Method for identifying volcanic rock weathering crust reservoir

Abstract

The invention relates to a volcanic rock weathering crust reservoir identification method, which comprises the following steps: S1, acquiring data of a plurality of exploratory wells in a research area, selecting the exploratory wells for drilling middle-acid volcanic rocks, and selecting volcanic rock samples; s2, collecting element composition data and mineral composition data of the volcanic rock sample; s3, calculating the clay mineral relative content and the element alteration index corresponding to the volcanic rock sample based on a preset mechanism according to the element composition data and the mineral composition data; and S4, based on a database of a preset statistical range, according to the clay mineral relative content and the element alteration index corresponding to the volcanic rock sample, determining whether the reservoir in which the volcanic rock sample is located is a volcanic rock weathering crust reservoir.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas development, and in particular to a method for identifying a volcanic rock weathering crust reservoir. Background Art

[0002] Volcanic rock is a special type of oil and gas reservoir. More than 150 volcanic rock-related oil and gas reservoirs have been discovered in nearly 40 basins around the world. As an important area of ​​oil and gas storage, volcanic rock oil and gas reservoirs can be briefly divided into three types: weathering crust type, fracture type, and weathering crust-fracture type.

[0003] At present, the research level of volcanic rock fracture reservoir detection technology is relatively high, and the main technologies include the comprehensive application of seismic and logging technology, numerical simulation of tectonic stress field, core test analysis, heavy electromagnetic method, etc. (Zhang Xiao et al., 2019). However, the development of weathering crust reservoirs is related to multiple factors such as lithology, climate, topography, and weathering-erosion, resulting in strong heterogeneity in its development degree in time and space. So far, the research on the identification and thickness determination of volcanic rock weathering crust in oil and gas exploration is relatively weak.

[0004] When volcanic rocks are formed, their physical properties are mostly low porosity and low permeability, making them difficult to serve as effective reservoirs. Once they undergo later transformations such as weathering and leaching, a large number of dissolution pores and fractures can develop in the upper part of the volcanic rocks, and their physical properties are significantly improved, thus forming an effective weathering crust reservoir. Based on this understanding, the thickness of the weathering crust is currently inferred by the time interval between volcanic rocks and overlying strata and the change in the porosity and permeability of volcanic rocks. However, these methods have obvious limitations and lack sufficient mechanistic understanding. On the one hand, the stratigraphic time interval is only one of the many factors that affect the development of the weathering crust. For example, the difference in weathering crust thickness between the paleo-geomorphic highlands and depressions in the Dixi 17 well area with consistent stratigraphic time intervals can be as high as 250m (Yi Zejun et al., 2015); on the other hand, the weathering crust reservoir of volcanic rocks does not have good overall physical properties. For example, the porosity of the soil zone in the weathering crust of the Carboniferous volcanic rocks in the Chepaizi bulge is significantly lower than that of the fresh volcanic rock section (Han Huimei et al., 2024). Therefore, it is particularly important to establish a technical method for accurately and efficiently identifying and determining the thickness of the weathering crust of volcanic rocks. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for identifying volcanic weathering crust reservoirs to support the study of the distribution law and development mechanism of volcanic weathering crust during the exploration of intermediate-acidic volcanic rock oil and gas, and to ensure the scientificity and accuracy of weathering crust thickness data in weathering crust reservoir prediction technology.

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

[0007] In a first aspect, the present application provides a method for identifying a volcanic rock weathering crust reservoir, the method comprising:

[0008] S1, obtain data from multiple exploration wells in the study area, select exploration wells that encounter intermediate-acidic volcanic rocks, and select volcanic rock samples;

[0009] S2, collecting element composition data and mineral composition data of the volcanic rock sample;

[0010] S3, calculating the relative content of clay minerals and the element alteration index corresponding to the volcanic rock sample according to the element composition data and the mineral composition data based on a preset mechanism;

[0011] S4, based on a database with a preset statistical range, and according to the relative content of clay minerals and the element alteration index corresponding to the volcanic rock sample, determining whether the reservoir where the volcanic rock sample is located is a volcanic rock weathering crust reservoir.

[0012] In one implementation of the present application, in S1, based on the wall core and rock thin section data, an exploration well that encounters intermediate-acidic volcanic rocks is selected;

[0013] Based on the stratigraphic stratification data, the volcanic rock section of the well was determined after correction with the wall core and rock thin section data, and the samples of non-volcanic lava in the section were eliminated.

[0014] In one implementation of the present application, in S2, the element composition data includes Na, K and Al element data.

[0015] In one implementation of the present application, in S2, the mineral composition data, including feldspar and clay mineral data, are calculated to obtain the total amount of feldspar and clay minerals, respectively.

[0016] In one implementation of the present application, the preset mechanism is specifically the weathering and leaching mechanism of intermediate-acidic volcanic rocks, and its specific chemical formula is:

[0017] 2KAlSi3O8+3H2O+2CO2=Al2Si2O5(OH)4+2KHCO3+4SiO2

[0018] 2NaAlSi3O8+2CO2+3H2O=Al2Si2O5(OH)4+4SiO2+2NaHCO3.

[0019] In one implementation of the present application, the calculation formula for the relative content of clay minerals is:

[0020] Q = 100*2N / (K+P+2N),

[0021] Among them, the number of potassium feldspar after alteration is K, the corresponding number of plagioclase is P, and the corresponding number of clay minerals is N.

[0022] In one implementation of the present application, the calculation formula of the element alteration index is:

[0023] AI (Alteration Index) = (δ K / 39+δ Na / 23) / (δ Al / 27)

[0024] Among them, δ K、Na、Al The content is the mass fraction of the element.

[0025] In one implementation of the present application, based on the element alteration index being less than 55 and the relative content of clay minerals being greater than 60, it is determined whether the reservoir where the volcanic rock sample is located is a volcanic rock weathering crust reservoir.

[0026] In one implementation of the present application, based on a database with a preset statistical range, the thickness of the reservoir where the volcanic rock sample is located is determined according to the correlation between two indicators: element alteration index and relative content of clay minerals.

[0027] In one implementation of the present application, the preset statistical range is specifically real-time updated logging data of the global sea area.

[0028] The technical solution of the present invention aims at the difficult problem of identifying and determining the thickness of volcanic rock weathering crust. With the formation mechanism of weathering crust as theoretical guidance and mineral and element composition logging data as the starting point, a set of methods and judgment criteria for rapid identification and thickness determination of intermediate-acidic volcanic rock weathering crust has been established. The method has clear ideas, is easy to understand, and has strong operability. It has guiding and application value for conducting volcanic rock buried hill oil and gas exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a flow chart of the method for determining and predicting the weathering crust of intermediate-acidic volcanic rocks;

[0030] Figure 2 The correlation between the relative content of clay minerals and the alteration index of the Mesozoic intermediate-acidic volcanic rocks in Bohai Sea;

[0031] Figure 3 This is a statistical chart of the relative content of clay minerals in relatively fresh Mesozoic intermediate-acidic volcanic rocks in the Bohai Sea area;

[0032] Figure 4 It is a statistical chart of the global relatively fresh intermediate-acidic volcanic rock alteration index;

[0033] Figure 5 Core and thin-section rock characteristics of Mesozoic acidic rhyolite in Well N3S, Bohai Sea;

[0034] Figure 6(a) Element alteration index and (b) relative content characteristics of clay minerals in the Mesozoic acidic rhyolite from Well N3S in Bohai Sea. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0036] In view of the defects and problems of the prior art, the present application provides a method for identifying a volcanic rock weathering crust reservoir, the method comprising:

[0037] S1, obtain data from multiple exploration wells in the study area, select exploration wells that encounter intermediate-acidic volcanic rocks, and select volcanic rock samples;

[0038] S2, collecting element composition data and mineral composition data of the volcanic rock sample;

[0039] S3, calculating the relative content of clay minerals and the element alteration index corresponding to the volcanic rock sample according to the element composition data and the mineral composition data based on a preset mechanism;

[0040] S4, based on a database with a preset statistical range, and according to the relative content of clay minerals and the element alteration index corresponding to the volcanic rock sample, determining whether the reservoir where the volcanic rock sample is located is a volcanic rock weathering crust reservoir.

[0041] The above method flow is described in more detail in the following embodiments in conjunction with the accompanying drawings of the present invention.

[0042] The method of the embodiment of the present application is applied in a device, such as Figure 1 , specifically including a first processing unit, a second processing unit, a third processing unit and a fourth processing unit. Among them,

[0043] The first processing unit is "drilling and sample screening", which includes screening out volcanic rock research objects based on stratigraphic layering data, wall cores and rock thin sections. The brief process is as follows:

[0044] (1) Based on the core and rock thin section data, select typical exploration wells that encounter intermediate-acidic volcanic rocks;

[0045] (2) Based on the stratigraphic data, the volcanic rock section of the well is determined by correcting the wall core and rock thin section data, and samples of non-volcanic lava in the section, including pyroclastic rocks, are eliminated;

[0046] The second processing unit is "data collection and integration", which collects samples from the screened volcanic rock samples. The corresponding element and mineral composition logging data are integrated with the Na, K and Al element data in the element logging data, and the feldspar (such as potassium feldspar and plagioclase) and clay mineral (such as kaolinite and montmorillonite) data in the mineral composition logging data, and the total amount of feldspar and clay minerals are calculated respectively.

[0047] The third processing unit is "data quantitative analysis", which is the core technical content of the present invention. Taking the total content of feldspar, the total content of clay minerals, and the logging data of Na, K and Al elements as the core data, and the weathering and leaching mechanism of volcanic rocks as the theoretical guidance, two sets of methods for identifying and determining the thickness of intermediate-acidic volcanic rock weathering crusts are established. The principle and quantitative analysis steps of the method are briefly as follows:

[0048] (1) Weathering and leaching mechanism of intermediate-acidic volcanic rocks: The main rock-forming minerals of intermediate-acidic volcanic rocks are potassium feldspar, plagioclase or quartz. During the natural weathering and leaching process, feldspar minerals are prone to alteration and clayification, producing clay minerals mainly composed of kaolinite. Among them, potassium feldspar will undergo kaolinization (Formula 1), resulting in a large loss of K element in the mineral, and the Al element will be retained in clay minerals such as kaolin; plagioclase will undergo kaolinization (Formula 2), resulting in a large loss of Na element in the mineral, and the Al element will be retained in clay minerals such as kaolin; quartz is relatively stable under natural conditions and is not affected by weathering and leaching.

[0049] 2KAlSi3O 8(钾长石) +3H2O+2CO2=Al2Si2O5(OH) 4(高岭石) +2KHCO3+4SiO2 (Formula 1)

[0050] 2NaAlSi3O 8(钠长石) +2CO2+3H2O=Al2Si2O5(OH) 4(高岭石) +4SiO2+2NaHCO3 (Formula 2)

[0051] (2) Method for determining the relative content of clay minerals: During the weathering and leaching process of intermediate-acidic volcanic rocks, the feldspar minerals are mainly clayified, which leads to a significant decrease in the content of feldspar minerals and a significant increase in the content of clay minerals. However, the content of feldspar minerals in primary intermediate-acidic volcanic rocks varies significantly, so the content of clay minerals cannot objectively reflect the actual degree of weathering and leaching of volcanic rocks. Therefore, it is more reliable to use the proportion of clay minerals relative to feldspar minerals (Q) as the basis for determination. Among them, the total content of feldspar before volcanic rock alteration can be calculated based on the reaction equation of feldspar alteration, which can be expressed as the sum of potassium feldspar (K), plagioclase (P) and clay minerals (N) after alteration. Therefore, the calculation formula for the relative content of clay minerals is:

[0052] Q = 100*2N / (K + P + 2N) (Formula 3),

[0053] Where "2" is the constant factor for kaolinite to transform into feldspar minerals

[0054] (3) Element alteration index identification method: In the process of weathering and alteration of feldspar minerals into clay minerals, intermediate-acidic volcanic rocks will release a large amount of free K + 、Na + ions. These free K + 、Na + Ions are easily leached and migrated by fluids, resulting in a significant decrease in the K and Na elements of the residual altered volcanic rocks and a significant increase in the alteration index (AI) content. Therefore, based on reaction formulas 1 and 2, a set of discrimination methods based on the content of K, Na and Al elements was established, and the calculation formula is:

[0055] AI (Alteration Index) = (d K / 39+d Na / 23) / (d Al / 27)(Formula 4), where d K、Na、Al The content is the mass fraction of the element.

[0056] The fourth processing unit is "Technical Standard Establishment". As shown above, the third unit established two sets of medium-acid volcanic rock The methods for identifying the weathering crust and determining its thickness are the relative content of clay minerals and the element alteration index. On this basis, with the weathering and leaching mechanism of intermediate-acidic volcanic rocks as the technical support, the element and mineral composition data of intermediate-acidic volcanic rocks worldwide (including Bohai Sea) were collected, and the technical standards for the identification and thickness determination of the weathering crust of intermediate-acidic volcanic rocks were established based on statistical characteristics.

[0057] (1) Correlation between the relative content of clay minerals and the identification method of elemental alteration index. Based on the common weathering and leaching mechanism, the two sets of identification methods for intermediate-acidic volcanic rock weathering crusts complement, restrict and verify each other, that is, the established relative content of clay minerals and the alteration index have a certain negative correlation ( Figure 2 ). Once the relative content of clay minerals and the alteration index are obviously decoupled and lack correlation, the two methods will fail to determine the thickness of the weathering crust of intermediate-acidic volcanic rocks. The two sets of weathering crust identification methods are interrelated and mutually restricted, and finally jointly implement the thickness of the weathering crust of intermediate-acidic volcanic rocks.

[0058] (2) The relative content of clay minerals is used to determine the standard of the weathering crust of intermediate-acidic volcanic rocks. To date, nearly 200 wells in the Bohai Sea have encountered Mesozoic volcanic rocks. However, the vast majority of wells do not target the Mesozoic, so the data on the mineral content of volcanic rocks are relatively small. The present invention uses fresh, intermediate-acidic volcanic rocks (excluding pyroclastic rocks) and complete mineral content data as the screening basis, and screens out 11 wells from the Bohai Sea, with a total of 145 sets of mineral content data; then completes the calculation of the relative content of clay minerals in each group of data, and establishes a box-type statistical chart with 10 as the unit ( Figure 3 ); In order to ensure the credibility of the relative content range of clay minerals in fresh intermediate-acidic volcanic rock samples, the thin section and data distribution characteristics are combined, and the 10% (weathering leaching zone) and 90% (fresh volcanic rock) of the total sample are used as the boundaries to determine the discrimination criteria for the weathering crust of intermediate-acidic volcanic rocks. Figure 3 It can be seen that the relative content of clay minerals in fresh intermediate-acidic volcanic rocks is less than 60, while the relative content of clay minerals in weathering crusts is generally greater than 60.

[0059] (3) The element alteration index discrimination method determines the standard of the weathering crust of intermediate-acidic volcanic rocks. At present, there are a lot of research materials on intermediate-acidic volcanic rocks worldwide, and the element composition data are rich. The present invention extracted 2112 sets of volcanic rock composition data from the Geochemical Rock Database (https: / / georoc.mpch-mainz.gwdg.de / georoc / ) based on fresh intermediate-acidic volcanic lava (excluding pyroclastic rocks); then, 1565 sets of intermediate-acidic volcanic rock data were selected according to the completeness of Na, K and Al element data; then, the alteration index calculation of each group of element data was completed, and a box-type statistical chart with 5 as the unit was established ( Figure 4 ); In order to ensure the credibility of the alteration index range of fresh intermediate-acidic volcanic rock samples, the discrimination criteria for the weathering crust of intermediate-acidic volcanic rocks are determined based on the data distribution characteristics, with 10% (weathering leaching zone) and 90% (fresh volcanic rocks) of the total samples as the boundaries. Figure 4 It can be seen that the alteration index of fresh intermediate-acidic volcanic rocks is greater than 55, and the alteration index of weathering crust is generally less than 55.

[0060] Combining the above two methods, the relative content of clay minerals in the weathering crust of intermediate-acidic volcanic rocks is generally greater than 60, and the element alteration index is usually less than 55. This standard range also falls within the correlation trend between the relative content of clay minerals and the alteration index ( Figure 2 ), its validity has been further verified. Therefore, the intermediate-acidic volcanic rock section with a clay mineral relative content greater than 60 and an alteration index less than 55 is the true thickness of the volcanic rock weathering crust. It is worth noting that Fresh volcanic rock sections can be There may be scattered abnormal points with high clay mineral content and low alteration index, which are caused by deepIt is caused by fluid dissolution in a small area, rather than the weathering crust of volcanic rocks.

[0061] In the following, a specific application example is used to illustrate the determination of intermediate-acidic volcanic rocks in the Mesozoic of Bohai Sea.

[0062] Taking the identification and determination of the thickness of the weathering crust of the Mesozoic acidic volcanic rocks in the Bohai Sea N3S well as an example

[0063] 1) Bohai N3S Well is an exploration well with Mesozoic volcanic rocks as the main target layer. The well depth is about 5300m. According to the stratigraphic data, the rock thin sections and well core sampling were used to identify the wellbore. Figure 5 ), it was determined that the 4900-5300m section of the well contained acidic rhyolite volcanic rocks. At the same time, based on the thin section identification results, the pyroclastic rocks in this volcanic rock section were eliminated, and the volcanic lava was retained as the research object.

[0064] 2) From the well logging data, the mineral and element composition data of the Mesozoic volcanic rocks in Well N3S were selected; the mineral composition of potassium feldspar, plagioclase and clay minerals and the logging data of Na, Al and K elements in the volcanic lava section were further selected, and a total of 11 sets of complete data with high credibility were integrated (Table 1).

[0065]

[0066] Table 1

[0067] 3) According to the clay mineral relative content determination method (Formula 3) and the element alteration index determination method (Formula 4), 11 sets of volcanic lava data were analyzed to calculate the clay mineral relative content and element alteration index. Among them, the clay mineral relative content ranged from 17.83 to 98.06, and the alteration index ranged from 42.42 to 106.97.

[0068] 4) Referring to the criteria for determining the intermediate-acidic volcanic rock weathering crust (relative clay mineral content greater than 60, alteration index less than 55), the 4900-5010 m section was finally determined as the Mesozoic acidic volcanic rock weathering crust development section of Well N3S, with a thickness range of 110 m ( Figure 6 This result was further verified by the thin section and wall core identification results ( Figure 5 ).

[0069] In summary, the present invention aims at the difficult problem of identifying and determining the thickness of volcanic rock weathering crust, takes the weathering crust formation mechanism as theoretical guidance, and uses mineral and element composition logging data as a starting point to establish a set of methods and judgment criteria for rapid identification and thickness determination of intermediate-acidic volcanic rock weathering crust. The method has clear ideas, is easy to understand, and has strong operability, which has guiding and application value for conducting volcanic rock buried hill oil and gas exploration.

[0070] In the several embodiments provided by the present invention, it should be understood that the disclosed method can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the above units is only a logical function division. There may be other division methods in actual implementation. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0071] The above-mentioned integrated unit implemented in the form of a software functional unit can be stored in a computer-readable storage medium. The above-mentioned software functional unit is stored in a storage medium, including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) or a processor (Processor) to perform some steps of the above-mentioned method of each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory, ROM), random access memory (Random Access Memory, RAM), disk or optical disk and other media that can store program codes.

[0072] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for identifying a volcanic rock weathering crust reservoir, characterized in that: The method comprises: S1, obtain data from multiple exploration wells in the study area, select exploration wells that encounter intermediate-acidic volcanic rocks, and select volcanic rock samples; S2, collecting element composition data and mineral composition data of the volcanic rock sample; S3, calculating the relative content of clay minerals and the element alteration index corresponding to the volcanic rock sample according to the element composition data and the mineral composition data based on a preset mechanism; S4, based on a database with a preset statistical range, and according to the relative content of clay minerals and the element alteration index corresponding to the volcanic rock sample, determining whether the reservoir where the volcanic rock sample is located is a volcanic rock weathering crust reservoir.

2. The method for identifying volcanic rock weathering crust reservoir according to claim 1, characterized in that: In S1, based on the core and rock thin section data, exploration wells that encounter intermediate-acidic volcanic rocks are selected; Based on the stratigraphic stratification data, the volcanic rock section of the well was determined after correction with the wall core and rock thin section data, and the samples of non-volcanic lava in the section were eliminated.

3. The method for identifying volcanic rock weathering crust reservoir according to claim 1, characterized in that: In S2, the element composition data includes Na, K and Al element data.

4. The method for identifying volcanic rock weathering crust reservoir according to claim 3, characterized in that: In S2, the mineral composition data, including feldspar and clay mineral data, are calculated to obtain the total amount of feldspar and clay minerals respectively.

5. The method for identifying volcanic rock weathering crust reservoir according to claim 4, characterized in that: The preset mechanism is specifically the weathering and leaching mechanism of intermediate-acidic volcanic rocks, and its specific chemical formula is: 2KAlSi3O8+3H2O+2CO2=Al2Si2O5(OH)4+2KHCO3+4SiO2 2NaAlSi3O8+2CO2+3H2O=Al2Si2O5(OH)4+4SiO2+2NaHCO3.

6. The method for identifying volcanic rock weathering crust reservoir according to claim 5, characterized in that: The calculation formula for the relative content of clay minerals is: Q = 100*2N / (K+P+2N), Among them, the number of potassium feldspar after alteration is K, the corresponding number of plagioclase is P, and the corresponding number of clay minerals is N.

7. The method for identifying volcanic rock weathering crust reservoir according to claim 6, characterized in that: The calculation formula of element alteration index is: AI(Alteration Index)=(δ K / 39+d Na / 23) / (d Al / 27) Among them, δ K、Na、Al The content is the mass fraction of the element.

8. The method for identifying volcanic rock weathering crust reservoir according to claim 7, characterized in that: According to the element alteration index being less than 55 and the relative content of clay minerals being greater than 60, it is determined whether the reservoir where the volcanic rock sample is located is a volcanic rock weathering crust reservoir.

9. The method for identifying volcanic rock weathering crust reservoir according to claim 8 is characterized in that: Based on preset The thickness of the reservoir where the volcanic rock sample is located is determined based on the correlation between the element alteration index and the relative content of clay minerals.

10. The method for identifying volcanic rock weathering crust reservoir according to claim 9, characterized in that: The preset statistical range is specifically the well logging data of the global sea area updated in real time.

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