reliable principle and simple and convenient operation, increases the non-uniform etching of the acid liquid in the hydraulic fracture by utilizing the viscous fingering phenomenon of an acid liquid system, can effectively improve the fracture flow conductivity and the effective acting distance of the acid liquid, and has wide market application prospect.
Description
Technical Field
The invention relates to the technical field of petroleum engineering, in particular to a reverse-order acid fracturing method for a carbonate reservoir.
Background
Deep carbonate rock oil and gas are usually stored in millimeter-centimeter-level hole reservoirs, the oil and gas reservoirs are not communicated with a well hole, and oil and gas cannot be produced naturally. The acid fracturing technology is a key technology for building and increasing the yield of the carbonate oil-gas well. Acid fracturing is to press open rocks to form artificial cracks, and then inject acid liquor to dissolve the wall surfaces of the cracks in a non-uniform way to form uneven grooves; after construction is finished, under the action of closed pressure, an acid liquid non-corrosion area is used as a supporting point, an acid corrosion crack with certain geometric dimension and flow conductivity is formed, and the 'oil and gas highway' is built underground.
The flow conductivity of the acid-etched fracture and the effective acting distance of the acid liquor are key factors influencing the acid fracturing effect. In order to improve the flow conductivity and the effective action distance of acid liquor of acid fracturing fractures of deep carbonate oil and gas reservoirs, two acid fracturing methods are commonly adopted: one is acid fracturing with high viscosity cross-linked acid, which utilizes the characteristics of high viscosity of acid liquor and low reaction rate of acid rock to increase the effective acting distance of the acid liquor, but the acid liquor has poor non-uniform etching effect and generally has low flow conductivity (Wu Yagong, wu Hu, wang Mingxing, luo, haoqing, gu Xunan, chen Panpan, cao Nai. Composite acid fracturing technology [ J ] based on flow conductivity evaluation experiment, 2020,20 (31): 12776-12781). The other acid fracturing method is to alternately inject high-viscosity fracturing fluid and acid liquor, wherein the viscosity of the acid liquor is usually slightly lower than that of the high-viscosity fracturing fluid, and the aims of increasing the length of an acid fracturing fracture and improving the flow conductivity of the fracture are hopefully fulfilled by forming viscous fingering. However, the biggest defect of the technology is that it is difficult to form a high viscosity difference between the fracturing fluid and the acid solution, and firstly, the adopted acid solution is usually a high viscosity acid solution, so the viscosity difference between the fracturing fluid and the acid solution is small; secondly, because the highly viscous Fracturing fluid is usually an alkaline fluid with high pH value, when the subsequent Acid fluid is injected, the Fracturing fluid is rapidly degraded when meeting Acid at the contact interface of the Fracturing fluid and the Acid fluid, the viscosity of the Fracturing fluid is rapidly reduced, so the viscous index effect is reduced, and the Acid Fracturing modification effect is not ideal (Russian Kalab eye v; dmitry Abdrazakov; yeltay Judulouv; et al. Advanced fracting Design silicon-Assisted Modeling Coupled with Application of Enhanced simulation Fluids indexes Performance of Acid fracture Wells [ C ]. Pat SPE-205139-MS presented at the SPE European affected impact 82and engineering contact, amsterdam, ober 2021).
Disclosure of Invention
The invention aims to provide a reverse acid fracturing method for a carbonate reservoir, which has the advantages of reliable principle and simple and convenient operation, increases the non-uniform etching of acid liquor in a hydraulic fracture by utilizing the viscous fingering phenomenon of an acid liquor system, can effectively improve the fracture flow conductivity and the effective action distance of the acid liquor, and has wide market application prospect.
In order to achieve the technical purpose, the invention adopts the following technical scheme.
The invention changes the traditional positive sequence acid injection concept of etching a far-end crack by using high-viscosity acid liquid to etch a long crack, and proposes a reverse sequence alternate injection mode by using the high-viscosity acid liquid and the low-viscosity acid liquid, namely: the high-viscosity acid liquid is adopted to fill the hydraulic fracture, a high-viscosity environment is provided, the low-viscosity acid liquid is quickly fed in the high-viscosity acid liquid, and the purposes of etching the far-end fracture and reducing the consumption of the high-viscosity acid liquid are achieved; meanwhile, because the acid liquor system with different viscosities is adopted, stable viscous finger advance is easily formed, non-uniform etching is increased, the limitation that the viscosity of the traditional fracturing fluid and the acid liquor injected alternately is unstable is overcome, and the dual purposes of etching a far-end crack and improving the non-uniform etching effect are achieved.
A reverse-order acid fracturing method for a carbonate reservoir sequentially comprises the following steps:
s1: calculating the geometric dimension of a hydraulic fracture and the average temperature in the hydraulic fracture formed under the condition of injecting a certain amount of pad fluid by adopting a fracturing simulator based on the engineering geological characteristics of a target reservoir, wherein the geometric dimension of the hydraulic fracture comprises a length L, a height h and an average width w;
s2: calculating the viscosity ratio and the acid injection amount of the high-viscosity acid liquid and the low-viscosity acid liquid required for forming stable viscosity finger advance in the hydraulic fracture according to the geometric dimension of the hydraulic fracture determined in the S1;
s3: determining the average temperature in the hydraulic fracture based on the S1, developing an indoor acid liquid rheological property experiment, and determining an acid liquid system meeting the viscosity ratio of reverse-order acid injection based on the viscosity ratio of the high-viscosity acid liquid and the low-viscosity acid liquid determined in the S2;
s4: and (4) carrying out reverse acid fracturing construction according to the acid liquor system determined in the step (S3) and the acid injection amount determined in the step (S2), namely, alternately injecting the high-viscosity acid liquor and the low-viscosity acid liquor in multiple stages.
Preferably, step S1 specifically includes the steps of:
the engineering geological characteristics of a target reservoir include the earth stress of a produced interlayer, the temperature and pressure of the reservoir, the rock mechanics, the porosity and the permeability, and the hydraulic fracture geometric dimension formed by hydraulic fracturing is calculated by adopting a fracturing simulator under the condition that a certain amount of pad fluid (fracturing fluid) is injected at constant discharge capacity by combining pad fluid rheological performance parameters, and meanwhile, the average temperature T in the hydraulic fracture after the pad fluid is injected is determined.
Preferably, step S2 specifically includes the following substeps:
s21: the viscosity ratio M of the high-viscosity liquid to the low-viscosity liquid required to form a stable viscous fingering in a hydraulic fracture is determined by the following formula:
in the formula, M is the viscosity ratio of the high-viscosity acid solution to the low-viscosity acid solution, and has no dimension; mu.s h 、μ l The viscosity of the high-viscosity acid solution and the viscosity of the low-viscosity acid solution are respectively mPas.
The derivation process of equation (1) is as follows:
assuming that the injection viscosity of the hydraulic fracture is mu at the discharge capacity q after the hydraulic fracture is formed h High viscosity acid liquid is injected into the hydraulic fracture with the same discharge q l The low-viscosity acid liquid forms viscosity fingering phenomenon (figure 1) in the high-viscosity acid liquid, so that a low-viscosity area and a high-viscosity area are formed in the hydraulic fracture. The reaction speed of the acid liquid in the low-viscosity area and the rock is high, the rock etching degree is deep, the reaction speed of the acid rock in the high-viscosity area is low, and the rock etching degree is shallow, so that the non-uniform etching degree of the whole rock surface is high. When the low-viscosity areas are communicated with each other, the deep etching channels are completely communicated, namely, a high-speed flow channel is formed.
Injecting the high viscosity acid first, the time t for injecting the high viscosity acid h (ii) a Immediately injecting low viscosity acid for a time t l . The contact part of the high-viscosity area and the low-viscosity area is the mixed phase area. The length Δ L of the miscible region is calculated from the Koval model as follows (E.J. Koval, A method for predicting the behavior of unstable perturbation in heterologous media [ J.].SPE J.3,145-155,1963)：
Wherein Δ L is the length of the miscible region, m; u. of h The moving speed of the acid liquid in the high-viscosity area is m/s; t is t l Is the low viscosity acid injection time, s; m e Is the equivalent viscosity ratio of the high-viscosity acid liquid and the low-viscosity acid liquid, and has no dimension.
Equivalent acid liquid viscosity ratio M e Calculated according to the following formula (Sahil, malhotra, mukul, et al. Experimental study of the growing of a missing zone in a missing viscosous sizing [ J)].Physics of Fluids,2015,27(1):1-14)：
M e ＝[0.094M 0.25 +(1-0.094)] 4 (4)
The acid liquor movement speed in the high-viscosity area is as follows:
wherein q is the discharge of injected acid, m 3 Min; w is the hydraulic fracture mean width, m; h is the hydraulic fracture height, m.
The condition that the stable viscosity finger-entering flow channel is formed is that the most end of the viscosity finger-entering distance of the low-viscosity acid is just equal to the most end of the high-viscosity acid, namely:
u h (t h +t l )＝u ltip t l (6)
in the formula, t h Is the high viscosity acid injection time, s; t is t l Is the low viscosity acid injection time, s; u. u ltip The acid liquid finger-feeding speed in the low-viscosity area is m/s.
Fitting the results of the experimental tests of Sahil (Sahil, malhotra, mukul, et al. Experimental study of the growth of the growing in a mixed viscous refining [ J ]. Physics of Fluids,2015,27 (1): 1-14), the relationship between the finger-feeding speed of the acid liquid in the low viscosity area and the moving speed of the acid liquid in the high viscosity area is:
u ltip ＝u h 0.9781M 0.1895 (7)
from the formulas (6) and (7), the injection time relationship between the high viscosity acid and the low viscosity acid can be obtained as follows:
t h ＝(0.9781M 0.1895 -1)t l (8)
to form a stable viscous fingering, the length Δ L of the miscible region needs to satisfy the following relationship:
L＞ΔL≥0.5L (9)
from formula (3) -formula (9), formula (1) can be easily obtained.
S22: and determining the injection volumes of the high-viscosity acid solution and the low-viscosity acid solution. When high-viscosity acid liquid and low-viscosity acid liquid are alternately injected in multiple stages, the volumes of the high-viscosity acid liquid and the low-viscosity acid liquid injected in a single stage are determined according to the following formula:
in the formula, V hn Is a single-stage high-viscosity acid liquid injection volume m 3 ；V ln Is a single-stage low-viscosity acid liquid injection volume, m 3 ；η h The liquid efficiency of the high-viscosity acid liquid in the hydraulic fracture is percent; eta l The liquid efficiency of the low-viscosity acid liquid in the hydraulic fracture is percent; n is the number of stages of the multi-stage alternate injection.
The derivation processes of the equations (10) and (11) are as follows:
when high viscous acid liquid and low viscous acid liquid are injected alternately in multiple stages, the volume of the high viscous acid liquid and the low viscous acid liquid injected in a single stage is as follows:
the low viscosity acid injection time is calculated by the following formula:
from formulas (5) and (7), formula (14) can be derived as:
by combining formula (12) and formula (15), formula (11) can be easily obtained. From formulae (8), (13) and (15), formulae (10) and (11) can be easily obtained.
Preferably, step S3 specifically includes the following substeps:
s31: according to the average temperature T in the hydraulic fracture formed after the pad fluid is injected, which is determined by S1, a rotational rheometer is adopted to test the average temperature T of the fracture in 100S -1 The shear rate is constant and the shear is carried out for 60min, and the apparent viscosities of different acid systems in the hydraulic fracture under the condition of temperature T are obtained;
s32: and determining high-viscosity acid liquid and low-viscosity acid liquid which meet the viscosity ratio of the reverse-order acid injection according to the viscosity ratio M of the acid liquid meeting the viscosity ratio of the reverse-order acid injection and the apparent viscosity of different acid liquid systems at the average temperature T of the crack of the S31.
Preferably, step S4 specifically includes the following substeps:
s41: the pad fluid (fracturing fluid) of S1 is fully injected at high discharge capacity;
s42: injecting the high-viscosity acid solution determined by the first stage S3 into the discharge capacity q, wherein the acid injection amount is V hn ；
S43: injecting the low-viscosity acid solution determined by the first stage S3 into the discharge capacity q, wherein the acid injection amount is V ln ；
S44: repeating S42 to S43 in sequence until the n-level alternate acid injection is completed;
s45: and (4) injecting a displacement liquid into the stratum to displace the acid liquid in the ground and the shaft into the stratum.
Compared with the prior art, the invention has the following beneficial effects:
compared with the conventional acid fracturing technology, on one hand, the invention fully utilizes the viscous fingering phenomenon of an acid liquid system to increase the non-uniform etching of the acid liquid in the hydraulic fracture, improve the fracture flow conductivity and overcome the limitation that the traditional high-viscosity fracturing liquid and the acid liquid are difficult to form stable viscous fingering; on the other hand, the invention adopts a reverse-order acid injection mode, fully utilizes the fingering phenomenon of the low-viscosity acid liquid in the high-viscosity acid liquid, changes the traditional mode of singly adopting the high-viscosity acid to provide the effective action distance of the acid liquid, and reduces the consumption of the high-viscosity acid liquid and the cost of the acid liquid. The invention realizes the double effects of improving the flow conductivity of the acid fracturing fracture and the effective length of the acid corrosion fracture, and simultaneously fully improves the efficiency of an acid liquor system.
Drawings
FIG. 1 is a schematic diagram of the secondary alternation of high and low viscosity acids.
Detailed Description
The invention is further illustrated by the following figures and examples.
It should be noted that, in the present application, the embodiments and the technical features of the embodiments may be combined with each other without conflict. It is to be noted that, unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
Examples
Taking western acid fracturing candidate well A as an example, the acid fracturing design and construction are carried out by adopting the reverse-order acid fracturing method for the carbonate reservoir, which is provided by the invention, and the method specifically comprises the following steps:
s1: based on engineering geological characteristic data (table 1) of a target reservoir of an A well, a FracpropT fracturing simulator is adopted, similar steps of acid fracturing simulation are carried out according to a patent 'method for determining acid fracturing fracture conductivity distribution of carbonate oil and gas reservoir by experiment' (201611218306. X), basic parameters of the A well are input into different modules of the fracturing simulator, and simulation calculation is carried out to obtain the target reservoir of the A well with the displacement of 4.0m 3 Min, 100m of pad fluid (fracturing fluid) injection 3 The hydraulic fracture formed under the conditions had a length L of 129.8m, a height h of 46.5m and an average width w of 0.008m, and the average temperature in the hydraulic fracture was 65 ℃.
S2: determining that the viscosity ratio of the high-viscosity acid solution to the low-viscosity acid solution meeting the reversed-order acid fracturing is about 25.0 according to the formula (1) in S21; the well A adopts three-level alternation, and the liquid efficiency eta of high-viscosity acid in hydraulic fractures h Is 37%; liquid efficiency eta of low-viscosity acid in fracture l Is 25%; the injection amount of the single-stage high-viscosity acid calculated from the hydraulic fracture geometry determined by the formulas (10) and S1 is 37m 3 (ii) a Similarly, the amount of the single-stage low-viscosity acid injected from the formula (11) was 80m 3 。
TABLE 1A well hydraulic fracturing simulation Primary basis data
S3: the average temperature in the hydraulic fracture determined by S1 is 65 ℃, and the temperature of 4 acid liquid systems commonly used in a work area is 65 ℃ and the shear rate is 100S by adopting a rotational rheometer -1 And the apparent viscosity under the shearing time of 60min, and the test result is shown in table 2, and the acid liquor viscosity ratio determined by S2 indicates that the H3 and H4 acid liquor system meets the requirement of reverse-order acid fracturing.
TABLE 2 apparent viscosity of 4 acid systems commonly used in work area
| Acid liquor system H1 | Acid system H2 | Acid system H3 | Acid liquor system H4 |
| 12.0 | 38.0 | 49.0 | 2.0 |
S4: the acid liquor system is optimized according to S3 and the acid injection amount is determined according to S2 (for convenience of on-site acid liquor preparation, the acid amount of the single-stage high-viscosity acid is 37m 3 Increased to 40m 3 ) The reverse acid fracturing construction was carried out according to the pump injection procedure of table 3.
TABLE 3A well reversed-order acid fracturing construction pump injection program
Compared with the conventional high-viscosity acid liquid deep acid fracturing, the reverse acid fracturing is adopted, the dosage of the A well Gao Niansuan is reduced by 67%, and the cost of an acid liquid system is reduced by nearly 30%. After the well A is constructed by adopting reverse acid fracturing, the gas production rate of a stable day is tested to be 4.5 multiplied by 10 4 m 3 And d, compared with the same-layer reservoir in the adjacent region, the breakthrough of zero yield is realized, the purpose of further recognizing and evaluating the reservoir is achieved, and the technology is shown to realize effective reformation of the gas reservoir.
Although the present invention has been described with reference to a preferred embodiment, those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit and scope of the invention, and it is intended to provide a novel and improved method for manufacturing a semiconductor device.
Claims (3)
1. A reverse-order acid fracturing method for a carbonate reservoir sequentially comprises the following steps:
s1: calculating the geometric dimension of a hydraulic fracture formed under the condition of injecting a certain amount of pad fluid and the average temperature in the hydraulic fracture by adopting a fracturing simulator based on the engineering geological characteristics of the target reservoir, wherein the geometric dimension of the hydraulic fracture comprises the lengthLHeight, heighthAnd average widthw；
S2: calculating the viscosity ratio and the acid injection amount of the high-viscosity acid liquid and the low-viscosity acid liquid required for forming stable viscosity fingering in the hydraulic fracture according to the geometric dimension of the hydraulic fracture determined by the S1, wherein the calculation method comprises the following steps:
s21: the viscosity ratio of high-viscosity liquid to low-viscosity liquid required to form stable viscous fingering in hydraulic fractures is determined by the following formulaM：
In the formula (I), the compound is shown in the specification,Mthe viscosity ratio of the high-viscosity acid solution to the low-viscosity acid solution is zero, and the dimension is not required;μ h 、μ l the viscosity of the high-viscosity acid solution and the viscosity of the low-viscosity acid solution are respectively mPa & s;
s22: when the high-viscosity liquid and the low-viscosity liquid are injected alternately in multiple stages, the volume of the high-viscosity liquid and the low-viscosity liquid injected in a single stage is determined according to the following formula:
in the formula (I), the compound is shown in the specification,V hn is a single-stage high-viscosity acid liquid injection volume m 3 ；V ln Is a single-stage low-viscosity acid injection volume, m 3 ；η h The liquid efficiency of the high-viscosity acid liquid in the hydraulic fracture is percent;η l the liquid efficiency of the low-viscosity acid liquid in the hydraulic fracture is percent;nthe number of stages is the number of stages of multi-stage alternate injection;
s3: determining the average temperature in the hydraulic fracture based on S1, developing an indoor acid liquid rheological property experiment, determining an acid liquid system meeting the viscosity ratio of reverse-order acid injection based on the viscosity ratio of the high-viscosity acid liquid and the low-viscosity acid liquid determined in S2, and comprising the following steps of:
s31: average temperature in hydraulic fracture determined from S1TThe average temperature in the crack is measured by adopting a rotational rheometerTUnder the condition of 100s -1 The shearing speed is constant and the shearing time is 60min, so as to obtain the apparent viscosities of different acid liquor systems;
s32: viscosity ratio determined by S2MAnd S31 obtaining different acid systems at average temperature of crackTDetermining high-viscosity acid liquid and low-viscosity acid liquid which meet the viscosity ratio of reverse-order acid injection;
s4: and (4) carrying out reverse acid fracturing construction according to the acid liquor system determined in the step (S3) and the acid injection amount determined in the step (S2), namely, alternately injecting the high-viscosity acid liquor and the low-viscosity acid liquor in multiple stages.
2. The reverse acid fracturing method for carbonate reservoirs according to claim 1, wherein step S1 comprises: engineering geological characteristics based on target reservoir include production interlayer ground stress, reservoir temperature and pressure, rock mechanics, porosity, permeabilityThe penetration rate is combined with the rheological property parameter of the pad fluid, a fracturing simulator is adopted to calculate the geometric dimension of the hydraulic fracture formed by hydraulic fracturing under the condition that a certain amount of pad fluid is injected at constant discharge capacity, and the average temperature in the hydraulic fracture after the pad fluid is injected is determined at the same timeT。
3. The reverse acid fracturing method for carbonate reservoirs according to claim 1, wherein the step S4 comprises:
s41: injecting a pad fluid;
s42: injecting the high-viscosity acid solution determined by the first stage S3 with the acid injection amount ofV hn ；
S43: injecting the low-viscosity acid solution determined by the first stage S3 with the acid injection amount ofV ln ；
S44: repeating S42 to S43 in sequence until completionnAcid is injected in a grade-alternate way;
s45: and (4) injecting a displacement fluid into the stratum to displace the acid liquor in the ground and the shaft into the stratum.
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