Method for identifying low-resistivity oil and gas layers by porosity-resistivity-lithology matching relationship

Abstract

The application discloses a method for identifying low-resistance oil and gas layers by using a matching relationship method of intra-layer porosity-resistivity-lithology, which comprises the following steps: S1, analyzing the lithology curve characteristics of the intra-layer; S2, analyzing the porosity curve characteristics of the intra-layer; S3, analyzing the resistivity curve characteristics of the intra-layer; S4, judging the reservoir fluid properties according to the matching relationship of the intra-layer porosity-resistivity-lithology; and S5, verifying the effect of the reservoir fluid properties. In the scheme, the matching relationship among the intra-layer porosity-resistivity-lithology curves is used to identify the low-resistance oil and gas layers, so that the oil and gas layers can be avoided to be misjudged, the cost is not increased while the correct rate of the logging identification of the oil and gas layers is improved, and the method is not only suitable for the evaluation of the low-resistance oil and gas layers but also suitable for the evaluation of the conventional intra-layer heterogeneous reservoirs.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil well logging, in particular to a method for identifying low-resistivity oil and gas layers by using porosity-resistivity-lithology matching relationship. BACKGROUND

[0002] In the drilling process, in order to meet the well control needs, the drilling fluid density is increased, and the reservoirs with good permeability, especially the fracture development, are seriously affected by mud invasion. The resistivity logging curve presents the non-typical oil and gas layer characteristics of "concave flat" and "low median value". The mud invasion weakens the indication of oil and gas by resistivity. In addition, the existence of high content of mud in the reservoir largely masks the indication of oil and gas by resistivity. The phenomenon of "low resistance oil and high resistance water" exists, and the identification of oil and gas layers cannot be solved by resistivity alone. At present, the methods for identifying oil and gas layers by well logging at home and abroad are usually based on the Archie formula, that is, the "resistivity-porosity" is used to identify oil and gas layers. For conventional oil and gas layers, "porosity-resistivity" can be used to identify them well. That is, in the conventional oil and gas layer, the resistivity logging curve presents "convex shape" and "high value". For water layers, the resistivity logging curve usually presents "concave flat shape" and "low value". Therefore, in the conventional oil and gas layer, "resistivity-porosity" can be used to effectively identify the fluid property. However, in the identification of low-resistivity oil and gas layers, the traditional "resistivity-porosity" method for identifying oil and gas layers is restricted.

[0003] In recent years, with the development of new logging technologies, more and more new logging technologies have been applied to the identification process of low-resistivity oil and gas layers, such as nuclear magnetic resonance logging. However, the nuclear magnetic resonance logging is expensive, resulting in high exploitation cost. Moreover, due to its shallow detection depth, it cannot achieve good results, and therefore, most wells do not have nuclear magnetic resonance logging.

[0004] Among them, one prior art can realize the identification of low-resistivity oil and gas layers. In the identification of low-resistivity oil and gas layers, the parameter Swi, i.e. irreducible water saturation, is needed. The parameter can be obtained according to nuclear magnetic resonance data or experimental data. However, in actual production, it is difficult to accurately obtain the value of Swi. Therefore, the method has low practicability and is not easy to solve the problems on site. SUMMARY

[0005] Therefore, the present application provides a method for identifying low-resistivity oil and gas layers by using intra-layer porosity-resistivity-lithology matching relationship. The method can identify low-resistivity oil and gas layers through the matching relationship between the intra-layer "porosity-resistivity-lithology" curves, can avoid misjudgment of oil and gas layers, can improve the correct rate of well logging identification of oil and gas layers without increasing the cost, and is not only suitable for low-resistivity oil and gas layer evaluation, but also suitable for conventional intra-layer heterogeneous reservoir evaluation.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0007] A method for identifying low-resistivity oil and gas layers by using intra-layer porosity-resistivity-lithology matching relationship, comprising:

[0008] Step S1, analyzing lithology curve characteristics in the layer;

[0009] Step S2, analyzing porosity curve characteristics in the layer;

[0010] Step S3, analyzing resistivity curve characteristics in the layer;

[0011] Step S4, determining reservoir fluid properties according to the intra-layer porosity-resistivity-lithology matching relationship.

[0012] Preferably, in the step S1, analyzing lithology curve characteristics in the layer comprises:

[0013] Finding a layer section in which natural gamma ray changes significantly, or finding a layer section in which natural potential changes significantly, to obtain a layer section in which shale content increases.

[0014] Preferably, in the step S2, analyzing porosity curve characteristics in the layer comprises:

[0015] Analyzing intra-layer three-porosity curve characteristics.

[0016] Preferably, the analyzing intra-layer three-porosity curve characteristics comprises:

[0017] In the layer section in which shale content increases, the acoustic time difference, compensated neutron and density of the porosity curve have no significant change range, indicating that the porosity is approximately constant.

[0018] Preferably, in the step S3, analyzing resistivity curve characteristics in the layer comprises:

[0019] Analyzing deep-induction resistivity value, curve shape and invasion characteristics in the reservoir, and analyzing deep-induction resistivity value change in the layer section in which shale content increases.

[0020] Preferably, in the step S4, determining reservoir fluid properties according to the intra-layer porosity-resistivity-lithology matching relationship comprises:

[0021] In the layer section in which shale content increases, and in the case that the porosity curve shows that the porosity is approximately constant, if the resistivity value increases, it is determined that the reservoir is a water layer; if the resistivity value decreases or remains unchanged, it is determined that the reservoir is an oil and gas layer.

[0022] Preferably, in the layer section in which shale content increases, and in the case that the porosity curve shows that the porosity is approximately constant, if the resistivity value increases, it is determined that the reservoir is a water layer; if the resistivity value decreases or remains unchanged, it is determined that the reservoir is an oil and gas layer comprises:

[0023] In the layer section where the shale content increases from top to bottom, and the porosity curve shows that the porosity is approximately constant, if the resistivity value increases from top to bottom, the reservoir is determined as a water layer; if the resistivity value decreases or remains unchanged from top to bottom, the reservoir is determined as an oil and gas layer.

[0024] Or, in the layer section where the shale content decreases from top to bottom, and the porosity curve shows that the porosity is approximately constant, if the resistivity value increases from top to bottom, the reservoir is an oil and gas layer; if the resistivity value decreases or remains unchanged from top to bottom, the reservoir is a water layer.

[0025] Preferably, in the step S4, the intra-layer porosity-resistivity-lithology matching relationship comprises:

[0026] In the case of approximately constant porosity, the resistivity value of the water layer increases with the increase of the shale content;

[0027] In the case of approximately constant porosity, the resistivity value of the oil and gas layer decreases or remains unchanged with the increase of the shale content;

[0028] The reservoir resistivity value increases with the decrease of the porosity.

[0029] Preferably, after the step S4, it further comprises:

[0030] Step S5, verifying the effect of reservoir fluid property.

[0031] Preferably, in the step S5, verifying the effect of reservoir fluid property comprises:

[0032] Comparing and analyzing the identification result with the test result, verifying the accuracy of the intra-layer porosity-resistivity-lithology matching relationship method in identifying the fluid property.

[0033] As can be seen from the above technical solution, the intra-layer porosity-resistivity-lithology matching relationship method provided by the present application for identifying the low-resistivity oil and gas layer, through the matching relationship between the intra-layer "porosity-resistivity-lithology" curves, the low-resistivity oil and gas layer can be identified, which can avoid misjudgment of the oil and gas layer, improve the correct rate of oil and gas layer logging identification without increasing the cost, and the method is not only suitable for low-resistivity oil and gas layer evaluation, but also suitable for conventional intra-layer heterogeneous reservoir evaluation. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creating any creative labor.

[0035] Figure 1 A schematic diagram of a conductive path of argillaceous sandstone and a schematic diagram of equivalent resistivity provided for an embodiment of the present application;

[0036] Figure 2 A flowchart of a method for identifying low-resistivity oil and gas layers by using the matching relationship method of porosity-resistivity-lithology provided for an embodiment of the present application;

[0037] Figure 3 A well logging curve result map for identifying low-resistivity oil and gas layers of well A by using the matching relationship method of porosity-resistivity-lithology provided for an embodiment one of the present application;

[0038] Figure 4 A well logging curve result map for identifying oil layers of well B by using the matching relationship method of porosity-resistivity-lithology provided for an embodiment two of the present application;

[0039] Figure 5 A well logging curve result map for identifying oil layers of well C by using the matching relationship method of porosity-resistivity-lithology provided for an embodiment three of the present application;

[0040] Figure 6 A well logging curve result map for identifying oil layers of well D by using the matching relationship method of porosity-resistivity-lithology provided for an embodiment four of the present application;

[0041] Figure 7 A well logging curve result map for identifying water layers of well E by using the matching relationship method of porosity-resistivity-lithology provided for an embodiment five of the present application;

[0042] Figure 8 Misjudgment of oil and gas layers of well F by using the traditional porosity-resistivity method provided for a comparative embodiment of the present application. DETAILED DESCRIPTION

[0043] In order to make up for the deficiencies of the traditional "porosity-resistivity" method and the above-mentioned prior art in identifying low-resistivity oil and gas layers, avoid missing oil and gas layers, and improve the accuracy of well logging identification, it is necessary to accurately identify low-resistivity oil and gas layers. The present application discloses a method for identifying low-resistivity oil and gas layers by using the matching relationship method of porosity-resistivity-lithology. When identifying low-resistivity oil and gas layers, the matching relationship between the "porosity-resistivity-lithology" curves in the layer can be used to identify low-resistivity oil and gas layers, improve the accuracy of oil and gas layer well logging identification, and not increase the cost, so as to achieve the purpose of increasing production and efficiency.

[0044] With reference to the accompanying drawings, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0045] Generally, the resistivity value is subject to the fluid property of the reservoir, the conductive path or the tortuosity of the pore channel, and changes with the change of the formation porosity and the formation lithology. A petrophysical volume model (appendix Figure 1 ) is constructed, and a theoretical derivation formula of the formation resistivity is obtained.

[0046]

[0047]

[0048] wherein, L w is the bending degree of the pore channel, i.e. the tortuosity of the pore channel, a decimal; R is the resistivity of the rock saturated with 100% formation water, Ω·m; Rt is the resistivity of the rock, Ω·m; Rw is the resistivity of the formation water, Ω·m; and Φ is the formation porosity, %.

[0049] Therefore, (1) the resistivity value of the reservoir increases with the increase of the fluid resistivity, i.e. increases with the increase of the resistivity of the formation water; (2) the resistivity value increases with the decrease of the porosity; and (3) the resistivity value of the reservoir increases with the increase of the tortuosity of the pore channel. The resistivity of the formation water and the porosity can be quantitatively characterized by the logging data, while the influence factors of the tortuosity are more, which refers to the distribution state of the non-conductive oil and gas and the skeleton, i.e. the flow channel of the formation water, and reflects the difficulty of the formation conduction. For a shale sandstone reservoir, since the sedimentary environment and the migration of oil and gas are basically the same, the properties of the formation water and the shale water (micro-pore water and water adsorbed on the surface of clay) are basically unchanged, and therefore, the resistivity values of the formation water and the shale water in the reservoir are basically unchanged.

[0050] For a muddy sandstone water layer, when the physical property is unchanged, with the increase of the mud, the tortuosity of the pore channel is undoubtedly increased, so that the water layer resistivity is increased with the increase of the mud content. For a muddy sandstone oil and gas layer, when the physical property is unchanged, with the increase of the mud, the increased tortuosity of the pore channel causes the increase of the resistivity, but at the same time, the increase of the mud content causes the increase of the water saturation, and then the decrease of the resistivity value. The final change of the oil and gas layer resistivity value with the increase of the mud content will depend on the influence degree of the pore channel tortuosity and the water saturation. Generally, the oil and gas layer resistivity value is decreased or unchanged with the increase of the mud content. Therefore, the in-layer porosity-resistivity-lithology logging response characteristics (i.e. the in-layer porosity-resistivity-lithology matching relationship) are obtained:

[0051] (1) In the case of approximately constant porosity, the water layer resistivity value is increased with the increase of the mud content;

[0052] (2) In the case of approximately constant porosity, the oil and gas layer resistivity value is decreased or unchanged with the increase of the mud content;

[0053] (3) The reservoir resistivity value is increased with the decrease of the porosity.

[0054] By using the above three resistivity values changing with the porosity and the mud content, the low-resistivity oil and gas layer can be well identified.

[0055] Correspondingly, as shown in Figure 2 , the in-layer porosity-resistivity-lithology matching relationship method provided by the embodiment of the present application for identifying the low-resistivity oil and gas layer comprises:

[0056] Step S1, analyzing the in-layer lithology curve characteristics, so as to determine the layer section with the increased mud content in the reservoir;

[0057] Step S2, analyzing the in-layer porosity curve characteristics, so as to determine the layer section with no obvious change amplitude of the porosity curve in the layer section with the increased mud content;

[0058] Step S3, analyzing the in-layer resistivity curve characteristics, so as to obtain the change of the deep induction resistivity value in the layer section with the increased mud content;

[0059] Step S4, judging the reservoir fluid property according to the in-layer porosity-resistivity-lithology matching relationship. That is, on the basis of the above steps, the three resistivity values changing with the porosity and the mud content are used to identify the low-resistivity oil and gas layer.

[0060] From the above technical solutions can be seen, the method for identifying low-resistivity oil and gas layers provided by the embodiment of the application, by matching relationship between the "porosity-resistivity-lithology" curves in the layer, the low-resistivity oil and gas layers can be identified, which can avoid misjudgment of oil and gas layers, improve the accuracy of well logging identification of oil and gas layers without increasing the cost, and the method is not only suitable for low-resistivity oil and gas layer evaluation, but also suitable for conventional in-layer heterogeneous reservoir evaluation.

[0061] In the present solution, the oil field mainly divides the reservoir lithology profile by the spontaneous potential, or the oil field mainly divides the reservoir lithology profile by the natural gamma, in order to take into account the above-mentioned cases, correspondingly, in the step S1, analyzing the in-layer lithology curve characteristics comprises:

[0062] Finding the layer section in which the natural gamma in the reservoir changes obviously, or finding the layer section in which the spontaneous potential in the reservoir changes obviously, i.e., obtaining the layer section in which the shale content increases. The present solution is thus designed to determine the layer section in which the shale content increases in the reservoir.

[0063] Further, in order to improve the accuracy of the analysis of the in-layer porosity curve characteristics, correspondingly, in the step S2, analyzing the in-layer porosity curve characteristics comprises:

[0064] Analyzing the in-layer three-porosity curve characteristics.

[0065] Specifically, the analysis of the in-layer three-porosity curve characteristics comprises:

[0066] In the layer section in which the shale content increases, the acoustic time difference, the compensated neutron and the density of the porosity curve have no obvious change range, indicating that the porosity is approximately constant. Based on this principle, it is thus helpful to determine the layer section in which the porosity curve has no obvious change range in the layer section in which the shale content increases.

[0067] Further, in the step S3, analyzing the in-layer resistivity curve characteristics comprises:

[0068] Analyzing the deep induction resistivity value, the curve shape and the invasion characteristics in the reservoir, and analyzing the change of the deep induction resistivity value in the layer section in which the shale content increases, so as to obtain the change of the deep induction resistivity value in the layer section in which the shale content increases. In addition, the present step also analyzes the deep induction resistivity value, the curve shape and the invasion characteristics in the reservoir, so as to form the "four-look-resistivity" method which is easy to popularize and apply among technicians in actual exploration and development, i.e., one looks at the resistivity value, two looks at the resistivity shape, three looks at the resistivity invasion characteristics, and four looks at the matching relationship between the resistivity and other curves, to quickly identify oil and gas layers.

[0069] In the present scheme, in the step S4, according to the matching relationship among the porosity, resistivity and lithology in the layer, the reservoir fluid property is determined, which comprises:

[0070] In the layer section with the increasing shale content, and in the case that the porosity curve shows that the porosity is approximately constant, if the resistivity value increases, the reservoir is determined as a water layer; if the resistivity value decreases or remains unchanged, the reservoir is determined as an oil and gas layer.

[0071] More specifically, in the layer section with the increasing shale content from top to bottom, and in the case that the porosity curve shows that the porosity is approximately constant, if the resistivity value increases from top to bottom, the reservoir is determined as a water layer; if the resistivity value decreases or remains unchanged from top to bottom, the reservoir is determined as an oil and gas layer;

[0072] Or, in the layer section with the decreasing shale content from top to bottom, and in the case that the porosity curve shows that the porosity is approximately constant, if the resistivity value increases from top to bottom, the reservoir is determined as an oil and gas layer; if the resistivity value decreases or remains unchanged from top to bottom, the reservoir is determined as a water layer. The present scheme is thus designed to improve the accuracy of the logging identification of the low-resistivity oil and gas layer.

[0073] In the present scheme, as shown in the step S4, it further comprises: Figure 2

[0074] Step S5, verifying the effect of the reservoir fluid property. The present scheme is thus designed to verify the accuracy of the method for determining the fluid property according to the matching relationship among the porosity, resistivity and lithology in the layer.

[0075] Specifically, in the step S5, verifying the effect of the reservoir fluid property comprises:

[0076] Comparing the identification result with the test result to verify the accuracy of the method for determining the fluid property according to the matching relationship among the porosity, resistivity and lithology in the layer.

[0077] The present scheme will be further described in combination with specific embodiments as follows:

[0078] In view of the deficiencies in the prior art, the present application aims to provide a method for identifying the low-resistivity oil and gas layer according to the matching relationship among the porosity, resistivity and lithology in the layer, which can avoid misjudging the oil and gas layer, improve the accuracy of the logging identification of the oil and gas layer without increasing the cost. The method is suitable for the evaluation of the low-resistivity oil and gas layer and the evaluation of the non-homogeneous reservoir in the conventional layer.

[0079] The method provided by the present application comprises the following steps:

[0080] Step S1, analyzing the lithology curve characteristics in the layer. That is, finding the well section with the natural gamma rising in the reservoir, or the well section with the significant change in the amplitude of the spontaneous potential curve in the reservoir, so as to obtain the layer section with the increasing shale content; ​

[0081] Step S2, analyze the characteristics of the porosity curve in the layer. That is, in the layer section with natural gamma rise, the porosity curve (acoustic travel time, compensated neutron, density) has no obvious change amplitude, indicating that the porosity is approximately constant;

[0082] Step S3, analyze the characteristics of the resistivity curve in the layer. That is, the value and curve shape of the deep induction (deep lateral) resistivity, the layer section with increased or decreased curve value;

[0083] Step S4, analyze the matching relationship of porosity-resistivity-lithology in the layer, so as to identify the reservoir fluid property. In the layer section with increased shale content, the porosity curve shows that the porosity is approximately constant, the resistivity value increases to be a water layer, and the resistivity value decreases or remains unchanged to be an oil and gas layer;

[0084] Step S5, verify the effect of the reservoir fluid property. Compare and analyze the test results to verify the accuracy of the matching relationship of porosity-resistivity-lithology in the layer to identify the fluid property.

[0085] In actual exploration and development, the "four-look-resistivity" method is formed, which is easy to popularize and apply among technical personnel, that is, one looks at the resistivity value, two looks at the resistivity shape, three looks at the resistivity invasion characteristics, and four looks at the matching relationship of resistivity and other curves, so as to quickly identify oil and gas layers. Compared with the prior art, the present application provides a matching relationship of porosity-resistivity-lithology in the layer to identify low-resistance oil and gas layers, which effectively solves the problem of misjudgment of oil and gas layers in the reservoir with serious mud invasion or high content of shale by using traditional porosity-resistivity. At the same time, the method is also applicable to conventional reservoirs with in-layer heterogeneity, and has strong universality.

[0086] The matching relationship of porosity-resistivity-lithology in the layer to identify low-resistance oil and gas layers in this embodiment is tested in Well A of Tahe Oilfield, Well B, Well C, Well D, Well E of Dongpu Sag and Well F (comparative example) of Tahe Oilfield:

[0087] Example 1

[0088] Example 1 of the present embodiment is used Figure 3 The matching relationship of porosity-resistivity-lithology in the layer to identify low-resistance oil and gas layers in Well A is taken as an example for illustration:

[0089] The 12th reservoir of Well A uses the matching relationship of porosity-resistivity-lithology in the layer to identify low-resistance oil and gas layers, which includes the following steps:

[0090] Step S1, analyze the characteristics of the lithology curve in the layer. That is, find the well section with natural gamma rise in the reservoir, or the well section with obvious amplitude change of the spontaneous potential curve in the reservoir, so as to obtain the layer section with increased shale content;

[0091] Well A is located in Tahe oilfield, Tahe oilfield is mainly divided into reservoir lithology profile by spontaneous potential, so the layer section in which the spontaneous potential changes obviously in the reservoir is searched. In No. 12 reservoir (4365.0-4386.5m), the spontaneous potential amplitude decreases from top to bottom in 4383.5-4386.0m section, which indicates that the argillaceous content increases successively in 4383.5-4386.0m section of No. 12 reservoir;

[0092] Step S2, analyzing the characteristics of three porosity curves in the layer. That is, in the layer section in which the argillaceous content increases, the three porosity curves (acoustic time difference, compensated neutron, density) have no obvious change amplitude, which indicates that the porosity is approximately constant;

[0093] In 4383.5-4386.0m section of No. 12 reservoir, the porosity curve has no obvious change amplitude, which indicates that the porosity in 4383.5-4386.0m section is approximately constant;

[0094] Step S3, analyzing the characteristics of resistivity curve in the layer. That is, analyzing the value size, curve shape and invasion characteristics of deep induction (deep lateral) resistivity in the reservoir; at the same time, analyzing the value size change of deep induction (deep lateral) resistivity in the layer section in which the argillaceous content increases;

[0095] In 4381.0-4386.5m section of lower part of No. 12 reservoir, the resistivity value is low, the curve shape is concave, and the invasion characteristics are high, which are the characteristics of obvious water layer. In 4383.5-4386.0m section of No. 12 reservoir, the deep induction resistivity curve is flat, and the value is approximately constant, and the lowest resistivity value is about 0.7Ω·m;

[0096] Step S4, analyzing the matching relationship of porosity-resistivity-lithology in the layer, so as to identify the fluid property of the reservoir. In the layer section in which the argillaceous content increases, the three porosity curves show that the porosity is approximately constant, the resistivity value increases to be water layer, and the resistivity value decreases or remains unchanged to be oil and gas layer;

[0097] In 4383.5-4386.0m section of No. 12 reservoir, the argillaceous content increases successively from top to bottom, the porosity is approximately constant, the deep induction resistivity curve is flat, and the value is approximately constant, which are the characteristics of oil and gas layer, so No. 12 layer is identified as oil and gas layer;

[0098] Step S5, verifying the effect of reservoir fluid property. Comparing and analyzing with the test results, the accuracy of identifying the fluid property by the matching relationship of porosity-resistivity-lithology in the layer is verified.

[0099] After perforating 4365.0-4386.5m, it is self-flowing, the daily oil production is 83.6 tons, the daily gas production is 11688 square meters, and there is no water. The test results are consistent with the interpretation conclusion.

[0100] Example two

[0101] This second embodiment uses... Figure 4 The following is an example of the logging curve results used to identify the low-resistivity oil and gas layer in well A using the intra-layer porosity-resistivity-lithology matching relationship method:

[0102] For reservoirs 56 and 58 in well B, low-resistivity oil and gas layers were identified using the intra-layer porosity-resistivity-lithology matching method, including the following steps:

[0103] Step S1: Analyze the lithological curve characteristics within the formation. This involves identifying well sections within the reservoir where the natural gamma ray increases or where the amplitude of the spontaneous potential curve changes significantly, thereby determining the formations with increased clay content.

[0104] Well B is located in the Zhongyuan Oilfield. In the Zhongyuan Oilfield, reservoir lithology profiles are primarily determined by natural gamma ray logging. Therefore, the search focused on identifying intervals within this reservoir where natural gamma ray logging showed significant changes. Within reservoir 56 (3693.8-3699.8m), the natural gamma ray logging values ​​increase from top to bottom in the 3697.5-3698.5m interval, indicating that the clay content in this interval increases sequentially from top to bottom. Similarly, within reservoir 58 (3703.0-3707.3m), the natural gamma ray logging values ​​increase sequentially from bottom to top in the 3705.0-3706.0m interval, indicating that the clay content in this interval also increases sequentially from bottom to top.

[0105] Step S2: Analyze the characteristics of the three-porosity curves within the layer. That is, in the layer section with increasing clay content, the three-porosity curves (acoustic transit time, compensated neutron, and density) show no significant changes, indicating that the porosity is approximately constant.

[0106] The porosity curves in the 3697.5-3698.5m section of reservoir 56 showed no significant variation, indicating that the porosity remained approximately constant in this section. Similarly, the porosity curves in the 3705.0-3706.0m section of reservoir 58 also showed no significant variation, indicating that the porosity remained approximately constant in this section.

[0107] Step S3: Analyze the characteristics of the resistivity curve within the layer. This involves analyzing the magnitude, shape, and invasion characteristics of the deep-induced (deep lateral) resistivity within the reservoir; and simultaneously analyzing the changes in the magnitude of the deep-induced (deep lateral) resistivity in the layers with increasing clay content.

[0108] Reservoirs 56 and 58 exhibit low resistivity values ​​and concave log shapes, and according to the logging interpretation standards for this region (resistivity > 2.8 Ω·m), both are interpreted as water-bearing layers. Within reservoir 56, the deep induced resistivity logging curves in the 3697.5-3698.5m range are flat, with values ​​remaining approximately constant. In reservoir 58, the deep induced resistivity values ​​in the 3705.0-3706.0m range gradually increase from top to bottom.

[0109] Step S4: Analyze the porosity-resistivity-lithology matching relationship within the layer to determine the reservoir fluid properties. In the interval where the clay content increases, the three-porosity curve shows that the porosity is approximately constant, the resistivity value increases to indicate a water layer, and the resistivity value decreases or remains unchanged to indicate an oil and gas layer.

[0110] Within reservoir 56, in the 3697.5-3698.5m interval, the clay content increases sequentially from top to bottom, the porosity remains approximately constant, and the deep induction resistivity logging curve is flat and the value remains approximately constant, which are characteristics of an oil and gas reservoir. Therefore, reservoir 56 is identified as an oil reservoir. Within reservoir 58, in the 3705.0-3706.0m interval, the clay content decreases sequentially from top to bottom, the porosity remains approximately constant, and the deep induction resistivity value gradually increases sequentially from top to bottom, which are characteristics of an oil and gas reservoir. Therefore, reservoir 58 is identified as an oil reservoir.

[0111] Step S5: Verification of reservoir fluid properties. Compare and analyze the results with the test results to verify the accuracy of the intra-layer porosity-resistivity-lithology matching method for determining fluid properties.

[0112] Perforations in layers 56 and 58, as interpreted, were put into production, yielding 3.5 tons of oil per day, with no water. The test results are consistent with the interpretation conclusions.

[0113] Example 3

[0114] This embodiment three uses Figure 5 The following is an example of the logging curve results used to identify the conventional oil and gas reservoir in Well C using the intra-layer porosity-resistivity-lithology matching relationship method:

[0115] The C well's No. 52 reservoir was used to identify low-resistivity oil and gas layers using the intra-layer porosity-resistivity-lithology matching method, including the following steps:

[0116] Step S1: Analyze the lithological curve characteristics within the formation. This involves identifying well sections within the reservoir where the natural gamma ray increases or where the amplitude of the spontaneous potential curve changes significantly, thereby determining the formations with increased clay content.

[0117] Well C is located in the Zhongyuan Oilfield. In the Zhongyuan Oilfield, reservoir lithology profiles are primarily determined by natural gamma ray logging. Therefore, the search was conducted to identify the intervals within this reservoir where natural gamma ray logging showed significant changes. Within reservoir 52 (3312.6-3319.1m), the natural gamma ray logging values ​​increased from top to bottom in the 3315.0-3318.0m interval, indicating that the clay content in this interval increased from top to bottom.

[0118] Step S2: Analyze the characteristics of the three-porosity curves within the layer. That is, in the layer section with increasing clay content, the three-porosity curves (acoustic transit time, compensated neutron, and density) show no significant changes, indicating that the porosity is approximately constant.

[0119] The porosity curves in the 3315.0-3318.0m section of reservoir 52 showed no significant variation, indicating that the porosity remained approximately constant in the 3315.0-3318.0m section.

[0120] Step S3: Analyze the characteristics of the resistivity curve within the layer. This involves analyzing the magnitude, shape, and invasion characteristics of the deep-induced (deep lateral) resistivity within the reservoir; and simultaneously analyzing the changes in the magnitude of the deep-induced (deep lateral) resistivity in the layers with increasing clay content.

[0121] The resistivity of reservoir No. 52 is high at the top and low at the bottom, showing a clear step. The highest value is 4 Ω·m, and the lowest is 2.0 Ω·m, which is significantly lower than the resistivity of the surrounding rock (3.0 Ω·m). Within reservoir No. 52, the deep induced resistivity value in the 3315.0-3318.0m section decreases from top to bottom.

[0122] Step S4: Analyze the porosity-resistivity-lithology matching relationship within the layer to determine the reservoir fluid properties. In the interval where the clay content increases, the three-porosity curve shows that the porosity is approximately constant, the resistivity value increases to indicate a water layer, and the resistivity value decreases or remains unchanged to indicate an oil and gas layer.

[0123] Within reservoir No. 52, in the 3315.0-3318.0m interval, the clay content increases from top to bottom, the porosity remains approximately constant, and the deep induction resistivity decreases from top to bottom, which are characteristics of an oil and gas reservoir. Based on this, reservoir No. 52 is identified as an oil reservoir.

[0124] Step S5: Verification of reservoir fluid properties. Compare and analyze the results with the test results to verify the accuracy of the intra-layer porosity-resistivity-lithology matching method for determining fluid properties.

[0125] The perforation of layer 52, as interpreted, has been put into production, yielding 6.8 tons of oil per day, with no water. The test results are consistent with the interpretation conclusions.

[0126] Example 4

[0127] This embodiment four uses Figure 6The following is an example of the logging curve results used to identify conventional oil and gas reservoirs in well D using the intra-layer porosity-resistivity-lithology matching relationship method:

[0128] The conventional oil and gas reservoir in well D, specifically reservoir 111, was identified using the intra-layer porosity-resistivity-lithology matching method, including the following steps:

[0129] Step S1: Analyze the lithological curve characteristics within the formation. This involves identifying well sections within the reservoir where the natural gamma ray increases or where the amplitude of the spontaneous potential curve changes significantly, thereby determining the formations with increased clay content.

[0130] Well D is located in the Zhongyuan Oilfield. In the Zhongyuan Oilfield, reservoir lithology profiles are primarily determined by natural gamma ray logging. Therefore, the search focused on identifying the intervals within this reservoir where natural gamma ray logging shows significant changes. Within reservoir 111 (3434.1-3437.8m), the natural gamma ray logging values ​​gradually increase from top to bottom in the 3435.5-3437.0m interval, indicating that the clay content in this interval increases sequentially from top to bottom.

[0131] Step S2: Analyze the characteristics of the three-porosity curves within the layer. That is, in the layer section with increasing clay content, the three-porosity curves (acoustic transit time, compensated neutron, and density) show no significant changes, indicating that the porosity is approximately constant.

[0132] The porosity curves in the 3435.5-3437.0m section of reservoir 111 show no significant variation, indicating that the porosity remains approximately constant in the 3435.5-3437.0m section.

[0133] Step S3: Analyze the characteristics of the resistivity curve within the layer. This involves analyzing the magnitude, shape, and invasion characteristics of the deep-induced (deep lateral) resistivity within the reservoir; and simultaneously analyzing the changes in the magnitude of the deep-induced (deep lateral) resistivity in the layers with increasing clay content.

[0134] Within reservoir 111, the deep induced resistivity value in the 3435.5-3437.0m section decreases from top to bottom;

[0135] Step S4: Analyze the porosity-resistivity-lithology matching relationship within the layer to determine the reservoir fluid properties. In the interval where the clay content increases, the three-porosity curve shows that the porosity is approximately constant, the resistivity value increases to indicate a water layer, and the resistivity value decreases or remains unchanged to indicate an oil and gas layer.

[0136] Within reservoir 111, in the 3435.5-3437.0m interval, the clay content increases from top to bottom, the porosity remains approximately constant, and the deep induction resistivity decreases from top to bottom, which are characteristics of an oil and gas reservoir. Based on this, reservoir 56 is identified as an oil and gas reservoir.

[0137] Step S5: Verification of reservoir fluid properties. Compare and analyze the results with the test results to verify the accuracy of the intra-layer porosity-resistivity-lithology matching method for determining fluid properties.

[0138] The perforation of layer 111, as interpreted, has been put into production, yielding 5.1 tons of oil and 3,000 cubic meters of gas per day. The test results are consistent with the interpretation conclusions.

[0139] Example 5

[0140] This embodiment five is based on Figure 7 The following is an example of the logging curve results used to identify the low water-resistivity layer in well E using the intra-layer porosity-resistivity-lithology matching relationship method:

[0141] For well E, layer 35 was used to identify low-water-resistivity layers using the intralayer porosity-resistivity-lithology matching method, including the following steps:

[0142] Step S1: Analyze the lithological curve characteristics within the formation. This involves identifying well sections within the reservoir where the natural gamma ray increases or where the amplitude of the spontaneous potential curve changes significantly, thereby determining the formations with increased clay content.

[0143] Well E is located in the Zhongyuan Oilfield. In the Zhongyuan Oilfield, reservoir lithology profiles are primarily determined by natural gamma ray logging. Therefore, the search was conducted to identify the intervals within this reservoir where natural gamma ray logging showed significant changes. Within layer 35 (3065.5-3070.3m), the natural gamma ray logging values ​​from top to bottom in the 3366.2-3367.5m interval increased sequentially, indicating that the clay content in layer 35 from top to bottom in the 3366.2-3367.5m interval increased sequentially.

[0144] Step S2: Analyze the characteristics of the three-porosity curves within the layer. That is, in the layer section with increasing clay content, the three-porosity curves (acoustic transit time, compensated neutron, and density) show no significant changes, indicating that the porosity is approximately constant.

[0145] The porosity curves in the 3366.2-3367.5m section within layer 35 show no significant variation, indicating that the porosity remains approximately constant within this section.

[0146] Step S3: Analyze the characteristics of the resistivity curve within the layer. This involves analyzing the magnitude, shape, and invasion characteristics of the deep-induced (deep lateral) resistivity within the reservoir; and simultaneously analyzing the changes in the magnitude of the deep-induced (deep lateral) resistivity in the layers with increasing clay content.

[0147] Within layer 35, the deep induced resistivity values ​​in the 3366.2-3367.5m section increase sequentially from top to bottom;

[0148] Step S4: Analyze the porosity-resistivity-lithology matching relationship within the layer to determine the reservoir fluid properties. In the interval where the clay content increases, the three-porosity curve shows that the porosity is approximately constant, the resistivity value increases to indicate a water layer, and the resistivity value decreases or remains unchanged to indicate an oil and gas layer.

[0149] Within reservoir No. 35, in the 3366.2-3367.5m interval, the clay content increases from top to bottom, the porosity remains approximately constant, and the deep induction resistivity increases from top to bottom, which are characteristics of a water-bearing layer. Therefore, layer No. 35 is identified as a water-bearing layer.

[0150] Step S5: Verification of reservoir fluid properties. Compare and analyze the results with the test results to verify the accuracy of the intra-layer porosity-resistivity-lithology matching method for determining fluid properties.

[0151] The test results for layer 35, which was interpreted, showed a daily water production of 8.2 cubic meters. The test results are consistent with the interpretation conclusions.

[0152] Comparative Examples

[0153] This comparative embodiment uses Figure 8 The following example illustrates how the "porosity-resistivity" method can be used to misidentify low-resistivity oil and gas layers as water layers:

[0154] The F well contains reservoirs 11-12 (4187.0-4202.0m). These two layers exhibit concave resistivity curves with low deep-induced resistivity values, the lowest being 0.5 Ω·m, and show clear characteristics of high water intrusion (ILD>ILM). The three porosity curves (sonic transit time, compensated density, and compensated neutron) indicate good reservoir properties, with porosity around 25%. The traditional porosity-resistivity method states that oil layers have high porosity, resulting in convex, high-value resistivity logging curves; while water layers typically have high porosity, resulting in concave, flat, low-value resistivity logging curves. Therefore, based on this traditional method, the layer was initially identified as a water layer. However, subsequent testing revealed a daily oil production of 50.1 tons, a daily gas production of 4185 cubic meters, and no water. The interpretation using the traditional porosity-resistivity method contradicted the test results.

[0155] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0156] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for identifying low-resistivity oil and gas layers by using the method of matching relationship between in-layer porosity, resistivity and lithology, characterized in that, The method comprises the following steps: Step S1, analyzing the lithology curve characteristics in the layer; Step S2, analyzing the porosity curve characteristics in the layer; Step S3, analyzing the resistivity curve characteristics in the layer; Step S4, determining the reservoir fluid property according to the matching relationship among the porosity, resistivity and lithology in the layer; In the step S4, determining the reservoir fluid property according to the matching relationship among the porosity, resistivity and lithology in the layer comprises: In the layer section with increasing shale content, and in the case that the porosity curve shows that the porosity is approximately constant, if the resistivity value increases, the reservoir is determined to be a water layer; if the resistivity value decreases or remains unchanged, the reservoir is determined to be an oil and gas layer; The step of determining the reservoir fluid property according to the matching relationship among the porosity, resistivity and lithology in the layer comprises: In the layer section with increasing shale content, and in the case that the porosity curve shows that the porosity is approximately constant, if the resistivity value increases from top to bottom, the reservoir is determined to be a water layer; if the resistivity value decreases or remains unchanged from top to bottom, the reservoir is determined to be an oil and gas layer; Or, in the layer section with decreasing shale content from top to bottom, and in the case that the porosity curve shows that the porosity is approximately constant, if the resistivity value increases from top to bottom, the reservoir is determined to be an oil and gas layer; if the resistivity value decreases or remains unchanged from top to bottom, the reservoir is determined to be a water layer; In the step S4, the matching relationship among the porosity, resistivity and lithology in the layer comprises: In the case that the porosity is approximately constant, the resistivity value of the water layer increases with the increasing shale content; In the case that the porosity is approximately constant, the resistivity value of the oil and gas layer decreases or remains unchanged with the increasing shale content; The resistivity value of the reservoir increases with the decreasing porosity.

2. The method of claim 1, wherein the method further comprises: In the step S1, analyzing the lithology curve characteristics in the layer comprises: Finding the layer section in which the natural gamma ray or the natural electric potential changes obviously in the reservoir to obtain the layer section with increasing shale content.

3. The method of claim 2, wherein the method further comprises: In the step S2, analyzing the porosity curve characteristics in the layer comprises: Analyzing the three porosity curve characteristics in the layer.

4. The method of claim 3, wherein the method further comprises: The step of analyzing the three porosity curve characteristics in the layer comprises: In the layer section with increasing shale content, the acoustic time difference, compensated neutron and density of the porosity curve have no obvious change range, which indicates that the porosity is approximately constant.

5. The method of claim 4, wherein the method further comprises: In the step S3, analyzing the resistivity curve characteristics in the layer comprises: Analyzing the deep induction resistivity value, curve shape and invasion characteristics in the reservoir, and analyzing the deep induction resistivity value change in the layer section with increasing shale content.

6. The method of claim 1, wherein the method further comprises: After the step S4, the method further comprises the following step: Step S5, verifying the reservoir fluid property effect.

7. The method of claim 6, wherein the method further comprises: In the step S5, verifying the reservoir fluid property effect comprises: Comparing and analyzing the identification result with the test result to verify the accuracy of the matching relationship among the porosity, resistivity and lithology in the layer in determining the fluid property.

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