A method for determining the content of free oil in a piedmont reworked volcanic material-bearing mixite

Abstract

The present application belongs to the technical field of oil and gas geological exploration, and particularly relates to a method for determining the free oil content in a piedmont reformation type mixed rock containing volcanic material. The method comprises the following steps: selecting a target block containing volcanic material shale sample, determining the content of volcanic material in the sample, and dividing the shale sample into different types according to the content of volcanic material; restoring the free oil content in the shale sample containing volcanic material; drawing a scatter plot of the movable oil recovery coefficient in the shale sample with different volcanic material content and the volcanic material content, establishing a numerical model of the volcanic rock and the movable oil recovery coefficient, and calculating the free oil content of the sample according to the model. The method provides a basis for oil-bearing property evaluation of special lithology shale.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas geological exploration technology, specifically relating to a method for determining the free oil content in piedmont modified volcanic mixed sedimentary rocks. Background Technology

[0002] With the increasing understanding of the potential of unconventional oil and gas resources and the advancement of engineering technologies such as horizontal wells and fracturing, oil and gas exploration is shifting from traditional conventional reservoir exploration to unconventional reservoir exploration. This means moving from searching for conventional oil within structural and lithological traps to searching for hydrocarbons stored in the micro and nanopores within source rocks that have not yet undergone significant secondary migration. These unconventional oils are often found in mudstones and shale rich in fels and carbonate rocks.

[0003] Currently, most methods for evaluating shale oil resources and calculating movable oil content are applied to tectonically stable areas, i.e., regions within basins that have not undergone significant erosion. These areas are typically tectonically stable with widespread distribution of mudstone and shale. Recent studies suggest that mudstone and shale systems often develop at basin-mountain junctions, i.e., areas adjacent to orogenic belts. These areas often have complex structures, diverse rock types, and well-developed volcanic rocks, representing modified shale oil. Due to over-uplift, they are shallowly buried (less than 4000m) and have a high degree of organic matter thermal evolution (generally greater than 0.9%). Calculations of movable oil content in these volcanic mudstone and shale formations are rarely reported, and the influence of volcanic material content on movable oil content is unclear. Therefore, lithofacies classification, oil-bearing assessment, and sweet spot prediction for this type of mudstone and shale are quite challenging.

[0004] The article "Technical Methods and Applications for Shale Oil Resource Evaluation" published by Song Guoqi et al. in *Earth Science Frontiers*, Vol. 20, No. 4, 2013, focuses on the influence of the degree of thermal evolution of organic matter in rocks on the recovery coefficients of chloroform bitumen "A" and pyrolysis S1 in shale. The research object was Paleogene carbonate-rich shale in the Bonan Depression of the Jiyang Depression, a tectonically stable area. No model was established for calculating the movable oil content in volcanic-bearing shale. The article "Key Parameters for Shale Oil Resource Evaluation—Correction of Oil Content" published by Xue Haitao et al. in *Petroleum & Gas Geology*, Vol. 37, No. 1, 2016, uses rock pyrolysis experiments and hydrocarbon generation kinetic experiments to conduct light hydrocarbon compensation and heavy hydrocarbon correction for free hydrocarbons in shale. The research object was tectonically very stable Qingshankou Formation felsic shale in the Songliao Basin. No research was conducted on modified shale in the piedmont zone, and no relationship was established between volcanic rock content and movable oil content.

[0005] Patent application CN 106153490 A discloses a method for evaluating the content of retained hydrocarbons in shale using chloroform bitumen A. The method focuses on restoring the light hydrocarbon loss coefficient in chloroform bitumen A, but does not carry out heavy hydrocarbon compensation, nor does it conduct research on how to determine volcanic material in mudstone and shale, or establish the relationship between the content of volcanic material and the content of movable oil in mudstone and shale.

[0006] Invention patent CN 106769618 B discloses a method for separating and extracting free hydrocarbons from shale. This method improves the extraction process for shale by using dichloromethane at room temperature through two extractions and centrifugation to extract free hydrocarbons from shale. Compared to chloroform bitumen A, this method can better obtain light components from the mobile oil in shale. However, this method does not address how to identify volcanic material in shale or establish the relationship between the content of volcanic material and the content of mobile oil in shale. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for determining the free oil content in piedmont modified volcanic sedimentary rocks. The method establishes a model relating volcanic rock content to free oil, providing a basis for evaluating the oil-bearing potential of special lithologies such as mudstone and shale.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a method for determining the free oil content in volcanic mixed sedimentary rocks modified in piedmont areas. The method includes the following steps: selecting volcanic mudstone and shale samples from the target block, determining the volcanic rock content in the samples, and classifying the mudstone and shale samples into different types based on the volcanic rock content; recovering the free oil content in the volcanic mudstone and shale samples; plotting the movable oil recovery coefficient and volcanic rock content scatter plots in mudstone and shale samples with different volcanic rock content, establishing a numerical model of the volcanic rock and movable oil recovery coefficient, and calculating the free oil content of the samples based on the model.

[0010] Furthermore, methods for determining the content of volcanic rock material in samples include:

[0011] (1) Based on whole-rock diffraction and microscopic thin section observation, the content of zeolite, felsic minerals and felsic minerals from clastic material sources in the rock samples were tested.

[0012] (2) The calculation model for the volcanic material content in mudstone and shale samples is as follows:

[0013] M V =M c -M+M a

[0014] In the formula, M VM represents the volcanic material content in the mudstone and shale sample, Mc represents the felsic mineral content, and M represents the volcanic material content in the mudstone and shale sample. a denoted as , where is the zeolite content in the rock sample, and M is the content of felsic minerals derived from clastic material.

[0015] Furthermore, based on the content of volcanic rock material, mudstone and shale are classified as follows:

[0016] Volcanic material content M V ≥30% is volcanic-rich mudstone and shale; <10% is volcanic-rich mudstone and shale. V <30%, consisting of volcanic material-bearing mudstone and shale, with a volcanic material content of M. V ≤10% is low in volcanic material, mudstone and shale.

[0017] Furthermore, the specific steps for restoring the free oil content in volcanic mudstone and shale samples include: dividing the mudstone and shale sample into two parts; obtaining the S1 and S2 values ​​of one part directly through a rock pyrolysis instrument; and extracting the other part with dichloromethane to remove residual hydrocarbons from the rock, followed by pyrolysis to obtain the extracted and pyrolyzed S1. 1 With S2 1 Obtain S1 1 With S2 1 The pyrolysis steps are the same as S1 and S2.

[0018] The movable oil recovery coefficient K of mudstone and shale samples:

[0019] K = (S1 + S2) 1 -S2) / S1

[0020] In the formula, S1 represents the content of free hydrocarbons with less than 13 carbon atoms in the shale, and S2 represents the sum of kerogen cracking hydrocarbons, hydrocarbons with 13-33 carbon atoms in the total hydrocarbons, and non-hydrocarbon and bituminous contents; S2 1 This refers to the content of hydrocarbons from kerogen cracking.

[0021] The free oil content in the restored volcanic mudstone and shale samples is as follows:

[0022] S = K * S1.

[0023] Further, the specific steps for obtaining S1 and S2 values ​​using a rock pyrolysis apparatus are as follows: the rock sample is crushed to 150-200 mesh, the rock sample is heated in a helium gas stream, the pyrolysis products are detected by a hydrogen flame ionization detector, after heating to 200-300℃, the temperature is held for 2-5 minutes, and the product mass is measured as S1 (mg / g), and then heated to 400-600℃ and held for 2-5 minutes, and the product mass is measured as S2 (mg / g).

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] This invention proposes a method combining petrology and organic geochemistry to determine the free oil content in volcanic mudstone and shale. The method utilizes a combination of whole-rock X-ray diffraction (XRD), thin section microscopy, and rock pyrolysis experiments to reconstruct the free oil content in volcanic mudstone and shale. This provides a basis for evaluating the oil-bearing potential of this special type of lithology and offers guidance for predicting sweet spots and selecting exploration targets in volcanic mudstone and shale formations. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the method for determining the free oil content in piedmont modified volcanic mixed sedimentary rocks according to an embodiment of the present invention;

[0027] Figure 2 This is a scatter plot showing the correlation between the movable oil correction coefficient and volcanic material content of a mudstone and shale sample according to an embodiment of the present invention.

[0028] Figure 3 This is a scatter plot showing the correlation between free oil content and volcanic material content according to an embodiment of the present invention. Detailed Implementation

[0029] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0030] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms "comprising" or "including" are used in this specification, they indicate the presence of features, steps, operations, and combinations thereof.

[0031] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0032] Example 1

[0033] like Figure 1 As shown, the method for determining the free oil content in piedmont modified volcanic sedimentary rocks includes the following steps:

[0034] Step 1. Select volcanic shale samples from the target block, determine the volcanic rock content in the samples, and classify the shale samples into different types based on the volcanic rock content; specifically, this includes the following steps:

[0035] (1) Based on whole-rock diffraction and microscopic thin section observation, test the content of zeolite, felsic minerals and felsic minerals from clastic material sources in the rock samples.

[0036] (2) The calculation model for the volcanic material content in mudstone and shale samples is as follows:

[0037] M V =M c -M+M a

[0038] In the formula, M V M represents the volcanic material content in the mudstone and shale sample, Mc represents the felsic mineral content, and M represents the volcanic material content in the mudstone and shale sample. a The value of denoted zeolite in the rock sample is given by denoted zeolite, and M represents the content of felsic minerals derived from clastic material.

[0039] (3) Based on the content of volcanic rock material, mudstone and shale are classified as follows:

[0040] Volcanic material content M V ≥30% is volcanic-rich mudstone and shale; <10% is volcanic-rich mudstone and shale. V <30%, consisting of volcanic material-bearing mudstone and shale, with a volcanic material content of M. V ≤10% is low in volcanic material, mudstone and shale.

[0041] Step 2. Recover the free oil content in volcanic mudstone and shale samples; the specific steps include: dividing the mudstone and shale sample into two parts, one part directly obtaining S1 and S2 values ​​using a rock pyrolysis apparatus; the other part is extracted with dichloromethane for 72 hours to remove residual hydrocarbons in the rock, and then pyrolyzed again to obtain the extracted and pyrolyzed S1. 1 With S2 1 ;

[0042] The movable oil recovery coefficient K of mudstone and shale samples:

[0043] K = (S1 + S2) 1 -S2) / S1

[0044] In the formula, S1 represents the content of free hydrocarbons with less than 13 carbon atoms in the shale, and S2 represents the sum of kerogen cracking hydrocarbons, hydrocarbons with 13-33 carbon atoms in the total hydrocarbons, and non-hydrocarbon and bituminous contents; S2 1 This refers to the content of hydrocarbons from kerogen cracking.

[0045] The free oil content in the restored volcanic mudstone and shale samples is as follows:

[0046] S = K * S1.

[0047] Movable oil (free hydrocarbons) in shale refers to the recoverable oil in shale that can be extracted using certain mining methods. It is typically equal to the difference between trapped hydrocarbons and residual hydrocarbons in the shale. It includes total hydrocarbons (saturated hydrocarbons and aromatic hydrocarbons, mainly C1-C1). 33 Hydrocarbons) as well as non-hydrocarbons (N, O, S compounds) and asphaltenes.

[0048] The pyrolysis parameter S1 obtained from rock-eval analysis can represent a portion of the free hydrocarbon content in shale. This parameter represents the hydrocarbons volatilized when the rock sample is heated to ≤300℃, and is primarily composed of hydrocarbons with a carbon number less than C. 13 Hydrocarbons, excluding C 13 -C 33 Saturated hydrocarbons, non-hydrocarbons, and bituminous substances. Piedmont mudstone and shale often undergo tectonic alteration, resulting in crude oil degradation and relatively high crude oil density (typically ρ greater than 0.88 g / cm³). 3 Therefore, a large amount of gum (non-hydrocarbon portion) and asphaltenes in the free hydrocarbons are not evaporated due to their boiling points being above 300℃. This results in the free hydrocarbon fraction measured using S1 lacking the relatively heavier hydrocarbon portion (i.e., the C content in saturated hydrocarbons and aromatic hydrocarbons). 13 -C 33 The hydrocarbons include compounds, as well as non-hydrocarbons (N, O, S compounds) and asphaltenes. Therefore, when calculating the movable oil content in the foreland zone, it is necessary to carry out heavy hydrocarbon recovery of S1.

[0049] Step 3. Plot a scatter plot of the movable oil recovery coefficient and volcanic material content in mudstone and shale samples with different volcanic rock material contents, establish a numerical model of the movable oil recovery coefficient of volcanic rock, and calculate the free oil content of the samples based on the model.

[0050] Example 2

[0051] Taking the Fengcheng Formation of the Permian system in the foreland belt of the Hala Alat Mountains (hereinafter referred to as Hala Alat Mountains) on the northern edge of the Junggar Basin as an example, the middle and lower parts of the Fengcheng Formation inherited the Early Permian volcanic eruption environment, with widespread development of volcanic rocks, especially intermediate-acidic tuff and extrusive rocks. Simultaneously, this period was a saline-alkaline environment, forming a set of mudstones and shale containing volcanic material and alkaline minerals, possessing high hydrocarbon generation potential and being a key stratum for shale oil exploration in the northern Junggar Basin. However, the incorporation of volcanic material has significantly altered the hydrocarbon generation potential and reservoir properties of the mudstones and shale, making it difficult to objectively evaluate the oil-bearing properties of this volcanic mudstone and shale system, thus affecting the understanding of the region's resource potential and the selection of sweet spots.

[0052] This embodiment focuses on the drilling Fengcheng Formation (P1f) of Hashenxie 1 and Haqian 6 in the Hashan area to establish the correlation between movable oil and volcanic material content in the volcanic mudstone and shale of the foreland belt, and to clarify the free oil content of the Permian Fengcheng Formation volcanic mudstone and shale in the Hashan foreland belt.

[0053] The method for determining the free oil content in piedmont modified volcanic mixed sedimentary rocks includes the following steps:

[0054] Step 1. Determine the content of volcanic rock material in mudstone and shale samples.

[0055] Twelve typical core samples from the Fengcheng Formation of the typical exploration wells Hashenxie 1 and Haqian 6 in the western foreland of Harbin were collected. The samples were divided into three parts. One part of the sample underwent whole-rock diffraction (XRD) and thin section observation under a microscope to determine the zeolite content M in the rock sample. a (%), felsic mineral content M (%), felsic mineral content Mc (%) (Table 1).

[0056] The content of volcanic material M in the shale sample was calculated according to formula (1). V (%), according to the calculation results, the volcanic material content of the Fengcheng Formation in the two wells is 6%-49.7%, and the mudstone and shale rich in volcanic material (volcanic material content M) V A total of 4 blocks (>30%) contain volcanic material, and a total of 6 blocks contain volcanic mudstone and shale (10% < volcanic material content M). V Two pieces of volcanic material-poor mudstone and shale (volcanic material content <30%) and one piece of volcanic material-poor mudstone and shale (volcanic material content M) V <10%).

[0057] Table 1. Volcanic material content in Permian Fengcheng Formation (P1f) mudstone and shale from well drilling in the Hashan area.

[0058]

[0059]

[0060] Step 2. Restore the movable oil content in volcanic mudstone and shale.

[0061] Movable oil in shale is generally equal to the difference between retained hydrocarbons and residual hydrocarbons in the shale. This includes total hydrocarbons (saturated hydrocarbons and aromatic hydrocarbons, mainly C1-C1). 33 Hydrocarbons) as well as non-hydrocarbons (N, O, S compounds) and asphaltenes.

[0062] (1) Pyrolysis Experiment

[0063] Two other mudstone and shale samples were used. One sample's S1 and S2 values ​​were directly measured using a rock pyrolysis apparatus. The other sample underwent dichloromethane extraction for 72 hours to remove residual hydrocarbons, followed by re-pyrolysis to obtain the extracted and pyrolyzed S1. 1 With S2 1 .

[0064] (2) Calculate the recoverable oil coefficient

[0065] C in total hydrocarbons of movable oil from mudstone and shale 13-33 Partial, non-hydrocarbon and asphaltenes ΔS

[0066] ΔS=S2 1 -S2 (Formula 2)

[0067] The movable oil recovery coefficient of mudstone and shale is obtained:

[0068] K = (S1 + S2) 1 -S2) / S1 (Formula 3)

[0069] The recoverable mobile oil content in the volcanic mudstone and shale samples is as follows:

[0070] S = K * S1 (Formula 4)

[0071] Table 2. Data on movable oil content in Permian Fengcheng Formation (P1f) mudstone and shale from drilling in the Hashan area.

[0072]

[0073]

[0074] Table 2 shows that the difference in pyrolysis S1 between pre-extraction and post-extraction, ΔS1, ranges from 0 to 3.3 mg / g, with an average of 0.66 mg / g. The difference in pyrolysis S2 between pre-extraction and post-extraction, ΔS2, ranges from 0.16 to 5.26 mg / g, with an average of 2.05 mg / g. The movable oil correction coefficient ranges from 1.16 to 7.36, with an average of 3.48. The movable oil content before recovery is 0.29 to 3.6 mg / g, with an average of 0.98 mg / g, while the movable oil content after recovery is 1.19 to 8.38 mg / g, with an average of 3.03 mg / g.

[0075] Step 3. Establish a numerical model of the recovery coefficient of volcanic rock and movable oil.

[0076] Calculate the content of volcanic material in mudstone and shale (volcanic material content M). V >30%), containing volcanic material mudstone and shale (10% < volcanic material content M) V <30%) and shale with poor volcanic material content (volcanic material content M) V The recoverability coefficient of movable oil (<10%) was used to recover the movable oil content. A scatter plot of the free hydrocarbon recovery coefficient K versus volcanic material content (Mv) in mudstone and shale samples with different volcanic rock material contents was plotted to determine the calculation model and obtain the formula:

[0077] K = f(Mv) (Formula 5)

[0078] from Figure 1The correlation between the free hydrocarbon recovery coefficient K in shale samples and the volcanic material content was obtained: K = f(Mv) = 5.42 - 0.08 * Mv (correlation index R = 0.69)

[0079] Based on the scatter plot of free oil content versus volcanic material content in the recovered volcanic mudstone and shale samples ( Figure 2 It can be seen that for volcanic material content less than 30%, i.e., for volcanic-poor mudstone and shale containing volcanic material, the free oil content tends to decrease with increasing volcanic material content. This is because as volcanic material increases, the organic matter (kerogen) content of the mudstone and shale decreases, reducing hydrocarbon generation. Simultaneously, since volcanic material is mainly tuff, and most of it has been devitrified, resulting in dense rock with low micron and nanopore content, the space for mobile oil storage is reduced, leading to low free hydrocarbon content. Conversely, for volcanic-rich mudstone and shale (volcanic material content above 30%), the mobile oil content tends to increase with increasing volcanic material content. This is because as volcanic material content increases, hydrocarbon fluids enter, causing dissolution of the tuff (volcanic material), forming dissolution pores, increasing the space for oil and gas storage, and increasing the content of adsorbed free hydrocarbons in the sample. The above analysis shows that the amount of volcanic material, i.e., the difference in lithofacies, affects the mobile oil content of volcanic-bearing mudstone and shale, showing a trend of first decreasing and then increasing.

[0080] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for determining the free oil content in piedmont altered volcanic sedimentary rocks, characterized in that, Includes the following steps: Select mudstone and shale samples containing volcanic material from the target block, determine the content of volcanic rock material in the samples, and classify the mudstone and shale samples into different types according to the content of volcanic rock material. To restore the free oil content in volcanic mudstone and shale samples; To construct scatter plots of the movable oil recovery coefficient versus volcanic material content in mudstone and shale samples with different volcanic rock material contents, the following steps were taken: the mudstone and shale samples were divided into two parts. One part was directly analyzed using a rock pyrolysis apparatus to obtain S1 and S2 values. The other part was extracted with dichloromethane to remove residual hydrocarbons from the rock, and then pyrolyzed again to obtain the S1 value after extraction and pyrolysis. 1 With S2 1 ; The movable oil recovery coefficient K of mudstone and shale samples: K = (S1 + S2 1 -S2) / S1; In the formula, S1 represents the content of free hydrocarbons with less than 13 carbon atoms in the shale, and S2 represents the sum of kerogen cracking hydrocarbons, hydrocarbons with 13-33 carbon atoms in the total hydrocarbons, and non-hydrocarbon and bituminous contents; S2 1 This refers to the content of hydrocarbons from kerogen cracking. A numerical model of the recovery coefficient of volcanic rock and movable oil was established, and the free oil content of the sample was calculated based on the model.

2. The method for determining the free oil content in piedmont altered volcanic sedimentary rocks according to claim 1, characterized in that, Methods for determining the content of volcanic rock material in a sample include: (1) Based on whole-rock diffraction and microscopic thin section observation, test the content of zeolite, felsic minerals and felsic minerals from clastic material sources in the rock samples; (2) The calculation model for the volcanic material content in mudstone and shale samples is as follows: M V =M c -M+M a ; In the formula, M V M represents the volcanic material content in the mudstone and shale sample, Mc represents the felsic mineral content, and M represents the volcanic material content in the mudstone and shale sample. a denoted as , where is the zeolite content in the rock sample, and M is the content of felsic minerals derived from clastic material.

3. The method for determining the free oil content in piedmont altered volcanic sedimentary rocks according to claim 1, characterized in that, Based on the content of volcanic rock materials, mudstone and shale are classified as follows: Volcanic material content M V ≥30% is volcanic material-rich mudstone and shale; <10% is volcanic material content M V <30%, consisting of volcanic material-bearing mudstone and shale, with a volcanic material content of M. V ≤10% is poor volcanic material mudstone and shale.

4. The method for determining the free oil content in piedmont altered volcanic sedimentary rocks according to claim 1, characterized in that, Free oil content in restored volcanic mudstone and shale samples: S = K * S1.

5. The method for determining the free oil content in piedmont altered volcanic sedimentary rocks according to claim 1, characterized in that, The specific steps for obtaining S1 and S2 values ​​using a rock pyrolysis apparatus are as follows: crush the rock sample to 150-200 mesh, heat the rock sample in a helium gas stream, detect the pyrolysis products using a hydrogen flame ionization detector, heat to 200-300℃ and hold for 2-5 minutes, and measure the product mass as S1 (mg / g), continue heating to 400-600℃ and hold for 2-5 minutes, and measure the product mass as S2 (mg / g).

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