Method for evaluating thermal evolution of Kuhu hydrocarbon source rocks by using ground temperature gradient and application of method for evaluating thermal evolution of Kuhu hydrocarbon source rocks

Abstract

The invention provides a method and application for evaluating thermal evolution of Hulu series hydrocarbon source rocks by utilizing a ground temperature gradient, and belongs to the technical field of geological analysis, and the method comprises the following steps: S1, determining residual stratum thickness distribution and stratum accumulated thickness of each period; s2, determining a drilling thermal evolution history; s3, in combination with the ground temperature gradient in the tectonic period, the denudation amount, calculated in the step S1, of the stratum in each period and the drilling thermal evolution history determined in the step S2, evaluating the thermal evolution condition of the Kuhu hydrocarbon source rocks by adopting the hydrocarbon source rock hydrocarbon generation chart; the invention further provides application of the method in oil and gas resource exploration. Compared with the prior art, the invention provides a method for constraining and evaluating the thermal evolution stage of the source rock by using reliable stratum thickness, relatively reliable denudation thickness, paleo-ground temperature gradient and change thereof, and solves the problem of lack of reliable temperature scale in identification of the maturity of the paleo-life source rock under macroscopic constraint. And the analyzed maturity and evolution stage credibility are higher.

Description

Technical Field

[0001] The present invention belongs to the technical field of geological analysis, and in particular relates to a method for evaluating the thermal evolution of Cambrian source rocks by estimating geothermal gradients. Background Art

[0002] The primary source rocks in the platform-basin region of the Tarim Basin are primarily Cambrian. These source rocks are old, deeply buried, thin, and poorly drilled, and have undergone multiple phases of tectonic evolution. The difficulty in determining the distribution and evolution of Paleozoic source rocks in this platform-basin region is a major constraint and obstacle to large-scale resource exploration. Research on the thermal history of Paleozoic source rocks in the Tarim Basin, particularly the thermal evolution of ultra-deep, ancient source rocks, remains controversial. A key challenge for those skilled in the art in this field is developing a method for evaluating the thermal evolution stages of Paleozoic source rocks.

[0003] Currently, the commonly used indicators reflecting maturity include vitrinite reflectance (Ro), inclusion temperature measurement, U-Th dating, isotope dating, color change index, Raman spectroscopy, and oil and gas geochemical characteristics. Commonly used indicators mainly focus on Ro%, or "equivalent vitrinite reflectance." Although the vitrinite reflectance Ro% can be used to evaluate the thermal evolution history of source rocks, there is no measurable homogeneous vitrinite in Paleozoic source rocks. Therefore, the main problem in evaluating the thermal evolution of Paleozoic source rocks can be attributed to the lack of reliable thermal evolution evaluation methods.

[0004] In their paper "Diagenetic Response to Thermal Evolution Events and High Geothermal Gradients in the Southern Pearl River Mouth Basin and Their Implications for Oil and Gas Exploration", Luo Jinglan and other scholars revealed the petrological evidence and geological records of the influence of thermal evolution events and high geothermal gradient background in the Baiyun Sag in the southern Pearl River Mouth Basin based on analytical methods such as microscopic thin sections, vitrinite reflectance (i.e., the aforementioned vitrinite reflectance Ro), clay mineral X-ray diffraction, fluid inclusions, scanning electron microscopy and isotope geochemistry, combined with research results such as geothermal gradient, regional tectonic background, reservoir physical properties and CO2 gas reservoir genesis. They analyzed the diagenetic response of thermal evolution events and high geothermal gradient and their influence on the diagenetic evolution process of reservoirs, and compared the diagenetic characteristics and diagenetic-pore evolution processes of Paleogene sandstone reservoirs in high and low geothermal gradient areas. However, according to the above analysis, it can be seen that the analytical methods provided are difficult to apply to the evaluation of thermal evolution of Cambrian source rocks.

[0005] Therefore, how to provide a reliable method for evaluating the thermal evolution of Cambrian source rocks to determine the thermal evolution history of source rocks and thus assist in the development of oil and gas resources is one of the important issues that technicians in this field are studying. Summary of the Invention

[0006] In view of the lack of a reliable method for evaluating the thermal evolution of Cambrian source rocks in the prior art, the present invention provides a method and application for evaluating the thermal evolution of Cambrian source rocks using the geothermal gradient. The method uses reliable formation thickness, relatively reliable erosion thickness, paleogeothermal gradient and its variation to constrain and evaluate the thermal evolution stage of source rocks. Under macroscopic constraints, the problem of lack of a reliable temperature scale for maturity identification is avoided, and the reliability of the analyzed maturity and stage is higher than that of the prior art.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] On the one hand, the present invention provides a method for evaluating the thermal evolution of Cambrian source rocks using the geothermal gradient, including the following steps:

[0009] S1. Define the distribution of residual formation thickness and the cumulative thickness of each formation stage;

[0010] S2. Determine the thermal evolution history of the well;

[0011] S3. Combine the geothermal gradient during the tectonic period, the erosion amount of each formation stage calculated in step S1, and the thermal evolution history of the well determined in step S2, and use the hydrocarbon generation chart of source rocks to evaluate the thermal evolution of Cambrian source rocks.

[0012] Preferably, in step S1, the basis for defining the distribution of residual formation thickness is the formation division mark.

[0013] Preferably, in step S1, the basis for defining the cumulative thickness of each formation stage is the erosion amount of each formation stage calculated based on paleotectonic restoration.

[0014] Preferably, the interpretation of the residual formation thickness and the determination basis of the cumulative thickness of each formation stage in step S1 also include single-well, connected-well residual formations, formation correlation and sedimentary evolution characteristics.

[0015] Preferably, the determination basis of the thermal evolution history of the well in step S2 includes the current low-temperature field, the vitrinite reflectance of the Carboniferous and overlying horizons, the equivalent vitrinite analysis data of Paleozoic source rocks below the Carboniferous, PVT temperature measurement data and hydrocarbon accumulation period data.

[0016] Preferably, the determination basis of the geothermal gradient during the tectonic period in step S3 is the historical surface temperature evolution data and the terrestrial heat flow value data.

[0017] Preferably, the specific combination method in step S3 is as follows:

[0018] Based on the geothermal gradient during the tectonic period, multiply the existing tectonic period thickness by the corresponding period geothermal gradient to obtain the increased temperature of the corresponding period, accumulate the temperature of one or more periods, and further constrain with the erosion amount of each formation stage calculated in step S1 and the thermal evolution history of the well determined in step S2.

[0019] Preferably, the use of the hydrocarbon source rock hydrocarbon generation chart in step S3 to evaluate the thermal evolution of the Cambrian hydrocarbon source rock includes the following steps:

[0020] (1) Use the single-well sediment thickness restoration and paleogeothermal gradient to obtain the single-well thermal evolution temperature during different tectonic periods; refer to the corresponding relationship between temperature and vitrinite reflectance to obtain the corresponding vitrinite reflectance value;

[0021] (2) Use the well-connected data to obtain the thermal evolution temperatures in different directions and different horizons; refer to the corresponding relationship between temperature and vitrinite reflectance to obtain the corresponding vitrinite reflectance value.

[0022] Further preferably, the corresponding relationship between the temperature and the vitrinite reflectance includes:

[0023] At 50 °C, Ro = 0.5%;

[0024] At 150 °C, Ro = 1.3%;

[0025] At 190 °C, Ro = 2.0%.

[0026] On the other hand, the present invention also provides an application of the above method for evaluating the thermal evolution of the Cambrian hydrocarbon source rock using the geothermal gradient in oil and gas resource exploration.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention provides a method for constraining and evaluating the thermal evolution stage of hydrocarbon source rocks by using reliable formation thickness, relatively reliable erosion thickness, paleogeothermal gradient and its variation, which solves the problem of lack of reliable temperature scale for identifying the maturity of Paleozoic hydrocarbon source rocks under macroscopic constraints, and the credibility of the analyzed maturity and evolution stage is higher than that of the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the traditional oil and gas generation and evolution model. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] In order to better understand the present invention, the technical solutions of the present invention will be described in detail below with specific examples, but the present invention is not limited thereto.

[0031] Example A method for evaluating the thermal evolution of the Cambrian hydrocarbon source rock using the geothermal gradient

[0032] S1. Determine the distribution of the residual formation thickness and the cumulative thickness of each stage of the formation

[0033] Conventional methods in this field were used to interpret residual stratigraphic thickness based on stratigraphic division markers. The amount of erosion during each period was calculated based on paleo-tectonic reconstruction, clarifying the distribution of residual stratigraphic thickness and the cumulative thickness of each period. Once the paleo-geothermal gradient values of the source areas during key periods were determined, the evolution of the Yurtusi Formation source rocks during each period was primarily determined by the cumulative thickness of the overlying strata during each period. Using residual stratigraphic data from single and connected wells, stratigraphic correlation, and sedimentary evolution characteristics, interpretation of residual stratigraphic thickness and calculation of the amount of erosion during each period were performed.

[0034] S2. Determine the thermal evolution history of drilling

[0035] Conduct a comprehensive study of the current geothermal field, Ro of the Carboniferous and above layers, and equivalent vitrinite reflectance Ro analysis data of the Paleozoic source rocks below the Carboniferous, PVT temperature measurement data, and reservoir formation period data to clarify the drilling thermal evolution history;

[0036] S3. Combining the geothermal gradient during the tectonic period, the amount of erosion per period calculated in step S1, and the thermal evolution history of the well determined in step S2, the source rock generation chart is used to evaluate the thermal evolution of the Cambrian source rock.

[0037] Based on the study of surface temperature evolution and geothermal heat flow values during the geological history of the Tarim Basin, the geothermal gradient of the main tectonic period is obtained. The temperature increase of the period is obtained by multiplying the thickness of the main tectonic period by the geothermal gradient of the period. The temperature of the previous period is then accumulated. The erosion amount of each period calculated in step S1 and the drilling thermal evolution history determined in step S2 are used for further constraints. The hydrocarbon generation plate of the source rock is used to evaluate the evolution stage of the source rock and the distribution of the effective source rock. The thermal evolution temperature of the single well in different tectonic periods is obtained by using the single well sedimentary thickness recovery and the paleo-geothermal gradient. The corresponding Ro value is obtained by referring to the corresponding relationship between temperature and Ro (such as Figure 1 Then, the connected wells are used to obtain the Ro values and their distributions of thermal evolution temperatures in different directions and layers, and to restore the formation thermal history.

[0038] Using this method, the cumulative thickness of the Upper Ordovician + Silurian strata multiplied by the geothermal gradient distribution of 3.0℃ / 100m shows that the hydrocarbon supply capacity of the Cambrian source rocks in the late stage of the "shrinkage" of the Caledonian period (the effective hydrocarbon generation area in the late stage is constantly decreasing and rapidly decreases after the maximum hydrocarbon generation peak) decreases significantly, the distribution of effective hydrocarbon source rocks in the late stage decreases significantly with the increase of thermal evolution, and the favorable hydrocarbon generation in the late stage is confined to the northwest of the northern Tarim and the central and western parts of the southern Tarim.

[0039] The method of the present invention can also well explain the effective source rocks and their distribution around the Manjiaer Depression, and provides a highly reliable analysis method for evaluating the evolution and stages of Paleozoic source rocks.

[0040] As can be seen from the above, this method rapidly evaluates the thermal evolution stage of source rocks based on formation residual thickness, denudation amount restoration, and paleogeothermal gradient, and to a certain extent solves the problem of the lack of a reliable temperature scale for identifying the maturity of Paleozoic source rocks. The relative credibility of the analyzed maturity and evolution stage is higher than that of traditional methods. This method can be widely used to evaluate and identify the maturity of source rocks and the distribution of effective source rocks in different tectonic periods in areas lacking effective temperature scales (such as the Paleozoic), and can also rapidly estimate and evaluate the thermal evolution of Mesozoic and Cenozoic series with reliable temperature scales (Ro%).

[0041] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than a limitation on the protection scope of the present invention. Any simple modification or equivalent replacement made by those of ordinary skill in the art to the technical solution of the present invention does not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A method for evaluating the thermal evolution of Cambrian source rocks using geothermal gradient, characterized in that, It includes the following steps: S1. Determine the distribution of the remaining formation thickness and the cumulative thickness of each stage of the formation; S2. Determine the thermal evolution history of the well; S3. Combine the geothermal gradient during the tectonic period, the amount of erosion of each stage of the formation calculated in step S1, and the thermal evolution history of the well determined in step S2, and use the hydrocarbon generation chart of the source rock to evaluate the thermal evolution of the Cambrian source rock.

2. The method according to claim 1, characterized in that, In step S1, the basis for determining the distribution of the remaining formation thickness is the formation division mark.

3. The method according to claim 1, wherein In step S1, the basis for determining the cumulative thickness of each stage of the formation is the amount of erosion of each stage of the formation calculated based on the paleotectonic restoration.

4. The method according to claim 1, wherein The interpretation of the remaining formation thickness and the basis for determining the cumulative thickness of each stage of the formation in step S1 also include single wells, the remaining formation of connected wells, formation correlation, and sedimentary evolution characteristics.

5. The method according to claim 1, characterized in that In step S2, the basis for determining the thermal evolution history of the well includes the current low-temperature field, the vitrinite reflectance of the Carboniferous and overlying horizons, the equivalent vitrinite analysis data of the Paleozoic source rock below the Carboniferous, PVT temperature measurement data, and the data of the hydrocarbon accumulation period.

6. The method according to claim 1, wherein In step S3, the basis for determining the geothermal gradient during the tectonic period is the historical surface temperature evolution data and the terrestrial heat flow value data.

7. The method according to claim 1, characterized in that, The specific method of combination in step S3 is as follows: Based on the geothermal gradient during the tectonic period, multiply the existing thickness during the tectonic period by the corresponding geothermal gradient to obtain the increased temperature of the corresponding period, accumulate the temperature of one or more periods, and further constrain it with the amount of erosion of each stage of the formation calculated in step S1 and the thermal evolution history of the well determined in step S2.

8. The method according to claim 1, characterized in that In step S3, using the hydrocarbon generation chart of the source rock to evaluate the thermal evolution of the Cambrian source rock includes the following steps: (1) Use the single-well sediment thickness restoration and the paleogeothermal gradient to obtain the thermal evolution temperature of the single well in different tectonic periods; refer to the corresponding relationship between the temperature and the vitrinite reflectance to obtain the corresponding vitrinite reflectance value; (2) Use the connected wells to obtain the thermal evolution temperatures in different directions and different horizons; refer to the corresponding relationship between the temperature and the vitrinite reflectance to obtain the corresponding vitrinite reflectance value.

9. The method according to claim 1, wherein The corresponding relationship between the temperature and the vitrinite reflectance described in steps (1) and (2) includes: At 50 °C, the vitrinite reflectance = 0.5%; At 150 °C, the vitrinite reflectance = 1.3%; At 190 °C, the vitrinite reflectance = 2.0%.

10. The application of the method according to any one of claims 1-9 in oil and gas resource exploration.

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