A preliminary classification method and system for the causes of low resistivity in fast sandstone oil reservoirs

Abstract

The present invention relates to a preliminary classification method and system for the causes of low resistivity in fast sandstone oil reservoirs, including: checking and calculating the matching between the oil saturation and porosity of the target sandstone oil reservoir. If the oil saturation and porosity do not match, the resistivity of the target sandstone oil reservoir does not conform to the electrical method saturation model, and equivalent water conductivity correction is required during logging saturation calculation. If the two match, the next step is entered; calculating the minimum resistivity and the lower limit value of the resistivity increase rate of the target sandstone oil reservoir according to the lower limit of the oil saturation, and judging whether the resistivity of the target sandstone oil reservoir conforms to the law of the traditional electrical method saturation model; determining whether equivalent water conductivity correction is required for logging saturation calculation of the sandstone low resistivity oil reservoir according to whether the target sandstone oil reservoir conforms to the law of the traditional saturation model, and preliminarily classifying the causes of low resistivity of the target sandstone oil reservoir. The present invention can be widely applied in the field of the oil and gas industry.

Description

Technical Field

[0001] The invention belongs to the field of petroleum and natural gas, and more specifically, relates to a method and system for quickly classifying the causes of low resistivity in sandstone oil layers based on well logging data. Background Art

[0002] There are many causes of low resistivity in sandstone oil layers, including high porosity, high mineralization water, high bound water saturation, high mud content and clay additional conductivity, microcrack development, rock wettability and hydrophilicity, thin interlayers of sand and mud, conductive minerals, poor oil-water anisotropy and mud invasion, etc. How to identify which causes are the causes of low resistivity in sandstone oil layers? No equivalent water conductivity correction is required. The traditional electrical saturation model can be used to accurately calculate the oil saturation of the oil layer; which causes do not meet the commonly used electrical saturation model and require equivalent water conductivity correction. This is very important for the logging saturation calculation of low-resistivity oil layers and directly affects the scale of oil layer reserve calculation.

[0003] By judging whether it is necessary to perform equivalent water conductivity correction when calculating the saturation of low-resistivity oil layers, and after a preliminary classification of the causes of low resistivity in oil layers, combined with qualitative understanding of experimental analysis and logging data, the causes of low resistivity in sandstone oil layers can be further clarified, and reasonable engineering and development plans can be designed in a targeted manner to improve the development effect of low-resistivity oil layers.

[0004] However, the current classification method of low-resistivity genesis has nothing to do with whether the traditional electrical saturation model is satisfied or not, and has nothing to do with whether equivalent water conductivity correction is required. Therefore, it is impossible to reasonably calculate the saturation of low-resistivity oil layers, and the causes of low resistivity cannot be effectively distinguished. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a method and system for rapid preliminary classification of the causes of low resistivity in sandstone oil layers. It can determine whether equivalent water conductivity correction is required when calculating the oil saturation of low resistivity oil layers in a variety of ways to clarify the preliminary classification of the causes of low resistivity in low resistivity oil layers, thereby improving the accuracy of oil saturation calculation in low resistivity oil layers.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for rapid preliminary classification of the causes of low resistivity in sandstone oil layers, comprising the following steps:

[0008] Check and calculate the matching of oil saturation and porosity of the target sandstone oil layer. If the oil saturation and porosity do not match, it is considered that the low resistivity of the target sandstone oil layer does not conform to the law of the electrical saturation model, and equivalent water conductivity correction is required when calculating the well logging saturation; if the two match, proceed to the next step for re-judgment;

[0009] Calculate the minimum resistivity and the lower limit value of the resistivity increase rate of the target sandstone oil layer according to the lower limit of oil saturation, and determine whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model and whether equivalent water conductivity correction is required during logging saturation calculation based on the calculated minimum resistivity and the lower limit value of the resistivity increase rate of the inverse calculated oil layer;

[0010] Determine the preliminary classification result of the low resistivity cause of the target sandstone oil layer according to whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model.

[0011] Further, the inspection calculation of the matching between the oil saturation and porosity of the target sandstone oil layer includes:

[0012] Calculate the curve LSOP of the natural logarithm ratio of the oil saturation to the porosity of the target sandstone oil layer;

[0013] Based on the calculated curve LSOP, determine the matching between the oil saturation and porosity;

[0014] Among them, the calculation formula is:

[0015] LSOP = LnSo / LnPOR

[0016] In the formula: LSOP is the ratio of the natural logarithm of the oil saturation to the natural logarithm of the porosity, dimensionless; LnSo is the natural logarithm of the oil saturation, dimensionless; LnPOR is the natural logarithm of the porosity, dimensionless.

[0017] Further, the calculation of the minimum resistivity and the lower limit value of the resistivity increase rate of the target sandstone oil layer according to the lower limit of oil saturation, and the determination of whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model include:

[0018] Determine the lower limit of the oil saturation of the target sandstone oil layer;

[0019] Calculate the minimum resistivity of the target sandstone oil layer based on the lower limit of the oil saturation of the target sandstone oil layer, compare the reservoir resistivity of the target sandstone oil layer with the calculated minimum resistivity of the inverse calculated oil layer, and determine whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model and whether equivalent water conductivity correction is required during logging saturation calculation according to the comparison result;

[0020] Calculate the lower limit value of the resistivity increase rate of the target sandstone oil layer based on the lower limit of the oil saturation of the target sandstone oil layer, compare the lower limit value of the resistivity increase rate of the target sandstone oil layer with the resistivity increase rate of the reservoir after shale correction, and determine whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model and whether equivalent water conductivity correction is required during logging saturation calculation according to the comparison result.

[0021] Further, when comparing the reservoir resistivity of the target sandstone oil layer with the minimum resistivity of the back-calculated oil layer, if the reservoir resistivity of the target sandstone oil layer is greater than the minimum resistivity of the back-calculated oil layer, it conforms to the law of the electrical method saturation model, and no equivalent water conductivity correction is required when calculating the logging saturation.

[0022] Further, calculating a lower limit value of the resistivity increase rate of the target sandstone oil layer based on the lower limit of the oil saturation of the target sandstone oil layer, and comparing the lower limit value of the resistivity increase rate of the target sandstone oil layer with the resistivity increase rate after shale correction, and judging whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model according to the comparison result, including:

[0023] Performing shale correction on the resistivity of the target sandstone oil layer;

[0024] Calculating the resistivity increase rate of the target sandstone oil layer based on the resistivity after shale correction;

[0025] Comparing the resistivity increase rate of the target sandstone oil layer with the lower limit value of the resistivity increase rate. If the resistivity increase rate is less than the lower limit value of the resistivity increase rate of the oil layer, the resistivity of the target sandstone oil layer does not conform to the law of the electrical method saturation model, and equivalent water conductivity correction is required when calculating the logging saturation.

[0026] Further, determining the classification of the low resistivity cause of the target sandstone oil layer according to whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model, including:

[0027] If the low resistivity of the target sandstone oil layer does not conform to the law of the electrical method saturation model, the causes of its low resistivity oil layer include microfracture development, thin interbedding of sand and shale, hydrophilic rock wettability, conductive minerals, poor oil-water differentiation, and mud invasion;

[0028] If the resistivity of the target sandstone oil layer conforms to the law of the electrical logging saturation model, the causes of its low resistivity oil layer include high porosity, high salinity water, high irreducible water saturation, high shale content, and additional conductivity of clay.

[0029] In a second aspect, the present invention provides a rapid preliminary classification system for the causes of low resistivity in sandstone oil layers, including:

[0030] A matching degree calculation module, configured to check and calculate the matching degree between the oil saturation and the porosity of the target sandstone oil layer. If the oil saturation and the porosity do not match, it is considered that the low resistivity of the target sandstone oil layer does not conform to the law of the electrical method saturation model, and equivalent water conductivity correction is required when calculating the logging saturation. If the two match, the comparison result is sent to the oil saturation lower limit judgment module for re-judgment;

[0031] An oil saturation lower limit judgment module, which is used to calculate the minimum resistivity and the lower limit value of the resistivity increase rate of the target sandstone oil layer according to the lower limit of oil saturation, and judge whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model and whether equivalent water conductivity correction is required during logging saturation calculation according to the back-calculated minimum resistivity and the lower limit value of the resistivity increase rate of the oil layer;

[0032] A low resistivity origin classification module, which is used to determine the preliminary classification result of the low resistivity origin of the target sandstone oil layer according to whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model.

[0033] Further, the oil saturation lower limit judgment module includes:

[0034] An oil saturation lower limit calculation module, which is used to determine the lower limit of oil saturation of the target sandstone oil layer;

[0035] A first judgment module, which is used to calculate the minimum resistivity of the target sandstone oil layer based on the lower limit of oil saturation of the target sandstone oil layer, compare the minimum resistivity of the target sandstone oil layer with the reservoir resistivity, and judge whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model and whether equivalent water conductivity correction is required during logging saturation calculation according to the comparison result;

[0036] A second judgment module, which is used to calculate the lower limit value of the resistivity increase rate of the target sandstone oil layer based on the lower limit of oil saturation of the target sandstone oil layer, compare the lower limit value of the resistivity increase rate of the target sandstone oil layer with the resistivity increase rate after shale correction, and judge whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model and whether equivalent water conductivity correction is required during logging saturation calculation according to the comparison result.

[0037] In a third aspect, the present invention provides a computer-readable storage medium storing one or more programs, where the one or more programs include instructions that, when executed by a computing device, cause the computing device to execute any one of the methods in the method.

[0038] In a fourth aspect, the present invention provides a computing device, including: one or more processors, a memory, and one or more programs, where the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any one of the methods in the method.

[0039] Due to the above technical solutions adopted by the present invention, it has the following advantages:

[0040] 1. The present invention determines the lower limit of oil saturation in low-resistivity oil layers by combining the characteristic values calculated by the traditional logging saturation model for the highest porosity section of low-resistivity oil layers with the regional saturation empirical parameters, modifies two discriminant conditions in the traditional definition of low-resistivity oil layers, and changes the resistivity increase rate limit 2 in the traditional definition of low-resistivity oil layers to determine the lower limit of the resistivity increase rate according to the lower limit of oil saturation in the oil layer.

[0041] 2. The present invention calculates the lower limit of oil layer resistivity according to the lower limit of oil saturation in the oil layer, determines whether the low-resistivity oil layer with absolute low resistivity is a normal resistivity oil layer, realizes the discrimination of whether equivalent water conductivity correction is needed during the calculation of oil saturation in low-resistivity oil layers, and then preliminarily classifies the causes of low resistivity in sandstone oil layers, avoiding human discrimination errors and fully meeting the selection of equivalent water conductivity correction during the calculation of oil saturation in low-resistivity oil layers.

[0042] 3. The present invention adds the calculation of the matching degree between oil saturation and porosity to quickly judge whether the low-resistivity oil layer conforms to the traditional saturation model, thereby discriminating whether equivalent water conductivity correction is needed during the calculation of oil saturation in low-resistivity oil layers and realizing the preliminary classification of the causes of low resistivity in oil layers.

[0043] Therefore, the present invention can be widely applied in the field of oil and gas industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0045] Figure 1 is the flowchart of the method for preliminary classification of the causes of low resistivity in fast sandstone oil layers provided by the embodiment of the present invention;

[0046] Figure 2 is the schematic diagram of the discrimination of oil saturation correction in the low-resistivity oil layer of Well A in the embodiment of the present invention;

[0047] Figure 3 is the schematic diagram of the discrimination of oil saturation correction in the low-resistivity oil layer of Well B in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the drawings of the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0049] It should be noted that the terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0050] Term Explanation:

[0051] Low resistivity oil layer: refers to those oil layers with hydrocarbon fluids of certain industrial value but relatively low resistivity values measured by well logging.

[0052] There are two traditional methods for defining low resistivity oil layers:

[0053] 1) According to the absolute resistivity value of the oil layer;

[0054] 2) According to the resistivity increase rate of the oil layer. In the same oil-water system, the ratio of the apparent resistivity of the oil layer to that of the pure water layer is less than 2, that is, the resistivity increase rate of the oil layer is less than 2.

[0055] Equivalent water conductivity: refers to the conductivity where all or part of the oil pore volume is water due to the network distribution state of a small amount of water in the oil layer.

[0056] The formation rule of the present invention is the understanding of the causes of low resistivity in sandstone oil layers, that is, high porosity, high salinity, high irreducible water saturation, high shale content, and additional conductivity of clay, which satisfy the common electrical method saturation models. These causes are not the reasons for the similar resistivity between the low resistivity oil layer and the water layer under the same reservoir conditions. Otherwise, these common electrical method saturation models do not hold. Therefore, these low resistivity causes do not require equivalent water conductivity correction when calculating saturation, and the traditional Archie and shale sandstone saturation models can accurately calculate the oil saturation of low resistivity oil layers; while the low resistivity causes that do not satisfy the common electrical method saturation models, such as developed microfractures, thin interbeds of sand and shale, hydrophilic rock wettability, conductive minerals, poor oil-water differentiation, and mud invasion, etc., the deep reason is that the equivalent water conductivity generated by the network distribution of a small amount of movable water or irreducible water leads to the low resistivity of the oil layer (and the conductivity generated by mud invading some pores can also be regarded as the equivalent water conductivity generated by equivalent water porosity), and these causes do not satisfy the common electrical method saturation models. The traditional logging saturation model can be used for high conductivity, that is, equivalent water conductivity correction to accurately calculate the oil saturation.

[0057] First, it is necessary to identify low resistivity oil layers. It is obviously inappropriate to use resistivity discrimination to judge low resistivity oil layers. Therefore, the identification of low resistivity oil layers can adopt the method of comparing the oil-bearing display in mud logging and gas logging anomalies with the effective porosity, or can also adopt methods such as stratigraphic correlation and formation testing to discriminate low resistivity oil layers.

[0058] After identifying low-resistivity oil layers, it is necessary to calculate the oil saturation. Due to the high porosity, high salinity, high irreducible water saturation, high shale content, and clay additional conductivity that satisfy the common electrical logging saturation models, although these factors can lead to low resistivity of oil layers, they are not the reasons why the resistivity of low-resistivity oil layers is similar to that of water layers under the same reservoir conditions. The saturation of these types of low-resistivity oil layers can be calculated using traditional logging saturation models, while for low-resistivity oil layers caused by other low-resistivity factors, high-conductivity correction, i.e., equivalent water conductivity correction, is required when calculating the saturation. Therefore, a suitable and rapid discrimination method is needed for low-resistivity oil layers to distinguish whether the resistivity of low-resistivity oil layers meets the traditional electrical method saturation model, and then the low-resistivity factors can be preliminarily classified.

[0059] Currently, there are many analyses on the causes of low resistivity in sandstone oil layers. The causes of low resistivity are mainly divided into internal factors (such as high porosity, high salinity water, high irreducible water saturation, high shale content, clay additional conductivity, well-developed microfractures, hydrophilic rock wettability, thin interbeds of sand and shale, etc.), external factors (such as mud invasion), and mixed factors. However, this classification cannot distinguish whether the causes of low-resistivity oil layers meet the traditional electrical method saturation model, and has nothing to do with whether high-conductivity correction, i.e., equivalent water conductivity correction, is required. In the previous work of the applicant, it was expounded that the main cause of low resistivity in oil layers is the high conductivity generated by the network distribution of a small amount of mobile water or irreducible water (abbreviated as a small amount of water), which is the main reason for the low resistivity of oil layers. The equivalent water conductivity correction method was studied, and a new corrected saturation calculation model was established. However, the various causes were not classified either, that is, which causes of low resistivity in oil layers require equivalent water conductivity correction and which do not, and the saturation of low-resistivity oil layers can be accurately calculated using traditional logging models.

[0060] Moreover, the two conditions for traditional low-resistivity oil layers to discriminate low-resistivity oil layers are also insufficient. For example, an oil layer with an absolute low resistivity may meet the traditional saturation model, that is, a normal resistivity oil layer; the ratio of the increase rate of the oil layer resistivity is 2, using the ratio of the apparent resistivity of the oil layer to the resistivity of the water layer, and the influence of shale on the apparent resistivity of the oil layer varies. Therefore, the lower limit of the increase rate of the oil layer resistivity being 2 (some literature says the lower limit of the resistivity increase rate is 3) is also inaccurate. In addition, the matching between the calculated saturation and porosity is increased to quickly determine whether to use equivalent water conductivity correction. At the same time, the method for determining the lower limit of the oil saturation in sandstone low-resistivity oil layers was studied, and the lowest resistivity of the oil layer and the lower limit of the resistivity increase rate were determined based on the lower limit of the oil saturation.

[0061] In some embodiments of the present invention, a rapid classification method for the causes of low resistivity in sandstone oil layers is provided. By determining whether to use equivalent water conductivity correction when calculating the saturation of low-resistivity oil layers and being able to quickly distinguish during the calculation process of the saturation of low-resistivity oil layers, a preliminary classification of the causes of low-resistivity oil layers is achieved.

[0062] Correspondingly, in some other embodiments of the present invention, a rapid classification system, device and storage medium for the causes of low resistivity in sandstone oil reservoirs are provided.

[0063] Embodiment 1

[0064] As Figure 1 shown, a preliminary classification method for the causes of low resistivity in sandstone oil reservoirs provided in this embodiment starts from two defining conditions of low resistivity oil layers, and comprehensively determines whether the resistance of low resistivity oil layers meets the traditional electrical method saturation model through various methods, and determines whether equivalent water conductivity correction is required, so as to classify the causes of reservoir low resistivity, including the following steps:

[0065] 1) Check and calculate the matching degree between the oil saturation and porosity of the target sandstone oil reservoir. If the oil saturation and porosity do not match, it is considered that the resistivity of the target sandstone oil reservoir does not conform to the law of the traditional electrical method saturation model. If the two match, go to step 2) for re-judgment.

[0066] In this embodiment, when identifying the target sandstone oil reservoir, the method of comparing the oil-bearing display in logging and gas logging anomalies with the effective porosity can be used, or methods such as stratigraphic correlation and formation testing can be used to identify low resistivity oil layers. The present invention does not limit the specific identification methods.

[0067] For a single sandstone oil reservoir, regardless of whether the resistivity is high or low, its geological law is that the better the physical properties, that is, the higher the porosity, the higher the oil saturation, that is, the oil saturation is proportional to the porosity, which is also the same as the expression law of the Archie saturation formula. The logging electrical method saturation model uses resistivity and porosity to calculate the oil saturation. When the oil saturation is certain, if the porosity increases, the resistivity of the oil layer can decrease regularly, and this change conforms to the traditional saturation model such as the Archie formula, that is, normal resistivity changes will not cause the matching degree of oil saturation and porosity to deteriorate; if the resistivity of the oil layer decreases abnormally, resulting in a decrease in the calculated oil saturation by the logging electrical method saturation model, so the ratio of oil saturation to porosity decreases, and the situation of non-matching between the calculated oil saturation and porosity appears. If it is the influence of shale and clay additional conductivity, the corresponding natural gamma curve value will be relatively high, so this shale influence part can be removed for analysis, or the shale corrected saturation model can be applied for analysis. All in all, the low resistivity of sandstone oil reservoirs can lead to non-conformity with the true oil saturation, but the porosity of sandstone oil reservoirs is consistent with the true oil saturation, otherwise the traditional logging saturation model such as the Archie formula will not hold at all.

[0068] According to the logging saturation calculation formula such as the Archie formula:

[0069]

[0070]

[0071] After taking the natural logarithm on both sides of formula (2), we have

[0072]

[0073] Since So = 1 - Sw, therefore

[0074] nLnSo = mLnPOR + LnRt - Ln(abR w ) (4)

[0075] In the formula: Rt is the reservoir resistivity, Ω·m; POR is the effective porosity, V / V; m is the cementation exponent, dimensionless; a is the lithology coefficient, dimensionless; b is the lithology saturation coefficient, dimensionless; n is the saturation exponent, dimensionless; Rw is the formation water resistivity, Ω·m; Sw is the water saturation, V / V; So is the oil saturation, V / V.

[0076] It can be seen from the above formula that the natural logarithm of the oil saturation is directly proportional to the natural logarithms of both the porosity and the resistivity. Due to the abnormal decrease of the low resistivity Rt, the calculated oil saturation So decreases, and the ratio of LnSo to LnPOR deviates from the original direct proportional line. Therefore, the matching of the oil saturation and the porosity can be judged by calculating the logarithmic ratio curve LSOP of the oil saturation and the porosity of the low resistivity oil layer, and then whether there is an abnormal change in the low resistivity can be judged.

[0077] LSOP = LnSo / LnPOR (5)

[0078] In the formula: LSOP is the ratio of the natural logarithm of the oil saturation to the natural logarithm of the porosity, dimensionless; LnSo is the natural logarithm of the oil saturation, dimensionless; LnPOR is the natural logarithm of the porosity, dimensionless.

[0079] At the same time, draw the logarithmic saturation curve LnSo and the porosity curve LnPOR, and visually indicate whether the resistivity of the low resistivity oil layer meets the traditional saturation model through the overlap of the two curves. If the shapes of the logarithmic saturation curve LnSo and the porosity curve LnPOR are inconsistent, that is, the matching is poor, and the ratio curve LSOP of the low resistivity sandstone oil layer changes greatly, then the resistivity does not meet the traditional electrical method saturation model, and the equivalent water conductivity correction needs to be carried out when calculating the saturation of the low resistivity oil layer; if the shapes of the logarithmic saturation curve LnSo and the porosity curve LnPOR are consistent and the matching is good, after removing the shale influence section of the high natural gamma section or using the shale corrected saturation, the ratio curve LSOP of the low resistivity sandstone oil layer is stable and approximately vertical. At this time, further discrimination is still needed to determine whether the equivalent water conductivity correction needs to be carried out when calculating the saturation of the low resistivity oil layer.

[0080] 2) Calculate the minimum resistivity and the lower limit value of the resistivity increase rate of the target sandstone oil layer according to the lower limit of oil saturation, and judge whether the resistivity of the target sandstone oil layer conforms to the law of the traditional electrical method saturation model based on the calculated minimum resistivity and the lower limit value of the resistivity increase rate of the oil layer.

[0081] 2.1) Determine the lower limit of oil saturation of the target sandstone oil layer by combining logging calculation of saturation with experimental analysis data and regional saturation empirical parameters.

[0082] The evaluation of low-resistivity sandstone oil layers has become a difficult problem in the logging profession mainly because the traditional logging saturation model based on electrical methods results in a low calculated oil saturation when the resistivity of the oil layer is extremely low. Therefore, the calculated result of the oil saturation of the sandstone oil layer is the key to identifying low-resistivity oil layers.

[0083] The lower limit of oil saturation in sandstone oil layers is generally 0.5 V / V. However, due to the influence of reservoir shale in some sandstone oil layers, the lower limit of oil saturation can be relaxed to 0.4 V / V (i.e., the upper limit of water saturation is 0.6 V / V). According to statistics, most of the lower limits of sandstone oil layer saturation declared for national reserves are currently 0.4 V / V for the lower limit of oil saturation.

[0084] Through research, it is found that the characteristic value calculated by the traditional logging saturation model at the highest porosity section of low-resistivity oil layers can be used as a reference for the lower limit of oil saturation in low-resistivity oil layers. The reason is that the oil saturation is theoretically the highest at the highest porosity section of low-resistivity oil layers. Due to the low-resistivity effect in low-resistivity oil layers, the oil saturation generally needs to be corrected. Therefore, the range that the oil saturation of low-resistivity oil layers can reach even without correction can be used to determine the lower limit of the oil saturation of this low-resistivity oil layer; while the calculated range of oil saturation in sandstone oil layers with normal resistivity can be very large, and there is no problem of saturation correction. Obviously, the saturation characteristic value at the highest porosity section cannot be used as a reference for the lower limit value of saturation. Whether the lower limit of oil saturation in sandstone low-resistivity oil layers is selected as 0.5 V / V or 0.4 V / V, or other even lower lower limits of oil saturation, can be determined by combining experimental analysis data. In the absence of experimental data, generally, when the oil saturation calculated by the traditional logging saturation model at the highest porosity section of low-resistivity oil layers is greater than or equal to 0.5 V / V, the lower limit of oil saturation in low-resistivity oil layers can be directly selected as 0.5 V / V; if the oil saturation calculated by the traditional logging saturation model at the highest porosity section of low-resistivity oil layers is less than or equal to 0.4 V / V, the lower limit of oil saturation in low-resistivity oil layers can be selected as 0.4 V / V; if the oil saturation calculated by the traditional logging saturation model at the highest porosity section of low-resistivity oil layers is greater than 0.4 V / V and less than 0.5 V / V, the lower limit of oil saturation in low-resistivity oil layers can be considered as appropriate, generally taken as 0.45 V / V.

[0085] It should be noted that when the oil saturation calculated by the traditional logging saturation model in the highest porosity section of the oil layer is greater than 0.5 V / V, the resistivity increase rate is greater than 4 at this time, and this oil layer is generally not regarded as a low-resistivity oil layer. Therefore, it is reasonable that the upper limit of the oil saturation of the current low-resistivity oil layer is up to 0.5 V / V at most; while the lower limit of the oil saturation of the selected sandstone oil layer is at least 0.4 V / V, considering the correction of the oil saturation of most low-resistivity sandstone oil layers, which meets the saturation requirements of the vast majority of sandstone oil layers.

[0086] If there is experimental analysis data proving that the lower limit of the oil saturation of the low-resistivity oil layer is lower, that is, the irreducible water saturation is very high. For sandstone oil layers with high irreducible water, whether it is caused by the development of small pores or the influence of shale, it is difficult for the mud to invade, and the deep and shallow resistivities generally overlap, which is relatively easy to identify. At this time, the calculated water saturation value by the traditional logging saturation model will also be relatively high (greater than 0.6 V / V), and the calculated oil saturation has a good match with the porosity. It is still possible to select a lower lower limit of the oil saturation according to the saturation characteristic value calculated by the traditional logging saturation model in the highest porosity section of the low-resistivity oil layer, and establish an empirical formula for the irreducible water saturation through logging methods; according to research, high resistivity, high porosity, and low shale content correspond to relatively low irreducible water saturation, and vice versa, the irreducible water saturation is high. Therefore, an empirical formula for the irreducible water saturation can be established using experimental data:

[0087] Swi = Cwi × Vsh / (POR × Rt) (6)

[0088] In the formula: Swi is the irreducible water saturation, V / V; Cwi is the coefficient of the empirical formula; Vsh is the shale content, V / V; POR is the effective porosity, V / V; Rt is the resistivity of the reservoir, Ω·m.

[0089] Therefore, the upper limit of the water saturation Swmx of the sandstone low-resistivity oil layer is:

[0090] Swmx = Swi (7)

[0091] Furthermore, the lower limit of the oil saturation Somn of the sandstone low-resistivity oil layer is obtained as:

[0092] Somn = 1 - Swmx (8)

[0093] 2.2) Calculate the minimum resistivity of the target sandstone oil layer based on the lower limit of the oil saturation of the target sandstone oil layer, and determine whether the resistivity of the target sandstone oil layer conforms to the law of the traditional electrical method saturation model according to the comparison result between the minimum resistivity of the target sandstone oil layer and the resistivity of the reservoir.

[0094] For low-resistivity oil layers, the minimum resistivity of the oil layer Rtmn can be calculated by back-calculation based on the upper limit of water saturation determined above, such as (0.6 V / V). By comparing Rtmn with the resistivity of the reservoir Rt, it can be determined whether the low-resistivity oil layer needs to be corrected for equivalent water conductivity. If the resistivity of the reservoir Rt is low but greater than the back-calculated minimum resistivity of the oil layer, it conforms to the traditional saturation model and does not require equivalent water conductivity correction. Thus, it can be determined that the main causes of low resistivity are high porosity, high salinity, high irreducible water saturation, high shale content, and additional conductivity of clay, etc. Therefore, low-resistivity oil layers with low absolute resistivity in the traditional sense may be normal resistivity oil layers, and this type of oil layer with low absolute resistivity can be distinguished by back-calculating the minimum resistivity of the oil layer and combining the following steps.

[0095] Taking the traditional shale correction model, the Simandoux model, as an example:

[0096]

[0097] If the upper limit of water saturation Swmx of the low-resistivity oil layer is taken as 0.6 V / V, then the back-calculated minimum resistivity of the oil layer is:

[0098]

[0099] If the upper limit of water saturation Swmx of the low-resistivity oil layer is taken as 0.5 V / V, then the back-calculated minimum resistivity of the oil layer is:

[0100]

[0101] Where: Rt is the resistivity of the reservoir, Ω·m; POR is the effective porosity, V / V; m is the cementation exponent, dimensionless; a is the lithology coefficient, dimensionless; b is the lithology saturation coefficient, dimensionless; n is the saturation exponent, dimensionless; Rw is the resistivity of formation water, Ω·m; Sw is the water saturation, V / V; Vsh is the shale content, V / V; Rsh is the resistivity of shale, Ω·m; Rtmn is the back-calculated minimum resistivity of the oil layer, Ω·m.

[0102] If Rt ≥ Rtmn, the apparent resistivity of the oil layer is relatively high and no equivalent water conductivity correction is required. Therefore, some traditional low-resistivity oil layers with low absolute resistivity are also normal resistivity oil layers; if Rt < Rtmn, the apparent resistivity of the low-resistivity oil layer is relatively low, and when calculating the saturation, not only shale correction but also equivalent water conductivity correction are required.

[0103] 2.3) Compare the resistivity increase rate of the target sandstone oil layer after shale correction with the lower limit value of the resistivity increase rate, and judge whether the resistivity of the target sandstone oil layer conforms to the law of the traditional electrical method saturation model according to the comparison result.

[0104] According to the definition condition 2 of low-resistivity oil layers: Based on the resistivity increase rate of the oil layer, the ratio of the apparent resistivity of the oil layer to that of the pure water layer in the same oil (gas) - water system is less than 2, that is, the resistivity increase rate of the oil layer is less than 2.

[0105] Defining the resistivity increase rate of the oil layer to be less than 2 or other values is actually inaccurate as it does not consider the difference in shale conductivity effects. Due to the influence of shale and additional conductivity, the measured apparent resistivity of the oil layer is generally reduced, but the shale influence can be large or small, which also affects the lower limit of the resistivity increase rate of the oil layer. Therefore, it is necessary to correct this shale - induced low resistivity of the oil layer, that is, to compare the resistivity of the shale - corrected oil layer with that of the water layer to determine whether the low - resistivity oil layer needs to be corrected for equivalent water conductivity, and whether the lower limit of the resistivity increase rate is 2 also needs to be determined after calculating based on the upper limit of water saturation.

[0106] Taking the traditional Simandoux model as an example, the calculation method of the resistivity of the shale - corrected oil layer is as follows:

[0107]

[0108] The above formula consists of three parts, reservoir conductivity: Oil layer conductivity: Shale conductivity: Therefore, the conductivity of the shale - corrected oil layer is:

[0109]

[0110] Or

[0111]

[0112] In the formula: Rt is the reservoir resistivity, Ω·m; POR is the effective porosity, V / V; m is the cementation exponent, dimensionless; a is the lithology coefficient, dimensionless; b is the lithology saturation coefficient, dimensionless; n is the saturation exponent, dimensionless; Rw is the formation water resistivity, Ω·m; Sw is the water saturation, V / V; Vsh is the shale content, V / V; Rsh is the shale resistivity, Ω·m; Rtxz is the resistivity of the shale - corrected oil layer, Ω·m.

[0113] Through formula (13) or formula (14), the resistivity of the shale - corrected oil layer can be calculated. The back - calculation of Rtxz for other shale - correction models such as Waxman - Smits, dual - water model, and Indonesian formula is similar to the above method. The formation resistivity increase rate is corrected as:

[0114]

[0115] Since the resistivity of the water layer Ro (at this time Sw = 1) of this layer can be expressed as:

[0116]

[0117] Therefore

[0118]

[0119] In the formula: I is the formation resistivity increase factor; Rtxz is the resistivity of the oil layer after shale correction, Ω·m; Ro is the resistivity of the water layer, Ω·m; Sw is the water saturation, V / V; POR is the effective porosity, V / V; m is the cementation exponent, dimensionless; a is the lithology coefficient, dimensionless; b is the lithology saturation coefficient, dimensionless; n is the saturation exponent, dimensionless.

[0120] If the upper limit of water saturation in the oil layer Swmx is taken as 0.6 V / V, the lower limit of the formation resistivity increase factor Imin is:

[0121]

[0122] If the upper limit of water saturation in the oil layer Swmx is taken as 0.5 V / V, the lower limit of the formation resistivity increase factor Imin is:

[0123]

[0124] If the upper limit of water saturation in the oil layer Swmx is taken as 0.55 V / V, the lower limit of the formation resistivity increase factor Imin is:

[0125]

[0126] Therefore, the condition that the resistivity increase factor satisfied by the low-resistivity oil layer can be relaxed to a maximum of 4.0 and a minimum of 2.78. The resistivity increase factor of the traditional low-resistivity oil layer is less than 2, and obviously many low-resistivity oil layers will be missed.

[0127] 3) Determine the classification of the causes of low resistivity in the target sandstone oil layer according to whether the low resistivity of the target sandstone oil layer conforms to the law of the traditional saturation model.

[0128] According to the analysis in steps 1) and 2), as long as one of the following conditions is met: that is, the shape of the oil saturation and porosity in the sandstone oil layer does not match and the natural logarithm ratio curve changes significantly, or the resistivity of the low-resistivity oil layer is less than the minimum resistivity of the back-calculated oil layer, or the increase rate of the formation resistivity after shale correction is less than the lower limit of the increase rate of the oil layer resistivity (the lower limit of the increase rate of the resistivity is 2.78 when the upper limit of the water saturation in the oil layer is 0.6 V / V, and the lower limit of the increase rate of the resistivity is 4.0 when the upper limit of the water saturation in the oil layer is 0.5 V / V), then the resistivity of the target sandstone oil layer does not conform to the law of the traditional logging saturation model, and equivalent water conductivity correction is required when calculating the saturation of the low-resistivity sandstone oil layer. The combination of various methods in the present invention can completely avoid the omission of the saturation correction of the low-resistivity oil layer by a single method; if the shape of the oil saturation and porosity of a single layer matches and the ratio curve is stable, and the resistivity of the low-resistivity oil layer is greater than the minimum resistivity of the back-calculated oil layer, and the increase rate of the formation resistivity after shale correction is greater than the lower limit of the increase rate of the resistivity, then the low resistivity of the sandstone oil layer conforms to the law of the traditional logging saturation model, and equivalent water conductivity correction is not required when calculating the saturation of the low-resistivity sandstone oil layer.

[0129] According to whether the low resistivity of the target sandstone oil layer conforms to the law of the traditional saturation model, the present invention preliminarily classifies the causes of the low resistivity of the target oil layer into 2 categories:

[0130] The low resistivity of the target sandstone oil layer does not conform to the law of the traditional electrical method saturation model, and equivalent water conductivity correction is required. The causes of the low resistivity of the relevant sandstone oil layer include the development of microfractures, thin interbedding of sand and shale, hydrophilic rock wettability, conductive minerals, poor oil-water differentiation, and mud invasion, etc.;

[0131] The resistivity of the low-resistivity oil layer satisfies the law of the traditional logging saturation model, and equivalent water conductivity correction is not required. The causes of the relevant low-resistivity oil layer include high porosity, high salinity water, high irreducible water saturation, high shale content, and additional conductivity of clay, etc.

[0132] It can be seen that the preliminary classification method of the causes of the low resistivity of the sandstone oil layer provided by the present invention improves the two discrimination conditions for the definition of the low-resistivity oil layer, can quickly distinguish whether the resistivity satisfies the traditional logging saturation model, and discriminates whether equivalent water conductivity correction is required when calculating the saturation of the low-resistivity oil layer, so as to realize the preliminary classification of the causes of the low resistivity of the sandstone oil layer and avoid the mistakes of manual discrimination.

[0133] Example 2

[0134] The following takes an actual well as an example to illustrate the above cause classification method and implementation process. Specific implementation method:

[0136] Taking Well A as an example, see the appendix Figure 2 .

[0137] Step 1: Select the low-resistivity oil layer sections to be analyzed, namely Layer 3 and Layer 4 in the figure

[0138] Step 2: Check the matching of the calculated oil saturation and porosity

[0139] Calculate the oil saturation using traditional logging models such as the Simandoux formula, calculate the porosity at the same time, and calculate the natural logarithm curves of the oil saturation and porosity and the ratio curve of the two. The results are shown as the water saturation (traditional model), porosity, and the logarithm of the oil saturation (traditional model), logarithm of the porosity, etc. curves in the figure

[0140] The fifth track in the figure shows the natural logarithm of the oil saturation calculated by the traditional logging model and the conventional calculated porosity. Due to the low-resistivity effect, the oil saturation curve in the figure does not change consistently with the porosity curve. The change of the ratio curve of the oil saturation calculated by the traditional logging model and the natural logarithm of the porosity in the seventh track of the figure is obvious. So far, by checking the matching of the calculated oil saturation and porosity, it is found that the matching of the two is poor and equivalent water conductivity correction is needed

[0141] Therefore, the causes of low resistivity in this type of reservoir can be preliminarily considered as the development of microfractures, thin interbedding of sand and mud, hydrophilic rock wettability, conductive minerals, poor oil-water differentiation, and mud invasion, etc. A more detailed analysis of the low-resistivity causes can be further determined in combination with logging data

[0142] There is an obvious difference in the deep and shallow resistivity in the third track of the figure. Therefore, the cause of low resistivity in this layer does not include high irreducible water saturation; in the section with the highest porosity (4834 - 4836 m), the oil saturation calculated by the traditional model is less than 0.4 V / V. Therefore, the lower limit of the oil saturation of this low-resistivity oil layer is selected as 0.4 V / V (corresponding to a water saturation of 0.6 V / V), and the minimum resistivity and the lower limit of the resistivity increase rate of the oil layer can be calculated backward

[0143] After the equivalent water conductivity correction, the sixth track in the figure shows that the natural logarithm curves of the oil saturation and porosity of Layer 3 and Layer 4 almost overlap, reflecting the consistency between physical properties and oiliness. The ratio curve of the oil saturation and the logarithm of the porosity of Layer 3 and Layer 4 in the seventh track of the figure is approximately a vertical line. The corrected water saturation in the tenth track of the figure is significantly lower than the result of the water saturation calculated by the traditional model, that is, the oil saturation of the oil layer increases significantly, and the calculated reserve scale of the sandstone oil layer can be increased

[0144] Example 3

[0145] Taking Well B as an example, see the appendix Figure 3 .

[0146] Step 1: Select the low-resistivity oil layer section, namely Layer 2 in the figure

[0147] Step 2: Check the matching of the calculated oil saturation and porosity

[0148] The traditional logging model such as Simandoux formula is used to calculate the oil saturation, and at the same time, the porosity is calculated, and the natural logarithm curve of the oil saturation and the porosity and the ratio curve of the two are calculated. The results are shown in the curves of water saturation (traditional model), porosity, and the logarithm of oil saturation (traditional model), and the logarithm of porosity in the figure.

[0149] The fifth track in the figure shows the natural logarithm of the oil saturation calculated by the traditional logging model and the conventional calculated porosity. The curves of the oil saturation and the porosity in the figure change relatively consistently, while the change of the ratio curve of the natural logarithm of the oil saturation calculated by the traditional logging model and the porosity in the seventh track in the figure is more obvious. It can be preliminarily judged that the equivalent water conductivity correction needs to be carried out for this layer. In order to further implement the equivalent water conductivity correction for the low-resistivity oil layer, the third step can be continued.

[0150] Step 3: Lower limit method for oil saturation of sandstone low-resistivity oil layer

[0151] In the highest porosity section (1659 - 1661 m) of the No. 2 low-resistivity layer, the oil saturation calculated by the traditional model is less than 0.5 V / V but greater than 0.4 V / V. Obviously, it is not a low-resistivity oil layer with high irreducible water saturation. Therefore, the lower limit value of the oil saturation of this section of the low-resistivity oil layer is selected as 0.45 V / V (corresponding to the water saturation of 0.55 V / V). Moreover, the water saturation processed by the traditional model in the lower No. 4 water layer has reached 0.6 V / V. Obviously, the lower limit value of the oil saturation of the low-resistivity oil layer should be higher than 0.4 V / V. Therefore, the lower limit value of the oil saturation of the No. 2 low-resistivity oil layer being 0.45 V / V is also reasonable and will not miss the low-resistivity oil layer. The fact that the corrected oil saturation of the No. 2 layer is greater than 0.5 V / V also verifies this point.

[0152] Back-calculate the minimum resistivity of the oil layer:

[0153] Taking the Simandoux formula as an example:

[0154]

[0155] The results are shown in Figure 3 Track 8 in the figure. It can be seen from it that the measured resistivity is less than the back-calculated minimum resistivity of the oil layer, indicating that the resistivity of the No. 2 layer is relatively low and the equivalent water conductivity correction is required during the saturation calculation.

[0156] Calculate the lower limit value of the resistivity increase rate

[0157]

[0158] The results are shown in the appendix Figure 3 Track 9 in the figure. In some sections of the resistivity increase rate of the No. 2 layer, it is less than the lower limit value of the resistivity increase rate, which also proves that the saturation calculation of this low-resistivity oil layer needs to be corrected.

[0159] In summary of the second and third steps above, it is completely possible to determine that the equivalent water conductivity correction is required for Layer 2. Therefore, the causes of low resistivity in this type of reservoir can be preliminarily considered as the development of microfractures, thin interbedding of sand and shale, hydrophilic rock wettability, conductive minerals, poor oil-water differentiation, and mud invasion. A more detailed analysis of the causes of low resistivity can be further determined in combination with logging data.

[0160] After applying the equivalent water conductivity correction, the 6th track in the figure shows that the shapes of the oil saturation and porosity natural logarithm curves of Layer 2 are consistent, reflecting the consistency between physical properties and oiliness. The oil saturation and porosity logarithm ratio curve of Layer 2 in the 7th track in the figure is approximately a vertical line. The resistivity increase rate after correction in the 9th track in the figure is greater than the lower limit value of the resistivity increase rate. The water saturation after correction in the 10th track in the figure is significantly lower than the result calculated by the traditional model, that is, the oil saturation of the low resistivity oil layer increases, which can improve the calculated reserve scale of this oil layer.

[0161] The present invention provides a rapid calculation and classification method for the definition and initial classification of low resistivity oil layers. Under the existing theoretical understanding conditions, it can fully meet the determination of whether to perform equivalent water conductivity correction when calculating the saturation of low resistivity oil layers, and then preliminarily distinguish the causes of low resistivity in oil layers, realize the accurate calculation of the saturation of low resistivity oil layers, and increase the reserve calculation scale of low resistivity oil layers. A more detailed classification of the causes of low resistivity requires qualitative understanding in combination with experimental analysis and logging data, and the use of artificial intelligence methods with big data for identification. To check the matching of the calculated oil saturation and porosity, the common logarithm can also be used. However, the common logarithm curves of porosity and saturation have a large compression amount. Although the ratio results are the same, the changes in the logarithm curves of porosity and saturation are small, which is not conducive to overlapping comparison.

[0162] Example 4

[0163] The above Example 1 provides a preliminary classification method for the causes of low resistivity in rapid sandstone oil layers. Correspondingly, this example provides a preliminary classification system for the causes of low resistivity in rapid sandstone oil layers. The system provided in this example can implement the preliminary classification method for the causes of low resistivity in rapid sandstone oil layers in Example 1, and this system can be implemented in a software, hardware, or a combination of software and hardware manner. For example, this system can include integrated or separate functional modules or functional units to execute the corresponding steps in each method of Example 1. Since the system in this example is basically similar to the method embodiment, the description process in this example is relatively simple, and the relevant parts can refer to the partial description of Example 1. The embodiments of the system provided in this example are only illustrative.

[0164] The preliminary classification system for the causes of low resistivity in rapid sandstone oil layers provided in this example includes:

[0165] A matching degree calculation module is used to check and calculate the matching degree between the oil saturation and porosity of the target sandstone oil layer. If the oil saturation and porosity do not match, it is considered that the low resistivity of the target sandstone oil layer does not conform to the law of the traditional electrical method saturation model. If the two match, the comparison result is sent to the secondary judgment module for re-judgment;

[0166] An oil saturation lower limit judgment module is used to calculate the minimum resistivity and the lower limit value of the resistivity increase rate of the target sandstone oil layer according to the lower limit of the oil saturation, and judge whether the low resistivity of the target sandstone oil layer conforms to the law of the traditional electrical method saturation model according to the calculated minimum resistivity and the lower limit value of the resistivity increase rate of the oil layer;

[0167] A low resistivity cause classification module is used to determine the low resistivity cause classification of the target sandstone oil layer according to whether the low resistivity of the target sandstone oil layer conforms to the law of the traditional saturation model.

[0168] Further, the oil saturation lower limit judgment module includes:

[0169] An oil saturation lower limit calculation module is used to determine the lower limit of the oil saturation of the target sandstone oil layer;

[0170] A first judgment module is used to calculate the minimum resistivity of the target sandstone oil layer based on the lower limit of the oil saturation of the target sandstone oil layer, compare the minimum resistivity of the target sandstone oil layer with the reservoir resistivity, and judge whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model according to the comparison result;

[0171] A second judgment module is used to calculate the lower limit value of the resistivity increase rate of the target sandstone oil layer based on the lower limit of the oil saturation of the target sandstone oil layer, compare the lower limit value of the resistivity increase rate of the target sandstone oil layer with the resistivity increase rate after shale correction, and judge whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model according to the comparison result.

[0172] Embodiment 5

[0173] This embodiment provides a processing device corresponding to the fast preliminary classification method for the low resistivity cause of sandstone oil layers provided in Embodiment 1. The processing device can be a processing device for a client, such as a mobile phone, a laptop computer, a tablet computer, a desktop computer, etc., to execute the method of Embodiment 1.

[0174] The processing device includes a processor, a memory, a communication interface, and a bus. The processor, the memory, and the communication interface are connected through the bus to complete communication with each other. A computer program that can run on the processor is stored in the memory, and when the processor runs the computer program, it executes the fast preliminary classification method for the low resistivity cause of sandstone oil layers provided in Embodiment 1 of this embodiment.

[0175] In some embodiments, the memory may be a high-speed random access memory (RAM), and may also include non-volatile memory, such as at least one disk memory.

[0176] In other embodiments, the processor may be various types of general-purpose processors such as a central processing unit (CPU), a digital signal processor (DSP), etc., which are not limited herein.

[0177] Embodiment 6

[0178] The preliminary classification method for the low resistivity origin of fast sandstone oil reservoirs in Embodiment 1 of the present invention may be specifically implemented as a computer program product. The computer program product may include a computer-readable storage medium, on which computer-readable program instructions for executing the preliminary classification method for the low resistivity origin of fast sandstone oil reservoirs described in Embodiment 1 of the present invention are uploaded.

[0179] The computer-readable storage medium may be a tangible device that holds and stores instructions used by an instruction execution device. The computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination of the above.

[0180] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications or equivalent replacements can still be made to the specific embodiments of the present invention. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A preliminary classification method for the causes of low resistivity in fast sandstone oil reservoirs, characterized in that It includes the following steps: Check and calculate the matching of the oil saturation and porosity of the target sandstone oil layer. If the oil saturation and porosity do not match, it is considered that the low resistivity of the target sandstone oil layer does not conform to the law of the electrical method saturation model, and equivalent water conductivity correction is required during logging saturation calculation; if they match, proceed to the next step for re-judgment; Calculate the minimum resistivity and the lower limit value of the resistivity increase rate of the target sandstone oil layer according to the lower limit of the oil saturation, and judge whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model and whether equivalent water conductivity correction is required during logging saturation calculation based on the calculated minimum resistivity and the lower limit value of the resistivity increase rate of the oil layer; Determine the preliminary classification result of the low resistivity cause of the target sandstone oil layer according to whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model; 2. The preliminary classification method for the low resistivity origin of fast sandstone oil reservoirs according to claim 1, characterized in that, The check and calculation of the matching of the oil saturation and porosity of the target sandstone oil layer includes: Calculate the natural logarithm ratio curve LSOP of the oil saturation and porosity of the target sandstone oil layer; Based on the calculated curve LSOP, discriminate the matching of the oil saturation and porosity; Among them, the calculation formula is: LSOP = LnSo / LnPOR In the formula: LSOP is the ratio of the natural logarithm of the oil saturation to the natural logarithm of the porosity, dimensionless; LnSo is the natural logarithm of the oil saturation, dimensionless; LnPOR is the natural logarithm of the porosity, dimensionless.

3. A preliminary classification method for the low resistivity origin of fast sandstone oil reservoirs according to claim 1, characterized in that, The calculation of the minimum resistivity and the lower limit value of the resistivity increase rate of the target sandstone oil layer according to the lower limit of the oil saturation, and the judgment of whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model based on the calculated minimum resistivity and the lower limit value of the resistivity increase rate of the oil layer includes: Determine the lower limit of the oil saturation of the target sandstone oil layer; Calculate the minimum resistivity of the target sandstone oil layer based on the lower limit of the oil saturation of the target sandstone oil layer, compare the reservoir resistivity of the target sandstone oil layer with the calculated minimum resistivity of the oil layer, and judge whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model and whether equivalent water conductivity correction is required during logging saturation calculation according to the comparison result; Calculate the lower limit value of the resistivity increase rate of the target sandstone oil layer based on the lower limit of the oil saturation of the target sandstone oil layer, compare the lower limit value of the resistivity increase rate of the target sandstone oil layer with the resistivity increase rate after shale correction, and judge whether the low resistivity of the target sandstone oil layer conforms to the law of the electrical method saturation model and whether equivalent water conductivity correction is required during logging saturation calculation according to the comparison result.

4. A preliminary classification method for the origin of low resistivity in fast sandstone oil reservoirs according to claim 3, characterized in that, When comparing the reservoir resistivity of the target sandstone oil layer with the calculated minimum resistivity of the oil layer, if the reservoir resistivity of the target sandstone oil layer is greater than the calculated minimum resistivity of the oil layer, it conforms to the law of the electrical method saturation model, and equivalent water conductivity correction is not required during logging saturation calculation.

5. The preliminary classification method for the low resistivity origin of fast sandstone oil reservoirs according to claim 3, characterized in that, The lower limit of the resistivity increase rate of the target sandstone oil reservoir is calculated based on the lower limit of the oil saturation of the target sandstone oil reservoir, and the lower limit of the resistivity increase rate of the target sandstone oil reservoir is compared with the resistivity increase rate after shale correction. According to the comparison result, it is judged whether the low resistivity of the target sandstone oil reservoir conforms to the law of the electrical method saturation model and whether equivalent water conductivity correction is required during logging saturation calculation, including: Perform shale correction on the resistivity of the target sandstone oil reservoir; Calculate the resistivity increase rate of the target sandstone oil reservoir based on the resistivity after shale correction; Compare the resistivity increase rate of the target sandstone oil reservoir with the lower limit of the resistivity increase rate. If the resistivity increase rate is less than the lower limit of the resistivity increase rate of the oil reservoir, the resistivity of the target sandstone oil reservoir does not conform to the law of the electrical method saturation model, and equivalent water conductivity correction is required during logging saturation calculation.

6. The preliminary classification method for the causes of low resistivity in fast sandstone oil reservoirs according to claim 1, characterized in that, The determination of the low resistivity cause classification of the target sandstone oil reservoir according to whether the low resistivity of the target sandstone oil reservoir conforms to the law of the electrical method saturation model includes: If the low resistivity of the target sandstone oil reservoir does not conform to the law of the electrical method saturation model, the causes of its low resistivity oil reservoir include microfracture development, thin interbedding of sand and shale, hydrophilic rock wettability, conductive minerals, poor oil-water differentiation, and mud invasion; If the resistivity of the target sandstone oil reservoir conforms to the law of the electrical method logging saturation model, the causes of its low resistivity oil reservoir include high porosity, high salinity water, high irreducible water saturation, high shale content, and additional conductivity of clay.

7. A preliminary classification system for the causes of low resistivity in fast sandstone oil reservoirs, characterized in that, Including: A matching degree calculation module for checking and calculating the matching degree between the oil saturation and porosity of the target sandstone oil reservoir. If the oil saturation and porosity do not match, it is considered that the low resistivity of the target sandstone oil reservoir does not conform to the law of the electrical method saturation model, and equivalent water conductivity correction is required during logging saturation calculation; if the two match, the comparison result is sent to the oil saturation lower limit judgment module for re-judgment; An oil saturation lower limit judgment module for calculating the minimum resistivity and the lower limit of the resistivity increase rate of the target sandstone oil reservoir based on the lower limit of the oil saturation, and judging whether the low resistivity of the target sandstone oil reservoir conforms to the law of the electrical method saturation model according to the calculated minimum resistivity and the lower limit of the resistivity increase rate of the oil reservoir; A low resistivity cause classification module for judging whether equivalent water conductivity correction is required during low resistivity oil reservoir saturation calculation according to whether the low resistivity of the target sandstone oil reservoir conforms to the law of the electrical method saturation model, and determining the preliminary classification result of the low resistivity cause of the target sandstone oil reservoir.

8. The preliminary classification system for the origin of low resistivity in fast sandstone oil reservoirs according to claim 7, characterized in that, The oil saturation lower limit judgment module includes: An oil saturation lower limit calculation module for determining the lower limit of the oil saturation of the target sandstone oil reservoir; A first judgment module for calculating the minimum resistivity of the target sandstone oil reservoir based on the lower limit of the oil saturation of the target sandstone oil reservoir, and comparing the minimum resistivity of the target sandstone oil reservoir with the reservoir resistivity, and judging whether the low resistivity of the target sandstone oil reservoir conforms to the law of the electrical method saturation model according to the comparison result; A second judgment module, configured to calculate a lower limit value of the resistivity increase rate of the target sandstone oil reservoir based on the lower limit of the oil saturation of the target sandstone oil reservoir, compare the lower limit value of the resistivity increase rate of the target sandstone oil reservoir with the resistivity increase rate after shale correction, and judge whether the low resistivity of the target sandstone oil reservoir conforms to the law of the electric method saturation model according to the comparison result.

9. A computer-readable storage medium storing one or more programs, characterized in that, The one or more programs include instructions that, when executed by a computing device, cause the computing device to execute any of the methods described in claims 1 to 6.

10. A computing device, characterized in that, Comprising: One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing any of the methods described in claims 1 to 6.

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