A method for oil source comparison using platinum-palladium ratio

Abstract

The present invention discloses a method for oil source comparison using a platinum-palladium ratio, and relates to the technical field of petroleum geological exploration. A method for oil source comparison using a platinum-palladium ratio comprises the following steps: collecting crude oil samples and source rock samples; pre-treating the crude oil samples and source rock samples respectively, and separating asphaltene and soluble organic matter from the crude oil samples; performing platinum group element determination on the asphaltene or the pre-treated source rock samples; simulating the platinum / palladium probability distribution of the target source rock samples according to the platinum group element determination results of the source rock samples, and predicting the crude oil platinum / palladium ratio range; comparing the platinum / palladium ratio results obtained by the crude oil sample determination with the crude oil platinum / palladium ratio range obtained by simulation. The present invention improves the accuracy and credibility of the oil source comparison results by using trace platinum group elements in source rocks to compare oil sources.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum geological exploration, and in particular to a method for oil source comparison using a platinum-palladium ratio. Background Art

[0002] Oil-source correlation plays a core role in petroleum geological research, and its importance is reflected in many aspects: it provides a scientific basis for formulating accurate exploration strategies, significantly improves the exploration success rate by identifying the main source rocks and favorable hydrocarbon generation areas; it reveals the laws of oil and gas migration, helps identify key migration pathways and major accumulation areas, and provides important clues for predicting favorable closures and enrichment areas; as an important tool for basin evolution analysis, it helps to reconstruct the basin's hydrocarbon generation and expulsion history.

[0003] However, traditional oil source correlation methods, such as biomarkers and stable carbon isotope analysis, often show obvious limitations when faced with crude oil with a high degree of evolution or that has undergone strong secondary transformation. Biomarkers are easily affected by secondary processes such as thermal evolution and biodegradation, which may cause their characteristics to change significantly and lose their significance as indicators of the parent source. Similarly, stable carbon isotope ratios may also change due to secondary transformations such as thermal cracking and thermochemical sulfate reduction (TSR), affecting their reliability as oil source indicators. These factors reduce the accuracy and credibility of the correlation results of traditional oil source methods under complex geological conditions.

[0004] Therefore, there is an urgent need to provide an oil-source correlation method with high accuracy and feasibility to make up for the shortcomings of traditional organic geochemical research methods, especially to support the study of crude oil with a high degree of thermal evolution in deep and ultra-deep layers and that has undergone secondary transformation. This is of great significance for identifying the main source rocks in complex oil and gas basins, revealing the laws of oil and gas migration, and improving the success rate of exploration. Summary of the invention

[0005] The technical problem to be solved by the present invention is that the existing oil source comparison method has obvious limitations when facing crude oil with a high degree of evolution or undergoing strong secondary transformation, and the accuracy and credibility of the results are low. The purpose is to provide a method for oil source comparison using the platinum-palladium ratio, which improves the accuracy and credibility of the oil source comparison results by using trace platinum group elements in source rocks to compare oil sources.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for oil source comparison using platinum-palladium ratio comprises the following steps:

[0008] Collect crude oil samples and source rock samples;

[0009] Pre-treating crude oil samples and source rock samples respectively, separating asphaltene and soluble organic matter from crude oil samples;

[0010] Platinum group elements were determined on asphaltene or pre-treated source rock samples;

[0011] According to the platinum group element determination results of source rock samples, the platinum / palladium probability distribution of crude oil generated by target source rock samples is simulated, and the range of platinum / palladium ratio of crude oil is predicted;

[0012] The Pt / Pd ratio results obtained from the crude oil samples were compared with the simulated Pt / Pd ratio range for crude oil.

[0013] In some embodiments of the present invention, the crude oil sample may be crude oil or an oil-bearing core.

[0014] When the crude oil sample is crude oil, the crude oil is a mid-test sample during the drilling stage or a sample of a single layer of stable output during the production stage. The collected crude oil is stored in a light-proof container, and the air in the container is exhausted;

[0015] When the crude oil sample is an oil-bearing core, the oil-bearing core is a freshly collected core section with high oil saturation. After the oil-bearing core is collected, it is wrapped with aluminum foil and then sealed.

[0016] Preferably, the oil-bearing core with high oil saturation is dark in color and has obvious fluorescence characteristics under white light.

[0017] Preferably, the known source rock samples can be core samples obtained by drilling or field outcrop samples. The lithology of source rocks is generally dark-black mudstone, limestone or marl containing organic matter. Field outcrops are subject to weathering, so new trenches must be dug during collection to collect fresh, non-weathered, and non-polluted source rock samples.

[0018] Preferably, when collecting core samples, the focus should be on avoiding the influence of hydrothermal fluids, abnormal mineralization areas, significant diagenetic zones, tectonic deformation zones, etc., and selecting stable source rock development layers. The samples should cover the entire source rock development layer as much as possible to reflect the changes in the vertical direction. When collecting core samples, it is necessary to avoid the outer parts that may be contaminated by drilling fluid. After the samples are collected, they are wrapped in tin foil and stored in a sealed bag.

[0019] As a possible design, the above-mentioned pretreatment of the crude oil sample includes the following steps:

[0020] The crude oil samples were separated into group components to obtain asphaltenes.

[0021] Preferably, the solvent is n-hexane.

[0022] Preferably, the chromatography column is a silica gel-alumina chromatography column, and the volume ratio of silica gel to alumina is 3:1.

[0023] In some embodiments of the present invention, when the crude oil sample is an oil-bearing core, the oil-bearing core sample is first crushed, then dried at low temperature, extracted with dichloromethane to obtain an oil-bearing core extract, and then asphaltene separation is performed.

[0024] Preferably, the oil-bearing core sample is crushed to a particle size of less than 2 mm.

[0025] As a possible design, the above-mentioned pre-treatment of the source rock sample is specifically to grind the source rock sample to 100-200 mesh after washing and drying.

[0026] As a possible design, the above-mentioned determination of platinum group elements includes the following steps:

[0027] Weigh a certain weight of asphaltene (generally 100 mg) or source rock sample (generally 150-200 mg), add the asphaltene or pretreated source rock sample into the Ir-Ru-Pt-Pd mixed diluent, add the sample dissolving reagent, heat and dissolve the platinum group elements enriched in the sample and reach isotopic equilibrium with the Ir-Ru-Pt-Pd mixed diluent, use anion exchange resin to separate the platinum group elements and matrix elements, elute the matrix elements with the eluent, and then determine the platinum group elements.

[0028] Preferably, the sample dissolving reagent is aqua regia, which includes concentrated hydrochloric acid (12 mol / L) and concentrated nitric acid (16 mol / L), and the volume ratio of the concentrated hydrochloric acid to the concentrated nitric acid is 1:2.

[0029] Preferably, the above-mentioned heating and dissolving is specifically treated at 220° C. for 72 hours.

[0030] Preferably, the anion exchange resin is 2.5 mL, 100-200 mesh AG 1×8 anion exchange resin.

[0031] Preferably, the eluent for eluting the matrix elements is 1 mol / L HCl and 0.8 mol / L HNO3.

[0032] As a possible design, after the matrix elements are eluted as above, Ru is eluted with 12 mol / L HNO3, Ir and Pt are eluted with 15 mL 13.5 mol / L HNO3, and finally Pd is eluted with 15 mL 10 mol / L HCl.

[0033] As a possible design, the above-mentioned determination of platinum group elements specifically adopts a plasma mass spectrometer to detect and determine the content of platinum group elements Pt and Pd.

[0034] Preferably, the above detection accuracy is 0.1 ppb.

[0035] Preferably, the above-mentioned plasma mass spectrometer is a Neptune multi-collector inductively coupled plasma mass spectrometer (Neptune MC-ICP-MS).

[0036] In some embodiments of the present invention, the above-mentioned simulation of the probability distribution of platinum / palladium of crude oil generated from the target hydrocarbon source rock sample is specifically performed through Monte Carlo simulation.

[0037] The present invention simulates the change of Pt / Pd ratio during the conversion process from source rock to crude oil through Monte Carlo simulation and statistical methods based on random sampling, taking into account the uncertainty of geological processes. Through a large number of random sampling and calculations, we can obtain a predicted range of crude oil Pt / Pd ratios, providing a theoretical basis for subsequent oil source comparison.

[0038] Preferably, the probability distribution characteristics of each parameter must be clarified before Monte Carlo simulation. Since the amount of source rock data may be small, before Monte Carlo simulation, the source rock data is used by the Kernal Density Estimation (KDE) method to create a continuous probability distribution curve of the source rock Pt / Pd ratio. The Scott method is used to determine the bandwidth during the calculation process. Compared with the original data, the newly obtained probability distribution curve effectively predicts the probability distribution characteristics of the missing data part. Based on geological knowledge and judgment, define the possible range and distribution of K. After the simulation parameters are set, Monte Carlo simulation is performed. The number of simulations is generally set to 10,000 times or more. The obtained simulation results are distributed at the 5% and 95% percentiles as the predicted crude oil Pt / Pd ratio range.

[0039] Because the Pt / Pd value of the source rock is not completely consistent with the Pt / Pd value of the crude oil it generates. In the process of estimating the Pt / Pd of the crude oil generated by the target source rock, the Pt / Pd of the crude oil is estimated by multiplying the coefficient K. The K value reflects various geological factors that may cause changes in the Pt / Pd ratio during hydrocarbon generation in the source rock, migration and accumulation of crude oil.

[0040] In some embodiments of the present invention, the above-mentioned prediction of the crude oil Pt / Pd ratio range is performed by the following formula:

[0041] Pt / Pd 原油 = Pt / Pd 烃源岩 *K

[0042] In the formula,

[0043] Pt / Pd 原油The Pt / Pd ratio of crude oil generated from a known source rock formation;

[0044] Pt / Pd 烃源岩 is source rock Pt / Pd;

[0045] K is the influencing factor of geological process.

[0046] Preferably, the above geological process influencing factor is mainly used to simulate the possible changes in the Pt / Pd ratio during the conversion process from source rock to crude oil, and its setting is determined by comprehensive judgment of regional geological knowledge. Preferably, the above K value ranges from 0.5 to 1.5, and more preferably, the K value ranges from 0.8 to 1.2.

[0047] As a possible design, if the platinum / palladium ratio result of the crude oil sample falls within the simulated crude oil platinum / palladium ratio range of 5 to 95%, the crude oil sample is considered to be derived from a source rock sample.

[0048] If the platinum / palladium ratio result of the crude oil sample is not within the range of 5-95% of the simulated crude oil platinum / palladium ratio, it is considered that the crude oil sample does not come from the source rock sample or that the crude oil sample contains contributions from other source rocks.

[0049] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0050] The inventors use the platinum-palladium ratio to perform oil source comparison, which is different from the traditional oil source comparison method based on biomarker compounds and stable carbon isotopes. It solves the shortcomings of traditional comparison methods that the parameters are greatly affected by thermal evolution and secondary effects and have strong multi-solution properties. It has the advantage of being less affected by the thermal evolution and secondary effects of source rocks. It plays an important role in determining the source of crude oil subjected to secondary transformation, and also has an important guiding role in the exploration of ancient marine carbonate oil reservoirs that have undergone complex migration, aggregation, and adjustment and transformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0052] Figure 1 is a flow chart of the present invention;

[0053] Figure 2 The measured Pt / Pd ratio and kernel density estimation distribution diagram of the source rock in the study area of ​​the present invention;

[0054] Figure 3is a probability distribution diagram of the K factor of the method steps of the present invention;

[0055] Figure 4 The Monte Carlo method for predicting the probability distribution of crude oil Pt / Pd in ​​the method steps of the present invention;

[0056] Figure 5 It is the asphaltene content and Pt / Pd distribution diagram of the samples in the method steps of the present invention. DETAILED DESCRIPTION

[0057] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with examples and drawings. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention. If specific conditions are not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0058] It should also be noted that, for the convenience of description, the drawings only show the parts related to the present invention rather than all the contents.

[0059] The inventors consider that in addition to organic compounds, crude oil also contains inorganic trace elements (such as rare earth elements, platinum group elements, etc.) with a certain abundance and indicative significance, and the trace elements are enriched in a certain abundance in the source rock kerogen, and the oil and gas generated can inherit the trace element composition of organic matter and its sedimentary rock diagenetic environment, and are not easily affected by thermal maturity, migration and secondary effects, and have potential significance for oil source comparison. Based on this, the inventors use the platinum-palladium ratio to compare oil sources, which is not only less affected by the thermal evolution and secondary effects of the source rock, but also plays an important role in judging the source of crude oil affected by secondary transformation, and also has an important guiding role in the exploration of ancient marine carbonate reservoirs with complex migration, aggregation and adjustment transformation.

[0060] The present invention is specifically described by taking samples from the Y-layer source rock and the O-series reservoir in the Tarim Basin as an example. Based on the distribution of source rocks revealed by actual drilling and the evaluation results of source rocks, predecessors have reached a consensus that the crude oil in the O-series reservoir comes from the Y-layer source rock.

[0061] Reference Figure 1 , the specific method includes the following steps:

[0062] S1. Collect crude oil samples and source rock samples.

[0063] Known source rock samples can be core samples obtained from drilling or field outcrop samples. The lithology of source rocks is generally dark-black mudstone, limestone or marl containing organic matter. When collecting core samples, the focus should be on avoiding the influence of hydrothermal fluids, abnormal mineralization areas, significant diagenetic zones, structural deformation zones, etc., and selecting stable source rock development layers. The samples should cover the entire source rock development layer as much as possible to reflect the changes in the vertical direction.

[0064] Because field outcrops are subject to weathering, new trenches must be dug during collection to collect fresh, non-weathered, and non-polluted source rock samples.

[0065] When collecting core samples, be careful to avoid the outer parts that may be contaminated by drilling fluid. After collecting the samples, wrap them in tin foil and store them in a sealed bag.

[0066] The crude oil samples to be compared can be crude oil collected from the wellhead or oil-bearing cores. Wellhead crude oil is collected from the wellhead oil-gas separator. The samples should be mid-test samples (DST) during the drilling phase or samples of stable output from a single layer during the production phase to avoid cross-contamination of crude oil samples from different layers. Residual liquid in the pipeline should be removed before collection. The collected crude oil is stored in brown glass bottles and filled as full as possible to avoid air oxidation. For oil-bearing cores, fresh core sections with high oil saturation are selected, wrapped in aluminum foil and placed in sealed plastic bags.

[0067] Since there are few wells that systematically encounter Y-layer source rocks, it is difficult to obtain samples, and it is known that Y-layer source rocks are exposed in some areas. Source rock samples are selected from typical stratigraphic sections that are completely exposed in the northwest margin of the basin. The target layer (Y layer) and the upper and lower strata here are completely exposed and representative. From the results of field observations, it can be divided into three sections: upper, middle and lower. The lower section is a thin layer of phosphorus-containing siliceous rock (early hydrothermal action), which transitions upward to interlayers of thin siliceous rock and black mudstone, and medium-thick dolomite is developed in the uppermost part. The middle stable shale section was selected for sample collection, and 16 black shale samples were systematically collected from bottom to top. After the samples were collected, they were wrapped in tin foil and placed in a sealed bag for storage.

[0068] The 11 crude oil samples and 3 oil-bearing core samples that need to be compared were collected from multiple areas of the Tabei Uplift in the northern Tarim Basin. The sample types include extra-heavy oil, heavy oil, normal oil, light oil and reservoir asphalt. The sample density is shown in Table 1. Among them, there are differences in the maturity of crude oil from the AD-YQ area to the TH area to the TP area, and significant biodegradation has occurred, and the degree of degradation has gradually decreased. The higher the degree of degradation, the greater the density of the crude oil. The asphalt enrichment in the SB oil-bearing core development and fault zone is the product of physical alteration of the early injected crude oil. After the early hydrocarbon injection, the reactivation of the fault zone caused the formation temperature and pressure to drop, resulting in the enrichment of local asphaltene.

[0069] Since the crude oil produced by some heavy oil wells has high density and viscosity, light oil is currently injected into the reservoir during the production process. Therefore, the crude oil samples collected at the wellhead are all mid-course test (DST) samples, which are not affected by dilution in the later production process. After the crude oil samples are collected, they are placed in brown glass bottles and kept as full as possible. The oil-bearing core samples are fresh core parts that are not contaminated by drilling fluid. After collection, they are wrapped in tin foil and stored in sealed bags.

[0070] S2. Pre-treat the crude oil sample and the source rock sample respectively, and separate asphaltene and soluble organic matter from the crude oil sample.

[0071] Since the metal elements in crude oil are mainly enriched in asphaltene in the form of organic metal complexes, asphaltene must be separated from crude oil and oil-bearing core samples before testing for platinum group elements. Oil-bearing core samples need to be extracted before separation. The samples are crushed to an appropriate particle size (<2mm) and then dried at low temperature. The dried samples are placed in a Soxhlet extractor and dichloromethane is used as the extracting fluid to extract the crude oil in the reservoir. Asphaltene separation is performed on the oil-bearing core extract and crude oil. A certain amount of reservoir extract or crude oil is taken, and the asphaltene is dissolved in n-hexane solution to precipitate the asphaltene.

[0072] The Y-layer source rock and O-series reservoir crude oil samples in the Tarim Basin are used as examples to illustrate. Asphaltene separation was performed on 14 crude oil samples collected at the wellhead. The relative asphaltene content of each sample (asphaltene mass to crude oil or extract mass) is shown in Table 1.

[0073] Table 1 Physical properties of crude oil samples asphaltene relative content characteristics

[0074] area Sample type Sample No. <![CDATA[Density (20 °C, g / cm 3 )]]> Asphaltene(%) AD-YQ Extra heavy crude oil AD1 1.01 33.3 AD2 0.91 41.9 AD3 1.05 55.2 YQ1 1.04 43 YQ 1.04 47.3 TH Heavy oil TH1 0.97 2.8 TH2 0.91 3.7 TH3 0.96 4.1 TH4 0.96 2.6 TP Light oil-Normal oil TP1 0.81 1.4 TP2 0.88 2.4 SB Oil-bearing core (reservoir bitumen) SB1 / 23.9 SB2 / 19.1 SB3 / 29.9

[0075] In some embodiments of the present invention, the above-mentioned pre-treatment of the source rock sample specifically comprises washing and drying the source rock sample and then grinding it to 100-300 meshes.

[0076] S3. Perform platinum group element determination on the asphaltene or pre-treated source rock samples.

[0077] The determination of platinum group elements (PGEs) in organic-rich samples (black shale, crude oil asphaltene obtained by pretreatment) was carried out by acid dissolution method (4 mL concentrated HCl + 8 mL concentrated HNO3).

[0078] The specific experimental steps are as follows:

[0079] S31, weighing about 200 mg of black shale or 100 mg of the crude oil asphaltene sample obtained by pretreatment, and adding a certain amount of Ir-Ru-Pt-Pd mixed diluent;

[0080] S32, using the Carius tube dissolution method with reverse aqua regia as the dissolution reagent, heating at 240 °C for 72 h to completely dissolve the enriched platinum group elements in the sample and achieve isotopic equilibrium with the diluent;

[0081] S33. After the platinum group elements (Ir, Ru, Pt, Pd) dissolved in the aqua regia phase were converted into chlorides, AG 1×8 anion exchange resin (2.5 mL; 100-200 mesh) was used to separate the platinum group elements and matrix elements. The matrix elements were eluted with 1 mol / L HCl and 0.8 mol / L HNO3, Ru was eluted with 12 mol / L HNO3, Ir and Pt were eluted with 15 mL 13.5 mol / L HNO3, and Pd was eluted with 15 mL 10 mol / L HCl. The content of platinum group elements Pt and Pd was determined by Neptune MC-ICP-MS with a measurement accuracy of 0.1 ppb.

[0082] The crude oil samples of the Y-layer source rock and the O-series reservoir in the Tarim Basin are used as examples for illustration. The crude oil and the asphaltene components of the oil-bearing core obtained in step S2 are tested for platinum group elements, and the test results are shown in Table 2.

[0083] Table 2 Platinum group element test results of source rocks and crude oil samples

[0084] Sample No. Sample type Pt(ppb) Pd(ppb) Pt / Pd Sample No. Sample type Pt(ppb) Pd(ppb) Pt / Pd A1 Source rock 2.1 6.8 0.31 S16 Source rock 1.9 6 0.31 A2 Source rock 2.5 5.4 0.46 AD1 Extra heavy crude oil 0.5 1 0.55 A3 Source rock 3.2 7.1 0.45 AD2 Extra heavy crude oil 0.8 2.2 0.38 A4 Source rock 2.4 6.9 0.35 AD3 Extra heavy crude oil 0.7 1.7 0.38 A5 Source rock 4 5.2 0.77 YQ1 Extra heavy crude oil 0.5 1.3 0.36 A6 Source rock 4 11.2 0.36 YQ Extra heavy crude oil 0.4 1.4 0.33 A7 Source rock 4.8 12.5 0.39 TH1 Heavy oil 0.3 0.8 0.41 A8 Source rock 4.9 12.9 0.38 TH2 Heavy oil 0.3 0.9 0.4 A9 Source rock 2.5 4.4 0.57 TH3 Heavy oil 0.3 0.9 0.35 A10 Source rock 3.1 9.7 0.31 TH4 Heavy oil 0.3 0.9 0.34 A11 Source rock 3.5 10.3 0.34 TP1 Light oil-Normal oil 1.7 1.9 0.52 A12 Source rock 2.9 9 0.32 TP2 Light oil-Normal oil 1.7 1.1 0.44 A13 Source rock 1.9 4.8 0.4 SB1 Reservoir Asphalt 0.8 1.4 0.53 A14 Source rock 2.7 5.5 0.49 SB2 Reservoir Asphalt 0.8 1.3 0.62 A15 Source rock 1.5 6.8 0.22 SB3 Reservoir Asphalt 2.3 3.4 0.68

[0085] S4. Based on the platinum group element determination results of the source rock samples, simulate the platinum / palladium probability distribution of the target source rock samples and predict the platinum / palladium ratio range of the crude oil.

[0086] Based on the platinum group element results obtained from source rock testing, the possible Pt / Pd probability distribution of crude oil generated by the target source rock is simulated through Monte Carlo to predict the Pt / Pd ratio range of crude oil. According to the formula:

[0087] Pt / Pd 原油 = Pt / Pd 烃源岩 *K

[0088] In the formula,

[0089] Pt / Pd 原油 is the Pt / Pd ratio of crude oil generated from a known source rock formation,

[0090] Pt / Pd 烃源岩 is the source rock Pt / Pd,

[0091] K is the influencing factor of geological processes, which is mainly used to simulate the possible changes in the Pt / Pd ratio during the conversion from source rock to crude oil. Its setting is obtained through comprehensive judgment of regional geological knowledge.

[0092] Before Monte Carlo simulation, the probability distribution characteristics of each parameter must be clarified. Since the amount of source rock data may be small, before Monte Carlo simulation, the source rock data is used by the kernel density estimation (KDE) method to create a continuous probability distribution curve of the source rock Pt / Pd ratio. The Scott method is used to determine the bandwidth during the calculation process. Compared with the original data, the newly obtained probability distribution curve effectively predicts the probability distribution characteristics of the missing data part. Based on geological knowledge and judgment, the possible range and distribution of K are defined. After the simulation parameters are set, the Monte Carlo simulation is performed. The number of simulations is generally set to 10,000 times or more. The simulation results obtained are distributed at the 5% and 95% percentiles as the predicted crude oil Pt / Pd ratio range.

[0093] The examples of Y-layer source rock and O-series reservoir crude oil samples in the Tarim Basin are used for illustration.

[0094] From the measured distribution characteristics of Pt / Pd in ​​source rock samples, the peak value appears at 0.3117-0.4033. The distribution characteristics of Pt / Pd in ​​source rock are obtained by kernel density estimation (KDE) of the existing data (refer to Figure 2 In the present invention, by using KDE to process limited source rock Pt / Pd ratio data, a continuous probability distribution curve is obtained. This curve not only reflects the characteristics of the existing data, but also reasonably estimates the possible data gaps, providing a reliable basis for subsequent simulation analysis.

[0095] When designing the K factor model, since there are currently few known source rock samples, it is believed that the change in Pt / Pd from source rock to crude oil is relatively small. Here, the distribution of K is set to conform to the normal distribution, with a mean (μ) of 1.0, a standard deviation (σ) of 0.05, and a cutoff range of 0.8-1.2 (refer to Figure 3 ).

[0096] In determining Pt / Pd 烃源岩 The distribution probability of the K factor is then used for Monte Carlo simulation.

[0097] This simulation is set to 100,000 times, and the simulated Pt / Pd 烃源岩 The value is multiplied by the randomly generated K factor to obtain the predicted Pt / Pd 原油 distributed.

[0098] The 5% and 95% percentiles of this distribution are calculated to be 0.2022 and 0.7052, respectively, and it is believed that the Pt / Pd ratio of crude oil generated from the target source rock is within this range ( Figure 4 The two dotted lines in the middle).

[0099] S5. Compare the platinum / palladium ratio results obtained by measuring the crude oil samples with the platinum / palladium ratio range of the crude oil generated from the target source rock obtained by simulation.

[0100] The Pt / Pd results obtained from the crude oil sample test are compared with the crude oil Pt / Pd range obtained from the Monte Carlo simulation. If it falls within the 5%-95% range of the Monte Carlo simulation, the crude oil sample is considered to be from the target source rock. If not, the crude oil sample is considered to be from other source rock samples.

[0101] From the Pt / Pd distribution characteristics of crude oil and oil-bearing core samples (refer to Figure 4 ), the Pt / Pd ratios of samples from different regions and types are all within the range of 5%-95% according to Monte Carlo simulation, and all come from known source rocks, which is consistent with previous understandings, indicating that the oil source comparison method based on the Pt / Pd ratio of platinum group elements is feasible. In addition, it can be seen from the relationship diagram between the Pt / Pd of the samples and asphaltene (refer to Figure 5 ), the Pt / Pd ratio of samples collected from different regions does not show regular changes with asphaltene content, but is relatively consistent. The Pt / Pd ratio is not affected by secondary effects such as crude oil migration (polar compounds are adsorbed by reservoir minerals, asphaltene content decreases), biodegradation (asphaltene content increases), etc., and has very good stability.

[0102] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for oil source comparison using platinum-palladium ratio, characterized in that: The steps include: Collect crude oil samples and source rock samples; Pre-treating crude oil samples and source rock samples respectively, separating asphaltene from the crude oil samples; Asphaltene and pre-treated source rock samples were subjected to platinum group element assays; According to the platinum group element determination results of source rock samples, the platinum / palladium probability distribution of crude oil generated by target source rock samples is simulated, and the range of platinum / palladium ratio of crude oil is predicted; Compare the Pt / Pd ratio results obtained from crude oil sample measurements with the simulated Pt / Pd ratio range for crude oil; The simulation of the probability distribution of platinum / palladium of crude oil generated by the target source rock sample is specifically to create a continuous probability distribution curve of the Pt / Pd ratio of the source rock through the kernel density estimation method for the source rock data, and the Scott method is used to determine the bandwidth during the calculation process; after the simulation parameters are set, a Monte Carlo simulation is performed based on a statistical method of random sampling, and the obtained simulation results are distributed at the 5% and 95% percentiles as the predicted crude oil Pt / Pd ratio range; The predicted crude oil Pt / Pd ratio range is performed by the following formula: Pt / Pd 原油 = Pt / Pd 烃源岩 *K In the formula, Pt / Pd 原油 The Pt / Pd ratio of crude oil generated from a known source rock formation; Pt / Pd 烃源岩 is source rock Pt / Pd; K is the influencing factor of geological process.

2. The method for oil source comparison using platinum-palladium ratio according to claim 1, characterized in that: The crude oil sample is crude oil or oil-bearing core, When the crude oil sample is crude oil, the crude oil is a mid-test sample during the drilling stage or a sample of a single layer of stable output during the production stage. The collected crude oil is stored in a light-proof container, and the air in the container is exhausted; When the crude oil sample is an oil-bearing core, the oil-bearing core is a freshly collected core section with high oil saturation. After the oil-bearing core is collected, it is wrapped with aluminum foil and then sealed.

3. The method for oil source comparison using platinum-palladium ratio according to claim 1, characterized in that: The crude oil sample pretreatment comprises the following steps: The crude oil sample is separated into group components to obtain a reservoir extract, which is then dissolved in a solvent to separate the precipitated asphaltene and soluble organic matter.

4. The method for oil source comparison using platinum-palladium ratio according to claim 3, characterized in that: When the crude oil sample is an oil-bearing core, the oil-bearing core sample is first crushed, then dried at low temperature, extracted to obtain an oil-bearing core extract, and then the asphaltene is separated.

5. The method for oil source comparison using platinum-palladium ratio according to claim 1, characterized in that: The pretreatment of the source rock sample specifically includes washing and drying the source rock sample and then grinding it to 100-300 meshes.

6. The method for oil source comparison using platinum-palladium ratio according to claim 1, characterized in that: The platinum group element determination comprises the following steps: Asphaltene or pretreated source rock samples are added to the Ir-Ru-Pt-Pd mixed diluent, and a sample dissolving reagent is added. The platinum group elements enriched in the sample are dissolved by heating and the isotopic equilibrium is achieved with the Ir-Ru-Pt-Pd mixed diluent. Anion exchange resin is used to separate the platinum group elements and matrix elements. The matrix elements are eluted with an eluent, and then the platinum group elements are determined.

7. The method for oil source comparison using platinum-palladium ratio according to claim 6, characterized in that: After eluting the matrix elements, Ru was eluted with 12 mol / L HNO3, Ir and Pt were eluted with 15 mL 13.5 mol / L HNO3, and finally Pd was eluted with 15 mL 10 mol / L HCl.

8. A method for oil source comparison using platinum-palladium ratio according to claim 6 or 7, characterized in that: The platinum group element determination specifically adopts a plasma mass spectrometer to detect and determine the content of platinum group elements Pt and Pd.

9. The method for oil source comparison using platinum-palladium ratio according to claim 1, characterized in that: If the Pt / Pd ratio of the crude oil sample falls within the range of 5-95% of the simulated Pt / Pd ratio of crude oil, the crude oil sample is considered to be derived from the source rock sample; If the platinum / palladium ratio result of the crude oil sample is not within the range of 5-95% of the simulated crude oil platinum / palladium ratio, it is considered that the crude oil sample does not come from the target source rock sample or that the crude oil sample contains contributions from other source rocks.

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