Low-resistivity oil layer identification method

Abstract

The invention relates to a low-resistivity oil reservoir identification method, and belongs to the field of low-resistivity oil reservoir identification, and the low-resistivity oil reservoir identification method comprises the steps: obtaining the porosity, resistivity and historical oil test and production test data in historical drilling data, building a corresponding physical property-electrical property-oil content relation chart for each sedimentary microfacies by using the data, and obtaining the corresponding physical property-electrical property-oil content relation chart for each sedimentary microfacies; acquiring a porosity lower limit and a resistivity lower limit corresponding to the oil reservoir under each sedimentary microfacies through the drawing board, and taking the porosity lower limit and the resistivity lower limit as standards for determining whether the corresponding sedimentary microfacies reservoir contains oil or not; different identification standards are set for different sedimentary microfacies reservoirs, so that the identification accuracy of the low-resistivity oil reservoir is improved.

Description

Technical Field

[0001] The invention belongs to the field of low-resistance oil reservoir identification, and particularly relates to a low-resistance oil layer identification method. Background Art

[0002] The oil-bearing reservoir with resistivity less than 3 is called low-resistivity oil layer. Due to the low resistivity of low-resistivity oil layer, it is easy to be regarded as water layer during electrical measurement, resulting in misidentification of oil layer.

[0003] There are two common methods for identifying low-resistivity oil layers: one is to identify low-resistivity oil layers based on conventional logging interpretation methods and multi-well comparison methods; the other is to identify them using new logging technologies such as nuclear magnetic resonance and array induction. Both methods do not consider the applicability of different geological conditions, resulting in inaccurate identification results; although the accuracy of nuclear magnetic resonance and array induction logging has been improved, this method is expensive and costly.

[0004] The existing technology has the problems of inaccurate identification of low-resistance oil layers and high identification cost. Summary of the invention

[0005] The purpose of the present invention is to provide a method for identifying a low-resistance oil layer, so as to solve the technical problems of inaccurate identification of low-resistance oil layers and high identification cost in the prior art.

[0006] To achieve the above object, the present invention provides a technical solution for a low-resistance oil layer identification method:

[0007] A method for identifying low-resistivity oil layers, the method comprising the following steps: 1) obtaining data of wells drilled in a development area, including the porosity, resistivity, and historical oil test and production data of each well reservoir; 2) dividing the development area into sedimentary microphases, and establishing a physical property-electrical property-oil content relationship chart under each sedimentary microphase according to the acquired porosity, resistivity, and historical oil test and production data; 3) determining the lower limit of porosity and the lower limit of resistivity under each sedimentary microphase oil layer from the chart of the physical property-electrical property-oil content relationship under each sedimentary microphase, and using the lower limit of porosity and the lower limit of resistivity as the identification standard of the corresponding sedimentary microphase oil layer; and 4) identifying whether the corresponding sedimentary microphase reservoir contains oil according to the identification standard.

[0008] The beneficial effect is: by analyzing the historical data of the reservoir, a plate of the relationship between physical properties, electrical properties and oil content under each sedimentary microphase is established, and the corresponding lower limits of porosity and resistivity are obtained from the plate, and the lower limits of porosity and resistivity are used as the identification criteria of the corresponding sedimentary microphase. By setting different identification criteria for different sedimentary microphase reservoirs, the measurement accuracy of low-resistivity oil layers is improved, and the data used in this method are all conventionally obtained logging data and oil production data, which further reduces the identification cost of low-resistivity oil layers.

[0009] As a further improvement, in step 3), the method for determining the lower limit of porosity and the lower limit of resistivity is as follows: the porosity and resistivity data of each sedimentary microphase when the oil content of the reservoir is oil-bearing are obtained from the plate of the relationship between physical properties, electrical properties and oil content of each sedimentary microphase, and the minimum porosity data and the minimum resistivity data of each sedimentary microphase are selected as the lower limit of porosity and the lower limit of resistivity.

[0010] The beneficial effect is: from the multiple porosity and resistivity data corresponding to each sedimentary micro-bacteria when the plate contains oil, the minimum value is selected from these data as the corresponding porosity lower limit value and resistivity lower limit. Because low resistivity or low porosity reservoirs are easily overlooked as water layers or dry layers, the minimum value of resistivity and porosity under oil-containing conditions is selected as the resistivity lower limit and porosity lower limit to prevent the oil layer with low resistivity and low porosity from being overlooked during the detection process.

[0011] As a further improvement, the types of sedimentary microfacies are divided according to the shape of the natural potential logging curve.

[0012] The beneficial effect is that natural potential logging refers to using the potential changes naturally generated in the well to distinguish between muddy and non-muddy formations. The shape of the natural potential logging curve can reflect the shape of the formation. Therefore, the shape of the natural potential logging curve is used to divide the sedimentary microfacies type of the oil layer, thereby improving the accuracy of the division.

[0013] As a further improvement, the types of sedimentary microfacies include underwater channel microfacies, underwater distributary channel microfacies, estuary bar microfacies, front sand microfacies and interchannel bay microfacies.

[0014] The beneficial effect is that the common sedimentary microfacies of low-resistivity reservoirs include the above five types, so the types of these five sedimentary microfacies are studied.

[0015] As a further improvement, the resistivity uses deep lateral resistivity.

[0016] The beneficial effect is that the deep lateral resistivity is greatly affected by high resistance. In this scheme, the low-resistance reservoir is mainly studied, so the deep lateral resistivity is selected. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of the method for identifying low-resistivity oil layers in the present invention;

[0018] Figure 2 It is a diagram of the division of sedimentary microfacies and oil testing results by electrical measurement curves in the method for identifying low-resistivity oil layers of the present invention;

[0019] Figure 3 It is the microfacies diagram of the underwater main channel in the method for identifying low-resistance oil layers of the present invention;

[0020] Figure 4 It is an underwater diversion channel map in the low-resistance oil layer identification method of the present invention;

[0021] Figure 5 It is the estuary bar map in the low-resistance oil layer identification method of the present invention;

[0022] Figure 6 It is the front edge sand map in the low-resistance oil layer identification method of the present invention;

[0023] Figure 7 It is the channel bay map in the low-resistance oil layer identification method of the present invention;

[0024] Figure 8 This is a morphological characteristic diagram of the logging curves of each sedimentary microfacies in the low-resistivity oil layer identification method of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0026] Low-resistivity oil layer identification method embodiment:

[0027] like Figure 1 As shown, the low-resistivity oil layer identification method includes the following steps:

[0028] 1) Obtain data on wells drilled in the development area.

[0029] The data of the wells that have been drilled include the porosity, resistivity, and historical oil and production test data of each well reservoir. Resistivity is the ratio of the oil layer resistance to the water layer resistance. Generally, the oil layer with a resistivity lower than 3 is called a low-resistivity oil layer.

[0030] The resistivity adopts deep lateral resistivity because deep lateral resistivity is less affected by low resistance than deep induction resistivity. This scheme mainly studies low-resistance reservoirs, so deep lateral resistivity is selected.

[0031] 2) Obtain the sedimentary microfacies type of the reservoir.

[0032] The types of sedimentary microfacies are divided according to the shape of the natural potential logging curve.

[0033] Different sedimentary microfacies have different characteristics. For example, the underwater main channel microfacies has a high sand / mud ratio and coarse particles, but the rapid sedimentation near the source leads to a mixture of sand and gravel, and the mud fillings are rich in authigenic minerals, which makes the reservoir performance of this phase worse. The underwater distributary channel and estuary bar have less mud content, mainly gravel-bearing sandstone and fine sandstone, with fine sand body size, less gravel and good sorting. The front sheet sand microfacies and the bay between distributary channels have a high mud content, mainly siltstone.

[0034] In the natural potential logging curve, the natural potential logging curve corresponding to the underwater channel micro-channel is mainly manifested as a combination of toothed box-shaped and bell-shaped negative anomalies; the natural potential logging curve corresponding to the underwater distributary channel micro-channel is mainly manifested as a combination of bell-shaped negative anomalies. The difference between it and the underwater channel is that the thickness of the sand body is smaller than that of the underwater channel; the natural potential logging curve corresponding to the estuary bar micro-channel is mainly manifested as a funnel-shaped negative anomaly; the natural potential logging curve corresponding to the front sand micro-channel is mainly manifested as a combination of low-amplitude bell-shaped and finger-shaped negative anomalies. Due to its high mud content, the bell-shaped amplitude is lower than that of the underwater channel, and the amplitude of the negative anomaly is smaller; the natural potential logging curve corresponding to the inter-channel bay micro-channel is mainly a low-amplitude toothed curve, sandwiched by a high-amplitude finger-shaped negative anomaly. According to the above characteristics, the corresponding relationship between the logging phase characteristics and the sedimentary micro-phase is obtained as shown in Table 1. The specific logging curve morphological characteristics of each sedimentary micro-phase are shown in Figure 8 .

[0035] Table 1

[0036] Serial number Sedimentary microfacies Well logging characteristics 1 Underwater main channel Toothed box-shaped and bell-shaped negative anomaly combinations. 2 Underwater diversion channel The natural potential curve is a bell-shaped negative anomaly combination, and the thickness of the single sand layer tends to thin upward. 3 Estuary dam The natural potential curve is funnel-shaped. 4 Front edge sand The natural potential curve is a combination of low-amplitude bell-shaped and finger-shaped negative anomalies. 5 Microfacies of bays between waterways The natural potential curve is a low-amplitude serrated curve with high-amplitude finger-shaped anomalies in between.

[0037] The corresponding porosity and resistivity are calculated according to the common sedimentary microfacies types of low-resistivity oil layers. Common sedimentary microfacies types include underwater channel microfacies, underwater distributary channel microfacies, estuary bar microfacies, front sand microfacies and interchannel bay microfacies.

[0038] Among them, the resistance of the underwater distributary channel microfacies is 2.0Ω and the porosity is 16%; the resistance of the front sand microfacies is 2.4Ω and the porosity is 18%, etc.

[0039] 3) Establish a chart showing the relationship between physical properties, electrical properties and oil content in each sedimentary microphase.

[0040] Based on the obtained porosity, resistivity, and historical oil test and production data, a chart of the physical property-electrical property-oil content relationship under each sedimentary microphase is established, where porosity corresponds to physical property, resistivity corresponds to electrical property, and historical oil test and production data corresponds to oil content. Figure 3 The plate showing the underwater main channel microfacies; Figure 4 The plate showing an underwater distributary channel; Figure 5 The plate showing an estuary bar; Figure 6 The plate shown is the front edge sand; Figure 7The plate shows a channel bay. 3) Identification criteria for obtaining oil layers of different types of sedimentary microfacies.

[0041] in Figure 3-7 In the figure, the circle represents the oil layer, the triangle represents the water layer, and the square represents the dry layer.

[0042] 4) Establish identification criteria for each sedimentary microfacies reservoir.

[0043] According to step 3), a physical property-electrical property-oil content relationship chart is established, and multiple porosity and resistivity data corresponding to oil layers of different types of sedimentary microfacies are obtained, from which the smallest porosity and resistivity are selected as the lower limit of porosity and the lower limit of resistivity, and the lower limit of porosity and the lower limit of resistivity are used as the identification standard of the corresponding sedimentary microfacies oil layer. The specific data are shown in Table 2. The dual standards of porosity and resistivity are used to detect whether the reservoir contains oil, which improves the accuracy of detecting whether the reservoir contains oil.

[0044] In order to meet the industry's profit requirements, when determining the lower limit of porosity and resistivity, the oil content data exceeds the industry's allowable threshold. The industry's allowable threshold means that the cost of mining under this oil-containing condition is lower than the benefit of oil production, that is, the oil-containing condition that can make a profit when the industry produces oil.

[0045] Table 2

[0046] Serial number Sedimentary microfacies Porosity lower limit (%) Resistivity lower limit (Ω·m) 1 Underwater main channel 16 1.6 2 Underwater diversion channel 16 2 3 Estuary dam 18 2.2 4 Front edge sand 18 2.4 5 Bay between rivers 20 3

[0047] After research, it was found that according to the sequence of underwater channel microfacies, underwater distributary channel microfacies, estuary bar microfacies, front sand microfacies and interchannel bay microfacies, the lower limit of resistivity of the oil layer gradually increases, and the lower limit of porosity of the oil layer gradually decreases.

[0048] 5) Application of identification standards.

[0049] The chart established in step 3) is used to identify whether the reservoir contains oil based on different porosities and resistivities under different types of sedimentary microfacies. Targeted exploitation is carried out for oil layers that are identified to contain oil or oil content that exceeds the industry's permitted threshold, and the oil production results are observed. Figure 2 As shown in the figure, by obtaining the natural potential logging curve and lithology and other related data of the formation, the identification criteria corresponding to the formation load of the underwater distributary channel microfacies and the front sand microfacies in the formation were identified, and good feedback was obtained for oil production in these two parts. The porosity is the physical property of the reservoir, the resistivity is the electrical property of the reservoir, and whether it contains oil is the oil content of the reservoir; that is to say, the low-resistivity oil layer identification method takes into account the three characteristics of the reservoir, making the identification criteria more comprehensive and accurate, that is, the low-resistivity oil layer can be more clearly understood.

[0050] The present invention first conducts a test production on the reservoir to detect whether the reservoir contains oil, and only detects the oil-containing reservoir, saving the implementation cost of the method. The porosity and resistivity corresponding to the oil layer are obtained, and then the sedimentary microphase type of the oil layer is detected, and the corresponding porosity and resistivity of different types of sedimentary microphase oil layers are obtained, and the corresponding porosity lower limit and resistivity lower limit are selected for the oil layers of different sedimentary microphases, and the porosity lower limit and resistivity lower limit are used as the identification standard of the corresponding sedimentary microphase. By setting different identification standards for different sedimentary microphase reservoirs, the measurement accuracy of low-resistance oil layers is improved, and the data used in this method are all well logging data that are easy to obtain, which further reduces the identification cost of low-resistance oil layers.

[0051] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments without creative work, or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for identifying a low-resistance oil layer, characterized in that: The method comprises the following steps: 1) Obtain data on wells drilled in the development area, including the porosity, resistivity, and historical oil and gas testing data of each well reservoir; 2) Divide the development area into sedimentary microfacies and establish a chart of the relationship between physical properties, electrical properties and oil content in each sedimentary microfacies based on the acquired porosity, resistivity and historical oil and gas testing data; 3) Determine the lower limit of porosity and resistivity of each sedimentary microphase from the diagram of the relationship between physical properties, electrical properties and oil content of each sedimentary microphase, and use the lower limit of porosity and resistivity as the identification criteria for the corresponding sedimentary microphase oil layer; 4) Identify whether the corresponding sedimentary microfacies reservoir contains oil based on the identification criteria.

2. The low-resistance oil layer identification method according to claim 1, characterized in that: In the step 3), the method for determining the lower limit of porosity and the lower limit of resistivity is as follows: the porosity and resistivity data of each sedimentary microphase when the oil content of the reservoir is oil-bearing are obtained from the plate of the relationship between physical properties, electrical properties and oil content of each sedimentary microphase, and the minimum porosity data and the minimum resistivity data of each sedimentary microphase are selected as the lower limit of porosity and the lower limit of resistivity.

3. The low-resistance oil layer identification method according to claim 1, characterized in that: In the step 2), the types of sedimentary microfacies are divided according to the shape of the natural potential logging curve.

4. The low-resistance oil layer identification method according to claim 3, characterized in that: The types of sedimentary microfacies include underwater channel microfacies, underwater distributary channel microfacies, estuary bar microfacies, front sand microfacies and interchannel bay microfacies.

5. The low-resistance oil layer identification method according to any one of claims 1 to 4, characterized in that: The resistivity adopts deep induction resistivity.

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