Prediction method for oil and gas favorable area of continental freshwater lake basin in low exploration area

Abstract

The invention relates to a prediction method for an oil gas favorable area of a continental freshwater lake basin in a low exploration area, and belongs to the technical field of oil gas exploration and development. The method comprises the following steps: firstly, carrying out oil source comparison on an independent oil-gas-containing system found in a continental freshwater lake basin in a low exploration area so as to determine a hydrocarbon generation lower limit value of an effective hydrocarbon source rock; then according to test analysis of a single well and a region, a development layer section and lithology of the effective hydrocarbon source rock are determined, and then plane distribution characteristics such as the thickness, the abundance and the thermal evolution degree of the effective hydrocarbon source rock are depicted; and finally, according to superposition of three elements of abundance, thickness and thermal evolution degree of the effective hydrocarbon source rocks, determining a plane distribution range of the effective hydrocarbon source rocks, and the distribution range is a favorable distribution range of the oil-gas low exploration area.

Description

Technical Field

[0001] The invention relates to a method for predicting favorable oil and gas areas in continental freshwater lake basins in low-exploration areas, belonging to the technical field of oil and gas exploration and development. Background Art

[0002] According to current statistics, the area of ​​prospecting rights of domestic oil companies is much larger than the area of ​​mining rights, of which mining rights / prospecting rights are less than 20%. The above data show that in many areas, large-scale oil and gas reserves have not yet been discovered, making it difficult to convert prospecting rights into mining rights. As of 2022, the area of ​​domestic oil and gas prospecting rights is about 2.56 million km 2 , while the mining rights area is only 210,000 km 2 , mining rights only account for about 8% of the prospecting rights area, and 92% of the prospecting rights have not been converted into mining rights. The most important factor for the failure to convert prospecting rights into mining rights is that no large-scale oil and gas reserves have been discovered, the oil and gas grade is low, and even no oil and gas has been discovered in some prospecting rights.

[0003] When conducting oil and gas exploration in a region, the first thing to do is to deploy pre-exploration wells in the region. If the deployed pre-exploration wells obtain oil and gas, it means that the region may have great oil and gas exploration potential; but the reality is that the pre-exploration wells often fail and no oil and gas is found. Does the fact that a region has deployed pre-exploration wells but no oil and gas is found mean that the oil and gas exploration potential of the region is small, or even that the region has no oil and gas potential? From the previous experience of oil and gas exploration, this conclusion cannot be drawn in a hurry. In the past exploration process, there are a large number of examples where an oil company conducted risky exploration in a region but did not find oil and gas, while another oil company took over the region and transformed its thinking, often discovering oil and gas in the region. Therefore, from this perspective, oil and gas exploration is full of contingency. Therefore, with the progress of oil and gas exploration and the transfer of oil and gas mining rights, whether low-exploration areas (hereinafter referred to as low-exploration areas) have oil and gas exploration potential has become a hot topic of concern in the exploration community.

[0004] Low exploration areas usually refer to those areas with complex geological features, high exploration difficulty, low resource potential or not fully developed in the field of geological exploration and resource development. These areas generally have the problems of few exploration data and low research level. Continental lake basins are widely developed in my country, including the Bohai Bay Basin, Songliao Basin, Ordos Basin, Sichuan Basin, Yin'e Basin, etc. Continental lake basins have unique geological characteristics and fluid properties, mainly including complex sedimentary environments, diverse sedimentary phases, special structural characteristics and rich source rocks and reservoirs. These characteristics make continental lake basins an important target for oil and gas resource exploration. Among the above basins, freshwater lake basins are the most widely developed. Although many areas have discovered and successfully exploited oil and gas, there are still many low exploration areas in continental lake basins. Whether they have further oil and gas exploration potential and selecting favorable areas from continental freshwater lake basins in low exploration areas are of great significance to increasing my country's oil and gas production.

[0005] The Chinese invention patent application document with publication date of October 7, 2015 and publication number CN104965237A discloses a method for quantitatively selecting favorable unconventional oil and gas areas. The software performs numerical calculations based on the plane contour distribution of different geological parameters; the different geological parameters are divided into positively correlated parameters and negatively correlated parameters according to their promoting and hindering effects on favorable unconventional oil and gas development areas, and the development favorableness is calculated separately. According to the unconventional oil and gas exploration practice and the actual geological conditions of the research area, the weights of each geological parameter are assigned and calculated to obtain the size of the favorableness of unconventional oil and gas development in the target layer at different positions on the plane; according to the favorable coefficients of unconventional oil and gas development at different positions on the plane, the favorable development areas are compared and analyzed for selection. This method can intuitively and quickly select the optimal exploration target area by quantitatively selecting favorable unconventional oil and gas development areas. However, this method has too much human intervention. For example, the weights of different geological parameters are assigned as 0.4, 0.3, and 0.4 respectively. It is not clear how to obtain and combine them with the actual geological conditions. In addition, this method is mainly aimed at unconventional oil and gas reservoirs and has a relatively narrow scope of application.

[0006] The Chinese invention patent application document with the publication date of August 29, 2017 and the publication number of CN107102376A discloses a comprehensive evaluation and prediction method for favorable areas of tight oil enrichment in continental lake basins. The overall steps are: data collection, processing and acquisition of key data; clarifying the source-reservoir configuration relationship and establishing a single well lithofacies model based on the vertical superposition relationship of different rock types in the well logging lithology profile; using the single well cloud-to-ground ratio and TOC data to form cloud-to-ground ratio contour map and TOC contour map, superimposing the cloud-to-ground ratio contour map, TOC contour map and source-reservoir configuration relationship plane distribution map, and determining the lithology plane distribution map; on the basis of the lithofacies plane map, superimposing the vitrinite reflectance contour map, and referring to the dolomite thickness contour map, comprehensively evaluating and predicting favorable areas of tight oil enrichment. This method can clearly and comprehensively reflect the plane distribution law of high-quality reservoirs, high-quality source rocks and their mutual configuration relationship, and has low economic cost and strong operability. However, this method is aimed at studying tight oil and gas in unconventional oil and gas reservoirs, which belong to special oil and gas reservoirs. Due to their unique geological characteristics and fluid properties, they are obviously not suitable for conventional terrestrial lake basin oil and gas reservoirs. Moreover, this method solves the sweet spot problem of unconventional oil and gas reservoirs and does not predict favorable areas. Summary of the invention

[0007] The purpose of the present invention is to provide a method for predicting favorable oil and gas areas in continental freshwater lake basins in low exploration areas, and to provide a simple and effective method for predicting favorable oil and gas areas in continental freshwater lake basins in low exploration areas.

[0008] In order to achieve the above-mentioned purpose, the technical scheme of a method for predicting favorable oil and gas areas in continental freshwater lake basins in low exploration areas in the present invention is:

[0009] A method for predicting favorable oil and gas areas in continental freshwater lake basins in low-exploration areas comprises the following steps:

[0010] (1) Conducting geochemical analysis on the crude oil that has been drilled in the independent oil-bearing system in the target area, and determining the lower limit of hydrocarbon generation of the effective source rock based on the analysis results;

[0011] (2) Based on the test analysis results of the single well and the lower limit of hydrocarbon generation obtained in step (1), determine the development interval and lithology of the effective source rock, and then determine the thickness and lower limit of thermal evolution of the effective source rock based on the logging data, crude oil maturity and oil and gas flow conditions;

[0012] (3) Using the lower limit of hydrocarbon generation of the effective source rock obtained in step (1) and the lower limit of thickness and thermal evolution degree obtained in step (2), single-element contour maps of abundance, thickness and thermal evolution degree of the effective source rock in the target area are drawn respectively, and the overlapping area of ​​the single-element contour maps is delineated as the favorable area for oil and gas in the target area.

[0013] The beneficial effect of the above technical scheme is that the prediction method of favorable oil and gas areas in continental freshwater lake basins in low exploration areas of the present invention is a pioneering invention. The present invention first compares the oil sources of crude oil found in independent oil-bearing systems in continental freshwater lake basins in low exploration areas, analyzes the geochemical characteristics of the main body of crude oil in the independent oil-bearing system, and then tests source rocks with different organic matter abundances, analyzes their geochemical characteristics and compares them with the geochemical characteristics of the main body of crude oil to determine the lower limit of hydrocarbon generation of effective source rocks. Second, based on the test analysis of single wells and regions, the development layer and lithology of effective source rocks are determined, and then the plane distribution characteristics of effective source rocks such as thickness, abundance, and degree of thermal evolution are characterized. Finally, based on the superposition of the three elements of abundance, thickness and degree of thermal evolution of effective source rocks, the plane distribution range of effective source kitchens is determined, and this distribution range is the favorable distribution range of low oil and gas exploration areas. The present invention discovers for the first time that the three factors of abundance, thickness and thermal evolution degree of effective source rocks can be used to predict favorable oil and gas areas in terrestrial freshwater basins in low-exploration areas. Field applications also show that the prediction method of the present invention has relatively accurate prediction results and can predict favorable areas in terrestrial freshwater basins in low-exploration areas, laying the foundation for the next step of development.

[0014] As a further improvement, the lower limit of hydrocarbon generation of the effective source rock in step (1) is the lower limit of TOC of the source rock that contributes to the composition characteristics of the crude oil.

[0015] Specifically, the contribution to the composition characteristics of crude oil refers to that the source rock sample has geochemical characteristic information similar to that of crude oil.

[0016] As a further improvement, the process of determining the lower limit of the thickness of the effective source rock in step (2) is as follows: based on the logging data, a correlation between the thickness of the effective source rock and the oil and gas display is established, and the thickness of the effective source rock is determined in combination with the production oil and gas flow conditions.

[0017] As a further improvement, the oil and gas display includes oil immersion, oil spots and oil traces.

[0018] As a further improvement, the lower limit of the thermal evolution degree of the effective source rock in step (2) is the maturity value of the crude oil in the target area where the oil and gas layer is the shallowest and there is a well producing oil and gas flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flowchart of a method for predicting favorable oil and gas areas in continental freshwater lake basins in low exploration areas in Example 1 of the present invention;

[0020] Figure 2 is a distribution diagram of the thickness of dark mudstone in XX depression in Example 1 of the present invention;

[0021] Figure 3This is a comparison and analysis diagram of the oil source of the XX depression in Example 1 of the present invention;

[0022] Figure 4 This is a graph showing the TOC variation with depth in the Guaican 1 well in the XX depression in Example 1 of the present invention;

[0023] Figure 5 is a correlation diagram between oil and gas display and shale thickness in XX depression in Example 1 of the present invention;

[0024] Figure 6 It is a contour map of the TOC of the organic matter abundance in the effective source rock development section of the XX sag in Example 1 of the present invention;

[0025] Figure 7 It is a contour map of the thermal evolution degree Ro of the effective source rock development section in the XX sag in Example 1 of the present invention;

[0026] Figure 8 It is a contour map of shale thickness in the effective source rock development section of XX Sag in Example 1 of the present invention;

[0027] Fig. 9 This is a distribution map of favorable oil and gas areas in the XX depression in Example 1 of the present invention. DETAILED DESCRIPTION

[0028] Since different blocks have different oil and gas resource potentials and face different oil and gas exploration risks, resource potential evaluation of oil and gas blocks is of great significance for reducing exploration risks and improving exploration benefits. However, low-exploration areas generally have problems such as little exploration data and low research level, and it is often difficult to carry out resource potential analysis using conventional methods. Continental freshwater lake basins are most widely developed in my country, and there are still many low-exploration areas. Evaluating these areas is of great significance to promoting the development of oil and gas exploration in my country. In view of this, the present invention provides a method for predicting favorable oil and gas areas in continental freshwater lake basins in low-exploration areas.

[0029] The present invention is further described below in conjunction with specific embodiments. It should be noted that, under the premise of no conflict, the embodiments or technical features described below can be arbitrarily combined to form new embodiments. The equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments are all conventional methods in the art unless otherwise specified.

[0030] In the following examples, unless otherwise specified, the experimental operations are routine operations in the art.

[0031] In the following examples, unless otherwise specified, all raw materials used are conventional commercial products in the art.

[0032] Specific embodiments of the method for predicting favorable oil and gas areas in continental freshwater lake basins in low exploration areas of the present invention:

[0033] Example 1

[0034] This embodiment takes a depression in Zhongyuan Oilfield as an example to explain the prediction method of favorable oil and gas areas in continental freshwater lake basins in low exploration areas of the present invention. The process of the prediction method is as follows: Figure 1 The specific steps are as follows:

[0035] The XX sag is a dustpan-shaped depression with faults in the east and overlaps in the west. The dark mudstone thickness analysis shows that the dark mudstone is mainly distributed in the central area of ​​the depression. The dark mudstone is thick in the center of the depression and gradually thins toward the surrounding areas. Drilling also found that oil and gas flow wells are mainly distributed around the thick mudstone development area in the center of the depression. It is comprehensively judged that the depression is an independent oil and gas system (such as Figure 2 shown).

[0036] 1. Determination of the lower limit of hydrocarbon generation of effective source rocks in the predicted area

[0037] Through geochemical analysis of crude oil samples from reference wells and industrial oil and gas flow wells in the XX Depression, it was found that the crude oil has the characteristic of high C30 rearranged hopane content, that is, the C30 rearranged hopane content is higher than the C30 hopane content.

[0038] After discovering that crude oil has this characteristic, based on the determination of the TOC of organic matter abundance in source rock samples from the same reference wells and industrial oil and gas flow wells as the crude oil samples, it was found that the TOC from high to low was 1.713%, 1.498%, 0.8790%, and 0.8384%, respectively, and all source rock samples had similar geochemical characteristic information as crude oil, that is, the C30 rearranged hoeane content was higher than the C30 hoeane content. However, after the TOC of the source rock was reduced to 0.2267%, it was found that it had a different pattern from crude oil, that is, the C30 rearranged hoeane content was lower than the C30 hoeane content. At the same time, in the verification, the source rock with a TOC of about 0.7 was tested and analyzed, and it was found that the source rock sample with TOC = 0.6983% also had the characteristic that the C30 rearranged hoeane content was lower than the C30 hoeane content. This indicates that the source rock has no contribution to crude oil. It can be inferred that the lower limit of TOC of the source rock that contributes to crude oil in the depression is TOC = 0.8% (e.g. Figure 3 shown).

[0039] 2. Determination of the lower limit of the thickness and thermal evolution degree of effective source rocks in the predicted area

[0040] From step 1, we know that the TOC lower limit of the effective source rock in the XX depression is 0.8%. According to the longitudinal large-scale sampling analysis test of Guaican 1 well, it is found that the source rocks with TOC greater than 0.8% are all shale, and their distribution layer is the first member of Ba. Therefore, it can be inferred that the crude oil in the Guaizihu depression mainly comes from the shale of the first member of Ba (such as Figure 4As shown in the figure, samples with TOC greater than 0.8% at around 2000 m are massive mudstone samples, not shale, and are not considered in the analysis. ).

[0041] According to statistics of a large amount of logging data, it is found that there is a certain correlation between the thickness of shale and oil and gas shows, such as Figure 5 The specific information of shale thickness and oil and gas display (oil invasion + oil spot + oil trace) is shown in Table 1.

[0042] Table 1 Relationship between shale thickness and oil and gas show thickness in exploration wells in XX Sag

[0043] Exploration well name Shale thickness (m) Oil invasion + oil stain + oil mark (m) Guaican 1 Well 60.8 23.25 Guai 6 Well 56 17 Guai 7 Well 19.5 12 Well 10 41 25 Well 11 22 18.9 Guai 3 Well 21 10.5 Well 5 0 6 Well 2 0 0 Guai 9 Well 0 0

[0044] pass Figure 5 It can be found that the thicker the shale is, the thicker the oil and gas display thickness is during oil and gas drilling, and vice versa. The correlation coefficient R 2 =0.7379, which has a strong correlation. When the thickness of shale is greater than 20m, its oil and gas indication thickness exceeds 10m; when the thickness of shale is greater than 60m, its oil and gas indication thickness is nearly 24m; when the thickness of shale is 0m, it can be found that the oil and gas indication thickness of some wells is 0m, and the oil and gas indication thickness of some wells is 6m. The oil and gas indication is relatively weak, and fracturing has not obtained industrial oil and gas wells. According to the situation of obtaining industrial oil and gas flow, combined with the oil and gas indication thickness, shale thickness greater than 20m is used as a standard for obtaining oil and gas flow.

[0045] Based on the aromatic mass spectrometry data of the three crude oils in the XX Sag, the maturity of the crude oil in the XX Sag can be calculated. Specifically, as shown in Table 2, the maturity of the crude oil in the oil and gas flow well Guai 8 located in the highest part of the XX Sag is Rc = 0.73%. The geological meaning of Rc of 0.73% is that the crude oil is generated when the vitrinite reflectance of the source rock Ro = 0.73%. From this, it can be inferred that the lower limit of the thermal evolution degree Ro of the source rock that forms a large-scale oil and gas reservoir in the freshwater environment of the XX Sag is about 0.7%.

[0046] Specifically, Well Guai 8 is the shallowest well that has obtained industrial oil and gas flow in the structural belt of the area. Although some wells are buried shallower, they are all empty wells and have never obtained oil and gas flow. Therefore, the shallowest well that has obtained industrial oil and gas flow in the area is used as the reference well, and the crude oil maturity value of this well is the lower limit of the thermal evolution degree of the effective hydrocarbon source.

[0047] Table 2. Rc distribution characteristics of crude oil in XX depression

[0048] well name Crude oil depth Crude oil maturity (%) Turn 8 2923 0.73 1 3419-3460 1.07 Turn 6 3957 1.15

[0049] 3. Draw single element contour maps of abundance, thickness and thermal evolution degree of effective source rocks in the predicted area

[0050] According to the analysis of the above steps, it can be found that the lower limits of several factors for the formation of large-scale oil and gas reservoirs in the freshwater environment XX depression area are: the lower limit of the TOC of the effective source rock is 0.8%, the lower limit of the thickness of the effective source rock (shale) is 20m, and the vitrinite reflectance Ro of the thermal evolution degree of the effective source rock is 0.7%. The plane distribution diagrams of each factor are as follows: Figure 6 , 7 、8.

[0051] Specifically, a large number of source rock samples in the area were used for field measurements, mainly testing the abundance TOC of the source rocks, the degree of thermal evolution Ro and the shale thickness of each well drilled. The locations of the exploration wells on the plane are different, and the analytical test data of their samples are also different. The test data of the above elements of each exploration well are first marked on the map, and then mapped according to the geological trend.

[0052] Then, according to the determined plane distribution diagram of each element ( Figure 6-8 ), the three elements of favorable source rocks in the XX sag were superimposed, namely, the organic matter abundance TOC of the source rocks, the thermal evolution degree Ro of the source rocks, and the shale thickness (H). By superimposing the three elements, the distribution area of ​​the effective source kitchen in the XX sag can be obtained, which is also the favorable distribution area of ​​oil and gas in the area. Fig. 9 shown.

[0053] The favorable exploration areas established by this method have been verified in the exploration practice in recent years. Some exploration wells deployed outside the favorable areas are often empty due to the lack of oil sources. The probability of obtaining oil and gas reservoirs for various wells deployed within the favorable area is greatly increased. For example, the recently deployed Guai 17 well is not within the favorable area. The drilling of the well also shows that shale is not developed. The well only has sporadic oil and gas shows, resulting in the well being an empty well.

[0054] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for predicting favorable oil and gas areas in continental freshwater lake basins in low-exploration areas, characterized by: The following steps are involved: (1) Conduct geochemical analysis on the crude oil that has been drilled in the independent oil-bearing system in the target area, and determine the lower limit of hydrocarbon generation of effective source rocks based on the analysis results; (2) Based on the test and analysis results of a single well and the lower limit of hydrocarbon generation obtained in step (1), determine the development interval and lithology of the effective source rock, and then determine the thickness and lower limit of thermal evolution of the effective source rock based on the logging data, crude oil maturity and oil and gas flow conditions; (3) Using the lower limit of hydrocarbon generation of the effective source rock obtained in step (1) and the lower limit of thickness and thermal evolution degree obtained in step (2), single-element contour maps of abundance, thickness and thermal evolution degree of the effective source rock in the target area are drawn respectively, and the overlapping area of ​​the single-element contour maps is delineated as the favorable area for oil and gas in the target area.

2. The method for predicting favorable oil and gas areas in continental freshwater lake basins in low exploration areas according to claim 1, characterized in that: The lower limit of hydrocarbon generation of the effective source rock in step (1) is the lower limit of TOC of the source rock that contributes to the composition characteristics of crude oil.

3. The method for predicting favorable oil and gas areas in continental freshwater lake basins in low-exploration areas according to claim 1, characterized in that: The process of determining the lower limit of the thickness of the effective source rock in step (2) is as follows: Based on the logging data, a correlation between the thickness of the effective source rock and the oil and gas display is established, and the thickness of the effective source rock is determined in combination with the production oil and gas flow conditions.

4. The method for predicting favorable oil and gas areas in continental freshwater lake basins in low-exploration areas according to claim 3 is characterized by: The oil and gas indications include oil immersion, oil spots and oil traces.

5. The method for predicting favorable oil and gas areas in continental freshwater lake basins in low exploration areas according to claim 1, characterized in that: The lower limit of the thermal evolution degree of the effective source rock in step (2) is the maturity value of the crude oil in the target area where the oil and gas layer is the shallowest and there is a well producing oil and gas flow.

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