Method for determining the true organic matter content of high-overmature cuttings source rock samples contaminated by oil-based mud

Abstract

The present invention provides a method for determining the true organic matter content of a high-overmature rock source rock sample contaminated by oil-based mud. The method comprises: determining the pyrolysis hydrocarbon value of the target high-overmature rock source rock sample contaminated by oil-based mud; determining the pyrolysis hydrocarbon value of the target high-overmature rock source rock sample contaminated by oil-based mud after oil washing; determining the organic matter content of the target high-overmature rock source rock sample contaminated by oil-based mud after oil washing; determining the true organic matter content of the target high-overmature rock source rock sample contaminated by oil-based mud based on the pyrolysis hydrocarbon value of the target high-overmature rock source rock sample contaminated by oil-based mud, the pyrolysis hydrocarbon value of the target high-overmature rock source rock sample contaminated by oil-based mud after oil washing, and the organic matter content of the target high-overmature rock source rock sample contaminated by oil-based mud after oil washing.

Description

Technical Field

[0001] The invention relates to a method for determining the true organic matter content of a high-overmature rock debris source rock sample contaminated by oil-based mud. Background Art

[0002] Fine-grained rocks that have been generated, are likely to be generated, or have the potential to generate oil and gas are called source rocks. Source rocks control the formation and distribution of oil and gas reservoirs in the basin. Clarifying the effectiveness, spatial distribution and development patterns of source rocks can effectively indicate favorable exploration areas. For some basins, their main source rocks are often buried deep and have high maturity. The main target layer of limited deep drilling coring is the reservoir section. The number of source rock cores is very limited, and rock cuttings often become an important object of source rock evaluation.

[0003] However, during oil and gas drilling, the single well source rock cuttings produced will be contaminated by oil-based mud and other pollutants. Since the oil-based mud contains organic matter such as asphalt and diesel, if it is not treated before conducting experiments, the free hydrocarbon and total organic carbon content of the mud-contaminated cuttings samples will be abnormally high. The data obtained will be very different from the actual organic matter abundance of the cuttings, and it cannot reflect the hydrocarbon generation capacity of the source rocks in the area. This will cause large errors in the evaluation of the source rocks in the area and may even affect the further exploration and development of the entire area. Summary of the invention

[0004] The object of the present invention is to provide a method for determining the true organic matter content of high-overmature debris source rock samples contaminated by oil-based mud.

[0005] In order to achieve the above object, the present invention provides a method for determining the true organic matter content of a high-overmature rock debris source rock sample contaminated by oil-based mud, wherein the method comprises:

[0006] Determine the pyrolysis hydrocarbon value (i.e., S2 value) of the target high-overmature lithic source rock sample contaminated by oil-based mud;

[0007] Determine the pyrolysis hydrocarbon value (i.e., S2 value) of the target high-overmature rock source rock sample contaminated by oil-based mud after oil washing;

[0008] Determine the organic matter content (TOC value) of high-overmature cuttings source rock samples contaminated by oil-based mud after oil washing;

[0009] Based on the pyrolysis hydrocarbon value of the target high-over mature lithic source rock sample contaminated by oil-based mud, the pyrolysis hydrocarbon value of the target high-over mature lithic source rock sample contaminated by oil-based mud after oil washing, and the organic matter content of the target high-over mature lithic source rock sample contaminated by oil-based mud after oil washing, the true organic matter content of the target high-over mature lithic source rock sample contaminated by oil-based mud (i.e., the organic matter content of the target high-over mature lithic source rock sample contaminated by oil-based mud before being contaminated by oil-based mud) is determined.

[0010] In the present invention, high-overmature source rock refers to a source rock with a vitrinite reflectance Ro value of not less than 1.3%.

[0011] In some preferred embodiments, the determining the true organic matter content of the target high-over mature lithic source rock sample contaminated by oil-based mud based on the pyrolysis hydrocarbon value of the target high-over mature lithic source rock sample contaminated by oil-based mud, the pyrolysis hydrocarbon value of the target high-over mature lithic source rock sample contaminated by oil-based mud after oil washing, and the organic matter content of the target high-over mature lithic source rock sample contaminated by oil-based mud after oil washing comprises:

[0012] Obtaining the actual organic matter content of the high-overmature debris source rock sample contaminated by oil-based mud; a calculation model for the pyrolysis hydrocarbon value of the high-overmature debris source rock sample contaminated by oil-based mud, the pyrolysis hydrocarbon value of the high-overmature debris source rock sample contaminated by oil-based mud after oil washing, and the organic matter content of the high-overmature debris source rock sample contaminated by oil-based mud after oil washing;

[0013] Based on the calculation model of the real organic matter content of the high-overmature lithic source rock sample contaminated by the oil-based mud about the pyrolysis hydrocarbon value of the high-overmature lithic source rock sample contaminated by the oil-based mud, the pyrolysis hydrocarbon value of the high-overmature lithic source rock sample contaminated by the oil-based mud after oil washing, and the organic matter content of the high-overmature lithic source rock sample contaminated by the oil-based mud after oil washing, the real organic matter content of the target high-overmature lithic source rock sample contaminated by the oil-based mud is determined in combination with the pyrolysis hydrocarbon value of the target high-overmature lithic source rock sample contaminated by the oil-based mud, the pyrolysis hydrocarbon value of the target high-overmature lithic source rock sample contaminated by the oil-based mud after oil washing, and the organic matter content of the target high-overmature lithic source rock sample contaminated by the oil-based mud after oil washing;

[0014] More preferably, the calculation model of the true organic matter content of the high-overmature lithic source rock sample contaminated by oil-based mud with respect to the pyrolysis hydrocarbon value of the high-overmature lithic source rock sample contaminated by oil-based mud, the pyrolysis hydrocarbon value of the high-overmature lithic source rock sample contaminated by oil-based mud after oil washing, and the organic matter content of the high-overmature lithic source rock sample contaminated by oil-based mud after oil washing is a calculation model of the true organic matter content of the high-overmature lithic source rock sample contaminated by oil-based mud with respect to the difference in pyrolysis hydrocarbon value before and after oil washing of the high-overmature lithic source rock sample contaminated by oil-based mud and the organic matter content of the high-overmature lithic source rock sample contaminated by oil-based mud after oil washing;

[0015] Further preferably, the calculation model of the real organic matter content of the high-overmature lithic source rock sample contaminated by oil-based mud with respect to the pyrolysis hydrocarbon value of the high-overmature lithic source rock sample contaminated by oil-based mud, the pyrolysis hydrocarbon value of the high-overmature lithic source rock sample contaminated by oil-based mud after oil washing, and the organic matter content of the high-overmature lithic source rock sample contaminated by oil-based mud after oil washing is:

[0016] TOC 0 =[(S2-S2 1 )×k]÷10+TOC 1

[0017] In the formula, TOC 1 is the percentage of organic matter content in the high-overmature lithic source rock sample contaminated by oil-based mud after oil washing, %; S2 is the pyrolysis hydrocarbon value of the high-overmature lithic source rock sample contaminated by oil-based mud, mg / g; S2 1 is the pyrolysis hydrocarbon value of high-overmature cuttings source rock samples contaminated by oil-based mud after oil washing, mg / g; TOC 0 is the percentage of the actual organic matter content of the high-overmature rock debris source rock sample contaminated by oil-based mud, %; k is the mass content percentage of organic carbon in pyrolysis hydrocarbons, %, usually 85%;

[0018] In the above calculation model, [(S2-S2 1 )×k] is divided by 10 to unify the unit to %.

[0019] In some preferred embodiments, the particle size of the target high-overmature debris source rock sample contaminated by oil-based mud does not exceed 0.2 mm (ie, above 80 mesh, i.e., the maximum particle size is 80 mesh).

[0020] In some preferred embodiments, the method further comprises the step of obtaining a target high-overmature debris source rock sample contaminated by oil-based mud;

[0021] The step of obtaining a target high-overmature rock debris source rock sample contaminated by oil-based mud comprises:

[0022] Conduct rock cutting sampling of target source rock layers contaminated by oil-based mud during drilling;

[0023] The rock cuttings samples obtained by sampling are selected to select pure source rock cuttings;

[0024] washing and drying the selected source rock cuttings;

[0025] The dried source rock cuttings are ground to obtain the target high-overmature cuttings source rock sample contaminated by oil-based mud.

[0026] More preferably, the rock cuttings samples obtained by sampling are selected, and the selection of pure source rock cuttings is achieved by the following method:

[0027] The rock cuttings samples obtained by sampling are sieved to remove the dried mud powder and rock powder, and then the miscellaneous rock cuttings fragments are removed, and the rock cuttings fragment samples with consistent lithology and appearance are retained to prevent the influence of other fragments or drilling mud solid blocks.

[0028] More preferably, when cuttings sampling is performed on the target source rock layer during drilling, a location with a thickness greater than 4 m and located in the middle of the target source rock layer is selected for cuttings sampling.

[0029] The purpose of oil washing is to remove the contaminated organic matter in the cuttings sample. In some preferred embodiments, the oil washing of the high-overmature cuttings source rock sample contaminated by oil-based mud is carried out by Soxhlet extraction;

[0030] More preferably, the oil washing of the high-overmature debris source rock sample contaminated by oil-based mud is achieved by:

[0031] The target high-overmature debris source rock samples contaminated by oil-based mud are packed in the extracted filter paper tube;

[0032] Put the wrapped sample into the Soxhlet extractor, add the copper sheet for purification and desulfurization into the bottom bottle, and add the mixture of organic solvents dichloromethane and methanol;

[0033] Extract at 63°C until the reagent in the extractor is colorless;

[0034] Take out the extracted samples and dry them;

[0035] More preferably, the volume ratio of dichloromethane to methanol in the mixture of dichloromethane and methanol is 93:7;

[0036] More preferably, the organic solvent is added to 1 / 3-1 / 2 of the capacity of the extractor;

[0037] More preferably, the extraction time is not less than 24 hours.

[0038] In some preferred embodiments, the pyrolysis hydrocarbon value of the sample is determined by:

[0039] Take a certain amount of sample and put it into Rock-eval rock pyrolysis analyzer workstation for pyrolysis analysis to obtain the pyrolysis hydrocarbon value of the sample;

[0040] More preferably, during the pyrolysis analysis process, the initial temperature of the Rock-eval rock pyrolysis analyzer is 300°C and the maximum temperature is 600°C.

[0041] In some preferred embodiments, the organic matter content of the target high-overmature lithic source rock sample contaminated by oil-based mud after oil washing is determined by:

[0042] A sample obtained after oil washing from a target high-overmature cuttings source rock contaminated by oil-based mud is subjected to acid treatment, and the sample obtained after the acid treatment is washed with water until it is neutral and then dried;

[0043] Adding iron flux and tungsten flux to the sample obtained after drying, and then using a carbon-sulfur analyzer to measure the organic matter content, to obtain the organic matter content of the target high-overmature cuttings source rock sample contaminated by oil-based mud after oil washing;

[0044] More preferably, the mass of the sample obtained after oil washing of the target high-overmature debris source rock contaminated by oil-based mud: the mass of the iron flux: the mass of the tungsten flux is 0.01-10:1.0:1.0;

[0045] More preferably, the acid treatment is carried out in the following manner: the sample obtained after oil washing of the target high-overmature lithic source rock sample contaminated by oil-based mud is immersed in hydrochloric acid at a temperature not exceeding 80° C. for more than 2 hours; further preferably, the hydrochloric acid is hydrochloric acid with a volume ratio of HCl to water of 1:7;

[0046] More preferably, the drying temperature is 60-80°C.

[0047] During the drilling process, it is inevitable that the cuttings source rock is contaminated by oil-based mud. In this case, the cuttings source rock sampled cannot be determined by conventional methods for organic matter content. How to determine the organic matter content of the contaminated cuttings source rock is a difficult problem that troubles those skilled in the art. The inventor started from how to determine the organic matter content of the contaminated cuttings source rock, and after a lot of research and comparative analysis of the organic matter content of the contaminated cuttings source rock before and after oil washing and the change rules of pyrolysis parameters including soluble hydrocarbons and pyrolysis hydrocarbons, proposed the technical solution claimed by the present invention.

[0048] The method for determining the true organic matter content of high-overmature cuttings source rock samples contaminated by oil-based mud provided by the present invention can achieve the purpose of restoring the true organic matter of contaminated single-well cuttings source rocks, and can effectively solve the problem that single-well source rock cuttings generated by oil and gas drilling are contaminated by oil-based mud and other pollutants, so that the restored organic matter content can effectively reflect the hydrocarbon generation capacity of the rocks in the area, can accurately evaluate the source rocks in the area, and promote further exploration and development of the entire area. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic flow chart of the method for determining the true organic matter content of a high-overmature debris source rock sample contaminated by oil-based mud in Example 1.

[0050] Figure 2 This is a data chart of the true organic matter content of a high-over-mature rock source rock sample from a well in Example 1 before and after oil washing and restoration. DETAILED DESCRIPTION

[0051] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0052] Example 1

[0053] This embodiment provides a method for determining the true organic matter content of a high-overmature rock debris source rock sample contaminated by oil-based mud. The process is as follows: Figure 1 As shown,

[0054] This method uses the cuttings source rocks of the first and second layers of a well as an example, where the first layer is 6594m-7234m deep and the second layer is 7266m-7272m deep. According to the drilling records of the well, before the "fourth opening", the technical casing was lowered to the upper part of 6895m. After the "fourth opening", the lithology of the mudstone cuttings of the 6895-7266m well section and the marlstone cuttings of the 7266-7272m well section are relatively simple and are not affected by the mixing of overlying strata. In the absence of core samples, the representativeness of the cuttings of the first and second layers above 6895m should have a high degree of confidence.

[0055] The method includes:

[0056] Step 1: Obtain target high-overmature rock debris source rock samples contaminated by oil-based mud;

[0057] Specifically include:

[0058] 1.1. Obtain 10 rock cuttings samples from the target layer;

[0059] 1.2. Select each rock cutting sample separately; specifically:

[0060] The rock cuttings samples obtained by sampling are sieved to remove the dried mud powder and rock powder, and then the miscellaneous rock cuttings fragments are removed, and the rock cuttings fragment samples with consistent lithology and appearance are retained to prevent the influence of other fragments or drilling mud solid blocks.

[0061] 1.3. Wash each selected rock cutting sample with distilled water and spread it out on high-temperature sterilized tin foil to dry;

[0062] A brown oil ring with a width of about 2-3 mm can be found around the cuttings sample, and a distinct oil smell can be smelled, indicating that the cuttings sample is indeed contaminated by oil-based mud;

[0063] 1.4. The selected pure source rock cuttings are crushed and sieved with an 80-mesh sieve. The samples with a particle size of less than or equal to 80 mesh obtained by sieving are the target cutting source rock samples contaminated by oil-based mud;

[0064] The well depth corresponding to each target high-overmature debris source rock sample contaminated by oil-based mud is shown in Table 1.

[0065] Step 2: Determine the pyrolysis hydrocarbon value S2, soluble hydrocarbon value S1 and organic carbon content TOC of the target high-overmature debris source rock sample contaminated by oil-based mud;

[0066] Specifically, for each target high-overmature cuttings source rock sample contaminated by oil-based mud, the following steps are performed:

[0067] Take 100mg (±0.5mg) of the target high-overmature rock debris source rock sample contaminated by oil-based mud, input the sample mass into the Rock-eval rock pyrolysis analyzer workstation, and use the Rock-eval rock pyrolysis analyzer workstation to perform pyrolysis analysis to obtain the pyrolysis hydrocarbon value S2 and soluble hydrocarbon value S1; during the pyrolysis analysis process, the initial temperature of the Rock-eval rock pyrolysis analyzer is 300℃ and the highest temperature is 600℃;

[0068] Take the target high-overmature debris source rock sample contaminated by oil-based mud, put 0.1g into the fired crucible, add hydrochloric acid with a volume ratio of 1:7 (HCl:H2O), and soak at 80℃ for 2 hours for acid treatment; then put the acid-treated sample on the suction filter and rinse it with distilled water every half an hour until the sample in the crucible is rinsed to neutral; put the rinsed sample and the crucible into a constant temperature drying oven at 80℃ for 8 hours; add 1.0g of iron flux and 1.0g of tungsten flux to the dried sample, enter the sample mass in the carbon-sulfur analyzer, and use the carbon-sulfur analyzer to determine the organic carbon content TOC;

[0069] The main component of the iron flux is iron (with a purity greater than 99.8%), and it also contains C≤0.0005% and S≤0.0005%; the particle size of the iron flux is 20-40 meshes;

[0070] The main component of tungsten flux is tungsten (purity greater than 99.95%), and it also contains C≤0.0008% and S≤0.0005%; the particle size of tungsten flux is 20-40 mesh;

[0071] Please see Table 1 for the results.

[0072] Step 3: Obtaining high-overmature rock debris source rock samples that are contaminated by oil-based mud after oil washing;

[0073] Specifically, for each target high-overmature cuttings source rock sample contaminated by oil-based mud, the following steps are performed:

[0074] Take 20g of the target high-overmature debris source rock sample contaminated by oil-based mud and pack it in the extracted filter paper tube; put the packed sample into a Soxhlet extractor, add the copper sheet for purification and desulfurization in the bottom bottle, and add the mixed solution of organic solvent dichloromethane and methanol (the volume ratio of dichloromethane to methanol is 93:7) to 1 / 3-1 / 2 of the capacity of the extractor, and continuously extract for 24 hours at a constant temperature of 63°C in a water bath until the reagent in the extractor is colorless (indicating that the crude oil contaminants on the surface of the sample have been washed away); separate the washed extract (containing mixed oil contaminants) from the source rock sample and weigh them; take out the extracted sample and dry it to obtain the target high-overmature debris source rock sample contaminated by oil-based mud after oil washing.

[0075] Step 4: Determine the pyrolysis hydrocarbon value S2 of the target high-overmature cuttings source rock sample contaminated by oil-based mud after oil washing 1 , Soluble hydrocarbon value S1 1 and organic carbon content TOC 1 ;

[0076] Specifically, for each high-overmature cuttings source rock sample contaminated by oil-based mud after oil washing, the following steps are performed:

[0077] Take 100 mg (± 0.5 mg) of the target high-overmature rock debris source rock sample contaminated by oil-based mud after oil washing, enter the sample mass in the Rock-eval rock pyrolysis analyzer workstation, and use the Rock-eval rock pyrolysis analyzer workstation to perform pyrolysis analysis to obtain the pyrolysis hydrocarbon value S2 1 and soluble hydrocarbon value S1 1 ; During the pyrolysis analysis process, the initial temperature of the Rock-eval rock pyrolysis analyzer is 300℃ and the highest temperature is 600℃;

[0078] Take 0.1g of the target high-overmature debris source rock sample contaminated by oil-based mud after oil washing, put it into a fired crucible, add hydrochloric acid with a volume ratio of 1:7, and soak it at 80℃ for 2 hours for acid treatment; then put the acid-treated sample on a suction filter and rinse it with distilled water every half an hour until the sample in the crucible is rinsed to neutral; put the rinsed sample together with the crucible into a constant temperature drying oven at a constant temperature of 80℃ for 8 hours; add 1.0g of iron flux and 1.0g of tungsten flux to the dried sample, enter the sample mass in the carbon-sulfur analyzer, and use the carbon-sulfur analyzer to determine the organic carbon content TOC 1 ;

[0079] The main component of the iron flux is iron (with a purity greater than 99.8%), and it also contains C≤0.0005% and S≤0.0005%; the particle size of the iron flux is 20-40 meshes;

[0080] The main component of tungsten flux is tungsten (purity greater than 99.95%), and it also contains C≤0.0008% and S≤0.0005%; the particle size of tungsten flux is 20-40 mesh;

[0081] Please see Table 1 for the results.

[0082] Step 5: based on the pyrolysis hydrocarbon value of the target high-over mature rock debris source rock sample contaminated by oil-based mud, the pyrolysis hydrocarbon value of the target high-over mature rock debris source rock sample contaminated by oil-based mud after oil washing, and the organic matter content of the target high-over mature rock debris source rock sample contaminated by oil-based mud after oil washing, determine the true organic matter content of the target high-over mature rock debris source rock sample contaminated by oil-based mud; specifically including:

[0083] Obtaining the true organic matter content of high-overmature debris source rock samples contaminated by oil-based mud Calculation model for the pyrolysis hydrocarbon value of high-overmature debris source rock samples contaminated by oil-based mud, the pyrolysis hydrocarbon value of high-overmature debris source rock samples contaminated by oil-based mud after oil washing, and the organic matter content of high-overmature debris source rock samples contaminated by oil-based mud after oil washing:

[0084] TOC0 =[(S2-S2 1 )×k]÷10+TOC 1

[0085] In the formula, TOC 1 is the percentage of organic matter content of the source rock sample contaminated by mixed oil mud after oil washing, %; S2 is the pyrolysis hydrocarbon value of the source rock sample contaminated by mixed oil mud, mg / g; S2 1 is the pyrolysis hydrocarbon value of the source rock sample contaminated by mixed oil mud after oil washing, mg / g; TOC 0 is the percentage of the original organic matter content of the source rock sample contaminated by the mixed oil mud, %; k is the mass content percentage of organic carbon in the pyrolysis hydrocarbon, %, and takes the value of 85%;

[0086] For each target high-over mature lithic source rock sample contaminated by oil-based mud after oil washing, respectively based on the calculation model of the real organic matter content of the high-over mature lithic source rock sample contaminated by oil-based mud about the pyrolysis hydrocarbon value of the high-over mature lithic source rock sample contaminated by oil-based mud, the pyrolysis hydrocarbon value of the high-over mature lithic source rock sample contaminated by oil-based mud after oil washing, and the organic matter content of the high-over mature lithic source rock sample contaminated by oil-based mud after oil washing, combined with the pyrolysis hydrocarbon value of the target high-over mature lithic source rock sample contaminated by oil-based mud, the pyrolysis hydrocarbon value of the target high-over mature lithic source rock sample contaminated by oil-based mud after oil washing, and the organic matter content of the target high-over mature lithic source rock sample contaminated by oil-based mud after oil washing, determine the real organic matter content of the target high-over mature lithic source rock sample contaminated by oil-based mud;

[0087] The results are shown in Table 1. Figure 2 shown.

[0088] As can be seen from Table 1, the mudstone in the first section and the marl in the second section all showed high organic matter abundance characteristics before oil washing. Among them, the organic carbon content of 7 source rock samples (No. 1-7) in the first section (6954-7234m well section) mudstone within the thickness range of 280m was as high as 0.76%-2.09%, with an average of 1.30%; the organic carbon content of 3 source rock samples (No. 8-10) in the second section (7266-7272m well section) with a total thickness of 7m of marl was also 0.49%-0.92%, with an average of 0.72%.

[0089] However, the correct evaluation of the organic matter abundance of the mudstone in the first layer and the marlstone in the second layer should also fully exclude the influence of oil-based mud contamination on the measured organic carbon content, that is, the organic carbon content of each source rock sample may contain the organic carbon components of the mixed oil contaminants on the surface of the source rock sample. Figure 2It can be seen that the organic carbon content of the 10 target source rock samples contaminated by oil-based mud in the 6954-7272m well section was greatly changed after Soxhlet extraction and oil washing. Among them, in the 6954-7054m well section, in the layer section of about 100m thick, the organic carbon content of 4 source rock samples after oil washing remained in the range of 0.56%-0.86%, with an average of 0.73%; in the 7114-7234m well section of about 120m thick, the organic carbon content of 3 source rock samples after oil washing ranged from 0.44% to 0.48%, with an average of 0.46%; in the 7266-7272m well section of only 7m thick marlstone layer, the organic carbon content of 3 source rock samples after oil washing was 0.36%-0.58%, with an average of 0.42%.

[0090] The soluble hydrocarbon values ​​obtained by Rock-eval pyrolysis analysis of source rock samples before oil washing include crude oil contaminants on the surface of the cuttings and two components of organic matter in the cuttings. As can be seen from Table 1, the soluble hydrocarbon values ​​of the source rock samples in the first section (6954-7234m well section) before oil washing range from 1.81 to 9.56 mg / g, and the soluble hydrocarbon values ​​after oil washing drop sharply to 0.06-0.30 mg / g, with a soluble hydrocarbon loss of up to 1.71-9.44 mg / g. Similarly, the soluble hydrocarbon loss of the marlstone in the second section (7266-7272m well section) before and after oil washing also reaches 1.14-1.37 mg / g.

[0091] Obviously, most of the soluble hydrocarbons in the source rock samples were washed out after oil washing. The effect of oil washing of source rock samples not only leads to a decrease in the soluble hydrocarbon value of source rock samples, but also has a significant impact on the pyrolysis hydrocarbon value. The distribution range of the pyrolysis hydrocarbon value of the mudstone source rock samples before oil washing in the first section (6954-7234m well section) was 1.48-8.23mg / g, and the pyrolysis hydrocarbon value of the remaining cuttings after oil washing also dropped sharply to 0.35-2.03mg / g, and the pyrolysis hydrocarbon loss was as high as 1.05-6.54mg / g. The distribution range of the pyrolysis hydrocarbon value of the marl source rock samples before oil washing in the second section (7266-7272m well section) was 0.32-1.32mg / g, and the pyrolysis hydrocarbon value of the remaining cuttings after oil washing also dropped sharply to 0.21-0.41mg / g, and the pyrolysis hydrocarbon loss was as high as 0.85-0.91mg / g. Since the pyrolysis hydrocarbon values ​​of source rock samples are completely unrelated to mixed oil contaminants, the large loss of pyrolysis hydrocarbons reflects the excessive cleaning of kerogen components by binary reagent Soxhlet extraction, which further proves that the mixed oil contaminants on the surface of the cuttings have indeed been completely removed.

[0092] The main reason why the abundance of organic matter in rocks becomes lower after oil washing is that the soluble hydrocarbons S1 and part of the pyrolysis hydrocarbons S2 in the rocks are washed out during the oil washing process. Since the soluble hydrocarbon S1 content of high-overmature source rocks is very low, the soluble hydrocarbons S1 lost after oil washing should be mainly contaminated hydrocarbons. Pyrolysis hydrocarbons are kerogen-degraded hydrocarbons, and their content is not affected by pollution. However, the pyrolysis hydrocarbons in rocks will also be partially washed out during the oil washing process. Therefore, it is necessary to make up for the carbon content of these washed out pyrolysis hydrocarbons to obtain the true abundance of organic matter in oil-based contaminated rock cuttings. In the calculation process, the organic carbon content in the pyrolysis hydrocarbons is calculated as 85% (see Table 2, the amount of organic carbon in petroleum can usually be taken as 85%). A mathematical relationship between the loss of pyrolysis hydrocarbons and the organic carbon content after oil washing is established, that is, the original organic matter TOC 0 =[(S2-S2 1 )×k]÷10+TOC 1 , thereby restoring the original organic matter content of the contaminated source rock samples.

[0093] Table 1 Example 1 Sample data

[0094]

[0095] Table 2 Elemental composition of some petroleum samples

[0096]

[0097]

[0098] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A method for determining the true organic matter content of high-overmature debris source rock samples contaminated by oil-based mud, wherein: The method includes: Determine the pyrolysis hydrocarbon value of the target high-overmature lithic source rock samples contaminated by oil-based mud; Determine the pyrolysis hydrocarbon value of the target high-overmature cuttings source rock sample contaminated by oil-based mud after oil washing; Determine the organic matter content of high-overmature lithic source rock samples contaminated by oil-based mud after oil washing; Determine the true organic matter content of the target high-overmature rock source rock contaminated by oil-based mud based on the pyrolysis hydrocarbon value of the target high-overmature rock source rock contaminated by oil-based mud, the pyrolysis hydrocarbon value of the target high-overmature rock source rock contaminated by oil-based mud after oil washing, and the organic matter content of the target high-overmature rock source rock contaminated by oil-based mud after oil washing; Among them, high-overmature source rocks refer to source rocks with a vitrinite reflectance Ro value of not less than 1.3%; Wherein, the determining of the true organic matter content of the target high-over mature rock debris source rock sample contaminated by oil-based mud based on the pyrolysis hydrocarbon value of the target high-over mature rock debris source rock sample contaminated by oil-based mud, the pyrolysis hydrocarbon value of the target high-over mature rock debris source rock sample contaminated by oil-based mud after oil washing, and the organic matter content of the target high-over mature rock debris source rock sample contaminated by oil-based mud after oil washing includes: Obtaining the actual organic matter content of the high-overmature debris source rock sample contaminated by oil-based mud; a calculation model for the pyrolysis hydrocarbon value of the high-overmature debris source rock sample contaminated by oil-based mud, the pyrolysis hydrocarbon value of the high-overmature debris source rock sample contaminated by oil-based mud after oil washing, and the organic matter content of the high-overmature debris source rock sample contaminated by oil-based mud after oil washing; Based on the calculation model of the real organic matter content of the high-overmature lithic source rock sample contaminated by the oil-based mud about the pyrolysis hydrocarbon value of the high-overmature lithic source rock sample contaminated by the oil-based mud, the pyrolysis hydrocarbon value of the high-overmature lithic source rock sample contaminated by the oil-based mud after oil washing, and the organic matter content of the high-overmature lithic source rock sample contaminated by the oil-based mud after oil washing, the real organic matter content of the target high-overmature lithic source rock sample contaminated by the oil-based mud is determined in combination with the pyrolysis hydrocarbon value of the target high-overmature lithic source rock sample contaminated by the oil-based mud, the pyrolysis hydrocarbon value of the target high-overmature lithic source rock sample contaminated by the oil-based mud after oil washing, and the organic matter content of the target high-overmature lithic source rock sample contaminated by the oil-based mud after oil washing; The calculation model of the actual organic matter content of the high-overmature lithic source rock sample contaminated by oil-based mud is about the pyrolysis hydrocarbon value of the high-overmature lithic source rock sample contaminated by oil-based mud, the pyrolysis hydrocarbon value of the high-overmature lithic source rock sample contaminated by oil-based mud after oil washing, and the organic matter content of the high-overmature lithic source rock sample contaminated by oil-based mud after oil washing is: <h2 style=";text-align:left;direction:ltr">TOC<h2 style=";text-align:left;direction:ltr"> 0 <h2 style=";text-align:left;direction:ltr"> (S2-S2<h2 style=";text-align:left;direction:ltr"> 1 <h2 style=";text-align:left;direction:ltr"> )×k]÷10+TOC<h2 style=";text-align:left;direction:ltr"> 1 In the formula, TOC 1 is the percentage of organic matter content in the high-overmature lithic source rock sample contaminated by oil-based mud after oil washing, %; S2 is the pyrolysis hydrocarbon value of the high-overmature lithic source rock sample contaminated by oil-based mud, mg / g; S2 1 is the pyrolysis hydrocarbon value of high-overmature cuttings source rock samples contaminated by oil-based mud after oil washing, mg / g; TOC 0 is the percentage of the true organic matter content of the high-overmature lithic source rock sample contaminated by oil-based mud, %; k is the mass content percentage of organic carbon in pyrolytic hydrocarbons, %.

2. The method according to claim 1, wherein: The particle size of the target high-overmature debris source rock sample contaminated by oil-based mud does not exceed 0.2 mm.

3. The method according to claim 1, wherein: The method further comprises the step of obtaining a target high-overmature debris source rock sample contaminated by oil-based mud; The step of obtaining a target high-overmature rock debris source rock sample contaminated by oil-based mud comprises: Cuttings sampling of high-overmature source rock layers contaminated by oil-based mud during drilling; Select the rock cuttings samples obtained by sampling; Washing and drying the selected source rock cuttings; The dried source rock cuttings are ground to obtain the target high-overmature cuttings source rock sample contaminated by oil-based mud.

4. The method according to claim 3, wherein: The rock cuttings samples obtained by sampling are selected in the following ways: The rock cuttings samples obtained by sampling are sieved to remove dried mud powder and rock powder, and then the mottled and strange rock cuttings fragments are removed, and the rock cuttings fragments with consistent lithology and appearance are retained to prevent the influence of other fragments or drilling mud solid blocks.

5. The method according to any one of claims 1, 3 and 4, wherein: The oil washing of the high-overmature debris source rock sample contaminated by oil-based mud is carried out by Soxhlet extraction.

6. The method according to claim 5, wherein: The oil washing of the high-overmature cuttings source rock sample contaminated by oil-based mud is achieved by the following method: The target high-overmature debris source rock sample contaminated by oil-based mud is packed in the extracted filter paper cylinder; Put the wrapped sample into the Soxhlet extractor, add the copper sheet for purification and desulfurization into the bottom bottle, and add the mixture of organic solvents dichloromethane and methanol; Extract at 63°C until the reagent in the extractor is colorless; The extracted samples were taken out and dried.

7. The method according to claim 1, wherein: The pyrolysis hydrocarbon value of the sample is determined in the following manner: Take a certain amount of sample and put it into the Rock-eval rock pyrolysis analyzer workstation for pyrolysis analysis to obtain the pyrolysis hydrocarbon value of the sample.

8. The method according to claim 1, wherein: The determination of the organic matter content of the target high-overmature lithic source rock samples contaminated by oil-based mud after oil washing is carried out in the following way: A sample obtained after oil washing from a target high-overmature cuttings source rock contaminated by oil-based mud is subjected to acid treatment, and the sample obtained after the acid treatment is washed with water until it is neutral and dried; Adding iron flux and tungsten flux to the sample obtained after drying, and then using a carbon-sulfur analyzer to measure the organic matter content, to obtain the organic matter content of the target high-overmature cuttings source rock sample contaminated by oil-based mud after oil washing; Among them, the mass of the sample obtained after oil washing of the target high-overmature lithic source rock contaminated by oil-based mud: the mass of the iron flux: the mass of the tungsten flux is 0.01-10:1.0:1.0.

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