A method for determining the controlled reserves of a fractured horizontal well

Abstract

The present application relates to a kind of determination methods of fracturing horizontal well controlled reserves, belong to oil and gas reservoir exploration and development technical field.The determination method of fracturing horizontal well controlled reserves of the present application, comprising the following steps: based on the length of horizontal section of fracturing horizontal well, the angle between horizontal section and maximum horizontal principal stress, limit drainage radius and the half fracture length of fracturing fracture, the area of the region surrounded by the maximum envelope line of fracturing horizontal well seepage field is calculated, and the control area of fracturing horizontal well is obtained;Based on the product of fracturing horizontal well control area, oil layer effective thickness and single storage coefficient, the control reserves of fracturing horizontal well is determined.The determination method of fracturing horizontal well controlled reserves of the present application simplifies single well control area into the maximum drainage area of single well that can control oil layer fluid seepage from the seepage angle, which can effectively simplify the calculation process and improve the calculation efficiency.

Description

Technical Field

[0001] This invention relates to a method for determining controlled reserves in fractured horizontal wells, belonging to the field of oil and gas reservoir exploration and development technology. Background Technology

[0002] Oil and gas reservoir reserves, including geological reserves and recoverable reserves, are crucial for oil and gas reservoir development and deployment. Therefore, determining oil and gas reservoir reserves is a vital task in the exploration and development field. Methods for determining oil and gas reservoir reserves mainly fall into two categories: static methods and dynamic methods. Static methods utilize static geological parameters of the reservoir, calculating reserves based on the volumetric space occupied by oil and gas fluids; this is also known as the volumetric method. Dynamic methods utilize dynamic production parameters that change over time, such as pressure, production rate, and cumulative production, and include methods like the mass balance method, water drive characteristic curve method, production decline method, and predictive model method. Correspondingly, reserves calculated using static methods are geological reserves, representing the reservoir's total reserves; reserves calculated using dynamic methods are dynamic recoverable reserves, representing the size of recoverable reserves under certain technical and economic conditions.

[0003] Controlled reserves in a single well refer to the geological reserves within the controlled fluid flow range of a single well; they can also be called dynamic reserves in a single well. Dynamic reserves are a key indicator in oil and gas reservoir development. Only by determining the size of dynamic reserves can we analyze the reserves that can be utilized for development, and thus understand the development status of the oil and gas reservoir.

[0004] Horizontal well development technology has been widely applied in the development of low-permeability, ultra-low-permeability, and tight oil and gas reservoirs. Studies have found that the orientation of the horizontal section of a horizontal well relative to the sedimentary facies source, as well as the arrangement of natural and artificial fractures, all play a crucial role in controlling the reserves of a single horizontal well. A favorable arrangement can maximize the controlled reserves of a single horizontal well, resulting in maximum production growth. Conversely, a poor arrangement fails to maximize the advantages of horizontal well development, significantly reducing the controlled reserves of a single well, increasing the number of wells drilled, leading to higher drilling costs, and decreasing the rate of production growth. Specifically, if there are no natural or artificial fractures, the horizontal section of the horizontal well is perpendicular to the source direction of the sedimentary facies, resulting in optimal controlled reserves. During production in the horizontal well, oil and gas can seep into the horizontal section along the direction of water flow during deposition. This direction has higher permeability and lower flow resistance than other directions, making it easier to seep into the horizontal section. If natural or artificial fractures exist, the direction of the natural or artificial fractures must be considered first, followed by the direction of the sedimentary source. When the horizontal section of the horizontal well is perpendicular to the extension direction of the natural or artificial fractures (the direction of fracture extension is the direction of the maximum horizontal principal stress), the fracture permeability is good, the flow resistance is minimal, and it is easier to seep into the horizontal section, resulting in the maximum controlled reserves per horizontal well. As the angle between the extension direction of the natural or artificial fractures and the horizontal section decreases, the controlled reserves per horizontal well decrease accordingly. When the extension direction of the natural or artificial fractures is consistent with the extension direction of the horizontal section, the controlled reserves per horizontal well reach their minimum, the oil production is minimal, and the efficiency is worst. Therefore, the use of horizontal well development technology and fracturing technology can significantly increase the controlled reserves of a single well, increase oil production, significantly reduce the number of wells drilled, and lower costs.

[0005] In existing technologies, methods for calculating controlled reserves in horizontal wells generally follow conventional methods for calculating single-well reserves in oil and gas reservoirs, such as the mass balance method and the static volumetric method. The mass balance method assumes that the properties of rocks and fluids remain spatially constant, that fluid flow in porous media reaches instantaneous equilibrium, and that the oil and gas reservoir is uniformly utilized. It calculates production under different formation pressures based on the underground equilibrium of oil and gas volume. This method is suitable for oil and gas reservoirs with good permeability and connectivity, but not for low-permeability reservoirs with strong heterogeneity. The static volumetric method, however, has wide applicability. The key to calculating controlled reserves in fractured horizontal wells using the static volumetric method lies in calculating the controlled area of ​​the horizontal well. Currently, the controlled area of ​​fractured horizontal wells is mainly determined by the following method: using the sum of the length of the horizontal section of the horizontal well and the two ultimate drainage radii as the length, and the sum of the half-fracture lengths of the two fractures and the two ultimate drainage radii as the width, the area of ​​the resulting rectangle is the controlled area of ​​the fractured horizontal well. The result is as follows: Figure 1As shown. However, when calculating the control area, this method assumes that the angle between the principal stress and the horizontal section of the horizontal well is 90°, without considering the case where the angle between the principal stress and the horizontal section of the horizontal well is not 90°, and also without considering the rounded corners of the four corners of the quadrilateral. Therefore, the calculated control area has a large error, resulting in inaccurate calculation results of the controlled reserves of the fractured horizontal well.

[0006] To this end, Chinese patent document CN105243182B discloses a method for calculating the dynamic reserves of a fractured horizontal well for tight oil. The method includes: dividing the fractured horizontal well for tight oil into a first seepage zone and a second seepage zone; dividing the production process of the fractured horizontal well for tight oil into a first stage and a second stage; calculating the first average formation pressure of the first seepage zone at each moment in the first stage, and calculating the second average formation pressure of the first seepage zone and the third average formation pressure of the second seepage zone at each moment in the second stage; determining the dynamic reserves of the first seepage zone in the first stage based on a pre-established material balance equation, as the dynamic reserves of the fractured horizontal well for tight oil in the first stage; determining the dynamic reserves of the first seepage zone and the second seepage zone in the second stage based on the pre-established material balance equation, and superimposing them to determine the dynamic reserves of the fractured horizontal well for tight oil in the second stage.

[0007] Chinese patent document CN113177322A discloses a method for calculating the controlled reserves of a fractured single well, including the following steps: establishing the vertical and lateral configuration patterns of a single sand body, thereby obtaining the vertical and lateral distribution characteristics of the single sand body; further clarifying the fluid seepage characteristics inside different single sand bodies; obtaining the morphological parameters and three-dimensional spatial volume of fractures within the fractured section of a single well; using the sum of the volume V1 of the basic fracture control unit and the seepage volume V2 of the matrix unit as the volume V of the fracture control unit after fracturing a single well; using the grid volume integral method to calculate the controlled reserves within the volume V of the fracture control unit after fracturing a single well, and accumulating them to obtain the final controlled reserves of the fractured single well. The basic fracture control unit volume V1 in this patent document refers to the fracture unit volume, which includes not only the fracture system volume but also the seepage volume of the matrix unit connected to the fracture. The fracture unit volume accounts for a very small proportion of the total control volume of the horizontal well because the fracture width is very narrow, rarely reaching the meter-scale except near the wellbore. Most fractures are only a few centimeters or millimeters / micrometers wide, which is negligible for the control volume of the fractured well. However, fractures can change the seepage conditions, significantly increasing the permeability of the fractures. The matrix volume connected to the fractures is very large, and the controlled reserves of the fractured horizontal well are mainly determined by the matrix unit seepage volume V2. This patent document is based on simulation results using fracturing simulation software under the assumption of a dual-medium model; otherwise, it would be impossible to obtain the grid-connected fracture control unit volume V1 and the grid-connected matrix unit seepage volume V2. Furthermore, this patent document uses the azimuth angle of the fracturing fracture to calculate the controlled reserves of a single fracturing well. However, the azimuth angle only reflects the direction of the fracturing fracture; the patent does not consider the angle between the fracturing fracture and the horizontal section. The calculation of the controlled reserves of a single fracturing well is only related to the angle between the fracturing fracture and the horizontal section, and has nothing to do with the azimuth angle of the individual fracturing fracture. Moreover, the patent's embodiments consider the special case where the angle between the fracturing fracture and the horizontal section is 90 degrees. This angle affects the calculation of the controlled area, leading to a large error in the calculation results. Additionally, the method used in the aforementioned document is computationally complex and inefficient. Summary of the Invention

[0008] The purpose of this invention is to provide a method for determining controlled reserves in fractured horizontal wells, which can solve the problems of complex calculations and low efficiency in current methods for determining controlled reserves in fractured horizontal wells.

[0009] To achieve the above objectives, the technical solution adopted by the method for determining controlled reserves in fractured horizontal wells of the present invention is as follows:

[0010] A method for determining the controlled reserves of a fractured horizontal well includes the following steps: based on the length of the horizontal section of the fractured horizontal well, the angle between the horizontal section and the maximum horizontal principal stress, the ultimate drainage radius, and the half-fracture length of the fracture, the area enclosed by the maximum outer envelope of the seepage field of the fractured horizontal well is calculated to obtain the controlled area of ​​the fractured horizontal well; based on the product of the controlled area of ​​the fractured horizontal well, the effective thickness of the oil layer, and the single reservoir coefficient, the controlled reserves of the fractured horizontal well are determined.

[0011] The method for determining the controlled reserves of fractured horizontal wells in this invention utilizes the "one-sink" principle of seepage mechanics and the seepage principle of the flat plate model to approximate the process of oil and gas seeping from the oil layer to the production well as the process of oil and gas seeping into the wellbore. From the perspective of seepage, the control area of ​​a single well is simplified to the maximum drainage area that a single well can control the seepage of fluids in the oil layer, that is, the area enclosed by the maximum outer envelope of the seepage field of a single well. The static volume method is used to calculate the controlled reserves of the horizontal well, which can effectively simplify the calculation process and improve the calculation efficiency.

[0012] Preferably, the region enclosed by the maximum outer envelope of the seepage field in the fractured horizontal well is a parallelogram with rounded corners. The radius of the rounded corners is equal to the limiting drainage radius. The formulas for calculating the length and width of the quadrilateral are as follows:

[0013]

[0014] Among them, L c L is the length of the quadrilateral, in meters. k α is the width of the quadrilateral, m; r is the ultimate oil leakage radius, m; L1 is the half-fracture length of the pressure fracture, m; L2 is the length of the horizontal section, m; α is the angle between the horizontal section and the maximum horizontal principal stress, °.

[0015] Preferably, the formula for calculating the controlled area of ​​a fractured horizontal well is as follows:

[0016] S = 10 -6 [2(L1 sinα+r)L2+4L1r+πr 2 ]

[0017] In the formula, S represents the area controlled by the horizontal well, in km². 2 ; r is the ultimate oil drainage radius, m; L1 is the half-fracture length of the pressure fracture, m; L2 is the length of the horizontal section, m; α is the angle between the horizontal section and the maximum horizontal principal stress, °.

[0018] Preferably, the formula for calculating the limiting oil leakage radius is as follows:

[0019]

[0020] ΔP=P e -P b ;

[0021] In the formula, r is the limiting drainage radius, m; k is the air permeability of the oil reservoir, mD; μ is the underground viscosity of crude oil, mPa·s; ΔP is the production pressure difference, MPa; P e P represents formation pressure, in MPa; b The bottom hole pressure is in MPa.

[0022] Preferably, the formula for calculating the single-storage coefficient is:

[0023]

[0024] Among them, I is the single-storage coefficient, 10 4 t / (km 2 ·m); For effective porosity, f; S oi The original oil saturation is f; ρ o Density of crude oil at ground level, g / cm³ 3 B oi f is the crude oil volume coefficient.

[0025] In this invention, the half-fracture length of the hydraulic fracture is determined based on the well pattern and well spacing. The half-fracture length is obtained through simulation using hydraulic fracturing design software or by monitoring fractures during fracturing operations. The fracture extension direction is obtained through the direction of the maximum horizontal principal stress and is consistent with the direction of the maximum horizontal principal stress.

[0026] The method for determining controlled reserves in fractured horizontal wells of the present invention is applicable to fractured horizontal wells with an air permeability of 0.1 to 50 mD. Attached Figure Description

[0027] Figure 1 This is a schematic diagram illustrating the method for calculating the controlled area of ​​a fractured horizontal well in this invention.

[0028] Figure 2 This is a schematic diagram of the region enclosed by the outer envelope of the seepage field in this invention;

[0029] Figure 3 This is a schematic diagram illustrating the determination of the length and width of a parallelogram with rounded corners, representing the maximum outer envelope of the seepage field in a fractured horizontal well according to the present invention.

[0030] Figure 4 This is a schematic diagram illustrating the calculation process of the control area in this invention;

[0031] Figure 5 This is a schematic diagram of the region enclosed by the maximum outer envelope of the seepage field when α is 90° in this invention;

[0032] Figure 6 This is a schematic diagram of the region enclosed by the maximum outer envelope of the seepage field when α is 0° in this invention;

[0033] Figure 7 This is a flowchart illustrating the method for determining controlled reserves in horizontal wells according to an embodiment of the present invention. Detailed Implementation

[0034] The method for determining controlled reserves in horizontal wells of this invention is an improved invention. This method addresses the problems of complex calculations and low efficiency in current methods for determining controlled reserves in horizontal wells. It utilizes the "single sink" principle of seepage mechanics and the seepage principle of a flat plate model to approximate the process of oil and gas seeping from the oil layer to the production well as the process of oil and gas seeping into the wellbore. From a seepage perspective, the controlled area of ​​a single well is simplified to the maximum drainage area that a single well can control the seepage of fluids in the oil layer, i.e., the area enclosed by the maximum outer envelope of the seepage field of a single well. The static volumetric method is then used to calculate the controlled reserves of the horizontal well.

[0035] After fracturing a horizontal well, several artificial fractures are formed. The flow field of the fracturing horizontal well is as follows: the flow at the outer end of the fracture approximates an arc with a radius equal to the ultimate drainage radius, and the fluid flow direction is from the arc towards the outer end of the fracture. Between two fractures, the fluid flow direction is from the centerline of the two fractures towards the fracture, similar to seepage in a flat plate model. Fluid flows from the fractures into the horizontal wellbore, and within the wellbore, fluid flows from the bottom to the wellhead. When the fractures are sufficiently dense, the schematic diagram of the region enclosed by the outer envelope of the flow field is shown below. Figure 2 As shown, it is a parallelogram with rounded corners, the radius of which is equal to the limit drainage radius. When a horizontal well is injected with water or fractured, the calculation principle of the horizontal well control area is based on the "one source" principle of seepage mechanics. The "one source" of seepage mechanics refers to the seepage of water into the formation from a single injection well in an infinitely large formation. The direction of fluid flow is opposite to the direction of seepage and the direction of "one confluence". The "one confluence" of seepage mechanics refers to the seepage of fluid from the formation into the production well in an infinitely large formation. The control area of ​​the horizontal well is the area enclosed by the maximum outer envelope of the seepage field. The outer envelope of the seepage field is an equipotential line. During horizontal well production, the pressure near the outer envelope is the formation pressure, and the fluid inside and outside the outer envelope does not flow.

[0036] The region enclosed by the maximum outer envelope of the seepage field in a fractured horizontal well is a parallelogram with rounded corners, as shown below. Figure 3 As shown, the radius of the fillet is equal to the ultimate drainage radius, and the four fillets form a complete circle. The length of the quadrilateral is determined by extending the horizontal segment to the maximum outer envelope, which is equal to the ultimate drainage radius divided by twice the sine of the angle between the horizontal segment and the maximum horizontal principal stress, plus the length of the horizontal segment. The width is determined by extending half the length of the pressure fracture to the maximum outer envelope parallel to the horizontal segment or the extension of the maximum outer envelope parallel to the horizontal segment, which is equal to the ultimate drainage radius divided by twice the sine of the angle between the horizontal segment and the maximum horizontal principal stress, plus twice the half length of the pressure fracture.

[0037] The formulas for calculating the length and width of a quadrilateral are as follows:

[0038]

[0039] Among them, L c L is the length of the quadrilateral, in meters. k α is the width of the quadrilateral, m; r is the ultimate oil leakage radius, m; L1 is the half-fracture length of the pressure fracture, m; L2 is the length of the horizontal section, m; α is the angle between the horizontal section and the maximum horizontal principal stress, °.

[0040] Therefore, from a seepage perspective, the control area of ​​a horizontal well is calculated by considering that the fluid first seeps into the fractures and then into the wellbore. The area enclosed by the maximum envelope of the seepage field after fracturing is calculated using the fracturing parameters of the horizontal well; this is the control area. A schematic diagram of the control area calculation process is shown below. Figure 4 As shown, the area enclosed by the maximum envelope of the seepage field is the superposition of the areas of multiple regions.

[0041] In this invention, the formula for calculating the controlled area of ​​a horizontal well is as follows:

[0042] S = 10 -6 [2(L1sinα+r)L2+4L1r+πr 2 ]

[0043] In the formula, S represents the area controlled by the horizontal well, in km². 2 ; r is the ultimate oil drainage radius, m; L1 is the half-fracture length of the pressure fracture, m; L2 is the length of the horizontal section, m; α is the angle between the horizontal section and the maximum horizontal principal stress, °.

[0044] As can be seen from the formula for calculating the controlled area of ​​a horizontal well, the controlled area gradually decreases as the angle α between the horizontal section and the maximum horizontal principal stress gradually changes from 90° to 0°.

[0045] When α is 90°, the schematic diagram of the region enclosed by the maximum outer envelope of the seepage field is shown below. Figure 5 As shown, it is a rectangle with rounded corners. The radius of the rounded corners is equal to the ultimate drainage radius. The length of the rectangle is equal to the length of the horizontal section plus twice the ultimate drainage radius, and the width is equal to twice the half-fracture length plus twice the ultimate drainage radius. At this point, the horizontal well controls the largest area, calculated using the following formula:

[0046] S_maximum_well_control = 10 -6 (2(L1+r)L2+4L1r+πr 2 )

[0047] In the formula, S 最大井控 For the maximum horizontal well controlled area, km 2; r is the ultimate oil drainage radius, m; L1 is the half-fracture length of the hydraulic fracture, m; L2 is the length of the horizontal section, m.

[0048] When α is 0°, the schematic diagram of the region enclosed by the maximum outer envelope of the seepage field is shown below. Figure 6 As shown, it consists of a rectangle and two semicircles. The width of the rectangle is equal to twice the ultimate drainage radius, and its length is equal to the horizontal section length plus twice the ultimate drainage radius. The radii of the two semicircles are equal to the ultimate drainage radius. At this point, the horizontal well control area is minimized, calculated using the following formula:

[0049] S minimum well control = 10 -6 (2rL2+4L1r+πr 2 )

[0050] In the formula, S 最小井控 Minimum horizontal well control area, km 2 ; r is the ultimate oil drainage radius, m; L1 is the half-fracture length of the hydraulic fracture, m; L2 is the length of the horizontal section, m.

[0051] After calculating the controlled area, the controlled reserves can be obtained by calculation. The calculation method is as follows: the controlled reserves are calculated based on the single reservoir coefficient, the effective thickness of the oil layer and the controlled area of ​​the horizontal well.

[0052] In this invention, the single-reservoir coefficient is the controlled reserve per unit area and unit thickness, that is, the geological reserve contained in a unit oil (gas) area and unit oil (gas) layer thickness. The calculation formula is as follows:

[0053]

[0054] In the formula, I is the single storage coefficient, 10 4 t / (km 2 ·m); For effective porosity, f; S oi The original oil saturation is f; ρ o Density of crude oil at ground level, g / cm³ 3 B oi f is the crude oil volume coefficient.

[0055] The controlled reserves are equal to the product of the single-reservoir coefficient, the effective thickness of the oil layer, and the controlled area of ​​the horizontal well. The calculation formula is as follows:

[0056] N = S × h × I

[0057] In the formula, N represents the controlled reserves, 10 4 t; S represents the area controlled by the horizontal well, in km² 2 I represents the single-storage coefficient, 10 4 t / (km 2 ·m).

[0058] The technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0059] Example

[0060] The method for determining controlled reserves in horizontal wells in this embodiment takes the KP1 fractured horizontal well (where the air permeability k of the KP1 fractured horizontal well reservoir is 0.75 mD) as an example. Figure 7 As shown, the specific steps include:

[0061] (1) Determine the angle α between the horizontal section of the KP1 fracturing horizontal well and the maximum horizontal principal stress.

[0062] The orientation of geostress is closely related to the orientation of wellbore collapse. Elliptical wellbores formed by stress collapse during drilling are usually formed by tangential stress acting on the well wall. The maximum value of tangential stress occurs in the direction of minimum principal stress. Stress collapse is most likely to occur in this direction, resulting in elliptical wellbores. The major axis of the elliptical wellbore is the direction of minimum horizontal principal stress, while its minor axis represents the direction of maximum horizontal principal stress in the formation.

[0063] In this embodiment, based on the formation dip angle logging analysis of KC2 well in the same block and layer adjacent to KP1 well, and considering that the wellbore collapse direction is the direction of minimum principal stress, the wellbore collapse direction of the 3429.5-3461.5m oil layer section of the Ba-2 section of well KC2 is 132°. The analysis shows that the current direction of the maximum horizontal principal stress in the Ba-2 section is 42°. The azimuth angle of the horizontal section extension of the KP1 horizontal well is 122°. The angle α between the horizontal section of the KP1 fractured horizontal well and the maximum horizontal principal stress is 122° - 42° = 80°. Therefore, the angle α between the horizontal section of the KP1 fractured horizontal well and the maximum horizontal principal stress is determined to be 80°.

[0064] (2) Calculate the ultimate drainage radius r of the KP1 fractured horizontal well.

[0065] Based on the KP1 combined logging interpretation method, the air permeability k of the KP1 fractured horizontal well was determined to be 0.75 mD; based on the crude oil analysis results of the same formation wells in the same block, the underground viscosity μ of the crude oil in the KP1 fractured horizontal well was determined to be 0.347 mPa·s; based on the formation pressure test results of adjacent production wells in the same formation in the same block, the formation pressure P of the KP1 fractured horizontal well was determined to be... e The pressure is 36.5 MPa; based on the production situation of adjacent wells, the bottom hole pressure P of the KP1 fracturing horizontal well is determined. b It is 16.9 MPa.

[0066] Calculate the production pressure difference ΔP using the following formula:

[0067] ΔP=P e -P b ;

[0068] In this embodiment, the calculated production pressure difference ΔP is 19.6 MPa.

[0069] Calculate the limiting oil drain radius r using the following formula:

[0070]

[0071] In this embodiment, the calculated limit drainage radius r of the KP1 fractured horizontal well is 100m.

[0072] (3) Determine the half-fracture length L1 of the horizontal well in KP1 fracturing.

[0073] In this embodiment, the half-fracture length L1 of the fracture is obtained by simulating the well pattern and well spacing of the KP1 fractured horizontal well using fracturing design software or by monitoring fractures during fracturing operations. In this embodiment, the half-fracture length L1 of the KP1 fractured horizontal well, determined by fracture monitoring during fracturing operations, is equal to 150m.

[0074] (4) Based on the horizontal section length L2 of the KP1 fractured horizontal well, the angle α between the horizontal section and the maximum horizontal principal stress, the ultimate oil drainage radius r, and the half-fracture length L1 of the fracture, calculate the area of ​​the region enclosed by the maximum outer envelope of the seepage field of the KP1 fractured horizontal well, and obtain the control area S of the KP1 fractured horizontal well.

[0075] In this embodiment, the horizontal section length L2 of the KP1 fractured horizontal well is 900m. The region enclosed by the maximum outer envelope of the KP1 fractured horizontal well's seepage field is a parallelogram with rounded corners. The radius of the rounded corners is equal to the ultimate drainage radius. The four rounded corners form a complete circle. The length of the quadrilateral is determined by extending the horizontal section to the maximum outer envelope, which equals the ultimate drainage radius divided by twice the sine of the angle between the horizontal section and the maximum horizontal principal stress, plus the length of the horizontal section. The width is determined by extending half the fracture length parallel to the maximum outer envelope of the horizontal section or parallel to the extension of the maximum outer envelope of the horizontal section, which equals the ultimate drainage radius divided by twice the sine of the angle between the horizontal section and the maximum horizontal principal stress, plus twice the half fracture length. In this embodiment, the calculation formulas and results for the length and width of the quadrilateral are as follows:

[0076]

[0077] Among them, L c L is the length of the quadrilateral, in meters. k α is the width of the quadrilateral, m; r is the ultimate oil leakage radius, m; L1 is the half-fracture length of the pressure fracture, m; L2 is the length of the horizontal section, m; α is the angle between the horizontal section and the maximum horizontal principal stress, °.

[0078] By performing geometric decomposition calculations on a parallelogram with rounded corners, the formula for calculating the horizontal well control area S is as follows:

[0079] S = 10 -6 [2(L1 sinα+r)L2+4L1r+πr 2 ]

[0080] In the formula, S represents the area controlled by the horizontal well, in km². 2 ; r is the ultimate oil drainage radius, m; L1 is the half-fracture length of the pressure fracture, m; L2 is the length of the horizontal section, m; α is the angle between the horizontal section and the maximum horizontal principal stress, °.

[0081] Substituting the horizontal section length L2 of the KP1 fractured horizontal well, the angle α between the horizontal section and the maximum horizontal principal stress, the ultimate drainage radius r, and the half-fracture length L1 of the fracture into the above formula, the controlled area S of the KP1 fractured horizontal well is calculated to be 0.53731 km². 2 .

[0082] (5) Determine the effective reservoir thickness h and reservoir coefficient I of the KP1 fractured horizontal well.

[0083] The effective thickness of an oil-bearing layer refers to the thickness of an oil-bearing (gas-bearing) layer with industrial oil (gas) production capacity that meets the reserve calculation standards under current economic and technological conditions. It is typically determined through comprehensive logging to obtain a comprehensive logging chart, which is then interpreted in conjunction with logging interpretation charts, considering the relationships between lithology and electrical properties, oil-bearing properties and electrical properties, physical properties and sonic logging, and density logging. In this embodiment, the specific method for determining the effective thickness h of the horizontal oil layer in the KP1 fractured well is as follows: An effective thickness contour map of the horizontal section of the KP1 horizontal well is obtained from adjacent wells, and the thickness is directly read from the contour map; or the length of the effective thickness section is determined through comprehensive interpretation of the comprehensive logging curve of the KP1 well, and then the effective thickness of the horizontal section of the oil layer is obtained through well inclination correction and formation dip correction. In this embodiment, using the effective thickness contour map of the horizontal section of the KP1 horizontal well obtained from KP1 and adjacent wells, the effective thickness h of the KP1 fractured horizontal well, directly read from the effective thickness contour map, is 12m.

[0084] Single storage coefficient I 单储系数 The calculation formula is as follows:

[0085]

[0086] Among them, I is the single-storage coefficient, 10 4 t / (km 2 ·m); For effective porosity, f; S oi The original oil saturation is f; ρ o Density of crude oil at ground level, g / cm³3 B oi f is the crude oil volume coefficient.

[0087] In the formula for calculating the single-storage coefficient I, effective porosity is... The porosity is obtained through comprehensive interpretation of the relationship between physical properties (porosity, permeability) and sonic logging and density logging. In this embodiment, the effective porosity is determined by the following method. By interpreting the sonic transit time of the effective thickness section using a comprehensive well logging combination diagram, the effective porosity is determined based on the relationship between effective porosity and sonic transit time. The initial oil saturation can be obtained through core testing, well logging, or calculation using the Archie formula. In this embodiment, the initial oil saturation is determined by the following methods: the initial water saturation is calculated using the Archie formula, and the initial oil saturation is equal to the difference between 1 and the initial water saturation. The surface crude oil density is obtained through crude oil density testing. The crude oil volume factor is obtained through high-pressure physical property analysis of the crude oil.

[0088] In this embodiment, the single storage coefficient

[0089] (6) Based on the controlled area S of the KP1 fractured horizontal well determined in step (4), the effective thickness h of the KP1 fractured horizontal oil layer and the single reservoir coefficient I determined in step (5) 单储系数 The controlled reserves of the KP1 fractured horizontal well were calculated, and the formula for calculating the controlled reserves is as follows:

[0090] N 井控 =S 井控 ×h×I 单储系数

[0091] Where, N 井控 For the controlled reserves of horizontal wells, 10 4 t;S 井控 The controlled area of ​​the horizontal well, in km² 2 h represents the effective thickness of the oil reservoir, in meters; I is the single reservoir coefficient, 10. 4 t / (km 2 ·m).

[0092] In this embodiment, the calculated controlled reserves of the KP1 fractured horizontal well are 28.2 × 10⁻⁶. 4 t.

[0093] Comparative Example

[0094] This comparative example uses the conventional method for determining controlled reserves in fractured horizontal wells to calculate the controlled reserves of fractured horizontal well KP1. The specific steps are as follows:

[0095] (1) The area of ​​the rectangle formed by the sum of the length of the horizontal section of the horizontal well and the two ultimate drainage radii is the length, and the sum of the half-fracture lengths of the two fractures and the two ultimate drainage radii is the width. This area is the control area of ​​the fractured horizontal well. The parameter values ​​used in the calculation are the same as those in the example. The calculation formula is as follows:

[0096] S1 = 10 -6 (2L1+2r)(L2+2r)=10 -6 (2×150+2×100)(900+2×100)=0.550km 2

[0097] In the formula, S1 represents the controlled area of ​​the fractured horizontal well, in km². 2 r is the ultimate drainage radius, in meters; L1 is the half-fracture length of the hydraulic fracture, in meters; L2 is the length of the horizontal section, in meters.

[0098] (2) The controlled reserves are calculated using the controlled area. The formula for calculating the controlled reserves is as follows:

[0099] N 井控 =S 井控 ×h×I 单储系数 =0.550×12.0×4.3736=28.87×10 4 t

[0100] Where, N 井控 For the controlled reserves of horizontal wells, 10 4 t;S 井控 The controlled area of ​​the horizontal well, in km² 2 h represents the effective thickness of the oil reservoir, in meters; I is the single reservoir coefficient, 10. 4 t / (km 2 ·m).

[0101] The controlled reserves of the KP1 fractured horizontal well calculated in this comparative study are 28.87 × 10⁻⁶. 4 t.

[0102] To evaluate the accuracy of the predicted results of the horizontal well controlled reserves determination methods in the examples and comparative cases, the actual controlled reserves of the KP1 fractured horizontal well were verified according to the well testing method, and the result was 28.1 × 10⁻⁶. 4Therefore, compared to the comparative example, the method for determining the controlled reserves of horizontal wells in this embodiment is closer to the actual controlled reserves. This is mainly because: firstly, the conventional method for determining the controlled reserves of fractured horizontal wells assumes that the angle between the principal stress and the horizontal section of the well is 90° when calculating the controlled area, without considering the case where the angle between the principal stress and the horizontal section of the well is not 90°; secondly, it does not consider the influence of the rounded corners at the four corners of the quadrilateral, thus causing a large error in the calculated controlled area, resulting in inaccurate calculation results for the controlled reserves of conventional fractured horizontal wells. In contrast, this invention comprehensively considers the influence of the angle α between the horizontal section of the fractured horizontal well and the maximum horizontal principal stress, and also considers seepage at the four corner endpoints of the quadrilateral, which is more consistent with actual seepage. The increased number of factors considered improves the calculation accuracy.

Claims

1. A method for determining controlled reserves in a fractured horizontal well, characterized in that, Includes the following steps: Based on the length of the horizontal section of the fractured horizontal well, the angle between the horizontal section and the maximum horizontal principal stress, the ultimate drainage radius, and the half-fracture length of the fracture, the area enclosed by the maximum outer envelope of the seepage field of the fractured horizontal well is calculated to obtain the controlled area of ​​the fractured horizontal well. Based on the product of the controlled area of ​​the fractured horizontal well, the effective thickness of the oil layer, and the single reservoir coefficient, the controlled reserves of the fractured horizontal well are determined.

2. The method for determining controlled reserves in a fractured horizontal well as described in claim 1, characterized in that, The region enclosed by the maximum outer envelope of the seepage field in a fractured horizontal well is a parallelogram with rounded corners. The radius of the rounded corners is equal to the limiting drainage radius. The formulas for calculating the length and width of the quadrilateral are as follows: Among them, L c L is the length of the quadrilateral, in meters (m); k α is the width of the quadrilateral, m; r is the ultimate oil leakage radius, m; L1 is the half-fracture length of the pressure fracture, m; L2 is the length of the horizontal section, m; α is the angle between the horizontal section and the maximum horizontal principal stress, °.

3. The method for determining controlled reserves in a fractured horizontal well as described in claim 2, characterized in that, The formula for calculating the controlled area of ​​a fractured horizontal well is as follows: S=10 -6 [2(L1 sinα+r)L2+4L1r+πr 2 ] In the formula, S represents the area controlled by the horizontal well, in km². 2 ; r is the ultimate oil drainage radius, m; L1 is the half-fracture length of the pressure fracture, m; L2 is the length of the horizontal section, m; α is the angle between the horizontal section and the maximum horizontal principal stress, °.

4. The method for determining controlled reserves in a fractured horizontal well as described in any one of claims 1-3, characterized in that, The formula for calculating the limiting oil drain radius is as follows: ΔP=P e -P b ; In the formula, r is the limiting drainage radius, m; k is the air permeability of the oil reservoir, mD; μ is the underground viscosity of crude oil, mPa·s; ΔP is the production pressure difference, MPa; P e P represents formation pressure, in MPa; b The bottom hole pressure is in MPa.

5. The method for determining controlled reserves in a fractured horizontal well as described in any one of claims 1-3, characterized in that, The formula for calculating the single storage coefficient is: Among them, I is the single-storage coefficient, 10 4 t / (km 2 ·m); For effective porosity, f; S oi The original oil saturation is f; ρ o Density of crude oil at ground level, g / cm³ 3 B oi f is the crude oil volume coefficient.

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