CN114278266A - Method for determining effective joint length of acid-etched sand-filled crack under in-situ condition - Google Patents
Method for determining effective joint length of acid-etched sand-filled crack under in-situ condition Download PDFInfo
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Abstract
The invention discloses a method for determining effective joint length of an acid-etched sand-filled crack under in-situ conditions, which comprises the following steps of: s1: preparing a plurality of experimental rock samples with the same underground hydraulic fracture morphology; s2: carrying out acid etching hydraulic fracture simulation experiments under different acid etching experimental conditions to obtain acid etching morphology under each experimental condition; s3: testing the flow conductivity of the sand-filled fracture in the hydraulic fracture range under the in-situ condition, and drawing a relation curve between the flow conductivity of the acid-etched sand-filled fracture and the length of the hydraulic fracture; s4: and determining the effective joint length of the acid-etched sand-filled fracture by combining the residual flow conductivity curve of the target reservoir when production is required to be stopped and determining the effective joint length of the acid-etched sand-filled fracture by the intersection point of the two curves. The method can embody the upward flow conductivity distribution of the acid-etched sand-filled cracks above the crack length, determine the effective crack length of the acid-etched sand-filled cracks by considering the production requirements, realize the dual purposes of objectively evaluating the flow conductivity of the acid-etched cracks and the length of the acid-etched sand-filled cracks under the in-situ condition, and provide reliable basis for acid-etched sand-filled fracturing of the deep carbonate rock.
Description
Technical Field
The invention relates to the technical field of petroleum engineering, in particular to a method for determining the effective joint length of an acid-etched sand-filled crack under an in-situ condition.
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 rock to form an artificial crack, and then inject acid liquor to non-uniformly erode the wall surface of the crack to form an uneven groove; after construction is finished, under the action of closed pressure, the acid liquor non-corrosion area is used as a supporting point to form an acid corrosion crack with a certain geometric size and flow conductivity, so that the 'oil and gas highway' is built underground.
The acid-etched fracture conductivity is one of the key factors influencing the acid fracturing effect. However, for the reservoir with higher closing pressure and lower mechanical strength of the reservoir rock, even though non-uniform etching is formed after acid etching and a plurality of non-eroded parts are left to form supporting points, the effective flow conductivity is difficult to form under the closing pressure due to the higher closing pressure and the lower mechanical strength of the supporting points rock; for carbonate rocks with homogeneous lithology, acid liquor uniformly etches rocks on the wall surfaces of cracks, supporting points formed after etching are few, and acid-etched cracks with certain flow conductivity are more difficult to form under closed pressure, so that the acid fracturing effect is seriously influenced by the two conditions.
The sand-adding acid fracturing technology combines the advantages of acid fracturing and hydraulic fracturing, can effectively improve the flow conductivity of acid-etched fractures, and can form acid-etched sand-filled fractures by enabling high-viscosity cross-linked acid or fracturing fluid gel to carry a propping agent into a stratum, and after construction is finished, the propping agent bears pressure to form effective support. The effective length of the acid-etched sand-filled fracture is a key parameter influencing the sand-adding acid fracturing effect, the effective length is short, and the technical advantage of sand-adding acid fracturing cannot be shown; the effective length is too long, the construction difficulty and the construction operation cost are increased, and the purpose of safely, economically and efficiently exploiting the deep carbonate reservoir cannot be achieved. Therefore, the determination of the effective joint length of the acid-etched sand-filled fracture is important for the design of sand-adding acid fracturing engineering and the evaluation of acid fracturing effect.
Disclosure of Invention
In view of the above problems, the present invention is directed to a method for determining an effective fracture length of an acid-etched sand-packed fracture under in-situ conditions.
The technical scheme of the invention is as follows:
a method of determining an effective joint length of an acid-etched sand-packed fracture under in-situ conditions, comprising the steps of:
s1: acquiring the topography of underground hydraulic fractures of a target reservoir, and preparing a plurality of experimental rock samples with the topography of the underground hydraulic fractures by adopting a fracture surface reconstruction carving technology;
s2: carrying out acid etching hydraulic fracture simulation experiments under different acid etching experimental conditions by using the plurality of experimental rock samples prepared in the step S1 to obtain acid etching morphology under different acid etching experimental conditions;
s3: determining effective closing pressure of a target reservoir and sand laying concentration in the length direction of a hydraulic fracture, testing the flow conductivity of the sand-filled fracture in the hydraulic fracture range under the on-site condition by using a flow guide instrument based on a plurality of experimental rock samples with different acid etching appearances and 1 group of non-etched experimental rock samples obtained in S2, and drawing a relation curve between the flow conductivity of the acid-etched sand-filled fracture and the length of the hydraulic fracture;
s4: and determining the effective joint length of the acid-etched sand-filled fracture from the intersection point of the two curves by combining the flow conductivity curve of the target reservoir which is remained when the production is required to be stopped based on the relation curve of the flow conductivity of the acid-etched sand-filled fracture and the length of the hydraulic fracture drawn in the step S3.
Preferably, step S1 specifically includes the following sub-steps: the method comprises the steps of obtaining underground rock samples of a target reservoir of the oil and gas field, obtaining the appearance of the underground hydraulic fracture in a Brazilian splitting mode, and preparing a plurality of experimental rock samples with the appearance of the underground hydraulic fracture by adopting a fracture surface reconstruction carving technology.
Preferably, step S2 specifically includes the following sub-steps:
s21: according to the amount of the pre-fracturing fluid injected into the acid fracturing well, simulating the hydraulic fracture expansion process by using an acid fracturing simulator, and determining the geometric size and the temperature distribution of the hydraulic fracture; the hydraulic fracture geometric dimension comprises a hydraulic fracture length, a hydraulic fracture height and a hydraulic fracture width;
s22: according to the acid injection amount of the acid fracturing well, an acid fracturing simulator is adopted to simulate the acid etching hydraulic fracture process, the effective acid etching seam length is determined, and the seam length, the seam height, the seam width and the temperature corresponding to a plurality of different characteristic points are determined by combining the step S21; the different characteristic points refer to a plurality of characteristic positions with different acid liquor concentrations in the crack;
s23: and (4) converting the parameters corresponding to the plurality of feature points determined in the step (S22) into acid etching experimental conditions, developing an acid etching hydraulic fracture simulation experiment by using the plurality of experimental rock samples prepared in the step (S1), and acquiring the acid etching morphology corresponding to each feature point and the increased seam width after acid etching.
Preferably, in step S22, the number of the feature points is 10, and 10 of the feature points correspond to 10 feature positions in which the acid solution concentration in the fracture is 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10% of the fresh acid mass concentration, respectively.
Preferably, in step S3, the target reservoir effective closing pressure is calculated by the following formula:
σe＝αH-p (1)
in the formula: sigmaeThe reservoir closing pressure is MPa when the oil-gas well stops production; alpha is the closing pressure gradient, MPa/m; h is the well depth of the target zone, m; and p is the formation pressure in the off-stream of the oil and gas well, and is MPa.
Preferably, in step S3, the sanding concentration in the hydraulic fracture length direction includes a sanding concentration within an acid-etching effective fracture length range and a sanding concentration within an acid-liquid ineffective etching range; wherein, the sand laying concentration in the acid etching effective gap length range is calculated by the following formula:
in the formula: ciThe sand laying concentration is within the range of the effective seam length of the ith characteristic point acid corrosion in kg/m2I ═ 2,3, … …, 10; m is the total proppant amount, Kg, used in the acid fracturing well; w is ai、wi-1The width of the tail end of the hydraulic crack of the ith characteristic point and the i-1 characteristic point is m; l isfIs the hydraulic fracture length, m; l is10The effective acid etching gap is long, m; w is aNIs the width of the end of the hydraulic fracture, m; w is a10Is the effective acid etching gap width, m; h isNThe seam height at the end of the hydraulic fracture is m; h is10The effective seam height of acid etching is m; l isi、Li-1The length of the tail end of the hydraulic crack of the ith characteristic point and the i-1 characteristic point is m; h isi、hi-1The height of the tail end of the hydraulic crack at the ith and the i-1 st characteristic points is m;
the sanding concentration of the 1 st characteristic point is approximately equal to that of the adjacent characteristic point, namely C1-C2;
the sanding concentration in the acid liquid ineffective etching range is calculated by the following formula:
in the formula: cNThe sanding concentration is kg/m in the range of the hydraulic fracture which is not effectively etched by the acid liquor2。
The invention has the beneficial effects that:
the method can embody the upward flow conductivity distribution of the acid-etched sand-filled cracks above the crack length, determines the effective crack length of the acid-etched sand-filled cracks by considering the production requirements, realizes the dual purposes of objectively evaluating the flow conductivity of the acid-etched cracks and the length of the acid-etched sand-filled cracks under the in-situ condition, and provides a reliable basis for acid-etched sand-filled fracturing of the deep carbonate rock.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a schematic diagram showing effective joint length of an acid-etched sand-packed fracture;
FIG. 2 is a graphical illustration of the results of determining the effective joint length of an acid-eroded sand-packed fracture in an embodiment.
Detailed Description
The invention is further illustrated with reference to 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 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. The use of the terms "comprising" or "including" and the like in the present disclosure is intended to mean that the elements or items listed before the term cover the elements or items listed after the term and their equivalents, but not to exclude other elements or items.
As shown in FIG. 1, the present invention provides a method for determining an effective joint length of an acid-eroded sand-packed fracture under in-situ conditions, comprising the steps of:
s1: and acquiring the morphology of the underground hydraulic fracture of the target reservoir, and preparing a plurality of experimental rock samples with the morphology of the underground hydraulic fracture by adopting a fracture surface reconstruction carving technology.
In a specific embodiment, step S1 specifically includes the following sub-steps: the method comprises the steps of obtaining underground rock samples of a target reservoir of the oil and gas field, obtaining the appearance of the underground hydraulic fracture in a Brazilian splitting mode, and preparing a plurality of experimental rock samples with the appearance of the underground hydraulic fracture by adopting a fracture surface reconstruction carving technology. It should be noted that the acquisition of the fracture morphology by brazilian splitting is only one acquisition method in the prior art, and other acquisition methods of the hydraulic fracture morphology in the prior art can also be applied to the present invention. The reconstruction and carving technology of the fracture surface is also the prior art, and the experimental rock sample is made by the method disclosed in CN 201911006463.8. Alternatively, in this example, 11 pairs of experimental rock samples required for the experiment were made.
S2: and (4) developing an acid etching hydraulic fracture simulation experiment under different acid etching experiment conditions by using the plurality of experimental rock samples prepared in the step S1, and obtaining the acid etching morphology under different acid etching experiment conditions.
In a specific embodiment, by using 10 experimental rock samples prepared in S1, acid fracturing numerical simulation is performed to obtain acid liquor temperature, concentration and other parameters of 10 feature points (the acid liquor concentration in the fracture is 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10% of 10 feature positions of the fresh acid mass concentration) within the effective acid etching joint length range in the in-situ environment, as acid etching experimental conditions, and an acid etching hydraulic fracture simulation experiment is performed to obtain acid etching features of 10 feature points. The method specifically comprises the following substeps:
s21: according to the amount of the pre-fracturing fluid injected into the acid fracturing well, simulating the hydraulic fracture expansion process by using an acid fracturing simulator, and determining the geometric size and the temperature distribution of the hydraulic fracture; the hydraulic fracture geometry comprises a hydraulic fracture length LfHydraulic fracture height h, hydraulic fracture width w0；
S22: according to the acid injection amount of the acid fracturing well, an acid fracturing simulator is adopted to simulate the acid etching hydraulic fracture process, the effective acid etching seam length is determined, and the seam length L corresponding to 10 characteristic points is determined by combining the step S21fH and w0And a temperature;
s23: and (4) converting the parameters corresponding to the 10 characteristic points determined in the step (S22) into acid etching experimental conditions, developing an acid etching hydraulic fracture simulation experiment by using the 10 experimental rock samples prepared in the step (S1), and acquiring the acid etching morphology corresponding to each characteristic point and the increased seam width after acid etching.
In a specific embodiment, the acid fracturing fracture conductivity distribution of the carbonate oil and gas reservoir can be determined experimentally according to the method disclosed in the applicant's invention patent cn201611218306.x, and an acid etching hydraulic fracture simulation experiment can be carried out.
It should be noted that the acid fracturing simulator is the prior art, and the specific structure and the using method are not described herein again.
In one specific embodiment, the increased slot width after acid etching is calculated by the following equation:
wi＝woi+Δwai i＝1,2,3...10 (4)
in the formula: w is aiThe width of the hydraulic fracture of the ith characteristic point is cm after acid etching; w is aoiThe width of a hydraulic fracture before acid etching of the ith characteristic point is cm; Δ waiIncreased hydraulic fracture width, cm, after acid etching of the ith feature point.
S3: determining effective closing pressure of a target reservoir and sand laying concentration in the length direction of a hydraulic fracture, testing the flow conductivity of the sand-filled fracture in the hydraulic fracture range under the on-site condition by using a flow guide instrument based on a plurality of experimental rock samples with different acid etching appearances and 1 group of non-etched experimental rock samples obtained in S2, and drawing a relation curve between the flow conductivity of the acid-etched sand-filled fracture and the length of the hydraulic fracture.
In a specific embodiment, in order to meet the long-term production stability requirement of the oil and gas well, the late production stage, the formation pore pressure attenuation, the formation closure pressure increase influence and the experimental closure pressure are taken as the pressure acting on the artificial fracture when the oil and gas well stops production, namely the effective closure pressure of the target reservoir is calculated according to the following formula:
σe＝αH-p (1)
in the formula: sigmaeThe reservoir closing pressure is MPa when the oil-gas well stops production; alpha is the closing pressure gradient, MPa/m; h is the well depth of the target zone, m; and p is the formation pressure in the off-stream of the oil and gas well, and is MPa.
It should be noted that the above calculation formula of the effective closing pressure is determined in consideration of the above requirements, and the like, and according to the field application requirements, the present invention may also use other calculation formulas of the effective closing pressure in the prior art to determine the effective closing pressure of the target reservoir.
According to the design propping agent amount of the acid fracturing well and the geometric characteristics (seam length, seam width and seam height) of the whole acid fracturing fracture, the acid fracturing fracture is divided into two parts: the effective seam length part is subjected to acid etching, and the acid liquid part is not effectively etched, so that the sand laying concentration in the hydraulic fracture length direction comprises the sand laying concentration within the effective seam length range of acid etching and the sand laying concentration within the ineffective etching range of acid liquid; in the above 10 characteristic point embodiment, the sanding concentration in the range of the acid etching effective gap length is calculated by the following formula:
in the formula: ciThe sand laying concentration is within the range of the effective seam length of the ith characteristic point acid corrosion in kg/m2I ═ 2,3, … …, 10; m is the total proppant amount, Kg, used in the acid fracturing well; w is ai、wi-1The width of the tail end of the hydraulic crack of the ith characteristic point and the i-1 characteristic point is m; l isfIs the hydraulic fracture length, m; l is10The effective acid etching gap is long, m; w is aNIs the width of the end of the hydraulic fracture, m; w is a10Is the effective acid etching gap width, m; h isNThe seam height at the end of the hydraulic fracture is m; h is10The effective seam height of acid etching is m; l isi、Li-1The length of the tail end of the hydraulic crack of the ith characteristic point and the i-1 characteristic point is m; h isi、hi-1The height of the tail end of the hydraulic crack at the ith and the i-1 st characteristic points is m;
the sanding concentration of the 1 st feature point is approximately equal to the sanding concentration of the adjacent feature points, namely C1＝C2；
The sanding concentration in the acid liquid ineffective etching range is calculated by the following formula:
in the formula: cNIs acid liquorThe sanding concentration in kg/m in the range of the hydraulic fracture is not effectively etched2。
The derivation process of the above equations (2) and (3) is as follows:
assuming that the proppant uniformly fills the entire acid-etched fracture and the non-acid-etched part of the hydraulic fracture within the effective length range of the acid-etched fracture, i.e., Li≤L10In time, the volume of the acid-etched crack of the adjacent characteristic points is as follows:
for the residual acid section to the end of the fracture, the fracture volume is:
the total sand pack fracture volume is then:
thus, the total proppant mass can be obtained:
assuming that the proppant is fully uniformly filled in the fracture, the proppant mass filled between adjacent feature points is:
then the sand concentration C is paved at any section in the sand filling crackiComprises the following steps:
by combining the above formulas (5) to (12), the formulas (2) and (3) can be derived. (5) - (12) formula (I), ViIs the fracture volume between adjacent feature segments, m3；VNM is the volume of the crack of the section which is not effectively etched by the acid liquid3；VfTo total fracture volume, m 3; phi is apIs proppant sand pile porosity, decimal; rhopIs proppant density, kg/m3。
S4: and determining the effective joint length of the acid-etched sand-filled fracture from the intersection point of the two curves by combining the flow conductivity curve of the target reservoir which is remained when the production is required to be stopped based on the relation curve of the flow conductivity of the acid-etched sand-filled fracture and the length of the hydraulic fracture drawn in the step S3.
In a specific embodiment, the method is used for determining the effective joint length of the acid-eroded sand-filled fracture under the in-situ condition by taking a western acid-fractured candidate well X as an example. The depth of a target layer of the well is 7670m, the formation temperature is 169 ℃, the closing pressure gradient is 0.016MPa/m, and the formation pressure is 57.5MPa when the production is stopped. Discharge capacity of liquid injection 6.0m in acid fracturing design3Min, fracturing fluid quantity 520m3Crosslinking acid amount 430m 340/60 mesh support dose of 42t (particle size: 0.225-0.45mm, density: 1.8 t/m)3) And the fracture conductivity of the X well when the X well is required to stop production can be kept at 2.0D-cm. The method for determining the effective joint length of the acid-etched sand-filled fracture under the in-situ condition specifically comprises the following steps:
s1: selecting an underground rock sample of a target reservoir of the oil and gas field, acquiring the appearance of an underground hydraulic fracture by adopting a splitting mode, and copying the rock sample for experiments by adopting a carving technology of fracture surface reconstruction. The method comprises the following specific steps:
(1) selecting an X well same-layer underground core to prepare an API standard rectangular rock sample (the rock sample is 180mm long, 37mm wide and 30mm high), and splitting the standard sample by adopting a Brazilian splitting method;
(2) acquiring rough appearance data of the crack surface of each rectangular rock plate by adopting a laser scanner;
(3) carrying out noise reduction on three-dimensional point cloud data of a selected square rock plate by adopting a standard deviation filtering method, then carrying out interpolation normalization on the point cloud data subjected to noise reduction according to a Krigin interpolation method, then importing the point cloud data into Geomagic software to convert the point cloud data into a NURBS (non-uniform rational B-spline) curved surface model, finally importing the curved surface model into a carving machine, and establishing a carving machine tool path by utilizing Artcam software of the carving machine;
(4) manufacturing a smooth square rock plate with a smooth and straight surface by using the exposed rock at the same layer position of the X well;
(5) and then carving the smooth square rock plate by utilizing a carving machine to manufacture the artificial rock sample with uniform surface appearance.
The further detailed rock sample preparation method is described in patent CN201911006463.8, and 11 pairs of rock samples meeting the experimental requirements are finally prepared.
And S2, carrying out an acid etching hydraulic fracture simulation experiment by using the rock sample processed and manufactured in the step S1 and combining acid liquor temperature, concentration and other parameters of 10 characteristic points in the length direction of the acid fracturing fracture in the in-situ environment obtained by acid fracturing numerical simulation as acid etching experimental conditions. The method comprises the following specific steps:
(1) according to the total amount of the injected front fracturing fluid of 520m3Discharge capacity of 6.0m3Permin, calculating hydraulic fracture length L using an acid fracturing simulator, e.g., FracpropTf84.9m, the simulation base parameters are shown in Table 1;
TABLE 1X well acid-pressure simulation input parameters
| Item | Parameter(s) | Item | Parameter(s) |
| Reservoir temperature (. degree.C.) | 160 | Flow state coefficient of fracturing fluid | 0.5655 |
| Lithology of target layer | Limestone | Viscosity coefficient of fracturing fluid (Pa.s)n) | 1.2451 |
| Stress gradient (MPa/m) | 0.0165 | Flow state coefficient of crosslinking acid | 0.3007 |
| Permeability (mD) | 0.1 | Consistency factor (Pa.s) of cross-linking acidn) | 1.2796 |
| Young's modulus (MPa) | 64000 | Front liquid (m)3) | 520 |
| Poisson ratio | 0.3 | Acid liquor (m)3) | 430 |
| Number of reaction stages | 1.3977 | Displacement (m)3/min) | 6.0 |
| Reaction Rate constant ((mol/L)1-m·s-1) | 8.61×10-7 | - | - |
(2) According to the on-site acid injection quantity of 430m3Effective seam length L of acid etching calculated by using acid pressure simulator, e.g. FracpropTef69.4 m;
(3) selecting 10 characteristic points according to the fresh acid concentration within the range of 69.4m of the effective acid etching seam length, obtaining parameters such as seam length, seam height, seam width, temperature and the like, and determining acid etching experiment parameters (acid liquid concentration, acid injection discharge capacity and acid injection time) according to the Reynolds number similarity criterion, wherein the results are shown in Table 2;
TABLE 2 acid etching experimental simulation conditions for 10 characteristic points of X well acid pressure gap length
(4) And (4) carrying out an acid etching simulation experiment by using the rock sample processed and manufactured by S1 and combining the data such as the acid liquor temperature, the concentration distribution and the like determined in the local environment.
The further detailed method is described in patent CN201611218306.X in the description of the method for determining the acid fracturing fracture conductivity distribution of carbonate oil and gas reservoirs.
S3, testing the hydraulic fracture L under the in-situ condition based on the 10 acid-etched rock samples obtained in the step S2fThe flow conductivity of the sand filling crack within the range. The method comprises the following specific steps:
(1) determining that the X well production stop stratum closing pressure is 65.2MPa according to the formula (1);
(2) as can be seen from Table 2, the maximum particle size of the proppant used in the X well is 0.45mm, 3 times its particle size is 1.35mm, which is less than 0.19mm of the width of the fracture at 84.9m from the tip of the fracture, so the farthest distance for proppant transport is the tip of the fracture. Determining the sand laying concentration of each characteristic section according to the formula (2) and the formula (3), and obtaining the results shown in the table 2;
(3) testing the flow conductivity of the acid-etched sand-filled fracture under the closing pressure of 65.2MPa within the effective action distance range of the acid-etched fracture by adopting 10 acid-etched rock samples obtained in the step S2 according to the sand laying concentration determined by the experiment; and step S1, testing the flow conductivity of the acid-etched sand-filled crack of the residual acid section by using a pair of unetched rock samples.
And S4, determining the effective joint length of the acid-etched sand-filled fracture according to the flow conductivity distribution of the acid-etched sand-filled fracture and the minimum flow conductivity of the production requirement. And drawing a relation curve of the flow conductivity of the acid-etched sand-filled fracture and the length of the hydraulic fracture according to the flow conductivity of the acid-etched sand-filled fracture, wherein the result is shown in fig. 2. And an abscissa value of 78.0m corresponding to an intersection point (78.0m, 2D-cm) of the relationship curve of the flow conductivity of the acid-etched sand-filled fracture and the length of the hydraulic fracture and the lowest flow conductivity is the effective fracture length of the acid-etched sand-filled fracture of the X well. According to the effective joint length result of the acid-etched sand-filled fracture, the effective joint length of the acid-etched sand-filled fracture is always larger than the effective acting distance of the acid liquid before the X well stops producing, and the fact that the well is effective in acid-etched sand-filled fracturing is shown.
In conclusion, the method can objectively evaluate the diversion capacity of the acid-etched fracture and the length of the acid-etched sand-filled fracture under the in-situ condition; compared with the prior art, the method has remarkable progress.
Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (6)
1. A method for determining an effective joint length of an acid-etched sand-packed fracture under in-situ conditions, comprising the steps of:
s1: acquiring the topography of underground hydraulic fractures of a target reservoir, and preparing a plurality of experimental rock samples with the topography of the underground hydraulic fractures by adopting a fracture surface reconstruction carving technology;
s2: carrying out acid etching hydraulic fracture simulation experiments under different acid etching experimental conditions by using the plurality of experimental rock samples prepared in the step S1 to obtain acid etching morphology under different acid etching experimental conditions;
s3: determining effective closing pressure of a target reservoir and sand laying concentration in the length direction of a hydraulic fracture, testing the flow conductivity of the sand-filled fracture in the hydraulic fracture range under the on-site condition by using a flow guide instrument based on a plurality of experimental rock samples with different acid etching appearances and 1 group of non-etched experimental rock samples obtained in S2, and drawing a relation curve between the flow conductivity of the acid-etched sand-filled fracture and the length of the hydraulic fracture;
s4: and determining the effective joint length of the acid-etched sand-filled fracture from the intersection point of the two curves by combining the flow conductivity curve of the target reservoir which is remained when the production is required to be stopped based on the relation curve of the flow conductivity of the acid-etched sand-filled fracture and the length of the hydraulic fracture drawn in the step S3.
2. The method for determining the effective joint length of the acid-eroded sand-filled fracture under the in-situ condition as claimed in claim 1, wherein the step S1 specifically comprises the following sub-steps: the method comprises the steps of obtaining underground rock samples of a target reservoir of the oil and gas field, obtaining the appearance of the underground hydraulic fracture in a Brazilian splitting mode, and preparing a plurality of experimental rock samples with the appearance of the underground hydraulic fracture by adopting a fracture surface reconstruction carving technology.
3. The method for determining the effective joint length of the acid-eroded sand-filled fracture under the in-situ condition as claimed in claim 1, wherein the step S2 specifically comprises the following sub-steps:
s21: according to the amount of the pre-fracturing fluid injected into the acid fracturing well, simulating the hydraulic fracture expansion process by using an acid fracturing simulator, and determining the geometric size and the temperature distribution of the hydraulic fracture; the hydraulic fracture geometric dimension comprises a hydraulic fracture length, a hydraulic fracture height and a hydraulic fracture width;
s22: according to the acid injection amount of the acid fracturing well, an acid fracturing simulator is adopted to simulate the acid etching hydraulic fracture process, the effective acid etching seam length is determined, and the seam length, the seam height, the seam width and the temperature corresponding to a plurality of different characteristic points are determined by combining the step S21; the different characteristic points refer to a plurality of characteristic positions with different acid liquor concentrations in the crack;
s23: and (4) converting the parameters corresponding to the plurality of feature points determined in the step (S22) into acid etching experimental conditions, developing an acid etching hydraulic fracture simulation experiment by using the plurality of experimental rock samples prepared in the step (S1), and acquiring the acid etching morphology corresponding to each feature point and the increased seam width after acid etching.
4. The method for determining the effective joint length of the acid-eroded sand-filled fracture under the in-situ condition of claim 3, wherein in step S22, the number of the feature points is 10, and 10 of the feature points respectively correspond to 10 feature positions where the acid liquid concentration in the fracture is 100%, 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20% or 10% of the fresh acid mass concentration.
5. The method for determining the effective joint length of an acid-eroded sand-filled fracture under in-situ conditions of claim 1, wherein in step S3, the target reservoir effective closing pressure is calculated by the following formula:
σe＝αH-p (1)
in the formula: sigmaeThe reservoir closing pressure is MPa when the oil-gas well stops production; alpha is the closing pressure gradient, MPa/m; h is the well depth of the target zone, m; and p is the formation pressure in the off-stream of the oil and gas well, and is MPa.
6. The method for determining the effective joint length of the acid-eroded sand-filled fracture under the in-situ condition as claimed in claim 4, wherein in step S3, the sand laying concentration in the hydraulic fracture length direction comprises a sand laying concentration in an acid-eroded effective joint length range and a sand laying concentration in an acid liquid non-effective etching range; wherein, the sand laying concentration in the acid etching effective gap length range is calculated by the following formula:
in the formula: ciThe sand laying concentration is within the range of the effective seam length of the ith characteristic point acid corrosion in kg/m2I ═ 2,3, … …, 10; m is the total proppant amount, Kg, used in the acid fracturing well; w is ai、wi-1The width of the tail end of the hydraulic crack of the ith characteristic point and the i-1 characteristic point is m; l isfIs the hydraulic fracture length, m; l is10The effective acid etching gap is long, m; w is aNIs the width of the end of the hydraulic fracture, m; w is a10Is the effective acid etching gap width, m; h isNThe seam height at the end of the hydraulic fracture is m; h is10The effective seam height of acid etching is m; l isi、Li-1The length of the tail end of the hydraulic crack of the ith characteristic point and the i-1 characteristic point is m; h isi、hi-1The height of the tail end of the hydraulic crack at the ith and the i-1 st characteristic points is m;
the sanding concentration of the 1 st feature point is approximately equal to the sanding concentration of the adjacent feature points, namely C1＝C2；
The sanding concentration in the acid liquid ineffective etching range is calculated by the following formula:
in the formula: cNThe sanding concentration is kg/m in the range of the hydraulic fracture which is not effectively etched by the acid liquor2。
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