Method for quantitatively recovering organic carbon in oil-based mud hydrocarbon source rock sample

Abstract

The invention relates to a method for quantitatively recovering organic carbon in an oil-based mud hydrocarbon source rock sample, which comprises the following steps: carrying out typical well selection on a research area, and carrying out systematic sampling to obtain a rock core sample; cleaning and pre-treating the rock core sample, and carrying out geochemical pyrolysis experimental analysis to obtain organic carbon parameters; performing a chromatography-mass spectrometry experiment on the obtained rock core sample to obtain a chromatography-mass spectrum of characteristic ions; calculating a set number of chromatography-mass spectrum parameters according to the graphic characteristics of the chromatography-mass spectrum; establishing a mathematical relationship between the organic carbon parameter of the rock core sample and each chromatography-mass spectrometry parameter; carrying out a chromatography-mass spectrometry experiment on an oil-based mud hydrocarbon source rock sample to be quantitatively recovered to obtain a chromatography-mass spectrum and a set number of chromatography-mass spectrum parameters, and reversely calculating an organic carbon parameter corresponding to each chromatography-mass spectrum parameter according to the mathematical relationship, and carrying out average calculation according to the organic carbon parameter corresponding to each chromatography-mass spectrometry parameter to obtain a recovered organic carbon parameter.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration, and particularly relates to a method for quantitatively judging different organic matter abundance source rocks after being contaminated by oil-based mud. Background Art

[0002] Due to high costs, oil-based mud is often used as drilling fluid in offshore oil and gas exploration operations to improve the efficiency of drilling operations. As a result, the formation cuttings returned to the surface with the circulating drilling fluid are covered with oil-based mud. Cuttings are the most important means of understanding formation characteristics in exploration geology. In particular, the geochemistry specialty completely relies on collecting source rock cuttings as samples for indoor laboratory analysis and testing, and then uses organic geochemical methods to evaluate the source rock intervals in the formation. However, for offshore cutting samples, especially source rock cutting samples collected in deepwater offshore drilling, since the cuttings are covered with oil-based mud, it causes very significant pollution during the experimental testing process. For example, during the determination of the organic matter abundance index of source rock - organic carbon, the presence of oil-based mud results in a very high organic carbon, which will seriously overestimate the organic matter abundance of the source rock, leading to serious deviations in geological understanding and affecting exploration decision-making and deployment.

[0003] However, in recent years, it has become increasingly difficult to correct geochemical experimental tests such as organic carbon and pyrolysis for source rock cutting samples contaminated by oil-based mud, and the correction methods are not unified. Each laboratory conducts manual correction based on experience. Often, more than half of the experimental results are lost after correction. However, the organic matter abundance index data such as organic carbon after correction are often too idealized. Often, the prediction is good, but the result is poor after drilling. That is, there is a great deal of subjectivity in the data of source rock organic matter abundance indexes - organic carbon, pyrolysis, etc. obtained by using traditional laboratory experience correction methods, and there is a great deal of uncertainty in understanding, especially in quantitative identification. This means that there is a great deal of uncertainty in the currently commonly used techniques and methods for empirically correcting the organic matter abundance index of source rock - organic carbon. Therefore, finding a new method for quantitatively judging the organic matter abundance index - organic carbon of source rock cuttings contaminated by oil-based mud is an urgent need to clarify the characteristics of source rocks in offshore areas, especially deepwater basins, and is also the primary task for evaluating deepwater depressions and calculating resource potential in the offshore area.

[0004] Currently, the correction and judgment of the organic matter abundance index - organic carbon of oil-based mud source rock cutting samples often rely on laboratory technical means and experience for prediction, and are often mainly qualitative, with relatively strong subjectivity. Generally speaking, the existing techniques and methods have the following deficiencies in correcting and judging the organic carbon of source rocks:

[0005] (1) In terms of experimental operations, the cuttings are stripped. The surface of the source rock cuttings is stripped layer by layer using a machine. However, the cuttings returned from deep-water oil-based mud drilling are often very fragmented, with extremely small particles, and the oil-based mud has penetrated thoroughly. Basically, the entire source rock cutting particles are soaked. Therefore, even if it is possible to strip, there is still oil-based mud contamination even when stripping to the core point of the cuttings. As a result, it is difficult to accurately obtain the original organic matter abundance index - organic carbon parameter of the source rock through experimental tests.

[0006] (2) Cleaning with chemical reagents, commonly known as "washing oil". This method is to clean the cuttings by using inorganic chemical reagents based on the principle of similar compatibility, and then obtain the organic matter abundance index - organic carbon parameter through experimental tests on the cleaned source rock cuttings. However, this method has a very large human factor and often has two problems. On the one hand, the cleaning time is too short and the oil is not cleaned thoroughly, resulting in the data obtained from the experimental tests still being on the high side. On the other hand, over-cleaning leads to the liquid hydrocarbons originally present in the source rock cuttings being washed out, resulting in the loss of the source rock samples, and thus the data obtained from the experimental tests being on the low side.

[0007] The complexity of testing the organic matter abundance index - organic carbon of oil-based mud source rock cuttings samples lies in the following points: 1. The cuttings are soaked by oil-based mud, resulting in the contribution of oil-based mud being included in the organic carbon tested by the pyrolysis experimental instrument, thus making the tested organic carbon on the high side. 2. There are often phenomena of insufficient cleaning or over-cleaning during the cleaning process of oil-based mud, resulting in the organic carbon parameter obtained from the test being on the high side or low side. Although there are many influencing factors in the organic carbon test of source rock cuttings affected by oil-based mud, from the geochemical system experiments carried out, the chromatographic-mass spectrometry experiments on the cuttings generally have little influence and can relatively completely display the source rock information. Especially for the source rock cuttings after over-cleaning, the geochemical parameter spectra and parameter indicators obtained from the chromatographic-mass spectrometry experiments can often comprehensively and truly reflect the source rock information. Based on this, starting from the chromatographic-mass spectrometry experiment spectra and parameters of source rock samples, especially over-cleaned source rock samples, and restoring the organic matter abundance index - organic carbon of the source rock through chromatographic-mass spectrometry parameters is an intuitive and accurate means. At the same time, in terms of economic cost and operability, directly conducting chromatographic-mass spectrometry experiments is a more economical, efficient and mature experimental analysis method than stripping and equilibrium cleaning. Summary of the Invention

[0008] The present invention provides a method for quantitatively restoring the organic carbon of oil-based mud source rock samples, which judges and restores the organic matter abundance of the source rock based on intuitive and efficient chromatographic-mass spectrometry parameters; this method can simply, quickly and efficiently solve the defects of large restoration deviation, high cost, long cycle and strong dependence on manual labor in the existing methods.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present application provides a method for quantitatively restoring the organic carbon of an oil-based mud source rock sample, including:

[0011] Step (1): Select typical wells from the wells drilled in the research area, and conduct systematic sampling based on the selected typical wells to obtain core samples;

[0012] Step (2): Clean and pre-treat the obtained core samples, and then conduct geochemical pyrolysis experimental analysis to obtain organic carbon parameters;

[0013] Step (3): Conduct a chromatography-mass spectrometry experiment on the obtained core samples to obtain a chromatography-mass spectrometry diagram of characteristic ions;

[0014] Step (4): Calculate a set number of chromatography-mass spectrometry parameters according to the graphical characteristics of the chromatography-mass spectrometry diagram;

[0015] Step (5): Establish a mathematical relationship between the organic carbon parameters of the core samples and each chromatography-mass spectrometry parameter;

[0016] Step (6): Conduct a chromatography-mass spectrometry experiment on the oil-based mud source rock sample to be quantitatively restored to obtain a chromatography-mass spectrometry diagram and a set number of chromatography-mass spectrometry parameters, and inversely calculate the organic carbon parameter corresponding to each chromatography-mass spectrometry parameter according to the mathematical relationship, and then perform an average calculation based on the organic carbon parameters corresponding to each chromatography-mass spectrometry parameter to obtain the restored organic carbon parameter.

[0017] In one implementation, in the step (1), select a coring well with a set long section, and conduct equidistant sampling on its longitudinal direction at an interval of 5 m. Specifically, conduct equidistant sampling on the cuttings of the source rock at different depths. The interval depends on the overall thickness. When the thickness is greater than 100 m, conduct equidistant sampling at an interval of 5 m on the longitudinal direction; when the thickness is small, conduct sampling at an interval of 1 m. It is advisable to have no less than 10 reservoir samples for each reservoir.

[0018] In one implementation, in the step (2), the organic carbon parameter is the total organic carbon TOC;

[0019] In the step (3), obtain a chromatography-mass spectrometry diagram of characteristic ion 217;

[0020] In the step (4), mark characteristic compounds S1, S2, and S3 on the chromatography-mass spectrometry diagram of characteristic ion 217, and calculate the shaded area according to the shaded area enclosed by the peak shapes of S1, S2, and S3. The shaded area is the parameter value of S1, S2, and S3;

[0021] Calculate three chromatography-mass spectrometry parameters: (S1 + S3) / S2, S1 / S2, and S1 / S3.

[0022] In one implementation, the chromatographic - chromatographic mass parameter (S1 + S3) / S2 and the organic matter abundance parameter - total organic carbon TOC in the rock samples selected based on the equal - spacing method were fitted to obtain a unary exponential formula:

[0023] y = 41.3297*X -1.0898 R 2 = 0.829 (R 2 is the correlation coefficient);

[0024] In the above - mentioned method, in step S7, the chromatographic - chromatographic mass parameter S1 / S2 and the organic matter abundance parameter - total organic carbon TOC in the rock samples selected based on the equal - spacing method were fitted to obtain a logarithmic formula:

[0025] y = 20.9625 - 7.23018*ln(X)R 2 = 0.806 (R 2 is the correlation coefficient);

[0026] In the above - mentioned method, in step S8, the chromatographic - chromatographic mass parameter S1 / S3 and the organic matter abundance parameter - total organic carbon TOC in the rock samples selected based on the equal - spacing method were fitted to obtain a logarithmic formula:

[0027] y = 17.6121 - 5.6512*ln(X)R 2 = 0.828 (R 2 is the correlation coefficient);

[0028] Furthermore:

[0029] TOC = 41.3297*(S1 + S3) / S2 -1.0898 R 2 = 0.829 (R 2 is the correlation coefficient).

[0030] TOC = 20.9625 - 7.23018*ln(S1 / S2)R 2 = 0.806 (R 2 is the correlation coefficient).

[0031] TOC = 17.6121 - 5.65121*ln(S1 / S3)R 2 = 0.828 (R 2 is the correlation coefficient).

[0032] In one implementation, drill cuttings contaminated by oil-based mud in the study area are selected, chromatographic-mass spectrometric experiments are carried out on the cuttings, chromatographic-mass spectrometric diagrams of characteristic ion 217 are collected, the shaded areas of characteristic compounds S1, S2, and S3 marked on the chromatographic-mass spectrometric diagrams of the drill cuttings contaminated by oil-based mud are read, and three parameters (S1 + S3) / S2, S1 / S2, and S1 / S3 are calculated using the shaded areas; then the parameters (S1 + S3) / S2, S1 / S2, and S1 / S3 of the drill cuttings contaminated by oil-based mud are substituted into S6, S7, and S8 to calculate TOC. By comparing the TOC data calculated from the three parameters, the arithmetic mean of the three parameters is used as the final organic matter abundance parameter - organic carbon TOC of the cuttings.

[0033] Due to the adoption of the above technical solutions, the present invention has the following advantages:

[0034] The method of the present invention is based on the simple, fast, and inexpensive experimental test and chromatographic-mass spectrometric parameter analysis of rock samples to restore the organic matter abundance of source rock cuttings samples contaminated by oil-based mud. This method effectively avoids the distortion and error of artificial empirical judgment, as well as the inaccuracy of testing caused by incomplete cleaning or over-cleaning during the laboratory oil washing process. It solves the shortcoming and dilemma of inaccurate quantitative restoration of the organic matter abundance of source rocks under the contamination of oil-based mud, which is widespread in the deep-water field, and also avoids the uncertainty and long-cycle lag in the laboratory operation process, greatly accelerating the timeliness and shortening the long waiting time. At the same time, fully considering the heterogeneity of source rocks, from a microscopic perspective, in the way of dense sampling, quantitative determination and analysis are carried out on rock samples; this method can simply and efficiently restore the organic matter abundance of source rock cuttings contaminated by oil-based mud, greatly improving the timeliness. At the same time, from the perspective of price promotion, it also has the advantages of high quality and low price. Therefore, the present invention provides a new method that is simple, fast, and has great promotion and application value. Description of the Drawings

[0035] Figure 1 It is the chromatographic-mass spectrometric diagram of characteristic ion 217;

[0036] Figure 2 It is the relationship diagram between organic carbon TOC parameter and chromatographic-mass spectrometric parameter (S1 + S3) / S2;

[0037] Figure 3 It is the relationship diagram between organic carbon TOC parameter and chromatographic-mass spectrometric parameter S1 / S2;

[0038] Figure 4 It is the relationship diagram between organic carbon TOC parameter and chromatographic-mass spectrometric parameter S1 / S3. Detailed Embodiments

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention fall within the scope of protection of the present invention.

[0040] In view of the deficiencies and problems of the prior art, the present application provides a method for quantitatively restoring the organic carbon of oil-based mud source rock samples, including:

[0041] Step (1), selecting typical wells from the wells drilled in the research area, and systematically sampling based on the selected typical wells to obtain core samples;

[0042] Step (2), cleaning and preprocessing the obtained core samples, and then conducting geochemical pyrolysis experimental analysis to obtain organic carbon parameters;

[0043] Step (3), conducting a chromatography-mass spectrometry experiment on the obtained core samples to obtain a chromatography-mass spectrometry diagram of characteristic ions;

[0044] Step (4), calculating a set number of chromatography-mass spectrometry parameters according to the graphical characteristics of the chromatography-mass spectrometry diagram;

[0045] Step (5), establishing a mathematical relationship between the organic carbon parameters of the core samples and each chromatography-mass spectrometry parameter;

[0046] Step (6), conducting a chromatography-mass spectrometry experiment on the oil-based mud source rock samples to be quantitatively restored to obtain a chromatography-mass spectrometry diagram and a set number of chromatography-mass spectrometry parameters, and inversely calculating the organic carbon parameter corresponding to each chromatography-mass spectrometry parameter according to the mathematical relationship, and then calculating the average value of the organic carbon parameters corresponding to each chromatography-mass spectrometry parameter to obtain the restored organic carbon parameter.

[0047] The above method will be described in a more detailed embodiment with reference to more accompanying drawings.

[0048] Detailed Embodiment

[0049] Unless otherwise specified, the experimental methods used in the following embodiments are all conventional experiments.

[0050] Unless otherwise specified, the materials, reagents, etc. used in the following embodiments can all be obtained from commercial channels.

[0051] Using the method of the present invention to restore the parameter value of the organic matter abundance parameter - organic carbon TOC of the Eocene source rock in the East China Sea Basin, the specific steps are as follows:

[0052] Typical wells were selected for equidistant sampling in the Eocene source rocks in the East China Sea Basin, with a sampling interval of 5 m. For thin layers, denser sampling was carried out at an interval of 1 m. It is advisable to have no less than 10 samples per well.

[0053] Geochemical pyrolysis experimental analysis was carried out on the obtained samples to obtain the experimental result of the organic carbon TOC parameter.

[0054] Chromatography - mass spectrometry experiments were carried out on all samples, and the chromatography - mass spectrometry diagrams of the characteristic ion 217 were collected. The organic carbon TOC parameter of each sample and the chromatography - mass spectrometry diagram of the characteristic ion 217 of the corresponding sample were taken as a group.

[0055] The identification characteristic compounds S1, S2, and S3 were read from the chromatography - mass spectrometry diagrams of the characteristic ion 217. According to the shaded areas delineated by the peak shapes of S1, S2, and S3, the shaded areas were calculated. Based on the shaded areas of S1, S2, and S3, the sums of the shaded areas of (S1 + S3) / S2 shaded area, S1 shaded area / S2 shaded area, and S1 shaded area / S3 shaded area were calculated respectively to obtain three parameters: (S1 + S3) / S2, S1 / S2, and S1 / S3;

[0056] Each set of data composed of the same samples: organic carbon TOC parameter, (S1 + S3) / S2, S1 / S2, and S1 / S3 were plotted and fitted in a two - dimensional coordinate system respectively; and it was obtained that:

[0057] A unary exponential formula was obtained by fitting the organic carbon TOC parameter and the (S1 + S3) / S2 parameter:

[0058] y = 41.3297*X -1.0898 R 2 = 0.829 (R 2 is the correlation coefficient); ( Figure 2 )

[0059] A unary logarithmic formula was obtained by fitting the organic carbon TOC parameter and the S1 / S2 parameter:

[0060] y = 20.9625 - 7.23018*ln(X)R 2 = 0.806 (R 2 is the correlation coefficient); ( Figure 3 )

[0061] A unary logarithmic formula was obtained by fitting the organic carbon TOC parameter and the S1 / S3 parameter:

[0062] y = 17.6121 - 5.65121*ln(X)R 2 = 0.828 (R 2 is the correlation coefficient); ( Figure 4 )

[0063] Substitute the chromatography-mass spectrometry parameters (S1 + S3) / S2, S1 / S2, and S1 / S3 of the oil-based mud-invaded drilling cuttings with unknown organic carbon TOC parameters into the above equation, and the organic carbon TOC parameter value of the oil-based mud-invaded drilling cuttings can be quickly obtained.

[0064] In this embodiment, the (S1 + S3) / S2 of the selected rock samples varies from 0.7 to 35, S1 / S2 varies from 0.005 to 16, and S1 / S3 varies from 0.0005 to 19. The minimum values of the three parameters are substituted into Figure 2 , Figure 3 , Figure 4 The formulae of, and the obtained organic carbon TOC parameter values are 60.96, 59.2, and 60.56 respectively. The average value of the three parameter values is 58.96, that is, the highest organic carbon TOC parameter of the oil-based mud-invaded drilling source rock cuttings is 60.26; the maximum values of the three parameters are substituted into Figure 2 , Figure 3 , Figure 4 The formulae of, and the obtained organic carbon TOC parameter values are 0.86, 0.92, and 0.97 respectively. The average value of the three parameter values is 0.91, that is, the lowest organic carbon TOC parameter of the oil-based mud-invaded drilling source rock cuttings is 0.91. The error of the C organic carbon TOC parameter values obtained by the above three equations is less than 3.0%, indicating that the present invention has high accuracy.

[0065] In several embodiments provided by the present invention, it should be understood that the disclosed method can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the above division of units is only a logical function division. In actual implementation, there may be other division methods. For example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the displayed or discussed coupling or direct coupling or communication connection between each other can be through some interfaces, and the indirect coupling or communication connection of devices or units can be in electrical, mechanical or other forms.

[0066] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for quantitatively recovering organic carbon from oil-based mud source rock samples, characterized in that, Including: Step (1): Select typical wells from the wells in the research area, and conduct systematic sampling based on the selected typical wells to obtain core samples. Step (2): Clean and pre-treat the obtained core samples, and then conduct geochemical pyrolysis experimental analysis to obtain organic carbon parameters. Step (3): Conduct chromatography-mass spectrometry experiments on the obtained core samples to obtain the chromatography-mass spectrometry diagram of characteristic ions. Step (4): Calculate a set number of chromatography-mass spectrometry parameters according to the graphic features of the chromatography-mass spectrometry diagram. Step (5): Establish a mathematical relationship between the organic carbon parameters of the core samples and each chromatography-mass spectrometry parameter. Step (6): Conduct chromatography-mass spectrometry experiments on the oil-based mud source rock samples to be quantitatively restored, obtain the chromatography-mass spectrometry diagram and a set number of chromatography-mass spectrometry parameters, and inversely calculate the organic carbon parameter corresponding to each chromatography-mass spectrometry parameter according to the mathematical relationship, and then perform average calculation according to the organic carbon parameter corresponding to each chromatography-mass spectrometry parameter to obtain the restored organic carbon parameter.

2. The method for quantitatively restoring the organic carbon of the source rock sample of oil-based mud according to claim 1, wherein In the said step (1), select a core-taking well with a set long section, and conduct equally spaced sampling at intervals of 5 m longitudinally.

3. The method for quantitatively restoring the organic carbon of the oil-based mud hydrocarbon source rock sample according to claim 1, characterized in that, In the said step (2), the organic carbon parameter is the total organic carbon TOC. In the said step (3), obtain the chromatography-mass spectrometry diagram of characteristic ion 217. In the said step (4), mark characteristic compounds S1, S2, and S3 on the chromatography-mass spectrometry diagram of characteristic ion 217, calculate the shaded area enclosed by the peak shapes of S1, S2, and S3, and the shaded area is the parameter value of S1, S2, and S3. Calculate three chromatography-mass spectrometry parameters: (S1 + S3) / S2, S1 / S2, and S1 / S3.

4. The method for quantitatively restoring the organic carbon of the oil-based mud hydrocarbon source rock sample according to claim 3, characterized in that, TOC = 41.3297 * (S1 + S3) / S2 -1.0898 , corresponding to the correlation coefficient R 2 = 0.

829.

5. The method for quantitatively restoring the organic carbon of a hydrocarbon source rock sample in oil-based mud according to claim 3, characterized in that, TOC = 20.9625 - 7.23018 * ln(S1 / S2), with the corresponding correlation coefficient R2 = 0.

806.

6. The method for quantitatively restoring the organic carbon of the oil-based mud hydrocarbon source rock sample according to claim 1, characterized in that, TOC = 17.6121 - 5.65121 * ln(S1 / S3), with the correlation coefficient R 2 = 0.828.

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