A method for determining open flow and production allocation in tight carbonate reservoirs

Abstract

The present invention belongs to the field of gas field technology, and specifically relates to a method for determining the unimpeded flow and production allocation of a dense carbonate reservoir. The unimpeded flow determination method first obtains the residual thickness of the dense carbonate reservoir, the thickness of the dolomite reservoir, the photoelectric absorption cross-sectional index, and the structural curvature of the factors related to the unimpeded flow model, and then substitutes them into the unimpeded flow model to obtain the unimpeded flow of the dense carbonate reservoir; and the unimpeded flow model is constructed based on the relationship between the unimpeded flow and at least two factors of the residual thickness, the dolomite reservoir thickness, the photoelectric absorption cross-sectional index, and the structural curvature, and the dolomite reservoir thickness and the structural curvature are both positively correlated with the unimpeded flow, and the residual thickness and the photoelectric absorption cross-sectional index are both negatively correlated with the unimpeded flow. The present invention uses the established unimpeded model to obtain the unimpeded flow, the method is simple, the calculation result is highly accurate, the prediction accuracy of the production capacity is high, and the development effect of the gas well is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of gas reservoir development research, and in particular relates to a method for determining the open flow rate and production allocation of a dense carbonate reservoir. Background Art

[0002] Gas well productivity is an important basis for rationally allocating gas well production and evaluating gas field production capacity. The reliability of the evaluation results is directly related to whether the gas field can achieve safe and stable production. Currently, the commonly used methods for determining gas well productivity can be divided into six categories, namely, the open flow method, the gas production indicator curve method, the production dynamic analysis method, the numerical simulation method, the empirical analogy method and the productivity determination method of special gas wells.

[0003] At present, in the early stage of gas field production, a single-point empirical formula is often used to calculate the unimpeded flow rate of the gas well, that is, a method of determining the gas well capacity by combining the gas well capacity equation and using a single-point stable flow test data.

[0004] The commonly used method in the prior art is based on seepage mechanics and gas reservoir engineering methods. It regards the reservoir as a uniformly distributed reservoir, and corresponds the porosity, permeability and other parameters of the reservoir to a numerical value to calculate the open flow rate. It is suitable for reservoirs with homogeneous single-pore media and does not consider the geological conditions of the reservoir. For dual-media reservoirs, such as carbonate gas reservoirs with developed fractures, the heterogeneity is strong and the gas content varies greatly. The above method is no longer applicable, and the prediction results of the open flow rate are inaccurate. Summary of the invention

[0005] The invention provides a method for determining the open flow rate and production allocation of a dense carbonate reservoir, so as to solve the problem that the open flow rate prediction method in the prior art is inaccurate.

[0006] In order to solve the above technical problems, the technical solutions and corresponding beneficial effects of the present invention are as follows:

[0007] The present invention provides a method for determining the open flow rate of a tight carbonate reservoir, comprising the following steps:

[0008] Obtain the factors related to the open flow model in the residual thickness of the tight carbonate reservoir, the thickness of the dolomite reservoir, the photoelectric absorption cross-section index and the structural curvature, and substitute them into the open flow model to obtain the open flow of the tight carbonate reservoir;

[0009] Among them, the unimpeded flow model is constructed based on the relationship between at least two factors of residual thickness, dolomite reservoir thickness, photoelectric absorption cross-section index and structural curvature and the unimpeded flow, and the dolomite reservoir thickness and structural curvature are both positively correlated with the unimpeded flow, and the residual thickness and photoelectric absorption cross-section index are both negatively correlated with the unimpeded flow.

[0010] The beneficial effects of the above technical solution are as follows: the present invention fully considers the main controlling factors affecting the high yield of gas reservoirs, including at least two factors of residual thickness, dolomite reservoir thickness, photoelectric absorption cross-section index and structural curvature, and constructs an unobstructed flow model with strong adaptability and more practical. The unobstructed flow is obtained by using the unobstructed model. The method is simple and the calculation results are highly accurate. It is suitable for dual-medium gas reservoirs, has high prediction accuracy for production capacity, and ensures the development effect of gas wells.

[0011] As a further improvement of the open-flow rate determination method, in order to simply and quickly calculate the open-flow rate model, the open-flow rate model is constructed using a linear multiple regression method.

[0012] As a further improvement of the method for determining the open flow rate, the open flow rate model is constructed based on the relationship between the residual thickness, dolomite reservoir thickness, photoelectric absorption cross-section index and structural curvature and the open flow rate, and the open flow rate is:

[0013]

[0014] In the formula, Q AOF is the unobstructed flow, H1 is the residual thickness, H2 is the dolomite reservoir thickness, Pe is the photoelectric absorption cross-section index, γ is the structural curvature, k1, k2, k3, k4, k5, k6 are all set coefficients, and are all greater than 0, and x1 is a set constant.

[0015] As a further improvement to the method for determining the open-flow rate, x1=-13.0936, k1=17.4923, k2=1.043, k3=6.0316, k4=2.0439, k5=0.012, k6=0.1396.

[0016] The present invention provides a method for determining production allocation based on open flow for a tight carbonate reservoir, comprising the following steps:

[0017] Obtain factors related to the open-flow flow model from the residual thickness of the tight carbonate reservoir, the thickness of the dolomite reservoir, the photoelectric absorption cross-sectional index and the structural curvature, and substitute them into the open-flow flow model to obtain the open-flow flow of the tight carbonate reservoir; wherein the open-flow flow model is constructed based on the relationship between the open-flow flow and at least two factors of the residual thickness, the thickness of the dolomite reservoir, the photoelectric absorption cross-sectional index and the structural curvature, and the dolomite reservoir thickness and the structural curvature are both positively correlated with the open-flow flow, and the residual thickness and the photoelectric absorption cross-sectional index are both negatively correlated with the open-flow flow; determine the degree of fracture development; determine the production allocation coefficient based on the degree of fracture development and the open-flow flow; determine the production allocation based on the production allocation coefficient.

[0018] The beneficial effects of the above technical solution are as follows: the present invention fully considers the main controlling factors affecting the high yield of gas reservoirs, including at least two factors of residual thickness, dolomite reservoir thickness, photoelectric absorption cross-section index and structural curvature, and constructs an unobstructed flow model with strong adaptability and more practical. The unobstructed flow is obtained by using the unobstructed model, and production is further differentiated for different reservoir types according to the degree of fracture development, thereby improving the pertinence and rationality of production allocation, having a good value for promotion and use, and effectively ensuring the development effect of gas wells.

[0019] As a further improvement of the production allocation determination method, in order to accurately determine the degree of fracture development, the degree of fracture development is determined based on the structural curvature and the fracturing operation curve.

[0020] As a further improvement of the production allocation determination method, in order to consider the impact of the development degree on production capacity to improve the rationality and pertinence of the production allocation, the crack development degree is crack development or crack underdevelopment; if the cracks are developed, the production allocation coefficient is related to the open flow rate, and the larger the open flow rate, the smaller the production allocation coefficient.

[0021] As a further improvement of the production allocation determination method, if cracks are developed: when the open flow rate is greater than the first set value and less than the second set value, the production allocation coefficient is 1 / 5-1 / 8; when the open flow rate is greater than or equal to the second set value, the production allocation coefficient is 1 / 8-1 / 10; if cracks are not developed, the production allocation coefficient is 1 / 3; the first set value is less than the second set value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1-1 is a graph showing the relationship between the unimpeded flow rate and the residual thickness of the present invention;

[0023] Figure 1-2 is a relationship diagram between the unimpeded flow rate and the thickness of the dolomite reservoir of the present invention;

[0024] Figure 1-3 is a relationship diagram between the unimpeded flow rate and the photoelectric absorption cross-sectional index of the present invention;

[0025] Figure 1-4 is a graph showing the relationship between the unimpeded flow rate and the structural curvature of the present invention;

[0026] Figure 2 It is a flow chart of the method for determining the open flow rate of a tight carbonate reservoir in implementation 1 of the method for determining the open flow rate of the present invention;

[0027] Figure 3 It is a flow chart of the method for determining production allocation based on open flow rate for a tight carbonate reservoir in Example 1 of the method for determining production allocation of the present invention;

[0028] Figure 4 It is a fracturing construction curve diagram in Example 1 of the production allocation determination method of the present invention;

[0029] Figure 5 This is a schematic diagram of the core in Example 1 of the production allocation determination method of the present invention;

[0030] Figure 6 It is a diagram of the production allocation results in Example 1 of the production allocation determination method of the present invention. DETAILED DESCRIPTION

[0031] When the unimpeded flow method is used to evaluate the gas well productivity, the present invention analyzes the logging, core, fracturing and production data of a carbonate gas well in a gas field, analyzes its structure, sedimentary phase, paleokarst and paleogeomorphological characteristics, and reservoir characteristics, and finds that the main factors affecting the gas well productivity include residual thickness, dolomite reservoir thickness, photoelectric absorption cross-section index and structural curvature.

[0032] Moreover, the corresponding relationship diagrams of the unimpeded flow rate and the residual thickness, dolomite reservoir thickness, photoelectric absorption cross-section index and structural curvature are drawn, as shown in Fig. Figure 1-1 , 1-2 , 1-3 and 1-4. Figure 1-1 In the figure, the relationship between the unimpeded flow rate y and the residual thickness x can be fitted as: y = 13.299e -0.012x , correlation R 2 =0.042; Figure 1-2 The relationship between the open flow rate y and the dolomite reservoir thickness x can be fitted as follows: y = 1.3801x-3.9158, and the correlation R 2 =0.52; Figure 1-3 The relationship between the unimpeded flow rate y and the photoelectric absorption cross-section index x can be fitted as: y = -4.8627x + 29.691, and the correlation R 2 =0.1001; Figure 1-4 The relationship between the unimpeded flow rate y and the photoelectric absorption cross-section index x can be fitted as: y = 0.4678x + 2.1905, and the correlation R 2 =0.9588. From these four figures, it can be found that the structural curvature and dolomite reservoir thickness are positively correlated with the open flow rate, while the residual thickness and photoelectric absorption cross-section index are negatively correlated with the open flow rate.

[0033] By utilizing this point, the method for determining the open-flow rate of a dense carbonate reservoir and the method for determining the production allocation based on the open-flow rate of a dense carbonate reservoir of the present invention can be realized.

[0034] Unimpeded flow determination method embodiment 1:

[0035] This embodiment provides a method for determining the open flow rate of a tight carbonate reservoir. Figure 2 As shown, the method process is as follows:

[0036] Firstly, the open flow model was constructed by using the linear multiple regression method based on the relationship between the open flow and residual thickness, dolomite reservoir thickness, photoelectric absorption cross-section index and structural curvature:

[0037]

[0038] In the formula, Q AOF is the unimpeded flow rate, the unit is 10 4 m 3 / d; H1 is the residual thickness, in m; H2 is the dolomite reservoir thickness, in m; Pe is the photoelectric absorption cross-section index, in bar electrons; γ is the structural curvature, in km -1 ; k1, k2, k3, k4, k5, k6 are all set coefficients, and are all greater than 0, x1 is a set constant, and the specific values ​​are: x1 = -13.0936, k1 = 17.4923, k2 = 1.043, k3 = 6.0316, k4 = 2.0439, k5 = 0.012, k6 = 0.1396, so the unimpeded flow model is:

[0039]

[0040] Then, the residual thickness of the tight carbonate reservoir, the thickness of the dolomite reservoir, the photoelectric absorption cross-section index and the structural curvature are obtained and substituted into the formula (2) to obtain the unimpeded flow of the tight carbonate reservoir to evaluate its gas reservoir production capacity. Among them, the residual thickness and dolomite reservoir thickness values ​​are obtained from the reservoir physical property parameters, the photoelectric absorption cross-section index is read from the well logging diagram, and the structural curvature is calculated using the structural deformation curvature method according to the relationship between rock formation deformation and curvature.

[0041] Unimpeded flow determination method embodiment 2:

[0042] In Example 1 of the method for determining the open flow rate, four factors, namely, residual thickness, dolomite reservoir thickness, photoelectric absorption cross-section index and structural curvature, are used to construct an open flow rate model.

[0043] The difference between this embodiment and the method for determining the open-flow rate in Embodiment 1 is that only two or three factors among the residual thickness, dolomite reservoir thickness, photoelectric absorption cross-section index and structural curvature are selected to construct the open-flow rate model. The model needs to characterize that the structural curvature and dolomite reservoir thickness are both positively correlated with the open-flow rate, and the residual thickness and photoelectric absorption cross-section index are both negatively correlated with the open-flow rate.

[0044] Unimpeded flow determination method embodiment 3:

[0045] In Example 1 of the method for determining the unobstructed flow rate, the values ​​of x1, k1, k2, k3, k4, k5, and k6 are respectively: x1 = -13.0936, k1 = 17.4923, k2 = 1.043, k3 = 6.0316, k4 = 2.0439, k5 = 0.012, and k6 = 0.1396.

[0046] In this embodiment, data obtained from other regions are used to construct an unimpeded flow model, which will cause the values ​​of these coefficients to no longer be the values ​​in Embodiment 1 of the unimpeded flow determination method, but will change.

[0047] Example 4 of method for determining unimpeded flow rate:

[0048] In Example 1 of the method for determining the open-flow rate, a linear multiple regression method is used to construct an open-flow rate model.

[0049] The only difference between this embodiment and the method for determining the open-flow rate in Embodiment 1 is that other existing methods are used to construct the open-flow rate model, for example, the polynomial fitting method, as long as the relationship between the open-flow rate and at least two factors among the residual thickness, dolomite reservoir thickness, photoelectric absorption cross-section index and structural curvature is ultimately reflected.

[0050] Production allocation determination method embodiment 1:

[0051] This embodiment provides a method for determining production allocation based on open flow for a tight carbonate reservoir. After determining the open flow, the method can determine the production allocation according to the degree of fracture development, open flow and production allocation coefficient, such as Figure 3 As shown, the method process is as follows:

[0052] First, the relationship between the open flow rate and the residual thickness, dolomite reservoir thickness, photoelectric absorption cross-sectional index and structural curvature is used to construct the open flow rate model by linear multiple regression method, as shown in formula (1) in embodiment 1 of the open flow rate determination method. The specific values ​​of each coefficient and parameter are as follows: x1=-13.0936, k1=17.4923, k2=1.043, k3=6.0316, k4=2.0439, k5=0.012, k6=0.1396, so as to obtain the open flow rate model as shown in formula (2) in embodiment 1 of the open flow rate determination method.

[0053] Then, the residual thickness of the tight carbonate reservoir, the thickness of the dolomite reservoir, the photoelectric absorption cross-section index and the structural curvature are obtained and substituted into the formula (2) to obtain the unimpeded flow of the tight carbonate reservoir. Among them, the residual thickness and the dolomite reservoir thickness values ​​are obtained from the reservoir physical property parameters, the photoelectric absorption cross-section index is read from the well logging diagram, and the structural curvature is calculated using the structural deformation curvature method according to the relationship between rock formation deformation and curvature.

[0054] Next, the fracture development degree is analyzed by combining the fracturing construction curve and the structural curvature. The fracture development degree is either developed or undeveloped. Among them, the structural curvature is greater than or equal to 5km -1 The fracturing construction curve is low-pressure straight or descending, indicating that cracks are developed; the structural curvature is less than 5km -1 , the fracturing construction curve is a high-pressure straight type, indicating that the fractures are underdeveloped. It should be noted that the limit value for judging the performance of the fracturing construction curve is different in different regions and is not necessarily 5km. -1 .

[0055] Finally, the production allocation coefficient is determined according to the degree of fracture development and the open flow rate; and the production allocation is determined based on the production allocation coefficient:

[0056] If cracks develop, the unimpeded flow rate Q calculated by formula (2) AOF When the daily volume is greater than 100,000 cubic meters and less than 200,000 cubic meters (10<Q AOF <20), the production allocation coefficient is 1 / 5-1 / 8, when the unimpeded flow calculated by formula (2) is greater than or equal to 200,000 cubic meters / day (Q AOF ≥20), the production allocation coefficient is 1 / 8-1 / 10. Therefore, the production allocation can be obtained by multiplying the unimpeded flow and the production allocation coefficient.

[0057] If the cracks are not developed, the production allocation coefficient is 1 / 3. Then multiply the unimpeded flow rate and the production allocation coefficient to get the production allocation.

[0058] The production allocation determination method based on open-flow rate for tight carbonate reservoirs is applied to the XX well in an actual project to demonstrate the effectiveness of this method.

[0059] First, collect relevant data: the residual thickness H1 of Well XX is 28.7m, the dolomite reservoir thickness H2 is 19.8m, the photoelectric absorption cross-section index Pe is 4.5bar, and the structural curvature γ is 25km -1 .

[0060] Then, substituting these values ​​into formula (2), the open flow rate of well XX is calculated as:

[0061] Q AOF =-13.0936+17.4923e -0.012*28.7 +1.0431e 0.1396*19.8 -6.0316ln(4.5)+2.0439*25=580,000m3 / day

[0062] Next, since the structural curvature of Well XX is 25km -1 , and combined with the fracturing construction curve of XX well (such as Figure 4As shown, it shows a decline) and core (as shown Figure 5 ), it can be seen that the well belongs to the fracture development area.

[0063] Finally, since its unimpeded flow is 580,000 cubic meters / day, the production allocation coefficient is selected as 1 / 8-1 / 10, and the resulting production allocation is 60,000 cubic meters / day, as shown in Figure 6 As shown, the gas well production is stable.

[0064] Production allocation determination method embodiment 2:

[0065] In Example 1 of the production allocation determination method, the degree of fracture development is determined based on the structural curvature and the fracturing operation curve.

[0066] The difference between this embodiment and the first embodiment of the production allocation determination method is that other methods of the prior art are used to determine the degree of fracture development. For example, the number of fracture development can be identified through conventional logging curves to determine the degree of fracture development.

[0067] Production allocation determination method embodiment 3:

[0068] In Example 1 of the production allocation determination method, for the case of fracture development, the open flow rate 10<Q AOF When <20, the production allocation coefficient is set to 1 / 5-1 / 8, and the unobstructed flow rate Q AOF When ≥20, the production allocation coefficient is set to 1 / 8-1 / 10. If the cracks are not developed, the production allocation coefficient is set to 1 / 3.

[0069] The difference between this embodiment and the first embodiment of the production allocation determination method is that the production allocation coefficient is slightly adjusted, which is slightly increased or decreased based on the above value, or the upper and lower limits of the value range of the unobstructed flow rate can be adjusted according to actual conditions.

Claims

1. A method for determining the open flow rate of a tight carbonate reservoir, characterized in that: The steps include: Obtain the factors related to the open flow model in the residual thickness of the tight carbonate reservoir, the thickness of the dolomite reservoir, the photoelectric absorption cross-section index and the structural curvature, and substitute them into the open flow model to obtain the open flow of the tight carbonate reservoir; The unimpeded flow model is constructed based on the relationship between the unimpeded flow and at least two factors among the residual thickness, dolomite reservoir thickness, photoelectric absorption cross-sectional index and structural curvature, and the dolomite reservoir thickness and structural curvature are both positively correlated with the unimpeded flow, and the residual thickness and photoelectric absorption cross-sectional index are both negatively correlated with the unimpeded flow; The unimpeded flow model is constructed based on the relationship between residual thickness, dolomite reservoir thickness, photoelectric absorption cross-section index, structural curvature and unimpeded flow, and the unimpeded flow is: In the formula, Q AOF is the unobstructed flow, H1 is the residual thickness, H2 is the dolomite reservoir thickness, Pe is the photoelectric absorption cross-section index, γ is the structural curvature, k1, k2, k3, k4, k5, k6 are all set coefficients, and all are greater than 0, x1 is a set constant; x1=-13.0936, k1=17.4923, k2=1.043, k3=6.0316, k4=2.0439, k5=0.012, k6=0.1396.

2. The method for determining the open flow rate of a tight carbonate reservoir according to claim 1, characterized in that: The unimpeded flow model is constructed by using a linear multiple regression method.

3. A method for determining production allocation based on open flow for a tight carbonate reservoir, characterized in that: The steps include: Obtaining factors related to the open-flow flow model from the residual thickness of the tight carbonate reservoir, the thickness of the dolomite reservoir, the photoelectric absorption cross-sectional index, and the structural curvature, and substituting them into the open-flow flow model to obtain the open-flow flow of the tight carbonate reservoir; wherein the open-flow flow model is constructed based on the relationship between the open-flow flow and at least two factors of the residual thickness, the thickness of the dolomite reservoir, the photoelectric absorption cross-sectional index, and the structural curvature, and the dolomite reservoir thickness and the structural curvature are both positively correlated with the open-flow flow, and the residual thickness and the photoelectric absorption cross-sectional index are both negatively correlated with the open-flow flow; Determine the extent of crack development; Determine the production allocation coefficient based on the degree of fracture development and open flow rate; Determine the production allocation based on the production allocation coefficient; If cracks are developed: when the open flow rate is greater than the first set value and less than the second set value, the production allocation coefficient is 1 / 5-1 / 8; when the open flow rate is greater than or equal to the second set value, the production allocation coefficient is 1 / 8-1 / 10; if cracks are not developed, the production allocation coefficient is 1 / 3; the first set value is less than the second set value.

4. The method for determining production allocation based on open flow for a tight carbonate reservoir according to claim 3, characterized in that: The degree of development of the fractures is determined based on the structural curvature and the fracturing construction curve.

5. The method for determining production allocation based on open flow for a tight carbonate reservoir according to claim 3 or 4, characterized in that: The degree of crack development is crack development or crack underdevelopment; If fractures are developed, the production allocation coefficient is related to the open flow rate, and the larger the open flow rate, the smaller the production allocation coefficient.

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