Dry rock model building method for high-water-cut-period reservoir of oil field

Abstract

The invention relates to the technical field of oil field oil reservoir development models, in particular to a dry rock model building method for a high-water-cut-period reservoir of an oil field. According to the dry rock model building method for the high-water-cut-period reservoir of the oil field, well drilling and well logging work is carried out on a target reservoir, data are collected, a curve is drawn through the data, consistency correction is carried out, total porosity is calculated according to the corrected data curve, and irreducible water porosity is obtained by subtracting effective porosity. And adding the obtained bound water porosity into dry clay data to obtain wet clay data, then combining the wet clay data with core data to establish a rock skeleton model, and then combining the rock skeleton model with the effective porosity to form a new dry rock model. According to the dry rock model building method for the high-water-cut-period reservoir of the oil field, the bound water porosity is calculated and added into the dry clay data to obtain the wet clay data, and the influence of long-time water injection exploitation on the structure in the reservoir is considered; and the reservoir sand body prediction precision and the fluid identification capability by using the longitudinal and transverse wave curves are improved.

Description

Technical Field

[0001] This invention relates to the field of oilfield reservoir development model technology, and in particular to a method for establishing a dry rock model of a reservoir during the high water-cut period in an oilfield. Background Technology

[0002] Pre-stack seismic reservoir prediction is currently the most effective method for predicting thin reservoirs and identifying remaining oil, and rock physics simulation is a necessary step in conducting pre-stack reservoir prediction. Rock physics simulation requires rock physics modeling, which mainly involves establishing different models and determining the equivalent elastic modulus of the corresponding models. This process mainly consists of three steps: first, establishing a rock skeleton model; second, establishing a dry rock model; and third, establishing a saturated rock model. The dry rock model refers to a model without the addition of fluids. Common dry rock models for sandstone reservoirs include quartz, dry clay, and total porosity models. In existing technologies, the establishment of dry rock models must both conform to the geological characteristics of the study area and reflect the development characteristics of the reservoir. However, commonly used dry rock models in reservoir rock physics modeling are based on the aforementioned common quartz, dry clay, and total porosity models, which are established when the reservoir rocks are in their original state and have not undergone long-term development. Some existing reservoirs have undergone long-term high-pressure water injection development. The "flushing effect" of long-term water injection development can alter the reservoir rock structure to some extent, leading to incompatibility between the existing dry rock model and the actual reservoir. Ultimately, the shear wave curves simulated by rock physics modeling are significantly inconsistent with the measured curves, thus affecting the accuracy of reservoir sand body prediction and fluid identification capabilities using P-wave and S-wave curves. Therefore, to address these shortcomings, a method for establishing a dry rock model for oilfield reservoirs in the high water-cut stage is proposed. Summary of the Invention

[0003] (a) Technical problems to be solved

[0004] To address the shortcomings of existing technologies, this invention provides a method for establishing a dry rock model for reservoirs in the high water-cut stage of oilfields. This method solves the problem that existing dry rock models are not compatible with actual reservoirs, resulting in a significant discrepancy between the shear wave curves simulated by rock physics modeling and the measured curves. Consequently, it affects the accuracy of reservoir sand body prediction and the ability to identify fluids using longitudinal and shear wave curves.

[0005] (II) Technical Solution

[0006] To address the above problems, this invention provides a method for establishing a dry rock model of a reservoir during the high water-cut period in an oilfield, comprising:

[0007] Step 1: Conduct drilling and logging operations at the target tool to obtain logging data and core data;

[0008] Step 2: Use the logging data and core data obtained in Step 1 to plot logging curves;

[0009] Step 3: Perform consistency correction on the logging curves from Step 2;

[0010] Step 4: Calculate the total porosity based on the corrected logging curves from Step 3;

[0011] Step 5: Calculate the effective porosity using the corrected logging curves from Step 3;

[0012] Step 6: Subtract the effective porosity from the total porosity in Step 5 to obtain the bound water porosity;

[0013] Step 7: Add the bound water porosity to the dry clay data using the equivalent medium splitting theory to obtain the wet clay data;

[0014] Step 8: Combine wet clay data and core data to establish a rock skeleton model;

[0015] Step 9: Combine the rock skeleton model and effective porosity from Step 8 to form a dry rock model.

[0016] Furthermore, the logging data in step one includes density logging curves.

[0017] Furthermore, the core data in step one includes rock thin section analysis data, rock mineral composition analysis data, rock porosity analysis data, and rock elastic modulus measurement data.

[0018] Furthermore, the expression for total porosity in step four is:

[0019] POR = (2.65 – DEN) / (2.65 – 1)

[0020] Where POR is total porosity, 2.65 is the theoretical density skeleton value of sandstone, DEN is the corrected density logging data, and 1 is the theoretical density skeleton value of water.

[0021] Furthermore, the expression for the effective porosity in step five is:

[0022] PORE=POR–Vm×0.15-Vq×0.05

[0023] Wherein, PORE is the effective porosity, POR is the total porosity, Vm is the dry clay content obtained from the analysis, and 0.15 is the proportion of ineffective pores in the clay; Vq is the quartz content obtained from the analysis, and 0.05 is the proportion of ineffective pores in the quartz.

[0024] Furthermore, the differential equivalent medium theory formula in step six is ​​as follows:

[0025]

[0026] Wherein, subscripts 1 and 2 represent phase 1 and phase 2 respectively, phase 1 refers to dry clay and phase 2 refers to wet clay; y is the concentration of phase 2, and for fluid-saturated or dry pores, y is equal to the porosity φ; P and Q are geometric factors for inclusions of different shapes (phase 2).

[0027] Furthermore, the expressions for P and Q are as follows:

[0028]

[0029] Where α is the porosity aspect ratio; K is the rock bulk modulus; μ is the shear modulus; and β is Poisson's ratio.

[0030] Furthermore, the expression for β is:

[0031] β=μ[(3K+μ) / (3K+4μ)].

[0032] (III) Beneficial Effects

[0033] This invention provides a method for establishing a dry rock model of a reservoir in the high water-cut stage of an oilfield. By calculating the effective porosity and total porosity in the reservoir to obtain the bound water porosity, and adding the bound water porosity to the dry clay data to obtain the wet clay data, the method takes into account the impact of long-term water injection and production on the internal structure of the reservoir during the dry clay modeling process. This eliminates the incompatibility between the dry rock model and the actual reservoir, making the final rock physics model consistent with the measured curves. This improves the accuracy of reservoir sand body prediction and the ability to identify fluids using P-wave and S-wave curves. Attached Figure Description

[0034] Figure 1 This is a flowchart of the process for establishing a physical dry rock model of reservoir rocks during the high water-cut period in oil fields;

[0035] Figure 2 This is the image before correction of the consistency analysis of multi-well logging curves;

[0036] Figure 3 This is a graph after consistency analysis and correction of multi-well logging curves;

[0037] Figure 4 It is a thin film of clay found in rock sections;

[0038] Figure 5 It is a leaf-shaped clay found in thin sections of rock;

[0039] Figure 6 This is a schematic diagram of the dry rock model. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] In the description of this invention, it is necessary to understand that the orientation or positional relationship indicated by terms such as "upper", "lower", "inner", "outer", "top", and "bottom" are based on the orientation or positional relationship shown in the accompanying drawings. The purpose is only to facilitate the description of this invention and to simplify the description. It is not intended to indicate or imply that the component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0042] like Figure 1-6 As shown, this invention provides a method for establishing a dry rock model of a reservoir during the high water-cut period in an oilfield, specifically including:

[0043] Step 1: Conduct drilling and logging operations at the target tool to obtain logging data and core data;

[0044] The well logging data includes density logging curves. The core data includes thin section analysis data, mineral composition analysis data, porosity analysis data, and elastic modulus measurement data.

[0045] Step 2: Use the logging data and core data obtained in Step 1 to plot logging curves;

[0046] The well logging curve can be directly generated by inputting well logging data and core data obtained from well logging work into the software. The generated well logging curve can directly reflect various parameters of the well environment.

[0047] Step 3: Perform consistency correction on the logging curves from Step 2;

[0048] In the process of obtaining various logging data and core data through well logging, it is usually necessary to drill multiple wells within the working range and compare the logging data and core data obtained from different wells. At this time, consistency correction is performed on each logging curve to make the data value range provided by each logging curve uniform, so that the curve can provide complete and reasonable logging data.

[0049] Step 4: Calculate the total porosity based on the corrected logging curves from Step 3;

[0050] The expression for the total porosity in step four is as follows:

[0051] POR = (2.65 – DEN) / (2.65 – 1)

[0052] In the formula, POR is the total porosity, 2.65 is the theoretical density skeleton value of sandstone, DEN is the corrected density logging data, and 1 is the theoretical density skeleton value of water.

[0053] The DEN in the formula can be obtained directly by reading the density logging data in the corrected logging curve.

[0054] Step 5: Calculate the effective porosity using the corrected logging curves from Step 3;

[0055] The expression for the effective porosity in step five is as follows:

[0056] PORE=POR–Vm×0.15-Vq×0.05

[0057] In the formula, PORE is the effective porosity, POR is the total porosity, Vm is the dry clay content obtained from the analysis, and 0.15 is the proportion of ineffective pores in the clay; Vq is the quartz content obtained from the analysis, and 0.05 is the proportion of ineffective pores in the quartz.

[0058] Based on the rock thin section analysis data in the corrected well logging curves, the characteristics of rock pore structure and the occurrence state of clay minerals were obtained; the mineral composition analysis data showed that the rock mineral types were quartz and dry clay.

[0059] Step 6: Subtract the effective porosity from the total porosity in Step 5 to obtain the bound water porosity; the formula for calculating the bound water porosity is POR-PORE.

[0060] Step 7: Add the bound water porosity to the dry clay data using the equivalent medium splitting theory to obtain the wet clay data;

[0061] The differential equivalent medium theory formula is as follows:

[0062]

[0063] Wherein, subscripts 1 and 2 represent phase 1 and phase 2, respectively. Phase 1 refers to dry clay, and phase 2 refers to wet clay. The values ​​of phase 1 dry clay are commonly used constant values ​​in oilfield production, while the values ​​of phase 2 wet clay are parameters within the reservoir under actual conditions, which can be directly measured by conventional measurement methods; y is the concentration of phase 2. For fluid-saturated or dry pores, y is equal to the porosity φ; P and Q are geometric factors for inclusions (phase 2) of different shapes.

[0064] In general, under the initial condition K DEM (0) = K1, μ DEM(0) = μ1. In the actual calculation process, if the calculation target is wet clay, the values ​​of K1 and μ1 need to be replaced with the corresponding values ​​of wet clay, i.e., phase 2.

[0065] In the above formula, P and Q are the geometric factors for phase 1 and phase 2, respectively, and their expressions are as follows:

[0066]

[0067] Where α is the porosity aspect ratio; K is the rock bulk modulus; μ is the shear modulus; and β is Poisson's ratio.

[0068] In this context, the subscript "ma" refers to quartz phase data, and the subscript "in" refers to fluid phase data. The quartz phase data are commonly used experimental parameters in oilfield development, and their values ​​are constants. After long-term water injection and development, the fluid phase data can directly use water-related parameters. However, the fluid in the reservoir is actually a mixture of water and oil. To improve the accuracy of modeling and subsequent data, measurements can be taken after sampling during the logging stage.

[0069] Furthermore, the expression for β is:

[0070] β = μ[(3K+μ) / (3K+4μ)]. In calculating β, the values ​​of K and μ are chosen to correspond to the subscripts of β; that is, the subscripts of K and μ are the same as the calculated β.

[0071] Step 8: Combine wet clay data and core data to establish a rock skeleton model;

[0072] In step seven, formulas (1) and (2) are the wet clay data obtained through calculation. By inputting formulas (1) and (2) together with the quartz data in the core data into the modeling program, a rock skeleton model can be obtained.

[0073] Step 9: Combine the rock skeleton model and effective porosity from Step 8 to form a dry rock model.

[0074] After combining the rock skeleton model obtained in step eight with the effective porosity in step five, the model can be input into the modeling program to obtain the required dry rock model.

[0075] according to Figures 2 to 6 The implementation process of the method of the present invention is illustrated by taking the SII oil reservoir group in the western part of a certain oilfield as an example:

[0076] Step 1, such as Figure 2 and Figure 3As shown, multiple previous logging curves within the target reservoir are obtained, and the data curve with the best quality and most complete variety is used as the standard well. Other logging curves are then corrected for consistency with the standard well so that the data range of other wells is in the same dimension as the standard well.

[0077] Step Two, as follows Figure 4 and Figure 5 As shown, the logging curves in step one can yield rock thin section analysis data, rock mineral composition analysis data, rock porosity analysis data, rock pore structure characteristics, and clay mineral occurrence state. Figure 4 and Figure 5 These are thin-film clay and leaf-shaped clay films in the reservoir, respectively. Meanwhile, the content of rock minerals, namely quartz and dry clay, can be obtained through the well logging data in step one. The effective porosity is obtained using the above rock porosity analysis data, and the total porosity is calculated using the corrected density well logging data. The bound water porosity is obtained by subtracting the effective porosity from the total porosity.

[0078] Step 3, as follows Figure 6 As shown, observations using thin sections and scanning electron microscopy reveal that the "flushing effect" of long-term water injection causes the clay mineral enrichment state in the reservoir section to change from approximately layered and film-like to small-particle and film-like. This "flushing effect" is similar to the "sorting effect" of a river, resulting in more rounded and finer mineral particles and the formation of many "large pores." For the reservoir, this is analogous to decompaction, with the clay's support for the reservoir framework decreasing. To mitigate the impact of clay on the framework model, the dry clay in the framework model was transformed into wet clay by incorporating bound water porosity using the Differential Equivalent Medium Theory (DEM). This wet clay was then incorporated into quartz using the DEM to form a rock framework model. Finally, effective porosity was added to the rock framework model to obtain... Figure 4 The dry rock model shown.

[0079] After practical operation, the results obtained by the dry rock model establishment method for oilfield high water-cut reservoirs proposed in this invention were compared with the previous results. The consistency rate between the shear wave curve and the measured curve increased from 72% to 83%, which laid an important foundation for pre-stack seismic inversion reservoir prediction and fluid identification, and greatly improved the accuracy of reservoir sand body prediction using P-wave and S-wave curves.

[0080] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for establishing a dry rock model of a reservoir in a high water cut stage of an oil field, characterized in that, The application relates to a method for calculating the bound water porosity of a target reservoir. Step one: drilling and logging work is carried out in the target reservoir to obtain logging data and core data; Step two: logging curves are drawn by using the logging data and core data obtained in step one; Step three: the logging curves in step two are corrected for consistency; Step four: total porosity is calculated according to the corrected logging curves in step three; Step five: effective porosity is calculated by using the corrected logging curves in step three; Step six: the bound water porosity is obtained by subtracting the effective porosity in step five from the total porosity in step four; Step seven: the bound water porosity is added to the dry clay data to obtain the wet clay data by splitting the equivalent medium theory; Step eight: the wet clay data and the core data are combined to establish a rock skeleton model; Step nine: the rock skeleton model in step eight and the effective porosity are combined to form a dry rock model.

2. The method for establishing a dry rock model of a reservoir in the high water cut stage of an oil field according to claim 1, characterized in that, The logging data in step one includes a density logging curve.

3. The method for establishing a dry rock model of a reservoir in a high water cut stage of an oil field according to claim 1, characterized in that, The core data in step one includes rock slice analysis data, rock mineral composition analysis data, rock porosity analysis data and rock elastic modulus determination data.

4. The method for establishing a dry rock model of a reservoir in a high water cut stage of an oil field according to claim 1, characterized in that, The expression of the total porosity in step four is: POR=(2.65-DEN) / (2.65-1) wherein POR is the total porosity, 2.65 is the theoretical density skeleton value of sandstone, DEN is the corrected density logging data, and 1 is the theoretical density skeleton value of water.

5. The method for establishing a dry rock model of a reservoir in a high water cut stage of a field according to claim 1, characterized in that, The expression of the effective porosity in step five is: PORE=POR-Vm*0.15-Vq*0.05 wherein PORE is the effective porosity, POR is the total porosity, Vm is the dry clay content obtained by analysis, 0.15 is the invalid porosity proportion of clay, Vq is the quartz content obtained by analysis, and 0.05 is the invalid porosity proportion of quartz.

6. The method for establishing a dry rock model of a reservoir in a high water cut stage of a field according to claim 1, characterized in that, The differential equivalent medium theory formula in step six is: wherein the subscripts 1 and 2 respectively represent phase state 1 and phase state 2, the phase state 1 refers to dry clay, and the phase state 2 refers to wet clay; y is the concentration of the phase state 2, and for a fluid-saturated or dry pore y is equal to the porosity phi; P and Q are geometric factors for different shapes of inclusions (phase state 2).

7. The method for establishing a dry rock model of a reservoir in the high water cut stage of a field according to claim 6, characterized in that, The expressions of P and Q are as follows: wherein alpha is the pore aspect ratio; K is the rock bulk modulus, mu is the shear modulus, and beta is the Poisson's ratio.

8. The method for establishing a dry rock model of a reservoir in a high water cut stage of a field according to claim 6, characterized in that, The expression of beta is: beta=mu[(3K+mu) / (3K+4mu)].

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