Establishment method of identification chart of oil-water dry layer and interpretation method of oil-water dry layer

Abstract

The invention relates to a method for establishing an identification chart of an oil-water dry layer and an interpretation method of the oil-water dry layer, and belongs to the technical field of oil and gas field exploration and development. The method for establishing the identification chart comprises the following steps of: i) acquiring resistivity logging values, interval transit time logging values, density logging values and oil-bearing level values of standard oil layers, standard water layers and standard dry layers of all wells put into production verification in a research area, and respectively calculating K1 values and K2 values of the standard oil layers, the standard water layers and the standard dry layers of all the wells by utilizing a formula I and a formula II; and ii) establishing an oil-water dry layer identification chart based on the K1 and K2 values of the standard oil layer, the standard water layer and the standard dry layer of each well calculated in the step i). According to the method for establishing the identification plate, the difference between the relative values (K1 and K2) of different reconstructed reservoirs is more obvious, so that the oil-water layer identification plate established according to the method is higher in distinction degree and clearer in range boundary.

Description

Technical Field

[0001] The present invention relates to a method for establishing an identification chart of an oil-water dry layer and a method for interpreting the oil-water dry layer, belonging to the technical field of oil and gas field exploration and development. Background Art

[0002] The Cretaceous strata are well developed in the northwestern margin of the Junggar Basin, characterized by thick strata, deep burial depths, and high crude oil viscosity. Cretaceous reservoirs differ significantly from other reservoirs, primarily in the thinness of individual reservoirs, deep burial depths, complex reservoir lithology, and difficulty identifying effective reservoir thickness. During development, significant discrepancies between effective reservoir thickness and actual production capacity have been observed. Currently, most interpretation methods, both domestically and internationally, employ methods such as the Pixler plate method, the triangle plate method, and the light hydrocarbon (3H) ratio method. These interpretations often use a single intersection interpretation plate parameter, resulting in extremely low agreement rates for highly heterogeneous Cretaceous reservoirs. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for establishing an identification chart of oil-water dry layers, and the identification chart of oil-water dry layers established by the method can significantly improve the consistency rate of reservoir interpretation of Cretaceous system and the like.

[0004] The present invention also provides an interpretation method for an oil-water dry layer.

[0005] In order to achieve the above objectives, the technical solution adopted by the method for establishing the identification plate of the oil-water dry layer of the present invention is:

[0006] A method for establishing an identification chart of an oil-water dry layer comprises the following steps:

[0007] i) Select standard oil layers, standard water layers, and standard dry layers in the study area, and obtain the resistivity logging values, acoustic transit time logging values, density logging values, and oil grade values of the standard oil layers, standard water layers, and standard dry layers of the verification wells in the study area that have been put into production;

[0008] Determine whether the resistivity logging values, acoustic transit time logging values, density logging values, and oil grade values of the standard oil layer, standard water layer, and standard dry layer of each production verification well need to be normalized;

[0009] If normalization is not required, the K1 and K2 values of the standard oil layer, standard water layer, and standard dry layer of each well are directly calculated using Formula I and Formula II; if normalization is required, the K1 and K2 values of the standard oil layer, standard water layer, and standard dry layer of each well are calculated using Formula I and Formula II after normalization.

[0010] K1=R×N (Formula I),

[0011] K2 = (AC-m) / DEN (Formula II);

[0012] In formula I and formula II, R is the layer resistivity logging value, dimensionless; N is the layer oil content value, dimensionless; AC is the layer acoustic wave time difference value, dimensionless; DEN is the layer density logging value, dimensionless; m is a constant, ranging from 0 to 200;

[0013] ii) Based on the K1 and K2 values of the standard oil layer, standard water layer and standard dry layer of each well calculated in step i), an oil-water-dry layer identification chart is established.

[0014] Compared to maps created using other methods, the method for establishing an oil-water dry layer identification chart in this invention only requires three types of well logging data (R, AC, and DEN) and oil content data for the reconstruction formula, making it simpler and easier to use. Furthermore, the relative values (K1 and K2) between different reservoirs after reconstruction are more distinct, resulting in a more discriminative oil-water layer identification chart with clearer range boundaries. Furthermore, the R, AC, and DEN logging data required for the reconstruction formula are normalized, eliminating the impact of different dimensions and dimensional units between the logging data and reducing errors.

[0015] It can be understood that in step ii), when establishing the oil-water layer identification chart, one of K1 and K2 is used as the horizontal coordinate and the other is used as the vertical coordinate, for example, K1 is used as the horizontal coordinate and K2 is used as the vertical coordinate.

[0016] Furthermore, the oil-water dry layer is a Cretaceous oil-water dry layer; in Formula II, m is 200. Since the minimum acoustic transit time of the currently known tightest Cretaceous reservoir is approximately 200 μs / m, an m value of 200 can better reflect the differences in Cretaceous oil-water dry layers, resulting in a clear differentiation effect. The established identification chart is used to identify Cretaceous oil-water dry layers.

[0017] The technical solution adopted by the oil-water dry layer interpretation method of the present invention is:

[0018] A method for interpreting an oil-water dry layer, characterized by comprising the following steps:

[0019] 1) Determine whether the resistivity logging values, acoustic transit time logging values, density logging values, and oil grade values of the layers to be interpreted in the wells in the study area need to be normalized;

[0020] If normalization processing is not required, the K1 and K2 values of the to-be-interpreted layers of the wells in the study area are directly calculated using Formula I and Formula II; if normalization processing is required, the K1 and K2 values of the to-be-interpreted layers of the wells in the study area are calculated using Formula I and Formula II after normalization processing respectively;

[0021] 2) Determining the type of the horizon to be interpreted based on the K1 and K2 values of the horizon to be interpreted and the boundaries of the oil layer, water layer, and dry layer determined by the oil-water-dry layer identification plate; the oil-water-dry layer identification plate is obtained by a method comprising the following steps:

[0022] i) Select standard oil layers, standard water layers, and standard dry layers in the study area, and obtain the resistivity logging values, acoustic transit time logging values, density logging values, and oil grade values of the standard oil layers, standard water layers, and standard dry layers of the verification wells in the study area that have been put into production;

[0023] Determine whether the resistivity logging values, acoustic transit time logging values, density logging values, and oil grade values of the standard oil layer, standard water layer, and standard dry layer of each production verification well need to be normalized;

[0024] If normalization is not required, the K1 and K2 values of the standard oil layer, standard water layer, and standard dry layer of each well are directly calculated using Formula I and Formula II; if normalization is required, the K1 and K2 values of the standard oil layer, standard water layer, and standard dry layer of each well are calculated using Formula I and Formula II after normalization.

[0025] ii) establishing an oil-water-dry layer identification chart based on the K1 and K2 values of the standard oil layer, standard water layer, and standard dry layer of each well calculated in step i);

[0026] K1=R×N (Formula I),

[0027] K2 = (AC-m) / DEN (Formula II);

[0028] In formulas I and II, R is the resistivity logging value of the layer, dimensionless; N is the oil-bearing grade value of the layer, dimensionless; AC is the acoustic time difference value of the layer, dimensionless; DEN is the density logging value of the layer, dimensionless; m is a constant, ranging from 0 to 200.

[0029] The oil-water dry layer interpretation method of the present invention is suitable for interpreting oil-water dry layers in Cretaceous or other stratum reservoirs, and is particularly suitable for interpreting oil-water dry layers in Cretaceous or other stratum reservoirs, especially in view of the complex lithology and strong heterogeneity of the Cretaceous system. The method can effectively distinguish oil, dry layers and water. By simply calculating the corresponding K1 and K2 and projecting points on a reservoir identification plate, the oil, dry layers and water layers can be quickly and accurately interpreted. The method can significantly improve the interpretation compliance rate of Cretaceous heterogeneous reservoirs, improve the development effect of the oil reservoir in the stratum, and ultimately increase the oil reservoir recovery rate, providing theoretical guidance for the fine development of Cretaceous reservoirs, and having a significant implementation effect.

[0030] It is understood that in step ii), when establishing the oil-water layer identification plate, one of K1 and K2 is used as the horizontal coordinate and the other as the vertical coordinate, for example, K1 is used as the horizontal coordinate and K2 is used as the vertical coordinate. The method and standard for normalization of the layer to be interpreted are the same as those in step i).

[0031] Furthermore, the oil-water dry layer is a Cretaceous oil-water dry layer; in formula II, m is 200.

[0032] In the present invention, the resistivity logging values, sonic transit time logging values, and density logging values of the standard oil layer, standard water layer, standard dry layer, and to-be-interpreted layer of each production verification well are the average values of the resistivity logging curve, sonic transit time logging curve, and density logging curve of the corresponding layer, respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a comparison diagram of the standard oil layer of Well C in Example 1;

[0034] Figure 2 This is a superimposed graph of the deep induction resistivity curve of Well B in Example 1;

[0035] Figure 3 This is a normalized processing diagram of the acoustic time difference parameters of Well B in Example 1;

[0036] Figure 4 This is an interpretation plate of the intersection of Cretaceous K1 and K2 in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further described below in conjunction with specific implementation methods.

[0038] The following describes the method for establishing an oil-water dry zone identification chart using the oil layers of Chun 10 Block (study area), a Cretaceous heavy oil reservoir, as an example. Because the study area utilizes different logging series and instruments from different periods, and considering the influence of human factors on logging data, before establishing the interpretation chart, the logging parameter data for the strata used to create the interpretation chart and the logging parameters for the strata to be interpreted must first be normalized. The oil content of the strata used to create the interpretation chart must also be normalized. For blocks operated with other widely used logging instruments, since interpretation charts are mostly based on the parameters of these logging instruments, the parameters are generally consistent with the normalized data, and therefore no normalization is required when creating the interpretation chart.

[0039] Example 1

[0040] The method for interpreting the oil-water dry layer of this embodiment includes the following steps:

[0041] Step 1: Standard layer selection

[0042] Standard layers are those with stable oil, gas, and water production, widespread distribution within the study area, significant stratigraphic thickness, distinct oil-bearing properties and logging response characteristics, ease of comparison, and consistent or regularly changing values on the same logging curve. Standard layers are widely distributed within the study area, with a continuous thickness greater than 4 meters (without significant interlayers) of the same lithology.

[0043] The data collected in the study area include core and cuttings analysis data, logging resistivity, acoustic wave time difference, density curve data, oil test, and production data; based on the collected data, from the well data with relatively clear oil test and production conclusions in the study area, the oil layers, dry layers, and dry layers with wide distribution in the study area, continuous thickness of more than 4m of the same lithology and no obvious interlayers were selected as standard oil layers, standard dry layers, and standard water layers.

[0044] Taking the selection of standard oil layers as an example, the oil layer at the bottom of a small layer (denoted as M small layer) in Chun 10 block is as follows: Figure 1 As shown in the figure, the marked oil layer has a stable lateral distribution and little variation in thickness. This oil layer is widely distributed and continuous within the study area, with a thickness greater than 4 m (no obvious interlayers), and can therefore be used as a standard oil layer for this reservoir. However, the oil layer at the top of another small layer in this block has large lateral thickness variations among wells and inconsistent oil content. Wells C, F, and G in the low structural position are oil layers, while Well H in the high structural position is a water layer. This is inconsistent with the characteristics of oil-water gravity differentiation (oil above, water below), and is clearly not an oil-water system. Therefore, this layer cannot be used as a standard oil layer.

[0045] Step 2: Data normalization

[0046] Because the logging series required by drilling geological design at different times are different, the logging instruments are quite different. The base numbers of logging curves of wells with large time differences are often different, resulting in inconsistent standards when making interpretation maps and unclear boundaries between oil and dry water layers. Therefore, it is necessary to compare the oil and water well curves of different periods under the same standard as much as possible. This requires normalization of the curve data. The processing method is as follows:

[0047] 2.1 Overall migration and superposition processing of logging curves

[0048] The standard wells in the study area (which are wells that have been put into production for verification) are selected, and then the curve overlap method is used to take the selected standard oil layer, standard water layer and standard water layer as the benchmark. The resistivity curves, acoustic time curves and density curves of the standard oil layer, standard water layer and standard dry layer of all the wells that have been put into production for verification in the study area except the standard well are compared with the corresponding logging curves of the standard oil layer, standard water layer and standard dry layer of the standard well, and left and right offset corrections are performed so that the resistivity logging curves, acoustic time difference logging curves and density logging curves of all the wells that have been put into production for verification except the standard well are coincident with the corresponding logging curves of the selected standard well as a whole.

[0049] Taking the resistivity logging curve of the known oil layer M in Chun 10 block as an example, the method of overall migration and superposition processing of the logging curve is explained: Since Well A in Chun 10 block was drilled and cored in the M layer, all basic data are complete, the logging response characteristics are obvious, and the production is pure oil, Well A is selected as the standard well. The average resistivity of the M layer in Well B in Chun 10 block is 30Ω·m, and the average resistivity of the standard oil layer selected in step 1 is 10Ω·m. The curve overlap method is used to translate the resistivity curve of the M layer in Well B to the resistivity curve of the standard oil layer in Well A, and the superposition processing is completed. Figure 2 Migration superposition processing can more realistically display the response of resistivity, acoustic wave travel time and density logging curves to changes in reservoir oil, gas and water.

[0050] 2.2 Normalization of logging data

[0051] Normalization is used to eliminate the influence of different dimensions and dimensional units among logging data. The resistivity curves, acoustic time difference curves, and density curves of all the verification wells in the study area that have been put into production are normalized after overall migration and superposition processing using the histogram translation method. These curves are used as the final interpretation data of the layer.

[0052] Specifically, the average values of the resistivity, acoustic transit time, and density logging data corresponding to the standard oil layer, standard water layer, and standard dry layer of the standard well in the study area and other wells that have been put into production after the overall migration and superposition processing are obtained (the interval of the values is 0.5m). Based on the calculated values, the histograms of the resistivity, acoustic transit time, and density corresponding to the standard oil layer, standard water layer, and standard dry layer of the standard well in the study area and other wells that have been put into production are drawn respectively;

[0053] Taking the three obtained histograms of the standard well as the standard, the histogram translation method is used to translate the corresponding histograms of the standard oil layer, standard water layer, and standard dry layer of other wells that have been put into production, until they are almost overlapped with the corresponding histograms of the standard oil layer, standard water layer, and standard dry layer of the standard well, that is, the average value of the resistivity, acoustic wave time difference, and density logging data of the standard oil layer, standard water layer, and standard dry layer of other wells that have been put into production is obtained.

[0054] Taking the acoustic transit time (AC) curve of Well D in Chun 10 Block as an example, the average value of the acoustic transit time logging data of the standard oil layer, standard dry layer, and standard water layer of Well A (standard well) is used. Based on the average value, the acoustic transit time histograms of the standard oil layer, standard dry layer, and standard water layer of Well D and Well A are drawn respectively. Figure 3 The acoustic time difference of each standard layer of the well to be normalized is slightly different from that of each standard layer of the standard well, and the whole is shifted upward to most of the columnar Figure 1 To, Figure 3 The middle dotted line is the acoustic time difference value (average value) of the oil layer, dry layer and water layer after translation. Other resistivity and density parameters are also normalized using the same method and used as the logging parameter values for the final interpretation plate.

[0055] 2.3 Normalization of oil content level

[0056] The oil content levels of the standard oil layer, standard water layer and standard dry layer of the standard well in the study area and other verification wells that have been put into production are normalized respectively.

[0057] The delineation of reservoir oil content grades is influenced by factors such as rock sample location, time, and human factors, and can vary. The oil content grades of proven oil-dry water layers within the same oil-water system or with similar reservoir characteristics should be compared with those of oil-dry water layers in reference wells. Layers similar to the reference layer can be assigned the same grade as the reference layer. If there are significant differences, the cause of the discrepancy should be analyzed, or the sample should be reanalyzed. The oil content grade should be determined by comparing it with the reference layer, aiming to return to the true value or minimize errors.

[0058] For Chun 10 Block, the core lithology of its Cretaceous standard oil layer is gray-brown oil spots, oil traces and gravel-bearing fine sandstone, and the series comparison level is 10. The field description of the E well shows that the lithology of the cuttings in the same layer is gray-brown oil spots and gravel-bearing fine sandstone, and the oil content level is 12, which is significantly higher. Compared with the gas logging, the overall values are basically consistent and the lithology is the same. Usually, the oil content level of the cuttings is lower than the lithology oil content level as a whole. Therefore, it is judged that the oil content level of the cuttings in this layer of Well E is too high, and the value should be regressed to 10 in data processing.

[0059] Step 3: Create an explanatory diagram

[0060] 3.1 Data Selection

[0061] The average values of the normalized resistivity data, acoustic wave transit time data, and density logging of the standard oil layer, standard water layer, and standard dry layer of the standard well in step 2 and other wells that have been put into production for verification are used as the resistivity values, acoustic wave transit time values, and density logging values of the standard oil layer, standard water layer, and standard dry layer of the standard well and other wells that have been put into production for verification.

[0062] 3.2 Data Processing

[0063] The resistivity values, acoustic transit time values, and density logging values of the standard oil layer, standard water layer, and standard dry layer of the standard well determined in step 3.1 and other wells that have been put into production for verification are mathematically reconstructed to obtain the K1 and K2 data of the standard oil layer, standard water layer, and standard dry layer of the standard well and other wells that have been put into production for verification; the reconstruction formula is:

[0064] K1=R×N;

[0065] K2 = (AC-200) / DEN;

[0066] Among them, K1 and K2 are relative values, dimensionless; AC is the normalized acoustic transit time value, dimensionless; R is the normalized resistivity logging value, dimensionless; N is the normalized oil grade value, dimensionless; DEN is the normalized density logging value, dimensionless;

[0067] 3.3 Explanation of the establishment of the plate

[0068] Using the specific K1 and K2 data of the reconstructed standard wells and other standard oil layers, standard water layers, and standard dry layers of each well that has been put into production, with K1 as the horizontal axis and K2 as the vertical axis, an oil and water layer identification chart is established, as shown in the following figure: Figure 4 As shown in the figure, a statistical analysis of K1 and K2 for different reservoir types was performed. Based on the range of K1 and K2 on the lithologic identification chart, the boundaries between oil layers, water layers, and dry layers were determined. This method was applied to Cretaceous oil and gas reservoirs, and the reservoirs were divided into three types: oil layers, water layers, and dry layers. For oil layers, K2>62.0, K1>30.0; for dry layers, K2<62.0; and for water layers, K2>62.0, K1<30.0.

[0069] 4. Use the identification plate to interpret the layers to be interpreted in the study area

[0070] Because the logging instruments of Well X in the study area are quite different from those of other verified wells, and the logging time is also quite different, it is necessary to first normalize the resistivity data, acoustic time difference data, density logging data, and oil-bearing grade of the to-be-interpreted strata of Well X in the study area.

[0071] If the horizon to be interpreted in well X of the study area is a standard horizon, the resistivity data, acoustic transit time data, density logging data and oil-bearing grade of the horizon to be interpreted are normalized according to the method in step 2;

[0072] If the horizon to be interpreted in Well X is a non-standard horizon (generally not widely distributed and with few commonalities between oil-dry and water-dry layers), the resistivity, acoustic transit time, and density logging data of the horizon to be interpreted, after being globally migrated and overlaid according to Step 2.1, are offset by the offset values used during normalization of the corresponding logging data from the adjacent standard layers of Well X. This normalization is achieved. Using the acoustic transit time (AC) curve from Well D in Block Chun 10 as an example, the AC values of the oil-dry and water-dry layers in the standard layers are increased by 10 μs / m during normalization. The adjacent non-standard layers can also be normalized by an additional 10 μs / m during regression. The same normalization method is used for the remaining logging data. Normalization of the oil-bearing grade of the non-standard layers is performed according to Step 2.3.

[0073] Then, calculate the K1 and K2 values of the horizon to be interpreted according to the method of steps 3.1 to 3.2, and project points on the identification plate established in step 3.3. The type of the horizon to be interpreted is determined based on the projected point positions.

[0074] In 2022, a review of the interpretation of Cretaceous oil and water layers in newly commissioned wells was conducted using a combined quantitative and qualitative interpretation method. A total of 12 layers / 5 wells were interpreted, 9 layers / 5 wells were put into production, and 8 layers / 5 wells were found to be compatible, for a compliance rate of 88.9%. A review of 45 layers / 32 wells in previously produced wells was conducted, and 38 layers / 30 wells were found to be compatible, for a compliance rate of 84.4%, with an average compliance rate of 85.2%, significantly improving the interpretation compliance rate. The low compliance rate of existing methods for interpreting layers in older wells is primarily due to the impact of early production measures on the accuracy of the results.

[0075] Example 2

[0076] The method for establishing the identification plate of the oil-water dry layer in this embodiment is the same as steps 1 to 3 of Example 1 and will not be repeated here.

Claims

1. A method for establishing an identification chart for an oil-water dry layer, characterized by: The following steps are involved: i) Select standard oil layers, standard water layers, and standard dry layers in the study area, and obtain the resistivity logging values, acoustic transit time logging values, density logging values, and oil grade values of the standard oil layers, standard water layers, and standard dry layers of the verification wells in the study area that have been put into production; Determine whether the resistivity logging values, acoustic transit time logging values, density logging values, and oil grade values of the standard oil layer, standard water layer, and standard dry layer of each production verification well need to be normalized; If normalization is not required, the K1 and K2 values of the standard oil layer, standard water layer, and standard dry layer of each well are directly calculated using Formula I and Formula II; if normalization is required, the K1 and K2 values of the standard oil layer, standard water layer, and standard dry layer of each well are calculated using Formula I and Formula II after normalization. K1=R×N (Formula I), K2 = (AC-m) / DEN (Formula II); In formula I and formula II, R is the layer resistivity logging value, dimensionless; N is the layer oil content value, dimensionless; AC is the layer acoustic wave time difference value, dimensionless; DEN is the layer density logging value, dimensionless; m is a constant, ranging from 0 to 200; ii) Based on the K1 and K2 values of the standard oil layer, standard water layer and standard dry layer of each well calculated in step i), an oil-water-dry layer identification chart is established.

2. The method for establishing an identification chart of an oil-water dry layer according to claim 1, wherein: The oil-water dry layer is a Cretaceous oil-water dry layer; in formula II, m is 200.

3. A method for interpreting an oil-water dry layer, characterized by: The following steps are involved: 1) Determine whether the resistivity logging values, acoustic transit time logging values, density logging values, and oil grade values of the layers to be interpreted in the wells in the study area need to be normalized; If normalization processing is not required, the K1 and K2 values of the to-be-interpreted layers of the wells in the study area are directly calculated using Formula I and Formula II; if normalization processing is required, the K1 and K2 values of the to-be-interpreted layers of the wells in the study area are calculated using Formula I and Formula II after normalization processing respectively; 2) Determining the type of the horizon to be interpreted based on the K1 and K2 values of the horizon to be interpreted and the boundaries of the oil layer, water layer, and dry layer determined by the oil-water-dry layer identification plate; the oil-water-dry layer identification plate is obtained by a method comprising the following steps: i) Select standard oil layers, standard water layers, and standard dry layers in the study area, and obtain the resistivity logging values, acoustic transit time logging values, density logging values, and oil grade values of the standard oil layers, standard water layers, and standard dry layers of the verification wells in the study area that have been put into production; Determine whether the resistivity logging values, acoustic transit time logging values, density logging values, and oil grade values of the standard oil layer, standard water layer, and standard dry layer of each production verification well need to be normalized; If normalization is not required, the K1 and K2 values of the standard oil layer, standard water layer, and standard dry layer of each well are directly calculated using Formula I and Formula II; if normalization is required, the K1 and K2 values of the standard oil layer, standard water layer, and standard dry layer of each well are calculated using Formula I and Formula II after normalization. ii) establishing an oil-water-dry layer identification chart based on the K1 and K2 values of the standard oil layer, standard water layer, and standard dry layer of each well calculated in step i); K1=R×N (Formula I), K2 = (AC-m) / DEN (Formula II); In formulas I and II, R is the resistivity logging value of the layer, dimensionless; N is the oil-bearing grade value of the layer, dimensionless; AC is the acoustic time difference value of the layer, dimensionless; DEN is the density logging value of the layer, dimensionless; m is a constant, ranging from 0 to 200.

4. The method for interpreting an oil-water dry layer according to claim 3, wherein: The oil-water dry layer is a Cretaceous oil-water dry layer; in formula II, m is 200.

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