A method for preparing rock cuttings for removing oil-based mud pollution

Abstract

The present invention provides a method for preparing rock cuttings for removing oil-based mud contamination. The method comprises cleaning and drying a sample of oil-based mud-contaminated rock cuttings, performing trace element determination on the cleaned and dried sample; physically grinding the cleaned and dried sample, and performing trace element determination on the ground rock cutting particles and rock cutting powder; and comparing and analyzing the multiple trace element determinations to analyze the degree of oil-based mud contamination in the rock cuttings and the effectiveness of removing the oil-based mud-contaminated rock cuttings. The present invention physically grinds mudstone rock cuttings contaminated by oil-based mud without using an organic solvent, gradually removing the oil-based mud adhering to the surface of the rock cuttings. This method preserves the original geochemical characteristics of the rock cuttings, accurately determines the degree of oil-based mud contamination, and completely removes the effects of organic mud contamination, providing accurate data support and technical guidance for various geochemical analysis tests and offshore oil and gas exploration.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas mining and exploration, and in particular to a method for preparing rock cuttings for removing oil-based mud pollution. Background Art

[0002] Marine oil and gas resources are one of my country's key energy successor areas. Clarifying the distribution of marine oil and gas resources and strengthening marine oil and gas exploration are crucial for strengthening my country's energy foundation. However, unlike onshore oil and gas exploration, marine oil and gas exploration is characterized by high difficulty, high cost, and high risk. Due to the small number of offshore wells and the difficulty of drilling several times that of onshore wells, offshore cores are extremely scarce, and the vast majority of drilling results are cuttings. To determine the fundamental geological characteristics of source rocks in offshore basins and improve the accuracy of offshore oil and gas exploration, geochemical analysis and testing of drilling cuttings has become a critical and reliable method. However, contamination of cuttings by oil-based mud in drilling fluid is unavoidable. Diesel oil and chemical treatment agents in oil-based mud can severely distort organic geochemical test results of drilling cuttings, making them less representative of the true geological reality and severely hindering the progress of offshore oil and gas exploration. The trace element Ba content in offshore drilling cuttings is most significantly affected by oil-based mud contamination. The Sr / Ba ratio, a trace element, is one of the most commonly used and reliable indicators for determining paleosalinity. However, contamination by oil-based mud renders the Sr / Ba ratio virtually unusable, severely impacting the identification of paleoenvironments in offshore source rocks.

[0003] Currently, there is limited research on methods for removing oil-based mud-contaminated cuttings. Conventional wisdom holds that organic geochemical data from cuttings sampled with water-based drilling fluids are free of contamination. Consequently, some studies have used test results from contaminated cuttings to interpret geological phenomena, often yielding inconsistent conclusions that fail to guide offshore oil and gas exploration. While prior art discloses methods for reducing oil-based mud contamination by washing cuttings with various organic solvents, these methods still present challenges, such as difficulty determining the extent of oil-based mud contamination and whether it has been removed, as well as the potential loss of some of the original geochemical characteristics of the cuttings during oil washing. These methods can significantly mislead oil and gas exploration.

[0004] Therefore, it is very necessary to provide a method to accurately judge the degree of oil-based mud pollution and completely remove organic mud pollution. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a method for preparing rock cuttings for removing oil-based mud contamination. This method, without using organic solvents, only requires physical grinding of the rock cuttings contaminated by the oil-based mud, and compares the trace element determination of the rock cutting particles and the ground rock cutting powder to evaluate the degree of oil-based mud contamination of the rock cuttings and the removal effect of the oil-based mud-contaminated rock cuttings. The method is simple and convenient to operate and has good feasibility and accuracy.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A method for preparing rock cuttings for removing oil-based mud contamination comprises the following steps:

[0008] S1. Select rock cuttings samples contaminated by oil-based mud, clean and dry them, and conduct trace element determination;

[0009] S2. Grinding the dried rock cuttings sample with silicon carbide particles and ceramic columns. After grinding, performing trace element determination on the rock cuttings sample powder and rock cuttings particles respectively.

[0010] S3. Analyze and evaluate the removal effect based on the trace element determination results.

[0011] Preferably, step S1 also includes sample screening and pretreatment: the oil-based mud-contaminated rock chips are screened to remove rock chip samples with a diameter of less than 2 mm, and then screened again to select rock chip samples with a diameter of 3-5 mm, and the mud on the surface of the rock chips is washed with deionized water and dried.

[0012] Preferably, in step S1, the trace element determination is to quantitatively weigh the dried rock cuttings sample and perform trace element Sr / Ba ratio determination.

[0013] Preferably, step S2 further includes pre-treating the silicon carbide and the ceramic column, specifically: using purified dichloromethane to clean and dry the silicon carbide particles and the ceramic column, and using the dried silicon carbide particles and the ceramic column to grind with the rock cuttings sample.

[0014] Further preferably, the diameter of the silicon carbide is 0.2-1.2 mm, and the mass is 25-50 g; the diameter of the ceramic column is 1 mm, the height is 0.5 cm, and the mass is 25-50 g.

[0015] Preferably, step S2 also includes, after the grinding is completed, sieving and separating the ground material, rinsing the silicon carbide particles, ceramic columns and the powder ground off the rock chip samples with deionized water, and drying them; separating the dried silicon carbide and rock chip powder, and conducting trace element determination on the ground rock chip particles and rock chip powder.

[0016] Further preferably, the grinding times are no less than 3 times, and the particle size of the rock chip powder after grinding is less than 425 μm.

[0017] Preferably, step S2 further includes determining whether to repeat step S2 again based on the detection result after obtaining the trace element determination.

[0018] Preferably, in step S3, the removal effect evaluation method includes determining the contamination degree and the removal effect by analyzing the trace element Sr / Ba ratio based on the trace element content of the oil-based mud contaminated cuttings.

[0019] Preferably, the contamination degree and removal effect are evaluated by the ratio of trace elements Sr / Ba in the oil-based mud contaminated cuttings: when the ratio of adjacent trace elements Sr / Ba tends to be stable, it indicates that the oil-based mud contaminants on the cuttings surface have been completely removed.

[0020] Preferably, based on the results of trace element Sr / Ba determination and comparison with the current normal seawater values, it is inferred that the sedimentary environment at that time was a saltwater or non-saltwater environment.

[0021] The present invention grinds rock cuttings contaminated by oil-based mud and then measures trace elements in the ground rock cutting particles and rock cutting sample powder to judge the degree of oil-based mud contamination of the rock cuttings and the effect of removing the oil-based mud contaminated rock cuttings.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention gradually removes oil-based mud contaminants from the surface of rock cuttings by physically grinding the rock cuttings contaminated with oil-based mud without using organic solvents, thereby preserving the original geochemical characteristics of the rock cuttings. The rock cuttings can be used to carry out various geochemical analysis tests, accurately reflecting paleoenvironmental and paleoclimatic conditions, and improving the progress of offshore oil and gas resource exploration. The present invention evaluates the degree of oil-based mud contamination and the removal effect through trace element determination results, effectively improving the accuracy of oil-based mud contamination calculations and providing technical guidance for offshore oil and gas exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below with reference to the accompanying drawings and examples:

[0025] Figure 1 This is a flow chart of the rock cuttings preparation process for removing oil-based mud contamination according to the present invention;

[0026] Figure 2 This is a rock chip sample contaminated by oil-based mud in Example 1 of the present invention;

[0027] Figure 3 The rock cuttings sample after grinding in Example 1 of the present invention;

[0028] In the figure, a is the rock cutting particles after grinding, and b is the rock cutting powder after grinding;

[0029] Figure 4 It is the Sr / Ba ratio of the long rock cuttings samples with different grinding times under three different sedimentary environments of the present invention. DETAILED DESCRIPTION

[0030] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials, reagents, etc. used in the following preparation examples and examples are all commercially available unless otherwise specified.

[0031] Due to the coarse particle size of rock chip samples, oil-based mud contaminants often adhere to the rock chip surface, affecting the results of chemical analysis. Grinding with silicon carbide and ceramic columns removes oil-based mud contaminants from the rock chip surface, exposing the uncontaminated interior of the rock chip, preserving the original chemical properties of the rock chip sample and providing reliable data support for geochemical analysis and testing. Repeated grinding is used to measure changes in the trace element ratios of the ground rock chip powder or rock chip particles. If the oil-based mud contaminants are completely removed, the Sr / Ba ratio within the rock chip particles will stabilize. After multiple grindings of the same sample, the trace element Sr / Ba ratio of the rock chip powder or rock chip particles tends to be stable, indicating that the oil contamination on the rock chip surface by the oil-based mud has been completely removed.

[0032] Terrigenous clastic sediments are transported to the ocean by rivers. Sr is not easily precipitated during this transport process, while Ba readily combines with sulfate ions in seawater to form precipitation. Ba content is high in terrestrial and transitional sediments, while it is low in the ocean. Therefore, the Sr / Ba ratio can be used to identify the sedimentary environment of rock debris samples and, in turn, the paleoenvironment of the source rock, thus guiding oil and gas exploration.

[0033] Sr / Ba>1 indicates marine saline water, Sr / Ba of 1-0.5 indicates brackish water, and Sr / Ba<0.5 indicates terrestrial fresh water.

[0034] The present invention provides a method for preparing rock cuttings for removing oil-based mud contamination, comprising the following steps:

[0035] S1. Clean and dry the rock cuttings samples contaminated by oil-based mud and conduct trace element determination:

[0036] S101. Sample screening and pretreatment: Raw samples of offshore drilling cuttings were screened to remove those with a diameter less than 2 mm. The pre-screened cuttings were further screened to select those with a diameter of 3-5 mm. The cuttings were quantitatively weighed and ultrasonically cleaned with deionized water until the surface was free of foam. The cuttings were then dried at 100°C for 8-12 hours.

[0037] S102. Quantitatively weigh the cleaned and dried rock cuttings sample and perform trace element Sr / Ba determination to obtain the Sr / Ba value;

[0038] S2. Grinding the cleaned and dried rock cuttings sample, silicon carbide particles, and ceramic column. After grinding, performing trace element determination on the rock cuttings sample powder and rock cuttings particles respectively;

[0039] S201 selection of silicon carbide particles 0.2-1.2mm diameter 25-50g, 1mm diameter, 0.5cm high ceramic column 25-50g, after washing with purified dichloromethane, 100 ℃ drying for 8-12 hours;

[0040] S202. The screened rock cuttings sample, silicon carbide particles and ceramic columns are added to a vibration grinder for grinding;

[0041] S203. The ground rock particles are separated using a sample sieve, and the silicon carbide particles, ceramic columns, and the ground rock sample powder are rinsed with deionized water and dried at 100°C for 8-12 hours;

[0042] S204. Separate the dried silicon carbide and rock chip powder mixture using a sample sieve, and perform trace element Sr / Ba determination on the rock chip sample powder and the ground rock chip particles to obtain an Sr / Ba value.

[0043] S205. Compare the trace element test results to determine whether to repeat steps S201-204;

[0044] S3. Evaluate the removal effect based on the trace element Sr / Ba determination data:

[0045] When there is no difference in adjacent Sr / Ba ratios, it indicates that the oil contamination on the surface of the cuttings caused by the oil-based mud has been completely removed.

[0046] Example 1

[0047] To verify the accuracy of the present invention, this embodiment provides a method for preparing rock cuttings for removing oil-based mud contamination, comprising the following steps:

[0048] 1. Take the rock cuttings sample contaminated by oil-based mud and pass it through a 10-mesh sample sieve to filter out the rock cuttings with a diameter of less than 2 mm;

[0049] 2. The rock cuttings sample screened out from the initial screening was further screened, and 100g of 3-5mm rock cuttings sample was selected. The surface of the rock cuttings was ultrasonically washed with deionized water for 10 minutes, and dried at 100℃ for 10 hours. 30g of the sample was taken out for trace element Sr / Ba determination A0;

[0050] 3. Select 40g of silicon carbide with a diameter of 0.5mm and 40g of a ceramic column with a diameter of 1mm and a height of 0.5cm. Wash the silicon carbide and ceramic column with purified dichloromethane three times and then dry them at 100℃ for 10 hours.

[0051] 4. Add the screened rock cuttings, silicon carbide particles, and ceramic columns into the grinding barrel of the grinder, cover the grinding barrel, turn on the grinder, and grind for 1 hour. The grinder is 30 cm high and 20 cm wide, the grinding barrel is 10 cm deep and has an inner diameter of 18 cm, and the grinder power is set to 50W.

[0052] 5. After 1 hour, the ground rock cuttings were separated using a sample sieve. The silicon carbide particles, ceramic columns, and the ground rock cuttings powder were rinsed three times with deionized water and then dried at 100°C for 10 hours. The dried silicon carbide and rock cuttings powder mixture was separated using a 40-mesh sample sieve. 10 g of rock cuttings powder was weighed and subjected to the trace element Sr / Ba determination A1 again.

[0053] 6. Grind the rock cuttings, dried silicon carbide particles, and ceramic columns ground in step 5 again for 9 hours. After grinding, separate the ground rock cuttings using a sample sieve. Rinse the silicon carbide particles, ceramic columns, and the ground rock cuttings powder three times with deionized water and dry at 100°C for 10 hours. Separate the dried silicon carbide and rock cuttings powder mixture using a 40-mesh sample sieve. Weigh 5 g of rock cuttings powder and perform trace element Sr / Ba determination A2 again.

[0054] 7. Grind the rock cuttings, dried silicon carbide particles, and ceramic columns ground in step 6 again for 38 hours. After grinding, separate the ground rock cuttings using a sample sieve. Ultrasonic rinse the silicon carbide particles, ceramic columns, and the ground rock cuttings powder three times with deionized water and then dry at 100°C for 10 hours. Separate the dried silicon carbide and rock cuttings powder mixture using a 40-mesh sample sieve. Weigh 10 g of rock cuttings powder and rock cuttings particles again for Sr / Ba determination A3 and A4.

[0055] 8. Comparing the trace element analysis results, when the Sr / Ba ratios A3 and A4 show little difference, the rock cuttings sample can be considered completely free of oil-based mud contamination. The results are shown in Table 1.

[0056] Table 1 Results of determination of the Sr / Ba ratio of trace elements in rock cuttings samples

[0057]

[0058] Table 1 shows that the original rock chip sample has a low B0 (Sr / Ba) ratio. With increasing grinding times, the Sr / Ba ratio of the rock chip powder gradually increases. After three grindings, the difference between rock chip powder A3 and particle A4 is not significant, indicating that the oil-based mud contaminants in the rock chip sample have been completely removed. At this point, the Sr / Ba ratio of the rock chip sample is greater than 1, indicating that the source rock sample was exposed to a saline environment. Therefore, geochemical analysis of decontaminated rock chip samples can accurately reflect paleoenvironmental and paleoclimatic conditions.

[0059] Example 2

[0060] The same method as in Example 1 was used to remove mud contaminants from the surface of rock cuttings, with the following differences: In this example, rock cutting samples (B and C) from two different water environments were selected and screened. After screening, the mud on the surface of the rock cutting samples was ultrasonically rinsed and dried, and the Sr / Ba ratio of the rock cutting samples was measured. The dried rock cutting samples were then ground in a grinding mill along with 1 mm silicon carbide particles and ceramic columns. After grinding, a 40-mesh sample sieve was used to separate the ground rock cutting particles and rock cutting powder. The powder adhering to the grinding pot was collected and combined. The rock cutting powder was ultrasonically cleaned with deionized water for 10 minutes, dried, and the Sr / Ba ratio of the rock cutting powder was measured. The rock cutting powder was ground again, and the Sr / Ba ratio of the rock cutting powder and rock cutting particles was measured until the mud contaminants on the rock cutting surface were completely removed. The specific grinding conditions and measurement results are shown in Table 2.

[0061] Table 2 Sr / Ba ratios of rock cuttings samples contaminated by oil-based mud at different grinding times

[0062]

[0063] As shown in Table 2, the contamination levels of rock cuttings samples in different water bodies vary, and their Sr / Ba ratios are also different. By grinding the rock cuttings samples multiple times, the Sr / Ba ratios of the final rock cutting particles and the ground powder are almost the same, indicating that the mud contaminants on the rock cutting surface have been removed, that is, the influence of the oil-based mud on Ba ions has been removed, making the Sr / Ba ratios of the ground powder on the outside of the sample and the rock cutting particles in the inner layer comparable. Therefore, it can be used for geochemical analysis and detection, accurately reflecting the sedimentary water environment of the rock cutting samples, and providing technical guidance for oil and gas exploration.

[0064] In summary, the present invention adopts a physical grinding method and establishes a method for removing mud contaminants from the surface of rock cuttings based on trace element determination. The degree of oil-based mud contamination and the removal effect are evaluated. At the same time, the sedimentary water environment and geochemical characteristics of the samples are determined based on the trace element ratios, providing technical guidance for offshore oil and gas exploration.

[0065] The above embodiments are merely preferred technical solutions of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention shall be the technical solutions set forth in the claims, including equivalent alternatives to the technical features of the technical solutions set forth in the claims. In other words, equivalent alternatives and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A method for preparing rock cuttings for removing oil-based mud contamination, characterized in that: The steps include: S1. Select rock cuttings samples contaminated by oil-based mud, clean and dry them, quantitatively weigh the dried rock cuttings samples, and determine the Sr / Ba ratio of the trace element; S2. Grinding the dried rock cuttings sample with silicon carbide particles and ceramic columns. After grinding, sieving and separating the ground material. Rinse the silicon carbide particles, ceramic columns, and the ground rock cuttings powder with deionized water and dry them. Separate the dried silicon carbide and rock cuttings powder, and perform trace element determination on the ground rock cutting particles and rock cuttings powder. Repeat the above steps and grind the rock cuttings multiple times. Carry out trace element determination on the ground rock cuttings particles and rock cutting powder. Use the Sr / Ba ratio of the oil-based mud contaminated rock cuttings to evaluate the degree of contamination and removal effect. That is, when the Sr / Ba ratio of the oil-based mud contaminated rock cuttings tends to be stable, it indicates that the oil-based mud contaminants on the surface of the rock cuttings have been completely removed.

2. The method for preparing rock cuttings for removing oil-based mud contamination according to claim 1, characterized in that: Step S1 also includes sample screening and pretreatment: the oil-based mud-contaminated rock chips are screened to remove rock chip samples with a diameter of less than 2 mm, and then screened again to select rock chip samples with a diameter of 3-5 mm. The mud on the rock chip surface is washed with deionized water and then dried.

3. The method for preparing rock chips for removing oil-based mud pollution according to claim 1, characterized in that: Step S2 also includes pre-treating the silicon carbide and the ceramic column: using purified dichloromethane to clean and dry the silicon carbide particles and the ceramic column respectively.

4. The method for preparing rock cuttings for removing oil-based mud pollution according to claim 1, characterized in that: In step S2, the grinding times are no less than 3 times, and the particle size of the rock chip powder after grinding is less than 425 μm.

5. The method for preparing rock cuttings for removing oil-based mud pollution according to claim 1, characterized in that: Based on the results of trace element Sr / Ba determination and comparison with the current normal seawater values, it is inferred that the sedimentary environment at that time was a saltwater or non-salty water environment.

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