A method and apparatus for fluid identification in tight sand reservoirs

Abstract

The present application belongs to the field of geophysical logging technology in oil and gas exploration, and particularly relates to a fluid identification method and device for tight sandstone reservoirs. The method comprises the following steps: (1) determining the tight layer in the reservoir by interpreting the reservoir porosity through conventional logging curves; (2) determining the drilling fluid invasion depth by using array induction logging data inversion, and selecting the tight layer with a relatively shallow drilling fluid invasion depth; (3) performing inversion and processing interpretation of the reservoir section by two-dimensional nuclear magnetic logging, and when the gas saturation of the selected tight layer with a relatively shallow drilling fluid invasion depth is greater than the gas saturation of the non-tight layer, using the gas saturation of the tight layer as the gas saturation of the reservoir section. The present application can effectively solve the problem of missing oil and gas layers due to the low coincidence rate of nuclear magnetic logging interpretation caused by the influence of drilling fluid invasion. Through actual application, the two-dimensional nuclear magnetic logging processing interpretation result of the physical property deviation reservoir section is closer to the actual situation of the reservoir.

Description

Technical Field

[0001] This invention belongs to the field of geophysical logging technology in oil and gas exploration, specifically relating to a fluid identification method and device for tight sandstone reservoirs. Background Technology

[0002] Two-dimensional nuclear magnetic resonance (2DNMR) logging is a novel nuclear magnetic resonance logging method developed by applying the concepts of 2DNMR spectroscopy to oil well logging. It can measure not only the lateral relaxation time (T2) of fluids, but also the longitudinal relaxation time (T1) and the fluid diffusion coefficient (D) simultaneously. 2DNMR logging utilizes the differences in the nuclear magnetic properties of fluids, allowing for intuitive identification of fluid properties and quantitative evaluation through two-dimensional characterization.

[0003] Chinese invention patent CN108049866B discloses a quantitative evaluation method for tight gas reservoirs using two-dimensional nuclear magnetic resonance (NMR) logging. After acquiring two-dimensional NMR logging information, it uses a T2-T1 cross-plot method to identify natural gas in the tight reservoir. Based on a clearly defined cross-plot method, targeted two-dimensional NMR logging evaluation methods for reservoir quality and gas-water relationships can be established, improving the application effectiveness of two-dimensional NMR logging in tight gas reservoirs.

[0004] For tight sandstone reservoirs with low porosity and low permeability, the porosity is small and the structure is complex. At the same time, due to the influence of drilling fluid invasion, the information obtained by nuclear magnetic resonance logging mainly reflects the fluid properties of the invasion zone. In addition, the lithology and physical properties of tight sandstone reservoirs vary greatly vertically. The better the reservoir physical properties, the deeper the drilling fluid invasion. Ultimately, this results in weak gas signals in the interpretation and evaluation of 2D nuclear magnetic resonance logging, making it difficult to extract effective gas signals. This leads to a lower interpretation level of 2D nuclear magnetic resonance logging, with the interpretation results mainly showing water content, which does not match the actual gas testing results of the reservoir.

[0005] In short, the accuracy of two-dimensional nuclear magnetic resonance logging interpretation is low for water-bearing tight gas reservoirs, which poses a significant challenge to the evaluation of reservoir fluid properties. Summary of the Invention

[0006] The purpose of this invention is to provide a fluid identification method for tight sandstone reservoirs to solve the problems of low accuracy of two-dimensional nuclear magnetic resonance logging interpretation and discrepancies with actual gas testing conditions in the reservoir.

[0007] A second objective of this invention is to provide a fluid identification device for tight sandstone reservoirs to solve the aforementioned problems.

[0008] To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0009] A method for fluid identification in tight sandstone reservoirs includes the following steps:

[0010] (1) Interpret reservoir porosity using conventional logging curves to identify tight layers in the reservoir;

[0011] (2) The drilling fluid invasion depth is determined by inversion of array induction logging data, and the dense layer with shallow drilling fluid invasion depth is selected.

[0012] (3) Perform two-dimensional nuclear magnetic resonance logging inversion and processing interpretation on the reservoir section, and compare the gas saturation of the tight layer with shallow drilling fluid penetration depth selected in step (2) with that of the non-tight layer in the same reservoir section; when the gas saturation of the tight layer with shallow drilling fluid penetration depth selected in step (2) is greater than that of the non-tight layer, the gas saturation of the tight layer is used as the gas saturation of the reservoir section.

[0013] The fluid identification method for tight sandstone reservoirs of this invention can effectively solve the problem of low accuracy in nuclear magnetic resonance (NMR) logging interpretation due to drilling fluid intrusion, thus preventing the omission of oil and gas layers. Through practical application, the interpretation results of two-dimensional NMR logging in reservoir sections with property deviations are closer to the actual reservoir conditions. This method can provide interpretation engineers with interpretation conclusions that are closer to the actual reservoir conditions, avoiding the omission of gas layers and effectively improving the accuracy of NMR logging interpretation.

[0014] In the case of the reservoir being affected by drilling fluid intrusion, in order to further improve the accuracy of the interpretation of two-dimensional nuclear magnetic logging, preferably, in step (3), the tight layer with shallow drilling fluid intrusion depth is interpreted as a gas layer, the non-tight layer is interpreted as a gas-bearing water layer, and the final interpretation conclusion of the reservoir section is a gas layer.

[0015] To further reduce the impact of drilling fluid intrusion, preferably, in step (1), the porosity of the dense layer is <5%.

[0016] To more effectively identify the dense layer, it is further preferred that, in step (1), the conventional logging curves include acoustic, density, and neutron curves; and the low acoustic value, high density value, and low neutron value segments are selected as the dense layer.

[0017] A fluid identification device for tight sandstone reservoirs includes a processor and a memory. The memory stores computer-executable instructions, and the processor executes the computer-executable instructions stored in the memory to implement the aforementioned fluid identification method for tight sandstone reservoirs.

[0018] The fluid identification device for tight sandstone reservoirs of this invention effectively improves the accuracy of two-dimensional nuclear magnetic resonance logging interpretation when the reservoir is affected by drilling fluid intrusion. The interpretation results in practical applications show a high degree of agreement with the actual reservoir conditions. Attached Figure Description

[0019] Figure 1This is a flowchart of the fluid identification method for tight sandstone reservoirs according to the present invention;

[0020] Figure 2 This is a diagram showing the intrusion profile and interpretation results of Well A in this invention;

[0021] Figure 3 This is the two-dimensional nuclear magnetic resonance theory explanation model of the present invention;

[0022] Figure 4 This is a comprehensive well logging curve diagram of an embodiment of the present invention;

[0023] Figure 5 This is a diagram showing the array sensing results of an embodiment of the present invention;

[0024] Figure 6 This is a two-dimensional NMR interpretation result at 3257.00m in an embodiment of the present invention;

[0025] Figure 7 This is a two-dimensional NMR interpretation result at 3261.00m in an embodiment of the present invention. Detailed Implementation

[0026] The concept of this invention is as follows: Combining array induction logging and two-dimensional nuclear magnetic resonance (NMR) logging, drilling fluid invasion data is obtained based on array induction logging data. This data includes the invasion radius values ​​of the flushing zone and transition zone. Conventional logging porosity curves (acoustic, density, and neutron curves) are used to interpret reservoir porosity. Porosity <5% (relative to low acoustic values, high density values, and low neutron values ​​in the surrounding rock) is identified as a tight reservoir in this well. The invasion profile is inverted using array induction logging to find a relatively tight reservoir section with minimal impact from drilling fluid invasion. A two-dimensional NMR interpretation model is used to invert and process the reservoir section using two-dimensional NMR methods, comparing the gas saturation of the selected tight and non-tight sections. When the gas saturation of the tight section with less invasion impact is greater than that of the non-tight section with greater invasion impact, the gas saturation of the tight section is adopted as the gas saturation of the reservoir section.

[0027] The flowchart of the fluid identification method for tight sandstone reservoirs of the present invention is as follows: Figure 1 As shown, it is based on the combination of two-dimensional nuclear magnetic resonance logging and array induction for fluid identification, including the following steps:

[0028] 1) Obtain drilling fluid invasion data based on array induction logging data;

[0029] 2) Combine conventional logging acoustic waves, density, neutron curves and array induction to determine the tight layers in the reservoir;

[0030] 3) The reservoir section is inverted and processed using two-dimensional NMR theory to interpret the model, comparing the gas saturation of the selected tight and non-tight sections. When the gas saturation of the tight section, which is less affected by intrusion, is greater than that of the non-tight section, which is more affected by intrusion, the gas saturation of the tight section is adopted as the gas saturation of the reservoir section. Fluid identification of the reservoir section is then performed based on the gas saturation.

[0031] The drilling fluid invasion data in step 1) includes the invasion radius values ​​of the flushing zone and transition zone.

[0032] Step 2) involves the specific steps of determining the tight layers in the reservoir by combining conventional well logging acoustic waves, density and neutron curves, and array induction inversion invasion profiles:

[0033] a) Porosity of the reservoir was interpreted by acoustic wave, density and neutron curves, and the low acoustic wave value, high density value and low neutron value range were selected as tight reservoirs.

[0034] b) Combining with step 1, locate the tight reservoir section with shallow drilling fluid intrusion based on array induction logging.

[0035] in, Figure 2 This is a diagram showing the invasion profile and interpretation results of Well A in this invention. The larger the invasion radius, the deeper the mud invasion.

[0036] Figure 3 This is a two-dimensional NMR interpretation model, meaning a two-dimensional NMR interpretation model adapted to dense sandstone. It simulates and constructs a two-dimensional T1-T2 gas and water identification chart containing clay-bound water, capillary-bound water, movable water, and natural gas. The porosity of each component fluid is set to 3.85%, 3.85%, 4.37%, and 7.78%, respectively, and the hydrogen content index (HI) of natural gas is 0.3.

[0037] The implementation process of the present invention will be described in detail below with reference to specific embodiments.

[0038] Example 1

[0039] The fluid identification method for tight sandstone reservoirs of the present invention includes the following steps:

[0040] (1) Drilling fluid invasion data were obtained based on array induction logging data. The drilling fluid invasion data included the invasion radius values ​​of the flushing zone and transition zone. The invasion characteristic data of well B is shown in Table 1 (the invasion radius, flushing zone resistivity, transition zone resistivity and original formation resistivity in Table 1 are all data obtained from logging inversion). It shows that the 6th (4th) layer is a low-resistivity gas layer, and the fluid properties are difficult to identify. Conventional logging interprets it as a gas-water co-layer with a gas saturation of 35.0%.

[0041] Table 1B Well Intrusion Characteristics Data Table

[0042]

[0043] Table 2B Well Nuclear Magnetic Interpretation Data

[0044]

[0045]

[0046] (2) Identify the tight layer within the reservoir. Conventional logging uses three porosity curves (sonic, density, and neutron curves) to interpret reservoir porosity. A porosity <5% indicates a tight reservoir section within this layer. The comprehensive logging curves for this well are as follows: Figure 4 As shown.

[0047] By combining array induction inversion of the invasion profile, a relatively dense reservoir section with minimal impact from drilling fluid invasion was identified. The invasion radius is smallest at 3257.00m in the upper part of the reservoir. Figure 5 This is the tight layer of the reservoir, with a porosity of 3.8%.

[0048] (3) The reservoir section was inverted and processed using two-dimensional nuclear magnetic resonance theory interpretation model, and the gas saturation of the selected tight and non-tight sections was compared.

[0049] like Figure 6 and Figure 7 As shown, when using two-dimensional nuclear magnetic resonance (NMR) logging for fluid property identification, at 3257.00m in the tight reservoir, the free pore gas saturation is 55.4% (gas porosity / mobile porosity). The two-dimensional NMR interpretation for this section of the tight layer is a gas layer. At 3261.00m in the middle and lower part of the reservoir, due to the influence of intrusion, the free pore gas saturation is lower at 20%, and the NMR interpretation is a gas-water layer. The two-dimensional NMR interpretation level of the reservoir section with good physical properties is relatively low.

[0050] Since the gas saturation of the tight layer, which is less affected by intrusion, is greater than that of the non-tight layer, which is more affected by intrusion, the interpretation conclusion at 3257.00m, which is least affected by intrusion, is the final interpretation conclusion for layer 6(4), with an interpreted gas saturation of 55.4%, and the interpretation conclusion is that it is a gas layer. This interpretation conclusion is consistent with the gas test conclusion.

[0051] Experiment Example 2

[0052] The fluid identification device for tight sandstone reservoirs in this embodiment includes a processor and a memory. The memory stores computer-executed instructions, and the processor executes the computer-executed instructions stored in the memory to implement the fluid identification method for tight sandstone reservoirs in Embodiment 1.

[0053] The processing steps in Example 1 can correspond to specific functional modules. Through the implementation of each functional module's function, fluid identification of tight sandstone reservoirs can ultimately be achieved. The integrated modules implemented as software functional modules described above can be stored in a computer-readable storage medium. These software functional modules, stored in a storage medium, include several instructions to cause a computer device or processor to execute the steps of the method described in the example.

[0054] The aforementioned processor can be a central processing unit, or other general-purpose processors, digital signal processors, application-specific integrated circuits, etc. The general-purpose processor can be a microprocessor or any conventional processor. The steps of the method disclosed in this invention can be directly manifested as being executed by a hardware processor, or being executed by a combination of hardware and software modules within the processor.

[0055] The memory may include high-speed RAM, and may also include non-volatile storage (NVM), such as at least one disk storage device, and may also be a USB flash drive, external hard drive, read-only memory, disk or optical disc, etc.

Claims

1. A method for fluid identification in tight sandstone reservoirs, characterized in that, Includes the following steps: (1) Interpret reservoir porosity using conventional logging curves to identify tight layers in the reservoir, wherein the porosity of the tight layers is <5%; (2) The drilling fluid invasion depth is determined by inversion of array induction logging data, and the dense layer with shallow drilling fluid invasion depth is selected; (3) Perform two-dimensional nuclear magnetic logging inversion and processing interpretation on the reservoir section, and compare the gas saturation of the tight layer with shallow drilling fluid penetration depth selected in step (2) with that of the non-tight layer in the same reservoir section. When the gas saturation of the tight layer with shallow drilling fluid penetration depth selected in step (2) is greater than the gas saturation of the non-tight layer, the gas saturation of the tight layer is used as the gas saturation of the reservoir section; the tight layer with shallow drilling fluid penetration depth is interpreted as a gas layer, the non-tight layer is interpreted as a gas-bearing water layer, and the final interpretation of the reservoir section is a gas layer.

2. The fluid identification method for tight sandstone reservoirs as described in claim 1, characterized in that, In step (1), the conventional logging curves include acoustic, density, and neutron curves; the low acoustic value, high density value, and low neutron value segments are selected as the dense layer.

3. A fluid identification device for tight sandstone reservoirs, characterized in that, The method includes a processor and a memory, wherein the memory stores computer-executable instructions, and the processor executes the computer-executable instructions stored in the memory to implement the fluid identification method for tight sandstone reservoirs as described in any one of claims 1 to 2.

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