A heterogeneous reservoir acid fracturing reconstruction parameter design method and system

Abstract

The application provides a heterogeneous reservoir acid fracturing parameter design method and system, the method constructs an acidification reconstruction geometric model for a reservoir to be reconstructed, introduces required acidification section length and section thickness data to calculate acid liquid flow rates in fractures under different construction discharge capacities in combination with fracture attribute data, further considers acid etching reaction rates and mass transfer coefficients to calculate acid concentrations on inner walls of fractures reacted with a reservoir matrix, determines etching widths of natural fracture walls according to attribute parameters of the reservoir matrix, further calculates reservoir etching volumes corresponding to different construction acid amounts and acid etching fracture widths and lengths, finally decides corresponding acid etching fracture conductivity capacities according to a correction principle of an N-K model, and selects optimal acid injection parameters according to preset optimization conditions. By using the scheme, the problems of small calculation scales and complicated operations in the prior art are effectively overcome, analytical solutions are flexibly used in the calculation process, and an acid injection scheme with optimal acid etching effects and conductivity capacities is accurately and efficiently selected.

Description

Technical Field

[0001] This invention relates to the field of oil reservoir stimulation and optimization technology, and in particular to a method and system for designing acid fracturing parameters for heterogeneous reservoirs. Background Technology

[0002] Heterogeneous reservoir gas reservoirs are the main battleground for natural gas development, such as carbonate reservoirs. Acidizing is one of the main means to achieve efficient development of such oil and gas reservoirs. Natural fracture systems are the main channels for acid flow, and the acid injection parameters directly affect the flow of acid in natural fractures, thereby affecting the acidizing operation effect and in turn affecting the production of oil and gas wells. Reasonable acid injection parameters are a basic requirement for the effective production of oil and gas wells.

[0003] The optimization design of acid injection parameters relies on acidification models. Previously, most acidification models considered natural fractures as a matrix with better porosity and permeability, treating natural fractures and reservoir matrix as the same medium. However, they ignored the different flow mechanisms of acid in natural fractures and its different characteristics in the matrix. In addition, although some scholars have described the flow behavior of acid in the matrix and natural fractures respectively, thus improving the accuracy of the models, they often suffer from small computational scale and large computational load, making it difficult to calculate the accurate acid injection parameters for acidification stimulation of heterogeneous reservoirs in a simple and efficient manner.

[0004] The information disclosed in the background section of this invention is intended only to enhance the understanding of the general background of this invention, and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] To address the above problems, this invention provides a method for designing acid fracturing parameters for heterogeneous reservoirs. In one embodiment, the method includes:

[0006] Step S1: Construct an acidizing stimulation geometric model for the reservoir to be stimulated, and then combine the geometric model and reservoir fracture attribute data to calculate the acid flow velocity in the fracture under different preset construction discharge conditions by introducing the required acidizing section length and acidizing section thickness data; the reservoir fracture data includes: reservoir fracture density and initial width of natural fractures.

[0007] Step S2: Based on the acid etching reaction rate calculated according to the Arrhenius equation, and combined with the mass transfer coefficient calculated according to the definition of Sherwood number, calculate the acid concentration on the fracture wall of the hydrochloric acid reaction with the reservoir.

[0008] Step S3: Assuming that all the acid that has filtered out from the hydraulic fracture wall into the matrix rock mass participates in the dissolution of the reservoir matrix, calculate the dissolution width of the natural fracture wall based on the acid concentration of the fracture wall and the matrix property parameters.

[0009] Step S4: Using the principle of mass conservation, determine the corresponding reservoir matrix dissolution volume according to different construction acid amounts, and then calculate the acid etching fracture width and acid etching fracture length by combining the reservoir matrix dissolution volume and the geometric model.

[0010] Step S5: Based on the obtained acid-etched fracture width, calculate the conductivity of the acid-etched fracture corresponding to different combinations of construction discharge rate and construction acid quantity according to the correction principle of the NK model. Select the optimal construction acid quantity and construction discharge rate for the current reservoir with the goal of achieving the optimal correlation between acid-etched fracture length and acid-etched fracture conductivity.

[0011] Preferably, in one embodiment, the wellbore direction corresponding to the fracture width direction is taken as the X-axis, the natural fracture extension direction is taken as the Y-axis, and the Z-axis is set perpendicular to the X-axis and Y-axis directions to characterize the acidizing stimulation geometric model of the reservoir to be stimulated in the fracture height direction.

[0012] As a further improvement of the present invention, when deciding on the acidizing section length parameter, the target is to be no less than the sum of the reservoir mud contamination range and the offset coefficient, wherein the offset coefficient is a positive number.

[0013] Furthermore, in one embodiment, in step S1, the acid flow velocity within the crack corresponding to different construction discharge rates is calculated according to the following logic:

[0014]

[0015] In the formula, v is the acid flow velocity within the crack, m / s; V is the corresponding construction discharge rate, m³ / s. 3 / min, where x is the length of the acidification section in m; D x Let m be the crack density. -1 ;w i denoted as the initial width of the natural crack, in meters; h is the thickness of the acidified section, in meters.

[0016] As a further improvement of the present invention, the acid concentration on the fracture wall surface in the reaction of hydrochloric acid with the reservoir is calculated according to the following formula:

[0017]

[0018] in, k g =D e N sh / w i N Sh =4.1 + 1.26N Pe +0.02675N Pe 2 N Pe <20; N Sh =2N Pe N Pe ≥20; NPe =vw i / 2D e ;

[0019] In the formula, c w The acid concentration at the crack wall, in mol / m 3 ;k c The acid etching reaction rate of the acid rock is given by k; k0 is the frequency factor, given by E. a R is the activation energy of acid etching reaction of acid rocks, J / mol; R is the gas constant, J / (K·mol); T w K represents absolute temperature; k represents absolute temperature. g The mass transfer coefficient is N, in m / s. Sh For Sherwood, dimensionless; N Pe D is the Peckley number for mass transfer, dimensionless; v is the acid flow velocity within the fracture, m / s; e For the effective diffusion coefficient, m 2 / s; c is the acid concentration, mol / m 3 ;w i Let be the initial width of the natural crack, in meters (m).

[0020] As a further improvement of the present invention, in one embodiment, in step S3, the dissolution width of the natural crack wall is calculated based on the acid concentration of the crack wall combined with the property parameters of the matrix, according to the following formula:

[0021]

[0022] in, t is the acid injection time, in seconds; Q is the amount of acid used in the process, in meters. 3 V represents the construction displacement in meters. 3 / min, w r β is the dissolution width of the natural fracture wall, in meters; β is the solubility of the acid in the matrix minerals, in kilograms; M is the molar mass of the matrix, in kilograms per mol; c w The acid concentration at the crack wall, in mol / m 3 ;k c The acid etching rate of acid rocks is given in m / s; ρ s The density of the matrix is ​​kg / m³. 3 φ represents matrix porosity, in percentages.

[0023] As a further improvement of the present invention, in step S4, the acid etching crack width and acid etching crack length are calculated according to the following formulas:

[0024] w = w i +w r

[0025]

[0026] In the formula, w is the width of the acid-etched crevices, in meters; w i V is the initial width of the natural crack, in meters; l is the length of the acid-etched crack, in meters; V C The volume of reservoir matrix dissolution is m. 3 h is the thickness of the acidified section, in meters; x is the length of the acidified section, in meters; D x This represents the crack density in the acidized section.

[0027] Furthermore, in one embodiment, in step S5, the conductivity of the acid-etched cracks is calculated according to the following formula:

[0028] wk f =7.797×10 5 w 2.466 e -0.006895σcα

[0029] in,

[0030] In the formula, wk f The equivalent conductivity of the fractured area due to volumetric acid fracturing is represented by D·cm; w is the acid etching fracture width corresponding to the current combination of discharge rate and acid volume; σ c For effective closure stress, MPa; S f denoted as matrix embedding strength, MPa.

[0031] Based on other aspects of the methods described in any one or more of the foregoing embodiments, the present invention also provides a storage medium storing program code that can implement the methods described in any one or more of the foregoing embodiments.

[0032] Based on the application aspects of the methods described in any one or more of the above embodiments, the present invention also provides a system for designing acid fracturing parameters for heterogeneous reservoirs, which performs the methods described in any one or more of the above embodiments.

[0033] Compared with the closest prior art, the present invention also has the following beneficial effects:

[0034] This invention provides a method and system for designing acid fracturing stimulation parameters in heterogeneous reservoirs. The method constructs a geometric model for acid fracturing stimulation of the reservoir to be stimulated, calculates the acid concentration on the fracture inner wall surface due to the reaction rate and mass transfer coefficient of acid-rock acid etching, and then determines the dissolution width of the natural fracture wall surface based on matrix properties. Considering the characteristic of acid changing fracture width on the natural fracture wall surface, the method makes rigorous calculations to determine the degree of fracture inner wall dissolution corresponding to different acid injection parameters, providing a reliable data foundation for subsequent calculations of reservoir matrix dissolution volume and acid-etched fracture width and length corresponding to different acid injection volumes. The analytical solution is flexibly applied during the calculation process to accurately and simply calculate the acid-etched fracture length, width, and conductivity under different acid injection parameters, providing reliable support for achieving acid fracturing stimulation of heterogeneous reservoirs based on reasonable acid injection parameters.

[0035] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims, and drawings. Attached Figure Description

[0036] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0037] Figure 1 This is a flowchart illustrating the method for designing acid fracturing parameters for heterogeneous reservoirs according to an embodiment of the present invention.

[0038] Figure 2 This is an example diagram of the acid fracturing geometric model of the acid fracturing stimulation method for designing parameters of heterogeneous reservoirs provided in this embodiment of the invention;

[0039] Figure 3 This is a schematic diagram of the structure of the acid fracturing stimulation parameter design system for heterogeneous reservoirs provided in an embodiment of the present invention. Detailed Implementation

[0040] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings and examples. Those skilled in the art will then fully understand how the present invention uses technical means to solve technical problems and achieve technical effects, and will be able to implement the present invention specifically based on the above-described implementation process. It should be noted that, as long as there is no conflict, the various embodiments and features of the present invention can be combined with each other, and the resulting technical solutions are all within the protection scope of the present invention.

[0041] Although the flowchart describes the operations as sequential processes, many of these operations can be performed in parallel, concurrently, or simultaneously. The order of the operations can be rearranged. A process can terminate when its operation is complete, but it may also have additional steps not included in the diagram. A process can correspond to a method, function, procedure, subroutine, subroutine, etc.

[0042] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms “a” and “an” as used herein are also intended to include the plural. It should also be understood that the terms “comprising” and / or “including” as used herein specify the presence of the stated features, integers, steps, operations, units, and / or components, without excluding the presence or addition of one or more other features, integers, steps, operations, units, components, and / or combinations thereof.

[0043] Heterogeneous reservoir gas reservoirs are the main focus of current and future natural gas development in China, and acidizing is one of the main methods to achieve efficient development of such reservoirs. Natural fracture systems are the main channels for acid flow, and acid injection parameters directly affect the flow of acid in natural fractures, thus affecting the acidizing operation effect and consequently the production of oil and gas wells. Reasonable acid injection parameters are a basic requirement for the effective production of oil and gas wells.

[0044] The optimization design of acid injection parameters relies on acidification models. Previously, most acidification models considered natural fractures as a matrix with better porosity and permeability, and regarded natural fractures and reservoir rock matrix as the same medium (Zhang Hewen, Zou Honglan, Yan Xuemei, Cui Mingyue, Jiang Weidong. Fractal model of acid etching wormholes in carbonate rocks and optimization of acidification parameters [J]. Journal of Southwest Petroleum University (Natural Science Edition), 2017, 39(02):105-110.). However, the flow mechanism of acid in natural fractures is different from that in the matrix (Zhang Liehui, Li Chengyong, Zhao Yulong, Wu Feng. Research progress on seepage mechanism of fractured carbonate oil and gas reservoirs [J]. Earth Science, 2017, 42(08):1273-1286).

[0045] Currently, many scholars have described the acid flow behavior in the matrix and natural fractures, respectively, and the accuracy of their models has been significantly improved. However, they often suffer from problems such as small computational scale and large computational cost (e.g., Qi Ning, Chen Guobin, Li Zhenliang, Liang Chong, He Long. Numerical simulation of large-scale acidification in fractured carbonate reservoirs based on step-by-step algorithm [J]. Acta Petrolei Sinica, 2020, 41(03):3).

[0046] (48-362+371). Currently, there is a lack of direct and simple methods to optimize acid injection parameters for acidizing heterogeneous carbonate reservoirs.

[0047] To meet the technical needs in this field, this invention provides a method and system for designing acid fracturing parameters for heterogeneous reservoirs. Addressing the current lack of direct and simple methods for optimizing acid injection parameters in heterogeneous reservoirs, this invention uses natural fractures as the flow channels for acid during the acidification process. It considers how the acid changes the fracture width on the fracture walls and uses the modified relationship of the NK model and the mass conservation equation to calculate the acid fracture width, length, and conductivity under different acid volumes and discharge rates. The optimal acid fracture length and conductivity for production needs are then used as indicators to optimize the acid volume and discharge rate.

[0048] The following describes the detailed flow of the method according to an embodiment of the present invention with reference to the accompanying drawings, the steps of which can be executed in a computer system containing, for example, a set of computer-executable instructions. Although the logical order of the steps is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than that shown here.

[0049] Example 1

[0050] Figure 1 This diagram illustrates a flowchart of the method for designing acid fracturing parameters for heterogeneous reservoirs according to Embodiment 1 of the present invention. (Refer to...) Figure 1 As can be seen, the method includes the following steps.

[0051] Step S1: Construct an acidizing stimulation geometric model for the reservoir to be stimulated, and then combine the geometric model and reservoir fracture attribute data to calculate the acid flow velocity in the fracture under different preset construction discharge conditions by introducing the required acidizing section length and acidizing section thickness data; the reservoir fracture data includes: reservoir fracture density and initial width of natural fractures.

[0052] Step S2: Based on the acid rock etching reaction rate calculated according to the Arrhenius equation, and combined with the mass transfer coefficient calculated according to the Sherwood number definition, calculate the acid concentration on the fracture wall of the hydrochloric acid reaction with the reservoir.

[0053] Step S3: Assuming that all the acid that has filtered out from the hydraulic fracture wall into the matrix rock mass participates in the dissolution of the reservoir matrix, calculate the dissolution width of the natural fracture wall based on the acid concentration of the fracture wall and the matrix property parameters.

[0054] Step S4: Using the principle of mass conservation, determine the corresponding reservoir matrix dissolution volume according to different construction acid amounts, and then calculate the acid etching fracture width and acid etching fracture length by combining the reservoir matrix dissolution volume and the geometric model.

[0055] Step S5: Based on the obtained acid-etched fracture width, calculate the conductivity of the acid-etched fracture corresponding to different combinations of construction discharge rate and construction acid quantity according to the correction principle of the NK model. Select the optimal construction acid quantity and construction discharge rate for the current reservoir with the goal of achieving the optimal correlation between acid-etched fracture length and acid-etched fracture conductivity.

[0056] Based on the operational guidelines in the above embodiments, and based on the constructed reservoir acidizing stimulation geometric model, considering the acid erosion on the natural fracture wall changing the fracture width, an analytical solution is used to calculate the acid erosion fracture length, acid erosion fracture width, and conductivity under different acid injection parameters in a relatively accurate and simple way. With the optimal acid erosion fracture length and acid erosion fracture conductivity as the target for production needs, the best matching construction acid quantity and construction discharge volume data are selected to provide support for the acidizing stimulation construction of heterogeneous reservoirs.

[0057] In one optional embodiment, the wellbore direction corresponding to the fracture width direction is used as the X-axis, the natural fracture extension direction is used as the Y-axis, and the Z-axis is set perpendicular to both the X-axis and Y-axis directions to characterize the acidizing stimulation geometry model of the reservoir to be stimulated in the fracture height direction.

[0058] In practical applications, establish such as Figure 2 The geometric model for acidizing and stimulating heterogeneous carbonate reservoirs shown is as follows: X direction is the wellbore direction, corresponding to the fracture width direction; Y direction is the natural fracture extension direction, corresponding to the fracture length direction; Z direction is perpendicular to both the wellbore and the natural fracture extension direction, corresponding to the fracture height direction; x is the length of the acidized section, Dx is the fracture density, wi is the initial width of the natural fracture, and h is the thickness of the acidized section.

[0059] Furthermore, in one embodiment, when deciding on the acidizing section length parameter, the target is to be no less than the sum of the reservoir mud contamination range and the offset coefficient, where the offset coefficient is a positive number.

[0060] Assuming a certain set of construction acid volume Q and construction discharge volume V, the corresponding acid injection time t can be obtained through logical calculation using the following formula:

[0061]

[0062] In the formula, Q represents the amount of acid used during construction, and m 3 V represents the construction displacement in meters. 3 / min, where t is the acid injection time, in seconds.

[0063] Specifically, in one embodiment, in step S1, the acid flow velocity in a single crack corresponding to different construction discharge rates is calculated according to the following logic:

[0064]

[0065] In the formula, v is the acid flow velocity within the crack, m / s; V is the corresponding construction discharge rate, m³ / s. 3 / min, where x is the length of the acidification section in m; D x Let m be the crack density. -1 ;w i denoted as the initial width of the natural crack, in meters; h is the thickness of the acidified section, in meters.

[0066] Next, by carrying out step S2, the acid etching reaction rate of the acid rock is calculated, and then the acid concentration on the fracture wall of the hydrochloric acid reaction with the reservoir is calculated by combining the mass transfer coefficient calculated according to the definition of Sherwood number.

[0067] In one embodiment, the acid etching reaction rate k of acid rocks is calculated according to the Arrhenius equation. c :

[0068]

[0069] Furthermore, based on the laminar flow assumption, the Sherwood number N is calculated using the Navier-Stokes formula. Sh :

[0070]

[0071] Also includes: based on Sherwood number N Sh Definition principle for calculating mass transfer coefficient k g :

[0072] k g =D e N sh / w i (5)

[0073] Therefore, based on boundary layer theory, assuming that the reaction between hydrochloric acid and the heterogeneous reservoir to be modified is a first-order reaction, in one embodiment, in step S2, the acid concentration at the fracture wall surface of the hydrochloric acid reaction with the reservoir can be calculated according to the following formula:

[0074]

[0075] in, k g =D e N sh / w i N Sh =4.1 + 1.26N Pe +0.02675N Pe 2 N Pe <20; N Sh =2N Pe N Pe ≥20; N Pe =vw i / 2D e ;

[0076] In the formula, c w The acid concentration at the crack wall, in mol / m 3 ;k c The acid etching reaction rate of the acid rock is given by k; k0 is the frequency factor, given by E. a R is the activation energy of acid etching reaction of acid rocks, J / mol; R is the gas constant, J / (K·mol); T w K represents absolute temperature; k represents absolute temperature. g The mass transfer coefficient is N, in m / s. Sh For Sherwood, dimensionless; N Pe D is the mass transfer Peckley number, dimensionless; e For the effective diffusion coefficient, m 2 / s; c is the acid concentration, mol / m 3 ;w i Let be the initial width of the natural crack, in meters (m).

[0077] Furthermore, assuming that all the acid that filters out from the hydraulic fracture wall into the matrix rock participates in dissolving the reservoir matrix and forming acid wormholes, but does not participate in dissolving the hydraulic fracture wall, in step S3, the dissolution width of the natural fracture wall is calculated based on the acid concentration at the fracture wall and the matrix property parameters according to the following logic:

[0078]

[0079] in, t represents the acid injection time, in seconds; w r β is the dissolution width of the natural fracture wall, in meters; β is the dissolution capacity of the acid on the reservoir matrix minerals, in kilograms; M is the molar mass of the matrix, in kilograms per mol; c w The acid concentration at the crack wall, in mol / m 3 ;k c The acid etching rate of acid rocks is given in m / s; ρ s The density of the matrix is ​​kg / m³. 3 φ represents matrix porosity, in percentages.

[0080] Next, by executing step S4, the corresponding reservoir matrix dissolution volume is determined according to the different construction acid amounts based on the principle of mass conservation. Then, the acid etching fracture width and acid etching fracture length are calculated by combining the reservoir matrix dissolution volume and the geometric model.

[0081] Specifically, based on the law of conservation of mass, assuming that all the acid participates in the dissolution of the modified reservoir matrix, then the injected acid volume V HCl The volume of reservoir matrix dissolution V can be calculated. C :

[0082]

[0083] In the formula, V C The volume of reservoir matrix dissolution is m. 3 ;wt HCl The mass concentration of hydrochloric acid is expressed as %; ρ HCl The density of hydrochloric acid is expressed in g / cm³. 3 V HCl For the amount of acid used in construction, m 3 M C M is the molar mass of the reservoir matrix, in g / mol; HCl ρ is the molar mass of hydrochloric acid, in g / mol; C The density of calcium carbonate, in g / cm³ 3 .

[0084] Furthermore, the width of the acid-etched fracture decreases along its length. Assuming the acid-etched fracture is wedge-shaped, in one embodiment, in step S4, based on the reservoir matrix dissolution volume V... C Combined with the acidizing stimulation model of heterogeneous carbonate reservoirs, and the dissolution width w obtained in step S3 above, r Calculate the width and length of the acid-etched cracks using the following formulas:

[0085] w = w i +w r (9)

[0086]

[0087] In the formula, w is the width of the acid-etched crevices, in meters; w i V is the initial width of the natural crack, in meters; l is the length of the acid-etched crack, in meters; V C The volume of reservoir matrix dissolution is m. 3 h is the thickness of the acidified section, in meters; x is the length of the acidified section, in meters; D x This represents the crack density in the acidized section.

[0088] Furthermore, in step S5, the conductivity of the acid-etched fracture corresponding to different combinations of construction discharge rate and construction acid quantity is calculated according to the correction principle of the NK model based on the obtained acid-etched fracture width. The optimal construction acid quantity and construction discharge rate of the current reservoir are selected with the goal of achieving the optimal correlation between the acid-etched fracture length and the acid-etched fracture conductivity.

[0089] Specifically, in one embodiment, in step S5, the conductivity of the acid-etched crack is calculated from the acid-etched crack width w corresponding to each crack length according to the following formula:

[0090] wk f =7.797×10 5 w 2.466 e -0.006895σcα (11)

[0091] in,

[0092] In the formula, wk f The equivalent conductivity of the fractured area due to volumetric acid fracturing is represented by D·cm; w is the acid etching fracture width corresponding to the current combination of discharge rate and acid volume; σ c For effective closure stress, MPa; α is used as an intermediate calculation factor; S f denoted as matrix embedding strength, MPa.

[0093] Based on the calculated data, with the goal of optimizing the correlation between acid etching fracture length and acid etching fracture conductivity, the optimal acid etching amount and discharge rate for the current reservoir were selected from multiple sets of construction acid amount and construction discharge rate.

[0094] In practical applications, multiple sets of construction acid quantity Q and construction discharge rate V can be pre-set and calculated simultaneously; or, after calculation based on a certain set of construction acid quantity data or construction discharge rate data, the construction acid quantity Q and construction discharge rate V can be further optimized and changed based on the calculation results. The above steps S1 to S5 are repeated to analyze the acid etching fracture width w, acid etching fracture length l, and acid etching fracture conductivity wk under different acid injection parameters in the acidizing construction of heterogeneous reservoirs. f Based on the optimal acid etching fracture length l and the acid etching fracture conductivity wk according to production requirements f The corresponding optimal acid injection quantity Q and the corresponding acid injection rate V are obtained and used as the target acid injection parameters for the current reservoir.

[0095] Implementation Case:

[0096] Taking a heterogeneous carbonate reservoir in a well area with known acidized section length and fracture properties as an example, the acid injection parameters for acidizing stimulation operations are designed through the following steps:

[0097] S1. Assuming the acidized section length x is 20m, and the natural fracture density D... x 0.5m -1 The initial width of the natural crack w i The thickness is 0.5mm, the acidification section thickness h is 40m, and the acid quantity Q is 400m³. 3 The construction displacement V is 2m. 3 / min, the acid injection time t is 12000s.

[0098] S2. The acid etching reaction rate k of the acid rock was calculated. c It is 8.06×10 -7 m / s, mass transfer coefficient k g The velocity is 0.1667 m / s, and the erosion width is w. r It is 0.0158m.

[0099] S3. The calculated acid etching groove width w is 0.0163m and the acid etching groove length l is 13.03m.

[0100] S4. Calculate the conductivity wk of the acid-etched cracks. f It is 1.30D·cm.

[0101] S5. By changing the amount of acid used in the construction and the flow rate, the morphology and conductivity of the acid-etched cracks under different acid injection parameters were obtained. The results are shown in the table below.

[0102] <![CDATA[Construction displacement, m 3 / min]]> 2 4 2 4 2 4 2 4 The acidification section is long, m 20 20 20 20 20 20 20 20 <![CDATA[Fracture density, m -1 > 0.5 0.5 0.5 0.5 1 1 1 1 Dissolution width, m 0.0158 0.0079 0.0079 0.0039 0.0158 0.0079 0.0079 0.0039 Acid etching crevices width, m 0.0163 0.0084 0.0084 0.0044 0.0163 0.0084 0.0084 0.0044 The length of the acid-etched crevices is m. 13.03 26.06 13.03 26.06 6.52 13.03 6.52 13.03 Conductivity of acid-etched cracks, D·cm 1.30 0.24 0.24 0.04 1.30 0.24 0.24 0.04

[0103] Based on the well data, the mud contamination range is 10m. To eliminate mud contamination, the acid-etched fracture length must be greater than 10m. Simultaneously, the acid dosage and discharge rate during acidizing should be optimized to achieve high conductivity, especially for fractures with a fracture density of 0.5m³. -1 For reservoirs, a construction acid volume of 400m³ is recommended. 3 Construction discharge volume 2m 3 / min; for a crack density of 1m -1 For reservoirs, a construction acid volume of 400m³ is recommended. 3 Construction discharge volume 4m 3 / min.

[0104] Compared with existing technologies, the acid injection parameter design scheme for acidizing stimulation provided by the above embodiments of the present invention can overcome the problems of small computational scale and complex process in existing acid injection parameter decision-making methods that describe and calculate the acid flow behavior in the matrix and natural fractures separately. The present invention is based on an acidizing stimulation geometric model constructed around the distribution of reservoir fractures, considering the change of fracture width by acid on the natural fracture wall, and uses the correction relationship of the NK model and the mass conservation equation to calculate the acid-etched fracture width, acid-etched fracture length and acid-etched fracture conductivity under different construction acid quantities and construction discharge rates. The construction acid quantity and construction discharge rate are optimized with the optimal acid-etched fracture length and acid-etched fracture conductivity for production needs as indicators. The analytical solution is flexibly used in the calculation process to calculate the acid-etched fracture length, acid-etched fracture width and conductivity under different acid injection parameters in a relatively accurate and simple way, providing reliable support for the acidizing stimulation of heterogeneous carbonate reservoirs based on reasonable acid injection parameters.

[0105] For the foregoing method embodiments, in order to simplify the description, they are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, because according to the present invention, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0106] It should be noted that, in other embodiments of the present invention, the method can also combine one or more of the above embodiments to obtain a new method for designing acid injection parameters for reservoir acidizing stimulation, so as to optimize the stimulation of heterogeneous well reservoirs and reservoir development.

[0107] It should be noted that, based on the methods in any one or more embodiments of the present invention described above, the present invention also provides a storage medium storing program code that can implement the methods described in any one or more embodiments. When the program code is executed by the operating system, it can implement the above-described method for designing parameters for acid fracturing stimulation of heterogeneous reservoirs.

[0108] Example 2

[0109] The methods described in detail in the above-disclosed embodiments of the present invention can be implemented using various forms of devices or systems. Therefore, based on other aspects of the methods described in any one or more of the above embodiments, the present invention also provides a system for designing acid fracturing parameters for heterogeneous reservoirs. This system is used to execute the method for designing acid fracturing parameters for heterogeneous reservoirs described in any one or more of the above embodiments. Specific embodiments are given below for detailed description.

[0110] Specifically, Figure 3 The diagram shows a schematic of the design system for acid fracturing parameters of heterogeneous reservoirs provided in an embodiment of the present invention. Figure 3 As shown, the system includes:

[0111] The modeling and basic calculation module is configured to construct an acidizing stimulation geometric model for the reservoir to be stimulated, and then combine the geometric model and reservoir fracture attribute data to calculate the acid flow velocity in the fracture under different preset construction discharge conditions by introducing the required acidizing section length and acidizing section thickness data; the reservoir fracture data includes: the fracture density of the reservoir and the initial width of the natural fractures.

[0112] The fracture wall acid concentration calculation module is configured to calculate the fracture wall acid concentration of the reservoir to be modified based on the acid rock acid etching reaction rate calculated according to the Arrhenius equation and the mass transfer coefficient calculated according to the Sherwood number definition.

[0113] The fracture wall acid etching determination module is configured to assume that all the acid that filters out from the hydraulic fracture wall and enters the matrix rock mass participates in dissolving the reservoir matrix, and calculates the dissolution width of the natural fracture wall based on the acid concentration of the fracture wall and the property parameters of the matrix.

[0114] The acid etching result analysis module is configured to determine the corresponding reservoir matrix dissolution volume according to different construction acid amounts based on the principle of mass conservation, and then calculate the acid etching width and acid etching length of the acid etching cracks by combining the reservoir matrix dissolution volume and the geometric model.

[0115] The acid injection scheme optimization module is configured to calculate the acid fracture conductivity corresponding to different combinations of construction discharge rate and construction acid quantity based on the obtained acid fracture width and the correction principle of the NK model, and select the optimal construction acid quantity and construction discharge rate for the current reservoir with the goal of achieving the optimal correlation between acid fracture length and acid fracture conductivity.

[0116] In one optional embodiment, the modeling and basic calculation module is further configured as follows: the wellbore direction corresponding to the fracture width direction is used as the X-axis, the natural fracture extension direction is used as the Y-axis, and the Z-axis is set perpendicular to both the X-axis and Y-axis directions to characterize the acidizing stimulation geometric model of the reservoir to be stimulated in the fracture height direction.

[0117] Specifically, in one embodiment, when the modeling and basic calculation module decides on the acidization section length parameter, it aims to be no less than the sum of the reservoir mud contamination range and the offset coefficient, where the offset coefficient is a positive number.

[0118] Furthermore, in one embodiment, the modeling and basic calculation module is configured to calculate the acid flow velocity within the crack corresponding to different construction discharge rates according to the following logic:

[0119]

[0120] In the formula, v is the acid flow velocity within the crack, m / s; V is the corresponding construction discharge rate, m³ / s. 3 / min, where x is the length of the acidification section in m; D x Let m be the crack density. -1 ;w i denoted as the initial width of the natural crack, in meters; h is the thickness of the acidified section, in meters.

[0121] In a preferred embodiment, the fracture wall acid concentration calculation module calculates the fracture wall acid concentration resulting from the reaction of hydrochloric acid with the reservoir according to the following formula:

[0122]

[0123] in, k g =D e N sh / w i N Sh =4.1 + 1.26N Pe +0.02675N Pe 2 NPe <20; N Sh =2N Pe N Pe ≥20; N Pe =vw i / 2D e ;

[0124] In the formula, c w The acid concentration at the crack wall, in mol / m 3 ;k c The acid etching reaction rate of the acid rock is given by k; k0 is the frequency factor, given by E. a R is the activation energy of acid etching reaction of acid rocks, J / mol; R is the gas constant, J / (K·mol); T w K represents absolute temperature; k represents absolute temperature. g The mass transfer coefficient is N, in m / s. Sh For Sherwood, dimensionless; N Pe D is the mass transfer Peckley number, dimensionless; e For the effective diffusion coefficient, m 2 / s; c is the acid concentration, mol / m 3 ;w i Let be the initial width of the natural crack, in meters (m).

[0125] Specifically, in one embodiment, the fracture wall acid etching determination module calculates the dissolution width of the natural fracture wall based on the acid concentration of the fracture wall combined with the matrix property parameters according to the following logic:

[0126]

[0127] in, t is the acid injection time, in seconds; Q is the amount of acid used in the process, in meters. 3 V represents the construction displacement in meters. 3 / min, w r ρ is the dissolution width of the natural fracture wall, in meters; β is the dissolving power of the acid on the matrix minerals, in kilograms; M is the molar mass of the matrix, in kilograms per mol; ρ s The density of the matrix is ​​kg / m³. 3 φ represents matrix porosity, in percentages.

[0128] Furthermore, in one embodiment, the acid etching result analysis module calculates the acid etching crack width and acid etching crack length according to the following formulas:

[0129] w = w i +w r

[0130]

[0131] In the formula, w is the width of the acid-etched crevices, in meters; w i V is the initial width of the natural crack, in meters; l is the length of the acid-etched crack, in meters; V C The volume of reservoir matrix dissolution is m. 3 h is the thickness of the acidified section, in meters; x is the length of the acidified section, in meters; D x This represents the crack density in the acidized section.

[0132] In a preferred embodiment, the acid injection scheme optimization module is configured to calculate the conductivity of the acid-etched cracks according to the following formula:

[0133] wk f =7.797×10 5 w 2.466 e -0.006895σcα

[0134] in,

[0135] In the formula, wk f The equivalent conductivity of the fractured area due to volumetric acid fracturing is represented by D·cm; w is the acid etching fracture width corresponding to the current combination of discharge rate and acid volume; σ c For effective closure stress, MPa; S f denoted as matrix embedding strength, MPa.

[0136] Furthermore, based on the calculated data, with the goal of optimizing the correlation between acid etching fracture length and acid etching fracture conductivity, the optimal acid etching amount and discharge rate for the current reservoir were selected from multiple sets of construction acid amount and construction discharge rate.

[0137] In practical applications, multiple sets of construction acid volume Q and construction discharge volume V can be pre-set and calculated simultaneously; or, after calculation based on a certain set of construction acid volume data or construction discharge volume data, the construction acid volume Q and construction discharge volume V can be further optimized and changed based on the calculation results. The above steps S1 to S5 are repeated to analyze the acid fracture width w, acid fracture length l, and acid fracture conductivity wk under different acid injection parameters in the acidizing construction of carbonate reservoirs. f Based on the optimal acid etching fracture length l and the acid etching fracture conductivity wk according to production requirements f The corresponding optimal acid injection quantity Q and the corresponding acid injection rate V are obtained and used as the target acid injection parameters for the current reservoir.

[0138] In the heterogeneous reservoir acid fracturing stimulation parameter design system provided in this embodiment of the invention, each module or unit structure can operate independently or in combination according to actual design requirements and optimization calculation requirements to achieve the corresponding technical effects.

[0139] It should be understood that the embodiments disclosed herein are not limited to the specific structures, processing steps, or materials disclosed herein, but should be extended to equivalent substitutions of these features as understood by those skilled in the art. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

[0140] The phrase "an embodiment" in the specification means that a specific feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Therefore, the phrase "an embodiment" appearing in various places throughout the specification does not necessarily refer to the same embodiment.

[0141] While the embodiments disclosed in this invention are as described above, the content is merely for the purpose of facilitating understanding of the invention and is not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in form and detail of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A method for designing parameters for acid fracturing stimulation of heterogeneous reservoirs, characterized in that, The method includes: Step S1: Construct an acidizing stimulation geometric model for the reservoir to be stimulated, and then combine the geometric model and reservoir fracture attribute data to calculate the acid flow velocity in the fracture under different preset construction flow rates by introducing the required acidizing section length and acidizing section thickness data; the reservoir fracture attribute data includes: reservoir fracture density and initial width of natural fractures. Step S2: Based on the acid etching reaction rate calculated according to the Arrhenius equation, and combined with the mass transfer coefficient calculated according to the definition of Sherwood number, calculate the acid concentration on the fracture wall of the hydrochloric acid reaction with the reservoir. Step S3: Assuming that all the acid that has filtered out from the hydraulic fracture wall into the matrix rock mass participates in the dissolution of the reservoir matrix, calculate the dissolution width of the natural fracture wall based on the acid concentration of the fracture wall and the matrix property parameters. Step S4: Using the principle of mass conservation, determine the corresponding reservoir dissolution volume according to different construction acid amounts, and then calculate the acid etching fracture width and acid etching fracture length by combining the reservoir dissolution volume and the geometric model. Step S5: Based on the obtained acid-etched fracture width, calculate the acid-etched fracture conductivity corresponding to different combinations of construction discharge rate and construction acid quantity according to the correction principle of the NK model. Select the optimal construction acid quantity and construction discharge rate for the current reservoir with the goal of achieving the optimal correlation between acid-etched fracture length and acid-etched fracture conductivity. In step S5, the conductivity of the acid-etched cracks is calculated according to the following formula: in, In the formula, wk f The volumetric acid fracturing equivalent modification of the fracture conductivity, D·cm; w This refers to the acid etching width corresponding to the current combination of construction discharge rate and construction acid volume. For effective closure stress, MPa ; As an intermediate operation factor; For reservoir matrix embedding strength, MPa .

2. The method according to claim 1, characterized in that, The wellbore direction corresponding to the fracture width is used as the X-axis, the natural fracture extension direction is used as the Y-axis, and the Z-axis is set perpendicular to both the X-axis and Y-axis directions to characterize the acidizing stimulation geometric model of the reservoir to be stimulated in the fracture height direction.

3. The method according to claim 1, characterized in that, When determining the acidizing section length parameter, the target is to make it no less than the sum of the reservoir mud contamination range and the offset coefficient, where the offset coefficient is a positive number.

4. The method according to claim 1, characterized in that, In step S1, the acid flow velocity within the crack corresponding to different construction discharge rates is calculated according to the following logic: In the formula, v The velocity of the acid within the crack is , in m / s; V For the corresponding construction displacement, m 3 / min, x The length of the acidification section is m; D x Let m be the crack density. -1 ; w i Let be the initial width of the natural crack, in meters. h The thickness of the acidification section is m.

5. The method according to claim 1, characterized in that, In step S2, the acid concentration on the fracture wall surface after the hydrochloric acid reacts with the reservoir is calculated according to the following formula: in, ; ; ; ; ; In the formula, c w The acid concentration at the crack wall, in mol / m 3 ; k c The acid etching reaction rate is expressed in m / s. k 0 represents the frequency factor, in m / s; E a R is the activation energy of the acid etching reaction, J / mol; R is the gas constant, J / (K·mol); T w K represents absolute temperature. k g The mass transfer coefficient is given in m / s. N Sh For Sherwood, there is no dimension; N Pe For mass transfer Peckley number, dimensionless; v The velocity of the acid within the crack is , in m / s; D e For the effective diffusion coefficient, m 2 / s; c The concentration of the acid solution is mol / m³. 3 ; w i Let be the initial width of the natural crack, in meters (m).

6. The method according to claim 1, characterized in that, In step S3, the dissolution width of the natural crack wall is calculated based on the acid concentration of the crack wall and the property parameters of the matrix, according to the following logic: in, ; t The acid injection time is in seconds; where, Q For the amount of acid used in construction, m 3 ; V For construction displacement, m 3 / min, w r The width of the dissolution along the natural crack wall, in meters (m). β The acid solution has the solubility for the reservoir matrix minerals, in kg / kg; M is the molar mass of the reservoir matrix, in kg / mol. c w The acid concentration at the crack wall, in mol / m 3 ; k c The acid etching reaction rate is expressed in m / s. ρ s The density of the reservoir matrix is ​​kg / m³. 3 ; φ The reservoir matrix porosity is expressed as %.

7. The method according to claim 1, characterized in that, In step S4, the width and length of the acid-etched cracks are calculated according to the following formulas: In the formula, w The width of the acid-etched crevices is in meters (m). w i Let be the initial width of the natural crack, in meters. w r The width of the dissolution along the natural crack wall, in meters (m). l The length of the acid-etched crevices is in meters (m). The volume of reservoir matrix dissolution is m. 3 ; h Thickness of the acidification section, m; x The length of the acidification section is in meters (m). D x This represents the crack density in the acidized section.

8. A storage medium, characterized in that, The storage medium stores program code capable of implementing the method as described in any one of claims 1 to 7.

9. A parameter design system for acid fracturing stimulation of heterogeneous reservoirs, characterized in that, The system performs the method as described in any one of claims 1 to 7.

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